Document ID: EPA-HQ-OAR-2006-0735-5433
Agency: epa
Document Type: Proposed Rule
Title: National Ambient Air Quality Standards for Lead
Posted Date: 2008-05-20T04:00Z

[Federal Register: May 20, 2008 (Volume 73, Number 98)]
[Proposed Rules]               
[Page 29183-29291]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr20my08-24]                         
 

[[Page 29183]]

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Part II

Environmental Protection Agency

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40 CFR Parts 50, 51, 53 et al.

National Ambient Air Quality Standards for Lead; Proposed Rule

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 50, 51, 53 and 58

[EPA-HQ-OAR-2006-0735; FRL-8563-9]
RIN 2060-AN83

 
National Ambient Air Quality Standards for Lead

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: Based on its review of the air quality criteria and national 
ambient air quality standards (NAAQS) for lead (Pb), EPA proposes to 
make revisions to the primary and secondary NAAQS for Pb to provide 
requisite protection of public health and welfare, respectively. EPA 
proposes to revise various elements of the primary standard to provide 
increased protection for children and other at-risk populations against 
an array of adverse health effects, most notably including neurological 
effects, particularly neurocognitive and neurobehavioral effects, in 
children. With regard to the level and indicator of the standard, EPA 
proposes to revise the level to within the range of 0.10 to 0.30 [mu]g/
m\3\ in conjunction with retaining the current indicator of Pb in total 
suspended particles (Pb-TSP) but with allowance for the use of Pb-
PM10 data, and solicits comment on alternative levels up to 
0.50 [mu]g/m\3\ and down below 0.10 [mu]g/m\3\. With regard to the 
averaging time and form of the standard, EPA proposes two options: To 
retain the current averaging time of a calendar quarter and the current 
not-to-be-exceeded form, revised to apply across a 3-year span; and to 
revise the averaging time to a calendar month and the form to the 
second-highest monthly average across a 3-year span. EPA also solicits 
comment on revising the indicator to Pb-PM10 and on the same 
broad range of levels on which EPA is soliciting comment for the Pb-TSP 
indicator (up to 0.50 [mu]g/m\3\). EPA also invites comment on when, if 
ever, it would be appropriate to set a NAAQS for Pb at a level of zero. 
EPA proposes to make the secondary standard identical in all respects 
to the proposed primary standard.
    EPA is also proposing corresponding changes to data handling 
procedures, including the treatment of exceptional events, and to 
ambient air monitoring and reporting requirements for Pb including 
those related to sampling and analysis methods, network design, 
sampling schedule, and data reporting. Finally, EPA is providing 
guidance on its proposed approach for implementing the proposed revised 
primary and secondary standards for Pb.
    Consistent with the terms of a court order, by September 15, 2008 
the Administrator will sign a notice of final rulemaking for 
publication in the Federal Register.

DATES: Comments must be received by July 21, 2008. Under the Paperwork 
Reduction Act, comments on the information collection provisions must 
be received by OMB on or before June 19, 2008.
    Public Hearings: EPA intends to hold public hearings on this 
proposed rule in June 2008 in St. Louis, Missouri and Baltimore, 
Maryland. These will be announced in a separate Federal Register notice 
that provides details, including specific times and addresses, for 
these hearings.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-
OAR-2006-0735 by one of the following methods:
     http://www.regulations.gov: Follow the online instructions 
for submitting comments.
     E-mail: a-and-r-Docket@epa.gov.
     Fax: 202-566-9744.
     Mail: Docket No. EPA-HQ-OAR-2006-0735, Environmental 
Protection Agency, Mail code 6102T, 1200 Pennsylvania Ave., NW., 
Washington, DC 20460. Please include a total of two copies.
     Hand Delivery: Docket No. EPA-HQ-OAR-2006-0735, 
Environmental Protection Agency, EPA West, Room 3334, 1301 Constitution 
Ave., NW., Washington, DC. Such deliveries are only accepted during the 
Docket's normal hours of operation, and special arrangements should be 
made for deliveries of boxed information.
    Instructions: Direct your comments to Docket ID No. EPA-HQ-OAR-
2006-0735. The EPA's policy is that all comments received will be 
included in the public docket without change and may be made available 
online at http://www.regulations.gov, including any personal 
information provided, unless the comment includes information claimed 
to be Confidential Business Information (CBI) or other information 
whose disclosure is restricted by statute. Do not submit information 
that you consider to be CBI or otherwise protected through http://
www.regulations.gov or e-mail. The http://www.regulations.gov Web site 
is an ``anonymous access'' system, which means EPA will not know your 
identity or contact information unless you provide it in the body of 
your comment. If you send an e-mail comment directly to EPA without 
going through http://www.regulations.gov, your e-mail address will be 
automatically captured and included as part of the comment that is 
placed in the public docket and made available on the Internet. If you 
submit an electronic comment, EPA recommends that you include your name 
and other contact information in the body of your comment and with any 
disk or CD-ROM you submit. If EPA cannot read your comment due to 
technical difficulties and cannot contact you for clarification, EPA 
may not be able to consider your comment. Electronic files should avoid 
the use of special characters, any form of encryption, and be free of 
any defects or viruses. For additional information about EPA's public 
docket, visit the EPA Docket Center homepage at http://www.epa.gov/
epahome/dockets.htm.
    Docket: All documents in the docket are listed in the http://
www.regulations.gov index. Although listed in the index, some 
information is not publicly available, e.g., CBI or other information 
whose disclosure is restricted by statute. Certain other material, such 
as copyrighted material, will be publicly available only in hard copy. 
Publicly available docket materials are available either electronically 
in http://www.regulations.gov or in hard copy at the Air and Radiation 
Docket and Information Center, EPA/DC, EPA West, Room 3334, 1301 
Constitution Ave., NW., Washington, DC. The Public Reading Room is open 
from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal 
holidays. The telephone number for the Public Reading Room is (202) 
566-1744 and the telephone number for the Air and Radiation Docket and 
Information Center is (202) 566-1742.

FOR FURTHER INFORMATION CONTACT: For further information in general or 
specifically with regard to sections I through III or VII, contact Dr. 
Deirdre Murphy, Health and Environmental Impacts Division, Office of 
Air Quality Planning and Standards, U.S. Environmental Protection 
Agency, Mail code C504-06, Research Triangle Park, NC 27711; telephone: 
919-541-0729; fax: 919-541-0237; e-mail: Murphy.deirdre@epa.gov. With 
regard to Section IV, contact Mr. Mark Schmidt, Air Quality Analysis 
Division, Office of Air Quality Planning and Standards, U.S. 
Environmental Protection Agency, Mail code C304-04, Research Triangle 
Park, NC 27711; telephone: 919-541-2416; fax: 919-541-1903; e-mail: 
Schmidt.mark@epa.gov. With regard to Section V, contact Mr. Kevin 
Cavender,

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Air Quality Analysis Division, Office of Air Quality Planning and 
Standards, U.S. Environmental Protection Agency, Mail code C304-06, 
Research Triangle Park, NC 27711; telephone: 919-541-2364; fax: 919-
541-1903; e-mail: Cavender.kevin@epa.gov. With regard to Section VI, 
contact Mr. Larry Wallace, Ph.D., Air Quality Policy Division, Office 
of Air Quality Planning and Standards, U.S. Environmental Protection 
Agency, Mail code C539-01, Research Triangle Park, NC 27711; telephone: 
919-541-0906; fax: 919-541-0824; e-mail: Wallace.larry@epa.gov.

SUPPLEMENTARY INFORMATION:

General Information

What Should I Consider as I Prepare My Comments for EPA?

    1. Submitting CBI. Do not submit this information to EPA through 
http://www.regulations.gov or e-mail. Clearly mark the part or all of 
the information that you claim to be CBI. For CBI information in a disk 
or CD-ROM that you mail to EPA, mark the outside of the disk or CD-ROM 
as CBI and then identify electronically within the disk or CD-ROM the 
specific information that is claimed as CBI. In addition to one 
complete version of the comment that includes information claimed as 
CBI, a copy of the comment that does not contain the information 
claimed as CBI must be submitted for inclusion in the public docket. 
Information so marked will not be disclosed except in accordance with 
procedures set forth in 40 CFR part 2.
    2. Tips for Preparing Your Comments. When submitting comments, 
remember to:
     Identify the rulemaking by docket number and other 
identifying information (subject heading, Federal Register date and 
page number).
     Follow directions--the agency may ask you to respond to 
specific questions or organize comments by referencing a Code of 
Federal Regulations (CFR) part or section number.
     Explain why you agree or disagree, suggest alternatives, 
and substitute language for your requested changes.
     Describe any assumptions and provide any technical 
information and/or data that you used.
     If you estimate potential costs or burdens, explain how 
you arrived at your estimate in sufficient detail to allow for it to be 
reproduced.
     Provide specific examples to illustrate your concerns, and 
suggest alternatives.
     Explain your views as clearly as possible, avoiding the 
use of profanity or personal threats.
     Make sure to submit your comments by the comment period 
deadline identified.

Availability of Related Information

    A number of documents relevant to this rulemaking, including the 
advance notice of proposed rulemaking (72 FR 71488), the Air Quality 
Criteria for Lead (Criteria Document) (USEPA, 2006a), the Staff Paper, 
related risk assessment reports, and other related technical documents 
are available on EPA's Office of Air Quality Planning and Standards 
(OAQPS) Technology Transfer Network (TTN) Web site at http://
www.epa.gov/ttn/naaqs/standards/pb/s_pb_index.html. These and other 
related documents are also available for inspection and copying in the 
EPA docket identified above.

Table of Contents

    The following topics are discussed in this preamble:

I. Background
    A. Legislative Requirements
    B. History of Lead NAAQS Reviews
    C. Current Related Lead Control Programs
    D. Current Lead NAAQS Review
II. Rationale for Proposed Decision on the Primary Standard
    A. Multimedia, Multipathway Considerations and Background
    1. Atmospheric Emissions and Distribution of Lead
    2. Air-Related Human Exposure Pathways
    3. Nonair-Related and Air-Related Background Human Exposure 
Pathways
    4. Contributions to Children's Lead Exposures
    B. Health Effects Information
    1. Blood Lead
    a. Internal Disposition of Lead
    b. Use of Blood Lead as Dose Metric
    c. Air-to-Blood Relationships
    2. Nature of Effects
    a. Broad Array of Effects
    b. Neurological Effects in Children
    3. Lead-Related Impacts on Public Health
    a. At-Risk Subpopulations
    b. Potential Public Health Impacts
    4. Key Observations
    C. Human Exposure and Health Risk Assessments
    1. Overview of Risk Assessment From Last Review
    2. Design Aspects of Exposure and Risk Assessments
    a. CASAC Advice
    b. Health Endpoint, Risk Metric and Concentration-response 
Functions
    c. Case Study Approach
    d. Air Quality Scenarios
    e. Categorization of Policy-Relevant Exposure Pathways
    f. Analytical Steps
    g. Generating Multiple Sets of Risk Results
    h. Key Limitations and Uncertainties
    3. Summary of Estimates and Key Observations
    a. Blood Pb Estimates
    b. IQ Loss Estimates
    D. Conclusions on Adequacy of the Current Primary Standard
    1. Background
    a. The Current Standard
    b. Policy Options Considered in the Last Review
    2. Considerations in the Current Review
    a. Evidence-Based Considerations
    b. Exposure- and Risk-Based Considerations
    3. CASAC Advice and Recommendations
    4. Administrator's Proposed Conclusions Concerning Adequacy
    E. Conclusions on the Elements of the Standard
    1. Indicator
    2. Averaging Time and Form
    3. Level for a Pb NAAQS With Pb-TSP Indicator
    a. Evidence-Based Considerations
    b. Exposure- and Risk-Based Considerations
    c. CASAC Advice and Recommendations
    d. Administrator's Proposed Conclusion Concerning Level
    4. Level for a Pb NAAQS With Pb-PM10 Indicator
    a. Considerations With Regard to Particles Not Captured by 
PM10
    b. CASAC Advice
    c. Approaches for Levels for a PM10-Based Standard
    F. Proposed Decision on the Primary Standard
III. Rationale for Proposed Decision on the Secondary Standard
    A. Welfare Effects Information
    B. Screening Level Ecological Risk Assessment
    1. Design Aspects of the Assessment and Associated Uncertainties
    2. Summary of Results
    C. The Secondary Standard
    1. Background on the Current Standard
    2. Approach for Current Review
    3. Conclusions on Adequacy of the Current Standard
    a. Evidence-Based Considerations
    b. Risk-Based Considerations
    c. CASAC Advice and Recommendations
    d. Administrator's Proposed Conclusions on Adequacy of Current 
Standard
    4. Conclusions and Proposed Decision on the Elements of the 
Secondary Standard
IV. Proposed Appendix R on Interpretation of the NAAQS for Lead and 
Proposed Revisions to the Exceptional Events Rule
    A. Background
    B. Interpretation of the NAAQS for Lead
    1. Interpretation of a Standard Based on Pb-TSP
    2. Interpretation of Alternative Elements
    C. Exceptional Events Information Submission Schedule
V. Proposed Amendments to Ambient Monitoring Requirements
    A. Sampling and Analysis Methods
    1. Background
    2. Proposed Changes
    a. Pb-TSP Sampling Method
    b. Pb-PM10 Sampling Method
    c. Analysis Method
    d. FEM Criteria
    e. Quality Assurance

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    B. Network Design
    1. Background
    2. Proposed Changes
    C. Sampling Schedule
    1. Background
    2. Proposed Changes
    D. Monitoring for the Secondary NAAQS
    1. Background
    2. Proposed Changes
    E. Other Monitoring Regulation Changes
    1. Reporting of Average Pressure and Temperature
    2. Special Purpose Monitoring Exemption
VI. Implementation Considerations
    A. Designations for the Lead NAAQS
    1. Potential Schedule for Designations of A Revised Lead NAAQS
    B. Lead Nonattainment Area Boundaries
    1. County-Based Boundaries
    2. MSA-Based Boundaries
    C. Classifications
    D. Section 110(a)(2) Lead NAAQS Infrastructure Requirements
    E. Attainment Dates
    F. Attainment Planning Requirements
    1. Schedule for Attaining a Revised Pb NAAQS
    2. RACM for Lead Nonattainment Areas
    3. Demonstration of Attainment for Lead Nonattainment Areas
    4. Reasonable Further Progress (RFP)
    5. Contingency Measures
    6. Nonattainment New Source Review (NSR) and Prevention of 
Significant Deterioration (PSD) Requirements
    7. Emissions Inventories
    8. Modeling
    G. General Conformity
    H. Transition From the Current NAAQS to a Revised NAAQS for Lead
VII. Statutory and Executive Order Reviews
    References

I. Background

A. Legislative Requirements

    Two sections of the Clean Air Act (Act) govern the establishment 
and revision of the NAAQS. Section 108 (42 U.S.C. 7408) directs the 
Administrator to identify and list each air pollutant that ``in his 
judgment, cause or contribute to air pollution which may reasonably be 
anticipated to endanger public health and welfare'' and whose 
``presence * * * in the ambient air results from numerous or diverse 
mobile or stationary sources'' and to issue air quality criteria for 
those that are listed. Air quality criteria are to ``accurately reflect 
the latest scientific knowledge useful in indicating the kind and 
extent of all identifiable effects on public health or welfare which 
may be expected from the presence of [a] pollutant in ambient air * * 
*''. Section 109 (42 U.S.C. 7409) directs the Administrator to propose 
and promulgate ``primary'' and ``secondary'' NAAQS for pollutants 
listed under section 108. Section 109(b)(1) defines a primary standard 
as one ``the attainment and maintenance of which in the judgment of the 
Administrator, based on [air quality] criteria and allowing an adequate 
margin of safety, are requisite to protect the public health.'' \1\ A 
secondary standard, as defined in Section 109(b)(2), must ``specify a 
level of air quality the attainment and maintenance of which, in the 
judgment of the Administrator, based on criteria, is requisite to 
protect the public welfare from any known or anticipated adverse 
effects associated with the presence of [the] pollutant in the ambient 
air.'' \2\
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    \1\ The legislative history of section 109 indicates that a 
primary standard is to be set at ``the maximum permissible ambient 
air level * * * which will protect the health of any [sensitive] 
group of the population,'' and that for this purpose ``reference 
should be made to a representative sample of persons comprising the 
sensitive group rather than to a single person in such a group.'' S. 
Rep. No. 91-1196, 91st Cong., 2d Sess. 10 (1970).
    \2\ Welfare effects as defined in section 302(h) (42 U.S.C. 
7602(h)) include, but are not limited to, ``effects on soils, water, 
crops, vegetation, man-made materials, animals, wildlife, weather, 
visibility and climate, damage to and deterioration of property, and 
hazards to transportation, as well as effects on economic values and 
on personal comfort and well-being.''
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    The requirement that primary standards include an adequate margin 
of safety was intended to address uncertainties associated with 
inconclusive scientific and technical information available at the time 
of standard setting. It was also intended to provide a reasonable 
degree of protection against hazards that research has not yet 
identified. Lead Industries Association v. EPA, 647 F.2d 1130, 1154 
(D.C. Cir 1980), cert. denied, 449 U.S. 1042 (1980); American Petroleum 
Institute v. Costle, 665 F.2d 1176, 1186 (D.C. Cir. 1981), cert. 
denied, 455 U.S. 1034 (1982). Both kinds of uncertainties are 
components of the risk associated with pollution at levels below those 
at which human health effects can be said to occur with reasonable 
scientific certainty. Thus, in selecting primary standards that include 
an adequate margin of safety, the Administrator is seeking not only to 
prevent pollution levels that have been demonstrated to be harmful but 
also to prevent lower pollutant levels that may pose an unacceptable 
risk of harm, even if the risk is not precisely identified as to nature 
or degree. The CAA does not require the Administrator to establish a 
primary NAAQS at a zero-risk level or at background concentration 
levels, see Lead Industries Association v. EPA, 647 F.2d at 1156 n. 51, 
but rather at a level that reduces risk sufficiently so as to protect 
public health with an adequate margin of safety.
    The selection of any particular approach to providing an adequate 
margin of safety is a policy choice left specifically to the 
Administrator's judgment. Lead Industries Association v. EPA, 647 F.2d 
at 1161-62. In addressing the requirement for an adequate margin of 
safety, EPA considers such factors as the nature and severity of the 
health effects involved, the size of the population(s) at risk, and the 
kind and degree of the uncertainties that must be addressed.
    In setting standards that are ``requisite'' to protect public 
health and welfare, as provided in section 109(b), EPA's task is to 
establish standards that are neither more nor less stringent than 
necessary for these purposes. Whitman v. American Trucking 
Associations, 531 U.S. 457, 473. Further the Supreme Court ruled that 
``[t]he text of Sec.  109(b), interpreted in its statutory and 
historical context and with appreciation for its importance to the CAA 
as a whole, unambiguously bars cost considerations from the NAAQS-
setting process * * *'' Id. at 472.\3\ Section 109(d)(1) of the Act 
requires that ``[n]ot later than December 31, 1980, and at 5-year 
intervals thereafter, the Administrator shall complete a thorough 
review of the criteria published under section 108 and the national 
ambient air quality standards promulgated under this section and shall 
make such revisions in such criteria and standards and promulgate such 
new standards as may be appropriate in accordance with section 108 and 
subsection (b) of this section.'' Section 109(d)(2)(A) requires that 
``The Administrator shall appoint an independent scientific review 
committee composed of seven members including at least one member of 
the National Academy of Sciences, one physician, and one person 
representing State air pollution control agencies.'' Section 
109(d)(2)(B) requires that, ``[n]ot later than January 1, 1980, and at 
five-year intervals thereafter, the committee referred to in 
subparagraph (A) shall complete a review of the criteria published 
under section 108 and the national primary and secondary ambient air 
quality standards promulgated under this section and shall recommend to 
the Administrator any new national ambient air quality standards and 
revisions of existing criteria and standards as may be appropriate 
under section 108 and subsection (b) of this

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section.'' Since the early 1980's, this independent review function has 
been performed by the Clean Air Scientific Advisory Committee (CASAC) 
of EPA's Science Advisory Board.
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    \3\ In considering whether the CAA allowed for economic 
considerations to play a role in the promulgation of the NAAQS, the 
Supreme Court rejected arguments that because many more factors than 
air pollution might affect public health, EPA should consider 
compliance costs that produce health losses in setting the NAAQS. 
531 U.S. at 466. Thus, EPA may not take into account possible public 
health impacts from the economic cost of implementation. Id.
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B. History of Lead NAAQS Reviews

    On October 5, 1978 EPA promulgated primary and secondary NAAQS for 
Pb under section 109 of the Act (43 FR 46246). Both primary and 
secondary standards were set at a level of 1.5 micrograms per cubic 
meter ([mu]g/m\3\), measured as Pb in total suspended particulate 
matter (Pb-TSP), not to be exceeded by the maximum arithmetic mean 
concentration averaged over a calendar quarter. This standard was based 
on the 1977 Air Quality Criteria for Lead (USEPA, 1977).
    A review of the Pb standards was initiated in the mid-1980s. The 
scientific assessment for that review is described in the 1986 Air 
Quality Criteria for Lead (USEPA, 1986a), the associated Addendum 
(USEPA, 1986b) and the 1990 Supplement (USEPA, 1990a). As part of the 
review, the Agency designed and performed human exposure and health 
risk analyses (USEPA, 1989), the results of which were presented in a 
1990 Staff Paper (USEPA, 1990b). Based on the scientific assessment and 
the human exposure and health risk analyses, the 1990 Staff Paper 
presented options for the Pb NAAQS level in the range of 0.5 to 1.5 
[mu]g/m3, and suggested the second highest monthly average 
in three years for the form and averaging time of the standard (USEPA, 
1990b). After consideration of the documents developed during the 
review and the significantly changed circumstances since Pb was listed 
in 1976, the Agency did not propose any revisions to the 1978 Pb NAAQS. 
In a parallel effort, the Agency developed the broad, multi-program, 
multimedia, integrated U.S. Strategy for Reducing Lead Exposure (USEPA, 
1991). As part of implementing this strategy, the Agency focused 
efforts primarily on regulatory and remedial clean-up actions aimed at 
reducing Pb exposures from a variety of nonair sources judged to pose 
more extensive public health risks to U.S. populations, as well as on 
actions to reduce Pb emissions to air, such as bringing more areas into 
compliance with the existing Pb NAAQS (USEPA, 1991).

C. Current Related Lead Control Programs

    States are primarily responsible for ensuring attainment and 
maintenance of national ambient air quality standards once EPA has 
established them. Under section 110 of the Act (42 U.S.C. 7410) and 
related provisions, States are to submit, for EPA approval, State 
implementation plans (SIPs) that provide for the attainment and 
maintenance of such standards through control programs directed to 
sources of the pollutants involved. The States, in conjunction with 
EPA, also administer the prevention of significant deterioration 
program (42 U.S.C. 7470-7479) for these pollutants. In addition, 
Federal programs provide for nationwide reductions in emissions of 
these and other air pollutants through the Federal Motor Vehicle 
Control Program under Title II of the Act (42 U.S.C. 7521-7574), which 
involves controls for automobile, truck, bus, motorcycle, nonroad 
engine, and aircraft emissions; the new source performance standards 
under section 111 of the Act (42 U.S.C. 7411); and the national 
emission standards for hazardous air pollutants under section 112 of 
the Act (42 U.S.C. 7412).
    As Pb is a multimedia pollutant, a broad range of Federal programs 
beyond those that focus on air pollution control provide for nationwide 
reductions in environmental releases and human exposures. In addition, 
the Centers for Disease Control and Prevention (CDC) programs provide 
for the tracking of children's blood Pb levels nationally and provide 
guidance on levels at which medical and environmental case management 
activities should be implemented (CDC, 2005a; ACCLPP, 2007).\4\ In 
1991, the Secretary of the Health and Human Services (HHS) 
characterized Pb poisoning as the ``number one environmental threat to 
the health of children in the United States'' (Alliance to End 
Childhood Lead Poisoning, 1991). In 1997, President Clinton created, by 
Executive Order 13045, the President's Task Force on Environmental 
Health Risks and Safety Risks to Children in response to increased 
awareness that children face disproportionate risks from environmental 
health and safety hazards (62 FR 19885).\5\ By Executive Orders issued 
in October 2001 and April 2003, President Bush extended the work for 
the Task Force for an additional three and a half years beyond its 
original charter (66 FR 52013 and 68 FR 19931). The Task Force set a 
Federal goal of eliminating childhood Pb poisoning by the year 2010 and 
reducing Pb poisoning in children was the Task Force's top priority.
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    \4\ As described in Section III below the CDC stated in 2005 
that no ``safe'' threshold for blood Pb levels in young children has 
been identified (CDC, 2005a).
    \5\ Co-chaired by the Secretary of the HHS and the Administrator 
of the EPA, the Task Force consisted of representatives from 16 
Federal departments and agencies.
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    Federal abatement programs provide for the reduction in human 
exposures and environmental releases from in-place materials containing 
Pb (e.g., Pb-based paint, urban soil and dust, and contaminated waste 
sites). Federal regulations on disposal of Pb-based paint waste help 
facilitate the removal of Pb-based paint from residences.\6\ Further, 
in 1991, EPA lowered the maximum levels of Pb permitted in public water 
systems from 50 parts per billion (ppb) to 15 ppb (56 FR 26460).
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    \6\ See ``Criteria for Classification of Solid Waste Disposal 
Facilities and Practices and Criteria for Municipal Solid Waste 
Landfills: Disposal of Residential Lead-Based Paint Waste; Final 
Rule'' EPA-HQ-RCRA-2001-0017.
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    Federal programs to reduce exposure to Pb in paint, dust, and soil 
are specified under the comprehensive federal regulatory framework 
developed under the Residential Lead-Based Paint Hazard Reduction Act 
(Title X). Under Title X and Title IV of the Toxic Substances Control 
Act, EPA has established regulations and associated programs in the 
following five categories: (1) Training and certification requirements 
for persons engaged in lead-based paint activities; accreditation of 
training providers; authorization of State and Tribal lead-based paint 
programs; and work practice standards for the safe, reliable, and 
effective identification and elimination of lead-based paint hazards; 
(2) ensuring that, for most housing constructed before 1978, lead-based 
paint information flows from sellers to purchasers, from landlords to 
tenants, and from renovators to owners and occupants; (3) establishing 
standards for identifying dangerous levels of Pb in paint, dust and 
soil; (4) providing grant funding to establish and maintain State and 
Tribal lead-based paint programs, and to address childhood lead 
poisoning in the highest-risk communities; and (5) providing 
information on Pb hazards to the public, including steps that people 
can take to protect themselves and their families from lead-based paint 
hazards.
    Under Title IV of TSCA, EPA established standards identifying 
hazardous levels of lead in residential paint, dust, and soil in 2001. 
This regulation supports the implementation of other regulations which 
deal with worker training and certification, Pb hazard disclosure in 
real estate transactions, Pb hazard evaluation and control in 
Federally-owned housing prior to sale and housing receiving Federal 
assistance, and U.S. Department of Housing and Urban Development grants 
to local jurisdictions to perform

[[Page 29188]]

Pb hazard control. The TSCA Title IV term ``lead-based paint hazard'' 
implemented through this regulation identifies lead-based paint and all 
residential lead-containing dust and soil regardless of the source of 
Pb, which, due to their condition and location, would result in adverse 
human health effects. One of the underlying principles of Title X is to 
move the focus of public and private decision makers away from the mere 
presence of lead-based paint, to the presence of lead-based paint 
hazards, for which more substantive action should be undertaken to 
control exposures, especially to young children. In addition the 
success of the program will rely on the voluntary participation of 
states and tribes as well as counties and cities to implement the 
programs and on property owners to follow the standards and EPA's 
recommendations. If EPA were to set unreasonable standards (e.g., 
standards that would recommend removal of all Pb from paint, dust, and 
soil), States and Tribes may choose to opt out of the Title X Pb 
program and property owners may choose to ignore EPA's advice believing 
it lacks credibility and practical value. Consequently, EPA needed to 
develop standards that would not waste resources by chasing risks of 
negligible importance and that would be accepted by States, Tribes, 
local governments and property owners. In addition, a separate 
regulation establishes, among other things, under authority of TSCA 
section 402, residential Pb dust cleanup levels and amendments to dust 
and soil sampling requirements (66 FR 1206).
    On March 31, 2008, the Agency issued a new rule (Lead: Renovation, 
Repair and Painting [RRP] Program) to protect children from lead-based 
paint hazards. This rule applies to renovators and maintenance 
professionals who perform renovation, repair, or painting in housing, 
child-care facilities, and schools built prior to 1978. It requires 
that contractors and maintenance professionals be certified; that their 
employees be trained; and that they follow protective work practice 
standards. These standards prohibit certain dangerous practices, such 
as open flame burning or torching of lead-based paint. The required 
work practices also include posting warning signs, restricting 
occupants from work areas, containing work areas to prevent dust and 
debris from spreading, conducting a thorough cleanup, and verifying 
that cleanup was effective. The rule will be fully effective by April 
2010. States and tribes may become authorized to implement this rule, 
and the rule contains procedures for the authorization of states, 
territories, and tribes to administer and enforce these standards and 
regulations in lieu of a federal program. In announcing this rule, EPA 
noted that almost 38 million homes in the United States contain some 
lead-based paint, and that this rule's requirements were key components 
of a comprehensive effort to eliminate childhood Pb poisoning. To 
foster adoption of the rule's measures, EPA also intends to conduct an 
extensive education and outreach campaign to promote awareness of these 
new requirements.
    Programs associated with the Comprehensive Environmental Response, 
Compensation, and Liability Act (CERCLA or Superfund) and Resource 
Conservation Recovery Act (RCRA) also implement abatement programs, 
reducing exposures to Pb and other pollutants. For example, EPA 
determines and implements protective levels for Pb in soil at Superfund 
sites and RCRA corrective action facilities. Federal programs, 
including those implementing RCRA, provide for management of hazardous 
substances in hazardous and municipal solid waste.\7\ For example, 
Federal regulations concerning batteries in municipal solid waste 
facilitate the collection and recycling or proper disposal of batteries 
containing Pb.\8\ Similarly, Federal programs provide for the reduction 
in environmental releases of hazardous substances such as Pb in the 
management of wastewater (http://www.epa.gov/owm/).
---------------------------------------------------------------------------

    \7\ See, e.g., ``Hazardous Waste Management System; 
Identification and Listing of Hazardous Waste: Inorganic Chemical 
Manufacturing Wastes; Land Disposal Restrictions for Newly 
Identified Wastes and CERCLA Hazardous Substance Designation and 
Reportable Quantities; Final Rule'', http://www.epa.gov/epaoswer/
hazwaste/state/revision/frs/fr195.pdf and http://www.epa.gov/
epaoswer/hazwaste/ldr/basic.htm.
    \8\ See, e.g., ``Implementation of the Mercury-Containing and 
Rechargeable Battery Management Act'' http://www.epa.gov/epaoswer/
hazwaste/recycle/battery.pdf and ``Municipal Solid Waste Generation, 
Recycling, and Disposal in the United States: Facts and Figures for 
2005'' http://www.epa.gov/epaoswer/osw/conserve/resources/msw-
2005.pdf.
---------------------------------------------------------------------------

    A variety of federal nonregulatory programs also provide for 
reduced environmental release of Pb containing materials through more 
general encouragement of pollution prevention, promotion of reuse and 
recycling, reduction of priority and toxic chemicals in products and 
waste, and conservation of energy and materials. These include the 
Resource Conservation Challenge (http://www.epa.gov/epaoswer/osw/
conserve/index.htm), the National Waste Minimization Program (http://
www.epa.gov/epaoswer/hazwaste/minimize/leadtire.htm), ``Plug in to 
eCycling'' (a partnership between EPA and consumer electronics 
manufacturers and retailers; http://www.epa.gov/epaoswer/hazwaste/
recycle/electron/crt.htm#crts), and activities to reduce the practice 
of backyard trash burning (http://www.epa.gov/msw/backyard/pubs.htm).
    Efforts such as those programs described above have been successful 
in that blood Pb levels in all segments of the population have dropped 
significantly from levels observed around 1990. In particular, blood Pb 
levels for the general population of children 1 to 5 years of age have 
dropped to a median level of 1.6 [mu]g/dL and a level of 3.9 [mu]g/dL 
for the 90th percentile child in the 2003-2004 National Health and 
Nutrition Examination Survey (NHANES) as compared to median and 90th 
percentile levels in 1988-1991 of 3.5 [mu]g/dL and 9.4 [mu]g/dL, 
respectively (http://www.epa.gov/envirohealth/children/body_burdens/
b1-table.htm). These levels (median and 90th percentile) for the 
general population of young children \9\ are at the low end of the 
historic range of blood Pb levels for general population of children 
aged 1-5 years. However, as discussed in Section II.B.1.b, levels have 
been found to vary among children of different socioeconomic status and 
other demographic characteristics (CD, p. 4-21) and racial/ethnic and 
income disparities in blood Pb levels in children persist. The decline 
in blood Pb levels in the United States has resulted from coordinated, 
intensive efforts at the national, state, and local levels. The Agency 
has continued to grapple with soil and dust Pb levels from the 
historical use of Pb in paint and gasoline and other sources.
---------------------------------------------------------------------------

    \9\ The 95th percentile value for the 2003-2004 NHANES is 5.1 
[mu]g/dL (Axelrad, 2008).
---------------------------------------------------------------------------

    EPA's research program, with other Federal agencies, defines, 
encourages and conducts research needed to locate and assess serious 
risks and to develop methods and tools to characterize and help reduce 
risks. For example, EPA's Integrated Exposure Uptake Biokinetic Model 
for Lead in Children (IEUBK model) for Pb in children and the Adult 
Lead Methodology are widely used and accepted as tools that provide 
guidance in evaluating site specific data. More recently, in 
recognition of the need for a single model that predicts Pb 
concentrations in tissues for children and adults, EPA is developing 
the All Ages Lead Model (AALM) to provide researchers and risk 
assessors with a

[[Page 29189]]

pharmacokinetic model capable of estimating blood, tissue, and bone 
concentrations of Pb based on estimates of exposure over the lifetime 
of the individual. EPA research activities on substances including Pb 
focus on better characterizing aspects of health and environmental 
effects, exposure, and control or management of environmental releases 
(see http://www.epa.gov/ord/researchaccomplishments/index.html).

D. Current Lead NAAQS Review

    EPA initiated the current review of the air quality criteria for Pb 
on November 9, 2004, with a general call for information (69 FR 64926). 
A project work plan (USEPA, 2005a) for the preparation of the Criteria 
Document was released in January 2005 for CASAC and public review. EPA 
held a series of workshops in August 2005, inviting recognized 
scientific experts to discuss initial draft materials that dealt with 
various lead-related issues being addressed in the Pb air quality 
criteria document. The first draft of the Criteria Document (USEPA, 
2005b) was released for CASAC and public review in December 2005 and 
discussed at a CASAC meeting held on February 28-March 1, 2006.
    A second draft Criteria Document (USEPA, 2006b) was released for 
CASAC and public review in May 2006, and discussed at the CASAC meeting 
on June 28, 2006. A subsequent draft of Chapter 7--Integrative 
Synthesis (Chapter 8 in the final Criteria Document), released on July 
31, 2006, was discussed at an August 15, 2006, CASAC teleconference. 
The final Criteria Document was released on September 30, 2006 (USEPA, 
2006a; cited throughout this preamble as CD). While the Criteria 
Document focuses on new scientific information available since the last 
review, it integrates that information with scientific criteria from 
previous reviews.
    In February 2006, EPA released the Plan for Review of the National 
Ambient Air Quality Standards for Lead (USEPA, 2006c) that described 
Agency plans and a timeline for reviewing the air quality criteria, 
developing human exposure and risk assessments and an ecological risk 
assessment, preparing a policy assessment, and developing the proposed 
and final rulemakings.
    In May 2006, EPA released for CASAC and public review a draft 
Analysis Plan for Human Health and Ecological Risk Assessment for the 
Review of the Lead National Ambient Air Quality Standards (USEPA, 
2006d), which was discussed at a June 29, 2006, CASAC meeting 
(Henderson, 2006). The May 2006 assessment plan discussed two 
assessment phases: A pilot phase and a full-scale phase. The pilot 
phase of both the human health and ecological risk assessments was 
presented in the draft Lead Human Exposure and Health Risk Assessments 
and Ecological Risk Assessment for Selected Areas (ICF, 2006; 
henceforth referred to as the first draft Risk Assessment Report) which 
was released for CASAC and public review in December 2006. The first 
draft Staff Paper, also released in December 2006, discussed the pilot 
assessments and the most policy-relevant science from the Criteria 
Document. These documents were reviewed by CASAC and the public at a 
public meeting on February 6-7, 2007 (Henderson, 2007a).
    Subsequent to that meeting, EPA conducted full-scale human exposure 
and health risk assessments, although no further work was done on the 
ecological assessment due to resource limitations. A second draft Risk 
Assessment Report (USEPA, 2007a), containing the full-scale human 
exposure and health risk assessments, was released in July 2007 for 
review by CASAC at a meeting held on August 28-29, 2007. Taking into 
consideration CASAC comments (Henderson, 2007b) and public comments on 
that document, we conducted additional human exposure and health risk 
assessments. A final Risk Assessment Report (USEPA, 2007b) and final 
Staff Paper (USEPA, 2007c) were released on November 1, 2007.
    The final Staff Paper presents OAQPS staff's evaluation of the 
public health and welfare policy implications of the key studies and 
scientific information contained in the Criteria Document and presents 
and interprets results from the quantitative risk/exposure analyses 
conducted for this review. Further, the Staff Paper presents OAQPS 
staff recommendations on a range of policy options for the 
Administrator to consider concerning whether, and if so how, to revise 
the primary and secondary Pb NAAQS. Such an evaluation of policy 
implications is intended to help ``bridge the gap'' between the 
scientific assessment contained in the Criteria Document and the 
judgments required of the EPA Administrator in determining whether it 
is appropriate to retain or revise the NAAQS for Pb. In evaluating the 
adequacy of the current standard and a range of alternatives, the Staff 
Paper considered the available scientific evidence and quantitative 
risk-based analyses, together with related limitations and 
uncertainties, and focused on the information that is most pertinent to 
evaluating the basic elements of national ambient air quality 
standards: indicator,\10\ averaging time, form,\11\ and level. These 
elements, which together serve to define each standard, must be 
considered collectively in evaluating the public health and welfare 
protection afforded by the Pb standards. The information, conclusions, 
and OAQPS staff recommendations presented in the Staff Paper were 
informed by comments and advice received from CASAC in its reviews of 
the earlier draft Staff Paper and drafts of related risk/exposure 
assessment reports, as well as comments on these earlier draft 
documents submitted by public commenters.
---------------------------------------------------------------------------

    \10\ The ``indicator'' of a standard defines the chemical 
species or mixture that is to be measured in determining whether an 
area attains the standard.
    \11\ The ``form'' of a standard defines the air quality 
statistic that is to be compared to the level of the standard in 
determining whether an area attains the standard.
---------------------------------------------------------------------------

    Subsequent to completion of the Staff Paper, EPA issued an advance 
notice of proposed rulemaking (ANPR) that was signed by the 
Administrator on December 5, 2007 (72 FR 71488-71544). The ANPR is one 
of the key features of the new NAAQS review process that EPA has 
instituted over the past two years to help to improve the efficiency of 
the process the Agency uses in reviewing the NAAQS while ensuring that 
the Agency's decisions are informed by the best available science and 
broad participation among experts in the scientific community and the 
public. The ANPR provided the public an opportunity to comment on a 
wide range of policy options that could be considered by the 
Administrator. The substantial number of comments we received on the Pb 
NAAQS ANPR helped inform the narrower range of options we are proposing 
and taking comment on today. The new process (described at http://
www.epa.gov/ttn/naaqs/.) is being incorporated into the various ongoing 
NAAQS reviews being conducted by the Agency, including the current 
review of the Pb NAAQS.
    A public meeting of the CASAC was held on December 12-13, 2007 to 
provide advice and recommendations to the Administrator based on its 
review of the ANPR and the previously released final Staff Paper and 
Risk Assessment Report. Information about this meeting was published in 
the Federal Register on November 20, 2007 (72 FR 65335-65336), 
transcripts of the meeting are in the Docket for this review and 
CASAC's letter to the Administrator (Henderson, 2008) is also available 
on the EPA Web site (http://www.epa.gov/sab).

[[Page 29190]]

    A public comment period for the ANPR extended from December 17, 
2007 through January 16, 2008 and comments received are in the Docket 
for this review. Comments were received from nearly 9000 private 
citizens (roughly 200 of them were not part of one of several mass 
comment campaign), 13 state and local agencies, one federal agency, 
three regional or national associations of government agencies or 
officials, 15 nongovernmental environmental or public health 
organizations (including one submission on behalf of a coalition of 23 
organizations) and five industries or industry organizations. Although 
the Agency has not developed formal responses to comments received on 
the ANPR, these comments have been considered in the development of 
this notice and are generally described in subsequent sections on 
proposed conclusions with regard to the adequacy of the standards and 
with regard to the Administrator's proposed decisions on revisions to 
the standards.
    The schedule for completion of this review is governed by a 
judicial order in Missouri Coalition for the Environment, v. EPA (No. 
4:04CV00660 ERW, Sept. 14, 2005). The order governing this review, 
entered by the court on September 14, 2005 and amended on April 29, 
2008, specifies that EPA sign, for publication, notices of proposed and 
final rulemaking concerning its review of the Pb NAAQS no later than 
May 1, 2008 and September 15, 2008, respectively. In light of the 
compressed schedule ordered by the court for issuing the final rule, 
EPA may be able to respond only to those comments submitted during the 
public comment period on this proposal. EPA has considered all of the 
comments submitted to date in preparing this proposal, but if 
commenters believe that comments submitted on the ANPR are fully 
applicable to the proposal and wish to ensure that those comments are 
addressed by EPA as part of the final rulemaking, the earlier comments 
should be resubmitted during the comment period on this proposal.
    This action presents the Administrator's proposed decisions on the 
review of the current primary and secondary Pb standards. Throughout 
this preamble a number of judgments, conclusions, findings, and 
determinations proposed by the Administrator are noted. While they 
identify the reasoning that supports this proposal, they are not 
intended to be final or conclusive in nature. The EPA invites general, 
specific, and/or technical comments on all issues involved with this 
proposal, including all such proposed judgments, conclusions, findings, 
and determinations.

II. Rationale for Proposed Decision on the Primary Standard

    This section presents the rationale for the Administrator's 
proposed decision that the current primary standard is not requisite to 
protect public health with an adequate margin of safety, and that the 
existing Pb primary standard should be revised. With regard to the 
primary standard for Pb, EPA is proposing options for the revision of 
the various elements of the standard to provide increased protection 
for children and other at-risk populations against an array of adverse 
health effects, most notably including neurological effects in 
children, particularly neurocognitive and neurobehavioral effects. With 
regard to the level and indicator of the standard, EPA proposes to 
revise the level of the standard to a level within the range of 0.10 to 
0.30 [mu]g/m\3\ in conjunction with retaining the current indicator of 
Pb in total suspended particles (Pb-TSP) but with allowance for the use 
of Pb-PM10 data. With regard to the form and averaging time of the 
standard, EPA proposes the following options: (1) To retain the current 
averaging time of a calendar quarter and the current not-to-be-exceeded 
form, revised so as to apply across a 3-year span, and (2) to revise 
the averaging time to a calendar month and the form to be the second-
highest monthly average across a 3-year span. EPA also solicits comment 
on revising the indicator to Pb-PM10.
    As discussed more fully below, this proposal is based on a thorough 
review, in the Criteria Document, of the latest scientific information 
on human health effects associated with the presence of Pb in the 
ambient air. This proposal also takes into account: (1) Staff 
assessments of the most policy-relevant information in the Criteria 
Document and staff analyses of air quality, human exposure, and health 
risks presented in the Staff Paper, upon which staff recommendations 
for revisions to the primary Pb standard are based; (2) CASAC advice 
and recommendations, as reflected in discussions of the ANPR and drafts 
of the Criteria Document and Staff Paper at public meetings, in 
separate written comments, and in CASAC's letters to the Administrator; 
and (3) public comments received during the development of these 
documents, either in connection with CASAC meetings or separately.
    In developing this proposal, EPA has drawn upon an integrative 
synthesis of the entire body of evidence, published through late 2006, 
on human health effects associated with Pb exposure. Some 6000 newly 
available studies were considered in this review. As discussed below in 
section II.B, this body of evidence addresses a broad range of health 
endpoints associated with exposure to Pb (EPA, 2006a, chapter 8), and 
includes hundreds of epidemiologic studies conducted in the U.S., 
Canada, and many countries around the world since the time of the last 
review (EPA, 2006a, chapter 6). This proposal also draws upon the 
results of the quantitative exposure and risk assessments, discussed 
below in section II.C. Evidence- and exposure/risk-based considerations 
that form the basis for the Administrator's proposed decisions on the 
adequacy of the current standard and on the elements of the proposed 
alternative standards are discussed below in section II.D.2 and II.D.3, 
respectively.

A. Multimedia, Multipathway Considerations and Background

1. Atmospheric Emissions and Distribution of Lead
    Lead is emitted into the air from many sources encompassing a wide 
variety of source types (Staff Paper, Section 2.2). Further, once 
deposited out of the air, Pb can subsequently be resuspended into the 
air (CD, pp. 2-62 to 2-66). There are over 100 categories of sources of 
Pb emissions included in the EPA's 2002 National Emissions Inventory 
(NEI),\12 \ the top five of which include: Mobile sources (leaded 
aviation gas) \13\; industrial, commercial, institutional and process 
boilers; utility boilers; iron and steel foundries; and primary Pb 
smelting (Staff Paper Section 2.2). Further, there are some 13,000 
industrial, commercial or institutional point sources in the 2002 NEI, 
each with one or more processes that emit Pb to the atmosphere. In 
addition to these 13,000 sources, there are approximately 3,000 
airports at which leaded gasoline is used (Staff Paper, p. 2-8). Among 
these sources, more than one thousand are estimated to emit at least a 
tenth of a ton of Pb per year (Staff Paper, Section 2.2.3). Because of 
its persistence, Pb emissions contribute to media

[[Page 29191]]

concentrations for some time into the future.
---------------------------------------------------------------------------

    \12\ As noted in the Staff Paper, quantitative estimates of 
emissions associated with resuspension of soil-bound Pb particles 
and contaminated road dust are not included in the 2002 NEI.
    \13\ The emissions estimates identified as mobile sources in the 
current NEI are currently limited to combustion of leaded aviation 
gas in piston-engine aircraft. Lead emissions estimates for other 
mobile source emissions of Pb (e.g., brake wear, tire wear, loss of 
Pb wheel weights and others) are not included in the current NEI.
---------------------------------------------------------------------------

    Lead emitted to the air is predominantly in particulate form, with 
the particles occurring in many sizes. Once emitted, Pb particles can 
be transported long or short distances depending on their size, which 
influences the amount of time spent in aerosol phase. In general, 
larger particles tend to deposit more quickly, within shorter distances 
from emissions points, while smaller particles will remain in aerosol 
phase and travel longer distances before depositing. Additionally, once 
deposited, Pb particles can be resuspended back into the air and 
undergo a second dispersal. Thus, the atmospheric transport processes 
of Pb contribute to its broad dispersal, with larger particles 
generally occurring as a greater contribution to total airborne Pb at 
locations closer to the point of emission than at more distant 
locations where the relative contribution from smaller particles is 
greater (CD, Section 2.3.1 and p. 3-3).
    Airborne concentrations of Pb in total suspended particulate matter 
(Pb-TSP) in the United States have fallen substantially since the 
current Pb NAAQS was set in 1978.\14\ Despite this decline, there have 
still been a small number of areas, associated with large stationary 
sources of Pb, that have not met the NAAQS over the past few years. The 
average maximum quarterly mean concentration for the time period 2003-
2005 among source-oriented monitoring sites in the U.S. is 0.48 [mu]g/
m3, while the corresponding average for non-source-oriented 
sites is 0.03 [mu]g/m3.\15\ The average and median among all 
monitoring-site-specific maximum quarterly mean concentrations for this 
time period are 0.17 [mu]g/m3 and 0.03 [mu]g/m3, 
respectively. Coincident with the historical trend in reduction in Pb 
levels, however, there has also been a substantial reduction in number 
of Pb-TSP monitoring sites. As described below in section II.B.3.b, 
many of the highest Pb emitting sources in the 2002 NEI do not have 
nearby Pb-TSP monitors, which may lead to underestimates of the extent 
of occurrences of relatively higher Pb concentrations (as recognized in 
the Staff Paper, Section 2.3.2 and, with regard to more recent 
analysis, in section II.B.3.b below).
---------------------------------------------------------------------------

    \14\ Air Pb concentrations nationally are estimated to have 
declined more than 90% since the early 1980s, in locations not known 
to be directly influenced by stationary sources (Staff Paper, pp. 2-
22 to 2-23).
    \15\ The data set included data for 189 monitor sites meeting 
the data analysis screening criteria. Details with regard to the 
data set and analyses supporting the values provided here are 
presented in Section 2.3.2 of the Staff Paper.
---------------------------------------------------------------------------

2. Air-Related Human Exposure Pathways
    As when the standard was set in 1978, we recognize that exposure to 
air Pb can occur directly by inhalation, or indirectly by ingestion of 
Pb-contaminated food, water or nonfood materials including dust and 
soil (43 FR 46247). This occurs as Pb emitted into the ambient air is 
distributed to other environmental media and can contribute to human 
exposures via indoor and outdoor dusts, outdoor soil, food and drinking 
water, as well as inhalation of air (CD, pp. 3-1 to 3-2). Accordingly, 
people are exposed to Pb emitted into ambient air by both inhalation 
and ingestion pathways. In general, air-related pathways include those 
pathways where Pb passes through ambient air on its path from a source 
to human exposure. EPA considers risks to public health from exposure 
to Pb that was emitted into the air as relevant to our consideration of 
the primary standard. Therefore , we consider these air-related 
pathways to be policy-relevant in this review. Air-related Pb exposure 
pathways include: Inhalation of airborne Pb (that may include Pb 
emitted into the air and deposited and then resuspended); and ingestion 
of Pb that, once airborne, has made its way into indoor dust, outdoor 
dust or soil, dietary items (e.g., crops and livestock), and drinking 
water (e.g., CD, Figure 3-1).
    Ambient air Pb contributes to Pb in indoor dust through transport 
of Pb suspended in ambient air that is then deposited indoors and 
through transport of Pb that has deposited outdoors from ambient air 
and is transported indoors in ways other than through ambient air (CD, 
Section 3.2.3; Adgate et al., 1998). For example, infiltration of 
ambient air into buildings brings airborne Pb indoors where deposition 
of particles contributes to Pb in dust on indoor surfaces (CD, p. 3-28; 
Caravanos et al., 2006a). Indoor dust may be ingested (e.g., via hand-
to-mouth activity by children; CD, p. 8-12) or may be resuspended 
through household activities and inhaled (CD, p. 8-12). Ambient air Pb 
can also deposit onto outdoor surfaces (including surface soil) with 
which humans may come into contact (CD, Section 2.3.2; Farfel et al., 
2003; Caravanos et al., 2006a, b). Human contact with this deposited Pb 
may result in incidental ingestion from this exposure pathway and may 
also result in some of this Pb being carried indoors (e.g., on clothes 
and shoes) adding to indoor dust Pb (CD, p. 3-28; von Lindern et al., 
2003a, b). Additionally, Pb from ambient air that deposits on outdoor 
surfaces may also be resuspended and carried indoors in the air where 
it can be inhaled. Thus, indoor dust receives air-related Pb directly 
from ambient air coming indoors and also more indirectly, after 
deposition from ambient air onto outdoor surfaces.
    As mentioned above, humans may contact Pb in dust on outdoor 
surfaces, including surface soil and other materials, that has 
deposited from ambient air (CD, Section 3.2; Caravanos et al., 2006a; 
Mielke et al., 1991; Roels et al., 1980). Human exposure to this 
deposited Pb can occur through incidental ingestion, and, when the 
deposited Pb is resuspended, by inhalation. Atmospheric deposition of 
Pb also contributes to Pb in vegetation, both as a result of contact 
with above ground portions of the plant and through contributions to 
soil and transport of Pb into roots (CD, pp. 7-9 and AXZ7-39; USEPA, 
1986a, Sections 6.5.3 and 7.2.2.2.1). Livestock may subsequently be 
exposed to Pb in vegetation (e.g., grasses and silage) and in surface 
soils via incidental ingestion of soil while grazing (USEPA 1986a, 
Section 7.2.2.2.2). Atmospheric deposition is estimated to comprise a 
significant proportion of Pb in food (CD, p. 3-48; Flegel et al., 1990; 
Juberg et al., 1997; Dudka and Miller, 1999). Atmospheric deposition 
outdoors also contributes to Pb in surface waters, although given the 
widespread use of settling or filtration in drinking water treatment, 
air-related Pb is generally a small component of Pb in treated drinking 
water (CD, Section 2.3.2 and p. 3-33).
    Air-related exposure pathways are affected by changes to air 
quality, including changes in concentrations of Pb in air and/or 
changes in atmospheric deposition of Pb. Further, because of its 
persistence in the environment, Pb deposited from the air may 
contribute to human and ecological exposures for years into the future 
(CD, pp. 3-18 to 3-19, pp. 3-23 to 2-24). Thus, because of the roles in 
human exposure pathways of both air concentration and air deposition, 
and of the persistence of Pb, once deposited, some pathways respond 
more quickly to changes in air quality than others. Pathways most 
directly involving Pb in ambient air and exchanges of ambient air with 
indoor air respond more quickly while pathways involving exposure to Pb 
deposited from ambient air into the environment generally respond more 
slowly (CD, pp. 3-18 to 3-19).

[[Page 29192]]

    Exposure pathways tied most directly to ambient air, and that 
consequently have the potential to respond relatively more quickly to 
changes in air Pb, include inhalation of ambient air, and ingestion of 
Pb in indoor dust directly contaminated with Pb from ambient air.\16\ 
Lead from ambient air contaminates indoor dust directly when outdoor 
air comes inside (through open doors or windows, for example) and Pb in 
that air deposits to indoor surfaces (Caravanos et al., 2006a; CD, p. 
8-22). This includes Pb that was previously deposited outdoors and is 
then resuspended and transported indoors. Lead in dust on outdoor 
surfaces also responds to air deposition (Caravanos et al., 2006). 
Pathways in which the air quality impact is reflected over a somewhat 
longer time frame generally are associated with outdoor atmospheric 
deposition, and include ingestion pathways such as the following: (1) 
Ingestion of Pb in outdoor soil; (2) ingestion of Pb in indoor dust 
indirectly contaminated with Pb from the outdoor air (e.g, ``tracking 
in'' of Pb deposited to outdoor surface soil, as compared to ambient 
air transport of resuspended outdoor soil); (3) ingestion of Pb in diet 
that is attributable to deposited air Pb, and; (4) ingestion of Pb in 
drinking water that is attributable to deposited air Pb (e.g., Pb 
entering water bodies used for drinking supply).
---------------------------------------------------------------------------

    \16\ We note that in the risk assessment, we only assessed 
alternate standard impacts on the subset of air-related pathways 
that respond relatively quickly to changes in air Pb.
---------------------------------------------------------------------------

3. Nonair-Related and Air-Related Background Human Exposure Pathways
    As when the standard was set in 1978, there continue to be multiple 
sources of exposure, both air-related and others (nonair-related). 
Human exposure pathways that are not air-related are those in which Pb 
does not pass through ambient air. These pathways as well as air-
related human exposure pathways that involve natural sources of Pb to 
air are considered policy-relevant background in this review. In the 
context of NAAQS for other criteria pollutants which are not multimedia 
in nature, such as ozone, the term policy-relevant background is used 
to distinguish anthropogenic air emissions from naturally occurring 
non-anthropogenic emissions to separate pollution levels that can be 
controlled by U.S. regulations from levels that are generally 
uncontrollable by the United States (USEPA, 2007d). In the case of Pb, 
however, due to the multimedia, multipathway nature of human exposures 
to Pb, policy-relevant background is defined more broadly to include 
not only the ``quite low'' levels of naturally occurring Pb emissions 
into the air from non-anthropogenic sources such as volcanoes, sea 
salt, and windborne soil particles from areas free of anthropogenic 
activity (see below), but also Pb from nonair sources. These are 
collectively referred to as ``policy-relevant background.''
    The pathways of human exposure to Pb that are not air-related 
include ingestion of Pb from indoor Pb paint \17\, Pb in diet as a 
result of inadvertent additions during food processing, and Pb in 
drinking water attributable to Pb in distribution systems (CD, Chapter 
3). Other less prevalent, potential pathways of Pb exposure that are 
not air-related include ingestion of some calcium supplements or of 
food contaminated during storage in some Pb glazed glassware, and hand-
to-mouth contact with some imported vinyl miniblinds or with some hair 
dyes containing Pb acetate, as well as some cosmetics and folk remedies 
(CD, pp. 3-50 to 3-51).
---------------------------------------------------------------------------

    \17\ Weathering of outdoor Pb paint may also contribute to soil 
Pb levels adjacent to the house.
---------------------------------------------------------------------------

    Some amount of Pb in the air derives from background sources, such 
as volcanoes, sea salt, and windborne soil particles from areas free of 
anthropogenic activity (CD, Section 2.2.1). The impact of these sources 
on current air concentrations is expected to be quite low (relative to 
current concentrations) and has been estimated to fall within the range 
from 0.00002 [mu]g/m3 and 0.00007 [mu]g/m3 based 
on mass balance calculations for global emissions (CD, Section 3.1 and 
USEPA 1986, Section 7.2.1.1.3). The midpoint in this range, 0.00005 
[mu]g/m3, has been used in the past to represent the 
contribution of naturally occurring air Pb to total human exposure 
(USEPA 1986, Section 7.2.1.1.3). The data available to derive such an 
estimate are limited and such a value might be expected to vary 
geographically with the natural distribution of Pb. Comparing this to 
reported air Pb measurements is complicated by limitations of the 
common analytical methods and by inconsistent reporting practices. This 
value is one half the lowest reported nonzero value in AQS. Little 
information is available regarding anthropogenic sources of airborne Pb 
located outside of North America, which would also be considered 
policy-relevant background. In considering contributions from policy-
relevant background to human exposures and associated health effects, 
however, any credible estimate of policy-relevant background in air is 
likely insignificant in comparison to the contributions from exposures 
to nonair media.
4. Contributions to Children's Lead Exposures
    As when the standard was set in 1978, EPA recognizes that there 
remain today contributions to blood Pb levels from nonair sources. The 
relative contribution of Pb in different exposure media to human 
exposure varies, particularly for different age groups. For example, 
some studies have found that dietary intake of Pb may be a predominant 
source of Pb exposure among adults, greater than consumption of water 
and beverages or inhalation (CD, p. 3-43).\18\ For young children, 
however, ingestion of indoor dust can be a significant Pb exposure 
pathway, such that dust ingested via hand-to-mouth activity can be a 
more important source of Pb exposure than inhalation, although indoor 
dust can also be resuspended through household activities and pose an 
inhalation risk as well (CD, p. 3-27 to 3-28; Melnyk et al. 2000).\19\
---------------------------------------------------------------------------

    \18\ ``Some recent exposure studies have evaluated the relative 
importance of diet to other routes of Pb exposure. In reports from 
the NHEXAS, Pb concentrations measured in households throughout the 
Midwest were significantly higher in solid food compared to 
beverages and tap water (Clayton et al., 1999; Thomas et al., 1999). 
However, beverages appeared to be the dominant dietary pathway for 
Pb according to the statistical analysis (Clayton et al., 1999), 
possibly indicating greater bodily absorption of Pb from liquid 
sources (Thomas et al., 1999). Dietary intakes of Pb were greater 
than those calculated for intake from home tap water or inhalation 
on a [mu]g/day basis (Thomas et al., 1999). The NHEXAS study in 
Arizona showed that, for adults, ingestion was a more important Pb 
exposure route than inhalation (O'Rourke et al., 1999).'' (CD, p. 3-
43)
    \19\ For example, the Criteria Document states the following: 
``Given the large amount of time people spend indoors, exposure to 
Pb in dusts and indoor air can be significant. For children, dust 
ingested via hand-to-mouth activity is often a more important source 
of Pb exposure than inhalation. Dust can be resuspended through 
household activities, thereby posing an inhalation risk as well. 
House dust Pb can derive both from Pb-based paint and from other 
sources outside the home. The latter include Pb-contaminated 
airborne particles from currently operating industrial facilities or 
resuspended soil particles contaminated by deposition of airborne Pb 
from past emissions.'' (CD, p. E-6)
---------------------------------------------------------------------------

    Estimating contributions from nonair sources is complicated by the 
existence of multiple and varied air-related pathways (as described in 
section II.A.2 above), as well as the persistent nature of Pb. For 
example, Pb that is a soil or dust contaminant today may have been 
airborne yesterday or many years ago. The studies currently available 
and reviewed in the Criteria Document that evaluate the multiple 
pathways of Pb exposure, when considering exposure contributions from 
outdoor dust/soil, do

[[Page 29193]]

not usually distinguish between outdoor soil/dust Pb resulting from 
historical emissions and outdoor soil/dust Pb resulting from recent 
emissions. Further, while indoor dust Pb has been identified as being a 
predominant contributor to children's blood Pb, available studies do 
not generally distinguish the different pathways (air-related and 
other) contributing to indoor dust Pb. The exposure assessment for 
children performed for this review has employed available data and 
methods to develop estimates intended to inform a characterization of 
these pathways (as described in section II.C below).
    Relative contributions to a child's total Pb exposure from air-
related exposure pathways (such as those identified in the sections 
above) compared to other (nonair-related) Pb exposures depends on many 
factors including ambient air concentrations and air deposition in the 
area where the child resides (as well as in the area from which the 
child's food derives), access to other sources of Pb exposure such as 
Pb paint, tap water affected by plumbing containing Pb and access to 
Pb-tainted products. Studies indicate that in the absence of paint-
related exposures, Pb from other sources such as stationary sources of 
Pb emissions may dominate a child's Pb exposures (CD, section 3.2). In 
other cases, such as children living in older housing with peeling 
paint or where renovations have occurred, the dominant source may be 
lead paint used in the house in the past (CD, pp. 3-50 and 3-51). 
Depending on Pb levels in a home's tap water, drinking water can 
sometimes be a significant source (CD, section 3.3). And in still other 
cases, there may be more of a mixture of contributions from multiple 
sources, with no one source dominating (CD, Chapter 3).
    As recognized in sections B.1.1 and II.B.3.a, blood Pb levels are 
the commonly used index of exposure for Pb and they reflect external 
sources of exposure, behavioral characteristics and physiological 
factors. Lead derived from differing sources or taken into the body as 
a result of differing exposure pathways (e.g., air- as compared to 
nonair-related), is not easily distinguished. As mentioned above, 
complications to consideration of estimates of air-related or 
conversely, nonair, blood Pb levels are the roles of air Pb in human 
exposure pathways and the persistence of Pb in the environment. As 
described in section II.A.2, air-related pathways (those in which Pb 
passes through the air on its path from source to human exposure) are 
varied, including inhalation and ingestion, indoor dust, outdoor dust/
soil and diet, Pb suspended in and deposited from air, and encompassing 
a range of time frames from more immediate to less so. Estimates of 
blood Pb levels associated with air-related exposure pathways or only 
with nonair exposure pathways will vary depending on how completely the 
air-related pathways are characterized.
    Consistent with reductions in air Pb concentrations (as described 
in section II.A.1 above) which contribute to blood Pb, nonair 
contributions have also been reduced. For example, the use of Pb paint 
in new houses has declined substantially over the 20th century, such 
that according to the National Survey of Lead and Allergens in Housing 
(USHUD, 2002) an estimated 24% of U.S. housing constructed between 1960 
and 1978; 69% of the housing constructed between 1940 and 1959; and 87% 
of the pre-1940 housing contains lead-based paint. Additionally, Pb 
contributions to diet have been reported to have declined significantly 
since 1978, perhaps as much as 70% or more between then and 1990 (WHO, 
1995) and the 2006 Criteria Document identifies a drop in dietary Pb 
intake by 2 to 5 year olds of 96% between the early 1980s and mid 1990s 
(CD, Section 3.4 and p. 8-14).\20\ These reductions are generally 
attributed to reductions in gasoline-related airborne Pb as well as the 
reduction in use of Pb solder in canning food products (CD, Section 
3.4).\21\ There have also been reductions in tap water Pb levels (CD, 
section 3.3 and pp. 8-13 to 8-14). Contamination from the distribution/
plumbing system appears to remain the predominant source of Pb in the 
drinking water (CD, section 3.3 and pp. 8-013 to 8-14).
---------------------------------------------------------------------------

    \20\ Additionally, the 1977 Criteria Document included a dietary 
Pb intake estimate for the general population of 100 to 350 [mu]g 
Pb/day, with estimates near and just below 100 [mu]g/day for young 
children (USEPA 1977, pp. 1-2 and 12-32) and the 2006 Criteria 
Document cites recent studies (for the mid-1990s) indicating a 
dietary intake ranging from 2 to 10 [mu]g Pb/day for children (CD, 
Section 3.4 and p. 8-14).
    \21\ Sources of Pb in food were identified in the 1986 Criteria 
Document as including air-related sources, metals used in processing 
raw foodstuffs, solder used in packaging and water used in cooking 
(1986a, section 3.1.2).
---------------------------------------------------------------------------

    The availability of estimates of blood Pb levels resulting only 
from air-related sources and exposures or only from those unrelated to 
air is limited and, given the discussion above, would be expected to 
vary for different populations. In addition to potential differences in 
air-related and nonair-related blood Pb levels among populations with 
different exposure circumstances (e.g., relatively more or lesser 
exposure to air-related Pb), the absolute levels may also vary among 
different age groups. As described in section II.B.1.b, average total 
blood Pb levels in the U.S. differ among age groups, with levels being 
highest in children aged one to five years old. We also note that 
behavioral characteristics that influence Pb exposures vary among age 
groups. For example as noted above, the predominant Pb exposure 
pathways may differ between adults and children. The extent of any 
quantitative impact of these differences on estimates of nonair blood 
Pb levels is unknown.\22\
---------------------------------------------------------------------------

    \22\ As noted earlier in this section, for children, dust 
ingestion by hand-to-mouth activity can be an important source of Pb 
exposure, while for adults, dietary Pb can be predominant.
---------------------------------------------------------------------------

    In their advice to the Agency on levels for the standard, the CASAC 
Pb Panel explored several approaches to deriving a level, one of which 
required an estimate of the nonair component of blood Pb for the 
average child. They recommended consideration of 1.0 to 1.4 [mu]g/dL or 
lower for such an estimate for the average nonair blood Pb level for 
young children (Henderson, 2007a, p. D-1). This range was developed 
with consideration of simulations of the integrated exposure and uptake 
biokinetic (IEUBK) model for lead for which the exposure concentration 
inputs included zero air concentration and concentrations for soil and 
dust of 50 ppm and 35 ppm, respectively (Henderson, 2007a, p. F-
60).\23\ \24\ \25\
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    \23\ The soil and dust levels are described as ``typical 
geochemical non-air input levels for dust and soil'' (Henderson, 
2007a, p. F-60). The values used for these levels in this simulation 
fall within the range of 1 to 200 ppm described in the Criteria 
Document for soil not influenced by sources (CD, p. 3-18).
    \24\ The other IEUBK inputs (e.g., exposure and biokinetic 
factors) were those used in the IEUBK modeling for the risk 
assessment in this review (Henderson, 2007a, p. F-60).
    \25\ Individual CASAC member comments describing the IEUBK 
simulations stated that the modeling produced a nonair blood Pb 
level of ``1.4 [mu]g/dL as a geometric mean'' (Henderson, 2007a, p. 
F-61).
---------------------------------------------------------------------------

    As is evident from the prior discussion, the many different 
exposure pathways contributing to children's blood Pb levels, and other 
factors, complicate our consideration of the available data with regard 
to characterization of levels particular to specific pathways, air-
related or otherwise.

B. Health Effects Information

    The following summary focuses on health endpoints associated with 
the range of exposures considered to be most relevant to current 
exposure levels and makes note of several key aspects of the health 
evidence for Pb. First (as

[[Page 29194]]

described in Section II.A, above), because exposure to atmospheric Pb 
particles occurs not only via direct inhalation of airborne particles, 
but also via ingestion of deposited ambient Pb, the exposure considered 
is multimedia and multipathway in nature, occurring via both the 
inhalation and ingestion routes. Second, the exposure index or dose 
metric most commonly used and associated with health effects 
information is an internal biomarker (i.e., blood Pb). Additionally, 
the exposure duration of interest (i.e., that influencing internal dose 
pertinent to health effects of interest) may span months to potentially 
years, as does the time scale of the environmental processes 
influencing Pb deposition and fate. Lastly, the nature of the evidence 
for the health effects of greatest interest for this review, 
neurological effects, particularly neurocognitive and neurobehavioral 
effects, in young children, are epidemiological data substantiated by 
toxicological data that provide biological plausibility and insights on 
mechanisms of action (CD, sections 5.3, 6.2 and 8.4.2).
    In recognition of the multi-pathway aspects of Pb, and the use of 
an internal exposure metric in health risk assessment, the next section 
describes the internal disposition or distribution of Pb, and the use 
of blood Pb as an internal exposure or dose metric. This is followed by 
a discussion of the nature of Pb-induced health effects that emphasizes 
those with the strongest evidence. Potential impacts of Pb exposures on 
public health, including recognition of potentially susceptible or 
vulnerable subpopulations, are then discussed. Finally, key 
observations about Pb-related health effects are summarized.
1. Blood Lead
    The health effects of Pb are remote from the portals of entry to 
the body (i.e., the respiratory system and gastrointestinal tract). 
Consequently, the internal disposition and distribution of Pb in the 
blood is an integral aspect of the relationship between exposure and 
effect. Additionally, the focus on blood Pb as the dose metric in 
consideration of the Pb health effects evidence, while reducing our 
uncertainty with regard to causality, leads to an additional 
consideration with regard to contribution of air-related sources and 
exposure pathways to blood Pb.
a. Internal Disposition of Lead
    This section briefly summarizes the current state of knowledge of 
Pb disposition pertaining to both inhalation and ingestion routes of 
exposure as described in the Criteria Document.
    Inhaled Pb particles deposit in the different regions of the 
respiratory tract as a function of particle size (CD, pp. 4-3 to 4-4). 
Lead associated with smaller particles, which are predominantly 
deposited in the pulmonary region, may, depending on solubility, be 
absorbed into the general circulation or transported to the 
gastrointestinal tract (CD, pp. 4-3). Lead associated with larger 
particles, which are predominantly deposited in the head and conducting 
airways (e.g., nasal pharyngeal and tracheobronchial regions of 
respiratory tract), may be transported into the esophagus and 
swallowed, thus making its way to the gastrointestinal tract (CD, pp. 
4-3 to 4-4), where it may be absorbed into the blood stream. Thus, Pb 
can reach the gastrointestinal tract either directly through the 
ingestion route or indirectly following inhalation.
    Once in the blood stream, where approximately 99% of the Pb 
associates with red blood cells, the Pb is quickly distributed 
throughout the body (e.g., within days) with the bone serving as a 
large, long-term storage compartment, and soft tissues (e.g., kidney, 
liver, brain, etc.) serving as smaller compartments, in which Pb may be 
more mobile (CD, sections 4.3.1.4 and 8.3.1.). Additionally, the 
epidemiologic evidence indicates that Pb freely crosses the placenta 
resulting in continued fetal exposure throughout pregnancy, and that 
exposure increases during the later half of pregnancy (CD, section 
6.6.2).
    During childhood development, bone represents approximately 70% of 
a child's body burden of Pb, and this accumulation continues through 
adulthood, when more than 90% of the total Pb body burden is stored in 
the bone (CD, section 4.2.2). Accordingly, levels of Pb in bone are 
indicative of a person's long-term, cumulative exposure to Pb. In 
contrast, blood Pb levels are usually indicative of recent exposures. 
Depending on exposure dynamics, however, blood Pb may--through its 
interaction with bone--be indicative of past exposure or of cumulative 
body burden (CD, section 4.3.1.5).
    Throughout life, Pb in the body is exchanged between blood and 
bone, and between blood and soft tissues (CD, section 4.3.2), with 
variation in these exchanges reflecting ``duration and intensity of the 
exposure, age and various physiological variables'' (CD, p. 4-1). Past 
exposures that contribute Pb to the bone, consequently, may influence 
current levels of Pb in blood. Where past exposures were elevated in 
comparison to recent exposures, this influence may complicate 
interpretations with regard to recent exposure (CD, sections 4.3.1.4 to 
4.3.1.6). That is, higher blood Pb concentrations may be indicative of 
higher cumulative exposures or of a recent elevation in exposure (CD, 
pp. 4-34 and 4-133).
    In several studies investigating the relationship between Pb 
exposure and blood Pb in children (e.g., Lanphear and Roghmann 1997; 
Lanphear et al., 1998), blood Pb levels have been shown to reflect Pb 
exposures, with particular influence associated with exposures to Pb in 
surface dust. Further, as stated in the Criteria Document ``these and 
other studies of populations near active sources of air emissions 
(e.g., smelters, etc.) substantiate the effect of airborne Pb and 
resuspended soil Pb on interior dust and blood Pb'' (CD, p. 8-22).
b. Use of Blood Lead as Dose Metric
    Blood Pb levels are extensively used as an index or biomarker of 
exposure by national and international health agencies, as well as in 
epidemiological (CD, sections 4.3.1.3 and 8.3.2) and toxicological 
studies of Pb health effects and dose-response relationships (CD, 
Chapter 5). The prevalence of the use of blood Pb as an exposure index 
or biomarker is related to both the ease of blood sample collection 
(CD, p. 4-19; Section 4.3.1) and by findings of association with a 
variety of health effects (CD, Section 8.3.2). For example, the U.S. 
Centers for Disease Control and Prevention (CDC), and its predecessor 
agencies, have for many years used blood Pb level as a metric for 
identifying children at risk of adverse health effects and for 
specifying particular public health recommendations (CDC, 1991; CDC, 
2005a). In 1978, when the current Pb NAAQS was established, the CDC 
recognized a blood Pb level of 30 [mu]g/dL as a level warranting 
individual intervention (CDC, 1991). In 1985, the CDC recognized a 
level of 25 [mu]g/dL for individual child intervention, and in 1991, 
they recognized a level of 15 [mu]g/dL for individual intervention and 
a level of 10 [mu]g/dL for implementing community-wide prevention 
activities (CDC, 1991; CDCa, 2005). In 2005, with consideration of a 
review of the evidence by their advisory committee, CDC revised their 
statement on Preventing Lead Poisoning in Young Children, specifically 
recognizing the evidence of adverse health effects in children with 
blood Pb levels below 10 [mu]g/dL \26\ and the data demonstrating that

[[Page 29195]]

no ``safe'' threshold for blood Pb had been identified, and emphasizing 
the importance of preventative measures (CDC, 2005a, ACCLPP, 2007).\27\
---------------------------------------------------------------------------

    \26\ As described by the Advisory Committee on Childhood Lead 
Poisoning Prevention, ``In 1991, CDC defined the blood lead level 
(BLL) that should prompt public health actions as 10 [mu]g/dL. 
Concurrently, CDC also recognized that a BLL of 10 [mu]g/dL did not 
define a threshold for the harmful effects of lead. Research 
conducted since 1991 has strengthened the evidence that children's 
physical and mental development can be affected at BLLS <10 [mu]g/
dL'' (ACCLPP, 2007).
    \27\ With the 2005 statement, CDC did not lower the 1991 level 
of concern and identified a variety of reasons, reflecting both 
scientific and practical considerations, for not doing so, including 
a lack of effective clinical or public health interventions to 
reliably and consistently reduce blood Pb levels that are already 
below 10 [mu]g/dL, the lack of a demonstrated threshold for adverse 
effects, and concerns for deflecting resources from children with 
higher blood Pb levels (CDC, 2005a). CDC's Advisory Committee on 
Childhood Lead Poisoning Prevention recently provided 
recommendations regarding interpreting and managing blood Pb levels 
below 10 [mu]g/dL in children and reducing childhood exposures to Pb 
(ACCLPP, 2007).
---------------------------------------------------------------------------

    Since 1976, the CDC has been monitoring blood Pb levels nationally 
through the National Health and Nutrition Examination Survey (NHANES). 
This survey monitors blood Pb levels in multiple age groups in the U.S. 
This information indicates variation in mean blood Pb levels across the 
various age groups monitored. For example, mean values in 2001-2002 for 
ages 1-5, 6-11, 12-19 and greater than or equal to 20 years of age, are 
1.70, 1.25, 0.94, and 1.56, respectively (CD, p. 4-22).
    The NHANES information has documented the dramatic decline in mean 
blood Pb levels in the U.S. population that has occurred since the 
1970s and that coincides with regulations regarding leaded fuels, 
leaded paint, and Pb-containing plumbing materials that have reduced Pb 
exposure among the general population (CD, Sections 4.3.1.3 and 8.3.3; 
Schwemberger et al., 2005). The Criteria Document summarizes related 
information as follows (CD, p. E-6).

    In the United States, decreases in mobile sources of Pb, 
resulting from the phasedown of Pb additives created a 98% decline 
in emissions from 1970 to 2003. NHANES data show a consequent 
parallel decline in blood-Pb levels in children aged 1 to 5 years 
from a geometric mean of ~15 [mu]g/dL in 1976-1980 to ~1-2 [mu]g/dL 
in the 2000-2004 period.

While levels in the U.S. general population, including geometric mean 
levels in children aged 1-5, have declined significantly, levels have 
been found to vary among children of different socioeconomic status 
(SES) and other demographic characteristics (CD, p. 4-21). For example, 
while the 2001-2004 median blood level for children aged 1-5 of all 
races and ethnic groups is 1.6 [mu]g/dL, the median for the subset 
living below the poverty level is 2.3 [mu]g/dL and 90th percentile 
values for these two groups are 4.0 [mu]g/dL and 5.4 [mu]g/dL, 
respectively. Similarly, the 2001-2004 median blood level for black, 
non-Hispanic children aged 1-5 is 2.5 [mu]g/dL, while the median level 
for the subset of that group living below the poverty level is 2.9 
[mu]g/dL and the median level for the subset living in more well-off 
households (i.e., with income more than 200% of the poverty level) is 
1.9 [mu]g/dL. Associated 90th percentile values for 2001-2004 are 6.4 
[mu]g/dL (for black, non-Hispanic children aged 1-5), 7.7 [mu]g/dL (for 
the subset of that group living below the poverty level) and 4.1 [mu]g/
dL (for the subset living in a household with income more than 200% of 
the poverty level).\28\ The recently released RRP rule (discussed above 
in section I.C) is expected to contribute to further reductions in BLL 
for children living in houses with Pb paint.
---------------------------------------------------------------------------

    \28\ This information is available at: http://www.epa.gov/
envirohealth/children/body_burdens/b1-table.htm (click on 
``Download a universal spreadsheet file of the Body Burdens data 
tables'').

    Bone measurements, as a result of the generally slower Pb turnover 
in bone, are recognized as providing a better measure of cumulative Pb 
exposure (CD, Section 8.3.2). The bone pool of Pb in children, however, 
is thought to be much more labile than that in adults due to the more 
rapid turnover of bone mineral as a result of growth (CD, p. 4-27). As 
a result, changes in blood Pb concentration in children more closely 
parallel changes in total body burden (CD, pp. 4-20 and 4-27). This is 
in contrast to adults, whose bone has accumulated decades of Pb 
exposures (with past exposures often greater than current ones), and 
for whom the bone may be a significant source long after exposure has 
ended (CD, Section 4.3.2.5).
c. Air-to-Blood Relationships
    As described in Section II.A, Pb in ambient air contributes to Pb 
in blood by multiple pathways, with the pertinent exposure routes 
including both inhalation and ingestion (CD, Sections 3.1.3.2, 4.2 and 
4.4; Hilts, 2003). The quantitative relationship between ambient air Pb 
and blood Pb, which is often termed a slope or ratio, describes the 
increase in blood Pb (in [mu]g/dL) per unit of air Pb (in [mu]g/m 
\3\).\29\
---------------------------------------------------------------------------

    \29\ Ratios are presented in the form of 1:x, with the 1 
representing air Pb (in [mu]g/m\3\) and x representing blood Pb (in 
[mu]g/dL). Description of ratios as higher or lower refers to the 
values for x (i.e., the change in blood Pb per unit of air Pb). 
Slopes are presented as simply the value of x.
---------------------------------------------------------------------------

    The evidence on this quantitative relationship is now, as in the 
past, limited by the circumstances in which the data are collected. 
These estimates are generally developed from studies of populations in 
various Pb exposure circumstances. The 1986 Criteria Document discussed 
the studies available at that time that addressed the relationship 
between air Pb and blood Pb,\30\ recognizing that there is significant 
variability in air-to-blood ratios for different populations exposed to 
Pb through different air-related exposure pathways and at different 
exposure levels.
---------------------------------------------------------------------------

    \30\ We note that the 2006 Criteria Document did not include a 
discussion of more recent studies on air-to-blood ratios.
---------------------------------------------------------------------------

    In discussing the available evidence, the 1986 Criteria Document 
observed that estimates of air-to-blood ratios that included air-
related ingestion pathways in addition to the inhalation pathway are 
``necessarily higher'' (in terms of blood Pb response) than those 
estimates based on inhalation alone (USEPA 1986a, p. 11-106). Thus, the 
extent to which studies account for the full set of air-related 
exposure pathways affects the magnitude of the resultant air-to-blood 
estimates, such that fewer pathways included as ``air-related'' yield 
lower ratios. The 1986 Criteria Document also observed that ratios 
derived from studies focused only on inhalation pathways (e.g., chamber 
studies, occupational studies) have generally been on the order of 1:2 
or lower, while ratios derived from studies including more air-related 
pathways were generally higher (USEPA, 1986a, p. 11-106). Further, the 
current evidence appears to indicate higher ratios for children as 
compared to those for adults (USEPA, 1986a), perhaps due to behavioral 
differences between the age groups.
    Reflecting these considerations, the 1986 Criteria Document 
identified a range of air-to-blood ratios for children that reflected 
both inhalation and ingestion-related air Pb contributions as generally 
ranging from 1:3 to 1:5 based on the information available at that time 
(USEPA 1986a, p. 11-106). Table 11-36 (p. 11-100) in the 1986 Criteria 
Document (drawn from Table 1 in Brunekreef, 1984) presents air-to-blood 
ratios from a number of studies in children (i.e., those with 
identified air monitoring methods and reliable blood Pb data). For 
example, air-to-blood ratios from the subset of those studies that used 
quality control protocols and presented adjusted slopes \31\ include

[[Page 29196]]

adjusted ratios of 3.6 (Zielhuis et al., 1979), 5.2 (Billick et al., 
1979, 1980), 2.9 (Billick et al., 1983), and 8.5 (Brunekreef et al, 
1983).
---------------------------------------------------------------------------

    \31\ Brunekreef et al. (1984) discusses potential confounders to 
the relationship between air Pb and blood Pb, recognizing that 
ideally all possible confounders should be taken into account in 
deriving an adjusted air-to-blood relationship from a community 
study. The studies cited here adjusted for parental education 
(Zielhuis et al., 1979), age and race (Billick et al., 1979, 1980) 
and additionally measuring height of air Pb (Billick et al., 1983); 
Brunekreef et al. (1984) used multiple regression to control for 
several confounders. The authors conclude that ``presentation of 
both unadjusted and (stepwise) adjusted relationships is advisable, 
to allow insight in the range of possible values for the 
relationship'' (p. 83). Unadjusted ratios were presented for two of 
these studies, including ratios of 4.0 (Zielhuis et al., 1979) and 
18.5 (Brunekreef et al., 1983). Note, that the Brunekreef et al., 
1983 study is subject to a number of sources of uncertainty that 
could result in air-to-blood Pb ratios that are biased high, 
including the potential for underestimating ambient air Pb levels 
due to the use of low volume British Smoke air monitors and the 
potential for ongoing (higher historical) ambient air Pb levels to 
have influenced blood Pb levels (see Section V.B.2 of the 1989 Pb 
Staff Report for the Pb NAAQS review, EPA, 1989). In addition, the 
1989 Staff Report notes that the higher air-to-blood ratios obtained 
from this study could reflect the relatively lower blood Pb levels 
seen across the study population (compared with blood Pb levels 
reported in other studies from that period).
---------------------------------------------------------------------------

    Additionally, the 1986 Criteria Document noted that ratios derived 
from studies involving higher blood and air Pb levels are generally 
smaller than ratios from studies involving lower blood and air Pb 
levels (USEPA, 1986a. p. 11-99). In consideration of this factor, we 
note that the range of 1:3 to 1:5 in air-to-blood ratios for children 
noted in the 1986 Criteria Document generally reflected study 
populations with blood Pb levels in the range of approximately 10-30 
[mu]g/dL (USEPA 1986a, pp. 11-100; Brunekreef, 1984), much higher than 
those common in today's population. This observation suggests that air-
to-blood ratios relevant for today's population of children would 
likely extend higher than the 1:3 to 1:5 range identified in the 1986 
Criteria Document.
    More recently, a study of changes in children's blood Pb levels 
associated with reduced Pb emissions and associated air concentrations 
near a Pb smelter in Canada (for children through six years of age) 
reports a ratio of 1:6 and additional analysis of the data by EPA for 
the initial time period of the study resulted in a ratio of 1:7 (CD, 
pp. 3-23 to 3-24; Hilts, 2003).\32\ Ambient air and blood Pb levels 
associated with the Hilts (2003) study range from 1.1 to 0.03 [mu]g/
m\3\, and associated population mean blood Pb levels range from 11.5 to 
4.7 [mu]g/dL, which are lower than levels associated with the older 
studies cited in the 1986 Criteria Document (USEPA, 1986).
---------------------------------------------------------------------------

    \32\ This study considered changes in ambient air Pb levels and 
associated blood Pb levels over a five-year period which included 
closure of an older Pb smelter and subsequent opening of a newer 
facility in 1997 and a temporary (3 month) shutdown of all smelting 
activity in the summer of 2001. The author observed that the air-to-
blood ratio for children in the area over the full period was 
approximately 1:6. The author noted limitations in the dataset 
associated with exposures in the second time period, after the 
temporary shutdown of the facility in 2001, including sampling of a 
different age group at that time and a shorter time period (3 
months) at these lower ambient air Pb levels prior to collection of 
blood Pb levels. Consequently, EPA calculated an alternate air-to-
blood Pb ratio based on consideration for ambient air Pb and blood 
Pb reductions in the first time period (after opening of the new 
facility in 1997).
---------------------------------------------------------------------------

    Sources of uncertainty related to air-to-blood ratios obtained from 
Hilts (2003) study have been identified. One such area of uncertainty 
relates to the pattern of changes in indoor Pb dustfall (presented in 
Table 3 in the article) which suggests a potentially significant 
decrease in Pb impacts to indoor dust prior to closure of an older Pb 
smelter and start-up of a newer facility in 1997. Some have suggested 
that this earlier reduction in indoor dustfall suggests that a 
significant portion of the reduction in Pb exposure (and therefore, the 
blood Pb reduction reflected in air-to-blood ratios) may have resulted 
from efforts to increase public awareness of the Pb contamination issue 
(e.g., through increased cleaning to reduce indoor dust levels) rather 
than reductions in ambient air Pb and associated indoor dust Pb 
contamination. In addition, notable fluctuations in blood Pb levels 
observed prior to 1997 (as seen in Figure 2 of the article) have raised 
questions as to whether factors other than ambient air Pb reduction 
could be influencing decreases in blood Pb.\33\
---------------------------------------------------------------------------

    \33\ In the publication, the author acknowledges that remedial 
programs (e.g., community and home-based dust control and education) 
may have been responsible for some of the blood Pb reduction seen 
during the study period (1997 to 2001). However, the author points 
out that these programs were in place in 1992 and he suggests that 
it is unlikely that they contributed to the sudden drop in blood Pb 
levels occurring after 1997. In addition, the author describes a 
number of aspects of the analysis, which could have implications for 
air-to-blood ratios including a tendency over time for children with 
lower blood Pb levels to not return for testing, and inclusion of 
children aged 6 to 36 months in Pb screening in 2001 (in contrast to 
the wider age range up to 60 months as was done in previous years).
---------------------------------------------------------------------------

    In addition to the study by Hilts (2003), we are aware of two other 
studies published since the 1986 Criteria Document that report air-to-
blood ratios for children (Tripathi et al., 2001 and Hayes et al., 
1994). These studies were not cited in the 2006 Criteria Document, but 
were referenced in public comments received by EPA during this 
review.\34\ The study by Tripathi et al. (2001) reports an air-to-blood 
ratio of approximately 1:3.6 for an analysis of children aged six 
through ten in India. The ambient air and blood Pb levels in this study 
(geometric mean blood Pb levels generally ranged from 10 to 15 [mu]g/
dL) are similar to levels reported in older studies reviewed in the 
1986 Criteria Document and are much higher than current conditions in 
the U.S. The study by Hayes (1994) compared patterns of ambient air Pb 
reductions and blood Pb reductions for large numbers of children in 
Chicago between 1971 and 1988, a period when significant reductions 
occurred in both measures. The study reports an air-to-blood ratio of 
1:5.6 associated with ambient air Pb levels near 1 [mu]g/m\3\ and a 
ratio of 1:16 for ambient air Pb levels in the range of 0.25 [mu]g/
m\3\, indicating a pattern of higher ratios with lower ambient air Pb 
and blood Pb levels consistent with conclusions in the 1986 Criteria 
Document.\35\
---------------------------------------------------------------------------

    \34\ EPA is not basing its proposed decisions on these two 
studies, but notes that these estimates are consistent with other 
studies that were included in the 1986 and 2006 Criteria Documents 
and accordingly considered by CASAC and the public.
    \35\ As with all studies, we note that there are strengths and 
limitations for these two studies which may affect the specific 
magnitudes of the reported ratios, but that the studies' findings 
and trends are generally consistent with the conclusions from the 
1986 Criteria Document.
---------------------------------------------------------------------------

    In their advice to the Agency, CASAC identified air-to-blood ratios 
of 1:5, as used by the World Health Organization (2000), and 1:10, as 
supported by an empirical analysis of changes in air Pb and changes in 
blood Pb between 1976 and the time when the phase-out of Pb from 
gasoline was completed (Henderson, 2007a).\36\
---------------------------------------------------------------------------

    \36\ The CASAC Panel stated ``The Schwartz and Pitcher analysis 
showed that in 1978, the midpoint of the National Health and 
Nutrition Examination Survey (NHANES) II, gasoline Pb was 
responsible for 9.1 [mu]g/dL of blood Pb in children. Their estimate 
is based on their coefficient of 2.14 [mu]g/dL per 100 metric tons 
(MT) per day of gasoline use, and usage of 426 MT/day in 1976. 
Between 1976 and when the phase-out of Pb from gasoline was 
completed, air Pb concentrations in U.S. cities fell a little less 
than 1 [mu]g/m\3\ (24). These two facts imply a ratio of 9-10 [mu]g/
dL per [mu]g/m\3\ reduction in air Pb, taking all pathways into 
account.'' (Henderson, 2007a, pp. D-2 to D-3).
---------------------------------------------------------------------------

    Beyond considering the evidence presented in the published 
literature and that reviewed in Pb Criteria Documents, we have also 
considered air-to-blood ratios derived from the exposure assessment for 
this review (discussed below in section II.C). In that assessment, 
current modeling tools and information on children's activity patterns, 
behavior and physiology (e.g., CD, Section 4.4) were used to estimate 
blood Pb levels associated with

[[Page 29197]]

multimedia and multipathway Pb exposure. The results from the various 
case studies included in this assessment, with consideration of the 
context in which they were derived (e.g., the extent to which the range 
of air-related pathways were simulated), are also informative to our 
understanding of air-to-blood ratios.
    For the general urban case study, air-to-blood ratios ranged from 
1:2 to 1:9 across the alternative standard levels assessed, which 
ranged from the current standard of 1.5 [mu]g/m\3\ down to a level of 
0.02 [mu]g/m\3\. This pattern of model-derived ratios generally 
supports the range of ratios obtained from the literature and also 
supports the observation that lower ambient air Pb levels are 
associated with higher air-to-blood ratios. There are a number of 
sources of uncertainty associated with these model-derived ratios. The 
hybrid indoor dust Pb model, which is used in estimating indoor dust Pb 
levels for the urban case studies, uses a HUD dataset reflecting 
housing constructed before 1980 in establishing the relationship 
between dust loading and concentration, which is a key component in the 
hybrid dust model (see Section Attachment G-1 of the Risk Assessment, 
Volume II). Given this application of the HUD dataset, there is the 
potential that the non-linear relationship between indoor dust Pb 
loading and concentration (which is reflected in the structure of the 
hybrid dust model) could be driven more by the presence of indoor Pb 
paint than contributions from outdoor ambient air Pb. We also note that 
only recent air pathways were adjusted in modeling the impact of 
ambient air Pb reductions on blood Pb levels in the urban case studies, 
which could have implications for the air-to-blood ratios.
    For the primary Pb smelter (subarea) case study, air-to-blood 
ratios ranged from 1:10 to 1:19 across the same range of alternative 
standard levels, from 1.5 down to 0.02 [mu]g/m\3\.\37\ Because these 
ratios are based on regression modeling developed using empirical data, 
there is the potential for these ratios to capture more fully the 
impact of ambient air on indoor dust Pb (and ultimately blood Pb), 
including longer timeframe impacts resulting from changes in outdoor 
deposition. Therefore, given that these ratios are higher than ratios 
developed for the general urban case study using the hybrid indoor dust 
Pb model (which only considers reductions in recent air), the ratios 
estimated for the primary Pb smelter (subarea) support the evidence-
based observation discussed above that consideration of more of the 
exposure pathways relating ambient air Pb to blood Pb, may result in 
higher air-to-blood Pb ratios. In considering this case study, some 
have suggested, however, that the regression modeling fails to 
accurately reflect the temporal relationship between reductions in 
ambient air Pb and indoor dust Pb, which could result in an over-
estimate of the degree of dust Pb reduction associated with a specified 
degree of ambient air Pb reduction, which in turn could produce air-to-
blood Pb ratios that are biased high.
---------------------------------------------------------------------------

    \37\ As noted below in section II.C.3.a, air-to-blood ratios for 
the primary Pb smelter (full study area) range from 1:3 to 1:7 
across the same range of alternative standard levels (from 1.5 down 
to 0.02 [mu]g/m\3\).
---------------------------------------------------------------------------

    In summary, in EPA's view, the current evidence in conjunction with 
the results and observations drawn from the exposure assessment, 
including related uncertainties, supports consideration of a range of 
air-to-blood ratios for children ranging from 1:3 to 1:7, reflecting 
multiple air-related pathways beyond simply inhalation and the lower 
air and blood Pb levels pertinent to this review. In light of the 
uncertainties that remain in the available information on air-to-blood 
ratios, EPA requests comment on this range and on the appropriate 
weight to place on specific ratios within this range.
2. Nature of Effects
a. Broad Array of Effects
    Lead has been demonstrated to exert ``a broad array of deleterious 
effects on multiple organ systems via widely diverse mechanisms of 
action'' (CD, p. 8-24 and Section 8.4.1). This array of health effects 
includes effects on heme biosynthesis and related functions; 
neurological development and function; reproduction and physical 
development; kidney function; cardiovascular function; and immune 
function. The weight of evidence varies across this array of effects 
and is comprehensively described in the Criteria Document. There is 
also some evidence of Pb carcinogenicity, primarily from animal 
studies, together with limited human evidence of suggestive 
associations (CD, Sections 5.6.2, 6.7, and 8.4.10).\38\
---------------------------------------------------------------------------

    \38\ Lead has been classified as a probable human carcinogen by 
the International Agency for Research on Cancer, based mainly on 
sufficient animal evidence, and as reasonably anticipated to be a 
human carcinogen by the U.S. National Toxicology Program (CD, 
Section 6.7.2). U.S. EPA considers Pb a probable carcinogen (http://
www.epa.gov/iris/subst/0277.htm; CD, p. 6-195).
---------------------------------------------------------------------------

    This review is focused on those effects most pertinent to ambient 
exposures, which given the reductions in ambient Pb levels over the 
past 30 years, are generally those associated with individual blood Pb 
levels in children and adults in the range of 10 [mu]g/dL and lower. 
Tables 8-5 and 8-6 in the Criteria Document highlight the key such 
effects observed in children and adults, respectively (CD, pp. 8-60 to 
8-62). The effects include neurological, hematological and immune 
effects for children, and hematological, cardiovascular and renal 
effects for adults. As evident from the discussions in Chapters 5, 6 
and 8 of the Criteria Document, ``neurotoxic effects in children and 
cardiovascular effects in adults are among those best substantiated as 
occurring at blood Pb concentrations as low as 5 to 10 [mu]g/dL (or 
possibly lower); and these categories are currently clearly of greatest 
public health concern'' (CD, p. 8-60).\39\ The toxicological and 
epidemiological information available since the time of the last review 
``includes assessment of new evidence substantiating risks of 
deleterious effects on certain health endpoints being induced by 
distinctly lower than previously demonstrated Pb exposures indexed by 
blood Pb levels extending well below 10 [mu]g/dL in children and/or 
adults'' (CD, p. 8-25). Some health effects associated with individual 
blood Pb levels extend below 5 [mu]g/dL, and some studies have observed 
these effects at the lowest blood levels considered.
---------------------------------------------------------------------------

    \39\ With regard to blood Pb levels in individual children 
associated with particular neurological effects, the Criteria 
Document states ``Collectively, the prospective cohort and cross-
sectional studies offer evidence that exposure to Pb affects the 
intellectual attainment of preschool and school age children at 
blood Pb levels <10 [mu]g/dL (most clearly in the 5 to 10 [mu]g/dL 
range, but, less definitively, possibly lower).'' (p. 6-269)
---------------------------------------------------------------------------

    With regard to population mean levels, the Criteria Document points 
to studies reporting ``Pb effects on the intellectual attainment of 
preschool and school age children at population mean concurrent blood-
Pb levels ranging down to as low as 2 to 8 [mu]g/dL'' (CD, p. E-9).
    We note that many studies over the past decade have, in 
investigating effects at lower blood Pb levels, utilized the CDC 
advisory level for individual children (10 [mu]g/dL) as a benchmark for 
assessment, and this is reflected in the numerous references in the 
Criteria Document to 10 [mu]g/dL. Individual study conclusions stated 
with regard to effects observed below 10 [mu]g/dL are usually referring 
to individual blood Pb levels. In fact, many such study groups have 
been restricted to individual blood Pb levels below 10 [mu]g/dL or 
below levels lower than 10 [mu]g/dL. We note that the

[[Page 29198]]

mean blood Pb level for these groups will necessarily be lower than the 
blood Pb level they are restricted below.
    Threshold levels, in terms of blood Pb levels in individual 
children, for neurological effects cannot be discerned from the 
currently available studies (CD, pp. 8-60 to 8-63). The Criteria 
Document states ``There is no level of Pb exposure that can yet be 
identified, with confidence, as clearly not being associated with some 
risk of deleterious health effects'' (CD, p. 8-63). As discussed in the 
Criteria Document, ``a threshold for Pb neurotoxic effects may exist at 
levels distinctly lower than the lowest exposures examined in these 
epidemiologic studies'' (CD, p. 8-67).\40\
---------------------------------------------------------------------------

    \40\ In consideration of the evidence from experimental animal 
studies with regard to the issue of threshold for neurotoxic 
effects, the CD notes that there is little evidence that allows for 
clear delineation of a threshold, and that ``blood-Pb levels 
associated with neurobehavioral effects appear to be reasonably 
parallel between humans and animals at reasonably comparable blood-
Pb concentrations; and such effects appear likely to occur in humans 
ranging down at least to 5-10 [mu]g/dL, or possibly lower (although 
the possibility of a threshold for such neurotoxic effects cannot be 
ruled out at lower blood-Pb concentrations)'' (CD, p. 8-38).
---------------------------------------------------------------------------

    In summary, the Agency has identified neurological, hematological 
and immune effects in children and neurological, hematological, 
cardiovascular and renal effects in adults as the effects observed at 
blood Pb levels near or below 10 [mu]g/dL and further considers 
neurological effects in children and cardiovascular effects in adults 
to be categories of effects that ``are currently clearly of greatest 
public health concern'' (CD, pp. 8-60 to 8-62). Neurological effects in 
children are discussed further below.
b. Neurological Effects in Children
    Among the wide variety of health endpoints associated with Pb 
exposures, there is general consensus that the developing nervous 
system in young children is among, if not, the most sensitive. As 
described in the Criteria Document, neurotoxic effects in children and 
cardiovascular effects in adults are categories of effects that are 
``currently clearly of greatest public health concern'' (CD, p. 8-
60).\41\ While also recognizing the occurrence of adult cardiovascular 
effects at somewhat similarly low blood Pb levels \42\, neurological 
effects in children are considered to be the sentinel effects in this 
review and are the focus of the quantitative risk assessment conducted 
for this review (discussed below in section III.C).
---------------------------------------------------------------------------

    \41\ The Criteria Document states ``neurotoxic effects in 
children and cardiovascular effects in adults are among those best 
substantiated as occurring at blood-Pb concentrations as low as 5 to 
10 [mu]g/dL (or possibly lower); and these categories of effects are 
currently clearly of greatest public health concern (CD, p. 8-60).''
    \42\ For example, the Criteria Document describes associations 
of blood Pb in adults with blood pressure in studies with population 
mean blood Pb levels ranging from approximately 2 to 6 [mu]g/dL (CD, 
section 6.5.2 and Table 6-2).
---------------------------------------------------------------------------

    The nervous system has long been recognized as a target of Pb 
toxicity, with the developing nervous system affected at lower 
exposures than the mature system (CD, Sections 5.3, 6.2.1, 6.2.2, and 
8.4). While blood Pb levels in U.S. children ages one to five years 
have decreased notably since the late 1970s, newer studies have 
investigated and reported associations of effects on the 
neurodevelopment of children with these more recent blood Pb levels 
(CD, Chapter 6). Functional manifestations of Pb neurotoxicity during 
childhood include sensory, motor, cognitive and behavioral impacts. 
Numerous epidemiological studies have reported neurocognitive, 
neurobehavioral, sensory, and motor function effects in children with 
blood Pb levels below 10 [mu]g/dL (CD, Sections 6.2 and 8.4). \43\ As 
discussed in the Criteria Document, ``extensive experimental laboratory 
animal evidence has been generated that (a) substantiates well the 
plausibility of the epidemiologic findings observed in human children 
and adults and (b) expands our understanding of likely mechanisms 
underlying the neurotoxic effects'' (CD, p. 8-25; Section 5.3).
---------------------------------------------------------------------------

    \43\ Further, neurological effects in general include behavioral 
effects, such as delinquent behavior (CD, sections 6.2.6 and 
8.4.2.2), sensory effects, such as those related to hearing and 
vision (CD, sections 6.2.7 and 8.4.2.3), and deficits in neuromotor 
function (CD, p. 8-36).
---------------------------------------------------------------------------

    The evidence for neurotoxic effects in children is a robust 
combination of epidemiological and toxicological evidence (CD, Sections 
5.3, 6.2 and 8.5). The epidemiological evidence is supported by animal 
studies that substantiate the biological plausibility of the 
associations, and contributes to our understanding of mechanisms of 
action for the effects (CD, Section 8.4.2).
    Cognitive effects associated with Pb exposures that have been 
observed in epidemiological studies have included decrements in 
intelligence test results, such as the widely used IQ score, and in 
academic achievement as assessed by various standardized tests as well 
as by class ranking and graduation rates (CD, Section 6.2.16 and pp 8-
29 to 8-30). As noted in the Criteria Document with regard to the 
latter, ``Associations between Pb exposure and academic achievement 
observed in the above-noted studies were significant even after 
adjusting for IQ, suggesting that Pb-sensitive neuropsychological 
processing and learning factors not reflected by global intelligence 
indices might contribute to reduced performance on academic tasks'' 
(CD, pp 8-29 to 8-30).
    Other cognitive effects observed in studies of children have 
included effects on attention, executive functions, language, memory, 
learning and visuospatial processing (CD, Sections 5.3.5, 6.2.5 and 
8.4.2.1), with attention and executive function effects associated with 
Pb exposures indexed by blood Pb levels below 10 [mu]g/dL (CD, Section 
6.2.5 and pp. 8-30 to 8-31). The evidence for the role of Pb in this 
suite of effects includes experimental animal findings (discussed in 
CD, Section 8.4.2.1; p. 8-31), which provide strong biological 
plausibility of Pb effects on learning ability, memory and attention 
(CD, Section 5.3.5), as well as associated mechanistic findings. With 
regard to persistence of effects the Criteria Document states the 
following (CD, p. 8-67):

    Persistence or apparent ``irreversibility'' of effects can 
result from two different scenarios: (1) Organic damage has occurred 
without adequate repair or compensatory offsets, or (2) exposure 
somehow persists. As Pb exposure can also derive from endogenous 
sources (e.g., bone), a performance deficit that remains detectable 
after external exposure has ended, rather than indicating 
irreversibility, could reflect ongoing toxicity due to Pb remaining 
at the critical target organ or Pb deposited at the organ post-
exposure as the result of redistribution of Pb among body pools. The 
persistence of effect appears to depend on the duration of exposure 
as well as other factors that may affect an individual's ability to 
recover from an insult. The likelihood of reversibility also seems 
to be related, at least for the adverse effects observed in certain 
organ systems, to both the age-at-exposure and the age-at-
assessment.

The evidence with regard to persistence of Pb-induced deficits observed 
in animal and epidemiological studies is described in discussion of 
those studies in the Criteria Document (CD, Sections 5.3.5, 6.2.11, and 
8.5.2). It is additionally important to note that there may be long-
term consequences of such deficits over a lifetime. Poor academic 
skills and achievement can have ``enduring and important effects on 
objective parameters of success in real life,'' as well as increased 
risk of antisocial and delinquent behavior (CD, Section 6.2.16).

    As discussed in the Criteria Document, while there is no direct 
animal test parallel to human IQ tests, ``in animals a wide variety of 
tests that assess attention, learning, and memory suggest that Pb 
exposure {of animals{time}  results in a global deficit in functioning,

[[Page 29199]]

just as it is indicated by decrements in IQ scores in children'' (CD, 
p. 8-27). The animal and epidemiological evidence for this endpoint are 
consistent and complementary (CD, p. 8-44). As stated in the Criteria 
Document (p. 8-44):

    Findings from numerous experimental studies of rats and of 
nonhuman primates, as discussed in Chapter 5, parallel the observed 
human neurocognitive deficits and the processes responsible for 
them. Learning and other higher order cognitive processes show the 
greatest similarities in Pb-induced deficits between humans and 
experimental animals. Deficits in cognition are due to the combined 
and overlapping effects of Pb-induced perseveration, inability to 
inhibit responding, inability to adapt to changing behavioral 
requirements, aversion to delays, and distractibility. Higher level 
neurocognitive functions are affected in both animals and humans at 
very low exposure levels (<10 [mu]g/dL), more so than simple 
cognitive functions.

    Epidemiologic studies of Pb and child development have demonstrated 
inverse associations between blood Pb concentrations and children's IQ 
and other cognitive-related outcomes at successively lower Pb exposure 
levels over the past 30 years (CD, p. 6-64). This is supported by 
multiple studies performed over the past 15 years (as discussed in the 
CD, Section 6.2.13). For example, the overall weight of the available 
evidence, described in the Criteria Document, provides clear 
substantiation of neurocognitive decrements being associated in 
children with mean blood Pb levels in the range of 5 to 10 [mu]g/dL, 
and some analyses indicate Pb effects on intellectual attainment of 
children for which population mean blood Pb levels in the analysis 
ranged from 2 to 8 [mu]g/dL (CD, Sections 6.2, 8.4.2 and 8.4.2.6).\44\ 
That is, while blood Pb levels in U.S. children have decreased notably 
since the late 1970s, newer studies have investigated and reported 
associations of effects on the neurodevelopment of children with blood 
Pb levels similar to the more recent blood Pb levels (CD, Chapter 6).
---------------------------------------------------------------------------

    \44\ ``The overall weight of the available evidence provides 
clear substantiation of neurocognitive decrements being associated 
in young children with blood-Pb concentrations in the range of 5-10 
[mu]g/dL, and possibly somewhat lower. Some newly available analyses 
appear to show Pb effects on the intellectual attainment of 
preschool and school age children at population mean concurrent 
blood-Pb levels ranging down to as low as 2 to 8 [mu]g/dL.'' (CD, p. 
E-9)
---------------------------------------------------------------------------

    The evidence described in the Criteria Document with regard to the 
effect on children's cognitive function of blood Pb levels at the lower 
concentration range includes the international pooled analysis by 
Lanphear and others (2005), studies of individual cohorts such as the 
Rochester, Boston, and Mexico City cohorts (Canfield et al., 2003a; 
Canfield et al., 2003b; Bellinger and Needleman, 2003; Tellez-Rojo et 
al., 2006), the study of African-American inner-city children from 
Detroit (Chiodo et al., 2004), the cross-sectional study of young 
children in three German cities (Walkowiak et al., 1998) and the cross-
sectional analysis of a nationally representative sample from the 
NHANES III \45\ (Lanphear et al., 2000). These studies included 
differing adjustments for different important potential confounders 
(e.g., parental IQ or HOME score) or surrogates of these measures 
(e.g., parental education and SES factors) through multivariate 
analyses.46 47 Each of these studies has individual 
strengths and limitations, however, a pattern of positive findings is 
demonstrated across the studies. In these studies, statistically 
significant associations of neurocognitive decrement \48\ with blood Pb 
were found in the full study cohorts, as well as in some subgroups 
restricted to children with lower blood Pb levels for which mean blood 
Pb levels extended below 5 [mu]g/dL. More specifically, a statistically 
significant association was reported for full-scale IQ with blood Pb at 
age five in a subset analysis (n=71) of the Rochester cohort for which 
the population mean blood Pb level was 3.32 [mu]g/dL, as well as in the 
full study group (mean=5.8 [mu]g/dL, n=171) (Canfield et al., 2003a; 
Canfield, 2008). Full-scale IQ was also significantly associated with 
blood Pb at age seven and a half in a subset analysis (n=200) in the 
Detroit inner-city study for which the population mean blood Pb level 
was 4.1 [mu]g/dL, as well as the other subgroup with higher blood Pb 
levels (mean=4.6 [mu]g/dL, n=224) and in the full study group (mean=5.4 
[mu]g/dL, n=246); additionally, performance IQ was significantly 
associated with blood Pb in those analyses as well as in the subset 
analysis (n=120) for which the population mean blood Pb level was 3 
[mu]g/dL (although full-scale IQ was not significantly associated with 
blood Pb in this lowest blood Pb subgroup) (Chiodo et al., 2004, 
Chiodo, 2008). Vocabulary, one of ten subtests of the full-scale IQ, 
was significantly associated with blood

[[Page 29200]]

Pb at age six in the German three-city study (n=384) in which the mean 
blood Pb level was 4.2 [mu]g/dL (Walkowiak et al., 1998). In a Mexico 
City cohort of infants age two, the mental development index (MDI) and 
psychomotor development index (PDI) were significantly associated with 
blood Pb in the full study group (mean=4.28 [mu]g/dL, n=294); further, 
the MDI (but not the PDI) was significantly associated with blood Pb in 
the subset analysis (n=193) for which the population mean blood Pb 
level was 2.9 [mu]g/dL, and PDI (but not the MDI) was significantly 
associated with blood Pb in the subset analysis (n=101) for which the 
population mean blood Pb was 6.9 [mu]g/dL (Tellez-Rojo et al., 2006; 
Tellez-Rojo, 2008). Scores on academic achievement tests for reading 
and math were significantly associated with blood Pb at age six through 
sixteen in a subgroup analysis (n=4043) of the NHANES III data for 
which the population mean blood Pb level was 1.7 [mu]g/dL, as discussed 
below (Lanphear et al. 2000; Auinger, 2008).
---------------------------------------------------------------------------

    \45\ The NHANES III survey was conducted in 1988-1994.
    \46\ Some studies also employed exclusion criteria which limited 
variation in socioeconomic status across the study population. 
Further, with regard to adjustment for potential confounders in the 
large pooled international analysis (Lanphear et al. 2005), 
discussed below, the authors adjusted for HOME score, birth weight, 
maternal IQ and maternal education. Canfield et al. (2003) adjusted 
for maternal IQ, maternal education, HOME score, birth weight, race, 
tobacco use during pregnancy, household income, gender, and iron 
status. Bellinger and Needleman (2003) adjusted for maternal IQ, 
HOME score, SES, child stress, maternal age, race, gender, birth 
order, marital status. Chiodo et al. (2004) adjusted for primary 
care-giver education and vocabulary, HOME score, family environment 
scale, SES, gender, number of children under 18, birth order. 
Tellez-Rojo et al. (2006) adjusted for maternal IQ, birth weight and 
gender; the authors also state that other potentially confounding 
variables that were not found to be significant at p<.10 were not 
adjusted for. Walkoviak et al. (1998) adjusted for parental 
education, breastfeeding, nationality and gender. In Lanphear et al. 
(2000), the authors adjusted for race/ethnicity and poverty index 
ratio, as surrogates for HOME score/SES status, and adjusted for the 
parental education level as a surrogate for maternal IQ; they also 
adjusted for gender, serum ferritin level and serum cotinine level.
    \47\ The Criteria Document notes that a ``major challenge to 
observational studies examining the impact of Pb on parameters of 
child development has been the assessment and control for 
confounding factors'' (CD, p. 6-73). However, the Criteria Document 
further recognizes that ``[m]ost of the important confounding 
factors in Pb studies have been identified, and efforts have been 
made to control them in studies conducted since the 1990 
Supplement'' (CD, p. 6-75). On this subject, the Criteria Document 
further concludes the following: ``Invocation of the poorly measured 
confounder as an explanation for positive findings is not 
substantiated in the database as a whole when evaluating the impact 
of Pb on the health of U.S. children (Needleman, 1995). Of course, 
it is often the case that following adjustment for factors such as 
social class, parental neurocognitive function, and child rearing 
environment using covariates such as parental education, income, and 
occupation, parental IQ, and HOME scores, the Pb coefficients are 
substantially reduced in size and statistical significance (Dietrich 
et al., 1991). This has sometimes led investigators to be quite 
cautious in interpreting their study results as being positive 
(Wasserman et al., 1997). This is a reasonable way of appraising any 
single study, and such extreme caution would certainly be warranted 
if forced to rely on a single study to confirm the Pb effects 
hypothesis. Fortunately, there exists a large database of high 
quality studies on which to base inferences regarding the 
relationship between Pb exposure and neurodevelopment. In addition, 
Pb has been extensively studied in animal models at doses that 
closely approximate the human situation. Experimental animal studies 
are not compromised by the possibility of confounding by such 
factors as social class and correlated environmental factors. The 
enormous experimental animal literature that proves that Pb at low 
levels causes neurobehavioral deficits and provides insights into 
mechanisms must be considered when drawing causal inferences 
(Bellinger, 2004; Davis et al., 1990; U.S. Environmental Protection 
Agency, 1986a, 1990).'' (CD, p. 6-75)
    \48\ The tests for cognitive function in these studies include 
age-appropriate Wechsler intelligence tests (Lanphear et al., 2005), 
the Stanford-Binet intelligence test (Canfield et al., 2003a), and 
the Bayley Scales of Infant Development (Tellez-Rojo et al., 2006). 
In some cases, individual subtests of the Wechsler intelligence 
tests (Lanphear et al., 2000; Walkowiak et al., 1998), and 
individual subtests of the Wide Range Achievement Test (Lanphear et 
al., 2000) were used. The Wechsler and Stanford-Binet tests are 
widely used to assess neurocognitive function in children and 
adults, however, these tests are not appropriate for children under 
age three. For such children, studies generally use the age-
appropriate Bayley Scales of Infant Development as a measure of 
cognitive development. See footnote 63 for further information.
---------------------------------------------------------------------------

    The study by Lanphear et al. (2000) is a large cross-sectional 
study using NHANES III dataset, with 4853 subjects in the full study 
and more than 4000 in the subgroup analyses, that reports statistically 
significant \49\ associations of concurrent blood Pb levels \50\ with 
neurocognitive decrements in the full study population and in subgroup 
analyses down to and including the subgroup with individual blood Pb 
levels below 5 [mu]g/dL (CD, pp. 6-31 to 6-32; Lanphear et al., 2000). 
Specifically the study by Lanphear et al. (2000) reported a 
statistically significant association between math (p<0.001), reading 
(p<0.001), block design (p=0.009), and digit span (p=0.04) scores and 
blood Pb levels in the analysis that included all study subjects. 
Additionally, the study reports statistically significant associations 
for block design and digit span scores down to and including the 
subgroup with individual blood Pb levels below 7.5 [mu]g/dL and 10 
[mu]g/dL, respectively.\51\ Further, statistically significant 
associations were observed for reading and math scores down to and 
including the subgroup with individual blood Pb levels below 5 [mu]g/
dL, which included 4043 of the 4853 children.\52\ A similar pattern in 
the magnitude of the effect estimates was observed across all the 
subgroup analyses and for all four tests, including the subgroup with 
individual blood Pb levels less than 2.5 [mu]g/dL, although not all the 
effect estimates were statistically significant (Lanphear et al., 
2000).\53\ In particular, the lack of statistical significance in the 
subset of individuals with blood Pb levels less than 2.5 [mu]g/dL may 
be attributable to the smaller sample size (2467 children) and reduced 
variability of blood Pb levels.\54\ Blood Pb levels in the full study 
population ranged from below detection to above 10 [mu]g/dL, with a 
population geometric mean of 1.9 [mu]g/dL, and the subgroups were 
composed of children with blood Pb levels less than 10 [mu]g/dL 
(geometric mean of 1.8 [mu]g/dL), less than 7.5 [mu]g/dL (geometric 
mean of 1.8 [mu]g/dL), less than 5 [mu]g/dL (geometric mean of 1.7 
[mu]g/dL), and less than 2.5 [mu]g/dL (geometric mean of 1.2 [mu]g/dL), 
respectively (Lanphear et al., 2000; Auinger, 2008).\55\
---------------------------------------------------------------------------

    \49\ The statistical significance refers to the effect estimate 
of the linear relationship across the range of data, as presented in 
Table 4 of Lanphear et al. (2000).
    \50\ A limitation noted for this study is with regard to the use 
of concurrent blood Pb levels in children of this age. The authors 
state that ``it is not clear whether the cognitive and academic 
deficits observed in the present analysis are due to lead exposure 
that occurred during early childhood or due to concurrent 
exposure'', however, they further note that ``concurrent blood lead 
concentration was the best predictor of adverse neurobehavioral 
effects of lead exposure in all but one of the published prospective 
studies''. The average blood Pb level for 1-5 year olds was 
approximately 15 [mu]g/dL in the 1976-1980 NHANES. When in that age 
range, some of the children included in the NHANES III dataset may 
have had blood Pb levels comparable to those of the earlier NHANES. 
The general issue regarding blood Pb metrics is further discussed in 
subsequent text.
    \51\ The associations with block design score were not 
statistically significant for subgroups limited to blood Pb of <5 
and <2.5 [mu]g/dL. The associations with digit span score were not 
statistically significant for the blood Pb subgroups of <7.5 and 
lower.
    \52\ The associations with math and reading scores were not 
statistically significant for the subgroup limited to blood Pb <2.5 
[mu]/dL.
    \53\ For example, for reading scores, effect estimates were -
0.99, -1.44, -1.53, -1.66, and -1.71 points per [mu]g/dL for all 
children, the subgroup with blood Pb <10 [mu]g/dL, the subgroup with 
blood Pb <7.5, the subgroup with blood Pb <5 and the subgroup with 
blood Pb<2.5, respectively (Lanphear et al., 2000, Table 4).
    \54\ The authors state ``Indeed, while the average effects of 
lead exposure on reading scores were not significant for blood lead 
concentrations less that 2.5 [mu]g/dL, the size of the effect and 
the borderline significance level ([beta] = -1.71, p=0.07) suggests 
that the smaller sample size and the imprecision of the relationship 
of blood Pb concentration with performance on the reading subtest--
as indicated by the large standard error--may be the reason we did 
not find a statistically significant association for children in 
that range.''
    \55\ We note that the datasets for each subgroup include 
children for the lower blood Pb subgroups (in Table 4 of Lanphear et 
al., 2000). For example, the dataset of children with blood Pb 
levels <2.5 is a component of the dataset of children with blood Pb 
levels <5 (Lanphear et al., 2000).
---------------------------------------------------------------------------

    The epidemiological studies that have investigated blood Pb effects 
on IQ (as discussed in the CD, Section 6.2.3) have considered a variety 
of specific blood Pb metrics, including: (1) Blood concentration 
``concurrent'' with the response assessment (e.g., at the time of IQ 
testing), (2) average blood concentration over the ``lifetime'' of the 
child at the time of response assessment (e.g., average of measurements 
taken over child's first 6 or 7 years), (3) peak blood concentration 
during a particular age range, and (4) early childhood blood 
concentration (e.g., the mean of measurements between 6 and 24 months 
age). With regard to the latter two, the Criteria Document (e.g., CD, 
chapters 3 and 6) has noted that age has been observed to strongly 
predict the period of peak exposure (around 18-27 months when there is 
maximum hand-to-mouth activity). The CD further notes, this maximum 
exposure period coincides with a period of time in which major events 
are occurring in central nervous system (CNS) development (CD, p. 6-
60). Accordingly, the belief that the first few years of life are a 
critical window of vulnerability is evident particularly in the earlier 
literature (CD, p. 6-60). However, more recent analyses have found even 
stronger associations between blood Pb at school age and IQ at school 
age (i.e., concurrent blood Pb), indicating the important role that is 
continued to be played by Pb exposures later in life. In fact, 
concurrent and lifetime averaged measurements were stronger predictors 
of adverse neurobehavioral effects (better than the peak or 24 month 
metrics) in all but one of the prospective cohort studies (CD, pp. 6-61 
to 6-62). While all four specific blood Pb metrics were correlated with 
IQ in the international pooled analysis by Lanphear and others (2005), 
the concurrent blood Pb level exhibited the strongest relationship with 
intellectual deficits (CD, p. 6-29).
    The Criteria Document presentation on toxicological evidence also 
recognizes neurological effects elicited by exposures subsequent to 
earliest childhood (CD, sections 5.3.5 and 5.3.7). For example, 
research with monkeys has indicated that while exposure only during 
infancy may elicit a response, exposures (with similar blood Pb levels) 
that only occurred post-infancy also elicit responses. Further, in the 
monkey research, exposures limited to post-infancy resulted in a 
greater response than exposures limited to infancy (Rice and Gilbert, 
1990; Rice, 1992).
    A study by Chen and others (2005) involving 622 children has 
attempted to directly address the question regarding periods of 
enhanced susceptibility to Pb effects (CD, pp. 6-62 to 6-64).\56\ The 
authors found that the concurrent blood

[[Page 29201]]

Pb association with IQ was always stronger than that for 24-month blood 
Pb. As children aged, the relationship with concurrent blood Pb grew 
stronger while that with 24-month blood Pb grew weaker. Further, in 
models including both prior blood Pb (at 24-months age) and concurrent 
blood Pb (at 7-years age), concurrent blood Pb was always more 
predictive of IQ. In fact, concurrent blood Pb explained most of Pb-
related variation in IQ such that prior blood Pb (at 24-months age) was 
rendered nonsignificant and nearly null.\57\ The effect estimate for 
concurrent blood Pb was robust and remained significant, little changed 
from its value without adjustment for 24-month blood Pb level. The 
Criteria Document concluded the following regarding the results of this 
study (CD, pp. 6-63 to 6-64).
---------------------------------------------------------------------------

    \56\ In the children in this study, the mean blood Pb 
concentration was 26.2 [mu]g/dL at age 2, 12.0 [mu]g/dL at age 5 and 
8.0 [mu]g/dL at age 7 (Chen et al. 2005).
    \57\ We note that blood Pb levels at any point in time are 
influenced by current as well as past exposures, e.g., through 
exchanges between blood and bone (as summarized in section II.B.1 
above and discussed in more detail in the Criteria Document).

    These results support the idea that Pb exposure continues to be 
toxic to children as they reach school age, and do not lend support 
to the interpretation that all the damage is done by the time the 
child reaches 2 to 3 years of age. These findings also imply that 
cross-sectional associations seen in children, such as the study 
recently conducted by Lanphear et al. (2000) using data from NHANES 
III, should not be dismissed. Chen et al. (2005) concluded that if 
concurrent blood Pb remains important until school age for optimum 
cognitive development, and if 6- and 7-year-olds are as or more 
sensitive to Pb effects than 2-year-olds, then the difficulties in 
preventing Pb exposure are magnified but the potential benefits of 
---------------------------------------------------------------------------
prevention are greater.

    In addition to findings of association with neurocognitive 
decrement (including IQ) at study group mean blood Pb levels well below 
10 [mu]g/dL, the evidence indicates that the slope for Pb effects on IQ 
is steeper at lower blood Pb levels (CD, section 6.2.13). As stated in 
the CD, ``the most compelling evidence for effects at blood Pb levels 
<10 [mu]g/dL, as well as a nonlinear relationship between blood Pb 
levels and IQ, comes from the international pooled analysis of seven 
prospective cohort studies (n=1,333) by Lanphear et al. (2005)'' (CD, 
pp. 6-67 and 8-37 and section 6.2.3.1.11).\58\ Using the full pooled 
dataset with concurrent blood Pb level as the exposure metric and IQ as 
the response from the pooled dataset of seven international studies, 
Lanphear and others (2005) employed mathematical models of various 
forms, including linear, cubic spline, log-linear, and piece-wise 
linear, in their investigation of the blood Pb concentration-response 
relationship (CD, p. 6-29; Lanphear et al., 2005). They observed that 
the shape of the concentration-response relationship is nonlinear and 
the log-linear model provides a better fit over the full range of blood 
Pb measurements \59\ than a linear one (CD, p. 6-29 and pp. 6-67 to 6-
70; Lanphear et al., 2005). In addition, they found that no individual 
study among the seven was responsible for the estimated nonlinear 
relationship between Pb and deficits in IQ (CD p. 6-30). Others have 
also analyzed the same dataset and similarly concluded that, across the 
range of the dataset's blood Pb levels, a log-linear relationship was a 
significantly better fit than the linear relationship (p=0.009) with 
little evidence of residual confounding from included model variables 
(CD, Section 6.2.13; Rothenberg and Rothenberg, 2005).
---------------------------------------------------------------------------

    \58\ We note that a public comment submitted on March 19, 2008 
on behalf of the Association of Battery Recyclers described concerns 
the commenter had with the conclusion by Lanphear et al. (2005) of a 
nonlinear relationship of blood Pb with IQ, citing a publication by 
Surkan et al. (2007), a study published since the completion of the 
Criteria Document, and the Tellez-Rojo et al. (2006) finding, 
discussed in the Criteria Document, of two different slopes for 
their study subgroups of young children with blood Pb levels below 5 
[mu]g/d (n=193, for which the slope of -1.7 was statistically 
significant, p=0.01) and those with blood Pb levels between 5 and 10 
[mu]g/dL (n=101, for which the slope of -0.94 was not statistically 
significant, p=0.12). The commenter also cites another publication 
published since the completion of the Criteria Document, Jusko et 
al. (2007) related to this issue. EPA notes that it is not basing 
its proposed decisions on studies that are not included in the 
Criteria Document.
    \59\ The geometric mean of the concurrent blood Pb levels 
modeled was 9.7 [mu]g/dL; the 5th and 95th percentile values were 
2.5 and 33.2 [mu]g/dL, respectively (Lanphear et al., 2005).
---------------------------------------------------------------------------

    The impact of the nonlinear slope is illustrated by the log-linear 
model-based estimates of IQ decrements for similar changes in blood Pb 
level at different absolute values of blood Pb level (Lanphear et al., 
2005). These estimates of IQ decrement are 3.9 (with 95% confidence 
interval, CI, of 2.4-5.3), 1.9 (95% CI, 1.2-2.6) and 1.1 IQ points per 
[mu]g/dL blood Pb (95% CI, 0.7-1.5), for increases in concurrent blood 
Pb from 2.4 to 10 [mu]g/dL, 10 to 20 [mu]g/dL, and 20 to 30 [mu]g/dL, 
respectively (Lanphear et al., 2005). For an increase in concurrent 
blood Pb levels from <1 to 10 [mu]g/dL, the log-linear model estimates 
a decline of 6.2 points in full scale IQ which is comparable to the 7.4 
point decrement in IQ for an increase in lifetime mean blood Pb levels 
up to 10 [mu]g/dL observed in the Rochester study (CD, pp. 6-30 to 6-
31).
    A nonlinear blood Pb concentration-response relationship is also 
suggested by several other analyses that have observed that each [mu]g/
dL increase in blood Pb may have a greater effect on IQ at lower blood 
Pb levels (e.g., below 10 [mu]g/dL) than at higher levels (CD, pp. 8-63 
to 8-64; Figure 8-7). As noted in the Criteria Document, while this may 
at first seem at odds with certain fundamental toxicological concepts, 
a number of examples of non- or supralinear dose-response relationships 
exist in toxicology (CD, pp. 6-76 and 8-38 to 8-39). With regard to the 
effects of Pb on neurodevelopmental outcome such as IQ, the CD suggests 
that initial neurodevelopmental effects at lower Pb levels may be 
disrupting very different biological mechanisms (e.g., early 
developmental processes in the central nervous system) than more severe 
effects of high exposures that result in symptomatic Pb poisoning and 
frank mental retardation (CD, p. 6-76).
    The Criteria Document describes this issue with regard to Pb as 
follows (CD, p. 8-39).

    In the case of Pb, this nonlinear dose-effect relationship 
occurs in the pattern of glutamate release (Section 5.3.2), in the 
capacity for long term potentiation (LTP; Section 5.3.3), and in 
conditioned operant responses (Section 5.3.5). The 1986 Lead AQCD 
also reported U-shaped dose-effect relationships for maze 
performance, discrimination learning, auditory evoked potential, and 
locomotor activity. Davis and Svendsgaard (1990) reviewed U-shaped 
dose-response curves and their implications for Pb risk assessment. 
An important implication is the uncertainty created in 
identification of thresholds and ``no-observed-effect-levels'' 
(NOELS). As a nonlinear relationship is observed between IQ and low 
blood Pb levels in humans, as well as in new toxicologic studies 
wherein neurotransmitter release and LTP show this same 
relationship, it is plausible that these nonlinear cognitive 
outcomes may be due, in part, to nonlinear mechanisms underlying 
these observed Pb neurotoxic effects.

    More specifically, various findings within the toxicological 
evidence presented in the Criteria Document provides biologic 
plausibility for a steeper IQ loss at low blood levels, with a 
potential explanation being that the predominant mechanism at very low 
blood-Pb levels is rapidly saturated and that a different, less-
rapidly-saturated process, becomes predominant at blood-Pb levels 
greater than 10 [mu]g/dL.\60\
---------------------------------------------------------------------------

    \60\ The toxicological evidence presented in the Criteria 
Document of biphasic dose-effect relationships includes: Suppression 
of stimulated hippocampal glutamate release at low exposure levels 
and induction of glutamate exocytosis at higher exposure levels (CD, 
Section 5.3.2); downregulation of NMDA receptors at low blood Pb 
levels and upregulation at higher levels (CD, section 5.3.2); Pb 
causes elevated induction threshold and diminished magnitude of 
long-term potentiation at low exposures, but not at higher exposures 
(CD, section 5.3.3); and low-level Pb exposures increase fixed-
interval response rates and high-level Pb exposures decrease fixed 
interval response rates in learning deficit testing in rats (CD, 
section 5.3.5). Additional in vitro evidence includes Pb stimulation 
of PKC activity at picomolar concentrations and inhibition of PKC 
activity at nano- and micro-molar concentrations (CD, section 
5.3.2).

---------------------------------------------------------------------------

[[Page 29202]]

    In addition to the observed associations between neurocognitive 
decrement (including IQ) and blood Pb at study group mean levels well 
below 10 [mu]g/dL (described above), the current evidence includes 
multiple studies that have examined the quantitative relationship 
between IQ and blood Pb level in analyses of children with individual 
blood Pb concentrations below 10 [mu]g/dL. In comparing across the 
individual epidemiological studies and the international pooled 
analysis, the Criteria Document observed that at higher blood Pb levels 
(e.g., above 10 [mu]g/dL), the slopes (for change in IQ with blood Pb) 
derived for log-linear and linear models are almost identical, and for 
studies with lower blood Pb levels, the slopes appear to be steeper 
than those observed in studies involving higher blood Pb levels (CD, p. 
8-78, Figure 8-7). In making these observations, the Criteria Document 
focused on the curves from the models from the 10th percentile to the 
90th percentile saying that the ``curves are restricted to that range 
because log-linear curves become very steep at the lower end of the 
blood Pb levels, and this may be an artifact of the model chosen.''
    The quantitative relationship between IQ and blood Pb level has 
been examined in the Criteria Document using studies where all or the 
majority of study subjects had blood Pb levels below 10 [mu]g/dL and 
also where an analysis was performed on a subset of children whose 
blood Pb levels have never exceeded 10 [mu]g/dL (CD, Table 6-1). The 
datasets for three of these studies included concurrent blood Pb levels 
above 10 [mu]g/dL; the C-R relationship reported for one of the three 
was linear while it was log-linear for the other two. For the one of 
these three studies with the linear C-R relationship, the highest blood 
Pb level was just below 12 [mu]g/dL (Kordas et al., 2006). Of the two 
studies with log-linear functions, one reported 69% of the children 
with blood Pb levels below 10 [mu]g/dL and a population mean blood Pb 
level of 7.44 [mu]g/dL (Al-Saleh et al., 2001), and the second reported 
a population median blood Pb level of 9.7 [mu]g/dL and a 95th 
percentile of 33.2 [mu]g/dL (Lanphear et al., 2005). In order to 
compare slopes across all of these studies (linear and log-linear), EPA 
estimated, for each, the average slope of change in IQ with change in 
blood Pb between the 10th percentile \61\ blood Pb level and 10 [mu]g/
dL (CD, Table 6-1). The resultant group of reported and estimated 
average linear slopes for IQ change with blood Pb levels up to 10 
[mu]g/dL range from -0.4 to -1.8 IQ points per [mu]g/dL blood Pb (CD, 
Tables 6-1 and 8-7), with a median of -0.9 IQ points per [mu]g/dL blood 
Pb (CD, pp. 8-80).\62\
---------------------------------------------------------------------------

    \61\ In the Criteria Document analysis, the 10th percentile was 
chosen as a common point of comparison for the loglinear (and 
linear) models at a point prior to the lowest end of the blood Pb 
levels.
    \62\ Among this group of slopes (CD, Table 6-1) is that from the 
analysis of the IQ-blood Pb (concurrent) relationship for children 
whose peak blood Pb levels are below 10 [mu]g/dL in the 
international pooled dataset studied by Lanphear and others (2005); 
these authors reported this slope along with the companion slope for 
blood Pb levels for the remaining children with peak blood Pb level 
equal to or above 10 [mu]g/dL (Lanphear et al., 2005). In the 
economic analysis for EPA's recent Lead Renovation, Repair and 
Painting (RRP) Program rule (described above in section I.C), 
changes in IQ loss as a function of changes in lifetime average 
blood Pb level were estimated using the corresponding piecewise 
model for lifetime average blood Pb derived from the pooled dataset 
(USEPA, 2008; USEPA, 2007e). Selection of this model for the RRP 
economic analysis reflects consideration of the distribution of 
blood Pb levels in that analysis, those for children living in 
houses with Pb-based paint. With consideration of these blood Pb 
levels, the economic analysis document states that ``[s]electing a 
model with a node, or changing one segment to the other, at a 
lifetime average blood Pb concentration of 10 [mu]g/dL rather than 
at 7.5 [mu]g/dL, is a small protection against applying an 
incorrectly rapid change (steep slope with increasingly smaller 
effect as concentrations lower) to the calculation''. We note that 
the slope for the less-than-10-[mu]g/dL portion of the model used in 
the RRP analysis (-0.88) is similar to the median for the slopes 
included in the Criteria Document analysis of quantitative 
relationships for distributions of blood Pb levels extending from 
just below 10 [mu]g/dL and lower.
---------------------------------------------------------------------------

    Among this group of quantitative IQ-blood Pb relationships examined 
in the Criteria Document (CD, Tables 6-1 and 8-7), the steepest slopes 
for change in IQ with change in blood Pb level are those derived for 
the subsets of children in the Rochester and Boston cohorts for which 
peak blood Pb levels were <10 [mu]g/dL; these slopes, in terms of IQ 
points per [mu]g/dL blood Pb, are -1.8 (for concurrent blood Pb 
influence on IQ) and -1.6 (for 24-month blood Pb influence on IQ), 
respectively. The mean blood Pb levels for children in these subsets of 
the Rochester and Boston cohorts are 3.32 and 3.8 [mu]g/dL, 
respectively, which are the lowest population mean levels among the 
datasets included in the table (Canfield, 2008; Bellinger, 2008). Other 
studies with analyses involving similarly low blood Pb levels (e.g., 
mean levels below 4 [mu]g/dL) also had slopes steeper than -1.5 points 
per [mu]g/dL blood Pb. These include the slope of -1.71 points per 
[mu]g/dL blood Pb \63\ for the subset of 24-month-old children in the 
Mexico City cohort with blood Pb levels less than 5 [mu]g/dL (n=193), 
for which the mean concurrent blood Pb level was 2.9 [mu]g/dL (Tellez-
Rojo et al. 2006, 2008) \64\ and also the slope of -2.94 points per 
[mu]g/dL blood Pb for the subset of 6-10-year-old children whose peak 
blood Pb levels never exceeded 7.5 [mu]g/dL (n=112), and for which the 
mean concurrent blood Pb level was 3.24 [mu]g/dL (Lanphear et al. 2005; 
Hornung 2008). Thus, from these subset analyses, the slopes range from 
-1.71 to -2.94 IQ points per [mu]g/dL of concurrent blood Pb. We also 
note that the nonlinear C-R function in which greatest confidence is 
placed in estimating IQ loss in the quantitative risk assessment 
(described below in section II.C) has a slope that falls

[[Page 29203]]

intermediate between these two for blood Pb levels up to approximately 
3.7 [mu]g/dL (USEPA, 2007b).
---------------------------------------------------------------------------

    \63\ This slope reflects effects on cognitive development in 
this cohort of 24-month-old children based on the age-appropriate 
test described earlier, and is similar in magnitude to slopes for 
the cohorts of older children described here. The strengths and 
limitations of this age-appropriate text, the Mental Development 
Index (MDI) of the Bayley Scales of Infant Development (BSID), were 
discussed in a letter to the editor by Black and Baqui (2005). The 
authors state that ``the MDI is a well-standardized, 
psychometrically strong measure of infant mental development.'' The 
MDI represents a complex integration of empirically-derived 
cognitive skills, for example, sensory/perceptual acuities, 
discriminations, and response; acquisition of object constancy; 
memory learning and problem solving; vocalization and beginning of 
verbal communication; and basis of abstract thinking. Black and 
Baqui state that although the MDI is one of the most well-
standardized, widely used assessment of infant mental development, 
evidence indicates low predictive validity of the MDI for infants 
younger than 24 months to subsequent measures of intelligence. They 
explain that the lack of continuity may be partially explained by 
``the multidimensional and rapidly changing aspects of infant mental 
development and by variations in performance during infancy, 
variations in tasks used to measure intellectual functioning 
throughout childhood, and variations in environmental challenges and 
opportunities that may influence development.'' Martin and Volkmar 
(2007) also noted that correlations between BSID performance and 
subsequent IQ assessments were variable, but they also reported high 
test-retest reliability and validity, as indicated by the 
correlation coefficients of 0.83 to 0.91, as well as high interrater 
reliability, correlation coefficient of 0.96, for the MDI. 
Therefore, the BSID has been found to be a reliable indicator of 
current development and cognitive functioning of the infant. Martin 
and Volkmar (2007) further note that ``for the most part, 
performance on the BSID does not consistently predict later 
cognitive measures, particularly when socioeconomic status and level 
of functioning are controlled''.
    \64\ In this study, the slope for blood Pb levels between 5 and 
10 [mu]g/dL (population mean blood Pb of 6.9 [mu]g/dL; n=101) was -
0.94 points per [mu]g/dL blood Pb but was not statistically 
significant, with a P value of 0.12. The difference in the slope 
between the <5 [mu]g/dL and the 5-10 [mu]g/dL groups was not 
statistically significant (Tellez-Rojo et al., 2006; Tellez-Rojo, 
2008).
---------------------------------------------------------------------------

    The C-R functions discussed above are presented in two sets in 
Table 1 below.

                        Table 1. Summary of Quantitative Relationships of IQ and Blood Pb for Two Sets of Studies Discussed Above
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                           Form of model      Average
                                                                                 Range BLL  ([mu]g/  Geometric mean BLL     from which      linear slope
        Study/Analysis             Study cohort     Analysis dataset      N         dL)  5th-95th         ([mu]g/dL)       average slope    \A\  (points
                                                                                     percentile]                              derived      per [mu]g/dL)
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                   Set of studies from which steeper slopes are drawn
--------------------------------------------------------------------------------------------------------------------------------------------------------
Tellez-Rojo <5 subgroup based   Mexico City, age   Children--BLL<5          193  0.8-4.9...........  2.9...............  Linear..........  -1.71
 on Lanphear et al. 2005,\B\     24 mo.             [mu]g/dL.
 Log-linear with low-exposure
 linearization (LLL) \B\.
                                   Dataset from which the log-linear function is derived is the pooled International     LLL\C\..........  -2.29 at 2
                                 dataset of 1333 children, age 6-10 yr, having median blood Pb of 9.7 [mu]g/dL and 5th-                     [mu]g/dL\C\
                                  95th percentile of 2.5-33.2 [mu]g/dL.Slope presented here is the slope at a blood Pb
                                                                 level of 2 [mu]g/dL.\C\
Lanphear et al. 2005,\B\ <7.5   Pooled             Children--peak           103  [1.3-6.0].........  3.24..............  Linear..........  -2.94
 peak subgroup.                  International,     BLL <7.5 [mu]g/
                                 age 6-10 yr.       dL.
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                         Set of studies with shallower slopes (Criteria Document, Table 6-1) \D\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Canfield et al. 2003 \B\, <10   Rochester, age 5   Children--peak            71  Unspecified.......  3.32..............  Linear..........  -1.79
 peak subgroup.                  yr.                BLL <10 [mu]g/dL.
Bellinger and Needleman         Boston\A\ \E\....  Children--peak            48  1-9.3\E\..........  3.8\E\............  Linear..........  -1.56
 2003\B\.                                           BLL <10 [mu]g/dL.
Tellez-Rojo et al. 2006.......  Mexico City, age   Full dataset.....        294  0.8-<10...........  4.28..............  Linear..........  -1.04
                                 24 mo.
Tellez-Rojo et al. 2006 full--  Mexico City, age   Full dataset.....        294  0.8-<10...........  4.28..............  Log-linear......  -0.94
 loglinear.                      24 mo.
Lanphear et al. 2005,\B\ <10    Pooled             Children--peak           244  [1.4-8.0].........  4.30..............  Linear..........  -0.80
 peak\F\ subgroup.               International,     BLL <10 [mu]g/dL.
                                 age 6-10 yr.
Al-Saleh et al. 2001 full--     Saudi Arabia, age  Full dataset.....        533  2.3-27.36\G\......  7.44..............  Log-linear......  -0.76
 loglinear.                      6-12 yr.
Kordas et al. 2006, <12         Torreon, Mexico,   Children--BLL<12         377  2.3-<12...........  7.9...............  Linear..........  -0.40
 subgroup.                       age 7 yr.          [mu]g/dL.
Lanphear et al. 2005\B\ full--  Pooled             Full dataset.....       1333  [2.5-33.2]........  9.7 (median)......  Log-linear......  -0.41
 loglinear.                      International,
                                 age 6-10 yr.
                                                                                                                         Median value....  -0.9 \D\
--------------------------------------------------------------------------------------------------------------------------------------------------------
\A\ Average slope for change in IQ from 10th percentile to 10 [mu]g/dL Slope estimates here are for relationship between IQ and concurrent blood Pb
  levels (BLL), except for Bellinger & Needleman which used 24 month BLLs with 10 year old IQ.
\B\ The Lanphear et al. 2005 pooled International study includes blood Pb data from the Rochester and Boston cohorts, although for different ages (6 and
  5 years, respectively) than the ages analyzed in Canfield et al. 2003 and Bellinger and Needleman 2003.
\C\ The LLL function (described in section II.C.2.b) was developed from Lanphear et al. 2005 loglinear model with a linearization of the slope at BLL
  below 1 [mu]g/dL. The slope shown is that at 2 [mu]g/dL. In estimating IQ loss with this function in the risk assessment (section II.C) and in the
  evidence-based considerations in section II.E.3, the nonlinear form of the model was used, with varying slope for all BLL above 1 [mu]g/dL.
\D\ These studies and quantitative relationships are discussed in the Criteria Document (CD, sections 6.2, 6.2.1.3 and 8.6.2).
\E\ The BLL for Bellinger and Needleman (2003) are for age 24 months.
\F\ As referenced above and in section II.C.2.b, the form of this function derived for lifetime average blood Pb was used in the economic analysis for
  the RRP rule. The slope for that function was -0.88 IQ points per [mu]g/dL lifetime averaged blood Pb.
\G\ 69% of children in Al-Saleh et al. (2001) study had BLL<10 [mu]g/dL.

[[Page 29204]]

3. Lead-Related Impacts on Public Health
    In addition to the advances in our knowledge and understanding of 
Pb health effects at lower exposures (e.g., using blood Pb as the 
index), there has been some change with regard to the U.S. population 
Pb burden since the time of the last Pb NAAQS review. For example, the 
geometric mean blood Pb level for U.S. children aged 1-5, as estimated 
by the U.S. Centers for Disease Control, declined from 2.7 [mu]g/dL 
(95% CI: 2.5-3.0) in the 1991-1994 survey period to 1.7 [mu]g/dL (95% 
CI: 1.55-1.87) in the 2001-2002 survey period (CD, Section 4.3.1.3) and 
1.8 [mu]g/dL in the 2003-2004 survey period (Axelrad, 2008).\65\ Blood 
Pb levels have also declined in the U.S. adult population over this 
time period (CD, Section 4.3.1.3).\66\ As noted in the Criteria 
Document, ``blood-Pb levels have been declining at differential rates 
for various general subpopulations, as a function of income, race, and 
certain other demographic indicators such as age of housing'' (CD, pp. 
8-21). For example, the geometric mean blood Pb level for children 
(aged one to five) living in poverty in the 2003-2004 survey period is 
2.4 [mu]g/dL. For black, non-Hispanic children, the geometric mean is 
2.7 [mu]g/dL, and for the subset of this group that is living in 
poverty, the geometric mean is 3.1 [mu]g/dL. Further, the 95th 
percentile blood Pb level in the 2003-2004 NHANES for children aged 1-5 
of all races and ethnic groups is 5.1 [mu]g/dL, while the corresponding 
level for the subset of children living below the poverty level is 6.6 
[mu]g/dL. The 95th percentile level for black, non-Hispanic children is 
8.9 [mu]g/dL, and for the subset of that group living below the poverty 
level, it is 10.5 [mu]g/dL (Axelrad, 2008).\67\
---------------------------------------------------------------------------

    \65\ These levels are in contrast to the geometric mean blood Pb 
level of 14.9 [mu]g/dL reported for U.S. children (aged 6 months to 
5 years) in 1976-1980 (CD, Section 4.3.1.3).
    \66\ For example, NHANES data for older adults (60 years of age 
and older) indicate a decline in overall population geometric mean 
blood Pb level from 3.4 [mu]g/dL in 1991-1994 to 2.2 [mu]g/dL in 
1999-2002; the trend for adults between 20 and 60 years of age is 
similar to that for children 1 to 5 years of age (http://
www.cdc.gov/mmwr/preview/mmwrhtml/mm5420a5.htm).
    \67\ Although the 90th percentile statistic for these subgroups 
is not currently available for the 2003-04 survey period, the 2001-
2004 90th percentile blood Pb level for children aged 1-5 of all 
races and ethnic groups is 4.0 [mu]g/dL, while the corresponding 
level for the subset of children living below the poverty level is 
5.4 [mu]g/dL, and that level for black, non-Hispanic children living 
below the poverty level is 7.7 [mu]g/dL (http://www.epa.gov/
envirohealth/children/body_burdens/b1-table.htm--then click on 
``Download a universal spreadsheet file of the Body Burdens data 
tables'').
---------------------------------------------------------------------------

a. At-Risk Subpopulations
    Potentially at-risk subpopulations include those with increased 
susceptibility (i.e., physiological factors contributing to a greater 
response for the same exposure) and those with increased exposure 
(including that resulting from behavior leading to increased contact 
with contaminated media) (USEPA 1986a, pp. 1-154). A behavioral factor 
of great impact on Pb exposure is the incidence of hand-to-mouth 
activity that is prevalent in very young children (CD, Section 4.4.3). 
Physiological factors include both conditions contributing to a 
subgroup's increased risk of effects at a given blood Pb level, and 
those that contribute to blood Pb levels higher than those otherwise 
associated with a given Pb exposure (CD, Section 8.5.3). These factors 
include nutritional status (e.g., iron deficiency, calcium intake), as 
well as genetic and other factors (CD, chapter 4 and sections 3.4, 
5.3.7 and 8.5.3).
    We also considered evidence pertaining to vulnerability to 
pollution-related effects which additionally encompasses situations of 
elevated exposure, such as residing in older housing with Pb-containing 
paint or near sources of ambient Pb, as well as socioeconomic factors, 
such as reduced access to health care or low socioeconomic status (SES) 
(USEPA, 2003, 2005c) that can contribute to increased risk of adverse 
health effects from Pb. With regard to elevated exposures in particular 
socioeconomic and minority subpopulations, we observe notably higher 
blood Pb levels in children in poverty and in black, non-Hispanic 
children compared to those for more economically well-off children and 
white children, in general (as recognized in section II.B.1.b above).
    Three particular physiological factors contributing to increased 
risk of Pb effects at a given blood Pb level are recognized in the 
Criteria Document (e.g., CD, Section 8.5.3): age, health status, and 
genetic composition. With regard to age, the susceptibility of young 
children to the neurodevelopmental effects of Pb is well recognized 
(e.g., CD, Sections 5.3, 6.2, 8.4, 8.5, 8.6.2), although the specific 
ages of vulnerability have not been established (CD, pp. 6-60 to 6-64). 
Early childhood may also be a time of increased susceptibility for Pb 
immunotoxicity (CD, Sections 5.9.10, 6.8.3 and 8.4.6). Further early 
life exposures have been associated with increased risk of 
cardiovascular effects in humans later in life (CD, pp. 8-74). Early 
life exposures have also been associated with increased risk, in 
animals, of neurodegenerative effects later in life (CD, pp. 8-74).\68\ 
Health status is another physiological factor in that subpopulations 
with pre-existing health conditions may be more susceptible (as 
compared to the general population) for particular Pb-associated 
effects, with this being most clear for renal and cardiovascular 
outcomes. For example, African Americans as a group have a higher 
frequency of hypertension than the general population or other ethnic 
groups (NCHS, 2005), and as a result may face a greater risk of adverse 
health impact from Pb-associated cardiovascular effects. A third 
physiological factor relates to genetic polymorphisms. That is, 
subpopulations defined by particular genetic polymorphisms (e.g., 
presence of the [delta]-aminolevulinic acid dehydratase-2 [ALAD-2] 
allele) have also been recognized as sensitive to Pb toxicity, which 
may be due to increased susceptibility to the same internal dose and/or 
to increased internal dose associated with the same exposure (CD, pp. 
8-71, Sections 6.3.5, 6.4.7.3 and 6.3.6).
---------------------------------------------------------------------------

    \68\ Specifically, among young adults who lived as children in 
an area heavily polluted by a smelter and whose current Pb exposure 
was low, higher bone Pb levels were associated with higher systolic 
and diastolic blood pressure (CD, pp. 8-74). In adult rats, greater 
early exposures to Pb are associated with increased levels of 
amyloid protein precursor, a marker of risk for neurodegenerative 
disease (CD, pp. 8-74).
---------------------------------------------------------------------------

    Childhood is well recognized as a time of increased susceptibility, 
and as summarized in section II.B.2.b above and described in more 
detail in the Criteria Document, a large body of epidemiological 
evidence describes neurological effects on children at low blood Pb 
levels. The toxicological evidence further helps inform an 
understanding of specific periods of development with increased 
vulnerability to specific types of neurological effect (CD, Section 
5.3). Additionally, the toxicological evidence of a differing 
sensitivity of the immune system to Pb across and within different 
periods of life stages indicates the potential importance of exposures 
of duration as short as weeks to months. For example, the animal 
studies suggest that, for immune effects, the gestation period is the 
most sensitive life stage followed by early neonatal stage, and that 
within these life stages, critical windows of vulnerability are likely 
to exist (CD, Section 5.9 and p. 5-245).
    In summary, there are a variety of ways in which Pb exposed 
populations might be characterized and stratified for consideration of 
public health impacts. Age or lifestage was used to distinguish

[[Page 29205]]

potential groups on which to focus the quantitative risk assessment 
because of its influence on exposure and susceptibility. Young children 
were selected as the priority population for the risk assessment in 
consideration of the health effects evidence regarding endpoints of 
greatest public health concern. The Criteria Document recognizes, 
however, other population subgroups as described above may also be at 
risk of Pb-related health effects of public health concern.
b. Potential Public Health Impacts
    As discussed in the Criteria Document, there are potential public 
health implications of low-level Pb exposure, indexed by blood Pb 
levels, associated with several health endpoints identified in the 
Criteria Document (CD, Section 8.6).\69\ These include potential 
impacts on population IQ, which is the focus of the quantitative risk 
assessment conducted for this review, as well as heart disease and 
chronic kidney disease, which are not included in the quantitative risk 
assessment (CD, Sections 8.6, 8.6.2, 8.6.3 and 8.6.4). It is noted that 
there is greater uncertainty associated with effects at the lower 
levels of blood Pb, and that there are differing weights of evidence 
across the effects observed.\70\ With regard to potential implications 
of Pb effects on IQ, the Criteria Document recognizes the ``critical'' 
distinction between population and individual risk, noting that a 
``point estimate indicating a modest mean change on a health index at 
the individual level can have substantial implications at the 
population level'' (CD, p. 8-77).\71\ A downward shift in the mean IQ 
value is associated with both substantial decreases in percentages 
achieving very high scores and substantial increases in the percentage 
of individuals achieving very low scores (CD, p. 8-81).\72\ For an 
individual functioning in the low IQ range due to the influence of 
developmental risk factors other than Pb, a Pb-associated IQ decline of 
several points might be sufficient to drop that individual into the 
range associated with increased risk of educational, vocational, and 
social handicap (CD, p. 8-77).
---------------------------------------------------------------------------

    \69\ The differing evidence and associated strength of the 
evidence for these different effects is described in detail in the 
Criteria Document.
    \70\ As is described in Section II.C.2.a, CASAC, in their 
comments on the analysis plan for the risk assessment described in 
this notice, placed higher priority on modeling the child IQ metric 
than the adult endpoints (e.g., cardiovascular effects).
    \71\ Similarly, ``although an increase of a few mmHg in blood 
pressure might not be of concern for an individual's well-being, the 
same increase in the population mean might be associated with 
substantial increases in the percentages of individuals with values 
that are sufficiently extreme that they exceed the criteria used to 
diagnose hypertension'' (CD, p. 8-77).
    \72\ For example, for a population mean IQ of 100 (and standard 
deviation of 15), 2.3% of the population would score above 130, but 
a shift of the population to a mean of 95 results in only 0.99% of 
the population scoring above 130 (CD, pp. 8-81 to 8-82).
---------------------------------------------------------------------------

    The magnitude of a public health impact is dependent upon the size 
of population affected and type or severity of the effect. As 
summarized above, there are several population groups that may be 
susceptible or vulnerable to effects associated with exposure to Pb, 
including young children, particularly those in families of low SES 
(CD, p. E-15), as well as individuals with hypertension, diabetes, and 
chronic renal insufficiency (CD, p. 8-72). Although comprehensive 
estimates of the size of these groups residing in proximity to sources 
of ambient Pb have not been developed, total estimates of these 
population subpopulations within the U.S. are substantial (as noted in 
Table 3-3 of the Staff Paper).\73\
---------------------------------------------------------------------------

    \73\ For example, approximately 4.8 million children live in 
poverty, while the estimates of numbers of adults with hypertension, 
diabetes or chronic kidney disease are on the order of 20 to 50 
million (see Table 3-3 of Staff Paper).
---------------------------------------------------------------------------

    With regard to estimates of the size of potentially vulnerable 
subpopulations living in areas of increased exposure related to ambient 
Pb, the information is still more limited. The limited information 
available on air and surface soil concentrations of Pb indicates 
elevated concentrations near stationary sources as compared with areas 
remote from such sources (CD, Sections 3.2.2 and 3.8). Air quality 
analyses (presented in Chapter 2 of the Staff Paper) indicate 
dramatically higher Pb concentrations at monitors near sources as 
compared with those more remote. As described in Section 2.3.2.1 of the 
Staff Paper, however, since the 1980s the number of Pb monitors has 
been significantly reduced by states (with EPA guidance that monitors 
well below the current NAAQS could be shut down) and a lack of monitors 
near some large sources may lead to underestimates of the extent of 
occurrences of relatively higher Pb concentrations. The significant 
limitations of our monitoring and emissions information constrain our 
efforts to characterize the size of at-risk populations in areas 
influenced by sources of ambient Pb. For example, the limited size and 
spatial coverage of the current Pb monitoring network constrains our 
ability to characterize current levels of airborne Pb in the U.S. 
Further, as noted above in section II.A.1, the Staff Paper review of 
the available information on emissions and locations of sources (as 
described in section 2.3.2.1 of the Staff Paper) indicates that the 
network is inconsistent in its coverage of the largest sources 
identified in the 2002 National Emissions Inventory (NEI). The most 
recent analysis of monitors near sources greater than 1 ton per year 
(tpy) indicates that less than 15% of stationary sources with emissions 
greater than or equal to 1 tpy have a monitor within one mile. 
Additionally, there are various uncertainties and limitations 
associated with source information in the NEI (as described in section 
2.2.5 of the Staff Paper; USEPA, 2007c).
    In recognition of the significant limitations associated with the 
currently available information on Pb emissions and airborne 
concentrations in the U.S. and the associated exposure of potentially 
at-risk populations, Chapter 2 of the Staff Paper summarizes the 
information in several different ways. For example, analyses of the 
current monitoring network indicated the numbers of monitoring sites 
that would exceed alternate standard levels, taking into consideration 
different statistical forms. These analyses are also summarized with 
regard to population size in counties home to those monitoring sites 
(as presented in Appendix 5.A of the Staff Paper). Information for the 
monitors and from the NEI indicates a range of source sizes in 
proximity to monitors at which various levels of Pb are reported. 
Together this information suggests that there is variety in the 
magnitude of Pb emissions from sources that could influence air Pb 
concentrations. Identifying specific emissions levels of sources 
expected to result in air Pb concentrations of interest, however, would 
be informed by a comprehensive analysis using detailed source 
characterization information, which was not feasible within the time 
and data constraints of this review. Instead, we have developed a 
summary of the emissions and demographic information for Pb sources 
that includes estimates of the numbers of people residing in counties 
in which the aggregate Pb emissions from NEI sources is greater than or 
equal to 0.1 tpy or in counties in which the aggregate Pb emissions is 
greater than or equal to 0.1 tpy per 1000 square miles (as presented in 
Tables 3-4 and 3-5, respectively, in the Staff Paper).
    Additionally, the potential for resuspension of recently and 
historically deposited Pb near roadways to contribute to increased 
risks of Pb exposure to populations residing nearby is suggested in the 
Criteria Document (e.g., CD, pp. 2-62 and 3-32).

[[Page 29206]]

4. Key Observations
    The following key observations are based on the available health 
effects evidence and the evaluation and interpretation of that evidence 
in the Criteria Document.
     Lead exposures occur both by inhalation and by ingestion 
(CD, Chapter 3). As stated in the Criteria Document, ``given the large 
amount of time people spend indoors, exposure to Pb in dusts and indoor 
air can be significant'' (CD, p. 3-27).
     Children, in general and especially those of low SES, are 
at increased risk for Pb exposure and Pb-induced adverse health 
effects. This is due to several factors, including enhanced exposure to 
Pb via ingestion of soil Pb and/or dust Pb due to normal childhood 
hand-to-mouth activity (CD, p. E-15, Chapter 3 and Section 6.2.1).
     Once inhaled or ingested, Pb is distributed by the blood, 
with long-term storage accumulation in the bone. Bone Pb levels provide 
a strong measure of cumulative exposure which has been associated with 
many of the effects summarized below, although difficulty of sample 
collection has precluded widespread use in epidemiological studies to 
date (CD, Chapter 4).
     Blood levels of Pb are well accepted as an index of 
exposure (or exposure metric) for which associations with the key 
effects (see below) have been observed. In general, associations with 
blood Pb are most robust for those effects for which past exposure 
history poses less of a complicating factor, i.e., for effects during 
childhood (CD, Section 4.3).
     Both epidemiological and toxicologic studies have shown 
that environmentally relevant levels of Pb affect many different organ 
systems (CD, p. E-8). With regard to the most important such effects 
observed in children and adults, the Criteria Document states (CD, p. 
8-60) that ``neurotoxic effects in children and cardiovascular effects 
in adults are among those best substantiated as occurring at blood-Pb 
concentrations as low as 5 to 10 [mu]g/dL (or possibly lower); and 
these categories of effects are currently clearly of greatest public 
health concern. Other newly demonstrated immune and renal system 
effects among general population groups are also emerging as low-level 
Pb-exposure effects of potential public health concern.''
     Many associations of health effects with Pb exposure have 
been found at levels of blood Pb that are currently relevant for the 
U.S. population, with individual children having blood Pb levels of 5-
10 [mu]g/dL and lower, being at risk for neurological effects (as 
described in the subsequent bullet). Supportive evidence from 
toxicological studies provides biological plausibility for the observed 
effects. (CD, Chapters 5, 6 and 8)
     Pb exposure is associated with a variety of neurological 
effects in children, notably intellectual attainment and school 
performance. Both qualitative and quantitative evidence, with further 
support from animal research, indicates a robust and consistent effect 
of Pb exposure on neurocognitive ability at mean concurrent blood Pb 
levels in the range of 5 to 10 [mu]g/dL. Specific epidemiological 
analyses have further indicated association with neurocognitive effects 
in analyses restricted to children with individual blood Pb levels 
below 5-10 [mu]g/dL, and for which group mean levels are lower. 
Further, ``[s]ome newly available analyses appear to show Pb effects on 
the intellectual attainment of preschool and school age children at 
population mean concurrent blood-Pb levels ranging down to as low as 2 
to 8 [mu]g/dL'' (CD, p. E-9; Sections 5.3, 6.2, 8.4.2 and 6.10).
     Deficits in cognitive skills may have long-term 
consequences over a lifetime. Poor academic skills and achievement can 
have enduring and important effects on objective parameters of success 
in life as well as increased risk of antisocial and delinquent 
behavior. (CD, Sections 6.1 and 8.4.2)
     The current epidemiological evidence indicates a steeper 
slope of the blood Pb concentration-response relationship at lower 
blood Pb levels, particularly those below 10 [mu]g/dL (CD, Sections 
6.2.13 and 8.6).
     At mean blood Pb levels, in children, on the order of 10 
[mu]g/dL, and somewhat lower, associations have been found with effects 
to the immune system, including altered macrophage activation, 
increased IgE levels and associated increased risk for autoimmunity and 
asthma (CD, Sections 5.9, 6.8, and 8.4.6).
     In adults, with regard to cardiovascular outcomes, the 
Criteria Document included the following summary (CD, p. E-10).

    Epidemiological studies have consistently demonstrated 
associations between Pb exposure and enhanced risk of deleterious 
cardiovascular outcomes, including increased blood pressure and 
incidence of hypertension.\74\ A meta-analysis of numerous studies 
estimates that a doubling of blood-Pb level (e.g., from 5 to 10 
[mu]g/dL) is associated with ~1.0 mm Hg increase in systolic blood 
pressure and ~0.6 mm Hg increase in diastolic pressure. Studies have 
also found that cumulative past Pb exposure ( e.g., bone Pb) may be 
as important, if not more, than present Pb exposure in assessing 
cardiovascular effects. The evidence for an association of Pb with 
cardiovascular morbidity and mortality is limited but supportive.
---------------------------------------------------------------------------

    \74\ The Criteria Document states that ``While several studies 
have demonstrated a positive correlation between blood pressure and 
blood Pb concentration, others have failed to show such association 
when controlling for confounding factors such as tobacco smoking, 
exercise, body weight, alcohol consumption, and socioeconomic 
status. Thus, the studies that have employed blood Pb level as an 
index of exposure have shown a relatively weak association with 
blood pressure. In contrast, the majority of the more recent studies 
employing bone Pb level have found a strong association between 
long-term Pb exposure and arterial pressure (Chapter 6). Since the 
residence time of Pb in the blood is relatively short but very long 
in the bone, the latter observations have provided rather compelling 
evidence for a positive relationship between Pb exposure and a 
subsequent rise in arterial pressure'' (CD, pp. 5-102 to 5-103). 
Further, in consideration of the meta-analysis also described here, 
the Criteria Document stated that ``The meta-analysis provides 
strong evidence for an association between increased blood Pb and 
increased blood pressure over a wide range of populations'' (CD, p. 
6-130) and ``the meta-analyses results suggest that studies not 
detecting an effect may be due to small sample sizes or other 
factors affecting precision of estimation of the exposure effect 
relationship'' (CD, p. 6-133).

Studies of nationally representative U.S. samples observed associations 
between blood Pb levels and increased systolic blood pressure at 
population mean blood Pb levels less than 5 [mu]g/dL, particularly 
among African Americans (CD, Section 6.5.2). With regard to gender 
---------------------------------------------------------------------------
differences, the Criteria Document states the following (CD, p. 6-154).

    Although females often show lower Pb coefficients than males, 
and Blacks higher Pb coefficients than Whites, where these 
differences have been formally tested, they are usually not 
statistically significant. The tendencies may well arise in the 
differential Pb exposure in these strata, lower in women than in 
men, higher in Blacks than in Whites. The same sex and race 
differential is found with blood pressure.

Animal evidence provides confirmation of Pb effects on cardiovascular 
functions (CD, Sections 5.5, 6.5, 8.4.3 and 8.6.3).

     Renal effects, evidenced by reduced renal filtration, have 
also been associated with Pb exposures indexed by bone Pb levels and 
also with mean blood Pb levels in the range of 5 to 10 [mu]g/dL in the 
general adult population, with the potential adverse impact of such 
effects being enhanced for susceptible subpopulations including those 
with diabetes, hypertension, and chronic renal insufficiency (CD, 
Sections 6.4, 8.4.5, and 8.6.4). The full significance of this effect 
is unclear,

[[Page 29207]]

given that other evidence of more marked signs of renal dysfunction 
have not been detected at blood Pb levels below 30-40 [mu]g/dL in large 
studies of occupationally exposed Pb workers (CD, pp. 6-270 and 8-
50).\75\
---------------------------------------------------------------------------

    \75\ In the general population, both cumulative and circulating 
Pb has been found to be associated with longitudinal decline in 
renal functions. In the large NHANES III study, alterations in 
urinary creatinine excretion rate (one indicator of possible renal 
dysfunction) were observed in hypertensives at a mean blood Pb of 
only 4.2 [mu]g/dL. These results provide suggestive evidence that 
the kidney may well be a target organ for effects from Pb in adults 
at current U.S. environmental exposure levels. The magnitude of the 
effect of Pb on renal function ranged from 0.2 to -1.8 mL/min change 
in creatinine clearance per 1.0 [mu]g/dL increase in blood Pb in 
general population studies. However, the full significance of this 
effect is unclear, given that other evidence of more marked signs of 
renal dysfunction have not been detected at blood Pb levels below 
30-40 [mu]g/dL among thousands of occupationally exposed Pb workers 
that have been studied (CD, p. 6-270).
---------------------------------------------------------------------------

     Other Pb associated effects in adults occurring at or just 
above 10 [mu]g/dL include hematological (e.g., impact on heme synthesis 
pathway) and neurological effects, with animal evidence providing 
support of Pb effects on these systems and evidence regarding mechanism 
of action (CD, Sections 5.2, 5.3, 6.3 and 6.9.2).

C. Human Exposure and Health Risk Assessments

    This section presents a brief summary of the human exposure and 
health risk assessments conducted by EPA for this review. The complete 
full-scale assessment, which includes specific analyses conducted to 
address CASAC comments and advice on an earlier draft assessment, is 
presented in the final Risk Assessment Report (USEPA, 2007b).
    The focus of this Pb NAAQS risk assessment is on characterizing 
risk resulting from exposure to policy-relevant Pb (i.e., exposure to 
Pb that has passed through ambient air on its path from source to human 
exposure--as described in section II.A.2). The design and 
implementation of this assessment needed to address significant 
limitations and complexity that go far beyond the situation for similar 
assessments typically performed for other criteria pollutants. Not only 
was the risk assessment constrained by the timeframe allowed for this 
review in the context of breadth of information to address, it was also 
constrained by significant limitations in data and modeling tools for 
the assessment, as discussed further in section II.C.2.h below. 
Furthermore, the multimedia and persistent nature of Pb, and the role 
of multiple exposure pathways (discussed in section II.A), add 
significant complexity to the assessment as compared to other 
assessments that focus only on the inhalation pathway. The impact of 
this on our estimates for air-related exposure pathways is discussed in 
section II.C.2.e.
    The remainder of this overview of the human health risk assessment 
is organized as follows. An overview of the human health risk 
assessment completed in the last review of the Pb NAAQS in 1990 (USEPA, 
1990a) is presented first. Next, design aspects of the current risk 
assessment are presented, including: (a) CASAC advice regarding the 
design of the risk assessment, (b) description of health endpoints and 
associated risk metrics modeled, including the concentration-response 
functions used, (c) overview of the case study approach employed, (d) 
description of air quality scenarios modeled, (e) explanation of air-
related versus background classification of risk results in the context 
of this analysis, (f) overview of analytical (modeling) steps completed 
for the risk assessment and (g) description of the multiple sets of 
risk results generated for the analysis. Then, key sources of 
uncertainty associated with the analysis are presented. And finally, a 
summary of exposure and risk estimates and key observations is 
presented.
1. Overview of Risk Assessment From Last Review
    The risk assessment conducted in support of the last review used a 
case study approach to compare air quality scenarios in terms of their 
impact on the percentage of modeled populations that exceeded specific 
blood Pb levels chosen with consideration of the health effects 
evidence at that time (USEPA, 1990b; USEPA, 1989). The case studies in 
that analysis, however, focused exclusively on Pb smelters including 
two secondary and one primary smelter and did not consider exposures in 
a more general urban context. The analysis focused on children (birth 
through 7 years of age) and middle-aged men. The assessment evaluated 
impacts of alternate NAAQS on numbers of children and men with blood Pb 
levels above levels of concern based on health effects evidence at that 
time. The primary difference between the risk assessment approach used 
in the current analysis and the assessment completed in 1990 involves 
the risk metric employed. Rather than estimating the percentage of 
study populations with exposures above blood Pb levels of interest as 
was done in the last review (i.e., 10, 12 and 15 [mu]g/dL), the current 
analysis estimates changes in health risk, specifically IQ loss, 
associated with Pb exposure for child populations at each of the case 
study locations with that estimated IQ loss further differentiated 
between air-related and background Pb exposure categories.
2. Design Aspects of Exposure and Risk Assessments
    This section provides an overview of key elements of the assessment 
design, inputs, and methods, and includes identification of key 
uncertainties and limitations.
a. CASAC Advice
    The CASAC conducted a consultation on the draft analysis plan for 
the risk assessment (USEPA, 2006c) in June, 2006 (Henderson, 2006). 
Some key comments provided by CASAC members on the plan included: (1) 
Placing a higher priority on modeling the child IQ metric than the 
adult endpoints (e.g., cardiovascular effects), (2) recognizing the 
importance of indoor dust loading by Pb contained in outdoor air as a 
factor in Pb-related exposure and risk for sources considered in this 
analysis, and (3) concurring with use of the IEUBK biokinetic blood Pb 
model. Taking these comments into account, a pilot phase assessment was 
conducted to test the risk assessment methodology being developed for 
the subsequent full-scale assessment. The pilot phase assessment is 
described in the first draft Staff Paper and accompanying technical 
report (ICF 2006), which was discussed by the CASAC Pb panel on 
February 6-7 (Henderson, 2007a).
    Results from the pilot assessment, together with comments received 
from CASAC and the public, informed the design of the full-scale 
analysis. The full-scale analysis included a substitution of a more 
generalized urban case study for the location-specific near-roadway 
case study evaluated in the pilot. In addition, a number of changes 
were made in the exposure and risk assessment approaches, including the 
development of a new indoor dust Pb model focused specifically on urban 
residential locations and specification of additional IQ loss 
concentration-response (C-R) functions to provide greater coverage for 
potential impacts at lower exposure levels.
    The draft full-scale assessment was presented in the July 2007 
draft risk assessment report (USEPA, 2007a) that was released for 
public comment and provided to CASAC for review. In their review of the 
July draft risk assessment report, the CASAC Pb Panel made several 
recommendations for additional exposure and health risk analyses 
(Henderson, 2007b). These included a recommendation that the general 
urban

[[Page 29208]]

case study be augmented by the inclusion of risk analyses in specific 
urban areas of the U.S. In this regard, they specifically stated the 
following (Henderson, 2007b, p. 3)

    * * * the CASAC strongly believes that it is important that EPA 
staff make estimates of exposure that will have national 
implications for, and relevance to, urban areas; and that, 
significantly, the case studies of both primary lead (Pb) smelter 
sites as well as secondary smelter sites, while relevant to a few 
atypical locations, do not meet the needs of supporting a Lead 
NAAQS. The Agency should also undertake case studies of several 
urban areas with varying lead exposure concentrations, based on the 
prototypic urban risk assessment that OAQPS produced in the 2nd 
Draft Lead Human Exposure and Health Risk Assessments. In order to 
estimate the magnitude of risk, the Agency should estimate exposures 
and convert these exposures to estimates of blood levels and IQ loss 
for children living in specific urban areas.

    Hence, EPA included additional case studies in the risk assessment 
focused on characterizing risk for residential populations in three 
specific urban locations. Further, CASAC recommended using a 
concentration-response function with a change in slope near 7.5 [mu]g/
dL. Accordingly, EPA included such an additional concentration-response 
function in the risk assessment. Results from the initial full-scale 
analyses, along with comments from CASAC, such as those described here, 
and the public resulted in a final version of the full-scale 
assessments which is briefly summarized here and presented in greater 
detail in the Risk Assessment Report and associated appendices (USEPA, 
2007b).
    In their review of the final risk assessment, CASAC expressed 
strong support, stating as follows (Henderson, 2008a, p. 4):

    The Final Risk Assessment report captures the breadth of issues 
related to assessing the potential public health risk associated 
with lead exposures; it competently documents the universe of 
knowledge and interpretations of the literature on lead toxicity, 
exposures, blood lead modeling and approaches for conducting risk 
assessments for lead.

b. Health Endpoint, Risk Metric and Concentration-Response Functions
    The health endpoint on which the quantitative health risk 
assessment focuses is developmental neurotoxicity in children, with IQ 
decrement (or loss) as the risk metric. Among the wide variety of 
health endpoints associated with Pb exposures, there is general 
consensus that the developing nervous system in young children is the 
most sensitive and that neurobehavioral effects (specifically 
neurocognitive deficits), including IQ decrements, appear to occur at 
lower blood levels than previously believed (i.e., at levels <10 [mu]g/
dL). The selection of children's IQ for the quantitative risk 
assessment reflects consideration of the evidence presented in the 
Criteria Document as well as advice received from CASAC (Henderson, 
2006, 2007a).
    Given the evidence described in detail in the Criteria Document 
(Chapters 6 and 8), and in consideration of CASAC recommendations 
(Henderson, 2006, 2007a, 2007b), the risk assessment for this review 
relies on the functions presented by Lanphear and others (2005) that 
relate absolute IQ as a function of concurrent blood Pb or of the log 
of concurrent blood Pb, and lifetime average blood Pb, respectively. As 
discussed in the Criteria Document (CD, p. 8-63 to 8-64), the slope of 
the concentration-response relationship described by these functions is 
greater at the lower blood Pb levels (e.g., less than 10 [mu]g/dL). As 
discussed in the Criteria Document and summarized in section II.B.2, 
threshold blood Pb levels for these effects cannot be discerned from 
the currently available epidemiological studies, and the evidence in 
the animal Pb neurotoxicity literature does not define a threshold for 
any of the toxic mechanisms of Pb (CD, Sections 5.3.7 and 6.2).
    In applying relationships observed with the international pooled 
analysis by Lanphear and others (2005) to the risk assessment, which 
includes blood Pb levels below the range represented by the pooled 
analysis, several alternative blood Pb concentration-response models 
were considered in recognition of a reduced confidence in our ability 
to characterize the quantitative blood Pb concentration-response 
relationship at the lowest blood Pb levels represented in the recent 
epidemiological studies. The functions considered and employed in the 
initial risk analyses for this review include the following.
     Log-linear function with low-exposure linearization, for 
both concurrent and lifetime average blood metrics, applies the 
nonlinear relationship down to the blood Pb concentration representing 
the lower bound of blood Pb levels for that blood metric in the pooled 
analysis and applies the slope of the tangent at that point to blood Pb 
concentrations estimated in the risk assessment to fall below that 
level.
     Log-linear function with cutpoint, for both concurrent and 
lifetime average blood metrics, also applies the nonlinear relationship 
at blood Pb concentrations above the lower bound of blood Pb 
concentrations in the pooled analysis dataset for that blood metric, 
but then applies zero risk to all lower blood Pb concentrations 
estimated in the risk assessment (this cutpoint is 1 [mu]g/dL for the 
concurrent blood Pb).
    In the additional risk analyses performed subsequent to the August 
2007 CASAC public meeting, the two functions listed above and the 
following two functions were employed (details on the forms of these 
functions as applied in this risk assessment are described in Section 
5.3.1 of the Risk Assessment Report).
     Population stratified dual linear function for concurrent 
blood Pb, derived from the pooled dataset stratified at peak blood Pb 
of 10 [mu]g/dL \76\ and
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    \76\ As mentioned above (section II.B.2.b), this function 
(derived for lifetime average blood Pb), was used in the economic 
analysis for the RRP rule. This model was selected for the RRP 
economic analysis with consideration of advice from CASAC and of the 
distribution of blood Pb levels being considered in that analysis, 
which focused on children living in houses with lead-based paint 
(USEPA, 2008). With consideration of these blood Pb levels, the 
economic analysis document states that ``[s]electing a model with a 
node, or changing one segment to the other, at a lifetime average 
blood Pb concentration of 10 [mu]g/dL rather than at 7.5 [mu]g/dL, 
is a small protection against applying an incorrectly rapid change 
(steep slope with increasingly smaller effect as concentrations 
lower) to the calculation'' (USEPA, 2008).
---------------------------------------------------------------------------

     Population stratified dual linear function for concurrent 
blood Pb, derived from the pooled dataset stratified at 7.5 [mu]g/dL 
peak blood Pb.
    In interpreting risk estimates derived using the various functions, 
consideration should be given to the uncertainties with regard to the 
precision of the coefficients used for each analysis. The coefficients 
for the log-linear model from Lanphear et al. (2005) had undergone a 
careful development process, including sensitivity analyses, using all 
available data from 1,333 children. The shape of the exposure-response 
relationship was first assessed through tests of linearity, then by 
evaluating the restricted cubic spline model. After determining that 
the log-linear model provided a good fit to the data, covariates to 
adjust for potential confounding were included in the log-linear model 
with careful consideration of the stability of the parameter estimates. 
After the multiple regression models were developed, regression 
diagnostics were employed to ascertain whether the Pb coefficients were 
affected by collinearity or influential observations. To further 
investigate the stability of the model, a random-effects model (with 
sites

[[Page 29209]]

random) was applied to evaluate the results and also the effect of 
omitting one of the seven cohorts on the Pb coefficient. In the various 
sensitivity analyses performed, the coefficient from the log-linear 
model was found to be robust and stable. The log-linear model, however, 
is not biologically plausible at the very lowest blood Pb 
concentrations as they approach zero; therefore, in the first two 
functions the log-linear model is applied down to a cutpoint (of 1 
[mu]g/dL for the concurrent blood Pb metric), selected based on the low 
end of the blood Pb levels in the pooled dataset, followed by a 
linearization or an assumption of zero risk at levels below that point.
    In contrast, the coefficients from the two analyses using the 
population stratified dual linear function with stratification at 7.5 
[mu]g/dL and 10 [mu]g/dL,\77\ peak blood Pb, have not undergone as 
careful development. These analyses were primarily done to compare the 
lead-associated decrement at lower blood Pb concentrations and higher 
blood Pb concentrations. For these analyses, the study population was 
stratified at the specified peak blood Pb level and separate linear 
models were fitted to the concurrent blood Pb data for the children in 
the two study population subgroups.\78\ While these analyses are quite 
suitable for the purpose of investigating whether the slope at lower 
concentration levels is greater compared to higher concentration 
levels, use of such coefficients as the primary C-R function in a risk 
analysis such as this may be inappropriate. Further, only 103 children 
had maximal blood Pb levels less than 7.5 [mu]g/dL and 244 children had 
maximal blood Pb levels less than 10 [mu]g/dL. While these children may 
better represent current blood Pb levels, not fitting a single model 
using all available data may lead to bias. Slob et al. (2005) noted 
that the usual argument for not considering data from the high dose 
range is that different biological mechanisms may play a role at higher 
doses compared to lower doses. However, this does not mean a single 
curve across the entire exposure range cannot describe the 
relationship. The fitted curve merely assumes that the underlying dose-
response follows a smooth curve over the whole dose range. If 
biological mechanisms change when going from lower to higher doses, 
this change will result in a gradually changing slope of the dose-
response. The major strength of the Lanphear et al. (2005) study was 
the large sample size and the pooled analysis of data from seven 
different cohorts. In the case of the study population subgroup with 
peak blood Pb below 7.5 [mu]g/dL, less than 10% of the available data 
is used in the analysis (103 of the 1333 subjects in the pooled 
dataset), with more than half of the data coming from one cohort 
(Rochester) and the six other cohorts contributing zero to 13 children 
to the analysis. Such an analysis consequently does not make full use 
of the strength of the pooled study by Lanphear and others (2005).
---------------------------------------------------------------------------

    \77\ See previous footnote.
    \78\ Neither fit of the model nor other sensitivity analyses 
were conducted (or reported) for these coefficients.
---------------------------------------------------------------------------

    In consideration of the preceding discussion and the range of blood 
Pb levels assessed in this analysis,\79\ greater confidence is placed 
in the log-linear model form compared to the dual-linear stratified 
models for purposes of the risk assessment described in this notice. 
Further, in considering risk estimates derived from the four core 
functions (log-linear function with low-exposure linearization, log-
linear function with cutpoint, dual linear function, stratified at 7.5 
[mu]g/dL peak blood Pb, and dual linear function, stratified at 10 
[mu]g/dL peak blood Pb), greatest confidence is assigned to risk 
estimates derived using the log-linear function with low-exposure 
linearization since this function (a) is a nonlinear function that 
describes greater response per unit blood Pb at lower blood Pb levels 
consistent with multiple studies identified in the discussion above, 
(b) is based on fitting a function to the entire pooled dataset (and 
hence uses all of the data in describing response across the range of 
exposures), (c) is supported by sensitivity analyses showing the model 
coefficients to be robust, and (d) provides an approach for predicting 
IQ loss at the lowest exposures simulated in the assessment (consistent 
with the lack of evidence for a threshold). Note, however, that risk 
estimates generated using the other three concentration-response 
functions are also presented to provide perspective on the impact of 
uncertainty in this key modeling step. We additionally note that the 
CASAC Pb Panel recommended that C-R function derived from the pooled 
dataset stratified at 7.5 [mu]g/dL, peak blood Pb, be given weight in 
this analysis (Henderson, 2008).
---------------------------------------------------------------------------

    \79\ The median concurrent values in all case studies and air 
quality scenarios are below 5 [mu]g/dL and those for air quality 
scenarios within the range of standard levels proposed in this 
notice are below 3 [mu]g/dL (as shown in Table 1).
---------------------------------------------------------------------------

c. Case Study Approach
    For the risk assessment described in this notice, a case study 
approach was employed as described in Sections 2.2 (and subsections) 
and 5.1.3 of the Risk Assessment Report (USEPA, 2007b). In summarizing 
the assessment in this proposal, we have focused on five \80\ case 
studies that generally represent two types of population exposures: (1) 
More highly air-pathway exposed children (as described below) residing 
in small neighborhoods or localized residential areas with air 
concentrations somewhat near the standard level being evaluated, and 
(2) urban populations with a broader range of air-related exposures. 
These five case studies are:
---------------------------------------------------------------------------

    \80\ A sixth case study (the secondary Pb smelter case study) is 
also described in the Risk Assessment Report. However, as discussed 
in Section 4.3.1 of that document (USEPA, 2007b), significant 
limitations in the approaches employed for this case study have 
contributed to large uncertainties in the corresponding estimates.
---------------------------------------------------------------------------

     A general urban case study: This case study is not based 
on a specific geographic location and reflects several simplifying 
assumptions used in representing exposure including uniform ambient air 
Pb levels associated with the standard of interest across the 
hypothetical study area and a uniform study population. This case study 
characterizes risk for a localized part of an urban area at different 
standard levels, but based on national average estimates of the 
relationships between the different standard form assessed and ambient 
air exposure concentrations. Thus, while this provides characterization 
of risk to children that are relatively more highly air pathway exposed 
(as compared to the location-specific case studies), this case study is 
not considered to represent a high-end scenario with regard to the 
characterization of ambient air Pb levels and associated risk.\81\
---------------------------------------------------------------------------

    \81\ In representing the different forms of each standard level 
assessed (maximum monthly or maximum quarterly) as annual air 
concentrations for input to the blood Pb model for this case study, 
however, we relied on averages of these relationships for large 
urban areas nationally. As the averages are higher than the medians, 
localized areas near more than half the urban monitoring locations 
would have higher exposures and associated risks than those reported 
for this case study. Further, we note that exposure concentrations 
would be twice those used here if the 25th percentile values for 
these relationships had been used in place of the averages. For this 
reason, this case study should not be interpreted as representing a 
high-end scenario with regard to the characterization of ambient air 
Pb levels and associated risk.
---------------------------------------------------------------------------

     A primary Pb smelter case study: \82\ This case study 
estimates risk for children living in an area currently not in 
attainment with the current NAAQS that is impacted by Pb emissions from 
a primary Pb smelter. Results described

[[Page 29210]]

here are those for the area within 1.5 km of the facility (the 
``subarea'') where airborne Pb concentrations are closest to the 
current standard. As such, this case study characterizes risk for a 
specific more highly exposed population and also provides insights on 
risk to child populations living in areas near large sources of Pb 
emissions.\83\
---------------------------------------------------------------------------

    \82\ See Section II.C.2.a for a summary of CASAC's comment with 
regard to the primary and secondary Pb smelter case studies.
    \83\ Result for the full study area, which extends 10 km out 
from the facility, are presented in the Risk Assessment Report 
(USEPA, 2007a), but are not presented here. Exposures in the full 
study area were dominated by modeled children farther from the 
facility where, as discussed in the ANPR (section III.B.2.h), there 
is likely underestimation of ambient air-related Pb exposure due to 
increasing influence of other sources relative to that of the 
facility, which were not included in the dispersion modeling 
performed to estimate air concentrations for this case study.
---------------------------------------------------------------------------

     Three location-specific urban case studies: These urban 
case studies focus on specific urban areas (Cleveland, Chicago and Los 
Angeles) to provide representations of the distribution of ambient air-
related risk in specific densely populated urban locations. These case 
studies represent areas with specific population distributions and that 
experience a broader range of air-related exposures due both to 
potential spatial gradients in ambient air Pb levels and population 
density. A large majority of the population in these case studies 
resides in areas with much lower air concentrations than those in the 
very small subareas of these case studies with the highest 
concentrations. Ambient air Pb concentrations are characterized using 
source-oriented and other Pb-TSP monitors in these cities, while 
location-specific U.S. Census demographic data are used to characterize 
the spatial distribution of residential child populations in these 
study areas.
    These different case studies generally represent two types of 
population exposures. The general urban and primary Pb smelter subarea 
provide estimates of risk for more highly air-pathway exposed children 
residing in small neighborhoods or localized residential areas with air 
concentrations somewhat near the standard level being evaluated. By 
contrast, the three location-specific urban case studies included in 
the analysis provide risk estimates for an urban population with a 
broader range of air-related exposures. In fact, for the location-
specific urban case studies, the majority of the modeled populations 
experience ambient air Pb levels significantly lower than the standard 
level being evaluated, with only a small population experiencing 
ambient air Pb levels at or near the standard.\84\
---------------------------------------------------------------------------

    \84\ Based on the nature of the population exposures represented 
by the two categories of case study, the first category (the general 
urban and primary Pb smelter case studies) relates more closely to 
the second evidence-based framework (see Sections II.D.2.a and 
II.E.3.a) with regard to estimates of air-related IQ loss. As 
mentioned above these case studies, as compared to the other 
category of case studies, include populations that are relatively 
more highly air pathway exposed to air Pb concentrations somewhat 
near the standard level evaluated.
---------------------------------------------------------------------------

    In considering risk results generated for the location-specific 
urban case studies, we note that, given the wide range of monitored Pb 
levels in urban areas, combined with the relatively limited monitoring 
network characterizing ambient levels in the urban setting, it is not 
possible to determine where these case studies fall within the 
distribution of ambient air-related risk in U.S. cities.
d. Air Quality Scenarios
    Air quality scenarios assessed include (a) a current conditions 
scenario for the location-specific urban case studies and the general 
urban case study, (b) a current NAAQS scenario for the location-
specific urban case studies, the general urban case study and the 
primary Pb smelter case study, and (c) a range of alternative NAAQS 
scenarios for all case studies. The alternative NAAQS scenarios include 
levels of 0.5, 0.2, 0.05, and 0.02 [mu]g/m\3\, with a monthly averaging 
time, as well as a level of 0.2 [mu]g/m\3\ scenario using a quarterly 
averaging time.\85\
---------------------------------------------------------------------------

    \85\ For further discussion of the air quality scenarios and 
averaging times included in the risk assessment, see section 2.3.1 
of the Risk Assessment Report (USEPA, 2007b).
---------------------------------------------------------------------------

    The current NAAQS scenario for the urban case studies assumes 
ambient air Pb concentrations higher than those currently occurring in 
nearly all urban areas nationally.\86\ While it is extremely unlikely 
that Pb concentrations in urban areas would rise to meet the current 
NAAQS and there are limitations and uncertainties associated with the 
roll-up procedure used for the location-specific urban case studies (as 
described in Section III.B.2.h below), this scenario was included for 
those case studies to provide perspective on potential risks associated 
with raising levels to the point that the highest level across the 
study area just meets the current NAAQS. When evaluating these results 
it is important to keep these limitations and uncertainties in mind.
---------------------------------------------------------------------------

    \86\ This scenario was simulated for the location-specific urban 
case studies using a proportional roll-up procedure. For the general 
urban case study, the maximum quarterly average ambient air 
concentration was set equal to the current NAAQS.
---------------------------------------------------------------------------

    Current conditions for the three location-specific urban case 
studies in terms of maximum quarterly average air Pb concentrations are 
0.09, 0.14 and 0.36 [mu]g/m\3\ for the study areas in Los Angeles, 
Chicago and Cleveland, respectively. In terms of maximum monthly 
average the values are 0.17 [mu]g/m\3\, 0.31 [mu]g/m\3\ and 0.56 [mu]g/
m\3\ for the study areas in Los Angeles, Chicago and Cleveland, 
respectively.
    Details of the assessment scenarios, including a description of the 
derivation of Pb concentrations for air and other media are presented 
in Sections 2.3 (and subsections) and Section 5.1.1 of the Risk 
Assessment Report (USEPA, 2007b).
e. Categorization of Policy-Relevant Exposure Pathways
    As discussed in Section IIA, this review focuses on air-related 
exposure pathways (i.e., those pathways where Pb passes through ambient 
air on its path from source to human exposure). These include both 
inhalation of ambient air Pb (including both Pb emitted directly into 
ambient air as well as resuspended Pb); and ingestion of Pb that, once 
airborne, has made its way into indoor dust, outdoor dust or soil, 
dietary items (e.g., crops and livestock), and drinking water. Because 
of the nonlinear response of blood Pb to exposure (simulated in the 
IEUBK blood Pb model) and also the nonlinearity reflected in the C-R 
functions for estimation of IQ loss, this assessment first estimates 
total blood Pb and risk (air- and nonair-related), and then separates 
out those estimates of blood Pb and associated risk associated with the 
pathways of interest in this review.
    To separate out risk for the pathways of interest in this review, 
we split the estimates of total (all-pathway) blood Pb and IQ loss into 
background and two air-related categories (referred to as ``recent 
air'' and ``past air''). However, significant limitations in our 
modeling tools and data resulted in an inability to parse specific risk 
estimates into specific pathways, such that we have approximated 
estimates for the air-related and background categories.
    Those Pb exposure pathways identified in section II.A.2 as being 
tied most directly to ambient air, which consequently have the 
potential to respond relatively more quickly to changes in air Pb 
(inhalation and ingestion of indoor dust loaded directly from ambient 
air Pb) were placed into the ``recent air'' category. The other air-
related Pb exposure pathways, associated with atmospheric deposition, 
were placed into the ``past air'' category. These include ingestion of 
Pb in

[[Page 29211]]

outdoor dust/soil and ingestion of the portion of Pb in indoor dust 
that after deposition from ambient air outdoors is carried indoors with 
humans (as described in section II.A.2 above).\87\
---------------------------------------------------------------------------

    \87\ As discussed below, due to technical limitations related to 
indoor dust Pb modeling, dust from Pb paint may be included to some 
extent in the ``past air'' category of exposure pathways.
---------------------------------------------------------------------------

    Thus, total blood Pb and IQ loss estimates were apportioned into 
the following pathways or pathway combinations:
     Inhalation of ambient air Pb (i.e., ``recent air'' Pb): 
This is derived using the blood Pb estimate resulting from Pb exposure 
limited to the inhalation pathway (and includes inhalation of Pb in 
ambient air from all sources contributing to the ambient air 
concentration estimate, including potentially resuspension).
     Ingestion of ``recent air'' indoor dust Pb: This is 
derived using the blood Pb estimate resulting from Pb exposure limited 
to ingestion of the Pb in indoor dust that is predicted in this 
assessment from infiltration of ambient air indoors and subsequent 
deposition.\88\
---------------------------------------------------------------------------

    \88\ Recent air indoor dust Pb was estimated using the 
mechanistic component of the hybrid blood Pb model (see Section 
3.1.4 of the Risk Assessment Report). For the primary Pb smelter 
case study, estimates for this pathway are not separated from 
estimates for the pathway described in the subsequent bullet due to 
uncertainty regarding this categorization with the model used for 
this case study (Section 3.1.4.2 of the Risk Assessment Report).
---------------------------------------------------------------------------

     Ingestion of ``other'' indoor dust Pb (considered part of 
``past air'' exposure): This is derived using the blood Pb estimate 
resulting from Pb exposure limited to ingestion of the Pb in indoor 
dust that is not predicted from infiltration of ambient air indoors and 
subsequent deposition.\89\ This is interpreted to represent indoor 
paint, outdoor soil/dust, and additional sources of Pb to indoor dust 
including historical air (as discussed in the Risk Assessment Report, 
Section 2.4.3). As the intercept in regression dust models will be 
inclusive of error associated with the model coefficients, this 
category also includes some representation of dust Pb associated with 
current ambient air concentrations (described in previous bullet). For 
the primary Pb smelter case study, estimates for this pathway are not 
separated from estimates for the pathway described above due to 
uncertainty regarding this categorization with the model used for this 
case study (Risk Assessment Report, Section 3.1.4.2). This pathway is 
included in the ``past air'' category.
---------------------------------------------------------------------------

    \89\ ``Other'' indoor dust Pb is estimated using the intercept 
in the dust models plus that predicted by the outdoor soil 
concentration coefficient (for models that include soil Pb as a 
predictor of indoor dust Pb) (Section 3.1.4 of the Risk Assessment 
Report).
---------------------------------------------------------------------------

     Ingestion of outdoor soil/dust Pb: This is derived using 
the blood Pb estimate resulting from Pb exposure limited to ingestion 
of outdoor soil/dust Pb. This pathway is included in the ``past air'' 
category (and could include contamination from historic Pb emissions 
from automobiles and Pb paint).
     Ingestion of drinking water Pb: This is derived using the 
blood Pb estimate resulting from Pb exposure limited to ingestion of 
drinking water Pb. This pathway is included in the policy-relevant 
background category.
     Ingestion of dietary Pb: This is derived using the blood 
Pb estimate resulting from Pb exposure limited to ingestion of dietary 
Pb. This pathway is included in the policy-relevant background 
category.
    As noted above, significant limitations in our modeling tools and 
data resulted in an inability to parse risk estimates for specific 
pathways, such that we approximated estimates for the air-related and 
background categories. Of note in this regard is the apportionment of 
background (nonair) pathways. For example, while conceptually indoor Pb 
paint contributions to indoor dust Pb would be considered background 
and included in the ``background'' category for this assessment, due to 
technical limitations related to indoor dust Pb modeling, ultimately, 
dust from Pb paint was included as part of ``other'' indoor dust Pb 
(i.e., as part of past air exposure). The inclusion of indoor lead Pb 
as a component of ``other'' indoor air (and consequently as a component 
of the ``past air'' category) represents a source of potential high 
bias in our prediction of exposure and risk associated with the ``past 
air'' category because conceptually, exposure to indoor paint Pb is 
considered part of background exposure. Further, Pb in ambient air does 
contribute to the exposure pathways included in the ``background'' 
category (drinking water and diet), and is likely a substantial 
contribution to diet (CD, p. 3-48). But we could not separate the air 
contribution from the nonair contributions, and the total contribution 
from both the drinking water and diet pathways are categorized as 
``background'' in this assessment. As a result, our ``background'' risk 
estimate includes some air-related risk.
    Further, we note that in simulating reductions in exposure 
associated with reducing ambient air Pb levels through alternative 
NAAQS (and increases in exposure if the current NAAQS was reached in 
certain case studies) only the exposure pathways categorized as 
``recent air'' (inhalation and ingestion of that portion of indoor dust 
associated with outdoor ambient air) were varied with changes in air 
concentration. The assessment did not simulate decreases in ``past 
air'' exposure pathways (e.g., reductions in outdoor soil Pb levels 
following reduction in ambient air Pb levels and a subsequent decrease 
in exposure through incidental soil ingestion and the contribution of 
outdoor soil to indoor dust). These exposures were held constant across 
all air quality scenarios. In comparing total risk estimates between 
alternate NAAQS scenarios, this aspect of the analysis will tend to 
underestimate the reductions in risk associated with alternative NAAQS. 
However, this does not mean that overall risk has been underestimated. 
The net effect of all sources of uncertainty or bias in the analysis, 
which may also tend to under- or overestimate risk, could not be 
quantified. Interpretation of risk estimates is discussed more fully in 
section II.C.3.b.
    In summary, because of limitations in the assessment design, data 
and modeling tools, our risk estimates for the ``past air'' category 
include both risks that are truly air-related and potentially, some 
background risk. Because we could not sharply separate Pb linked to 
ambient air from Pb that is background, some of the three categories of 
risk are underestimated and others overestimated. On balance, we 
believe this limitation leads to a slight overestimate of the risks in 
the ``past air'' category. At the same time, as discussed above, the 
``recent air'' category does not fully represent the risk associated 
with all air-related pathways. Thus, we consider the risk attributable 
to air-related exposure pathways to be bounded on the low end by the 
risk estimated for the ``recent air'' category and on the upper end by 
the risk estimated for the ``recent air'' plus ``past air'' categories.
f. Analytical Steps
    The risk assessment includes four analytical steps, briefly 
described below and presented in detail in Sections 2.4.4, 3.1, 3.2, 
4.1, and 5.1 of the Risk Assessment Report (USEPA, 2007b).
     Characterization of Pb in ambient air: The 
characterization of outdoor ambient air Pb levels uses different 
approaches depending on the case study (as explained in more detail 
below): (a) source-oriented and non-source oriented monitors are 
assumed to represent different exposure zones in the city-specific case 
studies, (b) a single exposure level is assumed for the entire

[[Page 29212]]

population in the general urban case study, and (c) ambient levels are 
estimated using air dispersion modeling based on Pb emissions from a 
particular facility in the primary Pb smelter case study.
     Characterization of outdoor soil/dust and indoor dust Pb 
concentrations: Outdoor soil Pb levels are estimated using empirical 
data and fate and transport modeling. Indoor dust Pb levels are 
predicted using a combination of (a) regression-based models that 
relate indoor dust to ambient air Pb and outdoor soil Pb, and (b) 
mechanistic models.\90\
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    \90\ Indoor dust Pb modeling for the urban case studies is based 
on a hybrid mechanistic-empirical model which considers the direct 
impact of Pb in ambient air on indoor dust Pb (i.e., which models 
the infiltration of ambient air indoors and subsequent deposition of 
Pb to indoor surfaces). This modeling does not consider other 
ambient air-related contributions to indoor dust, such as ``tracking 
in'' of outdoor soil Pb. By contrast, indoor dust Pb modeling for 
the primary Pb smelter case study subarea uses a site-specific 
regression model which relates average dust Pb values (based on a 
recent multi-year dataset) to annual average air Pb concentrations 
(based on air dispersion modeling). In this way, modeling for the 
primary Pb smelter subarea may reflect some contributions to indoor 
dust Pb that relate to longer term impacts of ambient air (e.g., 
``tracking in'' of outdoor soil), as well as contributions from 
infiltration of ambient air. Additional detail on the methods used 
in characterizing Pb concentrations in outdoor soil and indoor dust 
are presented in Sections 3.1.3 and 3.1.4 of the Risk Assessment, 
respectively. Data, methods and assumptions here used in 
characterizing Pb concentrations in these exposure media may differ 
from those in other analyses that serve different purposes.
---------------------------------------------------------------------------

     Characterization of blood Pb levels: Blood Pb levels for 
each exposure zone are derived from central-tendency blood Pb 
concentrations estimated using the Integrated Exposure and Uptake 
Biokinetic (IEUBK) model, and concurrent or lifetime average blood Pb 
is estimated from these outputs as described in Section 3.2.1.1 of the 
Risk Assessment Report (USEPA, 2007b). For the point source and 
location-specific urban case studies, a probabilistic exposure model is 
used to generate population distributions of blood Pb concentrations 
based on: (a) The central tendency blood Pb levels for each exposure 
zone, (b) demographic data for the distribution of children (less than 
7 years of age) across exposure zones in a study area, and (c) a 
geometric standard deviation (GSD) intended to characterize 
interindividual variability in blood Pb (e.g., reflecting differences 
in behavior and biokinetics related to Pb). For the general urban case 
study, as demographic data for a specific location are not considered, 
the GSD is applied directly to the central tendency blood Pb level to 
estimate a population distribution of blood Pb levels. Additional 
detail on the methods used to model population blood Pb levels is 
presented in Sections 3.2.2 and 5.2.2.3 of the Risk Assessment Report 
(USEPA, 2007b).
     Risk characterization (estimating IQ loss): Concurrent or 
lifetime average blood Pb estimates for each simulated child in each 
case study population are converted into total Pb-related IQ loss 
estimates using the concentration-response functions described above in 
section II.C.2.b.\91\
---------------------------------------------------------------------------

    \91\ The four C-R functions applied in the risk assessment, 
which are based on analyses presented in Lanphear et al. (2005) 
include a log-linear function with low-exposure linearization, a 
log-linear function with a cutpoint, and two dual linear functions 
(based on population stratification at peak blood Pb levels of 7.5 
and 10 [mu]g/dL) (see section II.C.2.b).
---------------------------------------------------------------------------

    We have also used the results of exposure modeling to estimate air-
to-blood ratios for two of the case studies (the general urban and 
primary Pb smelter case studies). Specifically, we compared the change 
in ambient air Pb between adjacent NAAQS levels with the associated 
reduction in concurrent blood Pb levels (for the median population 
percentile) to derive air-to-blood ratios. As they relate air 
concentrations \92\ input to the first analytical step to blood Pb 
estimates output from the third analytical step, they may be viewed as 
a collapsed alternate to the three steps for the exposure pathways 
directly linked to air concentrations in this assessment. The values 
for these ratios are affected by design aspects of the risk assessment, 
most notably those identified here:
---------------------------------------------------------------------------

    \92\ Because the IEUBK blood Pb model runs with an annual time 
step, the air concentrations input to the ``recent air'' pathways 
modeling steps were in terms of annual average air concentration.
---------------------------------------------------------------------------

     Because they are derived from differences in blood Pb 
estimates between air quality scenarios and the only pathways varied 
with air quality scenarios are ambient air and indoor dust (as 
described in section II.C.2.e above), the exposure pathways reflected 
in the ratios are generally the ``recent air'' pathways (described in 
section II.C.2.e above), which include inhalation of ambient air and 
ingestion of indoor dust loaded by infiltration of ambient air. Ratios 
for the primary Pb smelter case study subarea may additionally reflect 
some contributions to indoor dust from other ambient air-related 
pathways (e.g., ``tracking in'' of soil containing ambient air Pb), yet 
still not all air-related pathways. Thus, the air-to-blood ratios 
derived for both case studies (described in section II.C.3.a) are lower 
than they would be if they reflected all air-related pathways.
     The blood Pb estimates used in this calculation are for 
the ``concurrent'' metric (i.e., concentrations during the 7th year of 
life). Accordingly, the resultant air-to-blood ratios are lower than 
they would be if based on blood Pb estimates for the 2nd year of life 
(e.g., peak) or estimates averaged over the exposure period.
    Key limitations and uncertainties associated with the application 
of these specific analytical steps are summarized in Section III.B.2.k 
below.
g. Generating Multiple Sets of Risk Results
    In the initial analyses for the full-scale assessment (USEPA, 
2007a), EPA implemented multiple modeling approaches for each case 
study scenario in an effort to characterize the potential impact on 
exposure and risk estimates of uncertainty associated with the 
limitations in the tools, data and methods available for this risk 
assessment and with key analytical steps in the modeling approach. 
These multiple modeling approaches are described in Section 2.4.6.2 of 
the final Risk Assessment Report (USEPA, 2007b). In consideration of 
comments provided by CASAC (Henderson, 2007b) on these analyses 
regarding which modeling approach they felt had greater scientific 
support, a pared down set of modeling combinations was identified as 
the core approach for the subsequent analyses. The core modeling 
approach includes the following key elements:
     Ambient air Pb estimates (based on monitors or modeling 
and proportional rollbacks, as described below),
     Background exposure from food and water (as described 
above),
     The hybrid indoor dust model specifically developed for 
urban residential applications (which predicts Pb in indoor dust as a 
function of ambient air Pb and nonair contribution),
     The IEUBK blood Pb model (which predicts blood Pb in young 
children exposed to Pb from multiple exposure pathways),
     The concurrent blood Pb metric,
     A GSD for concurrent blood Pb of 2.1 to characterize 
interindividual variability in blood Pb levels for a given ambient 
level for the urban case studies,\93\ and
---------------------------------------------------------------------------

    \93\ In the economic analysis for the RRP rule, a GSD of 1.6 was 
used in its probabilistic simulations, reflecting the fact that the 
simulated exposures focus on a subset of Pb exposure pathways 
(exposure to dust and airborne Pb resulting from renovation 
activity) and a CASAC recommendation to use the IEUBK-recommended 
GSD with the Leggett model, where no GSD is provided. In addition, 
the accompanying sensitivity analysis used a GSD of 2.1 to consider 
the impact on IQ change estiamtes of using a larger GSD, which would 
reflect greater heterogeneity in the study population with regard to 
Pb exposure and blood Pb response.

---------------------------------------------------------------------------

[[Page 29213]]

     Four different functions relating concurrent blood Pb to 
IQ loss (described in section II.C.2.b), including two log-linear 
models (one with a cutpoint and one with low-exposure linearization) 
and two dual-linear models with stratification, one stratified at 7.5 
[mu]g/dL peak blood Pb and the other at 10 [mu]g/dL peak blood Pb.
    For each case study, the core modeling approach employs a single 
set of modeling elements to estimate exposure and the four different 
concentration-response functions referenced above to derive four sets 
of risk results from the single set of exposure estimates. The spread 
of estimates resulting from application of all four functions captures 
much of the uncertainty associated model choice in this analytical 
step. Among these four functions, EPA has greater confidence in 
estimates derived using the log-linear with low-exposure linearization 
concentration-response function as discussed above.
    In addition to employing multiple concentration-response functions, 
the assessment includes various sensitivity analyses to characterize 
the potential impact of uncertainty in other key analysis steps on 
exposure and risk estimates. The sensitivity analyses and uncertainty 
characterization completed for the risk analysis are described in 
Sections 3.5, 4.3, 5.2.5 and 5.3.3 of the Risk Assessment Report 
(USEPA, 2007b).
h. Key Limitations and Uncertainties
    As recognized above, EPA has made simplifying assumptions in 
several areas of this assessment due to the limited data, models, and 
time available. These assumptions and related limitations and 
uncertainties are described in the Risk Assessment Report (USEPA, 
2007b). Key assumptions, limitations and uncertainties are briefly 
identified below, with emphasis on those sources of uncertainty 
considered most critical in interpreting risk results. In the 
presentation below, limitations (and associated uncertainty) are 
listed, beginning with those regarding design of the assessment or case 
studies, followed by those regarding estimation of Pb concentrations in 
ambient air indoor dust, outdoor soil/dust, and blood, and lastly 
regarding estimation of Pb-related IQ loss.
     Temporal aspects: Exposure modeling uses a 7 year exposure 
period for each simulated child, during which time, media 
concentrations remain fixed (at levels associated with the ambient air 
Pb level being modeled) and the child remains at the same residence, 
while exposure factors and physiological parameters are adjusted to 
match the age of the child. These aspects are a simplification of 
population exposures that contributes some uncertainty to our exposure 
and risk estimates.
     General urban case study: As described in section 
II.C.2.c, this case study is not based on a specific location and is 
instead intended to represent a smaller neighborhood experiencing 
ambient air Pb levels at or near the standard of interest. 
Consequently, it assumes (a) a single exposure zone within which all 
media concentrations of Pb are assumed to be spatially uniform and (b) 
a uniformly distributed population of unspecified size. While these 
assumptions are reasonable in the context of evaluating risk for a 
smaller subpopulation located close to a monitor reporting values at or 
near the standard of interest, there is significant uncertainty 
associated with extrapolating these risks to a specific urban location, 
particularly if that urban location is relatively large, given that 
larger urban areas are expected to have increasingly varied patterns of 
ambient air Pb levels and population density. The risk estimates for 
this general urban case study, while generally representative of an 
urban residential population exposed to the specified ambient air Pb 
levels, cannot be readily related to a specific large urban population.
     Location-specific urban case studies: The Pb-TSP 
monitoring network is currently quite limited and consequently, the 
number of monitors available to represent air concentrations in these 
case studies is limited, ranged from six for Cleveland to 11 for 
Chicago. Accordingly, our estimates of the magnitude of and spatial 
variation of air Pb concentrations are subject to uncertainty 
associated with the limited monitoring data and method used in 
extrapolating from those data to characterize an ambient air Pb level 
surface for these modeled urban areas. Details on the approach used to 
derive ambient air Pb surfaces for the urban case studies based on 
monitoring data are presented in Section 5.1.3 of the Risk Assessment 
Report (USEPA, 2007b). As recognized in Section, III.B.2.a, the 
analyses for these case studies were developed in response to CASAC 
recommendations on the July 2007 draft Risk Assessment (Henderson, 
2007b). Subsequently, the CASAC has reviewed the approach used in 
conducting the final draft of the full-scale risk assessment, including 
the inclusion of the location-specific urban case studies and expressed 
broad support for the technical approach used (Henderson, 2008).
     Current NAAQS air quality scenarios: For the location-
specific urban case studies, proportional roll-up procedures were used 
to adjust ambient air Pb concentrations up to just meet the current 
NAAQS (a detailed discussion is provided in Sections 2.3.1 and 5.2.2.1 
of the Risk Assessment Report, USEPA, 2007b). This procedure was used 
to provide insights into the degree of risk which could be associated 
with ambient air Pb levels at or near the current standard in urban 
areas. EPA recognizes that it is extremely unlikely that Pb 
concentrations would rise to just meet the current NAAQS in urban areas 
nationwide and that there is substantial uncertainty with our 
simulation of such conditions. For the primary Pb smelter case study, 
where current conditions exceed the current NAAQS, attainment of the 
current NAAQS was simulated using air quality modeling, emissions and 
source parameters used in developing the 2007 proposed revision to the 
State Implementation Plan for the area (described in Section 3.1.1.2 of 
the Risk Assessment Report (USEPA, 2007b)).
     Alternative NAAQS air quality scenarios: In all case 
studies, proportional roll-down procedures were used to adjust ambient 
air Pb concentrations downward to attain alternative NAAQS (described 
in Sections 2.3.1 and 5.2.2.1 of the Risk Assessment Report, USEPA, 
2007b). There is significant uncertainty in simulating conditions 
associated with the implementation of emissions reduction actions to 
meet a lower standard.
     Estimates of outdoor soil/dust Pb concentrations: Outdoor 
soil Pb concentration for both the urban case studies and the primary 
Pb smelter case study are based on empirical data (as described in 
Section 3.1.3 of the Risk Assessment). To the extent that these data 
are from areas containing older structures, the impact of Pb paint 
weathered from older structures on soil Pb levels will be reflected in 
these empirical estimates. In the case of the urban case studies, a 
mean value from a sample of houses built between 1940 and 1998 was used 
to represent soil Pb levels (as described in Section 3.1.3.1 of the 
Risk Assessment). In the case of the primary Pb smelter case study 
subarea, site-specific data are used. As there has been remediation of 
soil in this subarea, the measurements do not reflect historical air 
quality. Additionally,

[[Page 29214]]

studies since remediation have reported increasing soil Pb levels 
indicating that soil concentrations are still responding to current air 
quality, and consequently underestimate eventual steady state 
conditions for the current air quality. In all case studies, the same 
outdoor soil/dust Pb concentrations (based on these datasets) are used 
for all air quality scenarios (i.e., the potential longer-term impact 
of reductions in ambient air Pb on outdoor soil/dust Pb levels and 
associated impacts on indoor dust Pb have not be simulated). In areas 
where air concentrations have been greater in the past, however, 
implementation of a reduced NAAQS might be expected to yield reduced 
soil Pb levels over the long term. As described in Section 2.3.3 of the 
Risk Assessment Report (USEPA, 2007b), however, there is potentially 
significant uncertainty associated with this conclusion, particularly 
with regard to implications for areas in which a Pb source may locate 
where one of comparable size had not been previously. Additionally, it 
is possible that control measures implemented to meet alternative NAAQS 
may result in changes to soil Pb concentrations; these are not 
reflected in the assessment.
     Estimates of indoor dust Pb concentrations for the urban 
case studies (application of the hybrid model): The hybrid mechanistic-
empirical model for estimating indoor dust Pb for the urban case 
studies (as described in Section 3.1.4.1 of the Risk Assessment Report, 
USEPA, 2007b) utilizes a mechanistic model to simulate the exchange of 
outdoor ambient air Pb indoors and subsequent deposition (and buildup) 
of Pb on indoor surfaces, which relies on a number of empirical 
measurements for parameterization (e.g., infiltration rates, deposition 
velocities, cleaning frequencies and efficiencies). There is 
considerable uncertainty associated with these parameter estimates. In 
addition, there is uncertainty associated with the partitioning of 
total indoor dust Pb estimates between the infiltration-related 
(``recent air'') component and other contributions (``other'' as 
described in section II.C.2.e).
     Estimates of indoor dust Pb concentrations for the primary 
Pb smelter case study (application of the site-specific regression 
model): There is uncertainty associated with the site-specific 
regression model applied in the remediation zone (as described in 
Section 3.1.4.2 of the Risk Assessment Report), and relatively greater 
uncertainty associated with its application to air quality scenarios 
that simulate notably lower air Pb levels (as is typically the case 
when applying regression-based models beyond the bounds of the datasets 
used in their derivation). The log-log form of the regression model 
prevents the ready identification of an intercept term handicapping us 
in partitioning estimates of air-related indoor dust (and consequently 
exposure and risk estimates) between ``recent air'' and ``other'' 
components. In addition, limitations in the model-derived air estimates 
used in deriving the regression model prevented effective consideration 
for the role of ambient air Pb related to resuspension in influencing 
indoor dust Pb levels. A public commenter suggested that indoor dust Pb 
levels using this model may be overestimated due to factors associated 
with the model's derivation. Factors identified by the commenter, 
however, may contribute to a potential for either over- or 
underestimation, and as noted by the commenter, additional research 
might reduce this uncertainty.
     Characterizing interindividual variability using a GSD: 
There is uncertainty associated with the GSD specified for each case 
study (as described in Sections 3.2.3 and 5.2.2.3 of the Risk 
Assessment Report). Two factors are described here as contributors to 
that uncertainty. Interindividual variability in blood Pb levels for 
any study population (as described by the GSD) will reflect, to a 
certain extent, spatial variation in media concentrations, including 
outdoor ambient air Pb levels and indoor dust Pb levels, as well as 
differences in physiological response to Pb exposure. For each case 
study, there is significant uncertainty in the specification of spatial 
variability in ambient air Pb levels and associated indoor dust Pb 
levels, as noted above. In addition, there are a limited number of 
datasets for different types of residential child populations from 
which a GSD can be derived (e.g., NHANES datasets \94\ for more 
heterogeneous populations and individual study datasets for likely more 
homogeneous populations near specific industrial Pb sources). This 
uncertainty associated with the GSDs introduces significant uncertainty 
in exposure and risk estimates for the 95th population percentile.
---------------------------------------------------------------------------

    \94\ The GSD for the urban case studies, in the risk assessment 
described in this notice, was derived using NHANES data for the 
years 1999-2000.
---------------------------------------------------------------------------

     Exposure pathway apportionment for higher percentile blood 
Pb level and IQ loss estimates: Apportionment of blood Pb levels for 
higher population percentiles is assumed to be the same as that 
estimated using the central tendency estimate of blood Pb in an 
exposure zone. This introduces significant uncertainty into projections 
of pathway apportionment for higher population percentiles of blood Pb 
and IQ loss. In reality, pathway apportionment may differ in higher 
exposure percentiles. For example, paint and/or drinking water 
exposures may increase in importance, with air-related contributions 
decreasing as an overall percentage of blood Pb levels and associated 
risk. Because of this uncertainty related to pathway apportionment, as 
mentioned earlier, greater confidence is placed in estimates of total 
Pb exposure and risk in evaluating the impact of the current NAAQS and 
alternative NAAQS relative to current conditions.
     Relating blood Pb levels to IQ loss: Specification of the 
quantitative relationship between blood Pb level and IQ loss is subject 
to significant uncertainty at lower blood Pb levels (e.g., below 5 
[mu]g/dL concurrent blood Pb). As discussed earlier, there are 
limitations in the datasets and concentration-response analyses 
available for characterizing the concentration-response relationship at 
these lower blood Pb levels. For example, the pooled international 
dataset analyzed by Lanphear and others (2005) includes relatively few 
children with blood Pb levels below 5 [mu]g/dL and no children with 
levels below 1 [mu]g/dL. In recognition of the uncertainty in 
specifying a quantitative concentration-response relationship at such 
levels, our core modeling approach involves the application of four 
different functions to generate a range of risk estimates (as described 
in Section 4.2.6 and Section 5.3.1 of the Risk Assessment Report, 
USEPA, 2007b). The difference in absolute IQ loss estimates for the 
four concentration-response functions for a given case study/air 
quality scenario combination is typically close to a factor of 3. 
Estimates of differences in IQ loss between air quality scenarios (in 
terms of percent), however, are more similar across the four functions, 
although the function producing higher overall risk estimates (the dual 
linear function, stratified at 7.5 [mu]g/dL, peak blood Pb) also 
produces larger absolute reductions in IQ loss compared with the other 
three functions.
3. Summary of Estimates and Key Observations
    This section presents blood Pb and IQ loss estimates generated in 
the exposure and risk assessments. Blood Pb estimates (and air-to-blood 
Pb ratios) are presented first, followed by IQ loss estimates.

[[Page 29215]]

a. Blood Pb Estimates
    This section presents a summary of blood Pb modeling results for 
concurrent blood Pb drawn from the more detailed presentation in the 
Staff Paper and the Risk Assessment Report (USEPA, 2007a, 2007b, 
2007c).
    Blood Pb level estimates for the current conditions air quality 
scenarios for these case studies differ somewhat from the national 
values associated with recent NHANES information. For example, median 
blood Pb levels for the current conditions scenario for the urban case 
studies are somewhat larger than the national median from the NHANES 
data for 2003-2004. Specifically, values for the three location-
specific urban case studies range from 1.7 to 1.8 [mu]g/dL with the 
general urban case study having a value of 1.9 [mu]g/dL (current-
conditions mean) (presented in Risk Assessment Report, Volume I, Table 
5-5), while the median value from NHANES (2003-2004) is 1.6 [mu]g/dL 
(http://www.epa.gov/envirohealth/children/body_burdens/b1-table.htm). 
Additionally, NHANES values for the 90th percentile (for 2003-2004) 
were identified and these values can be compared against 90th 
percentile estimates generated for the urban case studies (see Risk 
Assessment Report, Appendix O, Section O.3.2 for the location-specific 
urban case study and Appendix N, Section N.2.1.2 for the general urban 
case study). The 90th percentile blood Pb levels for the current 
conditions scenario, for the three location-specific urban case studies 
range from 4.5 to 4.6 [mu]g/dL, while the estimate for the general 
urban case study is 5.0 [mu]g/dL. These 90th percentile values for the 
case study populations are larger than the 90th percentile value of 3.9 
[mu]g/dL reported by NHANES for all children in 2003-2004. It is noted 
that ambient air levels reflected in the urban case studies are likely 
to differ from those underlying the NHANES data.\95\
---------------------------------------------------------------------------

    \95\ The maximum quarterly mean Pb concentrations in the 
location-specific case studies ranged from 0.09-0.36 [mu]g/m\3\, 
which are higher levels than the maximum quarterly mean values in 
most monitoring sites in the U.S. The median of the maximum 
quarterly mean values across all sites in the 2003-05 national 
dataset is 0.03 [mu]g/m\3\ (USEPA, 2007a, appendix A).
---------------------------------------------------------------------------

    Table 2 presents total blood Pb estimates for alternative 
standards, focusing on the median in the assessed population, and 
associated estimates for the air-related percentage of total blood Pb 
(i.e., bounded on the low end by the ``recent air'' contributions and 
on the high end by the ``recent'' plus ``past air'' contribution to 
total Pb exposure).
    Generally, 95th percentile blood Pb estimates across air quality 
scenarios for all case studies (not shown here) are 2-3 times higher 
than the median estimates in Table 2. For example, 95th percentile 
estimates of total blood Pb for the current NAAQS scenario are 10.6 
[mu]g/dL for the general urban case study, 12.3 [mu]g/dL for the 
primary Pb smelter subarea, and 7.4 to 10.2 [mu]g/dL for the three 
location-specific urban case studies (Staff Paper, Table 4-2). While 
the estimates indicate similar fractions of total blood Pb that is air-
related between the 95th percentile and median, there is greater 
uncertainty in pathway apportionment among air-related and other 
sources for higher percentiles, including the 95th percentile.

                                         Table 2.--Summary of Median Blood Pb Estimates for Concurrent Blood Pb
                                                                         [Total]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                    Total blood Pb ([mu]g/dL) (air-related percentage) \A\
                                    --------------------------------------------------------------------------------------------------------------------
 NAAQS Level simulated  ([mu]g/m\3\                                                                  Location-specific urban case studies
max monthly, except as noted below)    General urban case      Primary Pb smelter   --------------------------------------------------------------------
                                              study           (subarea) case studyB  Cleveland (0.56 [mu]g/  Chicago (0.31 [mu]g/    Los Angeles (0.17
                                                                        C                    m\3\)                  m\3\)               [mu]g/m\3\)
--------------------------------------------------------------------------------------------------------------------------------------------------------
1.5 max quarterly \D\..............  3.1 (61 to 84%).......  4.6 (up to 87%).......  2.1 \D\ (57 to 86%)..  3.0 \E\ (63 to 83%)..  2.6E (50 to 81%).
0.50...............................  2.2 (41 to 73%).......  3.2 (up to 81%).......  1.8 (39 to 72%)......  (\F\)................  (\F\)
0.20...............................  1.9 (26 to 74%).......  2.3 (up to 78%).......  1.7 (6 to 65%).......  1.8 (17 to 67%)......  1.7 (\G\) (18 to
                                                                                                                                    71%).
0.05...............................  1.7 (12 to 65%).......  1.7 (up to 65%).......  1.6 (1 to 63%).......  1.6 (6 to 69%).......  1.6 (13 to 69%).
0.02...............................  1.6 (6 to 69%)........  1.6 (up to 69%).......  1.6 (1 to 63%).......  1.6 (1 to 63%).......  1.6 (6 to 63%).
--------------------------------------------------------------------------------------------------------------------------------------------------------
\A\ --Blood Pb estimates are rounded to one decimal place. Air-related percentage is bracketed by ``recent air'' (lower bound of presented range) and
  ``recent'' plus ``past air'' (upper bound of presented range). The term ``past air'' includes contributions from the outdoor soil/dust contribution to
  indoor dust, historical air contribution to indoor dust, and outdoor soil/dust pathways; ``recent air'' refers to contributions from inhalation of
  ambient air Pb or ingestion of indoor dust Pb predicted to be associated with outdoor ambient air Pb levels, with outdoor ambient air also potentially
  including resuspended, previously deposited Pb (see Section II.C.2.e).
\B\ --In the case of the primary Pb smelter subarea, only recent plus past air estimates are available.
\C\ --Median blood Pb levels for the primary smelter (full study area) are estimated at 1.5 [mu]g/dL (for the 1.5 [mu]g/m\3\ max quarterly level) and
  1.4 [mu]g/dL for the remaining NAAQS levels simulated. The air-related percentages for these standard levels range from 36% to 79%.
\D\ --This corresponds to roughly 0.7-1.0 [mu]g/m\3\ maximum monthly mean, across the urban case studies.
\E\ --A ``roll-up'' was performed so that the highest monitor in the study area is increased to just meet this level.
\F\ --A ``roll-up'' to this level was not performed.
\G\ --A ``roll-up'' to this level was not performed; these estimates are based on current conditions in this area.

    As described in section II.C.2.f, the risk assessment also 
developed estimates for air-to-blood ratios, which are described in 
section 5.2.5.2 of the Risk Assessment Report (USEPA, 2007b). These 
ratios reflect a subset of air-related pathways related to inhalation 
and ingestion of indoor dust; inclusion of the remaining pathways would 
be expected to yield higher ratios. Additionally, these ratios are 
based on blood Pb estimates for the 7th year of exposure (concurrent 
blood Pb) which are lower than blood Pb estimates at younger ages (and 
than the lifetime-averaged blood Pb metric). Ratios based on other 
blood Pb estimates (e.g., lifetime-averaged or peak blood Pb) would be 
higher.
     For the general urban case study, estimates of air-to-
blood ratios, presented in section 5.2.5.2 of the Risk Assessment 
Report (USEPA, 2007b) ranged from 1:2 to 1:9, with the majority of the 
estimates ranging from 1:4 to 1:6.\96\ As noted in Section II.C.2.f,

[[Page 29216]]

because the risk assessment only reflects the impact of reductions on 
recent air-related pathways in predicting changes in indoor dust Pb for 
urban case studies, these ratios are lower than they would be if they 
had also reflected potential reductions in other air-related pathways 
(e.g., changes in outdoor surface soil/dust Pb levels and diet with 
changes in ambient air Pb levels). We also note that the median blood 
Pb levels associated with exposure pathways that were not varied in 
this assessment (and consequently are not reflected in these ratios) 
generally range from 1.3 to 1.5 [mu]g/dL for this case study.
---------------------------------------------------------------------------

    \96\ The ratios increase as the level of the alternate standard 
decreases. This reflects nonlinearity in the Pb response, which is 
greater on a per-unit basis for lower ambient air Pb levels.
---------------------------------------------------------------------------

     For the primary Pb smelter subarea, estimates of air-to-
blood ratios, presented in section 5.2.5.2 of the Risk Assessment 
Report (USEPA, 2007b) ranged from 1:10 and higher.97 98 One 
reason for these estimates being higher than those for the urban case 
study is that the dust Pb model used may reflect somewhat ambient air-
related pathways other than that of ambient air infiltrating a home (as 
described in Section II.C.2.f above).\99\
---------------------------------------------------------------------------

    \97\ As with such estimates for the urban case study, ratios are 
higher at lower ambient air Pb levels, reflecting the nonlinearity 
of the dust Pb response with air concentration.
    \98\ For the primary Pb smelter (full study area), for which 
limitations are noted above in section II.C.2.c, the air-to-blood 
ratio estimates, presented in section 5.2.5.2 of the Risk Assessment 
Report (USEPA, 2007b), ranged from 1:3 to 1:7. As in the other case 
studies, ratios are higher at lower ambient air Pb levels. It is 
noted that the underlying changes in both ambient air Pb and blood 
Pb across standard levels are extremely small, introducing 
uncertainty into ratios derived using these data.
    \99\ Also, as noted above (Section II.C.2.h), there is increased 
uncertainty with application of this regression-based model in air 
quality scenarios of notably lower air Pb levels than the data set 
used in its derivation.
---------------------------------------------------------------------------

b. IQ Loss Estimates
    The risk assessment estimated IQ loss associated with both total Pb 
exposure and air-related Pb exposure. This section focuses on findings 
in relation to air-related Pb exposure, since this is the category of 
risk results considered most relevant to the review in considering 
whether the current NAAQS and potential alternative NAAQS provide 
protection of public health with an adequate margin of safety 
(additional categories of risk results, including IQ loss estimates 
based on total Pb exposure and population incidence results, are 
presented at the end of the section).\100\
---------------------------------------------------------------------------

    \100\ The detailed results are provided in the Risk Assessment 
Report (USEPA, 2007b).
---------------------------------------------------------------------------

    In considering air-related risk results, we note that IQ loss 
associated with air-related exposure for each NAAQS scenario is bounded 
by recent-air on the low-end and recent plus past air on the high-end 
(as described in section II.C.2.e above). In considering differences in 
these risk estimates (or in the total risk estimates presented in the 
final Risk Assessment Report) for alternative NAAQS, we note that these 
comparisons underestimate the true impacts of the alternate NAAQS and 
accordingly, the benefit to public health that would result from lower 
NAAQS levels. This is due to our inability to simulate in this 
assessment reductions in several outdoor air deposition-related 
pathways (e.g., diet, ingestion of outdoor surface soil). The magnitude 
of this underestimation is unknown.
    As with the discussion of blood Pb results, the IQ loss estimates 
are summarized here according to air quality scenario and case study 
category (Table 3). In presenting these results, we have focused this 
presentation on estimates for the median in each case study population 
of children because of the greater confidence associated with estimates 
for the median as compared to those for 95th percentile.\101\ 
Generally, 95th percentile IQ loss estimates for all case studies are 
80 to 100% higher than the median results in Table 3. The fraction of 
total IQ loss that is air-related for the 95th percentile is generally 
similar to that for the median (for a particular combination of case 
study and air quality scenario).
---------------------------------------------------------------------------

    \101\ A complete presentation of risk estimates is available in 
the final Risk Assessment Report, including a presentation of 
estimates for the 95th percentile in Table 5-10 of that report.
---------------------------------------------------------------------------

    The risk estimates presented in boldface in Table 3 are those 
derived using the log-linear with low-exposure linearization 
concentration-response function, while the range of estimates 
associated with all four concentration-response functions is presented 
in parentheses. These functions are discussed above in section 
II.C.2.b.

[[Page 29217]]

                        Table 3.--Summary of Risk Attributable to Air-Related Pb Exposure
----------------------------------------------------------------------------------------------------------------
                                                          Median air-related IQ loss \A\
                                 -------------------------------------------------------------------------------
 NAAQS level simulated  ([mu]g/m                                       Location-specific urban case studies
\3\ max monthly, except as noted                    Primary Pb   -----------------------------------------------
             below)                General urban      smelter        Cleveland                      Los Angeles
                                    case study    (subarea) case   (0.56 [mu]g/m  Chicago  (0.31   (0.17 [mu]g/m
                                                   study \B, C\        \3\)        [mu]g/m \3\)        \3\)
----------------------------------------------------------------------------------------------------------------
1.5 max quarterly \D\...........         3.5-4.8             < 6     2.8-3.9 \E\     3.4-4.7 \E\     2.7-4.2 \E\
                                       (1.5-7.7)      <(3.2-9.4)       (0.6-4.6)       (1.4-7.4)       (1.1-6.2)
0.5.............................         1.9-3.6           < 4.5         0.6-2.9             \F\             \F\
                                       (0.7-4.8)      <(2.1-7.7)       (0.2-3.9)
0.2.............................         1.2-3.2           < 3.7         0.6-2.8         0.6-2.9     0.7-2.9 \G\
                                       (0.4-4.0)      <(1.2-5.1)       (0.1-3.2)       (0.3-3.6)       (0.2-3.5)
0.05............................         0.5-2.8           < 2.8         0.1-2.6         0.2-2.6         0.3-2.7
                                       (0.2-3.3)      <(0.9-3.4)      (<0.1-3.1)       (0.1-3.2)       (0.1-3.2)
0.02............................         0.3-2.6           < 2.9        <0.1-2.6         0.1-2.6         0.1-2.6
                                       (0.1-3.1)      <(0.9-3.3)      (<0.1-3.0)      (<0.1-3.1)     (<0.1-3.1)
----------------------------------------------------------------------------------------------------------------
\A\--Air-related risk is bracketed by ``recent air'' (lower bound of presented range) and ``recent'' plus ``past
  air'' (upper bound of presented range). While differences between standard levels are better distinguished by
  differences in the ``recent'' plus ``past air'' estimates (upper bounds shown here), these differences are
  inherently underestimates. The term ``past air'' includes contributions from the outdoor soil/dust
  contribution to indoor dust, historical air contribution to indoor dust, and outdoor soil/dust pathways;
  ``recent air'' refers to contributions from inhalation of ambient air Pb or ingestion of indoor dust Pb
  predicted to be associated with outdoor ambient air Pb levels, with outdoor ambient air also potentially
  including resuspended, previously deposited Pb (see Section II.C.2.e). Boldface values are estimates generated
  using the log-linear with low-exposure linearization function. Values in parentheses reflect the range of
  estimates associated with all four concentration-response functions.
\B\--In the case of the primary Pb smelter case study, only recent plus past air estimates are available.
\C\--Median air-related IQ loss estimates for the primary Pb smelter (full study area) range from <1.7 to <2.9
  points, with no consistent pattern across simulated NAAQS levels. This lack of a pattern reflects inclusion of
  a large fraction of the study population with relatively low ambient air impacts such that there is lower
  variation (at the population median) across standard levels (see Section 4.2 of the Risk Assessment, Volume
  1).
\D\--This corresponds to roughly 0.7--1.0 [mu]g/m3 maximum monthly mean, across the urban case studies
\E\--A ``roll-up'' was performed so that the highest monitor in the study area is increased to just meet this
  level.
\F\--A ``roll-up'' to this level was not performed.
\G\--A ``roll-up'' to this level was not performed; these estimates are based on current conditions in this
  area.

    Key observations regarding the median estimates of air-related risk 
for the current NAAQS and alternative standards presented in Table 3 
include:
     For the scenario for the current NAAQS (1.5 [mu]g/m\3\, 
maximum quarterly average), air-related risk exceeds 2 points IQ loss 
at the median and the upper bound of air-related risk is near or above 
4 points IQ loss in all five case studies.\102\
---------------------------------------------------------------------------

    \102\ As noted in Table 3 and section II.C.2.d above, and 
discussed further, with regard to associated limitations and 
uncertainties, in section II.C.2.h above, a proportional roll-up 
procedure was used to estimate air Pb concentrations in this 
scenario for the location-specific case studies.
---------------------------------------------------------------------------

     Alternate standards provide substantial reduction in 
estimates of air-related risk across the full set of alternative NAAQS 
considered in this analysis (i.e., 0.5 to 0.02 [mu]g/m\3\ max monthly). 
This is particularly the case for the lower bounds of the air-related 
estimates presented in Table 3, which reflect the estimates for 
``recent air''-related pathways, which are the pathways that were 
varied with changes in air concentrations (as described above in 
section II.C.2.e). There is less risk reduction associated with the 
upper bounds of these estimates as the upper bound values are inclusive 
of the exposure pathways categorized as ``past air'' which were not 
varied with changes in air concentrations (as described in section 
II.C.2.3). The upper bound estimates for the lowest level assessed 
(0.02 [mu]g/m\3\) are 2.6-2.9 points IQ loss.
     In the general urban case study, the lower bound of air-
related risk falls below 2 points IQ loss for an alternative NAAQS of 
0.5 [mu]g/m\3\ max monthly, and below 1 point IQ loss somewhere between 
an alternative NAAQS of 0.2 and 0.05 [mu]g/m\3\ max monthly.
     The upper-bound of air-related risk for the primary Pb 
smelter subarea is generally higher than that for the general urban 
case study, likely due to the difference in indoor dust models used for 
the two case studies. The indoor dust Pb model used for the primary Pb 
smelter considered more completely, the impact of outdoor ambient air 
Pb on indoor dust (compared to the hybrid indoor dust Pb model used in 
the urban case studies). Specifically, the regression model used for 
the primary Pb smelter included consideration for longer-term 
relationships between outdoor ambient air and indoor dust (e.g., 
changes in outdoor soil and subsequent tracking in of soil Pb).
     As noted above (section II.C.2.c), the three location-
specific urban case studies provide risk estimates for populations with 
a broader range of air-related exposures. Accordingly, because of the 
population distribution in these three case studies, the air-related 
risk is smaller for them than for the other case studies, particularly 
at the population median. Further, the majority of the population in 
each case study resides in areas with ambient air Pb levels well below 
each standard level assessed, particularly for levels above 0.05 [mu]g/
m\3\ max monthly. Consequently, risk estimates indicate little response 
to alternative standard levels above 0.05 [mu]g/m\3\ max monthly.
    In addition to the air-related risk results described above, we 
present two additional categories of risk results, including (a) 
estimates of median IQ loss based on total Pb exposure for each case 
study (Table 4) and (b) IQ loss incidence estimates for each of the 
location-specific case studies (Tables 4 and 5).\103\ Each of these 
categories of risk results are described in creater detail below:
---------------------------------------------------------------------------

    \103\ As recognized in section II.C.2.d above, to simulate air 
concentrations associated with the current NAAQS, a proportional 
roll-up of concentrations from those for current conditions was 
performed for the location-specific urban case studies. This was not 
necessary for the primary Pb smelter case study in which air 
concentrations currently exceed the current standard.
---------------------------------------------------------------------------

     Estimates of IQ loss for all air quality scenarios (based 
on total Pb exposure): Table 4 presents median IQ loss estimates for 
total Pb exposure for each of the air quality scenarios simulated for 
each case study (as noted earlier in this section, there is greater 
uncertainty associated with higher-end risk percentiles and therefore, 
they are

[[Page 29218]]

not presented in tabular format here--see Table 5-10 of Risk Assessment 
Volume 1 for 95th percentile total IQ loss estimates). As with the 
incremental risk results presented in Table 3 above, in order to 
reflect the variation in estimates derived from the four different 
concentration-response functions included in the analysis, three 
categories of estimates are presented in Table 4 including (a) IQ loss 
estimates generated using the low concentration-response function (the 
model that generated the lowest IQ loss estimates), (b) estimates 
generated using the log-linear with low-exposure linearization (LLL) 
model, and (c) IQ loss estimates generated using the high 
concentration-response function (the model that generated the highest 
IQ loss estimates). It is important to emphasize, that, as noted in 
Section II.C.2.e, because of limitations in modeling methods, we were 
only able to simulate reduction in recent air-related exposures in 
considering alternate standard levels and could not simulate reduction 
in past air-related exposures. This likely results in an underestimate 
of the total degree of reduction in exposure and risk associated with 
each standard level. Therefore, in comparing total risk estimates 
between alternate NAAQS scenarios (i.e., considering incremental risk 
reductions), this aspect of the analysis will tend to underestimate the 
reductions in risk associated with alternative NAAQS.
     IQ loss incidence estimates for the three location-
specific urban case studies: Estimates of the number of children for 
each location-specific urban case study projected to have total Pb-
related IQ loss greater than one point are summarized in Table 5, and 
similar estimates for IQ loss greater than 7 points are summarized in 
Table 6. Also presented are the changes in incidence of the current 
NAAQS and alternative NAAQS scenarios compared to current conditions, 
with emphasis placed on estimates generated using the LLL 
concentration-response function. Estimates are presented for each of 
the four concentration-response functions used in the risk analysis. 
This metric illustrates the overall number of children within a given 
urban case study location projected to experience various levels of IQ 
loss due to Pb exposure and how that distribution of incidence changes 
with alternate standard levels. These incidence estimates were only 
generated for the location-specific urban case studies, since these 
have larger enumerated study populations (additional detail on the 
derivation of these incidence estimates is presented in Section 5.3.1.2 
of the Risk Assessment Report). The complete set of incidence results 
is presented in Risk Assessment Report Appendix O, Section O.3.4.
    Total IQ loss results presented in Table 4 for the primary Pb 
smelter case study (full study area) illustrate the reason why these 
results were not presented earlier in summarizing air-related IQ loss 
estimates for the primary Pb smelter case study in Table 3 (and 
instead, results for the subarea were presented). As mentioned earlier 
in Section II.C.2.c, the full study area for the primary Pb smelter 
case study incorporates a large number of simulated children with 
relatively low air-related impacts, which results in little 
differentiation between alternate standard levels in terms of total IQ 
loss (as well as air-related IQ loss). This can be seen by considering 
the results in Table 4 for the primary Pb smelter (full study area). 
Those results suggest that total IQ loss varies little across alternate 
standard levels for the full study area simulation, with the only 
noticeable difference in total IQ loss resulting from analysis of the 
current standard (when compared to alternate levels). By contrast, 
there are notable differences in total IQ loss between alternative 
standard levels for the sub-area of the primary Pb smelter case study.

              Table 4.--Summary of Risk Estimates for Medians of Total-Exposure Risk Distributions
----------------------------------------------------------------------------------------------------------------
                                                                      Points IQ loss  (total Pb exposure) \a\
                                                                 -----------------------------------------------
               Case study and air quality scenario                    Low C-R                        High C-R
                                                                     function         LLL \b\        function
                                                                     estimate                        estimate
----------------------------------------------------------------------------------------------------------------
                                           Location-specific (Chicago)
----------------------------------------------------------------------------------------------------------------
Current NAAQS (1.5 [mu]g/m\3\, max quarterly)...................             2.4             5.6             8.8
Current conditions (0.14 [mu]g/m\3\ max quarterly; 0.31 [mu]g/               1.4             4.2             5.2
 m\3\ max monthly)..............................................
Alternative NAAQS (0.2 [mu]g/m\3\, max monthly).................             1.4             4.2             5.2
Alternative NAAQS (0.05 [mu]g/m\3\, max monthly)................             1.3             4.0             4.8
Alternative NAAQS (0.02 [mu]g/m\3\, max monthly)................             1.3             4.0             4.7
----------------------------------------------------------------------------------------------------------------
                                          Location-specific (Cleveland)
----------------------------------------------------------------------------------------------------------------
Current NAAQS (1.5 [mu]g/m\3\, max quarterly)...................             1.7             4.7             6.3
Current conditions (0.36 [mu]g/m\3\ max quarterly; 0.56 [mu]g/               1.4             4.2             5.2
 m\3\ max monthly)..............................................
Alternative NAAQS (0.5 [mu]g/m\3\, max monthly).................             1.4             4.2             5.2
Alternative NAAQS (0.2 [mu]g/m\3\, max quarterly)...............             1.4             4.1             5.0
Alternative NAAQS (0.2 [mu]g/m\3\, max monthly).................             1.3             4.1             4.9
Alternative NAAQS (0.05 [mu]g/m\3\, max monthly)................             1.3             4.0             4.7
Alternative NAAQS (0.02 [mu]g/m\3\, max monthly)................             1.2             3.9             4.6
----------------------------------------------------------------------------------------------------------------
                                         Location-specific (Los Angeles)
----------------------------------------------------------------------------------------------------------------
Current NAAQS (1.5 [mu]g/m\3\, max quarterly)...................             2.1             5.3             7.7
Current conditions (0.09 [mu]g/m\3\ max quarterly; 0.17 [mu]g/               1.4             4.2             5.1
 m\3\ max monthly)..............................................
Alternative NAAQS (0.05 [mu]g/m\3\, max monthly)................             1.3             4.0             4.8
Alternative NAAQS (0.02 [mu]g/m\3\, max monthly)................             1.3             4.0             4.7
----------------------------------------------------------------------------------------------------------------
                                                  General Urban
----------------------------------------------------------------------------------------------------------------
Current NAAQS (1.5 [mu]g/m\3\, max quarterly)...................             2.5             5.8             9.2

[[Page 29219]]

Alternative NAAQS (0.5 [mu]g/m\3\, max monthly).................             1.7             4.8             6.4
Current conditions--high-end (0.87 [mu]g/m\3\ max quarterly)....             1.7             4.7             6.3
Alternative NAAQS (0.2 [mu]g/m\3\, max quarterly)...............             1.6             4.6             5.9
Current conditions--mean (0.14 [mu]g/m\3\ max quarterly)........             1.5             4.5             5.6
Alternative NAAQS (0.2 [mu]g/m\3\, max monthly).................             1.5             4.4             5.6
Alternative NAAQS (0.05 [mu]g/m\3\, max monthly)................             1.3             4.1             5.0
Alternative NAAQS (0.02 [mu]g/m\3\, max monthly)................             1.3             4.0             4.8
----------------------------------------------------------------------------------------------------------------
                                       Primary Pb smelter--full study area
----------------------------------------------------------------------------------------------------------------
Current NAAQS (1.5 [mu]g/m\3\, max quarterly)...................             1.2             3.8             4.4
Alternative NAAQS (0.5 [mu]g/m\3\, max monthly).................             1.0             3.7             4.2
Alternative NAAQS (0.2 [mu]g/m\3\, max quarterly)...............             0.9             3.6             4.2
Alternative NAAQS (0.2 [mu]g/m\3\, max monthly).................             0.9             3.6             4.1
Alternative NAAQS (0.05 [mu]g/m\3\, max monthly)................             0.9             3.6             4.0
Alternative NAAQS (0.02 [mu]g/m\3\, max monthly)................             0.9             3.6             4.1
----------------------------------------------------------------------------------------------------------------
                                        Primary Pb smelter--1.5km subarea
----------------------------------------------------------------------------------------------------------------
Current NAAQS (1.5 [mu]g/m\3\, max quarterly)...................             3.7             6.8            11.2
Alternative NAAQS (0.5 [mu]g/m\3\, max monthly).................             2.6             5.8             9.4
Alternative NAAQS (0.2 [mu]g/m\3\, max quarterly)...............             2.0             5.2             7.4
Alternative NAAQS (0.2 [mu]g/m\3\, max monthly).................             1.9             5.0             6.9
Alternative NAAQS (0.05 [mu]g/m\3\, max monthly)................             1.4             4.2             5.1
Alternative NAAQS (0.02 [mu]g/m\3\, max monthly)................             1.3             4.0            4.8
----------------------------------------------------------------------------------------------------------------
\a\ --These columns present the estimates of total IQ loss resulting from total Pb exposure (policy-relevant
  plus background). Estimates below 1.0 are rounded to one decimal place, all values below 0.05 are presented as
  <0.1 and values between 0.05 and 0.1 as 0.1. All values above 1.0 are rounded to the nearest whole number.
\b\ --Log-linear with low-exposure linearization concentration-response function.

                                             Table 5.--Incidence of Children With >1 Point Pb-Related IQ Loss
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                   Dual linear--stratified       Log-linear with       Dual linear--stratified  Log-linear with cutpoint
                                                   at 7.5 mg/dl peak blood        linearization        at  10 m/dL peak blood  -------------------------
                                                             Pb            --------------------------            Pb
                                                 --------------------------                          --------------------------                 Delta
  Air quality scenario  (for location-specific                    Delta                     Delta                     Delta                   (change in
               urban case studies)                               (change     Incidence    (change in                (change in   Incidence    incidence
                                                   Incidence   inincidence  of >1 point   incidence    Incidence    incidence   of >1 point  compared to
                                                  of >1 point  compared to     IQ loss   compared to  of >1 point  compared to     IQ loss     current
                                                     IQ loss     current                   current       IQ loss     current                 conditions)
                                                               conditions)               conditions)               conditions)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Chicago (total modeled child population:
 396,511):
    Chicago Current Conditions..................      391,602  ...........      389,754  ...........      271,031  ...........      236,257
    Current NAAQS (1.5 mg/m\3\ Maximum                395,797        4,195      395,528        5,773      347,415       76,384      314,053       77,795
     Quarterly).................................
    Alternative NAAQS (0.2 mg/m\3\ Maximum            391,158         -444      389,461         -293      271,444          412      235,559         -698
     Monthly)...................................
    Alternative NAAQS (0.05 mg/m\3\ Maximum           389,572       -2,030      387,407       -2,347      253,775      -17,256      224,394      -11,864
     Monthly)...................................
    Alternative NAAQS (0.02 mg/m\3\ Maximum           389,176       -2,427      386,630       -3,125      249,865      -21,166      219,294      -16,963
     Monthly)...................................
Cleveland (total modeled child population:
 13,990):
    Cleveland Current Conditions................       13,809  ...........       13,745  ...........        9,526  ...........        8,515
    Current NAAQS (1.5 mg/m\3\ Maximum                 13,893           84       13,857          112       10,664        1,137        9,769        1,254
     Quarterly).................................
    Alternative NAAQS (0.2 mg/m\3\ Maximum             13,770          -38       13,703          -42        9,221         -305        8,160         -354
     Quarterly).................................
    Alternative NAAQS (0.5 mg/m\3\ Maximum             13,789          -20       13,720          -25        9,497          -29        8,464          -51
     Monthly)...................................
    Alternative NAAQS (0.2 mg/m\3\ Maximum             13,759          -50       13,694          -51        9,083         -443        8,010         -505
     Monthly)...................................
    Alternative NAAQS (0.05 mg/m\3\ Maximum            13,729          -80       13,642         -103        8,785         -741        7,720         -795
     Monthly)...................................
    Alternative NAAQS (0.02 mg/m\3\ Maximum            13,720          -88       13,628         -117        8,736         -790        7,668         -846
     Monthly)...................................
Los Angeles (total modeled child population:
 372,252):
    Los Angeles Current Conditions..............      282,216  ...........      280,711  ...........      191,675  ...........      170,474  ...........
    Current NAAQS (1.5 mg/m\3\ Maximum,               285,272        3,056      284,945        4,234      240,988       49,313      226,608       56,134
     Quarterly).................................

[[Page 29220]]

    Alternative NAAQS (0.05 mg/m\3\ Maximum           281,112       -1,104      279,658       -1,053      183,395       -8,280      161,914       -8,560
     Monthly)...................................
    Alternative NAAQS (0.02 mg/m\3\ Maximum           280,740       -1,476      279,057       -1,654      180,745      -10,929      158,234      -12,240
     Monthly)...................................
--------------------------------------------------------------------------------------------------------------------------------------------------------

                                            Table 6.--Incidence of Children With >7 Points Pb-Related IQ Loss
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                   Dual linear--stratified       Log-linear with       Dual linear--stratified  Log-linear with cutpoint
                                                   at 7.5 ug/dL peak blood        linearization        at  10 ug/dL peak blood -------------------------
                                                             Pb            --------------------------            Pb
                                                 --------------------------                          --------------------------                 Delta
  Air quality scenario (location-specific urban                   Delta                     Delta                     Delta      Incidence    (change in
                  case studies)                    Incidence    (change in   Incidence    (change in   Incidence    (change in     of > 7     incidence
                                                     of > 7     incidence      of > 7     incidence      of > 7     incidence    points IQ   compared to
                                                   points IQ   compared to   points IQ   compared to   points IQ   compared to      loss       current
                                                      loss       current        loss       current        loss       current                 conditions)
                                                               conditions)               conditions)               conditions)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Chicago (total modeled child population:
 396,511):
    Chicago Current Conditions..................      136,709  ...........       33,664  ...........           63  ...........        1,015  ...........
    Current NAAQS (1.5 [mu]g/m\3\ Maximum             244,401      107,692      100,159       66,495          555          492        5,226        4,211
     Quarterly).................................
    Alternative NAAQS (0.2 [mu]g/\3\ Maximum          136,067         -642       32,546       -1,118           48          -16        1,007           -8
     Monthly)...................................
    Alternative NAAQS (0.05 [mu]g/\3\ Maximum         120,706      -16,003       27,367       -6,297           16          -48          864         -151
     Monthly)...................................
    Alternative NAAQS (0.02 [mu]g/\3\ Maximum         117,819      -18,890       26,027       -7,637            8          -56          690         -325
     Monthly)...................................
Cleveland (total modeled child population:
 13,990):
    Cleveland Current Conditions................        4,834  ...........        1,212  ...........            3  ...........           46  ...........
    Current NAAQS (1.5 [mu]g/m\3\ Maximum               6,139        1,305        1,858          647            4            2          105           59
     Quarterly).................................
    Alternative NAAQS (0.2 [mu]g/m\3\ Maximum           4,525         -309        1,073         -139            1           -2           40           -6
     Quarterly).................................
    Alternative NAAQS (0.5 [mu]g/m\3\ Maximum           4,806          -28        1,180          -31            1           -2           43           -3
     Monthly)...................................
    Alternative NAAQS (0.2 [mu]g/m\3\ Maximum           4,424         -410        1,026         -186            1           -2           43           -3
     Monthly)...................................
    Alternative NAAQS (0.05 [mu]g/m\3\ Maximum          4,106         -728          886         -326            0           -3           24          -22
     Monthly)...................................
    Alternative NAAQS (0.02 [mu]g/m\3\ Maximum          4,051         -783          866         -345            0           -3           27          -18
     Monthly)...................................
Los Angeles (total modeled child population:
 372,252):
    Los Angeles Current Conditions..............       94,684  ...........       22,665  ...........           23  ...........          732  ...........
    Current NAAQS (1.5 [mu]g/m\3\ Maximum,            158,171       63,487       57,834       35,168          183          160        3,771        3,038
     Quarterly).................................
    Alternative NAAQS (0.05 [mu]g/m\3\ Maximum,        87,303       -7,382       19,781       -2,884           11          -11          624         -109
     Monthly)...................................
    Alternative NAAQS (0.02 [mu]g/m\3\ Maximum,        83,909      -10,775       17,939       -4,726           17           -6          498         -235
     Monthly)...................................
--------------------------------------------------------------------------------------------------------------------------------------------------------

D. Conclusions on Adequacy of the Current Primary Standard

    The initial issue to be addressed in the current review of the 
primary Pb standard is whether, in view of the advances in scientific 
knowledge and additional information, the existing standard should be 
retained or revised. In evaluating whether it is appropriate to retain 
or revise the current standard, the Administrator builds on the general 
approach used in the initial setting of the standard, as well as that 
used in the last review, and reflects the broader body of evidence and 
information now available.
    The approach used is based on an integration of information on 
health effects associated with exposure to ambient Pb; expert judgment 
on the adversity of such effects on individuals; and policy judgments 
as to when the standard is requisite to protect public health with an 
adequate margin of safety, which are informed by air quality and 
related analyses, quantitative exposure and risk assessments when 
possible, and qualitative assessment of impacts that could not be 
quantified.
    The Administrator has taken into account both evidence-based \104\ 
and quantitative exposure- and risk-based considerations in developing 
conclusions on the adequacy of the current primary Pb standard. 
Evidence-based considerations include the assessment of evidence for a 
variety of

[[Page 29221]]

Pb-related health endpoints from epidemiological, and animal 
toxicological studies. Consideration of quantitative exposure- and 
risk-based information draws from the results of the exposure and risk 
assessments described above. More specifically, estimates of the 
magnitude of Pb-related exposures and risks associated with air quality 
levels associated with just meeting the current primary Pb NAAQS have 
been considered.\105\
---------------------------------------------------------------------------

    \104\ The term ``evidence-based'' as used here refers to the 
drawing of information directly from published studies, with 
specific attention to those reviewed and described in the Criteria 
Document, and is distinct from considerations that draw from the 
results of the quantitative exposure and risk assessement.
    \105\ As described in seciton II.C.2.d above, levels in the 
location-specific urban case studies were increased from current 
conditions such that the portion of each case study with highest 
concentrations would just meet the current NAAQS.
---------------------------------------------------------------------------

    In this review, a series of general questions frames the approach 
to reaching a decision on the adequacy of the current standard, such as 
the following: (1) To what extent does newly available information 
reinforce or call into question evidence of associations of Pb 
exposures with effects identified when the standard was set?; (2) to 
what extent has evidence of new effects or at-risk populations become 
available since the time the standard was set?; (3) to what extent have 
important uncertainties identified when the standard was set been 
reduced and have new uncertainties emerged?; and (4) to what extent 
does newly available information reinforce or call into question any of 
the basic elements of the current standard?
    The question of whether the available evidence supports 
consideration of a standard that is more protective than the current 
standard includes consideration of: (1) Whether there is evidence that 
associations with blood Pb in epidemiological studies extend to ambient 
Pb concentration levels that are as low as or lower than had previously 
been observed, and the important uncertainties associated with that 
evidence; (2) the extent to which exposures of potential concern and 
health risks are estimated to occur in areas upon meeting the current 
standard and the important uncertainties associated with the estimated 
exposures and risks; and (3) the extent to which the Pb-related health 
effects indicated by the evidence and the exposure and risk assessments 
are considered important from a public health perspective, taking into 
account the nature and severity of the health effects, the size of the 
at-risk populations, and the kind and degree of the uncertainties 
associated with these considerations.
    This approach is consistent with the requirements of the NAAQS 
provisions of the Act and with how EPA and the courts have historically 
interpreted the Act. These provisions require the Administrator to 
establish primary standards that, in the Administrator's judgment, are 
requisite to protect public health with an adequate margin of safety. 
In so doing, the Administrator seeks to establish standards that are 
neither more nor less stringent than necessary for this purpose. The 
Act does not require that primary standards be set at a zero-risk level 
but rather at a level that avoids unacceptable risks to public health, 
including the health of sensitive groups.
    The following discussion starts with background information on the 
current standard (section II.D.1), including both the basis for 
derivation of the current standard and considerations and conclusions 
from the 1990 Staff Paper (USEPA, 1990b). This is followed by a 
discussion of the Agency's approach in this review for evaluating the 
adequacy of the current standard, in section II.D.2, including both 
evidence-based and exposure/risk-based considerations (sections 
II.D.2.a and b, respectively). CASAC advice and recommendations 
concerning adequacy of the current standard are summarized in section 
II.D.3. Lastly, the Administrator's proposed conclusions with regard to 
the adequacy of the current standard are presented in section II.D.4.
1. Background
a. The Current Standard
    The current primary standard is set at a level of 1.5 [mu]g/m\3\, 
measured as Pb-TSP, not to be exceeded by the maximum arithmetic mean 
concentration averaged over a calendar quarter. The standard was set in 
1978 to provide protection to the public, especially children as the 
particularly sensitive population subgroup, against Pb-induced adverse 
health effects (43 FR 46246). In setting the standard, EPA relied on 
conclusions regarding sources of exposure, air-related exposure 
pathways, variability and susceptibility of young children, the most 
sensitive health endpoints, blood Pb level thresholds for various 
health effects and the stability and distributional characteristics of 
Pb (both in the human body and in the environment) (43 FR 46247). The 
specific basis for selecting each of the elements of the standard is 
described below.
i. Level
    EPA's objective in selecting the level of the current standard was 
``to estimate the concentration of Pb in the air to which all groups 
within the general population can be exposed for protracted periods 
without an unacceptable risk to health'' (43 FR 46252). As stated in 
the notice of final rulemaking, ``This estimate was based on EPA's 
judgment in four key areas:
    (1) Determining the `sensitive population' as that group within the 
general population which has the lowest threshold for adverse effects 
or greatest potential for exposure. EPA concludes that young children, 
aged 1 to 5, are the sensitive population.
    (2) Determining the safe level of total lead exposure for the 
sensitive population, indicated by the concentration of lead in the 
blood. EPA concludes that the maximum safe level of blood lead for an 
individual child is 30 [mu]g Pb/dl and that population blood lead, 
measured as the geometric mean, must be 15 [mu]g Pb/dl in order to 
place 99.5 percent of children in the United States below 30 [mu]g Pb/
dl.
    (3) Attributing the contribution to blood lead from nonair 
pollution sources. EPA concludes that 12 [mu]g Pb/dl of population 
blood lead for children should be attributed to nonair exposure.
    (4) Determining the air lead level which is consistent with 
maintaining the mean population blood lead level at 15 [mu]g Pb/dl [the 
maximum safe mean level]. Taking into account exposure from other 
sources (12 [mu]g Pb/dl), EPA has designed the standard to limit air 
contribution after achieving the standard to 3 [mu]g Pb/dl. On the 
basis of an estimated relationship of air lead to blood lead of 1 to 2, 
EPA concludes that the ambient air standard should be 1.5 [mu]g Pb/
m\3\.'' (43 FR 46252)
    EPA's judgments in these key areas, as well as margin of safety 
considerations, are discussed below.
    The assessment of the science that was presented in the 1977 
Criteria Document (USEPA, 1977), indicated young children, aged 1 to 5, 
as the population group at particular risk from Pb exposure. Children 
were recognized to have a greater physiological sensitivity than adults 
to the effects of Pb and a greater exposure. In identifying young 
children as the sensitive population, EPA also recognized the 
occurrence of subgroups with enhanced risk due to genetic factors, 
dietary deficiencies or residence in urban areas. Yet information was 
not available to estimate a threshold for adverse effects for these 
subgroups separate from that of all young children. Additionally, EPA 
recognized both a concern regarding potential risk to pregnant women 
and fetuses, and a lack of information to establish that these 
subgroups are more at risk than young children. Accordingly, young 
children, aged 1 to 5, were identified as the group which has the 
lowest threshold for adverse

[[Page 29222]]

effects of greatest potential for exposure (i.e., the sensitive 
population) (43 FR 46252).
    In identifying the maximum safe exposure, EPA relied upon the 
measurement of Pb in blood (43 FR 46252-46253). The physiological 
effect of Pb that had been identified as occurring at the lowest blood 
Pb level was inhibition of an enzyme integral to the pathway by which 
heme (the oxygen carrying protein of human blood) is synthesized, i.e., 
delta-aminolevulinic acid dehydratase ([delta]-ALAD). The 1977 Criteria 
Document reported a threshold for inhibition of this enzyme in children 
at 10 [mu]g Pb/dL. The 1977 Criteria Document also reported a threshold 
of 15-20 [mu]g/dL for elevation of erythrocyte protoporphyrin (EP), 
which is an indication of some disruption of the heme synthesis 
pathway. EPA concluded that this effect on the heme synthesis pathway 
(indicated by EP) was potentially adverse. EPA further described a 
range of blood levels associated with a progression in detrimental 
impact on the heme synthesis pathway. At the low end of the range (15-
20 [mu]g/dL), the initial detection of EP associated with blood Pb was 
not concluded to be associated with a significant risk to health. The 
upper end of the range (40 [mu]g/dL), the threshold associated with 
clear evidence of heme synthesis impairment and other effects 
contributing to clinical symptoms of anemia, was regarded by EPA as 
clearly adverse to health. EPA also noted that for some children with 
blood Pb levels just above those for these effects (e.g., 50 [mu]g/dL), 
there was risk for additional adverse effects (e.g., nervous system 
deficits). Additionally, in the Agency's statement of factors on which 
the conclusion as to the maximum safe blood Pb level for an individual 
child was based, EPA stated that the maximum safe blood level should be 
``no higher than the blood Pb range characterized as undue exposure by 
the Center for Disease Control of the Public Health Service, as 
endorsed by the American Academy of Pediatrics, because of elevation of 
erythrocyte protoporphyrin (above 30 [mu]g Pb/dL)''.\106\
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    \106\ The CDC subsequently revised their advisory level for 
children's blood Pb to 25 [mu]g/dL in 1985, and to 10 [mu]g/dL in 
1991. In 2005, with consideration of a review of the evidence by 
their advisory committee, CDC revised their statement on Preventing 
Lead Poisoning in Young Children, specifically recognizing the 
evidence of adverse health effects in children with blood Pb levels 
below 10 [mu]g/dL and the data demonstrating that no ``safe'' 
threshold for blood Pb in children had been identified, and 
emphasizing the importance of preventative measures (CDC, 2005a). 
Recently, CDC's Advisory Committee on Childhood Lead Poisoning 
Prevention noted the 2005 CDC statements and reported on a review of 
the clinical interpretation and management of blood Pb levels below 
10 [mu]g/dL (ACCLPP, 2007). More details on this level are provided 
in Section II.B.1.
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    Having identified the maximum safe blood level in individual 
children, EPA next made a public health policy judgment regarding the 
target mean blood level for the U.S. population of young children (43 
FR 46252-46253). With this judgment, EPA identified a target of 99.5 
percent of this population to be brought below the maximum safe blood 
Pb level. This judgment was based on consideration of the size of the 
sensitive subpopulation, and the recognition that there are special 
high-risk groups of children within the general population. The 
population statistics available at the time (the 1970 U.S. Census) 
indicated a total of 20 million children younger than 5 years of age, 
with 15 million residing in urban areas and 5 million in center cities 
where Pb exposure was thought likely to be ``high''. Concern about 
these high-risk groups influenced EPA's determination of 99.5 percent, 
deterring EPA from selecting a population percentage lower than 99.5 
(43 FR 46253). EPA then used standard statistical techniques to 
calculate the population mean blood Pb level that would place 99.5 
percent of the population below the maximum safe level. Based on the 
then available data, EPA concluded that blood Pb levels in the 
population of U.S. children were normally distributed with a GSD of 
1.3. Based on standard statistical techniques, EPA determined that a 
thus described population in which 99.5 percent of the population has 
blood Pb levels below 30 [mu]g/dL would have a geometric mean blood 
level of 15 [mu]g/dL. EPA described 15 [mu]g/dL as ``the maximum safe 
blood lead level (geometric mean) for a population of young children'' 
(43 FR 46247).
    When setting the current NAAQS, EPA recognized that the air 
standard needed to take into account the contribution to blood Pb 
levels from Pb sources unrelated to air pollution. Consequently, the 
calculation of the current NAAQS included the subtraction of Pb 
contributed to blood Pb from nonair sources, from the estimate of a 
safe mean population blood Pb level. Without this subtraction, EPA 
recognized that the combined exposure to Pb from air and nonair sources 
would result in a blood Pb concentration exceeding the safe level (43 
FR 46253). In developing an estimate of this nonair contribution, EPA 
recognized the lack of detailed or widespread information about the 
relative contribution of various sources to children's blood Pb levels, 
such that an estimate could only be made by inference from other 
empirical or theoretical studies, often involving adults. Additionally, 
EPA recognized the expectation that the contribution to blood Pb levels 
from nonair sources would vary widely, was probably not in constant 
proportion to air Pb contribution, and in some cases may alone exceed 
the target mean population blood Pb level (43 FR 46253-46254). The 
amount of blood Pb attributed to nonair sources was selected based 
primarily on findings in studies of blood Pb levels in areas where air 
Pb levels were low relative to other locations in U.S. The air Pb 
levels in these areas ranged from 0.1 to 0.7 [mu]g/m\3\. The average of 
the reported blood Pb levels for children of various ages in these 
areas was on the order of 12 [mu]g/dL. Thus, 12 [mu]g/dL was identified 
as the nonair contribution, and subtracted from the population mean 
target level of 15 [mu]g/dL to yield a value of 3 [mu]g/dL as the limit 
on the air contribution to blood Pb.
    In determining the air Pb level consistent with an air contribution 
of 3 [mu]g Pb/dL, EPA reviewed studies assessed in the 1977 Criteria 
Document that reported changes in blood Pb with different air Pb 
levels. These studies included a study of children exposed to Pb from a 
primary Pb smelter, controlled exposures of adult men to Pb in fine 
particulate matter, and a personal exposure study involving several 
male cohorts exposed to Pb in a large urban area in the early 1970s (43 
FR 46254).\107\ Using all three studies, EPA calculated an average 
slope or ratio over the entire range of data. That value was 1.95 
(rounded to 2 [mu]g/dL blood Pb concentration to 1 [mu]g/m\3\ air Pb 
concentration), and is recognized to fall within the range of values 
reported in the 1977 Criteria Document. On the basis of this 2-to-1 
relationship, EPA concluded that the ambient air standard should be 1.5 
[mu]g Pb/m\3\ (43 FR 46254).
---------------------------------------------------------------------------

    \107\ Mean blood Pb levels in the adult study groups ranged from 
10 [mu]g/dL to approximately 30 [mu]g/dL and in the child groups 
they ranged from approximately 20 [mu]g/dL up to 65 [mu]g/dL (USEPA, 
1986a, section 11.4.1).
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    In consideration of the appropriate margin of safety during the 
development of the current NAAQS, EPA identified the following factors: 
(1) The 1977 Criteria Document reported multiple biological effects of 
Pb in practically all cell types, tissues and organ systems, of which 
the significance for health had not yet been fully studied; (2) no 
beneficial effects of Pb at then current environmental levels were 
recognized;

[[Page 29223]]

(3) data were incomplete as to the extent to which children are 
indirectly exposed to air Pb that has moved to other environmental 
media, such as water, soil and dirt, and food; (4) Pb is chemically 
persistent and with continued uncontrolled emissions would continue to 
accumulate in human tissue and the environment; and (5) the possibility 
that exposure associated with blood Pb levels previously considered 
safe might influence neurological development and learning abilities of 
the young child (43 FR 46255). Recognizing that estimating an 
appropriate margin of safety for the air Pb standard was complicated by 
the multiple sources and media involved in Pb exposure, EPA chose to 
use margin of safety considerations principally in establishing a 
maximum safe blood Pb level for individual children (30 [mu]g Pb/dL) 
and in determining the percentage of children to be placed below this 
maximum level (about 99.5 percent). Additionally, in establishing other 
factors used in calculating the standard, EPA used margin of safety 
considerations in the sense of making careful judgment based on 
available data, but these judgments were not considered to be at the 
precautionary extreme of the range of data available at the time (43 FR 
46251).
    EPA further recognized that, because of the variability between 
individuals in a population experiencing a given level of Pb exposure, 
it was considered impossible to provide the same margin of safety for 
all members in the sensitive population or to define the margin of 
safety in the standard as a simple percentage. EPA believed that the 
factors it used in designing the standards provided an adequate margin 
of safety for a large proportion of the sensitive population. The 
Agency did not believe that the margin was excessively large or on the 
other hand that the air standard could protect everyone from elevated 
blood Pb levels (43 FR 46251).
ii. Averaging Time, Form, and Indicator
    The averaging time for the current standard is a calendar quarter. 
In the decision for this aspect of the standard, the Agency also 
considered a monthly averaging period, but concluded that ``a 
requirement for the averaging of air quality data over calendar quarter 
will improve the validity of air quality data gathered without a 
significant reduction in the protectiveness of the standards.'' As 
described in the notice for this decision (43 FR 46250), this 
conclusion was based on several points, including the following:
     An analysis of ambient measurements available at the time 
indicated that the distribution of air Pb levels was such that there 
was little possibility that there could be sustained periods greatly 
above the average value in situations where the quarterly standard was 
achieved.
     A recognition that the monitoring network may not actually 
represent the exposure situation for young children, such that it 
seemed likely that elevated air Pb levels when occurring would be close 
to Pb air pollution sources where young children would typically not 
encounter them for the full 24-hour period reported by the monitor.
     Medical evidence available at the time indicated that 
blood Pb levels re-equilibrate slowly to changes in air exposure, a 
finding that would serve to dampen the impact of short-term period of 
exposure to elevated air Pb.
     Direct exposure to air is only one of several routes of 
total exposure, thus lessening the impact of a change in air Pb on 
blood Pb levels.
    The statistical form of the current standard is a not-to-be-
exceeded or maximum value. EPA set the standard as a ceiling value with 
the conclusion that this air level would be safe for indefinite 
exposure for young children (43 FR 46250).
    The indicator is total airborne Pb collected by a high volume 
sampler (43 FR 46258). EPA's selection of Pb-TSP as the indicator for 
the standard was based on explicit recognition both of the significance 
of ingestion as an exposure pathway for Pb that had deposited from the 
air and of the potential for Pb deposited from the air to become re-
suspended in respirable size particles in the air and available for 
human inhalation exposure. As stated in the final rule, ``a significant 
component of exposure can be ingestion of materials contaminated by 
deposition of lead from the air,'' and that, ``in addition to the 
indirect route of ingestion and absorption from the gastrointestinal 
tract, non-respirable Pb in the environment may, at some point become 
respirable through weathering or mechanical action'' (43 FR 46251).
b. Policy Options Considered in the Last Review
    During the 1980s, EPA initiated a review of the air quality 
criteria and NAAQS for Pb. CASAC and the public were fully involved in 
this review, which led to the publication of a criteria document with 
associated addendum and a supplement (USEPA, 1986a, 1986b, 1990a), an 
exposure analysis methods document (USEPA, 1989), and a staff paper 
(USEPA, 1990b).
    Total emissions to air were estimated to have dropped by 94 percent 
between 1978 and 1987, with the vast majority of it attributed to the 
reduction of Pb in gasoline. Accordingly, the focus of the last review 
was on areas near stationary sources of Pb emissions. Although such 
sources were not considered to have made a significant contribution (as 
compared to Pb in gasoline) to the overall Pb pollution across large-
urban or regional areas, Pb emissions from such sources were considered 
to have the potential for a significant impact on a local scale. Air Pb 
concentrations, and especially soil and dust Pb concentrations, had 
been associated with elevated levels of Pb absorption in children and 
adults in numerous Pb point source community studies. Exceedances of 
the current NAAQS were found at that time only in the vicinity of 
nonferrous smelters or other point sources of Pb.
    In summarizing and interpreting the health evidence presented in 
the 1986 Criteria Document and associated documents, the 1990 Staff 
Paper described the collective impact on children of the effects at 
blood Pb levels above 15 [mu]g/dL as representing a clear pattern of 
adverse effects worthy of avoiding. This is in contrast to EPA's 
identification of 30 [mu]g/dL as a safe blood Pb level for individual 
children when the NAAQS was set in 1978. The Staff Paper further stated 
that at blood Pb levels of 10-15 [mu]g/dL, there was a convergence of 
evidence of Pb-induced interference with a diverse set of physiological 
functions and processes, particularly evident in several independent 
studies showing impaired neurobehavioral function and development. 
Further, the available data did not indicate a clear threshold in this 
blood Pb range. Rather, it suggested a continuum of health risks down 
to the lowest levels measured.\108\
---------------------------------------------------------------------------

    \108\ In 1991, the CDC reduced their advisory level for 
children's blood Pb from 25 [mu]g/dL to 10 [mu]g/dL.
---------------------------------------------------------------------------

    For the purposes of comparing the relative protectiveness of 
alternative Pb NAAQS, the staff conducted analyses to estimate the 
percentages of children with blood Pb levels above 10 [mu]g/dL and 
above 15 [mu]g/dL for several air quality scenarios developed for a 
small set of stationary source exposure case studies. The results of 
the analyses of child populations living near two Pb smelters indicated 
that substantial reductions in Pb exposure could be achieved through 
just meeting the current Pb NAAQS. According to the best estimate 
analyses, over 99.5% of children living in areas significantly affected 
by the smelters would have blood Pb levels below 15

[[Page 29224]]

[mu]g/dL if the current standard was achieved. Progressive changes in 
this number were estimated for the alternative monthly Pb NAAQS levels 
evaluated in those analyses, which ranged from 1.5 [mu]g/m\3\ to 0.5 
[mu]g/m\3\.
    In light of the health effects evidence available at the time, the 
1990 Staff Paper presented air quality, exposure, and risk analyses, 
and other policy considerations, as well as the following staff 
conclusions with regard to the primary Pb NAAQS (USEPA, 1990b, pp. xii 
to xiv):
    (1) ``The range of standards * * * should be from 0.5 to 1.5 [mu]g/
m\3\.''
    (2) ``A monthly averaging period would better capture short-term 
increases in lead exposure and would more fully protect children's 
health than the current quarterly average.''
    (3) ``The most appropriate form of the standard appears to be the 
second highest monthly averages {sic{time}  in a 3-year span. This form 
would be nearly as stringent as a form that does not permit any 
exceedances and allows for discounting of one `bad' month in 3 years 
which may be caused, for example, by unusual meteorology.''
    (4) ``With a revision to a monthly averaging time more frequent 
sampling is needed, except in areas, like roadways remote from lead 
point sources, where the standard is not expected to be violated. In 
those situations, the current 1-in-6 day sampling schedule would 
sufficiently reflect air quality and trends.''
    (5) ``Because exposure to atmospheric lead particles occurs not 
only via direct inhalation, but via ingestion of deposited particles as 
well, especially among young children, the hi-volume sampler provides a 
reasonable indicator for determining compliance with a monthly standard 
and should be retained as the instrument to monitor compliance with the 
lead NAAQS until more refined instruments can be developed.''
    Based on its review of a draft Staff Paper, which contained the 
above recommendations, the CASAC strongly recommended to the 
Administrator that EPA should actively pursue a public health goal of 
minimizing the Pb content of blood to the extent possible, and that the 
Pb NAAQS is an important component of a multimedia strategy for 
achieving that goal (CASAC, 1990, p. 4). In noting the range of levels 
recommended by staff, CASAC recommended consideration of a revised 
standard that incorporates a ``wide margin of safety, because of the 
risk posed by Pb exposures, particularly to the very young whose 
developing nervous system may be compromised by even low level 
exposures'' (id., p. 3). More specifically, CASAC judged that a 
standard within the range of 1.0 to 1.5 [mu]g/m\3\ would have 
``relatively little, if any, margin of safety;'' that greater 
consideration should be given to a standard set below 1.0 [mu]g/m\3\; 
and, to provide perspective in setting the standard, it would be 
appropriate to consider the distribution of blood Pb levels associated 
with meeting a monthly standard of 0.25 [mu]g/m\3\, a level below the 
range considered by staff (id.).
    After consideration of the documents developed during the review, 
EPA chose not to propose revision of the NAAQS for Pb. During the same 
time period, the Agency published and embarked on the implementation of 
a broad, multi-program, multi-media, integrated national strategy to 
reduce Pb exposures (USEPA, 1991). As discussed above in section I.C., 
as part of implementing this integrated Pb strategy, the Agency focused 
efforts primarily on regulatory and remedial clean-up actions aimed at 
reducing Pb exposures from a variety of nonair sources judged to pose 
more extensive public health risks to U.S. populations, as well as on 
actions to reduce Pb emissions to air, particularly near stationary 
sources.\109\
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    \109\ A description of the various programs implemented since 
1990 to reduce Pb exposures, including the recent RRP rule, is 
provided in section I.C.
---------------------------------------------------------------------------

2. Considerations in the Current Review
a. Evidence-Based Considerations
    In considering the broad array of health effects evidence assessed 
in the Criteria Document with respect to the adequacy of the current 
standard, the discussion here, like that in the Staff Paper and ANPR, 
focuses on those health endpoints associated with the Pb exposure and 
blood levels most pertinent to ambient exposures. In so doing, EPA 
gives particular weight to evidence available today that differs from 
that available at the time the standard was set with regard to its 
support of the current standard.
    First, with regard to the sensitive population, the susceptibility 
of young children to the effects of Pb is well recognized, in addition 
to more recent recognition of effects of chronic or cumulative Pb 
exposure with advancing age (CD, Sections 5.3.7 and pp. 8-73 to 8-75). 
The prenatal period and early childhood are periods of increased 
susceptibility to Pb exposures, with evidence of adverse effects on the 
developing nervous system that generally appear to persist into later 
childhood and adolescence (CD, Section 6.2).\110\ Thus, while the 
sensitivity of the elderly and other particular subgroups is 
recognized, as at the time the standard was set, young children 
continue to be recognized as a key sensitive population for Pb 
exposures.
---------------------------------------------------------------------------

    \110\ For example, the following statement is made in the 
Criteria Document ``Negative Pb impacts on neurocognitive ability 
and other neurobehavioral outcomes are robust in most recent studies 
even after adjustment for numerous potentially confounding factors 
(including quality of care giving, parental intelligence, and 
socioeconomic status). These effects generally appear to persist 
into adolescence and young adulthood.'' (CD, p.E-9)
---------------------------------------------------------------------------

    With regard to the exposure levels at which adverse health effects 
occur, the current evidence demonstrates the occurrence of adverse 
health effects at appreciably lower blood Pb levels than those 
demonstrated by the evidence at the time the standard was set, at which 
time the Agency identified 30 [mu]g/dL as the maximum safe blood Pb 
level for individual children and 15 [mu]g/dL as the maximum safe 
geometric mean blood Pb level for a population of children (as 
described in section II.D.1.a above). This change in the evidence since 
the time the standard was set is reflected in changes made by the CDC 
in their advisory level for Pb in children's blood, and changes they 
have made in their characterization of that level (as described in 
section II.B.1.b). Although CDC recognized a level of 30 [mu]g/dL blood 
Pb as warranting individual intervention in 1978 when the Pb NAAQS was 
set, in 2005 they recognized the evidence of adverse health effects in 
children with blood Pb levels below 10 [mu]g/dL and the data 
demonstrating that no ``safe'' threshold for blood Pb had been 
identified (CDC, 1991; CDC, 2005).
    As summarized in section II.B above, the Criteria Document 
describes current evidence regarding the occurrence of a variety of 
health effects, including neurological effects in children associated 
with blood Pb levels extending well below 10 [mu]g/dL (CD, Sections 
6.2, 8.4 and 8.5).\111\ As stated

[[Page 29225]]

in the Criteria Document, ``The overall weight of the available 
evidence provides clear substantiation of neurocognitive decrements 
being associated in young children with blood-Pb concentrations in the 
range of 5-10 [mu]g/dL, and possibly somewhat lower. Some newly 
available analyses appear to show Pb effects on the intellectual 
attainment of preschool and school age children at population mean 
concurrent blood-Pb levels ranging down to as low as 2 to 8 [mu]g/dL'' 
(CD, p. E-9). With regard to the evidence of neurological effects at 
these low levels, EPA notes, in particular (and discusses more 
completely in section II.B.2.b above), the international pooled 
analysis by Lanphear and others (2005), studies of individual cohorts 
such as the Rochester, Boston, and Mexico City cohorts (Canfield et 
al., 2003a; Canfield et al., 2003b; Bellinger and Needleman, 2003; 
Tellez-Rojo et al., 2006), the study of African-American inner-city 
children from Detroit (Chiodo et al., 2004), the cross-sectional study 
of young children in three German cities (Walkowiak et al., 1998) and 
the cross-sectional analysis of a nationally representative sample from 
the NHANES III (collected from 1988-1994) (Lanphear et al., 2000). In 
the study by Lanphear et al (2000), the mean blood Pb for the full 
study group was 1.9 [mu]g/dL and the mean blood Pb level in the lowest 
blood Pb subgroup with which a statistically significant association 
with neurocognitive effects was found (individual blood Pb values <5 
[mu]g/dL) was 1.7 [mu]g/dL (CD, pp. 6-31 to 6-32; Lanphear et al., 
2000; Auinger, 2008).\112\ These studies and associated limitations are 
discussed above in section II.B.2.b.
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    \111\ For context, it is noted that the 2001-2004 median blood 
level for children aged 1-5 of all races and ethnic groups is 1.6 
[mu]g/dL, the median for the subset living below the poverty level 
is 2.3 [mu]g/dL and 90th percentile values for these two groups are 
4.0 [mu]g/dL and 5.4 [mu]g/dL, respectively. Similarly, the 2001-
2004 median blood level for black, non-hispanic children aged 1-5 is 
2.5 [mu]g/dL, while the median level for the subset of that group 
living below the poverty level is 2.9 [mu]g/dL and the median level 
for the subset living in a household with income more than 200% of 
the poverty level is 1.9 [mu]g/dL. Associated 90th percentile values 
for 2001-2004 are 6.4 [mu]g/dL (for black, non-hispanic children 
aged 1-5), 7.7 [mu]g/dL (for the subset of that group living below 
the poverty level) and 4.1 [mu]g/dL (for the subset living in a 
household with income more than 200% of the poverty level). (http://
www.epa.gov/envirohealth/children/body_burdens/b1-table.htm--then 
click on ``Download a universal spreadsheet file of the Body Burdens 
data tables'').
    \112\ These findings include significant associations in some of 
the study sample subsets of children, namely those with blood Pb 
levels less than 10 [mu]g/dL, less than 7.5 [mu]g/dL, and less than 
5 [mu]g/dL. The mean blood Pb level in the third subset was 1.7 
[mu]g/dL (Auinger, 2008). A positive, but not statistically 
significant association, was observed in the less than 2.5 [mu]g/dL 
subset (mean blood Pb of 1.2 [mu]g/dL [Auinger, 2008]), although the 
effect estimate for this subset was largest among all the subsets 
(Lanphear et al., 2000). The lack of statistical significance for 
this subset may be due to the smaller sample size of this subset 
which would lead to lower statistical power.
---------------------------------------------------------------------------

    As stated in the Criteria Document with regard to the 
neurocognitive effects in children, the ``weight of overall evidence 
strongly substantiates likely occurrence of type of effect in 
association with blood-Pb concentrations in range of 5-10 [mu]g/dL, or 
possibly lower, as implied by (???) [in associated Table 8-5 of 
Criteria Document]. Although no evident threshold has yet been clearly 
established for those effects, the existence of such effects at still 
lower blood-Pb levels cannot be ruled out based on available data.'' 
(CD, p. 8-61). The Criteria Document further notes that any such 
threshold may exist ``at levels distinctly lower than the lowest 
exposures examined in these epidemiological studies'' (CD, p. 8-67).
i. Evidence-Based Framework Considered in the Staff Paper
    In considering the adequacy of the current standard, the Staff 
Paper considered the evidence in the context of the framework used to 
determine the standard in 1978, as adapted to reflect the current 
evidence. In so doing, the Staff Paper recognized that the health 
effects evidence with regard to characterization of a threshold for 
adverse effects has changed since the standard was set in 1978, as have 
the Agency's views on the characterization of a safe blood Pb level. As 
described in section II.D.1.a, parameters for this framework include 
estimates for average nonair blood Pb level, and air-to-blood ratio, as 
well as a maximum safe individual and/or geometric mean blood Pb level. 
For this last parameter, the Staff Paper for the purposes of this 
evaluation considered the lowest population mean blood Pb levels with 
which some neurocognitive effects have been associated in the evidence.
    As when the standard was set in 1978, there remain today 
contributions to blood Pb levels from nonair sources. In 1978, the 
Agency estimated the average blood Pb level for young children 
associated with nonair sources to be 12 [mu]g/dL (as described in 
section II.D.1.a). However, consistent with reductions since that time 
in air Pb concentrations \113\ which contribute to blood Pb, nonair 
contributions have also been reduced (as described in section II.A.4 
above). The Staff Paper noted that the current evidence is limited with 
regard to estimates of the aggregate reduction since 1978 of all nonair 
sources to blood Pb and with regard to an estimate of current nonair 
blood Pb levels (discussed in sections II.A.4). In recognition of 
temporal reductions in nonair sources discussed in section II.A.4 and 
in the context of estimates pertinent to an application of the 1978 
framework, the CASAC Pb Panel recommended consideration of 1.0-1.4 
[mu]g/dL or lower as an estimate of the nonair component of blood Pb 
pertinent to average blood Pb levels (as more fully described in 
section II.A.4 above; Henderson, 2007b).
---------------------------------------------------------------------------

    \113\ Air Pb concentrations nationally are estimated to have 
declined more than 90% since the early 1980s, in locations not known 
to be directly influenced by stationary sources (Staff Paper, pp. 2-
22 to 2-23).
---------------------------------------------------------------------------

    As in 1978, the evidence demonstrates that Pb in ambient air 
contributes to Pb in blood, with the pertinent exposure routes 
including both inhalation and ingestion (CD, Sections 3.1, 3.2, 4.2 and 
4.4). In 1978, the evidence indicated a quantitative relationship 
between ambient air Pb and blood Pb in terms of an air-to-blood ratio 
that ranged from 1:1 to 1:2 (USEPA, 1977). In setting the standard, the 
Agency relied on a ratio of 1:2, i.e., 2 [mu]g/dL blood Pb per 1 [mu]g/
m\3\ air Pb (as described in section II.D.1.a above). The Staff Paper 
observed that ``[W]hile there is uncertainty and variability in the 
absolute value of an air-to-blood relationship, the current evidence 
indicates a notably greater ratio * * * e.g., on the order of 1:3 to 
1:10'' (USEPA, 2007c).
    Based on the information described above, the Staff Paper concluded 
that young children remain the sensitive population of primary focus in 
this review, ``there is now no recognized safe level of Pb in 
children's blood and studies appear to show adverse effects at 
population mean concurrent blood Pb levels as low as approximately 2 
[mu]g/dL (CD, pp. 6-31 to 6-32; Lanphear et al., 2000)'' (USEPA, 
2007c). The Staff Paper further stated that ``while the nonair 
contribution to blood Pb has declined, perhaps to a range of 1.0-1.4 
[mu]g/dL, the air-to-blood ratio appears to be higher at today's lower 
blood Pb levels than the estimates at the time the standard was set, 
with current estimates on the order of 1:3 to 1:5 and perhaps up to 
1:10'' (USEPA, 2007c). Adapting the framework employed in setting the 
standard in 1978, the Staff Paper concluded that ``the more recently 
available evidence suggests a level for the standard that is lower by 
an order of magnitude or more'' (USEPA, 2007c).
ii. Air-Related IQ Loss Evidence-Based Framework
    Since completion of the Staff Paper and ANPR, the Agency has 
further considered the evidence with regard to adequacy of the current 
standard using an approach other than the adapted 1978 framework 
considered in the Staff Paper. This alternative evidence-based 
framework, referred to as the air-related IQ loss framework, shifts 
focus from identifying an appropriate target population mean blood lead 
level and instead focuses on the magnitude of effects of air-related Pb 
on neurocognitive functions. This framework builds on a recommendation 
by the CASAC Pb Panel to consider the evidence in a more quantitative 
manner,

[[Page 29226]]

and is discussed in more detail below in section II.E.3.a, concerning 
the level of the standard.
    In this air-related IQ loss framework, we have drawn from the 
entire body of evidence as a basis for concluding that there are causal 
associations between air-related Pb exposures and population IQ 
loss.\114\ We have also drawn more quantitatively from the evidence by 
using evidence-based C-R functions to quantify the association between 
air Pb concentrations and air-related population mean IQ loss. Thus, 
this framework more fully considers the evidence with regard to the 
concentration-response relationship for the effect of Pb on IQ, and it 
also draws from estimates for air-to-blood ratios.
---------------------------------------------------------------------------

    \114\ For example, as stated in the Criteria Document, 
``Fortunately, there exists a large database of high quality studies 
on which to base inferences regarding the relationship between Pb 
exposure and neurodevelopment. In addition, Pb has been extensively 
studied in animal models at doses that closely approximate the human 
situation. Experimental animal studies are not compromised by the 
possibility of confounding by such factors as social class and 
correlated environmental factors. The enormous experimental animal 
literature that proves that Pb at low levels causes neurobehavioral 
deficits and provides insights into mechanisms must be considered 
when drawing causal inferences (Bellinger, 2004; Davis et al., 1990; 
U.S. Environmental Protection Agency, 1986a, 1990).'' (CD, p. 6-75)
---------------------------------------------------------------------------

    While we note the evidence of steeper slope for the C-R 
relationship for blood Pb concentration and IQ loss at lower blood Pb 
levels (described in sections II.B.2.b and II.E.3.a), for purposes of 
consideration of the adequacy of the current standard we are concerned 
with the C-R relationship for blood Pb levels that would be associated 
with exposure to air-related Pb at the level of the current standard. 
For this purpose, we have focused on a median linear estimate of the 
slope of the C-R function for blood Pb levels up to, but no higher 
than, 10 [mu]g/dL (described in section II.B.2.b above). The median 
slope estimate is -0.9 IQ points per [mu]g/dL blood Pb \115\ (CD, p. 8-
80).
---------------------------------------------------------------------------

    \115\ As noted above (in section II.B.2.b), this slope is 
similar to the slope for the below 10 [mu]g/dL piece of the 
piecewise model used in the RRP rule economic analysis.
---------------------------------------------------------------------------

    Applying estimates of air-to-blood ratios ranging from 1:3 to 1:5, 
drawing from the discussion of air-to-blood ratios in section II.B.1.c 
above, a population of children exposed at the current level of the 
standard might be expected to result in an average air-related blood Pb 
level above 4 [mu]g/dL.\116\ Multiplying these blood Pb levels by the 
slope estimate, identified above, for blood Pb levels extending up to 
10 [mu]g/dL (-0.9 IQ points per [mu]g/dL), would imply an average air-
related IQ loss for such a group of children on the order of 4 or more 
IQ points.
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    \116\ This is based on the calculation in which 1.5 [mu]g/m\3\ 
is multiplied by a ratio of 3 [mu]g blood Pb per 1 [mu]g/m\3\ air Pb 
to yield an air-related blood Pb estimate of 4.5 [mu]g/dL; using a 
1:5 ratio yields an estimate of 7.5 [mu]g/dL. As with the 1978 
framework considered in the Staff Paper, the context for use of the 
air-to-blood ratio here is a population being exposed at the level 
of the standard.
---------------------------------------------------------------------------

b. Exposure- and Risk-Based Considerations
    As discussed above in section II.C, we have estimated exposures and 
health risks associated with air quality that just meets the current 
standard to help inform judgments about whether or not the current 
standard provides adequate protection of public health, taking into 
account key uncertainties associated with the estimated exposures and 
risks (summarized above in section II.C and more fully in the Risk 
Assessment Report).
    As discussed above, children are the sensitive population of 
primary focus in this review. The exposure and risk assessment 
estimates Pb exposure for children (less than 7 years of age), and 
associated risk of neurocognitive effects in terms of IQ loss. In 
addition to the risks (IQ loss) that were quantitatively estimated, EPA 
recognizes that there may be long-term adverse consequences of such 
deficits over a lifetime, and there are other, unquantified adverse 
neurocognitive effects that may occur at similarly low exposures which 
might additionally contribute to reduced academic performance, which 
may have adverse consequences over a lifetime (CD, pp. 8-29 to 8-
30).\117\ Other impacts at low levels of childhood exposure that were 
not quantified in the risk assessment include: other neurological 
effects (sensory, motor, cognitive and behavioral), immune system 
effects (including some related to allergic responses and asthma), and 
early effects related to anemia. Additionally, as noted in section 
II.B.2, other health effects evidence demonstrates associations between 
Pb exposure and adverse health effects in adults (e.g., cardiovascular 
and renal effects).\118\
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    \117\ For example, the Criteria Document notes particular 
findings with regard to academic achievement as ``suggesting that 
Pb-sensitive neuropsychological processing and learning factors not 
reflected by global intelligence indices might contribute to reduced 
performance on academic tasks'' (CD, pp. 8-29 to 8-30).
    \118\ The weight of the evidence differs for the different 
endpoints.
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    As noted in the Criteria Document, a modest change in the 
population mean of a health index, that is quantified for each 
individual, can have substantial implications at the population level 
(CD, p. 8-77, Sections 8.6.1 and 8.6.2; Bellinger, 2004; Needleman et 
al., 1982; Weiss, 1988; Weiss, 1990)). For example, for an individual 
functioning in the low range of IQ due to the influence of risk factors 
other than Pb, a Pb-associated IQ loss of a few points might be 
sufficient to drop that individual into the range associated with 
increased risk of educational, vocational, and social handicap (CD, p. 
8-77), while such a decline might create less significant impacts for 
the individual near the mean of the population. Further, given a 
uniform manifestation of Pb-related decrements across the range of IQ 
scores in a population, a downward shift in the mean IQ value is 
associated not only with a substantial increase in the percentage of 
individuals achieving very low scores, but also with substantial 
decreases in percentages achieving very high scores (CD, p. 8-81). The 
CASAC Pb Panel has advised on this point that ``a population loss of 1-
2 IQ points is highly significant from a public health perspective'' 
(Henderson, 2007a, p. 6).
    In considering exposure and risk estimates with regard to adequacy 
of the current standard, EPA has focused on IQ loss for air-related 
exposure pathways. As described in section II.C.2.e above, limitations 
in our data and modeling tools have resulted in an inability to develop 
specific estimates such that we have approximated estimates for the 
air-related pathways, bounded on the low end by exposure/risk estimated 
for the ``recent air'' category and on the upper end by the exposure/
risk estimated for the ``recent air'' plus ``past air'' categories. 
Thus, the following discussion presents air-related IQ loss estimates 
in terms of upper and lower bounds. In addition, as noted above 
(section II.C.3.b), this discussion focuses predominantly on risk 
estimates derived using the log-linear with low-exposure linearization 
(LLL) C-R function, with the range associated with the other three 
functions used in the assessment also being noted. Further, air-related 
risk estimates are presented for the median and for an upper percentile 
(i.e., the 95th percentile of the population assessed).
    EPA and CASAC recognize uncertainties in the risk estimates in the 
tails of the distribution and consequently the 95th percentile is 
reported as the estimate of the high end of the risk distribution 
(Henderson, 2007b, p. 3). In so doing, however, EPA notes that it is 
important to consider that there are individuals in the population 
expected to have higher risk, particularly in light of the risk 
management objectives for the current standard which was set in 1978 to

[[Page 29227]]

protect the 99.5th percentile. Further, we note an increased 
uncertainty in our estimates of air-related risk for the upper 
percentiles, such as the 95th percentile, due to limitations in the 
data and tools available to us to estimate pathway contributions to 
blood Pb and associated risk for individuals at the upper ends of the 
distribution.
    In order to consider exposure and risk associated with the current 
standard, EPA developed estimates for a case study based on air quality 
projected to just meet the standard in a location of the country where 
air concentrations currently do not meet the current standard (the 
primary Pb smelter case study). Estimates of median air-related IQ loss 
associated with just meeting the current NAAQS in the primary Pb 
smelter case study subarea had a lower bound estimate of <3.2 points IQ 
loss (``recent air'' category of Pb exposures) and an upper bound 
estimate of <9.4 points IQ loss (``recent air'' plus ``past air'' 
category) for the range of C-R functions (Table 3). This estimate 
(recent air plus past air) for the subarea based on the LLL C-R 
function is 6.0 points IQ loss for the median and 8.0 points IQ loss 
for the 95th percentile, with which we note a greater uncertainty than 
for the median estimate (as discussed above).\119\ Modeling limitations 
have affected our ability to derive lower bound estimates for this case 
study (as described above in section II.C.2.c).
---------------------------------------------------------------------------

    \119\ We note that while we have termed risk estimates derived 
for the sum of ``recent air'' plus ``past air'' exposure pathways as 
``upper bound'' estimates of air-related risk, the primary Pb 
smelter subarea is an area where soil has been remediated and thus 
does not reflect any historical deposition. Further, soil Pb 
concentrations in this area are not stable and may be increasing, 
seeming to indicate ongoing response to current atmospheric 
depositon in the area. Thus, for this case study, the ``recent air'' 
plus ``past air'' estimates are less of an ``upper bound'' for air-
related risk than in other case studies where historical Pb 
deposition may have some representation in the ``past air'' soil 
ingestion pathway.
---------------------------------------------------------------------------

    Additionally, we developed estimates of blood Pb and associated IQ 
loss associated with the current standard for the urban case studies. 
We note that we consider it extremely unlikely that air concentrations 
in urban areas across the U.S. that are currently well below the 
current standard would increase to just meet the standard. However, we 
recognize the potential, although not the likelihood, for air Pb 
concentrations in some limited areas currently well below the standard 
to increase to just meet the standard by way of, for example, expansion 
of existing sources (e.g., facilities operating as secondary smelters 
may exercise previously used capabilities as primary smelters) or by 
the congregation of multiple Pb sources in adjacent locations. We have 
simulated this scenario (increased Pb concentrations to just meet the 
current standard) in a general urban case study and three location-
specific urban case studies. For the location-specific urban case 
studies, we note substantial uncertainty in simulating how the profile 
of Pb concentrations might change in the hypothetical case where 
concentrations increase to just meet the current standard.
    Turning first to the exposure/risk estimates for the current NAAQS 
scenario simulated for the general urban case study, which is a 
simplified representation of a location within an urban area (described 
in section II.C.2.h above), median estimates of air-related IQ loss 
range from 1.5 to 7.7 points (across all four C-R functions), with an 
estimate based on the LLL function bounded at the low end by 3.4 points 
and at the high end by 4.8 points (Table 3). At the 95th percentile for 
total IQ loss (LLL estimate), IQ loss associated with air-related Pb is 
estimated to fall somewhere between 5.5 and 7.6 points (Staff Paper, 
Table 4-6).
    In considering the estimates for the three location-specific urban 
case studies, we first note the extent to which exposures associated 
with increased air Pb concentrations that simulate just meeting the 
current standard are estimated to increase blood Pb levels in young 
children. The magnitude of this for the median total blood Pb ranges 
from 0.3 [mu]g/dL (an increase of 20 percent) in the case of the 
Cleveland study area (where the highest monitor is estimated to be 
approximately one fourth of the current NAAQS), up to approximately 1 
[mu]g/dL (an increase of 50 to 70%) for the Chicago and Los Angeles 
study areas, where the highest monitor is estimated to be at or below 
one tenth of the current NAAQS (Table 1). Median estimates of air-
related risk for these case studies range from 0.6 points IQ loss 
(recent air estimate using low-end C-R function) to 7.4 points IQ loss 
(recent plus past air estimate using the high-end C-R function). The 
corresponding estimates based on the LLL C-R function range from 2.7 
points (lowest location-specific recent air estimate) to 4.7 points IQ 
loss (highest location-specific recent plus past air estimate). The 
comparable estimates of air-related risk for children at the 95th 
percentile in these three case studies range from 2.6 to 7.6 points IQ 
loss for the LLL C-R function (Staff paper, Table 4-6), although we 
note increased uncertainty in the magnitude of these 95th percentile 
air-related estimates.
    Another way in which the risk assessment results might be 
considered is by comparing current NAAQS scenario estimates to current 
conditions, although in so doing, it is important to recognize that, as 
stated below and described in section II.C., this will underestimate 
air-related impacts associated with the current NAAQS. In making such a 
comparison of estimates for the three location-specific urban case 
studies, the estimated difference in total Pb-related IQ loss for the 
median child is about 0.5 to 1.4 points using the LLL C-R function and 
a similar magnitude of difference is estimated for the 95th percentile. 
The corresponding comparison for the general urban case study indicates 
the current NAAQS scenario median total Pb-related IQ loss is 1.1 to 
1.3 points higher than the two current conditions scenarios. As 
described in section II.C, such comparisons are underestimates of air-
related impacts brought about as a result of increased air Pb 
concentrations, and consequently they are inherently underestimates of 
the true impact of an increased NAAQS level on public health.
    In considering the exposure/risk information with regard to 
adequacy of the current standard, the Staff Paper first considered the 
estimates described above, particularly those associated with air-
related risk.\120\ The Staff Paper described these estimates for the 
current NAAQS as being indicative of levels of IQ loss associated with 
air-related risk that may ``reasonably be judged to be highly 
significant from a public health perspective'' (USEPA, 2007c).
---------------------------------------------------------------------------

    \120\ As recognized in section III.B.2.d above, to simulate air 
concentrations associated with the current NAAQS, a proportional 
roll-up of concentrations from those for current conditions was 
performed for the location-specific urban case studies. This was not 
necessary for the primary Pb smelter case study in which air 
concentrations currently exceed the current standard, nor for the 
general urban case study.
---------------------------------------------------------------------------

    The Staff Paper also describes a different risk metric that 
estimated differences in the numbers of children with different amounts 
of Pb-related IQ loss between air quality scenarios for current 
conditions and for the current NAAQS in the three location-specific 
urban case studies. For example, estimates of the additional number of 
children with IQ loss greater than one point (based on the LLL C-R 
function) in these three study areas, for the current NAAQS scenario as 
compared to current conditions, range from 100 to 6,000 across the 
three locations (as shown above in Table 5). The corresponding 
estimates for the additional number of children with IQ

[[Page 29228]]

loss greater than seven points, for the current NAAQS as compared to 
current conditions, range from 600 to 66,000 (as shown above in Table 
6). These latter values for the change in incidence of children with 
greater than seven points Pb-related IQ loss represent 5 to 17 percent 
of the children (aged less than 7 years of age) in these study areas. 
This increase corresponds to approximately a doubling in the number of 
children with this magnitude of Pb-related IQ loss in the study area 
most affected. The Staff Paper concluded that these estimates indicate 
the potential for significant numbers of children to be negatively 
affected if air Pb concentrations increased to levels just meeting the 
current standard.
    Beyond the findings related to quantified IQ loss, the Staff Paper 
recognized the potential for other, unquantified adverse effects that 
may occur at similarly low exposures. In summary, the Staff Paper 
concluded that taken together, ``the quantified IQ effects associated 
with the current NAAQS and other, nonquantified effects are important 
from a public health perspective, indicating a need for consideration 
of revision of the standard to provide an appreciable increase in 
public health protection'' (USEPA, 2007c).
3. CASAC Advice and Recommendations and Public Comment
    CASAC's recommendations in this review builds upon the CASAC 
recommendations during the 1990 review, which also advised on 
consideration of more health protective NAAQS. In CASAC's review of the 
1990 Staff Paper, as discussed in Section II.D.1.b, they generally 
recommended consideration of levels below 1.0 [mu]g/m\3\, specifically 
recommended analyses of a standard set at 0.25 [mu]g/m\3\, and also 
recommended a revision to a monthly averaging time (CASAC, 1990).
    In its letter to the Administrator subsequent to consideration of 
the ANPR, the final Staff Paper and the final Risk Assessment Report, 
the CASAC Pb Panel unanimously and fully supported ``Agency staff's 
scientific analyses in recommending the need to substantially lower the 
level of the primary (public-health based) Lead NAAQS, to an upper 
bound of no higher than 0.2 [mu]g/m\3\ with a monthly averaging time'' 
(Henderson, 2008, p. 1). This recommendation is consistent with their 
recommendations conveyed in two earlier letters in the course of this 
review (Henderson, 2007a, 2007b). Further, in their advice to the 
Agency over the course of this review, CASAC has provided rationale for 
their conclusions that has included their statement that the current Pb 
NAAQS ``are totally inadequate for assuring the necessary decreases of 
lead exposures in sensitive U.S. populations below those current health 
hazard markers identified by a wealth of new epidemiological, 
experimental and mechanistic studies'', and stated that ``Consequently, 
it is the CASAC Lead Review Panel's considered judgment that the NAAQS 
for Lead must be decreased to fully-protect both the health of children 
and adult populations'' (Henderson, 2007a, p. 5). CASAC drew support 
for their recommendation from the current evidence, described in the 
Criteria Document, of health effects occurring at dramatically lower 
blood Pb levels than those indicated by the evidence available when the 
standard was set and of a recognition of effects that extend beyond 
children to adults.
    The Agency has also received comments from the public on drafts of 
the Staff Paper and related technical support document, as well as on 
the ANPR.\121\ Public comments received to date that have addressed 
adequacy of the current standard overwhelmingly concluded that the 
current standard is inadequate and should be substantially revised, in 
many cases suggesting specific reductions to a level at or below 0.2 
[mu]g/m\3\. Two comments were received from specific industries 
expressing the view that the current standard might need little or no 
adjustment. One comment received early in the review stated that 
current conditions justified revocation of the standard.
---------------------------------------------------------------------------

    \121\ All written comments submitted to the Agency are available 
in the docket for this rulemaking, are transcripts of the public 
meetings held in conjunction with CASAC's review of the Staff Paper, 
the Risk Assessment Report, the Criteria Document and the ANPR.
---------------------------------------------------------------------------

4. Administrator's Proposed Conclusions Concerning Adequacy
    Based on the large body of evidence concerning the public health 
impacts of Pb, including significant new evidence concerning effects at 
blood Pb concentrations substantially below those identified when the 
current standard was set, the Administrator proposes that the current 
standard does not protect public health with an adequate margin of 
safety and should be revised to provide additional public health 
protection.
    In considering the adequacy of the current standard, the 
Administrator has carefully considered the conclusions contained in the 
Criteria Document, the information, exposure/risk assessments, 
conclusions, and recommendations presented in the Staff Paper, the 
advice and recommendations from CASAC, and public comments received on 
the ANPR and other documents to date.
    The Administrator notes that the body of available evidence, 
summarized above in section III.B and discussed in the Criteria 
Document, is substantially expanded from that available when the 
current standard was set three decades ago. The Criteria Document 
presents evidence of the occurrence of health effects at appreciably 
lower blood Pb levels than those demonstrated by the evidence at the 
time the standard was set. Subsequent to the setting of the standard, 
the Pb NAAQS criteria review during the 1980s and the current review 
have provided (a) expanded and strengthened evidence of still lower Pb 
exposure levels associated with slowed physical and neurobehavioral 
development, lower IQ, impaired learning, and other indicators of 
adverse neurological impacts; and (b) other effects of Pb on 
cardiovascular function, immune system components, calcium and vitamin 
D metabolism and other health endpoints (discussed fully in the 
Criteria Document).
    The Administrator notes particularly the robust evidence of 
neurotoxic effects of Pb exposure in children, both with regard to 
epidemiological and toxicological studies. While blood Pb levels in 
U.S. children have decreased notably since the late 1970s, newer 
studies have investigated and reported associations of effects on the 
neurodevelopment of children with these more recent blood Pb levels. 
The toxicological evidence includes extensive experimental laboratory 
animal evidence that substantiates well the plausibility of the 
epidemiologic findings observed in human children and expands our 
understanding of likely mechanisms underlying the neurotoxic effects. 
Further, the Administrator notes the current evidence that suggests a 
steeper dose-response relationship at these lower blood Pb levels than 
at higher blood Pb levels, indicating the potential for greater 
incremental impact associated with exposure at these lower levels.
    In addition to the evidence of health effects occurring at 
significantly lower blood Pb levels, the Administrator recognizes that 
the current health effects evidence together with findings from the 
exposure and risk assessments (summarized above in section III.B), like 
the information available at the time the standard was set, supports 
our finding that air-related Pb exposure pathways contribute to blood 
Pb levels in young children, by inhalation and ingestion. Furthermore, 
the Administrator takes

[[Page 29229]]

note of the information that suggests that the air-to-blood ratio 
(i.e., the quantitative relationship between air concentrations and 
blood concentrations) is now likely larger, when air inhalation and 
ingestion are considered, than that estimated when the standard was 
set.
    Based on evidence discussed above, the Administrator first 
considered the evidence in the context of an adaptation of the 1978 
framework, as presented in the Staff Paper, recognizing that the health 
effects evidence with regard to characterization of a threshold for 
adverse effects has changed dramatically since the standard was set in 
1978. As discussed above, however, the 1978 framework was premised on 
an evidentiary basis that clearly identified an adverse health effect 
and a health-based policy judgment that identified a level that would 
be safe for an individual child with respect to this adverse health 
effect. The adaptation to the 1978 framework applies this framework to 
a situation where there is no longer an evidentiary basis to determine 
a safe level for individual children. In addition, this approach does 
not address explicitly what magnitude of effect should be considered 
adverse. Given these two limitations, the Administrator has focused 
primarily instead on the air-related IQ loss evidence-based framework 
described above in considering the adequacy of the current standard.
    In considering the application the air-related IQ loss framework to 
the current evidence as discussed above in section II.D.2.a, the 
Administrator notes that this framework suggests an average air-related 
IQ loss for a population of children exposed at the level of the 
current standard on the order of 4 or more IQ points. The Administrator 
judges that an air-related IQ loss of this magnitude is large from a 
public health perspective and that this evidence-based framework 
supports a conclusion that the current standard does not protect public 
health with an adequate margin of safety. Further, the Administrator 
believes that the current evidence indicates the need for a standard 
level that is substantially lower than the current level to provide 
increased public health protection, especially for at-risk groups, 
including most notably children, against an array of effects, most 
importantly including effects on the developing nervous system.
    The Administrator has also considered the results of the exposure 
and risk assessments conducted for this review, which provides some 
further perspective on the potential magnitude of air-related IQ loss. 
However, taking into consideration the uncertainties and limitations in 
the assessments, notably including questions as to whether the 
assessment scenarios that roll up current air quality to simulate just 
meeting the current standard are realistic in wide areas across the 
U.S., the Administrator has not placed primary reliance on the exposure 
and risk assessments. Nonetheless, the Administrator observes that in 
areas projected to just meet the current standard, the quantitative 
estimates of IQ loss associated with air-related Pb, as summarized 
above in section II.D.2.b, indicate risk of a magnitude that in his 
judgment is significant from a public health perspective. Further, 
although the current monitoring data indicate few areas with airborne 
Pb near or just exceeding the current standard, the Administrator 
recognizes significant limitations with the current monitoring network 
and thus the potential that the prevalence of such levels of Pb 
concentrations may be underestimated by currently available data.
    The Administrator believes that the air-related blood Pb and IQ 
loss estimates discussed in the Staff Paper and Risk Assessment Report, 
summarized above, as well as the estimates of air-related IQ loss 
suggested by this evidence-based framework, are important from a public 
health perspective and are indicative of potential risks to susceptible 
and vulnerable groups. In reaching this proposed judgment, the 
Administrator considered the following factors: (1) The estimates of 
blood Pb and IQ loss for children from air-related Pb exposures 
associated with the current standard, (2) the estimates of numbers of 
children with different amounts of increased Pb-related IQ loss 
associated with the current standard, (3) the variability within and 
among areas in both the exposure and risk estimates, (4) the 
uncertainties in these estimates, and (5) the recognition that there is 
a broader array of Pb-related adverse health outcomes for which risk 
estimates could not be quantified and that the scope of the assessment 
was limited to a sample of case studies and to some but not all at-risk 
populations, leading to an incomplete estimation of public health 
impacts associated with Pb exposures across the country.\122\ In 
addition to the evidence-based and risk-based conclusions described 
above, the Administrator also notes that it was the unanimous 
conclusion of the CASAC Panel that EPA needed to ``substantially 
lower'' the level of the primary Pb NAAQS to fully protect the health 
of children and adult populations (Henderson, 2007a, 2007b, 2008).
---------------------------------------------------------------------------

    \122\ While recognizing that there are significant uncertainties 
associated with the risk estimates from the case studies, EPA places 
an appropriate weight on the risk assessment results for purposes of 
evaluating the adequacy of the current standard, given the strength 
of the evidence of the existence of effects at blood Pb levels 
associated with exposures at the level of the current standard, the 
magnitude of the IQ losses that are estimated, and the consistency 
of these IQ losses with the estimates of IQ loss derived from the 
alternative evidence-based framework. The weight to place on the 
risk assessment results for purposes of evaluating alterative levels 
of the standard is discussed later in the discussion on the level of 
the standard.
---------------------------------------------------------------------------

    Based on all of these considerations, the Administrator proposes 
that the current Pb standard is not requisite to protect public health 
with an adequate margin of safety because it does not provide 
sufficient protection, and that the standard should be revised to 
provide increased public health protection, especially for members of 
at-risk groups.

E. Conclusions on the Elements of the Standard

    The four elements of the standard--indicator, averaging time, form, 
and level--serve to define the standard and must be considered 
collectively in evaluating the health and welfare protection afforded 
by the standard. In considering revisions to the current primary Pb 
standard, as discussed in the following sections, EPA considers each of 
the four elements of the standard as to how they might be revised to 
provide a primary standard for Pb that is requisite to protect public 
health with an adequate margin of safety. Considerations and proposed 
conclusions on indicator are discussed in section II.E.1, and on 
averaging time and form in section II.E.2. Considerations and proposed 
conclusions on a level for a Pb NAAQS with a Pb-TSP indicator are 
discussed in section II.E.3, and considerations on a level for a Pb 
NAAQS with a Pb-PM10 indicator are discussed in section 
II.E.4.
1. Indicator
    The indicator for the current standard is Pb-TSP (as described in 
section II.D.1.a above).\123\ When the standard was set in 1978, the 
Agency proposed Pb-TSP as the indicator, but considered identifying Pb 
in particulate matter less than or equal to 10 [mu]m in diameter (Pb-
PM10) as the indicator. EPA had received comments expressing 
concern

[[Page 29230]]

that because only a fraction of airborne particulate matter is 
respirable, an air standard based on total air Pb would be 
unnecessarily stringent. The Agency responded that while it agreed that 
some Pb particles are too small or too large to be deposited in the 
respiratory system, a significant component of exposures can be 
ingestion of materials contaminated by deposition of Pb from the air. 
In addition to the route of ingestion and absorption from the 
gastrointestinal tract, nonrespirable Pb in the environment may, at 
some point, become respirable through weathering or mechanical action. 
EPA concluded that total airborne Pb, both respirable and nonrespirable 
fractions, should be addressed by the air standard (43 FR 46251). The 
federal reference method (FRM) for Pb-TSP specifies the use of the 
high-volume FRM sampler for TSP.
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    \123\ The current standard specifies the measurement of airborne 
Pb with a high-volume TSP federal reference method (FRM) sampler 
with atomic absorption spectrometry of a nitric acid extract from 
the filter for Pb, or with an approved equivalent method.
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    In the 1990 Staff Paper, this issue was reconsidered in light of 
information regarding limitations of the high-volume sampler used for 
the Pb-TSP measurements, and the continued use of Pb-TSP as the 
indicator was recommended in the Staff Paper (USEPA, 1990):

    Given that exposure to lead occurs not only via direct 
inhalation, but via ingestion of deposited particles as well, 
especially among young children, the hi-vol provides a more complete 
measure of the total impact of ambient air lead. * * * Despite its 
shortcomings, the staff believes the high-volume sampler will 
provide a reasonable indicator for determination of compliance * * *

    In the current review, the Staff Paper evaluated the evidence with 
regard to the indicator for a revised primary standard. This evaluation 
included consideration of the basis for using Pb-TSP as the current 
indicator, information regarding the sampling methodology for the 
current indicator, and CASAC advice with regard to indicator (described 
below). Based on this evaluation, the Staff Paper recommended retaining 
Pb-TSP as the indicator for the primary standard. The Staff Paper also 
recommended activities intended to encourage collection and development 
of datasets that will improve our understanding of national and site-
specific relationships between Pb-PM10 (collected by low-
volume sampler) and Pb-TSP to support a more informed consideration of 
indicator during the next review. The Staff Paper suggested that such 
activities might include describing a federal equivalence method (FEM) 
in terms of PM10 and allowing its use for a TSP-based 
standard in certain situations, such as where sufficient data are 
available to adequately demonstrate a relationship between Pb-TSP and 
Pb-PM10 or, in combination with more limited Pb-TSP 
monitoring, in areas where Pb-TSP data indicate Pb levels well below 
the NAAQS level.
    The ANPR further identified issues and options associated with 
consideration of the potential use of Pb-PM10 data for 
judging attainment or nonattainment with a Pb-TSP NAAQS. These issues 
included the impact of controlling Pb-PM10 for sources 
predominantly emitting Pb in particles larger than those captured by 
PM10 monitors \124\ (i.e., ultra-coarse), \125\ and the 
options included potential application of Pb-PM10 FRM/FEMs 
at sites with established relationships between Pb-TSP and Pb-
PM10, and use of Pb-PM10 data, with adjustment, 
as a surrogate for Pb-TSP data. The ANPR broadly solicited comment in 
these areas.
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    \124\ For simplicity, the discussion here and below speaks as if 
PM10 samplers have a sharp size cut-off. In reality, they 
have a size selection behavior in which 50% of particles 10 microns 
in size are captured, with a progressively higher capture rate for 
smaller particles and a progressively lower capture rate for larger 
particles. The ideal capture efficiency curve for PM10 
samplers specifies that particles above 15 microns not be captured 
at all, although real samplers may capture a very small percentage 
of particles above 15 microns. TSP samplers have 50% capture points 
in the range of 25 to 50 microns, which is broad enough to include 
virtually all particles capable of being transported any significant 
distance from their source except under extreme wind events. As 
explained below, the capture efficiency of a high-volume TSP sampler 
for any given size particle is affected by wind speed and wind 
direction.
    \125\ In this notice, we use ``ultra-coarse'' to refer to 
particles collected by a TSP sampler but not by a PM10 
sampler (we note that CASAC has variously also referred to these 
particles as ``very coarse'' or ``larger coarse-mode'' particles), 
``fine'' to refer to particles collected by a PM2.5 
sampler, and ``coarse'' to refer to particles collected by a 
PM10 sampler but not by a PM2.5 sampler, 
recognizing that there will be some overlap in the particle sizes in 
the three types of collected material.
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    In the current review, both the CASAC Pb Panel and members of the 
CASAC Ambient Air Monitoring and Methods (AAMM) Subcommittee have 
recommended that EPA consider a change in the indicator to 
PM10, utilizing low-volume PM10 sampling 
(Henderson, 2007a, 2007b, 2008; Russell, 2008). \126\ In their January 
2008 letter, the CASAC Lead Panel unanimously recommended that EPA 
revise the Pb NAAQS indicator to rely on low-volume PM10 
sampling (Henderson, 2008). They indicated support for their 
recommendation in a range of areas. First, they noted poor precision in 
high-volume TSP sampling, wide variation in the upper particle size-cut 
as a function of wind speed and direction, and greater difficulties in 
capturing the spatial non-homogeneity of ultra-coarse particles with a 
national monitoring network. They stated that the low-volume 
PM10 collection method is a much more accurate and precise 
collection method, and would provide a more representative 
characterization on a large spatial scale of monitored particles which 
remain airborne longer, thus providing a characterization that is more 
broadly representative of ambient exposures over large spatial scales. 
They also noted the automated sequential sampling capability of low-
volume PM10 monitors which would be particularly useful if 
the averaging time is revised (i.e., to a monthly averaging time, as 
recommended by CASAC), which, in CASAC's view would necessitate an 
increased monitoring frequency. Further, they noted the potential for 
utilization of the more widespread PM10 sampling network 
(Henderson, 2007a, 2007b, 2008).\127\ In their advice, CASAC also 
stated that they ``recognize the importance of coarse dust 
contributions to total Pb ingestion and acknowledge that TSP sampling 
is likely to capture additional very coarse particles which are 
excluded by PM10 samplers'' (Henderson 2007b). They 
suggested that an adjustment of the NAAQS level would accommodate the 
loss of these ultra-coarse Pb particles, and that development of such a 
quantitative adjustment might appropriately be based on concurrent Pb-
PM10 and Pb-TSP sampling data \128\ (Henderson, 2007a, 
2007b, 2008).
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    \126\ ``Low-volume PM10 sampling'' refers to sampling 
using any of a number of monitor models that draw 16.67 liters/
minute (1 m3/hour) of air through the filter, in contrast 
to ``high-volume'' sampling of either TSP or PM10 in 
which the monitor draws 1500 liters/minute (90 m3/hour). 
All commercial TSP FRM samplers at this time are high-volume 
samplers; both high-volume and low-volume PM10 FRM 
samplers are available. Low-volume sampling is the more recently 
introduced method. Low-volume and high-volume samplers differ in 
many other ways also, including filter size, accuracy of the flow 
control, and degree of computerization.
    \127\ EPA notes that costs, including those of operating a 
monitoring network, may not be considered in establishing or 
revising the NAAQS.
    \128\ In their advice, CASAC recognized the potential for site-
to-site variability in the relationship between Pb-TSP and Pb-
PM10 (Henderson, 2007a, 2007b). They also stated in their 
September 2007 letter, ``The Panel urges that PM10 
monitors, with appropriate adjustments, be used to supplement the 
data. * * * A single quantitative adjustment factor could be 
developed from a short period of collocated sampling at multiple 
sites; or a PM10 Pb/TSP Pb 'equivalency ratio' could be 
determined on a regional or site-specific basis.''
---------------------------------------------------------------------------

    The Agency received comments on the discussion of the indicator in 
the ANPR from several state and local agencies and national/regional 
air pollution control organizations, as well as a national 
environmental organization. These public comments

[[Page 29231]]

were somewhat mixed. Most of these commenters recommended maintaining 
Pb-TSP as the indicator to ensure that Pb emitted in larger particles 
is not overlooked by the Pb NAAQS. Some of those comments and others 
suggested keeping TSP as the indicator but revising the FRM to a low-
volume TSP method \129\ and considering tighter sampling height 
criteria to reduce variability.\130\ Others, in considering a potential 
PM10-based indicator or the use of PM10 data as a 
surrogate for Pb-TSP, noted the need for characterization of the 
relationship between Pb-PM10 and Pb-TSP, which varies with 
proximity to some sources. One state agency and a national organization 
of regulatory air agencies expressed clear support for revising the 
indicator to Pb-PM10, predominantly citing advantages 
associated with improved technology and efficiency in data collection.
---------------------------------------------------------------------------

    \129\ The Pb-TSP FRM specification, 40 CFR 50 appendix G, 
currently explicitly requires the use of the high-volume TSP FRM 
sampler which is required by appendix B for the mass of TSP. 
Therefore it would require amendments to 40 CFR 50 appendix B and/or 
G (or a new dedicated appendix) to establish a low-volume TSP 
sampler as the only FRM, or as an alternative FRM, for TSP and/or 
Pb-TSP measurement. A number of researchers have utilized both self-
built and commercially available low-volume TSP samplers in ambient 
air studies. Typically, these samplers are identical to low-volume 
PM10 FRM samplers with the exception that their inlets 
and other size separation devices (or lack thereof) are aimed at 
collecting TSP. EPA is not aware of any rigorous evaluation of the 
performance of these available, non-designated low-volume TSP 
samplers or their equivalence to the TSP FRM. No one has applied to 
date for designation of a low-volume TSP sampler as a FEM, either 
for TSP measurement per se or for purposes of Pb-TSP measurement.
    \130\ Currently, probe heights for Pb-TSP and PM10 
sampling are allowed to be between 2 and 15 meters above ground 
level for neighborhood-scale monitoring sites (those intended to 
represent concentrations over a relatively large area around the 
site) and between 2 and 7 meters for microscale sites. Near very 
low-height sources of TSP, including fugitive dust sources at ground 
level, concentrations of TSP, especially the concentrations of 
particles larger than 10 microns, can vary substantially across this 
height range with higher concentrations closer to the ground; near-
ground concentrations can also vary more in time than concentrations 
higher up.
---------------------------------------------------------------------------

    In considering these issues concerning the appropriate indicator, 
EPA takes note of previous Agency conclusions that the health evidence 
indicates that Pb in all particle size fractions, not just respirable 
Pb, contributes to Pb in blood and to associated health effects. 
Further, the evidence and exposure/risk estimates in the current review 
indicate that ingestion pathways dominate air-related exposure. Lead is 
unlike other criteria pollutants, where inhalation of the airborne 
pollutant is the key contributor to exposure. For Pb it is the quantity 
of Pb in ambient particles with the potential to deposit indoors or 
outdoors, thereby leading to a role in ingestion pathways, that is the 
key contributor to air-related exposure. As recognized by the Agency in 
setting the standard, and as noted by CASAC in their advice during this 
review, these particles include ultra-coarse particles. Thus, choosing 
the appropriate indicator requires consideration of the impact of the 
indicator on protection from both the inhalation and ingestion pathways 
of exposure and Pb in all particle sizes, including ultra-coarse 
particles.
    As discussed in section V.A., the Agency recognizes the body of 
evidence indicating that the high-volume Pb-TSP sampling methodology 
contributes to imprecision in resultant Pb measurements due to 
variability in the efficiency of capture of particles of different 
sizes and thus, in the mass of Pb measured. For example, the measured 
values from a high-volume TSP sampler may differ substantially, 
depending on wind speed and direction, for the same actual ambient 
concentration of Pb-TSP.\131\ Variability is most substantial in 
samples with a large portion of Pb particles greater than 10 microns, 
such as those samples collected near sources with emissions of ultra-
coarse particles. The result is a clear risk of error from 
underestimating the ambient level of total Pb in the air, especially in 
areas near sources of ultra-coarse particles, by underestimating the 
amount of the ultra-coarse particles. There is also the potential for 
overestimation of individual sampling period measurements associated 
with high wind events.\132\
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    \131\ As noted in section V, the collection efficiency (over the 
24-hour collection period) of particles larger than approximately 10 
microns in a high-volume TSP FRM sampler varies with wind speed due 
to aerodynamic effects, with a lower collection efficiency under 
high winds. The collection efficiency also varies with wind 
direction due to the non-cylindrical shape of the TSP sampler inlet. 
These characteristics tend in the direction of reporting less than 
the true TSP concentration over the 24-hour collection period.
    \132\ We note that it is possible for high winds to blow Pb 
particles onto a high-volume TSP sampler's filter after the end of 
its 24-hour collection period before the filter is retrieved, 
causing the reported concentration for the 24-hour period to be 
higher than the actual 24-hour concentration.
---------------------------------------------------------------------------

    The low-volume PM10 sampling methodology does not 
exhibit such variability \133\ due both to increased precision of the 
monitor and decreased spatial variation of Pb-PM10 
concentrations. As a result, greater precision is associated with 
sample measurements for Pb collected using the PM10 sampling 
methodology. The result is a lower risk of error in measuring the 
ambient Pb in the PM10 size class than there is risk of 
error in measuring the ambient Pb in the TSP size class using Pb TSP 
samplers. On the other hand, PM10 samplers do not include 
the Pb in particles greater than PM10 that also contributes 
to the health risks posed by air-related Pb, especially in areas 
influenced by sources of ultra-coarse particles. There are also 
concerns over whether control strategies put in place to meet a NAAQS 
with a Pb-PM10 indicator will be effective in controlling 
ultra-coarse Pb-containing particles. In evaluating these two 
indicators, the differences in the nature and degree of these sources 
of error between Pb-TSP and Pb-PM10 need to be considered 
and weighed, to determine the appropriate way to protect the public 
from exposure to air-related Pb.
---------------------------------------------------------------------------

    \133\ Low-volume PM10 samplers are equipped with an 
omni-directional (cylindrical) inlet, which reduces the effect of 
wind direction, and a sharp particle separator which excludes most 
of the particles greater than 10-15 microns in diameter whose 
collection efficiency is most sensitive to wind speed. Also, in low-
volume samplers, the filter is protected from post-sampling 
contamination.
---------------------------------------------------------------------------

    As noted above, EPA is concerned about the total mass of all Pb 
particles emitted into the air and subsequently inhaled or ingested. 
Measurements of Pb-TSP address a greater fraction of the particles of 
concern from a public health perspective than measurements of Pb-
PM10, but limitations with regard to the sampler mean that 
these data are less precise. EPA recognizes substantial variability in 
the high-volume Pb-TSP method, meaning there is a risk of not 
consistently identifying sites that fail to achieve the standard, both 
across sites and across time periods for the same site.
    Alternatively, using low-volume Pb-PM10 as the indicator 
would allow the use of a technology that has better precision in 
measuring PM10. In addition, since Pb-PM10 
concentrations have less spatial variability, such monitoring data may 
be representative of Pb-PM10 air quality conditions over a 
larger geographic area (and larger populations) than would Pb-TSP 
measurements. The larger scale of representation for Pb-PM10 
would mean that reported measurements of this indicator, and hence 
designation outcomes, would be less sensitive to exact monitor siting 
than with Pb-TSP as the indicator.\134\ However, there would be a 
different source of error, in that larger Pb particles not captured by 
PM10 samplers would not be measured.

[[Page 29232]]

The fraction of Pb collected with a TSP sampler that would not be 
collected by a PM10 sampler varies depending on proximity to 
sources of ultra-coarse Pb particles and the size mix of the particles 
they emit (as well as the sampling variability inherent in the method 
discussed above). This means that this error is of most concern in 
locations in closer proximity to such sources, which may also be 
locations with some of the higher ambient air levels. As discussed 
below, such variability would be a consideration in determining the 
appropriate level for a standard based on a Pb-PM10 
indicator.
---------------------------------------------------------------------------

    \134\ The larger scale would also make comparisons between two 
or more monitoring sites more indicative of the true comparison 
between the areas surrounding the monitoring sites, with regard to 
the Pb captured by Pb-PM10 monitors, which could be 
informative in studies of Pb uptake and health effects in 
populations.
---------------------------------------------------------------------------

    Accordingly, we believe it is reasonable to consider continued use 
of a Pb-TSP indicator, focusing on the fact that it specifically 
includes the ultra-coarse Pb particles in the air that are of concern 
and need to be addressed in protecting public health from air-related 
exposures. In considering the option of retaining Pb-TSP as the 
indicator, EPA recognizes that high-volume FRM TSP samplers would 
continue to be used at many monitoring sites operated by State and 
local agencies. In addition, it is possible that one or more low-volume 
TSP monitors would be approved as FEM, under the provisions of 40 CFR 
53, Ambient Air Monitoring Reference and Equivalent Methods. EPA 
believes, along with some commenters as noted above, that low-volume 
Pb-TSP sampling would have important advantages over high-volume Pb-TSP 
sampling.\135\ To facilitate the ability of monitor vendors and 
monitoring agencies to gain FEM status for low-volume Pb-TSP monitors, 
EPA is proposing certain revisions to the side-by-side equivalence 
testing requirements in 40 CFR 53 regarding the ambient Pb 
concentrations required during testing so that testing is more 
practical for a monitor vendor to conduct, as described in more detail 
in section V below. We note that 40 CFR 53.7, Testing of Methods at the 
Initiative of the Administrator, allows EPA itself to conduct the 
required equivalence testing for a method and then determine whether 
the requirements for equivalence are met. It would also be possible for 
EPA to promulgate amendments to 40 CFR 50 establishing one or more 
particular designs of a low-volume sampler as a Pb-TSP FRM, or to 
establish performance specifications that would facilitate the approval 
of low-volume samplers as FRM on a performance basis rather than a 
design basis; this could be done as a replacement for the high-volume 
TSP and Pb-TSP FRM or as an alternative TSP and/or Pb-TSP FRM. Either 
path to FRM status would avoid the need for the side-by-side testing, 
prescribed by 40 CFR 53, of low-volume samplers to demonstrate 
equivalence to the high-volume FRM sampler, although some amount and 
type of new testing in the field or in a wind tunnel may be appropriate 
before such changes should be made. EPA invites comments on the low-
volume TSP sampler concept.
---------------------------------------------------------------------------

    \135\ Low-volume Pb-TSP samplers could be assembled by making 
low-cost parts substitution to either low-volume PM10 or 
low-volume PM2.5 samplers; some models would have the 
same sequential sampling ability as CASAC has noted for low-volume 
Pb-PM10 samplers; sensitivity to wind direction would be 
eliminated; and their flow control and data processing and reporting 
abilities would be substantially better than high-volume Pb-TSP 
samplers. Low-volume Pb-TSP sampling data would have the same 
geographic variability as high-volume Pb-TSP sampling data, however. 
The size-specific capture efficiency curves of currently available 
commercial low-volume sampling systems are not well characterized, 
nor their sensitivity to wind speed. EPA therefore recognizes some 
uncertainty about their equivalence to high-volume samplers in terms 
of the capture of ultra-coarse particles.
---------------------------------------------------------------------------

    Within the option of continued use of a Pb-TSP indicator, EPA 
recognizes that some State, local, or tribal monitoring agencies, or 
other organizations, for the sake of the advantages noted above, may 
wish to deploy low-volume Pb-PM10 samplers rather than Pb-
TSP samplers. In anticipation of this, we have also considered an 
approach within the option of retaining Pb-TSP as the indicator that 
would allow the use of Pb-PM10 data (when and if low-volume 
Pb-PM10 samplers have been approved by EPA as either FRM or 
FEM), with adjustment(s), for monitoring for compliance with the Pb-TSP 
NAAQS. This approach would have five components: (1) The establishment 
of a FRM specification for low-volume Pb-PM10 monitoring 
including both a PM10 sampler specification and a reference 
chemical analysis method for determination of Pb in the collected 
particulate matter; (2) the establishment of a path to FEM designation 
for Pb-PM10 monitoring methods that differ from the FRM in 
either the sampler or the analytical method; (3) flexibility for 
monitoring agencies to deploy low-volume Pb-PM10 monitors 
anywhere that Pb monitoring is required by the revised Pb monitoring 
requirements to help implement the revised NAAQS; (4) specific steps 
for applying an adjustment to low-volume Pb-PM10 data for 
purposes of making comparisons to the level of the NAAQS specified in 
terms of Pb-TSP, and (5) a provision in the data interpretation 
guidelines that, whenever and wherever Pb-TSP data from a monitoring 
site is available and sufficient for determining whether or not the Pb-
TSP standard has been exceeded, any collocated Pb-PM10 data 
from that site for the associated time period will not be considered. 
The first three and the last components are discussed in depth in 
sections IV and V below. Because the issue of adjustment to low-volume 
Pb-PM10 data is linked closely to considerations of the 
advantages of one indicator option versus another, it is discussed 
here.
    In considering how to identify the appropriate adjustment(s) to be 
made to Pb-PM10 data for purposes of making comparisons to 
the level of the NAAQS specified in terms of Pb-TSP, we recognize the 
importance to protecting public health of taking into account the 
ultra-coarse particles that are not included in Pb-PM10 
measurement. As discussed below, one approach to doing so would be to 
adjust or scale Pb-PM10 data upwards before comparison to a 
Pb-TSP NAAQS level where the data are collected in an area that can be 
expected to have ultra-coarse particles present.
    Pb-PM10/Pb-TSP relationships vary from site to site and 
time to time. These Pb-PM10/Pb-TSP relationships have a 
systematic variation with distance from emissions sources emitting 
particles larger than would be captured by Pb-PM10 samplers, 
such that generally there are larger differences between Pb-
PM10 and Pb-TSP near sources. This is due to the faster 
deposition of the ultra-coarse particles (as described in section 
II.A.1). The exact size mix of particles at the point(s) of emissions 
release and the height of the release point(s) also affect the 
relationship. Accordingly, EPA is proposing to require the one-time 
development and the continued use of site-specific adjustments for Pb-
PM10 data, for those sites for which a State prefers to 
conduct Pb-PM10 monitoring rather than Pb-TSP monitoring. 
Site-specific studies to establish the relationships between Pb-TSP and 
Pb-PM10, conducted using side-by-side paired samplers, would 
allow Pb-PM10 monitoring using locally determined factors 
based on local study data to determine compliance with a NAAQS based on 
Pb-TSP.
    In addition, EPA invites comment on also providing in the final 
rule default scaling factor(s) for use of Pb-PM10 data in conjunction 
with a Pb-TSP indicator, as an alternative for States which wish to 
conduct Pb-PM10 monitoring rather than Pb-TSP monitoring near Pb 
sources but prefer not to conduct a site-specific scaling factor study. 
EPA has identified and analyzed available collocated Pb-PM10 and Pb-TSP 
data from 23 monitoring sites in seven States. (Schmidt and Cavender, 
2008). This analysis considered both source-

[[Continued on page 29233]]

From the Federal Register Online via GPO Access [wais.access.gpo.gov]
]                         
 
[[pp. 29233-29282]] National Ambient Air Quality Standards for Lead

[[Continued from page 29232]]

[[Page 29233]]

oriented and nonsource-oriented sites. In this analysis, EPA identified 
only three of the 23 monitoring sites with collocated data as being 
source-oriented. One of these sites was near an operating Pb smelter at 
the time of the collocated monitoring; Pb emissions from smelters 
typically contain both ultra-coarse particles from materials handling 
and resuspension of contaminated dust, and fine and coarse particles 
from the high temperature smelting operation itself. However, since 
this study was conducted, EPA has promulgated a Maximum Achievable 
Control Technology (MACT) standard for primary lead smelting that 
controls process and fugitive dust emissions. (64 FR 30194, June 4, 
1999). The other two source-oriented sites include one located near a 
battery manufacturer, and one located near an automobile plant. The 
data for the smelter site was collected in 1988 and indicate an average 
Pb-TSP concentration of about 2.5 [mu]g/m\3\. The data for the battery 
manufacturer site were collected in the mid-1990s and indicate an 
average Pb-TSP concentration of about 0.09 [mu]g/m\3\; data for the 
third site, located near an automotive plant, collected within the past 
5 years, indicate an average Pb-TSP concentration at that site of about 
0.03 [mu]g/m\3\. As discussed in Schmidt and Cavender (2008), ratios 
between Pb-TSP and Pb-PM10 concentrations varied somewhat 
within the data for each site, but the ratios between the Pb-TSP and 
Pb-PM10 concentration averages were 2.0 for the smelter site 
(based on 20 data pairs), 1.6 at the site near the battery manufacturer 
(based on 107 data pairs), and 1.1 at the site located near an 
automotive plant (based on 167 data pairs).
    Collectively, these three monitoring sites suggest that site-
specific scaling factors for source-oriented monitoring sites may vary 
between 1.1 and 2.0; the range may also be greater. EPA notes that in 
selecting a default factor for source-oriented monitoring sites, if 
that approach is taken in the final rule, it may be appropriate to 
consider default adjustment factors from within the mid to upper part 
of this range rather than the lower end to avoid the possibility of 
underestimating the appropriate scaling factor for a large proportion 
of the source-oriented sites for which States might choose the default 
factor rather than conduct a local study. On this basis, EPA invites 
comment on the possibility of providing a default factor(s) for source-
oriented sites and on the selection of a value(s) from within this 
range for all source-oriented monitoring sites, as an option to the 
proposed requirement for development a site-specific factor through 
analysis of paired monitoring data. EPA invites comment on the 
selection of a single or multiple default factors for source-oriented 
sites from within this range. While the selection of the scaling factor 
in concept could depend on a characterization of the particle size mix 
emitted by the Pb source, we note that reliable information on the mix 
of coarse and ultra-coarse particles may often be unavailable. For 
example, EPA could select a default factor that is at or near the upper 
end of the range, 2.0, to avoid the risk of underprotection in 
situations in which there is as high or nearly as high a proportion of 
ultra-coarse Pb as at the smelter site. Alternatively, EPA could 
discount the smelter data set on the basis that the 1988 data set does 
not reasonably represent any likely current or future smelter 
situation. Similarly, EPA could rely on the data taken near the 
automotive plant since it is the most recent and largest dataset. EPA 
also invites comment on other sets of paired data from near Pb sources 
of which we may be unaware, and comment on other approaches of 
selecting a default factor for the final rule based on paired data, 
including approaches that might use more than one default factor for 
source-oriented monitoring sites with the selection of the factor for a 
given monitoring site depending on the characteristics of the nearby 
sources, the ambient concentration of Pb-PM10, or other 
factors.
    EPA also invites comment on whether and what default scaling 
factor(s) should be established for monitoring sites which, as far as 
is known, are not influenced by nearby emission sources. We have 
reviewed paired data from the 20 monitoring sites that appear to fit 
this description (Schmidt and Cavender, 2008). Average Pb-TSP 
concentrations at nearly all these sites were near to or below the 
lowest concentration on which comments are invited as to the NAAQS 
level. Judging from ratios at these 20 sites, it appears that site-
specific factors generally range from 1.0 to 1.4 (with the factors for 
three sites ranging from 1.8 to 1.9), and the ratios may be influenced 
by measurement variability in both samplers as well as by actual air 
concentrations. Given the relatively low ambient concentrations that we 
believe currently prevail at nonsource-oriented sites, the value of a 
default scaling factor selected within the range of 1.0 to 1.4 would 
have little effect on the NAAQS compliance determination at such sites. 
EPA invites comment on the approach of requiring use of a default 
factor(s) for adjusting Pb-PM10 data at nonsource-oriented 
sites and on the selection of a value(s) from within the range of 1.0 
to 1.4 and also solicits comment on selection of a default scaling 
factor from within the broader range of 1.0 to 1.9. We note that 
allowing the use of a default scaling factor of 1.0 for nonsource-
oriented sites would in effect allow a State the option of comparing 
Pb-PM10 data directly to the level of the Pb-TSP standard at 
nonsource-oriented monitoring sites, without conducting a site-specific 
study. Below, and in section II.E.4, EPA discusses the possibility of 
revising the indicator to Pb-PM10, which would result in 
such unadjusted comparisons of Pb-PM10 data to the standard 
at all monitoring sites.
    EPA recognizes that the available data from collocated monitoring 
of Pb-TSP and Pb-PM10, described above, have limitations 
which make their interpretation and use in selecting default scaling 
factors subject to considerable uncertainty. All of the Pb-
PM10 measurements at these sites were made with high-volume 
PM10 samplers, which are more variable than the low-volume 
samplers for which scaling factors would actually be applied after the 
final rule; this greater variability no doubt has added to the 
variation in ratios discussed above. Only three source-oriented sites 
have collocated data; with such a small sample of sites both the range 
of ratios and the distribution of ratios among all current and future 
source-oriented sites remains uncertain. There were many more 
nonsource-oriented sites which tended to show notably lower ratios, 
implying lower scaling factors, but all had relatively low 
concentrations; these ratios may or may not be representative of 
monitoring sites near well controlled Pb sources. In many cases, the 
period of collocated testing was only a few months; ratios observed in 
such a short period may not be representative of ratios that occur at 
other times of the year that may be more critical to attainment status. 
Also, EPA has not yet had the benefit of CASAC review of the detailed 
compilation of these data, as (Schmidt and Cavender, 2008) was prepared 
subsequent to the most recent consultation with CASAC's AAMM 
Subcommittee. Because of these uncertainties, EPA is proposing to 
require States that wish to use Pb-PM10 data for a Pb-TSP 
standard to develop site-specific scaling factors based on their own 
collocated monitoring using paired Pb-TSP and low-volume Pb-
PM10 samplers over at least a one-year period, as described 
in section IV. EPA intends

[[Page 29234]]

to encourage States to consider conducting local studies, even if the 
final rule allows the use of default factors. Also, EPA invites comment 
on whether to provide for the use of default scaling factors, and the 
values of those factors.
    As a possible second option, taking into consideration the advice 
of the CASAC Pb Panel and members of the CASAC AAMM Subcommittee, EPA 
has also considered potential revision of the indicator to Pb-
PM10. In so doing, we recognize several potential important 
benefits of such a revision, as well as the need to reflect such a 
revision in the selection of level of the standard.\136\ We recognize 
that the low volume PM10 sampler provides better precision 
and size selection characteristics which would make the associated data 
more comparable across sites.
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    \136\ EPA recognizes and has specifically considered that such a 
decision would affect the selection of the level of the standard, 
recognizing that it is the combination of indicator and level (with 
averaging and time and form) that determine the degree of protection 
afforded by the standard. Section II.E.4 further considers the 
impact of adoption of a Pb-PM10 indicator on the 
selection of a level for the standard.
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    In considering a potential revision of the indicator to Pb-
PM10, we recognize that an important issue is whether 
regulating concentrations of Pb-PM10 will lead to 
appropriate controls on all particle size Pb emissions from sources. 
For example, it would be of concern if a NAAQS based on a Pb-
PM10 indicator resulted in different emissions control 
decisions at sources with a large percentage of Pb in the size range 
not substantially captured by PM10 sampling (e.g., fugitive 
dust emissions from Pb smelters) than the emission control decisions 
that would be made if the NAAQS was based on Pb-TSP. In that case, a 
PM10-based NAAQS might not yield emissions changes by some 
Pb sources which under a Pb-TSP indicator would have contributed to 
NAAQS exceedances and subsequent emissions changes. Alternatively, 
while collocated Pb-TSP and Pb-PM10 data are lacking for a 
broad range of source types, there are likely many sources (e.g., high 
temperature combustion processes) for which virtually all of the 
emitted particles represented in a Pb-TSP measurement would be captured 
by a Pb-PM10 measurement. Further, there are likely other 
source types with a range of particle sizes extending beyond Pb-
PM10, for which controls adopted to meet a Pb-
PM10 requirement would also achieve a proportional reduction 
in ultra-coarse particles. In these situations, one might not expect 
any difference in emissions control decisions whether the NAAQS is Pb-
PM10-based or Pb-TSP-based.
    If the indicator were to be revised to Pb-PM10, low-
volume Pb-PM10 samplers would become the required approach 
to Pb monitoring at required monitoring sites and would be a logical 
choice wherever else NAAQS-oriented Pb monitoring is undertaken. 
Nonetheless EPA notes that retaining Pb-TSP monitors at some relatively 
small subset of the Pb-PM10 monitoring sites would be 
beneficial for purposes of scientific understanding of both ambient 
conditions and the performance of the two types of measurement systems.
    For reasons discussed here, and taking into account information and 
assessments presented in the Criteria Document, Staff Paper, and ANPR, 
the advice and recommendations of CASAC and of members of the CASAC 
AAMM Subcommittee, and public comments to date, the Administrator 
proposes to retain the current indicator of Pb-TSP, measured by the 
current FRM, a current FEM, or an FEM approved under the proposed 
revisions to 40 CFR part 53, but with expansion of the measurements 
accepted for determining attainment or nonattainment of the Pb NAAQS to 
provide an allowance for use of Pb-PM10 data, measured by 
the new low-volume Pb-PM10 FRM specified in the proposed 
appendix Q to 40 CFR part 50 or by a FEM approved under the proposed 
revisions to 40 CFR part 53, with site-specific scaling factors as 
described above and more specifically below in section IV. The 
Administrator invites comment on also providing States the option of 
using default scaling factors instead of conducting the testing that 
would be needed to develop the site-specific scaling factors. In 
consideration of all of the issues discussed above, the Administrator 
also invites comment on a second option, a revision of the current 
indicator to Pb-PM10. (Considerations related to the level 
of a standard based on a PM10 indicator are discussed below 
in section II.E.4.) The Administrator solicits comment on all of the 
issues discussed above, and specifically with regard to the potential 
for a Pb-PM10 indicator to influence implementation of 
controls in ways that would lead to less control associated with larger 
particles than might be achieved with a Pb-TSP-based NAAQS, taking into 
account the variability noted above for TSP sampling.
2. Averaging Time and Form
    The statistical form of the current standard is a not-to-be-
exceeded or maximum value, averaged over a calendar quarter. This might 
also be described as requiring that no average air Pb concentration 
representing a time period of duration as long as calendar quarter (or 
longer) may exceed the level of the standard. As noted in section 
II.D.1.a, EPA set the standard in 1978 as a ceiling value with the 
conclusion that this air level would be safe for indefinite exposure 
for young children (43 FR 46250).
    The basis for selection of the current standard's averaging time of 
calendar quarter reflects consideration of the evidence available when 
the Pb NAAQS were promulgated in 1978. At that time, the Agency had 
concluded that the level of the standard, 1.5 [mu]g/m\3\, would be a 
``safe ceiling for indefinite exposure of young children'' (43 FR 
46250), and that the slightly greater possibility of elevated air Pb 
levels for shorter periods within the quarterly averaging period as 
contrasted to the monthly averaging period proposed in 1977 (43 FR 
63076), was not significant for health. These conclusions were based in 
part on the Agency's interpretation of the health effects evidence as 
indicating that 30 [mu]g/dL was the maximum safe level of blood Pb for 
an individual child.
    With regard to averaging time, after consideration of the evidence 
available at that time, the 1990 Staff Paper concluded that ``[a] 
monthly averaging period would better capture short-term increases in 
lead exposure and would more fully protect children's health than the 
current quarterly average'' (USEPA, 1990b). The 1990 Staff Paper 
further concluded that ``[t]he most appropriate form of the standard 
appears to be the second highest monthly average in a 3-year span. This 
form would be nearly as stringent as a form that does not permit any 
exceedances and allows for discounting of one `bad' month in 3 years 
which may be caused, for example, by unusual meteorology.'' In their 
review of the 1990 Staff Paper, the CASAC Pb Panel concurred with the 
staff recommendation to express the lead NAAQS as a monthly standard 
not to be exceeded more than once in three years.
    As summarized in section II.B above and discussed in detail in the 
Criteria Document, the currently available health effects evidence 
\137\ indicates a wider variety of neurological effects, as well as 
immune system and hematological effects, associated with substantially 
lower blood Pb levels in children than were recognized when the 
standard was set in 1978. Further, the health effects evidence with 
regard to characterization of a threshold for

[[Page 29235]]

adverse effects has changed since the standard was set in 1978, as have 
the Agency's views on the characterization of a safe blood Pb 
level.\138\ In consideration of averaging time for the Pb NAAQS, we 
note the following aspects of the current health effects evidence.
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    \137\ The differing evidence and associated strength of the 
evidence for these different effects is described in detail in the 
Criteria Document.
    \138\ For example, EPA recognizes today that ``there is no level 
of Pb exposure that can yet be identified, with confidence, as 
clearly not being associated with some risk of deleterious health 
effects'' (CD, p. 8-63).
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     Children are exposed to ambient Pb via inhalation and 
ingestion, with Pb that is taken into the body absorbed through the 
lungs and through the gastrointestinal tract. Studies on Pb uptake, 
elimination, and distribution show that Pb is absorbed into peripheral 
tissues in adults within a few days (USEPA 1986a; USEPA 1990b, p. IV-
2). Absorption of Pb from the gastrointestinal tract appears to be 
greater and faster in children as compared to adults (CD, Section 
4.2.1). Once absorbed, it is quickly distributed from plasma to red 
blood cells and throughout the body.
     Lead accumulates in the body and is only slowly removed, 
with bone Pb serving as a blood Pb source for years after exposure and 
as a source of fetal Pb exposure during pregnancy (CD, Sections 4.3.1.4 
and 4.3.1.5).
     Blood Pb levels, including levels of the toxicologically 
active fraction, respond quickly to increased Pb exposure, such that an 
abrupt increase in Pb uptake rapidly changes blood Pb levels. The 
associated time to reach a new quasi-steady state with the total body 
burden after such an occurrence is projected to be approximately 75 to 
100 days (CD, p. 4-27).
     The elimination half-life, which describes the time for 
blood Pb levels to stabilize after a reduction in exposure, for the 
dominant phase for blood Pb responses to changes in exposure is on the 
order of 20 to 30 days for adults (CD, p. 4-25). Blood elimination 
half-lives are influenced by contributions from bone. Given the tighter 
coupling in children of bone stores with blood levels, children's blood 
Pb is expected to respond more quickly than adults (CD, pp. 4-20 and 4-
27).
     Data from NHANES II and an analysis of the temporal 
relationship between gasoline consumption data and blood lead data 
generally support the inference of a prompt response of children's 
blood Pb levels to changes in exposure. Children's blood Pb levels and 
the number of children with elevated blood Pb levels appear to respond 
to monthly variations in Pb emissions from Pb in gasoline (EPA, 1986a, 
p. 11-39; Rabinowitz and Needleman, 1983; Schwartz and Pitcher, 1989; 
USEPA, 1990b).
     The evidence with regard to sensitive neurological effects 
is limited in what it indicates regarding the specific duration of 
exposure associated with effect, although it indicates both the 
sensitivity of the first 3 years of life and a sustained sensitivity 
throughout the lifespan as the human central nervous system continues 
to mature and be vulnerable to neurotoxicants (CD, Section 8.4.2.7). 
The animal evidence supports our understanding of periods of 
development with increased vulnerability to specific types of effect 
(CD, Section 5.3), and indicates a potential importance of exposures on 
the order of months.
     Evidence of a differing sensitivity of the immune system 
to Pb across and within different periods of life stages indicates a 
potential importance of exposures as short as weeks to months duration. 
For example, the animal evidence suggests that the gestation period is 
the most sensitive life stage followed by early neonatal stage, and 
within these life stages, critical windows of vulnerability are likely 
to exist (CD, Section 5.9 and p. 5-245).
    Evidence described in the Criteria Document and the risk assessment 
indicate that ingestion of dust can be a predominant exposure pathway 
for young children to air-related Pb, and that there is a strong 
association between indoor dust Pb levels and children's blood Pb 
levels. As stated in the Criteria Document, ``given the large amount of 
time people spend indoors, exposure to Pb in dusts and indoor air can 
be significant'' (CD, p. 3-27). The Criteria Document further describes 
studies that evaluated the influence of dust Pb exposure on children's 
blood Pb: ``Using a structural equation model, Lanphear and Roghmann 
(1997) also found the exposure pathway most influential on blood Pb was 
interior dust Pb loading, directly or through its influence on hand Pb. 
Both soil and paint Pb influenced interior dust Pb; with the influence 
of paint Pb greater than that of soil Pb. Interior dust Pb loading also 
showed the strongest influence on blood Pb in a pooled multivariate 
regression analysis (Lanphear et al., 1998).'' (CD, p. 4-134). Further, 
a recent study of dustfall near an open window in New York City 
indicates the potential for a relatively rapid response of indoor dust 
Pb loading to ambient airborne Pb, on the order of weeks (CD, p. 3-28; 
Caravanos et al., 2006a).
    We note that the health effects evidence identifies varying length 
durations in exposure that may be relevant and important. In light of 
uncertainties in aspects such as response times of children's exposure 
to airborne Pb, we recognize, as in the past, that this evidence 
provides a basis for consideration of both calendar quarter and 
calendar month as averaging times.
    In considering averaging time and form, EPA has combined the 
current quarterly averaging time with the current not-to-be exceeded 
(maximum) form and has also combined a monthly averaging time with a 
second maximum form, so as to provide an appropriate degree of year-to-
year stability that a maximum monthly form would not afford. We also 
note that, as discussed below, the second maximum monthly form provides 
a roughly comparable degree of protection on a broad national scale.
    In this consideration of averaging time and form, EPA has taken 
into account analyses using air quality data for 2003-2005 that are 
presented in the Staff Paper (chapter 2). These analyses consider both 
a period of three calendar years and a period of one calendar year 
(with the form of the current standard being the maximum quarterly 
mean). These analyses indicate that, with regard to either single-year 
or 3-year statistics for the 2003-2005 dataset, a second maximum 
monthly mean yields very similar, although just slightly greater, 
numbers of sites exceeding various alternative levels as a maximum 
quarterly mean, with both yielding fewer exceedances than a maximum 
monthly mean.\139\ That is, these two averaging time and form 
combinations resulted in roughly the same number of areas that would 
not attain a standard at any given level on a broad national scale, 
suggesting roughly comparable public health protection. However, the 
relative protection provided by these two forms may differ from area to 
area. For example, some of the areas meeting a maximum quarterly mean 
standard over the 2003-2005 period at a given level did not meet a 
second maximum monthly mean standard at the same level because there 
were at least two months with high monthly concentrations which were 
averaged with a lower concentration month in the same quarter. On the 
other hand,

[[Page 29236]]

theoretically it is possible for an area to meet a given standard level 
with a second maximum monthly mean averaging time and form and not meet 
it for a maximum quarterly mean (e.g., the second highest monthly 
average may be below the standard level while the quarterly average may 
exceed it). Moreover, control programs to reduce quarterly mean 
concentrations may not have the same protective effect as control 
programs aimed at reducing concentrations in every individual month. 
Given the limited scope of the current monitoring network which lacks 
monitors near many significant Pb sources and uncertainty about Pb 
source emissions and possible controls, it is difficult to more 
quantitatively compare the protectiveness of the quarterly mean versus 
the second maximum monthly mean approaches.
---------------------------------------------------------------------------

    \139\ For example, 49 sites (of 189) exceed a standard level of 
0.10 [mu]g/m\3\ based on a form of maximum quarterly mean while 54 
sites exceed based on a form of second maximum monthly mean. 
Further, 25 sites exceed a standard level of 0.30 [mu]g/m\3\ based 
on a form of maximum quarterly mean while 29 sites exceed based on a 
form of second maximum monthly mean (Staff Paper, Table 2-6).
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    In their advice to the Agency in this review, CASAC has recommended 
that consideration be given to changing from a calendar quarter to a 
monthly averaging time (Henderson, 2007a, 2007b, 2008). In making that 
recommendation, CASAC emphasizes support from studies that suggest that 
blood Pb concentrations respond at shorter time scales than would be 
captured completely by quarterly values, as indicated by their 
description of their recommendation for adoption of a monthly averaging 
time as ``more protective of human health in light of the response of 
blood lead concentrations that occur at sub-quarterly time scales'' 
(Henderson, 2007a). With regard to form of the standard, CASAC has 
stated that one could ``consider having the lead standards based on the 
second highest monthly average, a form that appears to correlate well 
with using the maximum quarterly value'', while also indicating that 
``the most protective form would be the highest monthly average in a 
year'' (Henderson, 2007a).
    Among the public comments the Agency received on the discussion of 
averaging time and form in the ANPR, the majority concurred with the 
CASAC recommendation for a revision of the averaging time to a calendar 
month.
    The 1990 Staff Paper and the Staff Paper for this review both 
recommended that the Administrator consider specifying, in the form of 
the NAAQS, that compliance with the NAAQS will be evaluated over a 3-
year period. The Administrator has considered this recommendation and 
is proposing to adopt it. In the 3-year approach, a monitor would be 
considered to be in violation of the NAAQS as of a certain date if in 
any of the three previous calendar years with sufficiently complete 
data (as explained in detail in section IV below), the value of the 
selected form of the indicator (e.g., second maximum monthly average or 
maximum quarterly average) exceeded the level of the NAAQS. A monitor, 
initially or after once having violated the NAAQS, would not be 
considered to have attained the NAAQS until three years have passed 
without the form and level of the standard being violated. Many types 
of Pb sources have variable emissions from day-to-day and year-to-year 
due to market conditions for their products and/or weather variations 
that can affect the generation of fugitive dust from contaminated 
roadways and grounds. In addition, variations in wind patterns from 
year to year can cause a near-source Pb monitor to be exposed to high 
concentrations on more days in one year than in another, even if source 
emissions are constant, especially if it operates on only some days. 
Thus, it is possible for a monitor to indicate a violation of a 
hypothetical form and level in one period but not in another, even if 
no permanent controls have been applied at nearby source(s). Analysis 
of historical Pb air concentration data has confirmed that this pattern 
of fluctuating monitoring results can happen at the levels and forms 
being proposed. It would potentially reduce the public health 
protection afforded by the standard if areas fluctuated in and out of 
formal nonattainment status so frequently that states do not have 
opportunity and incentive to identify sources in need of more emission 
control and to require those controls to be put in place. The 3-year 
approach would help ensure that areas initially found to be violating 
the NAAQS have effectively controlled the contributing lead emissions 
before being redesignated to attainment/maintenance.
    In considering averaging time and form for the standard, the 
Administrator has considered the information summarized above 
(described in more detail in Criteria Document and Staff Paper), as 
well as the advice from CASAC and public comments. The Administrator 
recognizes that there is support in the evidence for a monthly 
averaging time consistent with the following observations: (1) The 
health evidence indicates that very short exposures can lead to 
increases in blood Pb levels, (2) the time period of response of indoor 
dust Pb to airborne Pb can be on the order of weeks, and (3) the health 
evidence indicates that adverse effects may occur with exposures during 
relatively short windows of susceptibility, such as prenatally and in 
developing infants.\140\ The Administrator also recognizes limitations 
and uncertainties in the evidence including the limited available 
evidence specific to the consideration of the particular duration of 
sustained airborne Pb levels having the potential to contribute to the 
adverse health effects identified as most relevant to this review, as 
well as variability in the response time of indoor dust Pb loading to 
ambient airborne Pb.
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    \140\ The health evidence with regard to the susceptibility of 
the developing fetus and infants is well documented in the evidence 
as described in the 1986 Criteria Document, the 1990 Supplement 
(e.g., chapter III) and the 2006 Criteria Document. For example, 
``[n]eurobehavioral Neurobehavioral effects of Pb-exposure early in 
development (during fetal, neonatal, and later postnatal periods) in 
young infants and children (7 years old) have been observed 
with remarkable consistency across numerous studies involving 
varying study designs, different developmental assessment protocols, 
and diverse populations.'' (CD, p. E-9)
---------------------------------------------------------------------------

    Based on these considerations and the air quality analyses 
summarized above, the Administrator concludes that this information 
provides support for an averaging time no longer than a calendar 
quarter. Further, the Administrator recognizes that if substantial 
weight is given to the evidence of even shorter times for response of 
dust Pb, blood Pb, and associated effects to airborne Pb, a monthly 
averaging time may be appropriate. Accordingly, the Administrator is 
proposing two options with regard to the form and averaging time for 
the standard, and with both he proposes making the time period 
evaluated in considering attainment be 3 years. One option is to retain 
the current not-to-be-exceeded form with an averaging time of a 
calendar quarter, such that the form would be maximum quarterly average 
across a 3-year span. The second option is to revise the averaging time 
to a calendar month and the form to be the second highest monthly 
average across a 3-year span. Based on the considerations discussed 
above, EPA requests comment on whether a level for a NAAQS with a 
monthly averaging time and a second-highest monthly average form should 
be based on an adjustment to a higher level than the level for a NAAQS 
with a quarterly averaging time and a not-to-be-exceeded form, and, if 
so, on the magnitude of the adjustment that would be appropriate.
3. Level for a Pb NAAQS With a Pb-TSP Indicator
    With regard to level of the standard, for a standard using a Pb-TSP 
indicator, we first discuss evidence-based and exposure/risk-based 
considerations, including considerations and

[[Page 29237]]

conclusions of the Staff Paper, in sections II.E.3.a and II.E.3.b 
below. This is followed by a summary of CASAC advice and 
recommendations and public comments (section II.E.3.c) and the 
Administrator's proposed conclusions (section II.E.3.d). In addition, 
we discuss considerations and solicit comment with regard to a level of 
a standard using a Pb-PM10 indicator in section II.E.4 
below.
a. Evidence-Based Considerations
    As a general matter, EPA recognizes that in the case of Pb there 
are several aspects to the body of epidemiological evidence that add 
complexity to the selection of an appropriate level for the primary 
standard. As summarized above and discussed in greater depth in the 
Criteria Document (CD, Sections 4.3 and 6.1.3), the epidemiological 
evidence that associates Pb exposures with health effects generally 
focuses on blood Pb for the dose metric.\141\ In addition, exposure to 
Pb comes from various media, only some of which are air-related. This 
presents a more complex situation than does evidence of associations 
between occurrences of health effects and ambient air concentrations of 
an air pollutant, such as is the case for particulate matter and ozone. 
Further, for the health effects receiving greatest emphasis in this 
review (neurological effects, particularly neurocognitive and 
neurobehavioral effects, in children), no threshold levels can be 
discerned from the evidence. As was recognized at the time of the last 
review, estimating a threshold for toxic effects of Pb on the central 
nervous system entails a number of difficulties (CD, pp. 6-10 to 6-11). 
The task is made still more complex by support in the evidence for a 
nonlinear rather than linear relationship of blood Pb with 
neurocognitive decrement, with greater risk of decrement-associated 
changes in blood Pb at the lower levels of blood Pb in the exposed 
population (Section 3.3.7; CD, Section 6.2.13). In this context EPA 
notes that the health effects evidence most useful in determining the 
appropriate level of the NAAQS is this large body of epidemiological 
studies. Unlike the recent review of the NAAQS for ozone, there are no 
clinical studies useful for informing a determination of the 
appropriate level for a standard.\142\ The discussion below therefore 
focuses on the epidemiological studies, recognizing and taking into 
consideration the complexity and resulting uncertainty in using this 
body of evidence to determine the appropriate level for the NAAQS.
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    \141\ Among the studies of Pb health effects, in which blood Pb 
level is generally used as an index of exposure, the sources of 
exposure vary and are inclusive of air-related sources of Pb such as 
smelters (e.g., CD, chapter 6).
    \142\ See, e.g., 72 FR 37878-9 (July 11, 2007) (Ozone NAAQS 
Notice of Proposed Rulemaking).
---------------------------------------------------------------------------

    In considering the evidence with regard to selection of the level 
of the standard, the Agency has considered the same evidence-based 
frameworks discussed above in section II.D.2.a on the adequacy of the 
current standard. That is, the Staff Paper considered how to apply an 
adapted 1978 framework to the much expanded body of evidence that is 
now available, and the Agency has further considered this evidence in 
the context of the air-related IQ loss evidence-based framework that 
builds on a recommendation by the CASAC Pb Panel. These evidence-based 
approaches are discussed below in considering the appropriate standard 
levels to propose.
    As noted in section II.D.2.a above, this review focuses on young 
children as a key sensitive population for Pb exposures. In this 
sensitive population, the current evidence demonstrates the occurrence 
of health effects, including neurological effects, associated with 
blood Pb levels extending well below 10 [mu]g/dL (CD, sections 6.2, 8.4 
and 8.5). As further described in section II.D.2.a above, some studies 
indicate Pb effects on intellectual attainment of children for which 
population mean blood Pb levels in the analysis ranged from 
approximately 2 to 8 [mu]g/dL (CD, Sections 6.2, 8.4.2 and 8.4.2.6). 
Further, as noted above, the current evidence does not indicate a 
threshold for the more sensitive health endpoints such as neurological 
effects in children (CD, pp. 5-71 to 5-74 and Section 6.2.13).\143\
---------------------------------------------------------------------------

    \143\ This differs from the Agency's recognition in the 1978 
rulemaking of a threshold of 40 [mu]g/dL blood Pb for an individual 
child for effects of Pb considered clearly adverse to health at that 
time, i.e., impairment of heme synthesis and other effects which 
result in anemia.
---------------------------------------------------------------------------

    As when the standard was set in 1978, there remain today 
contributions to blood Pb levels from nonair sources. As discussed 
above (section II.D.2), current evidence is limited with regard to 
estimates of the aggregate reduction since 1978 of all nonair sources 
to blood Pb and with regard to an estimate of current nonair blood Pb 
levels (discussed more fully in sections II.A.4) In recognition of 
temporal reductions in nonair sources discussed in section II.A.4 and 
in the context of estimates pertinent to an application of the 1978 
framework, the CASAC Pb Panel recommended consideration of 1.0 to 1.4 
[mu]g/dL or lower as an estimate of the nonair component of blood Pb 
pertinent to average blood Pb levels in children (as described in 
section II.A.4 above; Henderson, 2007a). The Staff Paper considered 
this range of 1.0 to 1.4 [mu]g/dL for the nonair component of blood Pb 
in its application of the adapted 1978 evidence-based framework.
    As discussed in section II.B.1.c, the current evidence in 
conjunction with the results and observations drawn from the exposure 
assessment support a focus on air-to-blood ratios for children in the 
range of 1:3 to 1:7, based on consideration of both inhalation and 
ingestion exposure pathways and on the lower air and blood Pb levels 
pertinent to this review. In considerations here, we have described the 
value of 1:5 as falling somewhat central within the range supported by 
the evidence.
i. Evidence-Based Framework Considered in the Staff Paper
    Recommendations in the Staff Paper on standard levels were based 
upon an approach that built upon and adapted the general approach used 
by EPA in setting the standard in 1978. In adapting this approach to 
the currently available information, the Staff Paper recognized the 
more extensive and stronger body of evidence now available on a broader 
range of health effects associated with exposure to Pb. For example, 
EPA recognizes that today ``there is no level of Pb exposure that can 
yet be identified, with confidence, as clearly not being associated 
with some risk of deleterious health effects'' (CD, p. 8-63). This is 
in contrast to the situation in 1978 when the Agency judged that the 
maximum safe individual and geometric mean blood Pb levels for a 
population of young children were 30 [mu]g/dL and 15 [mu]g/dL, 
respectively.\144\
---------------------------------------------------------------------------

    \144\ More specifically, when the standard was set in 1978, the 
Agency stated that the population mean, measured as the geometric 
mean, must be 15 [mu]g/dL in order to ensure that 99.5 percent of 
children in the United States would have a blood Pb level below 30 
[mu]g/dL, which was identified as the maximum safe blood Pb level 
for individual children based on the information available at that 
time (43 FR 46247-46252).
---------------------------------------------------------------------------

    In the Staff Paper application of an adapted 1978 framework, the 
focus shifted away from identifying a safe blood Pb level for an 
individual child (and then determining an ambient air level that would 
keep a very high percentage of children at or below that safe level), 
because information was no longer available to identify such a level. 
Rather, the Staff Paper approach focused on identifying an appropriate 
population mean blood Pb level, and then identifying an ambient air 
level that would keep the mean blood Pb levels of children exposed at 
that air level below the target population mean blood Pb level. Based 
on the review of

[[Page 29238]]

the evidence, the Staff Paper approach substituted a level of 2 [mu]g/
dL for the target population geometric mean blood Pb of 15 [mu]g/dL 
used in 1978. In the absence of a demonstrated safe level, at either an 
individual or a population level, the Staff Paper used 2 [mu]g/dL as 
representative of the lowest population mean level for which there is 
evidence of a statistically significant association between blood lead 
levels and health effects (e.g., CD, p. E-9; Lanphear et al., 2000).
    This approach does not evaluate the magnitude or degree of health 
effects occurring across the population at that mean blood lead level. 
In this adaptation of the 1978 approach the focus is solely on the 
existence of a relationship between blood lead levels and 
neurocognitive effects. The approach takes as the public health goal 
the identification of an ambient air lead level that can be expected to 
keep the mean blood lead level of an exposed population of children at 
or below the lowest level at which a statistically significant 
association has been demonstrated between blood lead level and 
neurocognitive effects.\145\
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    \145\ There are some similarities between this approach and the 
approach employed in determining the levels for the daily and annual 
PM standards in the latest PM review, where EPA determined an 
ambient PM level based on the ambient levels in the epidemiology 
studies that found statistically significant associations between 
changes in ambient PM levels and changes in occurrences of health 
effects. See 71 FR 61144 (October 17, 2006). However, there are 
several important differences in this adaptation to the 1978 
approach for lead. For example, the health effects evaluated in the 
PM epidemiological studies were clearly adverse health effects, 
ranging from hospital admissions to premature mortality. In 
addition, the studies looked directly at the association between 
ambient level and occurrences of health effects. Here the 
epidemiology studies look at the association between blood lead 
level and neurocognitive effect, and there is an additional step to 
link the blood lead level to air-related lead. In addition, at a 
population level there is a less clear delineation of when the 
neurocognitive effect is adverse to public health. This is discussed 
below in this section with respect to the impact on public health of 
a shift in the mean IQ of a population of children.
---------------------------------------------------------------------------

    Starting with a target population geometric mean blood lead level 
of 2 [mu]g/dL for the population of exposed children, then subtracting 
1 to 1.4 [mu]g/dL for the nonair component of blood Pb, yields 0.6 to 1 
[mu]g/dL as a target for the geometric mean air contribution to blood 
Pb. The adapted 1978 approach divides the air-related target by 5, an 
air-to-blood ratio somewhat central within the range of air Pb to blood 
Pb ratios generally supported by the currently available evidence. This 
resulted in a potential standard level of 0.1 to 0.2 [mu]g/m\3\.
    The Staff Paper conclusions on level for the primary Pb standard 
built on the staff's conclusion that the overall body of evidence 
clearly calls into question the adequacy of the current standard with 
regard to health protection afforded to at-risk populations. Based on 
consideration of the health effects evidence, as described above, the 
Staff Paper concluded that it is reasonable to consider a range for the 
level of the standard, for which the upper part is represented by 0.1 
to 0.2 [mu]g/m\3\.
ii. Air-related IQ Loss Evidence-Based Framework
    As mentioned above, in analyses subsequent to the Staff Paper and 
ANPR, the Agency has primarily considered the evidence in the context 
of an alternative evidence-based framework, referred to as the air-
related IQ loss framework. This framework focuses on the contribution 
of air-related Pb to neurocognitive effects, with a public health goal 
of identifying the appropriate ambient air level of Pb to protect 
exposed children from health effects that are considered adverse, and 
are associated with their exposure to air-related Pb. This framework 
does not focus on overall blood lead levels or on nonair contribution 
to blood lead levels. While this avoids some of the limitations noted 
above with the adapted 1978 approach, EPA recognizes that looking at 
air-related Pb in isolation from other sources of Pb could be 
considered a limitation for this framework. The different limitations 
of each of these frameworks derive from the limitations in the 
underlying body of evidence available for this review.
    In this air-related IQ loss evidence-based framework, we have drawn 
from the entire body of evidence as a basis for concluding that there 
are causal associations between air-related Pb exposures and population 
IQ loss. We have drawn more quantitatively from the evidence by 
combining air-to-blood ratios with evidence-based C-R functions from 
the epidemiological studies to quantify the association between air Pb 
concentrations and air-related population mean IQ loss in exposed 
children. This air-related IQ loss framework focuses on selecting a 
standard that would prevent air-related IQ loss (and related effects) 
of a magnitude judged by the Administrator to be of concern in 
populations of children exposed to the level of the standard, taking 
into consideration such factors as the uncertainties inherent in such 
estimates. In addition to this judgment by the Administrator, this 
framework is also based on specifying an air-to-blood ratio (also used 
in the adapted 1978 framework) and a C-R function(s) for population 
mean IQ response associated with blood Pb level.
    In considering the evidence with regard to C-R functions, and in 
recognition of the finding in the evidence of a steeper slope at lower 
blood Pb levels (i.e., the nonlinear relationship), we have identified 
two sets of C-R functions (discussed more fully above in section 
II.B.2.b). The first set focuses on C-R functions reflecting population 
mean concurrent blood Pb levels of approximately 3 [mu]g/dL.\146\ The 
second set (CD, pp. 8-78 to 8-80) considers functions descriptive of 
the C-R relationship from a larger set of studies that include 
population mean blood Pb levels ranging from a mean of 3.3 up to a 
median of 9.7 [mu]g/dL (see Table 1).\147\
---------------------------------------------------------------------------

    \146\ As noted above in section II.B.2.b, the log-linear C-R 
function with low-exposure linearization (LLL) used in the 
quantitative risk assessment, based on log-linear model in Lanphear 
et al 2005), has a slope that falls intermediate within this first 
set of functions at low blood Pb levels. The log-linear model by 
Lanphear et al (2005) is derived from the pooled International 
dataset for which the median blood Pb is 9.7 [mu]g/dL.
    \147\ For context, it is noted that the 2001-2004 median blood 
level for children aged 1-5 of all races and ethnic groups is 1.6 
[mu]g/dL, the median for the subset living below the poverty level 
is 2.3 [mu]g/dL and 90th percentile values for these two groups are 
4.0 [mu]g/dL and 5.4 [mu]g/dL, respectively. Similarly, the 2001-
2004 median blood level for black, non-hispanic children aged 1-5 is 
2.5 [mu]g/dL, while the median level for the subset of that group 
living below the poverty level is 2.9 [mu]g/dL and the median level 
for the subset living in a household with income more than 200% of 
the poverty level is 1.9 [mu]g/dL. Associated 90th percentile values 
for 2001-2004 are 6.4 [mu]g/dL (for black, non-hispanic children 
aged 1-5), 7.7 [mu]g/dL (for the subset of that group living below 
the poverty level) and 4.1 [mu]g/dL (for the subset living in a 
household with income more than 200% of the poverty level). (http://
www.epa.gov/envirohealth/children/body_burdens/b1-table.htm--then 
click on ``Download a universal spreadsheet file of the Body Burdens 
data tables'').
---------------------------------------------------------------------------

    As discussed above in section II.B.2.b, the C-R functions from 
analyses involving the lower mean blood Pb levels, that are closer to 
current mean blood Pb levels in U.S. children, provide slopes of IQ 
loss with increasing blood Pb that range from -1.71 to -2.94 IQ points 
per [mu]g/dL blood Pb. These include C-R function from Lanphear et al. 
(2005) recommended for consideration by CASAC, in light of the current 
blood Pb levels of U.S. children (Henderson, 2008),\148\ and also the 
C-R function

[[Page 29239]]

given greatest weight in the risk assessment (discussed above in 
section II.C.2.b), the loglinear function with low-exposure 
linearization (the LLL function). The function yielding the lowest 
slope in this range is from the analysis by Tellez-Rojo and others 
(2006) of very young children with blood Pb levels below 5 [mu]g/dL, 
with a group mean blood Pb level of 2.9 [mu]g/dL. The function yielding 
the highest slope in this range is from the analysis by Lanphear and 
others (2005) of children whose blood Pb levels never exceeded 7.5 
[mu]g/dL, with a group mean blood Pb level of 3.24 [mu]g/dL. The LLL 
function falls within the range of the other two functions at lower 
blood Pb levels, with an average slope of -2.29 IQ points per [mu]g/dL 
across blood Pb levels extending below 2 [mu]g/dL.
---------------------------------------------------------------------------

    \148\ In their September 2007 letter, the CASAC Pb Panel 
``recommends using the two-piece linear function for relating IQ 
alterations to current blood lead levels with a slope change or 
``hinge'' point closer to 7.5 [mu]g/dL than 10.82 [mu]g/dL as used 
by EPA staff in the second draft exposure/risk assessments document. 
The higher value used by staff underestimates risk at lower blood Pb 
levels, where most of the population will be located. Epidemiologic 
data indicate that the slope of the line below 7.5 [mu]g/dL is 
approximately minus three (-3) IQ decrements per 1 [mu]g/dL blood 
lead and the vast majority of children in the U.S. have maximal 
baseline Pb blood levels below 7.5 [mu]g/dL (Lanphear et al., EHP 
2005; MMWR 2005). On a population level, the mean increase in blood 
lead concentration from airborne lead would generally be up to, but 
not exceeding, a blood lead concentration of 7.5 [mu]g/dL. This 
approach should also account for sensitive subpopulations of 
children.'' In in their January 2008 letter, the Panel also points 
to several other studies ``confirming that the relationship of lead 
exposure is non-linear and per-sists at blood lead levels 
considerably lower than 5 [mu]g/dL (Lanphear, 2000; Wasserman, 2003; 
Kordas, 2006; Tellez-Rojo, 2006). In particular, Tellez-Rojo and co-
workers reported that the slope of the association between 24-month 
blood lead and the 24-month Mental Development Index (MDI) for 294 
children who had peak blood lead levels below 5 [mu]g/dL was 
negative (-1.7 points for each 1 [mu]g/dL increase in blood lead 
concentration, p=0.01). Collectively, these studies indicate that 
there is sufficient evidence to support the use of the dose-response 
relationship from the pooled analysis at blood lead levels < 5 
[mu]g/dL (Lanphear, 2005), as described in the Final Lead Staff 
Paper and previously recommended by CASAC.''
---------------------------------------------------------------------------

    The second set of C-R functions discussed in section II.B.2.b is 
drawn from a larger group of studies, although these studies include 
groups of children with higher blood Pb levels (CD, pp. 8-78 to 8-80) 
such that the population mean levels for these studies include 
population mean blood Pb levels ranging from a mean of 3.3 up to a 
median of 9.7 [mu]g/dL (see Table 1). This second set of C-R functions 
is represented by a median of -0.9 IQ points per [mu]g/dL blood Pb (CD, 
p. 8-80).\149\
---------------------------------------------------------------------------

    \149\ As noted above (in section II.B.2.b), this slope is 
similar to the slope for the below 10 [mu]g/dL piece of the 
piecewise model used in the RRP rule economics analysis.
---------------------------------------------------------------------------

    In applying the air-related IQ loss evidence-based framework, as 
with the adapted 1978 framework, we recognize uncertainty in our 
estimates for the two input parameters (air-to-blood ratio and C-R 
function slope). Accordingly, in associating various standard levels 
with the estimated magnitudes of air-related mean IQ loss that would 
likely be prevented by keeping exposed populations below such standard 
levels, we have considered combinations of parameter estimates that are 
potentially supportable within this framework. With regard to the C-R 
functions we have drawn estimates from both sets of functions. For the 
first set of C-R functions, we have relied on the upper and lower-end 
values to provide a range at lower blood Pb levels, and have focused on 
the LLL function for blood Pb levels above approximately 2.5 to 3.0 
[mu]g/dL, as shown in Table 7.\150\ From the second set of C-R 
functions, we have relied on the median estimate across the range of 
blood Pb levels considered. For air-to-blood ratios, we have focused on 
the estimate of 1:5 as above, and also provided IQ loss estimates using 
higher and lower estimates of air-to-blood ratio (i.e., 1:3 and 1:7) 
within the range supported by the evidence. These estimates are 
presented in Table 7 below.
---------------------------------------------------------------------------

    \150\ We derived estimates of air-related IQ loss using the LLL 
(nonlinear) function giving equal weight to all contributions of Pb 
to total blood Pb as illustrated by the following example. For a 
level of 0.30 [mu]g/m\3\, and an air-to-blood ratio of 1:5, the 
resultant estimate of air-related blood Pb is 1.5 [mu]g/dL. Using 
estimates for nonair blood Pb levels of 1 and 1.4 [mu]g/dL, the 
estimates of total blood Pb are 2.5 and 2.9 [mu]g/dL. The 
corresponding total Pb-related IQ loss estimates based on the LLL 
function are 5.2 and 5.6 points IQ loss. These estimates are then 
multiplied by the fraction of total Pb that is air-related (i.e., 
1.5/2.5 and 1.5/2.9) to derive the estimated range of air-related IQ 
loss (2.9-3.1 points).

                      Table 7.--Estimates of Air-Related Population Mean IQ Loss for Children Exposed at the Level of the Standard
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                              Air-related population mean IQ loss (points) for children exposed at level of the standard
                             ---------------------------------------------------------------------------------------------------------------------------
                               Air-to-blood ratio of    Air-to-blood ratio of    Air-to-blood ratio of    Air-to-blood ratio of    Air-to-blood ratio of
Potential level for standard            1:3                      1:4                      1:5                      1:6                      1:7
         ([mu]g/m\3\)        ---------------------------------------------------------------------------------------------------------------------------
                               1st group   2nd group    1st group   2nd group    1st group   2nd group    1st group   2nd group    1st group   2nd group
                                of C-R       of C-R      of C-R       of C-R      of C-R       of C-R      of C-R       of C-R      of C-R      of C-R
                               functions   functions    functions   functions    functions   functions    functions   functions    functions   functions
--------------------------------------------------------------------------------------------------------------------------------------------------------
0.50........................   * 2.9-3.1         1.4    * 3.5-3.8         1.8    * 4.1-4.3         2.3    * 4.6-4.8         2.7    * 5.0-5.3         3.2
0.40........................   * 2.4-2.6         1.1    * 3.0-3.2         1.4    * 3.5-3.8         1.8    * 4.0-4.2         2.2    * 4.4-4.6         2.5
0.30........................     1.5-2.6         0.8    * 2.4-2.6         1.1    * 2.9-3.1         1.4    * 3.3-3.5         1.6    * 3.6-3.9         1.9
0.20........................     1.0-1.8         0.5      1.4-2.4         0.7      1.7-2.9         0.9    * 2.4-2.6         1.1    * 2.7-3.0         1.3
0.10........................     0.5-0.9         0.3      0.7-1.2         0.4      0.9-1.5         0.5      1.0-1.8         0.5      1.2-2.1         0.6
0.05........................     0.3-0.4         0.14     0.3-0.6         0.18     0.4-0.7         0.2      0.5-0.9         0.27     0.6-1.0         0.3
0.02........................     0.1-0.2         0.05     0.1-0.2         0.07     0.2-0.3         0.09     0.2-0.4         0.1      0.2-0.4        0.1
--------------------------------------------------------------------------------------------------------------------------------------------------------
* These estimates were derived using only the nonlinear C-R function from the risk assessment which, given its nonlinearity, EPA considers to better
  assess risk across the range that includes extending into these higher standard levels (and the associated higher blood Pb levels). That is, the upper
  and lower values presented in the asterisked cells are both derived using the LLL function, as described in the text and associated footnote above,
  rather than using the two linear functions of -1.71 from Tellez-Rojo, 2005 (<5 [mu]g/dL subgroup) and -2.94 from Lanphear, 2005 (<7.5 [mu]g/dL peak
  blood Pb subgroup) as is the case in the cells without asterisks.

    Using the air-to-blood ratio of 1:5 with the range of slopes from 
the first set of C-R functions indicates an air-related mean IQ loss 
estimate of 0.9 to 1.5 points for a population of children exposed at 
the standard level of 0.10 [mu]g/m\3\. Similarly, the air-related mean 
IQ loss estimate for a standard level of 0.20 [mu]g/m\3\ is 1.7 to 2.9 
points. Using the air-to-blood ratio of 1:5 and the slope from the 
second set of C-R functions (from blood Pb levels extending up to 10 
[mu]g/dL) in the calculation indicates an air-related mean IQ loss of 
0.5 points for a population of children exposed at the standard level 
of 0.10 [mu]g/m\3\; the corresponding air-related mean IQ loss estimate 
for a standard level of 0.20 [mu]g/m\3\ is 0.9 points. Using the 1:5 
air-to-blood ratio with first set of C-R functions indicates an air-
related mean IQ loss estimate of approximately 3 points for a 
population of children exposed at the standard level of 0.30 [mu]g/
m\3\. Using the slope from the second set of C-R functions indicates an 
air-related mean IQ loss estimate of 1.4 points for a population of 
children exposed at the standard level of 0.30 [mu]g/m\3\.

[[Page 29240]]

    As mentioned above, we recognize uncertainty in the air-to-blood 
values, and have accordingly also considered estimates of air-to-blood 
ratio that are lower and higher than the 1:5 value used above. 
Accordingly, we note that using a lower air-to-blood ratio, such as 1:3 
(low end of range from evidence) generally results in lower air-related 
IQ loss estimates with either set of C-R functions (approximately 40% 
lower than those using a ratio of 1:5). Similarly, use of a higher air-
to-blood ratio, such as 1:7, yields higher air-related mean IQ loss 
estimates with either set of C-R functions (approximately 40% higher 
than those using a ratio of 1:5).
    In applying this framework, we have also considered higher standard 
levels, above 0.30 [mu]g/m\3\ up to the highest alternative level 
included in the risk assessment (e.g., up to 0.50 [mu]g/m\3\). Using 
the 1:5 air-to-blood ratio with the first set of C-R functions, the 
air-related mean IQ loss estimate for a standard level of 0.50 [mu]g/
m\3\ is approximately 4 points. Using the slope from the second set of 
C-R functions indicates an air-related mean IQ loss estimate of 2.3 
points for a population of children exposed at the standard level of 
0.50 [mu]g/m\3\. Using the 1:3 air-to-blood ratio with the first set of 
C-R functions indicates an air-related mean IQ loss estimate of 
approximately 3 points for a population of children exposed at the 
standard level of 0.50 [mu]g/m\3\. Using the 1:3 air-to-blood ratio and 
the slope for the second set of C-R functions indicates an air-related 
mean IQ loss estimate of 1.4 points for a population of children 
exposed at the standard level of 0.50 [mu]g/m\3\.
    Further, we have also considered lower standard levels, down to the 
lowest alternative levels included in the risk assessment (e.g., 0.05 
to 0.02 [mu]g/m\3\). For example, across both sets of C-R functions and 
the range of air-to-blood ratios considered above (1:3 to 1:7), a 
standard level of 0.05 [mu]g/m\3\ indicates an air-related mean IQ loss 
of approximately 0.1 to 1 point. The estimates for either set of C-R 
functions are approximately 50% lower at the standard level of 0.02 
[mu]g/m\3\.
b. Exposure- and Risk-Based Considerations
    To inform judgments about a range of levels for the standard that 
could provide an appropriate degree of public health protection, in 
addition to considering the health effects evidence, EPA also 
considered the quantitative estimates of exposure and health risks 
attributable to air-related Pb upon meeting specific alternative levels 
of alternative Pb standards and the uncertainties in the estimated 
exposures and risks, as discussed above in Section III.B. As discussed 
above, the risk assessment conducted by EPA is based on exposures that 
have been estimated for children of less than 7 years of age in several 
case studies. The assessment estimated the risk of adverse 
neurocognitive effects in terms of IQ loss associated with total and 
air-related Pb exposures, including incidence of different magnitudes 
of IQ loss in the three location-specific case studies. In so doing, 
EPA is mindful of the important uncertainties and limitations that are 
associated with the exposure and risk assessments. For example, with 
regard to the risk assessment important uncertainties include those 
related to estimation of blood Pb C-R functions, particularly for blood 
Pb concentrations at and below the lower end of those represented in 
the epidemiological studies characterized in the Criteria Document.
    EPA also recognizes important limitations in the design of, and 
data and methods employed in, the exposure and risk analyses. For 
example, the available monitoring data for Pb relied upon for 
estimating current conditions for the urban case studies are quite 
limited, in that monitors are not located near many of the larger known 
Pb sources, which results in potential underestimation of current 
conditions, and there is uncertainty about the proximity of existing 
monitors to other Pb sources potentially influencing exposures, such as 
old urban roadways and areas where housing with Pb paint has been 
demolished or has undergone extensive exterior renovation. All of these 
limitations raise uncertainty as to whether these data adequately 
capture the magnitude of ambient Pb concentrations to which the target 
population is currently exposed. Additionally, EPA recognizes that 
there is not sufficient information available to evaluate all relevant 
sensitive groups (e.g., adults with chronic kidney disease) or all Pb-
related health effects (e.g., neurological effects other than IQ loss, 
immune system effects, adult cardiovascular or renal effects), and the 
scope of our analyses was generally limited to estimating exposures and 
risks in case studies intended to illustrate a variety of Pb exposure 
situations across the U.S., with three of them focused on specific 
areas in three cities. As noted above, however, coordinated intensive 
efforts over the last 20 years have yielded a substantial decline in 
blood Pb levels in the United States. Recent NHANES data (2003-2004) 
yield blood lead level estimates for children age 1 to 5 years of 1.6 
[mu]g/dL (median) and 3.9 [mu]g/dL (90th percentile). These median and 
90th percentile national-level data are lower than modeled values 
generated for the three location-specific urban case studies current 
conditions scenarios (described in section II.C.3.a above). As noted in 
section II.C.3.a, however, the urban case studies and the NHANES study 
are likely to differ with regard to factors related to Pb exposure, 
including ambient air levels (e.g., the national median ambient air Pb 
concentrations are generally lower than those in the location-specific 
case studies).
    As described in section II.C.2.e, we also recognize limitations in 
our ability to characterize the contribution of air-related Pb to total 
Pb exposure and Pb-related health risk. As a result, we have 
approximated estimates for the air-related pathways, bounded on the low 
end by exposure/risk estimated for the ``recent air'' category and on 
the upper end by the exposure/risk estimated for the ``recent air'' 
plus ``past air'' categories.\151\
---------------------------------------------------------------------------

    \151\ As noted in section II.C.2.e above, the recent air 
category does not include a variety of air-related categories 
(including some associated with air deposition to outdoor surfaces 
and diet) and both the recent air and past categories may include 
some Pb in soil or dust from the historical use of Pb in paint.
---------------------------------------------------------------------------

    We generally focus in this discussion on risk estimates derived 
using the LLL (log-linear with low exposure linearization) C-R 
function. Further, in considering the risk estimates in light of IQ 
loss estimates (described in section II.E.3.a) of the air-related IQ 
loss evidence-based framework, we focus here on risk estimates for the 
general urban and primary Pb smelter subarea case studies as these 
cases studies generally represent population exposures for more highly 
air-pathway exposed children residing in small neighborhoods or 
lozalized residential areas with air concentrations nearer the standard 
level being evaluated than do the location-specific case studies in 
which populations have a broader range of air-related exposures 
including many well below the standard level being evaluated.
    In considering the results of the risk assessment for the 
alternative standard levels assessed, we note that the risk estimates 
are roughly consistent with and generally supportive of the evidence-
based mean air-related IQ loss estimates described above (section 
II.E.3.a). For example, at a standard level of 0.20 [mu]g/m\3\, the 
evidence-based approach indicates estimates of mean air-related IQ loss 
ranging from less than

[[Page 29241]]

1 to approximately 3 points IQ loss, while the median air-related risk 
estimates for this level in the general urban case study are 
represented by a lower bound near 1 point IQ loss and an upper bound 
near 3 points IQ loss. The corresponding upper bound air-related IQ 
loss estimate for the primary Pb smelter case study subarea is 3.7 
points. Alternatively, at a standard level of 0.50 [mu]g/m\3\, the 
evidence-based approach indicates estimates of mean air-related IQ loss 
ranging from approximately 1.5 points to greater than 4 points, while 
the median air-related risk estimates for this level for the general 
urban case study are represented by a lower bound near 2 points IQ loss 
and an upper bound just below 4 points IQ loss (section II.C.3.b). The 
corresponding upper bound air-related IQ loss estimate for the primary 
Pb smelter case study subarea is 4.5 points. Also, while the risk 
assessment did not specifically assess the standard levels of 0.10 and 
0.30 [mu]g/m\3\, we note that estimates for these levels based on 
interpolation from the estimates described above are also roughly 
consistent with and generally supportive of the evidence-based mean 
air-related IQ loss estimates described in section II.E.3.a above 
(Murphy and Pekar, 2008).
    As mentioned above (section II.E.3.a), the Staff Paper conclusions 
on level for the primary Pb standard built on staff 's conclusion that 
the overall body of evidence clearly calls into question the adequacy 
of the current standard with regard to health protection afforded to 
at-risk populations. Drawing from both consideration of the evidence 
and consideration of the quantitative risk and exposure information 
(described in section II.E.3.b), staff concluded that the available 
information provides strong support for consideration of a range of 
standard levels that are appreciably below the level of the current 
standard in order to provide increased public health protection for 
these populations, with support for this conclusion. With regard to the 
risk estimates, the Staff Paper recognized that, to the extent one 
places weight on risk estimates for the lower standard levels, those 
estimates may suggest consideration of a range of levels that extend 
down to the lowest levels assessed in the risk assessment, 0.02 to 0.05 
[mu]g/m\3\. In summary, the Staff Paper concluded that ``a level for 
the standard set in the upper part of [the staff] recommended range 
(0.1-0.2 [mu]g/m\3\, particularly with a monthly averaging time) is 
well supported by the evidence and also supported by estimates of risk 
associated with policy-relevant Pb that overlap with the range of IQ 
loss that may reasonably be judged to be highly significant from a 
public health perspective, and is judged to be so by CASAC'' (USEPA, 
2007c). Further, the Staff Paper concluded that ``a standard set in the 
lower part of the range would be more precautionary and would place 
weight on the more highly uncertain range of estimates from the risk 
assessment'' (USEPA, 2007c).
c. CASAC Advice and Recommendations and Public Comments
    Beyond the evidence- and risk/exposure-based information discussed 
above, EPA's consideration of the level for the TSP-based standard also 
takes into account the advice and recommendations of CASAC, based on 
their review of the Criteria Document, the Staff Paper and the related 
technical support document, and the ANPR, as well as comments from the 
public on drafts of the Staff Paper and related technical support 
document and the ANPR.
    In their advice to the Agency during this review CASAC has 
recognized the importance of both the health effects evidence and the 
exposure and risk information in selecting the level for the TSP-based 
standard (Henderson, 2007a, 2007b, 2008). In two separate letters sent 
prior to publication of the ANPR, CASAC stated that it is the unanimous 
judgment of the CASAC Lead Panel that the primary NAAQS should be 
``substantially lowered'' to ``a level of about 0.2 [mu]g/m\3\ or 
less,'' reflecting their view of the health effects evidence 
(Henderson, 2007a,b). In their most recent letter, reflecting their 
review of the ANPR and Staff Paper, the Panel reiterated their earlier 
judgment, stating that ``[t]he Committee unanimously and fully supports 
Agency staff's scientific analyses in recommending the need to 
substantially lower the level of the primary (public-health based) Lead 
NAAQS, to an upper bound of no higher than 0.2 [mu]g/m\3\ with a 
monthly averaging time.''
    The CASAC Pb Panel also provided advice regarding how the Agency 
should consider IQ loss estimates derived from the risk assessment in 
selecting a level for the standard (Henderson, 2007a). The Panel stated 
that they consider a population loss of 1-2 IQ points to be ``highly 
significant from a public health perspective''.
    Among the many public comments the Agency has received in this 
review regarding the level of the standard, the overwhelming majority 
recommended appreciable reductions in the level, e.g., setting it at 
0.2 [mu]g/m\3\ or less, while only a few recommended that the Agency 
make no or only a modest adjustment. Among the comments recommending 
appreciable reduction, many noted the importance of considering 
exposures and risks to vulnerable and susceptible populations. Some 
recognized that blood Pb levels are disproportionately elevated among 
minority and low-income children, and recommended more explicit 
consideration of issues of environmental justice. And some comments 
also noted the need for the standard to provide an adequate margin of 
safety, indicating that such a need might provide support for 
consideration of much lower levels. The American Academy of Pediatrics 
recommended that EPA set the level at 0.2 or lower, and also 
recommended that EPA consider the approach developed by the State of 
California Environmental Protection Agency (Cal-EPA) for the purposes 
of school site assessment, which has at its goal prevention of a rise 
in blood Pb level that Cal-EPA has predicted to be associated with an 
incremental increase estimated to decrease IQ by 1 point.
d. Administrator's Proposed Conclusion Concerning Level
    For the reasons discussed below, and taking into account 
information and assessments presented in the Criteria Document and 
Staff Paper, the advice and recommendations of CASAC, and the public 
comments to date, the Administrator proposes to revise the existing 
primary Pb standard. Specifically, the Administrator proposes to revise 
the level of the primary Pb standard, defined in terms of the current 
Pb-TSP indicator, to within the range of 0.10 to 0.30 [mu]g/m\3\, 
conditional on judgments as to the appropriate values of key parameters 
to use in the context of the air-related IQ loss evidence-based 
framework discussed below.
    Further, in recognition of alternative views of the science, the 
exposure and risk assessments, the uncertainties inherent in the 
science and these assessments, and the appropriate public health policy 
responses based on the currently available information, the 
Administrator also solicits comments on whether to proceed instead with 
alternative levels of a primary Pb-TSP standard within ranges from 
above 0.30 [mu]g/m\3\ up to 0.50 [mu]g/m\3\ and below 0.10 [mu]g/m\3\. 
Based on the comments received and the accompanying rationales, the 
Administrator may adopt other standards within the range of the 
alternative levels identified above in lieu of the standards he is 
proposing today. In addition, as discussed below, the Administrator 
also solicits comments on when, if ever, it would be

[[Page 29242]]

appropriate to set a NAAQS for Pb at a level of zero.
    The Administrator's consideration of alternative levels of the 
primary Pb-TSP standard builds on his proposed conclusion, discussed 
above in section II.D.4, that the overall body of evidence indicates 
that the current Pb standard is not requisite to protect public health 
with an adequate margin of safety and that the standard should be 
revised to provide increased public health protection, especially for 
members of at-risk groups, notably including children, against an array 
of adverse health effects. These effects range from IQ loss, a health 
outcome that could be quantified in the risk assessment, to health 
outcomes that could not be directly estimated, including decrements in 
other neurocognitive functions, other neurological effects and immune 
system effects, as well as cardiovascular and renal effects in adults. 
In reaching a proposed decision about the level of the Pb primary 
standard, the Administrator has considered: the evidence-based 
considerations from the Criteria Document and the Staff Paper and those 
based on the air-related IQ loss evidence-based framework discussed 
above; the results of the exposure and risk assessments discussed above 
and in the Staff Paper, giving weight to the exposure and risk 
assessments as judged appropriate; CASAC advice and recommendations, as 
reflected in discussions of the Criteria Document, Staff Paper, and 
ANPR at public meetings, in separate written comments, and in CASAC's 
letters to the Administrator; EPA staff recommendations; and public 
comments received during the development of these documents, either in 
connection with CASAC meetings or separately. In considering what 
standard is requisite to protect public health with an adequate margin 
of safety, the Administrator is mindful that this choice requires 
judgment based on an interpretation of the evidence and other 
information that neither overstates nor understates the strength and 
limitations of the evidence and information nor the appropriate 
inferences to be drawn.
    In reaching a proposed decision on a range of levels for a revised 
standard, as in reaching a proposed decision on the adequacy of the 
current standard, the Administrator primarily considered the evidence 
in the context of the air-related IQ loss evidence-based framework 
described above in section II.E.3.a.ii. As a general matter, in 
considering this evidence-based framework, the Administrator recognizes 
that in the case of Pb there are several aspects to the body of 
epidemiological evidence that add complexity to the selection of an 
appropriate level for the primary standard. As discussed above, these 
complexities include evidence based on blood Pb as the dose metric, 
exposure pathways that are both air-related and nonair-related, and the 
absence of any discernible threshold levels in the health effects 
evidence. Further, the Administrator recognizes that there are a number 
of important uncertainties and limitations inherent in the available 
health effects evidence and related information, including 
uncertainties in the evidence of associations between total blood Pb 
and neurocognitive effects in children, especially at the lowest blood 
Pb levels evaluated in such studies, as well as uncertainties in key 
parameters used in this evidence-based framework, including C-R 
functions and air-to-blood ratios. In addition, the Administrator 
recognizes that there are currently no commonly accepted guidelines or 
criteria within the public health community that would provide a clear 
basis for reaching a judgment as to the appropriate degree of public 
health protection that should be afforded to neurocognitive effects in 
sensitive populations, such as IQ loss in children.
    The air-related IQ loss evidence-based framework considered by the 
Administrator focuses on quantitative relationships between air-related 
Pb and neurocognitive effects (e.g., IQ loss) in children, building on 
recommendations from CASAC to consider the body of evidence in a more 
quantitative manner. More specifically, this framework is premised on a 
public health goal of selecting a standard level that would prevent 
air-related IQ loss (and related effects) of a magnitude judged by the 
Administrator to be of concern in populations of children exposed to 
the level of the standard, taking into consideration uncertainties 
inherent in such estimates. In addition to this public health policy 
judgment regarding IQ loss, two other parameters are relevant to this 
framework--a C-R function for population IQ response associated with 
blood Pb level and an air-to-blood ratio. Based on the discussion of 
these parameters in section II.E.3.a above, the Administrator concludes 
that, in considering alternative standard levels below the level of the 
current standard, it is appropriate to take into account the same two 
sets of C-R functions, recognizing uncertainties in the related 
evidence, as was done in considering the adequacy of the current 
standard (as discussed above in section II.D). He notes that the first 
set of C-R functions reflects the evidence indicative of steeper slopes 
in relationships between blood Pb and IQ in children, and that the 
second set of C-R functions reflects relationships with shallower 
slopes between blood Pb and IQ in children. In addition, the 
Administrator concludes that it is appropriate to consider various air-
to-blood ratios, again recognizing the uncertainties in the relevant 
evidence. He notes that an air-to-blood ratio of 1:5 is within the 
reasonable range of values that EPA considers to be generally supported 
by the available evidence, which includes ratios of 1:3 up to 1:7.
    With regard to making a public health policy judgment as to the 
appropriate level of protection against air-related IQ loss and related 
effects, the Administrator first notes that ideally air-related (as 
well as other) exposures to environmental Pb would be reduced to the 
point that no IQ impact in children would occur. The Administrator 
recognizes, however, that in the case of setting a NAAQS, he is 
required to make a judgment as to what degree of protection is 
requisite to protect public health with an adequate margin of safety. 
The NAAQS must be sufficient but not more stringent than necessary to 
achieve that result, and does not require a zero-risk standard. 
Considering the advice of CASAC and public comments on this issue, 
notably including the comments of the American Academy of Pediatrics, 
the Administrator proposes to conclude that an air-related population 
mean IQ loss within the range of 1 to 2 points could be significant 
from a public health perspective, and that a standard level should be 
selected to provide protection from air-related population mean IQ loss 
in excess of this range.
    The Administrator considered the application of this air-related IQ 
loss framework with this target degree of protection in mind, drawing 
from the information presented in Table 7 above in section II.E.3.a.ii 
that addresses a broad range of standard levels. In so doing, the 
Administrator first focused on the estimates associated with the first 
set of C-R functions in conjunction with the range of air-to-blood 
ratios considered by EPA in this framework. Specifically, using an air-
to-blood ratio of 1:5, the Administrator notes that a standard level of 
0.10 [mu]g/m\3\ would limit the estimated degree of impact on 
population mean IQ loss from air-related Pb to no more than 1.5 points, 
the mid-point of the proposed range of protection. Using the full range 
of air-to-blood ratios considered in this framework (1:3 to 1:7), he 
notes that a standard set at this level (0.10 [mu]g/m\3\) would limit 
the estimated degree of air-

[[Page 29243]]

related impact on population mean IQ loss to a range from less than 1 
point to around 2 points. Again based on the first set of C-R 
functions, the Administrator notes that a standard level of 0.20 [mu]g/
m\3\ would also limit the estimated degree of air-related impact on 
population mean IQ loss to within the proposed range of protection 
based on using an air-to-blood ratio of 1:3.
    In considering the use of the second set of C-R functions in 
conjunction with the range of air-to-blood ratios considered in this 
framework (1:3 to 1:7), the Administrator notes for example that a 
standard set within the range of 0.10 to 0.30 [mu]g/m\3\ would limit 
the estimated degree of air-related impact on population mean IQ loss 
to a range from less than one-half point to just under 2 points. More 
specifically, based on using an air-to-blood ratio of 1:5 (the 
approximately central estimate) in conjunction with the second set of 
C-R functions, the Administrator notes that a standard level of 0.30 
[mu]g/m\3\ would limit the estimated degree of impact on population 
mean IQ loss from air-related Pb to just under 1.5 points, the mid-
point of the proposed range of protection.
    Taking these considerations into account, and based on the full 
range of information presented in Table 7 above on estimates of air-
related IQ loss in children over a broad range of alternative standard 
levels, the Administrator concludes that it is appropriate to propose a 
range of standard levels, and that a range of levels from 0.10 to 0.30 
[mu]g/m\3\ is consistent with his target for protection from air-
related IQ loss in children. In recognition of the uncertainties in 
these key parameters, the Administrator believes that the selection of 
a standard level from within this range is conditional on judgments as 
to the most appropriate parameter values to use in the context of this 
evidence-based framework. For example, he notes that placing more 
weight on the use of a C-R function with a relatively steeper slope 
would tend to support a standard level in the lower part of the 
proposed range, while placing more weight on a C-R function with a 
shallower slope would tend to support a level in the upper part of the 
proposed range. Similarly, placing more weight on a higher air-to-blood 
ratio would tend to support a standard level in the lower part of the 
proposed range, whereas placing more weight on a lower ratio would tend 
to support a level in the upper part of the range. In soliciting 
comment on a standard level within this proposed range, the 
Administrator specifically solicits comment on the appropriate values 
to use for these key parameters in the context of this evidence-based 
framework, reflecting that his proposal to revise the level of the 
primary Pb standard, defined in terms of the current Pb-TSP indicator, 
to within the range of 0.10 to 0.30 [mu]g/m\3\ is conditional on 
judgments as to the appropriate values of key parameters to use in this 
context.
    The Administrator has also considered the results of the exposure 
and risk assessments conducted for this review to provide some further 
perspective on the potential magnitude of air-related IQ loss. The 
Administrator finds that these quantitative assessments provide a 
useful perspective on the risk from air-related Pb. However, in light 
of the important uncertainties and limitations associated with these 
assessments, as discussed above in sections II.C and II.E.3.b, for 
purposes of evaluating potential new standards, the Administrator 
places less weight on the risk estimates than on the evidence-based 
assessments. Nonetheless, the Administrator finds that the risk 
estimates are roughly consistent with and generally supportive of the 
evidence-based air-related IQ loss estimates described above, as 
discussed above in section II.E.3.b. This lends support to the proposed 
range based on this evidence-based framework.
    In the Administrator's view, the above considerations, taken 
together, provide no evidence- or risk-based bright line that indicates 
a single appropriate level. Instead, there is a collection of 
scientific evidence and judgments and other information, including 
information about the uncertainties inherent in many relevant factors, 
which needs to be considered together in making this public health 
policy judgment and in selecting a standard level from a range of 
reasonable values. Based on consideration of the entire body of 
evidence and information available at this time, as well as the 
recommendations of CASAC and public comments, the Administrator is 
proposing that a standard level within the range of 0.10 to 0.30 [mu]g/
m\3\ would be requisite to protect public health, including the health 
of sensitive groups, with an adequate margin of safety. He also 
recognizes that selection of a level from within this range is 
conditional on judgments as to what C-R function and what air-to-blood 
ratio are most appropriate to use within the context of the air-related 
IQ loss framework. The Administrator notes that this proposed range 
encompasses the specific level of 0.20 [mu]g/m\3\, the upper end of the 
range recommended by CASAC and by many public commenters. The 
Administrator provisionally concludes that a standard level selected 
from within this range would reduce the risk of a variety of health 
effects associated with exposure to Pb, including effects indicated in 
the epidemiological studies at low blood Pb levels, particularly 
including neurological effects in children, and cardiovascular and 
renal effects in adults.
    Because there is no bright line clearly directing the choice of 
level within this reasonable range, the choice of what is appropriate, 
considering the strengths and limitations of the evidence, and the 
appropriate inferences to be drawn from the evidence and the exposure 
and risk assessments, is a public health policy judgment. To further 
inform this judgment, the Administrator solicits comment on the air-
related IQ loss evidence-based framework considered by the Agency and 
on appropriate parameter values to be considered in the application of 
this framework. More specifically, we solicit comment on the 
appropriate C-R function and air-to-blood ratio to be used in the 
context of the air-related IQ loss framework. The Administrator also 
solicits comment on the degree of impact of air-related Pb on IQ loss 
and other related neurocognitive effects in children considered to be 
significant from a public health perspective, and on the use of this 
framework as a basis for selecting a standard level.
    For the reasons discussed above, the Administrator proposes to 
revise the level of the primary Pb standard, defined in terms of the 
current Pb-TSP indicator, to within the range of 0.10 to 0.30 [mu]g/
m\3\, conditional on judgments as to the appropriate C-R functions and 
air-to-blood ratio to use in the context of the air-related IQ loss 
framework.
    The Administrator notes that this framework indicates that for 
standard levels above 0.30 [mu]g/m\3\ up to 0.50 [mu]g/m\3\, the 
estimated degree of impact on population mean IQ loss from air-related 
Pb would range from approximately 2 points to 5 points or more with the 
use of the first set of C-R functions and the full range of air-to-
blood ratios considered, and would extend from somewhere within the 
proposed range of 1 to 2 points IQ loss to above that range when using 
the second set of C-R functions and the full range of air-to-blood 
ratios considered. The Administrator proposes to conclude in light of 
his consideration of the evidence in the framework discussed above that 
the magnitude of air-related Pb effects at the higher blood Pb levels 
that would be allowed by standards above 0.30 up to 0.50 [mu]g/m\3\ 
would be greater than what is requisite to protect

[[Page 29244]]

public health with an adequate margin of safety.
    In addition, the Administrator notes that for standard levels below 
0.10 [mu]g/m\3\, the estimated degree of impact on population mean IQ 
loss from air-related Pb would generally be somewhat to well below the 
proposed range of 1 to 2 points air-related population mean IQ loss 
regardless of which set of C-R functions or which air-to-blood ratio 
within the range of ratios considered are used. The Administrator 
proposes to conclude that the degree of public health protection that 
standards below 0.10 [mu]g/m\3\ would likely afford would be greater 
than what is requisite to protect public health with an adequate margin 
of safety.
    Having reached this proposed decision based on the interpretation 
of the evidence, the evidence-based frameworks, the exposure/risk 
assessment, and the public health policy judgments described above, the 
Administrator recognizes that other interpretations, frameworks, 
assessments, and judgments are possible. There are also potential 
alternative views as to the range of values for relevant parameters 
(e.g., C-R function, air-to-blood ratio) in the evidence-based 
framework that might be considered supportable and the relative weight 
that might appropriately be placed on any specific value for these 
parameters within such ranges. In addition, the Administrator 
recognizes that there may be other views as to the appropriate degree 
of public health protection that should be afforded in terms of air-
related population mean IQ loss in children that would provide support 
for alternative standard levels different from the proposed range. 
Further, there may be other views as to the appropriate weight and 
interpretation to give to the exposure/risk assessment conducted for 
this review. Consistent with the goal of soliciting comment on a wide 
array of issues, the Administrator solicits comment on these and other 
issues.
    In particular, the Administrator solicits comment on alternative 
levels of a primary Pb-TSP standard of above 0.30 [mu]g/m\3\ up to 0.50 
[mu]g/m\3\. In considering the air-related IQ loss framework and the 
case when the second set of C-R functions is used in conjunction with 
the lowest air-to-blood ratio considered in this framework (i.e., 1:3), 
a standard level as high as 0.50 [mu]g/m\3\ would still limit the 
estimated degree of impact on population mean IQ loss from air-related 
Pb to no more than 1.5 points, the mid-point of the proposed range of 
protection. Comment is solicited on levels within this range and the 
associated rationale for selecting such a level in terms of the 
appropriate weight to place on relevant parameter values that may 
extend to values outside the ranges of values considered by EPA, or in 
terms of alternative evidence- or risk-based frameworks that might 
support standard levels within this range.
    In addition, the Administrator solicits comment on alternative 
levels below 0.10 [mu]g/m\3\. In considering the evidence-based 
framework discussed above, a standard level within this range would 
likely provide a degree of protection in terms of air-related 
population mean IQ loss that is greater than the proposed range based 
on the use of any of the relevant parameter values within the ranges 
considered by EPA. Comment is solicited on levels within this range and 
the associated rationale for selecting such a level in terms of the 
appropriate weight to place on relevant parameter values that may 
extend to values outside of the ranges considered by EPA, or 
alternative public health policy judgments as to the degree of 
protection that is warranted, or the appropriate weight to place on the 
results of the risk assessment.
    More broadly, as discussed above, the Administrator recognizes that 
Pb can be considered a non-threshold pollutant.\152\ In recognizing 
that no threshold has been identified below which we are scientifically 
confident that there is no risk of harm, EPA's views are consistent 
with the views of the CDC, the Federal agency that tracks children's 
blood Pb levels nationally and provides guidance on levels at which 
medical and environmental case management activities should be 
implemented (CDC, 2005a; ACCLPP, 2007). In 2005, CDC revised its 
statement on Preventing Lead Poisoning in Young Children, specifically 
recognizing the evidence of adverse health effects in children and the 
data demonstrating that no ``safe'' threshold for blood Pb had been 
identified (CDC, 2005a). EPA's views are also consistent with other 
organizations, including, for example, the American Academy of 
Pediatrics that recognized in commenting on the ANPR that ``[t]here is 
no known ``safe'' level of blood lead in children'' (AAP, 2008). In 
addition, the California Environmental Protection Agency, in a recent 
risk assessment report, recognizes that ``no safe level has been 
definitively established'' for effects of Pb in children (CalEPA, 2007, 
p. 1). Given the current state of scientific evidence, which does not 
resolve the question of whether or not there is a threshold, we 
recognize that there is no level below which we can say with scientific 
confidence that there is no risk of harm from exposure to ambient air 
related lead.
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    \152\ Similarly, in the most recent reviews of the NAAQS for 
ozone and PM, EPA recognized that the available epidemiological 
evidence neither supports nor refutes the existence of thresholds at 
the population level, while noting uncertainties and limitations in 
studies that make discerning thresholds in populations difficult 
(e.g., 73 FR 16444, March 27, 2008; 71 FR 61158, October 17, 2006).
---------------------------------------------------------------------------

    The Administrator also recognizes, as discussed in section I.A 
above, that the CAA does not require that NAAQS be established at a 
zero-risk level, but rather at a level that reduces risk sufficiently 
so as to protect public health with an adequate margin of safety. In 
setting primary standards that are ``requisite'' to provide the this 
degree of public health protection, the Supreme Court has affirmed that 
EPA's task is to establish standards that are neither more nor less 
stringent than necessary for this purpose. The question then becomes 
how the Agency should reconcile these scientific and legal 
understandings in reviewing the Pb NAAQS.
    As discussed above, EPA is proposing a range of levels for the 
primary Pb NAAQS, with the range extending down to 0.10 [mu]g/m\3\. 
This range reflects the Administrator's proposed conclusion that lower 
levels would be more than necessary to protect public health with an 
adequate margin of safety. This proposed conclusion is based in large 
part on EPA's evaluation of the evidence, recognizing important 
uncertainties in the scientific evidence and related assessments, and 
reflects the proposed public heath policy judgment of the Administrator 
on these issues. As discussed above, these uncertainties stem in part 
from the complexities of determining the health impact of air-related 
Pb given the multi-media exposure pathways for exposure to lead and the 
persistence of Pb in the environment. The major areas of uncertainty 
include the appropriate air-to-blood ratio; the apportionment of Pb 
between air-related and nonair Pb; the increasing uncertainty at lower 
blood Pb levels as to the existence, nature, and degree of health 
effects; and the uncertainty over the public health significance of 
smaller and smaller impacts on IQ or other similar neurocognitive 
metrics from exposure to air-related Pb. In recognition of such 
uncertainties, EPA is also soliciting comment on a lower range of 
standard levels below 0.10 [mu]g/m\3\.
    In so doing, EPA fully recognizes that a standard set at the lowest 
proposed level of 0.10 [mu]g/m\3\, or any non-zero level, would not be 
a risk-free standard.

[[Page 29245]]

As in numerous prior NAAQS reviews, we recognize that the CAA does not 
require that EPA set a risk-free standard. Instead, EPA is to recognize 
and take risk into account, and set a standard that is requisite to 
protect public health with an adequate margin of safety based on the 
currently available information. This calls for a public health policy 
judgment informed by many factors, most notably the nature and severity 
of the health effects at issue, the size of the population(s) at risk, 
and the kind and degree of uncertainties involved. After considering 
all of these factors in this review, the Administrator's proposed 
judgment is that a standard set below 0.10 [mu]g/m\3\ would not satisfy 
this statutory directive.
    The Administrator recognizes that the current state of the 
scientific evidence clearly indicates that health effects from Pb occur 
at much lower blood Pb levels than we understood in the past, and that 
the appropriate level for ambient air Pb is much lower than we thought 
in the past. Further the Administrator expects that, as time goes on, 
future scientific studies will continue to enhance our understanding of 
Pb, and anticipates that such studies might lead to a situation where 
there is very little, if any, remaining uncertainty about human health 
impacts from even extremely low levels of Pb in the ambient air. As 
noted above, this has the potential to raise fundamental questions as 
to how the Agency can continue to reconcile such evidence with the 
statutory provision calling for the NAAQS to be set at a level that is 
requisite to protect public health with an adequate margin of safety. 
Faced with scientific evidence that could reasonably be interpreted as 
demonstrating that any ambient Pb level above zero contributes to 
adverse health effects in at-risk populations, some might conclude that 
the only standard requisite to protect public health with an adequate 
margin of safety would be a standard set at zero. While EPA's proposed 
conclusions on the current scientific evidence and an appropriate 
standard based on that evidence and on its interpretation of the 
statute clearly differ from such a view, EPA nonetheless believes that 
inviting comment in this review on the views described above and the 
issues raised by such circumstances is appropriate.
    More specifically, EPA invites comment on when, if ever, it would 
be appropriate to set a NAAQS for Pb at a level of zero. Comments on 
this question might address issues such as: The level of scientific 
certainty that would be needed to support such a decision; the level of 
harm, e.g., severity of health effect and size of affected population, 
that would be needed to support such a decision; and whether there are 
normative or quantitative criteria that could be applied in deciding 
whether, and if so, when it would be appropriate to set a standard at 
zero. EPA invites comment on how to reconcile the above issues in this 
and subsequent NAAQS reviews.
4. Level for a Pb NAAQS with a Pb-PM10 Indicator
    EPA is requesting comment on the option of revising the indicator 
for the Pb NAAQS from Pb-TSP to Pb-PM10, based on low-volume 
sample collection as discussed above in section II.E.1 and below in 
section V.A. In this section, we discuss considerations important to 
selection of a level for such a Pb-PM10-based standard 
(section II.E.4.a) and CASAC's advice and public comments on this issue 
(section II.E.4.b). Approaches for adjusting the level of a Pb NAAQS 
with Pb-TSP indicator for a Pb-PM10-based standard, and a 
range of levels for a Pb-PM10-based standard, under 
consideration and on which EPA is soliciting comment are presented in 
II.E.4.c.
a. Considerations With Regard to Particles Not Captured by 
PM10
    In the course of deciding to propose the Pb-TSP indicator approach 
as described in section II.E.1 above, EPA has noted the important role 
of both respirable and non-respirable Pb particles in air-related Pb 
exposure of concern and the lesser capture of these particles by 
PM10 samplers compared to TSP samplers. We recognize that 
the health evidence indicates that Pb in all particle size fractions, 
not just respirable Pb, contributes to Pb in blood and to associated 
health effects. Further, the quantity of Pb in ambient particles with 
the potential to deposit (indoors and outdoors, leading to a role in 
ingestion pathways) is a key contributor to air-related exposure, and 
these particles include ultra-coarse mode particles that are not 
captured by PM10 samplers (as discussed in section II.E.1 
above). In recognition of these considerations, both of the indicator 
options discussed in this notice recognize the need to consider use of 
an adjustment related to the use of PM10 measurements, 
either when considering the optional use of Pb-PM10 data for 
comparison with a Pb-TSP-based NAAQS, or when considering a level for a 
NAAQS based on a Pb-PM10 indicator.
    Section II.E.1 above contains extensive discussion of the 
relationship between Pb-PM10 and Pb-TSP, including the fact 
that Pb-PM10/Pb-TSP relationships vary from site to site and 
from time to time, but have a systematic variation with distance from 
emissions sources emitting particles larger than would be captured by 
Pb-PM10 samplers, such that generally there are larger 
differences between Pb-PM10 and Pb-TSP near sources. Section 
II.E.1 goes on to identify and solicit comment on two ranges from which 
scaling factors could be chosen that would be applied to the Pb-
PM10 measurements to derive surrogate Pb-TSP concentrations 
for use in making comparisons to a Pb-TSP-based NAAQS. In recognition 
of the influence of proximity to sources on the relationship between 
Pb-TSP and Pb-PM10 measurements for source types with a high 
fraction of ultra-coarse particles containing Pb, different scaling 
factors are identified for source-oriented monitoring sites and 
nonsource-oriented monitoring sites (as described in section II.E.1). 
These ranges have been developed based on analyses of the available 
collocated Pb-TSP and Pb-PM10 data (Schmidt and Cavender, 
2008) and recognition of variability and uncertainty inherent in this 
data set.
    The data supporting the range for source-oriented scaling factors, 
as discussed in Schmidt and Cavender (2008), indicate the potential, in 
areas influenced by some types of sources (e.g., Pb smelters), for 
PM10 samplers to capture as little as approximately 50% of 
the Pb that is measured with Pb-TSP monitors. The data from 20 sites 
not known to be near Pb sources show a range of ratios between Pb-TSP 
and Pb-PM10 that vary from day to day and between sites. 
When rounded to one decimal place, these ratios of the multi-day mean 
concentration of Pb-TSP to the same statistic for Pb-PM10 at 
each site ranged from 1.0 to 1.9.\153\ Eighty-five percent of the sites 
had ratios between 1.0 and 1.4, and slightly over one-half the sites 
had ratios between 1.0 and 1.2. This is consistent with the conceptual 
model that concentrations of ultra-coarse particles of Pb are quite low 
at sites not near the primary sources of such particles, such that Pb-
PM10 monitors at such sites would tend to collect the large 
majority, but generally not all, of total airborne Pb.
---------------------------------------------------------------------------

    \153\ On individual days, the ratio between the two measures was 
sometimes below 1.0 or well over 2.0, which may be the result of 
sampler errors and data rounding particularly when concentrations of 
one or both measures were low. Accordingly, EPA considers the ratio 
of the multi-day mean concentration of Pb-TSP to the same statistic 
for Pb-PM10 at each site to be a better indicator of 
typical monitor behavior.
---------------------------------------------------------------------------

    In considering the need for and magnitude of a potential adjustment 
to derive a standard level for a Pb-PM10-

[[Page 29246]]

based NAAQS, we note the inherent variability in the TSP sampling 
methodology which will contribute variability to relationships derived 
between Pb-PM10 and Pb-TSP data. We also note the influence 
on such relationships of proximity to sources of Pb particles that 
would not be captured by PM10 samplers. This latter 
influence is evident in the difference between the two ranges of 
scaling factors proposed in section II.E.1 above.
    We are also aware of the limitations of the dataset available on 
which to base these decisions, including those related to the quantity 
of collocated measurements and particularly the very limited number of 
source-influenced monitors for which such measurements are available, 
and the correspondingly limited number of types of sources represented. 
Moreover, the available collocated measurements suggesting the above-
referenced 50% figure in a source-influenced location are from 
conditions in which ambient concentrations were above the current 
standard level and well above the proposed range of levels. If the 
contributing emissions sources had been controlled so that local 
concentrations were within or near the range proposed for the revised 
standard, it is unclear whether the relationship between Pb-
PM10 and Pb-TSP data would have been different or not. The 
Pb-TSP concentrations at sites in the dataset analyzed that were not 
known to be source-influenced were well below the proposed range of 
standard levels, leaving uncertainty about typical proportions of 
ultra-coarse particles in nonsource areas with Pb-TSP concentrations 
near the proposed range of levels.
    If EPA adopts a PM10 indicator, the approach of using 
two adjustment factors representing source-oriented and nonsource-
oriented sites, or the approach of site-specific adjustment factors, 
would not be used in setting a standard level.\154\ Rather, the 
complexity of the site-to-site variability in the Pb-TSP/Pb-
PM10 relationship would have to be reflected in a decision 
about whether and how to adjust the level of the standard to account 
for the fact that a Pb-PM10 indicator would be less 
inclusive of Pb particles than would a Pb-TSP indicator.
---------------------------------------------------------------------------

    \154\ As discussed below in sections IV and VI, however, EPA is 
soliciting comment on the potential use of Pb-TSP data for initial 
designations for Pb-PM10 standard and whether the 
associated use of scaling factors would be appropriate.
---------------------------------------------------------------------------

b. CASAC Advice
    As noted above, CASAC has described the use of an adjustment of the 
NAAQS level to accommodate the loss of the ultra-coarse Pb particles 
that are important contributions to Pb exposure but that are excluded 
by PM10 samplers (section II.E.1). For example, in 
discussion of the recommendation for the Agency to revise the Pb NAAQS 
indicator to Pb-PM10 (using low-volume samplers) in their 
February 2007 letter, the CASAC Pb Panel stated that ``Presumably a 
downward scaling of the level of the Lead NAAQS could accommodate the 
loss of very large coarse-mode lead particles * * * '' (Henderson, 
2007a). With regard to the magnitude of such scaling, CASAC has 
recognized the usefulness of some ``short period of concurrent 
PM10 and TSP lead sampling'' to ``help develop site-specific 
scaling factors at sites with highest concentrations'' (Henderson, 
2007a) and also indicated an expectation that, in general, Pb-
PM10 will represent a large fraction of, and be highly 
correlated with TSP Pb (Henderson, 2007b). In their most recent letter, 
the Panel stated generally that ``it would be well within EPA's range 
of discretionary options to accept a slight loss of ultra-coarse lead 
at some monitoring sites by selecting an appropriately conservative 
level for the revised Pb NAAQS'' (Henderson, 2008). In summary, while 
the CASAC recognized the appropriateness of making an adjustment to the 
level for a Pb-PM10-based NAAQS, they did not provide a 
quantitative value, but did note interest in sites with highest 
concentrations. Further, CASAC expressed the view that the overall 
health-related benefits from moving to a PM10-based standard 
could outweigh a small loss in protection from exposure to ultra-coarse 
particles in some areas.
    The Agency received few public comments with regard to a standard 
level for a revised indicator of Pb-PM10. Of these, some 
generally agreed with CASAC that an adjustment to the level was 
appropriate, recognizing the difference in the two sampling methods. 
Some were concerned that the current data may not support the 
derivation of a single scaling or adjustment factor that would provide 
requisite protection for some communities near some large point source 
emitters of dust.
c. Approaches for Levels for a PM10-Based Standard
    For the reasons identified in the preceding section and in section 
II.E.1 above, EPA's consideration of a Pb-PM10 indicator is 
accompanied by consideration of an adjustment of the proposed level for 
the standard, in recognition of the importance for public health of 
those ultra-coarse dust contributions not captured by PM10 
samplers.
    In considering the appropriate level for a standard for which the 
indicator is Pb-PM10, EPA recognizes the importance of all 
particle size fractions and the dominant role of the ingestion pathway 
in contributing to human exposures to air-related Pb. We also recognize 
that the proportion of Pb captured by TSP monitors that is not captured 
by PM10 monitors will vary, not only in reflection of the 
inherent greater variability of the TSP sampler (as compared to the 
PM10 sampler), but also based on proximity to sources 
emitting ultra-coarse Pb particles. An appreciably lower proportion of 
the Pb captured by TSP monitors will be captured by PM10 
monitors in areas near such sources (e.g., Pb smelters).
    However, we are also aware of the limitations with regard to the 
available Pb monitoring data on which to base a decision with regard to 
an adjustment that appropriately recognizes these considerations. EPA 
notes that at lower levels, there is increased uncertainty as to the 
appropriate scaling factor to use, particularly in light of the very 
limited data we have on which to base an analysis. Additionally, we 
take note of advice from CASAC and public comments with regard to 
considerations for a level to accompany a Pb-PM10 indicator.
    Based on these and other considerations summarized above (II.E.1 
and II.E.4.a), including the data indicating the proportion of Pb-TSP 
that may not be captured by PM10 samplers in some source-
oriented locations, EPA requests comment on whether a level for a NAAQS 
with a Pb-PM10 indicator should be based on an adjustment to 
a lower level than the level for a NAAQS with a Pb-TSP indicator, and, 
if so, on the magnitude of the adjustment that would be appropriate. 
Taking into consideration uncertainties in the appropriate adjustment 
for a Pb-PM10 based level (due to the very limited 
collocated dataset with which to evaluate relationships between Pb-TSP 
and Pb-PM10), and the appropriate policy responses based on 
the currently available information, EPA specifically solicits comment 
on the appropriate level for a Pb-PM10-based primary 
standard within the full range of levels on which comment is being 
solicited for a Pb-TSP standard, i.e., levels up to 0.50 [mu]g/m\3\. 
Based on the comments received and the accompanying rationales, EPA may 
adopt standards within this broad range of alternative levels.

[[Page 29247]]

F. Proposed Decision on the Primary Standard

    For the reasons discussed above, and taking into account 
information and assessments presented in the Criteria Document and 
Staff Paper, the advice and recommendations of CASAC, and the public 
comments to date, the Administrator is proposing options for the 
revision of the various elements of the standard to provide increased 
protection for children and other at-risk populations against an array 
of adverse health effects, most notably including neurological effects, 
including neurocognitive and neurobehavioral effects, in children. 
Specifically, with regard to the indicator and level of the standard, 
the Administrator proposes to revise the level of the standard to a 
level within the range of 0.10 to 0.30 [mu]g/m\3\ in conjunction with 
retaining the current indicator of Pb-TSP but with allowance for the 
use of Pb-PM10 data. The Administrator also solicits comment 
on alternative levels up to 0.50 [mu]g/m\3\ and down below 0.10 [mu]g/
m\3\. With regard to the form and averaging time of the standard, the 
Administrator proposes two options: (1) To retain the current averaging 
time of a calendar quarter and the current not-to-be-exceeded form, to 
apply across a 3-year span, and (2) to revise the averaging time to a 
calendar month and the form to be the second-highest monthly average 
across a 3-year span.
    Corresponding revisions to data handling conventions and the 
schedule for States to request exclusion of ambient Pb concentration 
data affected by exceptional events are specified in proposed revisions 
to Appendix R, as discussed in section IV below. Corresponding 
revisions to aspects of the ambient air monitoring and reporting 
requirements for Pb are discussed in section V below, including 
sampling and analysis methods (e.g., a new Federal reference method for 
monitoring Pb in PM10, quality assurance requirements), 
network design, sampling schedule, data reporting, and other 
miscellaneous requirements.
    In recognition of alternative views of the science and the exposure 
and risk assessments, the uncertainties inherent in this information, 
and the appropriate policy responses based on the currently available 
information, the Administrator also solicits comments on other options. 
More specifically, the Administrator solicits comment on revising the 
indicator to Pb-PM10 and on the same broad range of levels 
on which EPA is soliciting comment for the proposed Pb-TSP indicator, 
i.e., up to 0.50 [mu]g/m\3\. In addition, the Administrator invites 
comment on when, if ever, it would be appropriate to set a NAAQS for Pb 
at a level of zero. Based on the comments received and the accompanying 
rationales, the Administrator may adopt other standards within the 
range of the alternative levels identified above in lieu of the 
standards he is proposing today.

III. Rationale for Proposed Decision on the Secondary Standard

    This section presents the rationale for the Administrator's 
proposed decision to revise the existing secondary NAAQS. In 
considering the currently available evidence on Pb-related welfare 
effects, the Staff Paper notes that there is much information linking 
Pb to potentially adverse effects on organisms and ecosystems. However, 
given the evaluation of this information in the Criteria Document and 
Staff Paper which highlighted the substantial limitations in the 
evidence, especially the lack of evidence linking various effects to 
specific levels of ambient Pb, the Administrator concludes that the 
available evidence supports revising the secondary standard but does 
not provide a sufficient basis for establishing a distinct secondary 
standard for Pb.

A. Welfare Effects Information

    Welfare effects addressed by the secondary NAAQS include, but are 
not limited to, effects on soils, water, crops, vegetation, manmade 
materials, animals, wildlife, weather, visibility and climate, damage 
to and deterioration of property, and hazards to transportation, as 
well as effects on economic values and on personal comfort and well-
being. A qualitative assessment of welfare effects evidence related to 
ambient Pb is summarized in this section, drawing from Chapter 6 of the 
Staff Paper. The presentation here first recognizes several key aspects 
of the welfare evidence for Pb. Lead is persistent in the environment 
and accumulates in soils, aquatic systems (including sediments), and 
some biological tissues of plants, animals, and other organisms, 
thereby providing long-term, multipathway exposures to organisms and 
ecosystems.
    Additionally, EPA recognizes that there have been a number of uses 
of Pb, especially as an ingredient in automobile fuel but also in other 
products such as paint, lead-acid batteries, and some pesticides, which 
have significantly contributed to widespread increases in Pb 
concentrations in the environment, a portion of which remains today 
(e.g., CD, Chapters 2 and 3).
    Ecosystems near smelters, mines, and other industrial sources of Pb 
have demonstrated a wide variety of adverse effects including decreases 
in species diversity, loss of vegetation, changes to community 
composition, decreased growth of vegetation, and increased number of 
invasive species. These sources may have multiple pathways for 
discharging Pb to ecosystems, and apportioning effects between air-
related pathways and other pathways (e.g. discharges to water) in such 
cases is difficult. Likewise, apportioning these effects between Pb and 
other stressors is complicated because these point sources also emit a 
wide variety of other heavy metals and sulfur dioxide which may cause 
toxic effects. There are no field studies which have investigated 
effects of Pb additions alone but some studies near large point sources 
of Pb have found significantly reduced species composition and altered 
community structures. While these effects are significant, they are 
spatially limited: the majority of contamination occurs within 20 to 50 
km of the emission source (CD, AX7.1.4.2).
    By far, the majority of air-related Pb found in terrestrial 
ecosystems was deposited in the past during the use of Pb additives in 
gasoline. This gasoline-derived Pb was emitted predominantly in small 
size particles which were widely dispersed and transported across large 
distances. Many sites receiving Pb predominantly through such long-
range transport have accumulated large amounts of Pb in soils (CD, p. 
AX7-98). There is little evidence that terrestrial sites exposed as a 
result of this long range transport of Pb have experienced significant 
effects on ecosystem structure or function (CD, AX7.1.4.2, p. AX7-98). 
Strong complexation of Pb by soil organic matter may explain why few 
ecological effects have been observed (CD, p. AX7-98). Studies have 
shown decreasing levels of Pb in vegetation which seems to correlate 
with decreases in atmospheric deposition of Pb resulting from the 
removal of Pb additives to gasoline (CD, AX 7.1.4.2).
    Terrestrial ecosystems remain primarily sinks for Pb but amounts 
retained in various soil layers vary based on forest type, climate, and 
litter cycling (CD, section 7.1). Once in the soil, the migration and 
distribution of Pb is controlled by a multitude of factors including 
pH, precipitation, litter composition, and other factors which govern 
the rate at which Pb is bound to organic materials in the soil (CD, 
section 2.3.5).
    Like most metals the solubility of Pb is increased at lower pH. 
However, the

[[Page 29248]]

reduction of pH may in turn decrease the solubility of dissolved 
organic material (DOM). Given the close association between Pb mobility 
and complexation with DOM, a reduced pH does not necessarily lead to 
increased movement of Pb through terrestrial systems and into surface 
waters. In areas with moderately acidic soil (i.e., pH of 4.5 to 5.5) 
and abundant DOM, there is no appreciable increase in the movement of 
Pb into surface waters compared to those areas with neutral soils 
(i.e., pH of approximately 7.0). This appears to support the theory 
that the movement of Pb in soils is limited by the solubilization and 
transport of DOM. In sandy soils without abundant DOM, moderate 
acidification appears likely to increase outputs of Pb to surface 
waters (CD, AX 7.1.4.1).
    Lead exists in the environment in various forms which vary widely 
in their ability to cause adverse effects on ecosystems and organisms. 
Current levels of Pb in soil also vary widely depending on the source 
of Pb but in all ecosystems Pb concentrations exceed natural background 
levels. The deposition of gasoline-derived Pb into forest soils has 
produced a legacy of slow moving Pb that remains bound to organic 
materials despite the removal of Pb from most fuels and the resulting 
dramatic reductions in overall deposition rates. For areas influenced 
by point sources of air Pb, concentrations of Pb in soil may exceed by 
many orders of magnitude the concentrations which are considered 
harmful to laboratory organisms. Adverse effects associated with Pb 
include neurological, physiological, and behavioral effects which may 
influence ecosystem structure and functioning. Ecological soil 
screening levels (Eco-SSLs) have been developed for Superfund site 
characterizations to indicate concentrations of Pb in soils below which 
no adverse effects are expected to plants, soil invertebrates, birds, 
and mammals. Values like these may be used to identify areas in which 
there is the potential for adverse effects to any or all of these 
receptors based on current concentrations of Pb in soils.
    Atmospheric Pb enters aquatic ecosystems primarily through the 
erosion and runoff of soils containing Pb and deposition (wet and dry). 
While overall deposition rates of atmospheric Pb have decreased 
dramatically since the removal of Pb additives from gasoline, Pb 
continues to accumulate and may be re-exposed in sediments and water 
bodies throughout the United States (CD, section 2.3.6).
    Several physical and chemical factors govern the fate and 
bioavailability of Pb in aquatic systems. A significant portion of Pb 
remains bound to suspended particulate matter in the water column and 
eventually settles into the substrate. Species, pH, salinity, 
temperature, turbulence, and other factors govern the bioavailability 
of Pb in surface waters (CD, section 7.2.2).
    Lead exists in the aquatic environment in various forms and under 
various chemical and physical parameters which determine the ability of 
Pb to cause adverse effects either from dissolved Pb in the water 
column or Pb in sediment. Current levels of Pb in water and sediment 
also vary widely depending on the source of Pb. Conditions exist in 
which adverse effects to organisms and thereby ecosystems may be 
anticipated given experimental results. It is unlikely that dissolved 
Pb in surface water constitutes a threat to ecosystems that are not 
directly influenced by point sources. For Pb in sediment, the evidence 
is less clear. It is likely that some areas with long term historical 
deposition of Pb to sediment from a variety of sources as well as areas 
influenced by point sources have the potential for adverse effects to 
aquatic communities. The long residence time of Pb in sediment and its 
ability to be resuspended by turbulence make Pb likely to be a factor 
for the foreseeable future. Criteria have been developed to indicate 
concentrations of Pb in water and sediment below which no adverse 
effects are expected to aquatic organisms. These values may be used to 
identify areas in which there is the potential for adverse effects to 
receptors based on current concentrations of Pb in water and sediment.

B. Screening Level Ecological Risk Assessment

    This section presents a brief summary of the screening-level 
ecological risk assessment conducted by EPA for this review. The 
assessment is described in detail in Lead Human Exposure and Health 
Risk Assessments and Ecological Risk Assessment for Selected Areas, 
Pilot Phase (ICF, 2006). Funding constraints have precluded performance 
of a full-scale ecological risk assessment. The discussion here is 
focused on the screening level assessment performed in the pilot phase 
(ICF, 2006) and takes into consideration CASAC recommendations with 
regard to interpretation of this assessment (Henderson, 2007a, b). The 
following summary focuses on key features of the approach used in the 
assessment and presents only a brief summary of the results of the 
assessment. A complete presentation of results is provided in the pilot 
phase Risk Assessment Report (ICF, 2006) and summarized in Chapter 6 of 
the Staff Paper.
1. Design Aspects of Assessment and Associated Uncertainties
    The screening level risk assessment involved several location-
specific case studies and a national-scale surface water and sediment 
screen. The case studies included areas surrounding a primary Pb 
smelter and a secondary Pb smelter, as well as a location near a 
nonurban roadway. An additional case study for an ecologically 
vulnerable location was identified and described (ICF, 2006), but 
resource constraints have precluded risk analysis for this location.
    The case study analyses were designed to estimate the potential for 
ecological risks associated with exposures to Pb emitted into ambient 
air. Soil, surface water, and/or sediment concentrations were estimated 
from available monitoring data or modeling analysis, and then compared 
to ecological screening benchmarks to assess the potential for 
ecological impacts from Pb that was emitted into the air. Results of 
these comparisons are not definitive estimates of risk, but rather 
serve to identify those locations at which there is the greatest 
likelihood for adverse effect. Similarly, the national-scale screening 
assessment evaluated surface water and sediment monitoring locations 
across the United States for the potential for ecological impacts 
associated with atmospheric deposition of Pb. The reader is referred to 
the pilot phase Risk Assessment Report (ICF, 2006) for details on the 
use of this information and models in the screening assessment.
    The measures of exposure for these analyses are total Pb 
concentrations in soil, dissolved Pb concentrations in fresh surface 
waters (water column), and total Pb concentrations in freshwater 
sediments. The hazard quotient (HQ) approach was then used to compare 
Pb media concentrations with ecological screening values. The exposure 
concentrations were estimated for the three case studies and the 
national-scale screening analyses as described below:
     For the primary Pb smelter case study, measured 
concentrations of total Pb in soil, dissolved Pb in surface waters, and 
total Pb in sediment were used to develop point estimates for sampling 
clusters thought to be associated with atmospheric Pb deposition, 
rather than Pb associated with nonair sources, such as runoff from 
waste storage piles.
     For the secondary Pb smelter case study, concentrations of 
Pb in soil were

[[Page 29249]]

estimated using fate and transport modeling based on EPA's MPE 
methodology (USEPA, 1998) and data available from similar locations.
     For the near roadway nonurban case study, measured soil 
concentration data collected from two interstate sampling locations, 
one with fairly high-density development (Corpus Christi, Texas) and 
another with medium-density development (Atlee, Virginia), were used to 
develop estimates of Pb in soils for each location.
     For the national-scale surface water and sediment 
screening analyses, measurements of dissolved Pb concentrations in 
surface water and total Pb in sediment for locations across the United 
States were compiled from available databases (USGS, 2004). Air 
emissions, surface water discharge, and land use data for the areas 
surrounding these locations were assessed to identify locations where 
atmospheric Pb deposition may be expected to contribute to potential 
ecological impacts. The exposure assessment focused on these locations.
    The ecological screening values used in this assessment were 
developed from the Eco-SSLs methodology, EPA's recommended ambient 
water quality criteria, and sediment screening values developed by 
MacDonald and others (2000, 2003). Soil screening values were derived 
for this assessment using the Eco-SSL methodology with the toxicity 
reference values for Pb (USEPA, 2005d, 2005e) and consideration of the 
inputs on diet composition, food intake rates, incidental soil 
ingestion, and contaminant uptake by prey (details are presented in 
section 7.1.3.1 and Appendix L, of ICF, 2006). Hardness-specific 
surface water screening values were calculated for each site based on 
EPA's recommended ambient water quality criteria for Pb (USEPA, 1984). 
For sediment screening values, the assessment relied on sediment 
``threshold effect concentrations'' and ``probable effect 
concentrations'' developed by MacDonald et al (2000). The methodology 
for these sediment criteria is described more fully in section 7.1.3.3 
and Appendix M of the pilot phase Risk Assessment Report (ICF, 2006).
    The HQ is calculated as the ratio of the media concentration to the 
ecotoxicity screening value, and represented by the following equation:

HQ = (estimated Pb media concentration)/(ecotoxicity screening value)

    For each case study, HQ values were calculated for each location 
where either modeled or measured media concentrations were available. 
Separate soil HQ values were calculated for each ecological receptor 
group for which an ecotoxicity screening value has been developed 
(i.e., birds, mammals, soil invertebrates, and plants). HQ values less 
than 1.0 suggest that Pb concentrations in a specific medium are 
unlikely to pose significant risks to ecological receptors. HQ values 
greater than 1.0 indicate that the expected exposure exceeds the 
ecotoxicity screening value and that there is a potential for adverse 
effects.
    There are several uncertainties that apply across case studies 
noted below:
     The ecological risk screen is limited to specific case 
study locations and other locations for which dissolved Pb data were 
available and evaluated in the national-scale surface water and 
sediment screens. In identifying sites for inclusion in the assessment, 
efforts were made to ensure that the Pb exposures assessed were 
attributable to airborne Pb and not dominated by nonair sources. 
However, there is uncertainty as to whether other sources might have 
actually contributed to the Pb exposure estimates.
     A limitation to using the selected ecotoxicity screening 
values is that they might not be sufficient to identify risks to some 
threatened or endangered species or unusually sensitive aquatic 
ecosystems (e.g., CD, p. AX7-110).
     The methods and database from which the surface water 
screening values (i.e., the AWQC for Pb) were derived is somewhat 
dated. New data and approaches (e.g., use of pH as indicator of 
bioavailability) may now be available to estimated the aquatic toxicity 
of Pb (CD, sections AX7.2.1.2 and AX7.2.1.3).
     No adjustments were made for sediment-specific 
characteristics that might affect the bioavailability of Pb in 
sediments in the derivation of the sediment quality criteria used for 
this ecological risk screen (CD, sections 7.2.1 and AX7.2.1.4; Appendix 
M, ICF, 2006). Similarly, characteristics of soils for the case study 
locations were not evaluated for measures of bioavailability.
     Although the screening value for birds used in this 
analysis is based on reasonable estimates for diet composition and 
assimilation efficiency parameters, it was based on a conservative 
estimate of the relative bioavailability of Pb in soil and natural 
diets compared with water soluble Pb added to an experimental pellet 
diet (Appendix L, ICF, 2006).
2. Summary of Results
    The following is a brief summary of key observations related to the 
results of the screening-level ecological risk assessment. A more 
complete discussion of the results is provided in Chapter 6 of the 
Staff Paper and the complete presentation of the assessment and results 
is presented in the pilot phase Risk Assessment Report (ICF, 2006).
     The national-scale screen of surface water data initially 
identified some 42 sample locations of which 15 were then identified as 
unrelated to mining sites and having water column levels of dissolved 
Pb that were greater than hardness adjusted chronic criteria for the 
protection of aquatic life (with one location having a HQ of 15), 
indicating a potential for adverse effect if concentrations were 
persistent over chronic periods. Acute criteria were not exceeded at 
any of these locations. The extent to which air emissions of Pb have 
contributed to these surface water Pb concentrations is unclear.
     In the national-scale screen of sediment data associated 
with the 15 surface water sites described above, threshold effect 
concentration-based HQs at nine of these sites exceeded 1.0. 
Additionally, HQs based on probable effect concentrations exceeded 1.0 
at five of the sites, indicating probable adverse effects to sediment 
dwelling organisms. Thus, sediment Pb concentrations at some sites are 
high enough that there is a likelihood that they would cause adverse 
effects to sediment dwelling organisms. However, the contribution of 
air emissions to these concentrations is unknown.
     In the primary Pb smelter case study, for which 
measurements were used to estimate nonair media concentrations, all 
three of the soil sampling clusters (including the ``reference areas'') 
had HQs that exceeded 1.0 for birds. Samples from one cluster also had 
HQs greater than 1.0 for plants and mammals. The surface water sampling 
clusters all had measurements below the detection limit of 3.0 [mu]g/L. 
However, three sediment sample clusters had HQs greater than 1.0. In 
summary, the concentrations of Pb in soil and sediments exceed 
screening values for these media indicating potential for adverse 
effects to terrestrial organisms (plants, birds and mammals) and to 
sediment dwelling organisms. While the contribution to these Pb 
concentrations from air as compared to nonair sources is not 
quantified, air emissions from this facility are substantial (Appendix 
D, USEPA 2007b; ICF 2006). Further, the contribution of air Pb under 
the current NAAQS to these concentrations as compared to that prior to 
the current NAAQS is unknown.

[[Page 29250]]

     In the secondary Pb smelter case study, the soil 
concentrations, developed from soil data for similar locations, 
resulted in avian HQs greater than 1.0 for all distance intervals 
evaluated. The soil concentrations within 1 km of the facility, scaled 
using a combination of measurements and modeling (as described in the 
Staff Paper, Chapter 6) also showed HQs greater than 1.0 for plants, 
birds, and mammals. These estimates indicate a potential for adverse 
effect to those receptor groups. We note that the contribution of 
nonair sources to these concentrations is unknown. Further, the 
contribution of air Pb under the current NAAQS to these concentrations 
as compared to that prior to the current NAAQS is also unknown.
     In the nonurban, near roadway case study, HQs for birds 
and mammals were greater than 1.0 at all but one of the distances from 
the road. Plant HQs were greater than 1.0 at the closest distance. In 
summary, HQs above one were estimated for plants, birds and mammals, 
indicating potential for adverse effect to these receptor groups. We 
note that the contribution of air Pb under the current NAAQS to these 
concentrations as compared to that prior to the current NAAQS is 
unknown.

C. The Secondary Standard

    The NAAQS provisions of the Act require the Administrator to 
establish secondary standards that, in the judgment of the 
Administrator, are requisite to protect the public welfare from any 
known or anticipated adverse effects associated with the presence of 
the pollutant in the ambient air. In so doing, the Administrator seeks 
to establish standards that are neither more nor less stringent than 
necessary for this purpose. The Act does not require that secondary 
standards be set to eliminate all risk of adverse welfare effects, but 
rather at a level requisite to protect public welfare from those 
effects that are judged by the Administrator to be adverse.
    The following discussion starts with background information on the 
current standard (section III.C.1). The general approach for this 
current review is summarized in section III.C.2. Considerations and 
conclusions with regard to the adequacy of the current standard are 
discussed in section III.C.3, with evidence and exposure-risk-based 
considerations in sections III.C.3.a and b, respectively, followed by a 
summary of CASAC advice and recommendations (section III.C.3.c) and the 
Administrator's proposed conclusions (section III.C.3.d). 
Considerations, conclusions and the Administrator's proposed decision 
with regard to elements of the secondary standard are discussed in 
section III.C.4.
1. Background on the Current Standard
    The current standard was set in 1978 to be identical to the primary 
standard (1.5 [mu]g Pb/m\3\, as a maximum arithmetic mean averaged over 
a calendar quarter), the basis for which is summarized in Section 
II.C.1. At the time the standard was set, the Agency concluded that the 
primary air quality standard would adequately protect against known and 
anticipated adverse effects on public welfare, as the Agency stated 
that it did not have evidence that a more restrictive secondary 
standard was justified. In the rationale for this conclusion, the 
Agency stated that the available evidence cited in the 1977 Criteria 
Document indicated that ``animals do not appear to be more susceptible 
to adverse effects from lead than man, nor do adverse effects in 
animals occur at lower levels of exposure than comparable effects in 
humans'' (43 FR 46256). The Agency recognized that Pb may be deposited 
on the leaves of plants and present a hazard to grazing animals. With 
regard to plants, the Agency stated that Pb is absorbed but not 
accumulated to any great extent by plants from soil, and that although 
some plants may be susceptible to Pb, it is generally in a form that is 
largely nonavailable to them. Further the Agency stated that there was 
no evidence indicating that ambient levels of Pb result in significant 
damage to manmade materials and Pb effects on visibility and climate 
are minimal.
    The secondary standard was subsequently considered during the 1980s 
in development of the 1986 Criteria Document (USEPA, 1986a) and the 
1990 Staff Paper (USEPA, 1990). In summarizing OAQPS staff conclusions 
and recommendations at that time, the 1990 Staff Paper stated that a 
qualitative assessment of available field studies and animal 
toxicological data suggested that ``domestic animals and wildlife are 
as susceptible to the effects of lead as laboratory animals used to 
investigate human lead toxicity risks.'' Further, the 1990 Staff Paper 
highlighted concerns over potential ecosystem effects of Pb due to its 
persistence, but concluded that pending development of a stronger 
database that more accurately quantifies ecological effects of 
different Pb concentrations, consideration should be given to retaining 
a secondary standard at or below the level of the then-current 
secondary standard of 1.5 [mu]g/m\3\.
2. Approach for Current Review
    In evaluating whether it is appropriate to retain the current 
secondary Pb standard, or whether revision is appropriate, the 
Administrator has considered the evidence and risk analyses presented 
in the Criteria Document, the Staff Paper, the ANPR and the associated 
technical support documents, [together with the associated 
uncertainties] and CASAC advice and public comment on these documents. 
The Staff Paper and ANPR recognize that the available welfare effects 
evidence generally reflects laboratory-based evidence of toxicological 
effects on specific organisms exposed to concentrations of Pb at which 
scientists generally agree that adverse effects are likely to occur. It 
is widely recognized, however, that environmental exposures are likely 
to be at lower concentrations and/or accompanied by significant 
confounding factors (e.g., other metals, acidification), which 
increases our uncertainty about the likelihood and magnitude of the 
organism and ecosystem response.
3. Conclusions on Adequacy of the Current Standard
a. Evidence-Based Considerations
    In considering the welfare effects evidence with respect to the 
adequacy of the current standard, the Administrator considers not only 
the array of evidence newly assessed in the Criteria Document but also 
that assessed in the 1986 Criteria Document and summarized in the 1990 
Staff Paper. As discussed extensively in the latter two documents, 
there was a significantly improved characterization of environmental 
effects of Pb in the ten years after the Pb NAAQS was set. And in the 
subsequent nearly 20 years, many additional studies on Pb effects in 
the environment are now available (2006 Criteria Document). Some of the 
more relevant aspects of the evidence available since the standard was 
set include the following:
     A more quantitative determination of the mobility, 
distribution, uptake, speciation, and fluxes of atmospherically 
delivered Pb in terrestrial ecosystems shows that the binding of Pb to 
organic materials in the soil slows its mobility through soil and may 
prevent uptake by plants (CD, Sections 7.1.2, 7.1.5, AX7.1.4.1, 
AX7.1.4.2, AX7.1.4.3 and AX7.1.2 ). Therefore, while atmospheric 
deposition of Pb has decreased, Pb may be more persistent in some 
ecosystems than others and may remain in the active zone of the soil, 
where exposure

[[Page 29251]]

may occur, for decades (CD, Sections 7.1.2, AX7.1.2 and AX7.1.4.3).
     Plant toxicity may occur at lower levels than previously 
identified as determined by data considered in development of Eco-SSLs 
(CD, pp. 7-11 to 7-12, AX7-16 and Section AX7.1.3.2), although the 
range of reported soil Pb effect levels is large (tens to thousands of 
mg/kg soil).
     Avian and mammalian toxicity may occur at lower levels 
than those previously identified, although the range of Pb effect 
levels is large (<1 to >1,000 mg Pb/kg bw-day) (CD, p. 7-12, Section 
AX7.1.3.3).
     There is an expanded understanding of the fate and effects 
of Pb in aquatic ecosystems and of the distribution and concentrations 
of Pb in surface waters throughout the United States (CD, Section 
AX7.2.2).
     New methods for assessing the toxicity of metals to water 
column and sediment-dwelling organisms and data collection efforts (CD, 
Sections 7.2.1, 7.2.2, AX7.2.2, and AX7.2.2.2) have improved our 
understanding of Pb aquatic toxicity and findings include an indication 
that in some estuarine systems Pb deposited during historic usage of 
leaded gasoline may remain in surface sediments for decades. (CD, p. 7-
23).
     A larger dataset of aquatic species assessed with regard 
to Pb toxicity, and findings of lower effect levels for previously 
untested species (CD, p. AX7-176 and Section AX7.2.4.3).
     Currently available studies have also shown effects on 
community structure, function and primary productivity, although some 
confounders (such as co-occurring pollutants) have not been well 
addressed (CD, Section AX7.1.4.2).
     Evidence in ecological research generally indicates the 
value of a critical loads approach; however, current information on Pb 
critical loads is lacking for many processes and interactions involving 
Pb in the environment and work is ongoing (CD, Section 7.3).
    Given the full body of current evidence, despite wide variations in 
Pb concentrations in soils throughout the country, Pb concentrations 
are likely in excess of concentrations expected from geologic or other 
non-anthropogenic forces. In particular, the deposition of gasoline-
derived Pb into forest soils has produced a legacy of slow moving Pb 
that remains bound to organic materials despite the removal of Pb from 
most fuels and the resulting dramatic reductions in overall deposition 
rates (CD, Section AX7.1.4.3). For areas influenced by point sources of 
air Pb that meet the current standard, concentrations of Pb in soil may 
exceed by many orders of magnitude the concentrations which are 
considered harmful to laboratory organisms (CD, Section 3.2 and 
AX7.1.2.3).
    There are several difficulties in quantifying the role of current 
ambient Pb in the environment: some Pb deposited before the standard 
was enacted is still present in soils and sediments; historic Pb from 
gasoline continues to move slowly through systems as does current Pb 
derived from both air and nonair sources. Additionally, the evidence of 
adversity in natural systems is very sparse due in no small part to the 
difficulty in determining the effects of confounding factors such as 
multiple metals or factors influencing bioavailability in field 
studies. However, the evidence summarized above and in Section 4.2 of 
the Staff Paper and described in detail in the Criteria Document 
informs our understanding of Pb in the environment today and evidence 
of environmental Pb exposures of potential concern.
    Conditions exist in which Pb-associated adverse effects to aquatic 
organisms and thereby ecosystems may be anticipated given experimental 
results. While the evidence does not indicate that dissolved Pb in 
surface water constitutes a threat to those ecosystems that are not 
directly influenced by point sources, the evidence regarding Pb in 
sediment is less clear (CD, Sections AX7.2.2.2.2 and AX7.2.4). It is 
likely that some areas with long term historical deposition of Pb to 
sediment from a variety of sources as well as areas influenced by point 
sources have the potential for adverse effects to aquatic communities. 
The Staff Paper concluded based on looking to laboratory studies and 
current media concentrations in a wide range of areas, it seems likely 
that adverse effects are occurring, particularly near point sources, 
under the current standard. The long residence time of Pb in sediment 
and its ability to be resuspended by turbulence make Pb contamination 
likely to be a factor for the foreseeable future. Based on this 
information, the Staff Paper concluded that the evidence suggests that 
the environmental levels of Pb occurring under the current standard, 
set nearly thirty years ago, may pose risk of adverse environmental 
effect.
b. Risk-Based Considerations
    In addition to the evidence-based considerations described in the 
previous section, the screening level ecological risk assessment is 
informative, taking into account key limitations and uncertainties 
associated with the analyses.
    The screening level risk assessment involved a comparison of 
estimates of environmental media concentrations of Pb to ecological 
screening levels to assess the potential for ecological impacts from Pb 
that was emitted into the air. Results of these comparisons are not 
considered to be definite predictors of risk, but rather serve to 
identify those locations at which there is greatest likelihood for 
adverse effect. Similarly, the national-scale screening assessment 
evaluated the potential for ecological impacts associated with the 
atmospheric deposition of Pb released into ambient air at surface water 
and sediment monitoring locations across the United States.
    The ecological screening levels employed in the screening level 
risk assessment for different media are drawn from different sources. 
Consequently there are somewhat different limitations and uncertainties 
associated with each. In general, their use here recognizes their 
strength in identifying media concentrations with the potential for 
adverse effect and their relative nonspecificity regarding the 
magnitude of risk of adverse effect.
    As discussed in the previous section, as a result of its 
persistence, Pb emitted in the past remains today in aquatic and 
terrestrial ecosystems of the United States. Consideration of the 
environmental risks associated with the current standard is complicated 
by the environmental burden associated with air Pb concentrations that 
exceeded the current standard, predominantly in the past.
    Concentrations of Pb in soil and sediments associated with the 
primary Pb smelter case study exceeded screening values for those 
media, indicating potential for adverse effect in terrestrial organisms 
(plants, birds, and mammals) and in sediment dwelling organisms. While 
the contribution to these Pb concentrations from air as compared to 
nonair sources has not been quantified, air emissions from this 
facility are substantial (Appendix D, USEPA 2007b; ICF 2006). 
Additionally, estimates of Pb concentration in soils associated with 
the nonurban near roadway case study and the secondary Pb smelter case 
study were also associated with HQs above 1 for plants, birds and 
mammals, indicating potential for adverse effect to those receptor 
groups. The industrial facility in the secondary Pb smelter case study 
is much younger than the primary Pb smelter and apparently became 
active less than ten years prior to the establishment of the current 
standard.

[[Page 29252]]

    The national-scale screens, which are not focused on particular 
point source locations, indicate the ubiquitous nature of Pb in aquatic 
systems of the United States today. Further, the magnitude of Pb 
concentrations in several aquatic systems exceeded screening values. In 
the case of the national-scale screen of surface water data, 15 
locations were identified with water column levels of dissolved Pb that 
were greater than hardness-adjusted chronic criteria for the protection 
of aquatic life (with one location having a HQ as high as 15), 
indicating a potential for adverse effect if concentrations were 
persistent over chronic periods. Further, sediment Pb concentrations at 
some sites in the national-scale screen were high enough that the 
likelihood that they would cause adverse effects to sediment dwelling 
organisms may be considered ``probable''.
    A complicating factor in interpreting the findings for the 
national-scale screening assessments is the lack of clear apportionment 
of Pb contributions from air as compared to nonair sources, such as 
industrial and municipal discharges. While the contribution of air 
emissions to the elevated concentrations has not been quantified, 
documentation of historical trends in the sediments of many water 
bodies has illustrated the sizeable contribution that airborne Pb can 
have on aquatic systems (e.g., Staff Paper, section 2.8.1). This 
documentation also indicates the greatly reduced contribution in many 
systems as compared to decades ago (presumably reflecting the banning 
of Pb-additives from gasoline used by cars and trucks). However, the 
timeframe for removal of Pb from surface sediments into deeper sediment 
varies across systems, such that Pb remains available to biological 
organisms in some systems for much longer than in others (Staff Paper, 
section 2.8; CD, pp. AX7-141 to AX7-145).
    The case study locations included in the screening assessment, with 
the exception of the primary Pb smelter site, are currently meeting the 
current Pb standard, yet Pb occurs in some locations at concentrations, 
particularly in soil, and aquatic sediment above the screening levels, 
indicative of a potential for harm to some terrestrial and sediment 
dwelling organisms. While the role of airborne Pb in determining these 
Pb concentrations is unclear, the historical evidence indicates that 
airborne Pb can create such concentrations in sediments and soil. 
Further, environmental concentrations may be related to emissions prior 
to establishment of the current standard and such concentrations appear 
to indicate a potential for harm to ecological receptors today.
c. CASAC Advice and Recommendations
    In the CASAC letter transmitting advice and recommendations 
pertaining to the review of the ANPR and final Staff Paper and Pb 
Exposure and Risk Assessments, the CASAC Pb panel provided 
recommendations regarding the need for a Pb NAAQS, and the adequacy of 
the current Pb NAAQS, as well as comments on the documents. With regard 
to the revision of the primary and secondary NAAQS, this CASAC letter 
(Henderson, 2008) said:

    The Committee unanimously and fully supports Agency staff's 
scientific analyses in recommending the need to substantially lower 
the level of the primary (public-health based) Lead NAAQS, to an 
upper bound of no higher than 0.2 [mu]g/m\3\ with a monthly 
averaging time. The CASAC is also unanimous in its recommendation 
that the secondary (public-welfare based) standard for lead needs to 
be substantially lowered to a level at least as low as the 
recommended primary NAAQS for Lead.

    In earlier comments on the December 2006 draft documents, the CASAC 
Pb Panel concluded they presented ``compelling scientific evidence that 
current atmospheric Pb concentrations and deposition--combined with a 
large reservoir of historically deposited Pb in soils, sediments and 
surface waters--continue to cause adverse environmental effects in 
aquatic and/or terrestrial ecosystems, especially in the vicinity of 
large emissions sources.'' The Panel went on to state that ``These 
effects persist in some cases at locations where current airborne lead 
concentrations are below the level of the current primary and secondary 
lead standards'' and ``Thus, from an environmental perspective, there 
are convincing reasons to both retain lead as a regulated criteria air 
pollutant and to lower the level of the current secondary standard'' 
(Henderson, 2007a).
    In making this recommendation, the CASAC Pb Panel also cites the 
persistence of Pb in the environment, the possibility of some of the 
large amount of historically deposited Pb becoming resuspended by 
natural events, and the expectation that humans are not uniquely 
sensitive among the many animal and plant species in the environment.
    CASAC provided further advice and recommendations on the Agency's 
consideration of the secondary standard in this review in their letter 
of September 2007 (Henderson, 2007b). In that letter they recognized 
the role of the secondary standard in influencing the long-term 
environmental burden of Pb and a need for environmental monitoring to 
assess the success of the standard in this role.
    Similarly, in CASAC's advice on the ANPR and final Staff Paper they 
concluded:

    [I]t is critical that the secondary Lead NAAQS be set at a 
sufficiently-stringent level so as to ensure that there is no 
reversal of the current downward trend in lead concentrations in the 
environment. Therefore, at a minimum, the level of the secondary 
Lead NAAQS should be at least as low as the level of the recommended 
primary lead standard. Moreover, the Agency needs to give greater 
priority to the monitoring of environmental lead in the ambient air.

    However, CASAC also recognized that EPA ``lacks the relevant data 
to provide a clear, quantitative basis for setting a secondary Pb NAAQS 
that differs from the primary in indicator, averaging time, level or 
form'' (Henderson, 2007a).
d. Administrator's Proposed Conclusions on Adequacy of Current Standard
    In considering the adequacy of the current standard in providing 
requisite protection from Pb-related adverse effects on public welfare, 
the Administrator has considered the body of available evidence 
(briefly summarized above in Section III.A). Depending on the 
interpretation, the available data and evidence, primarily qualitative, 
suggests the potential for adverse environmental impacts under the 
current standard. Given the limited data on Pb effects in ecosystems, 
it is necessary to look at evidence of Pb effects on organisms and 
extrapolate to ecosystem effects. Therefore, taking into account the 
available evidence and current media concentrations in a wide range of 
areas, the Administrator concludes that there is potential for adverse 
effects occurring under the current standard, however there are 
insufficient data to provide a quantitative basis for setting a 
secondary standard different than the primary. While the role of 
current airborne emissions is difficult to apportion, it is conclusive 
that deposition of Pb from air sources is occurring and that this 
ambient Pb is likely to be persistent in the environment. Historically 
deposited Pb has persisted, although location-specific dynamics of Pb 
in soil result in differences in the timeframe during which Pb is 
retained in surface soils or sediments where it may be available to 
ecological receptors (USEPA, 2007b, section 2.3.3).

[[Page 29253]]

    There is only very limited information available pertinent to 
assessing whether groups of organisms which influence ecosystem 
function are subject to similar effects as those in humans. The 
screening-level risk information, while limited and accompanied by 
various uncertainties, also suggests occurrences of environmental Pb 
concentrations existing under the current standard that could have 
adverse environmental effects. Environmental Pb levels today are 
associated with atmospheric Pb concentrations and deposition that have 
combined with a large reservoir of historically deposited Pb in 
environmental media.
    In considering this evidence, as well as the views of CASAC, 
summarized above, the Staff Paper and associated support documents, and 
views of public commenters on the adequacy of the current standard, the 
Administrator proposes to conclude that the current secondary standard 
for Pb is not requisite to protect public welfare from known or 
anticipated adverse effects.
4. Conclusions and Proposed Decision on the Elements of the Secondary 
Standard
    The secondary standard is defined in terms of four basic elements: 
indicator, averaging time, level and form, which serve to define the 
standard and must be considered collectively in evaluating the welfare 
protection afforded by the standards.
    With regard to the pollutant indicator for use in a secondary NAAQS 
that provides protection for public welfare from exposure to Pb, EPA 
notes that Pb is a persistent pollutant to which ecological receptors 
are exposed via multiple pathways. While the evidence indicates that 
the environmental mobility and ecological toxicity of Pb are affected 
by various characteristics of its chemical form, and the media in which 
it occurs, information is insufficient to identify an indicator other 
than total Pb that would provide protection against adverse 
environmental effect in all ecosystems nationally. Thus, the same 
concerns regarding the relative advantages of TSP and PM10 
as the basis for the indicator apply here as for the primary standard.
    Lead is a cumulative pollutant with environmental effects that can 
last many decades. In considering the appropriate averaging time for a 
secondary standard for such a pollutant the concept of critical loads 
may be useful (CD, section 7.3). However, information is currently 
insufficient for such use in this review.
    There is a general lack of data that would indicate the appropriate 
level of Pb in environmental media that may be associated with adverse 
effects. The EPA notes the influence of airborne Pb on Pb in aquatic 
systems and of changes in airborne Pb on aquatic systems, as 
demonstrated by historical patterns in sediment cores from lakes and Pb 
measurements (section 2.8.1; CD, section AX7.2.2; Yohn et al., 2004; 
Boyle et al., 2005), as well as the comments of the CASAC Pb panel that 
a significant change to current air concentrations (e.g., via a 
significant change to the standard) is likely to have significant 
beneficial effects on the magnitude of Pb exposures in the environment 
and Pb toxicity impacts on natural and managed terrestrial and aquatic 
ecosystems in various regions of the U.S., the Great Lakes and also 
U.S. territorial waters of the Atlantic Ocean (Henderson, 2007a, 
Appendix E). EPA concurs with CASAC's conclusion that the Agency lacks 
the relevant data to provide a clear, quantitative basis for setting a 
secondary Pb NAAQS that differs from the primary in indicator, 
averaging time, level or form. The Administrator concurs with CASAC's 
conclusion that the Agency lacks the relevant data to provide a clear, 
quantitative basis for setting a secondary Pb NAAQS that differs from 
the primary in indicator, averaging time, level, or form.
    Based on these considerations, and taking into account the 
observations, analyses, and recommendations discussed above, the 
Administrator proposes to revise the current secondary Pb standard by 
making it identical in all respects to the proposed primary Pb standard 
(described in section II.D.4 above).

IV. Proposed Appendix R--Interpretation of the NAAQS for Lead and 
Proposed Revisions to the Exceptional Events Rule

    The EPA is proposing to add Appendix R, Interpretation of the 
National Ambient Air Quality Standards for Pb, to 40 CFR part 50 in 
order to provide data handling procedures for the proposed Pb standard. 
The proposed Appendix R would detail the computations necessary for 
determining when the proposed Pb NAAQS is met. The proposed appendix 
also would address data reporting; sampling frequency and data 
completeness considerations; the use of scaled Pb-PM10 data 
as a surrogate for Pb-TSP data (or vice versa), including associated 
scaling instructions; and rounding conventions. Although the 
Administrator is proposing one indicator and inviting comment on 
another, and proposing several possible combinations of different 
averaging times, forms, and levels, for simplicity the proposed data 
handling appendix text only directly addresses one combination: a Pb-
TSP indicator with an option for using scaled Pb-PM10 data 
for NAAQS comparisons, an averaging time of monthly, a second maximum 
(over three years) form, and a level of 0.20 [mu]g/m\3\. The proposed 
appendix text indicates in brackets, as examples, the change that would 
be needed if the level of the standard is set at 0.10 or 0.30 [mu]g/
m\3\ rather than at 0.20 [mu]g/m\3\. A decision to adopt Pb-
PM10 as the indicator, to adopt a different indicator, 
averaging time, and/or form, or not to make use of surrogate data would 
require other differences in the text of the appendix; the proposed 
differences in the appendix text to accommodate such difference are 
described below, after the explanation of the proposed version of the 
appendix.
    The EPA is also proposing Pb-specific changes to the deadlines, in 
40 CFR 50.14, by which States must flag ambient air data that they 
believe has been affected by exceptional events and submit initial 
descriptions of those events, and the deadlines by which States must 
submit detailed justifications to support the exclusion of that data 
from EPA determinations of attainment or nonattainment with the NAAQS. 
The deadlines now contained in 40 CFR 50.14 are generic, and are not 
always appropriate for Pb given the anticipated schedule for the 
designations of areas under the proposed Pb NAAQS.

A. Background

    The purpose of a data interpretation guideline in general is to 
provide the practical details on how to make a comparison between 
multi-day, possibly multi-monitor, and (in the unique instance of this 
proposed Pb NAAQS) possibly multi-parameter (i.e., Pb-TSP and/or Pb-
PM10) ambient air concentration data to the level of the 
NAAQS, so that determinations of compliance and violation are as 
objective as possible. Data interpretation guidelines also provide 
criteria for determining whether there are sufficient data to make a 
NAAQS level comparison at all. When data are insufficient, for example 
because of failure to collect valid ambient data on enough days in 
enough months (because of operator error or events beyond the control 
of the operator), then no determination of current compliance or 
violation is possible.
    The regulatory language for the current Pb NAAQS, originally 
adopted in 1977, contains no data interpretation instructions. Because 
of that, the EPA

[[Page 29254]]

has issued various guidance documents and memoranda relevant to the 
topic. This situation contrasts with the situations for ozone, 
PM2.5, and PM10 for which there are detailed data 
interpretation appendices in 40 CFR part 50. EPA has used its 
experience drafting and applying these other data interpretation 
appendices to develop the proposed text for appendix R.
    An exceptional event is an event that affects air quality, is not 
reasonably controllable or preventable, is an event caused by human 
activity that is unlikely to recur at a particular location or a 
natural event, and is determined by the Administrator in accordance 
with 40 CFR 50.14 to be an exceptional event. Air quality data affected 
by an exceptional event in certain specified ways may be excluded from 
consideration when EPA makes a determination that an area is meeting or 
violating the associated NAAQS, subject to EPA review and concurrence. 
Section 50.14 contains both substantive criteria that an event and the 
associated air concentration data must meet in order to be excluded, 
and process steps and deadlines for a State to submit specified 
information to EPA. The key deadlines are that a State must initially 
notify EPA that data have been affected by an event and provide an 
initial description of the event by July 1 of the year after the data 
are collected, and that the State must submit the full justification 
for exclusion within 3 years after the quarter in which the data were 
collected. However, if a regulatory decision based on the data, for 
example a designation action, is anticipated, the schedule is 
foreshortened and all information must be submitted to EPA no later 
than a year before the decision is to be made. This schedule presents 
problems when a NAAQS has been recently revised, as discussed below.
    The Staff Paper did not address data interpretation details, and 
although the ANPR discussed data handling to a limited extent, there 
has been only limited comment by CASAC or the public to date (other 
than comments on the related issues of form and indicator for the 
standard, including scaling factor issues). Similarly, no comments were 
received on exceptional event issues.

B. Interpretation of the NAAQS for Lead

1. Interpretation of a Standard Based on Pb-TSP
    The purpose of a data interpretation rule for the Pb NAAQS is to 
give effect to the form, level, averaging time, and indicator specified 
in the proposed regulatory text at 40 CFR 50.16, anticipating and 
resolving in advance various future situations that could occur. The 
proposed Appendix R, like the existing NAAQS interpretation appendices 
for ozone, PM2.5, and PM10, addresses the 
possible situation of there being less than 100% complete data 
available, which is an issue in common across NAAQS pollutants. It also 
addresses several issues which are specific to the proposed Pb NAAQS, 
as described below.
    With regard to data completeness, the proposed Appendix follows 
past EPA practice for other NAAQS pollutants by requiring that in 
general at least 75% of the monitoring data that should have resulted 
from following the planned monitoring schedule in a period must be 
available for the key air quality statistic from that period to be 
considered valid. For the combination of NAAQS parameters addressed in 
the proposed text, the key air quality statistic is the mean 
concentration in an individual month, and so the 75% requirement is 
applied for that time period. With the proposed required sampling 
schedule of one day in three under a monthly mean form for the standard 
(section V), typically there will be 10 required sampling days so a 
monthly mean would be considered valid if there were data available for 
at least 8 of those days.\155\ EPA invites comment on this proposed 75% 
requirement, recognizing that for the current NAAQS based on a 
quarterly mean concentration form with a required one-day-in-six 
schedule, the current EPA policy is effectively that there be at least 
11 days of data in a quarterly mean.
---------------------------------------------------------------------------

    \155\ Fewer than 10 days could be required, and fewer needed for 
the monthly average to be valid, for February at all sites and in 
all months for sites approved for only one-day-in-six sampling 
because they have a history of recording concentrations well below 
the level of the NAAQS. See Section V for more detail on required 
sampling schedules.
---------------------------------------------------------------------------

    The proposed rule text for Pb data interpretation, like the 
corresponding existing rule for PM2.5, has two provisions 
that help a monitoring agency guard against a month ending up with data 
completeness below 75%. First, there is a provision to allow data from 
secondary, collocated samplers to substitute for data from a primary 
monitor on a day when the primary monitor for some reason fails to 
deliver valid data. There is also a provision which would allow a 
monitoring agency to make up a sampling day on which no valid data were 
collected, and to count the make-up sampling data in the assessment of 
data completeness. To help insure that sampling days are well 
distributed across the month and that a make-up day will generally fall 
within the same source emissions and meteorological regime as the 
missed sampling day, a number of specific restrictions are proposed on 
the number of make-up days per month and on how soon after the missed 
scheduled sampling day they must occur. These restrictions are stated 
in the proposed rule text, and are adapted from current practice for 
PM2.5 with adaptations to fit the monthly form of the 
proposed Pb standard.
    A monthly mean Pb concentration for Pb-TSP would be calculated from 
all available daily mean concentrations within that calendar month, 
including successfully completed sampling days, allowed make-up 
sampling days, and any other sampling days actually completed 
successfully by the primary monitor or by secondary monitors if there 
is no data from a primary monitor. These other sampling days would not 
be used in calculating data completeness, however; this follows the 
example of the current requirements for PM2.5 data 
interpretation.
    Recognizing that even allowing for make-up samples, there may be 
months with fewer than 75% complete data, the proposed text provides 
for two diagnostic tests which are intended to identify those cases 
with completeness less than 75% in which it nevertheless is very 
likely, if not virtually certain, that the monthly mean concentration 
would have been observed to be either above or below the level of the 
NAAQS if monitoring data had been complete. One test, to be applied if 
the mean of the incomplete data is above the NAAQS level, substitutes 
low hypothetical concentrations for as much of the missing data as 
needed to meet the 75% requirement; if the resulting mean is still 
above the NAAQS level, then the NAAQS level is considered to have been 
exceeded for the month. The hypothetical low values would be set equal 
to the lowest concentration observed in the same month over the 3-year 
period being evaluated, in effect giving the benefit of the doubt as to 
the actual concentrations on the days with missing data. If the monthly 
mean nevertheless is above the NAAQS, it is virtually certain that the 
mean of complete data would also have been above the NAAQS. The other 
test, to be applied if the mean of the incomplete data is below the 
NAAQS level, works similarly except that at most 50% of the scheduled 
data can be missing and all missing data is substituted with the 
highest value observed in the same month over the 3-year period, with 
the same rationale. If the monthly mean nevertheless is below the 
NAAQS, it is virtually certain that the mean of complete data would 
also have been

[[Page 29255]]

below the NAAQS. Data substitution tests similar to these are currently 
used for ozone and PM2.5. It should be noted that one 
outcome of applying the substitution tests proposed for Pb is that a 
month with incomplete data may still be determined to not have a valid 
monthly mean and to be unusable in making NAAQS exceedance 
determinations for that monthly time period. In turn, this may make it 
impossible to make a determination of compliance or violation for the 
3-year period, depending on the completeness and levels of the 
concentration data from the other months.
    EPA invites comment on also incorporating into the final rule two 
other possible tests that could allow a NAAQS exceedance determination 
to be made on the basis of monthly data that is not at least 75% 
complete. EPA may incorporate a version of either or both of these 
additional tests into the final rule. The first additional test would 
allow use of the monthly mean based on data that is between 50% and 75% 
complete if that monthly mean were below some percentage (for example, 
50%) the NAAQS, on the rationale that if the available daily values 
(typically there would be 5 values in a month with 50% complete data) 
have a mean below some sufficiently low limit, day-to-day variability 
at the site must be small and the actual concentrations on the days 
with missing data are very unlikely to have been high enough to make 
the true monthly mean exceed the NAAQS level.
    The second additional test would be more statistically rigorous, 
yet will allow compliance determinations to be made on some smaller 
data sets by considering uncertainty bounds. The test would use the 
available data to create a two-sided statistical confidence interval 
around the calculated monthly mean concentration. A reduced minimum 
completeness percentage such as 50% would still be applied to ensure 
that there are enough sampling days that they could not all be from 
within a very short period of time. As expected, the uncertainty range 
about the monthly mean would increase as the number of samples 
decreases, and as there is more variability in the data that were 
collected (more high concentrations days mixed with low concentration 
days). If the prescribed two-sided confidence interval is entirely 
above the level of the NAAQS, then the NAAQS would be deemed to have 
been exceeded in that month. Note that the calculated monthly mean in 
this situation would also have been above the NAAQS level. If the 
confidence interval is entirely below the level of the NAAQS, then the 
NAAQS would be deemed to have not been exceeded in that month. EPA 
invites comment on the statistical assumptions that should be 
considered to create a confidence interval from the available data, for 
example the assumed distribution of the underlying ambient data and how 
the confidence intervals should be constructed. For example, the 
confidence interval could be constructed based on an assumption of a 
log-normal distribution for daily concentrations combined with the 
concept of a ``finite population correction factor,'' where means based 
on data with between 50 and 75% completeness would have an associated 
uncertainty range.\156\ Any data that is at least 75% complete could be 
considered ``complete'' and would have no confidence interval. This 
approach would make the general completeness test and this statistical 
test yield the same result for a month with at least 75% completeness. 
EPA notes that such a statistical confidence interval approach is not 
presently used in data interpretation for any other NAAQS, but no other 
NAAQS involves the combination of an averaging period as short as a 
month with a sampling schedule as infrequent as one day in three.
---------------------------------------------------------------------------

    \156\ See, for example, the explanation of the finite population 
correction factor approach at grants.nih.gov/grants/funding/modular/
eval/Sample--MGAP.doc. Another useful reference is ``Sampling: 
Design and Analysis'', Lohr, Sharon L., Brooks/Cole Publishing Co., 
Pacific Grove, CA, 1999.
---------------------------------------------------------------------------

    Section V.C. contains provisions which interact with the proposed 
data completeness requirements described above. EPA invites comment on 
whether the proposed data completeness provisions taken together 
provide a good balance between avoiding situations in which no 
determination of attainment or nonattainment can be made until more 
data are collected during another calendar year, and avoiding erroneous 
determinations caused by reliance on small sample sizes affected by 
data variability. EPA also plans to explore this question prior to the 
final rule, by analyzing hypothetical cases reflecting the variability 
seen in historical monitoring data, and may make adjustments to the 
proposed provisions for the final rule.\157\
---------------------------------------------------------------------------

    \157\ This exploration will be somewhat similar to the work EPA 
did on data quality objectives for the PM2.5 monitoring 
network, but likely will be more simplistic in light of the more 
limited available data. See ``Data Quality Objectives (DQOs) for 
PM2.5,'' July 25, 2001, http://www.epa.gov/ttn/amtic/
files/ambient/pm25/qa/2001Dqo.pdf.
---------------------------------------------------------------------------

    The proposed rule text would require that only a minimum of two 
valid monthly means be available over the 3-year period in order to 
determine that a site has violated the NAAQS, since if the NAAQS has 
been observed to be exceeded twice the concentrations in the other 
months would be irrelevant to a finding of NAAQS violation. Valid 
monthly means would be required for all 36 possible months in the 3-
year period in order to make a finding that the NAAQS has been met. An 
exception would be allowed if there are 35 valid monthly means and none 
of them exceed the NAAQS, because in that case it is irrelevant whether 
the one month with incomplete data experienced an exceedance or not.
    The proposed text of Appendix R has provisions to implement the 
proposal that Pb-PM10 data adjusted by the application of 
site-specific scaling factors be treated as surrogate Pb-TSP data. 
These provisions are somewhat complex, to be able to address various 
possible situations without ambiguity. These situations arise from the 
possibility that both Pb-TSP and Pb-PM10 monitoring might 
take place at a single site, with differences from day to day within 
the 3-year period as to which samplers were operating and yielded valid 
data for the day. The proposed approach is to consider all Pb-TSP and 
Pb-PM10 data that have been collected and submitted by the 
monitoring agency, i.e., once Pb-PM10 data have been 
collected and submitted the monitoring agency could not choose to have 
them ignored.\158\ However, where and when both types of data exist, 
the Pb-TSP data would be given first consideration. Specifically the 
proposed approach is to treat as separate questions whether the Pb-TSP 
monitor and the Pb-PM10 monitor have produced a valid 
monthly mean concentration, taking into account the provisions for 
make-up samples and data substitution from secondary monitors, but not 
mixing Pb-TSP and Pb-PM10 data within the month. If valid 
monthly means for both Pb-TSP and Pb-PM10 have been 
achieved, i.e., the main or a supplemental data completeness test has 
been passed, the Pb-TSP data takes precedence and the Pb-
PM10 data for

[[Page 29256]]

that month are ignored. However, across the 3-year period, monthly 
means for Pb-TSP and scaled Pb-PM10 can be considered 
together in determining whether more than one monthly mean Pb 
concentration has exceeded the level of the NAAQS. This allows for the 
possibility that a monitoring agency may have switched from one type of 
monitoring to the other during the 3 years, or that it has been more 
successful in getting complete Pb-TSP data in some months than in 
others.
---------------------------------------------------------------------------

    \158\ Section 3(a) of the proposed Appendix R has a more 
detailed statement of what ambient data will be considered when 
determining compliance with the NAAQS than is given in other data 
interpretation appendices to 40 CFR part 50. EPA invites comment on 
this codification of current practice. One new feature is a 
provision for the use of data collected before the promulgation of 
the proposed changes and additions to the FRM/FEM criteria, to make 
it clear that these changes and additions are in effect retroactive. 
FRM/FEM revisions and new FRM/FEM designations have not always been 
treated as retroactive but in the case of the revised Pb NAAQS EPA 
wishes to maximize the available data for making designations.
---------------------------------------------------------------------------

    The proposed Appendix R addresses the procedures and criteria for 
development and use of site-specific scaling factors for Pb-
PM10 data. The scaling factor is the number that would 
multiply Pb-PM10 data to get a surrogate for Pb-TSP data. 
The proposal would require States to develop a site-specific scaling 
factor for each monitoring site at which the State wishes to use Pb-
PM10 data as a surrogate for Pb-TSP data, either to allow it 
to only operate a Pb-PM10 monitor or to make a Pb-
PM10 monitor eligible as a back-up source of Pb data for 
greater data completeness. The site-specific scaling factor would have 
to be based on at least a year of measurements of both types at the 
site in question. EPA invites comment on the detailed criteria for 
developing such local scaling factors, given in section 2(b) of the 
proposed Appendix.
    The existing FRM for Pb-TSP, Appendix G of 40 CFR part 50, contains 
procedures for calculating Pb concentration data in micrograms per 
cubic meter at standard conditions of temperature and pressure (STP). 
The proposed FRM for low-volume Pb-PM10, Appendix Q of 40 
CFR part 50, requires reporting of concentration data at local 
conditions of temperature and pressure, for reasons explained in 
section V. For consistency going forward, we are proposing in the 
proposed appendix R that for monitoring conducted on or after January 
1, 2009, Pb-TSP data should be reported at local conditions of 
temperature and pressure also. The first deadline for such reporting 
will be about June 30, 2009 (to be exact, 90 days from March 31, 2009) 
so monitoring agencies will have ample lead time to change their 
reporting procedures. However, EPA believes it would be an unnecessary 
burden to require monitoring agencies to re-submit pre-January 1, 2009 
Pb-TSP data corrected to local conditions, given that the adjustment 
would in most cases be small. The proposed Appendix R would provide 
that pre-2009 Pb-TSP data reported in STP is to be compared directly to 
the level of the standard with no adjustment for the difference in 
reporting forms, but gives the monitoring agency the option of re-
submitting the data corrected to local conditions. EPA invites comment 
on this approach.
    Both FRM rules require reporting of daily Pb concentrations with 
three decimal places. When monthly means are calculated, they are to be 
rounded to two decimal places for purposes of comparing to the level of 
the NAAQS, which is expressed to two decimal places.
2. Interpretation of Alternative Elements
    This section addresses changes that would be made to the proposed 
Appendix R as printed at the end of this notice, if the Administrator 
decides to adopt certain features which are being proposed today in the 
alternative to those described above, or on which comment is invited.
    If a quarterly maximum mean form is adopted for the final standard, 
we propose that the basic period for assessing completeness would still 
be the month. An equation would be added for calculating a quarterly 
mean from three monthly means. The two supplemental diagnostic 
completeness tests would be changed so that the outcome depends on 
whether the quarterly mean with substituted data included for one or 
more incomplete months meets or exceeds the standard, rather than the 
monthly mean. The design value would be defined as the maximum 
quarterly mean concentration in the 3-year period. To be determined to 
violate the standard, at least one valid quarterly mean in the 3-year 
period would be required. To be determined to meet the standard, 12 
valid quarterly means in the 3-year period would be required. EPA 
invites comment on the alternative of applying completeness tests only 
for whole calendar quarters rather than individual months, an approach 
that might allow attainment determinations to be made in some cases in 
which the by-month approach just described would prevent a 
determination.
    As discussed in section II.E.1, EPA is inviting comment on the 
possibility of the final rule containing default scaling factors for 
adjusting Pb-PM10 data for use as a surrogate for Pb-TSP 
data. This would give States the option of using a default scaling 
factor rather than conducting the site-specific paired monitor testing 
required in the proposed text of Appendix R. If EPA adopts this 
approach in the final rule, Appendix R would be modified to provide the 
default scaling factor values and explain their application. The 
appropriate default scaling factor would be used in calculation 
formulas exactly as the proposed Appendix R text requires the use of a 
site-specific scaling factor; other provisions would be unaffected. 
Because TSP samplers collect a broader range of particle sizes than 
PM10 samplers, the scaling factor logically can not be less 
than 1.0. EPA is inviting comment on the selection of default scaling 
factors from within two ranges. The first range is 1.1 to 2.0 and would 
apply to Pb-PM10 data collected at source-oriented 
monitoring sites. The other range is 1.0 to 1.4 \159\ and would apply 
to Pb-PM10 data collected at monitoring sites that are not 
source-oriented. These ranges are based on historical data from sites 
where the two types of monitors were operated on the same days, as 
explained in section II.E.1. Because there would be different default 
scaling factors for the two monitoring site types, a modification of 
the proposed Appendix R text would require for each monitoring agency 
to determine and designate, subject to EPA review, whether each Pb-
PM10 site is in fact source-oriented and to document that 
determination in the Annual Monitoring Plan required by 40 CFR 58.10 
(see section V for more information on the requirement for this plan 
and for designating sites as source-oriented or not).
---------------------------------------------------------------------------

    \159\ EPA is also soliciting comment on a broader range of 1.0 
to 1.9 for nonsource-oriented sites as discussed in section II.E.1.
---------------------------------------------------------------------------

    As explained in section II.E, EPA is inviting comment on the 
possibility of revising the Pb indicator to be Pb-PM10. If a 
Pb-PM10 indicator is adopted in the final rule, references 
to the two types of data would be reversed from the way they appear in 
the proposed text of Appendix R, so that Pb-PM10 data when 
available would have primacy over scaled Pb-TSP data. If Pb-
PM10 is adopted as the indicator for the final standard, 
many areas may not have sufficient Pb-PM10 data to allow a 
determination of compliance or violation with the Pb standard within 
the two or three years allowed under the Clean Air Act for initial 
designations. EPA is inviting comment on an approach that would allow 
the use of Pb-TSP data, with adjustment(s), for comparing ambient 
concentrations of Pb to a Pb-PM10 NAAQS for the sole purpose 
of making initial designations. The scaling issues, relevant data, and 
possible approaches are similar to those described in section II.E.1. 
We invite comment on adding language to Appendix R restricting the use 
of scaled Pb-TSP data to determinations made for purposes of 
designations within three years of promulgation of the revised 
standard. (See section VI for discussion

[[Page 29257]]

of the schedule for designations.) This generally would mean that 
scaling factors would be used only on 2007-2009 and possibly on earlier 
Pb-TSP data, because Pb-PM10 monitoring is proposed to be 
required to begin by January 1, 2010. Because scaling factors would 
need to be available for designations decisions which must be made 
within three years of promulgation of the NAAQS, there would be limited 
time for a State to do collocated testing to develop local scaling 
factors and then have them reviewed and approved by EPA. Requiring 
development of site-specific scaling factors might effectively prevent 
use of scaled Pb-TSP data in many States, resulting in more areas 
having to be designated unclassifiable initially. Therefore, we invite 
comment on removing the passages requiring the development of site-
specific scaling factors from Appendix R and providing default scaling 
factors instead. Scaling factors would be 1.0 or less. EPA invites 
comment on the selection of appropriate default scaling factors for 
this situation.

C. Exceptional Events Information Submission Schedule

    As explained above, 40 CFR 50.14 contains generic deadlines for a 
State to submit to EPA specified information about exceptional events 
and associated air concentration data. A State must initially notify 
EPA that data has been affected by an event by July 1 of the year after 
the data are collected; this is done by flagging the data in AQS. The 
State must also provide an initial description of the event by July 1. 
Also, the State must submit the full justification for exclusion within 
3 years after the quarter in which the data were collected; however, if 
a regulatory decision based on the data (for example, a designation 
action) is anticipated, the schedule for the full justification is 
foreshortened and all information must be submitted to EPA no later 
than a year before the decision is to be made.
    These generic deadlines are suitable for the period after initial 
designations have been made under a NAAQS, when the decision that may 
depend on data exclusion is a redesignation from attainment to 
nonattainment or from nonattainment to attainment. However, these 
deadlines present problems with respect to initial designations under a 
revised NAAQS. One problem is that some of the deadlines, especially 
the deadlines for flagging data, can have already passed for some 
relevant data by the time the revised NAAQS is promulgated. However, 
until the level and form of the NAAQS have been promulgated a State 
does not know whether the criteria for excluding data (which are tied 
to the level and form of the NAAQS) were met on a given day, so the 
only way a State can be sure to have flagged all data of concern and 
possible eligibility for exclusion by the deadline is to flag far more 
data than will eventually be eligible for exclusion. Another problem is 
that some of the data that may be used for final designations may not 
be collected and submitted to EPA until later than one year before the 
final designation decision, making it impossible to flag that data one 
year before the decision. When Section 50.14 was revised to add these 
deadlines in March 2007, EPA was mindful that designations were needed 
under the recently revised PM2.5 NAAQS, and so exceptions to 
the generic deadline were included for PM2.5 only.
    The EPA was also mindful that similar issues would arise for 
subsequent new or revised NAAQS. The Exceptional Events Rule at section 
51.14(c)(2)(v) indicates ``when EPA sets a NAAQS for a new pollutant, 
or revises the NAAQS for an existing pollutant, it may revise or set a 
new schedule for flagging data for initial designation of areas for 
those NAAQS.'' For the specific case of Pb, EPA anticipates that 
designations under the revised NAAQS may be made in September 2011 
based on 2008-2010 data (or possibly in September 2010 based on 2007-
2009 data if sufficient data is available), and thus will depend in 
part on air quality data collected as late as December 2010 (or 
December 2009). (See Section VI below for more detailed discussion of 
the designation schedule and what data EPA intends to use.) There is no 
way for a State to flag and submit documentation regarding events that 
happen in October, November, and December 2010 (or 2009) by one year 
before designation decisions that are made in September 2011 (or 2010).
    The proposed revisions to 40 CFR 50.14 involve only changes in 
submission dates for information regarding claimed exceptional events 
affecting Pb data. In the proposed rule text at the end of this notice, 
only the changes that would apply if designations are made three years 
after promulgation are shown; where a deadline would be different if 
designations were made at the two-year point, the difference in 
deadline is noted in the description immediately below. We propose to 
extend the generic deadline for flagging data (and providing a brief 
initial description of the event) of July 1 of the year following the 
data collection, to July 1, 2009 for data collected in 2006-2007. The 
extension includes 2006 and 2007 data because Governors' designation 
recommendations will consider 2006-2008 data, and possibly EPA will 
consider 2006-2008 or 2007-2009 data if complete data for 2008-2010 are 
not available at the time of final designations. EPA does not intend to 
use data prior to 2006 in making Pb designation decisions. The generic 
event flagging deadline in the Exceptional Events Rule would continue 
to apply to data from 2008, and would thus be July 1, 2009. This would 
allow a State time following the September 2008 promulgation of the 
revised Pb NAAQS to consider what data it wishes to flag and to submit 
those flags. The Governor of a State would be required to submit 
designation recommendations to EPA in September 2009, and would 
therefore know what 2008 data have been flagged when formulating those 
recommendations.
    For data collected in 2010 (or 2009), we propose to move up the 
generic deadline of July 1 for data flagging to May 1, 2011 (or May 1, 
2010) (which is also the applicable deadline for certifying data in AQS 
as being complete and accurate to the best knowledge of the responsible 
monitoring agency head). This would give a State less time, but EPA 
believes still sufficient time, to decide what 2010 (or 2009) data to 
flag, and would allow EPA to have access to the flags in time for EPA 
to develop its own proposed and final plans for designations.
    Finally, EPA proposes to make the deadline for submission of 
detailed justifications for exclusion of data collected in 2006 through 
2008 be September 15, 2010 for the three year designation schedule, or 
September 15, 2009 under the two year designation schedule. EPA 
generally does not anticipate data from 2006 and 2007 being used in 
final Pb designations. Under the three year designation schedule, for 
data collected in 2010, EPA proposes to make the deadline for 
submission of justifications be May 1, 2011. This is less than a year 
before the designation decisions would be made, but we believe it is a 
good compromise between giving a State a reasonable period to prepare 
the justifications and EPA a reasonable period to consider the 
information submitted by the State. Similarly, under the two year 
designation schedule, for data collected in 2009, EPA proposes to make 
the deadline for submission of justifications be May 1, 2010. Table 8 
summarizes the proposed three year designation deadlines discussed in 
this section, and Table 9 summarizes the two year designation 
deadlines.

[[Page 29258]]

     Table 8.--Proposed Schedule for Exceptional Event Flagging and
   Documentation Submission if Designations Promulgated in Three Years
------------------------------------------------------------------------
                                                           Detailed
 Air quality data collected for     Event flagging       documentation
          calendar year                deadline           submission
                                                           deadline
------------------------------------------------------------------------
2006............................  July 1, 2009*.....  September 15,
                                                       2010*.
2007............................  July 1, 2009*.....  September 15,
                                                       2010.
2008............................  July 1, 2009......  September 15,
                                                       2010*.
2009............................  July 1, 2010......  September 15,
                                                       2010*.
2010............................  May 1, 2011*......  May 1, 2011*.
------------------------------------------------------------------------
* Indicates proposed change from generic schedule in 40 CFR 50.14.

     Table 9.--Proposed Schedule for Exceptional Event Flagging and
    Documentation Submission If Designations Promulgated in Two Years
------------------------------------------------------------------------
                                                           Detailed
 Air quality data collected for     Event flagging       documentation
          calendar year                deadline           submission
                                                           deadline
------------------------------------------------------------------------
2006............................  July 1, 2009*.....  September 15,
                                                       2009.
2007............................  July 1, 2009*.....  September 15,
                                                       2009*.
2008............................  July 1, 2009......  September 15,
                                                       2009*.
2009............................  May 1, 2010*......  May 1, 2010*.
------------------------------------------------------------------------
* Indicates proposed change from generic schedule in 40 CFR 50.14.

    EPA invites comment on these proposed changes in the exceptional 
event flagging and documentation submission deadlines.

V. Proposed Amendments to Ambient Monitoring and Reporting Requirements

    As part of our proposal to revise and implement the Pb NAAQS, we 
are proposing several changes to the ambient air monitoring and 
reporting requirements for Pb. Ambient Pb monitoring data are used to 
determine whether an area is in violation of the Pb NAAQS. Ambient data 
are collected and reported by State, local, and Tribal monitoring 
agencies (``monitoring agencies'') according to the monitoring 
requirements contained in 40 CFR parts 50, 53, and 58. This section 
explains aspects of the existing Pb monitoring and reporting 
requirements as background and discusses the changes we are proposing 
to support the changes being proposed in the Pb NAAQS and other options 
for the NAAQS on which EPA is inviting comments, discussed above in 
section II.E. These aspects include the sampling and analysis methods 
(including quality assurance requirements), network design, sampling 
schedule, data reporting, and other miscellaneous requirements.

A. Sampling and Analysis Methods

    We are proposing changes to the sampling and analysis methods for 
the Pb monitoring network. Specifically, we are proposing a new Federal 
Reference Method (FRM) for Pb in PM10 (Pb-PM10) 
and revised Federal Equivalent Method (FEM) criteria. We are 
maintaining the current FRM for Pb in TSP (Pb-TSP) and lowering the Pb 
concentration range required during Pb-TSP and Pb-PM10 
candidate FEM comparability testing. The following sections provide 
background, rationale, and details for the proposed changes to the 
sampling and analysis methods.
1. Background
    Lead monitoring data must be collected and analyzed using FRM or 
FEM methods in order to be comparable to the NAAQS. The current FRM for 
Pb sampling and analysis is based on the use of a high-volume TSP FRM 
sampler to collect the particulate matter sample and the use of atomic 
absorption (AA) spectrometry for the analysis of Pb in a nitric acid 
extract of the filter sample (40 CFR part 50, Appendix G). There are 21 
FEMs currently approved for Pb-TSP \160\. All 21 FEMs are based on the 
use of high-volume TSP samplers and a variety of approved equivalent 
analysis methods.\161\
---------------------------------------------------------------------------

    \160\ For a list of currently approved FRM/FEMs for Pb-TSP refer 
to: http://www.epa.gov/ttn/amtic/criteria.html.
    \161\ The 21 distinct approved FEMs represent less than 21 
fundamentally different analysis methods, as some differ in only in 
minor aspects.
---------------------------------------------------------------------------

    Concerns have been raised over the use of the high-volume TSP 
samplers to collect samples for subsequent Pb analysis. It is known 
that the high-volume TSP sampler's particulate matter capture 
efficiency varies as a function of wind speed and wind direction due to 
the non-symmetrical inlet design and the lack of an integral particle 
separator. Early evaluations of the high-volume TSP sampler 
demonstrated that the sampler's 50% collection efficiency cutpoint can 
vary between 25 and 50 [mu]m depending on wind speed and direction 
(Wedding et al., 1977, McFarland and Rodes, 1979). More recently, a 
study was conducted during the last Pb NAAQS review to evaluate the 
effect of wind speed and direction on sampler efficiency (Purdue, 
1988). This study showed that despite the effect of wind speed and wind 
direction on the sampler's collection efficiency for larger particles, 
for particle distributions typical of those near industrial sources the 
overall Pb collection efficiency of the high-volume TSP sampler ranged 
from 80% to 90% over a wide range of wind speeds and directions.
    CASAC commented in the context of their review of the Staff Paper 
that TSP samplers have poor precision, that the upper particle cut size 
of TSP samplers varies widely as a function of wind speed and 
direction, and that the spatial non-homogeneity of very coarse 
particles cannot be efficiently captured by a national monitoring 
network (Henderson, 2007a, Henderson, 2008). For these reasons, CASAC 
recommended considering a revision to the Pb reference method to allow 
sample collection using low-volume PM10 samplers.\162\
---------------------------------------------------------------------------

    \162\ PM10 can be measured with either a ``low-
volume'' or a ``high-volume'' sampler. CASAC specifically 
recommended the low-volume sampler, for reasons explained here and 
in section II.E.1.
---------------------------------------------------------------------------

    As part of preparing the ANPR for this rulemaking, we performed and 
reported in the ANPR the results of an analysis of the precision and 
bias of the high-volume TSP sampler based on Pb-TSP

[[Page 29259]]

data reported to AQS for collocated samplers and the results of in-
field sampler flow audits and laboratory audits for lead (Camalier and 
Rice, 2007). The average precision of the high-volume Pb-TSP sampler 
was approximately 12% with a standard deviation of 19% and average 
sampling bias (based on flow audits) was -0.7% with a standard 
deviation of 4.2%. The average bias for the lab analyses of Pb-spiked 
audit strips was -1.1% with a standard deviation of 5.5%. Total bias, 
which includes bias from both sampling and laboratory analysis, was 
estimated at -1.7% with a standard deviation of 3.4%. These findings 
are specific for the times and sites of the sampling, including the 
nature and total quantity of TSP and Pb-TSP that prevailed during the 
sampling, and may not be indicative of the TSP FRM performance in other 
places. Also, we did not investigate to determine whether the physical 
arrangement of the collocated samplers was such as to provide a good 
test of sensitivity to wind speed and wind direction.\163\ However, we 
note that at face value these bias and precision results are not 
greatly different than has historically been considered acceptable for 
other criteria pollutants.
---------------------------------------------------------------------------

    \163\ If the collocated TSP samplers were always oriented in the 
same direction, they would be exposed to the same wind speed and 
wind direction, and the appearance of good precision between them 
would not necessarily be indicative of the sensitivity of Pb-TSP 
measurements to wind speed and wind direction.
---------------------------------------------------------------------------

    The CASAC and some public comments on the ANPR again stressed 
concerns with the use of the high-volume TSP sampler and a strong 
interest in moving to a low-volume Pb-PM10 sampler. The 
CASAC reiterated the disadvantages of retaining TSP and of utilizing it 
as the ``gold standard'' against which new and better technologies are 
compared (Henderson 2008). On March 25, 2008, the AAMM Subcommittee of 
CASAC and EPA staff conducted a consultation by conference call, at 
which the subcommittee members confirmed and elaborated on the views 
CASAC expressed in their comments on the ANPR. Public comments were 
also generally supportive of moving away from the current high-volume 
PM sampling technology and moving toward modern, sequential, low-volume 
PM10 monitors, especially if sampling frequencies are 
increased. On the other hand, several monitoring agencies cautioned 
against moving to Pb-PM10 as the indicator because samplers 
for Pb-PM10 would miss much of the Pb in the atmosphere 
especially near Pb sources.
    CASAC recommended that Pb-PM10 be measured with low-
cost, multi-element analysis methods with improved detection limits 
(e.g., x-ray fluorescence, XRF) for measuring concentrations typical of 
today's ambient air. One public commenter suggested that the MDL be 
significantly reduced to enable measurement of average Pb levels of 
0.08 [mu]g/m\3\ or below.
    The current post-sampling FRM analysis method for Pb-TSP is atomic 
absorption (AA) spectrometry. A typical or nominal lower detectable 
limit (LDL) for Pb, for high-volume sample collection followed by AA 
analysis, stated in the FRM regulation in Appendix G to Part 50 for 
informational purposes only, is 0.07 [mu]g/m\3\. This value was 
calculated by doubling the between-laboratory standard deviation 
obtained for the lowest measurable lead concentration (Long 1979). This 
value can be considered a conservative (i.e., upper bound) estimate of 
the sensitivity for the AA method currently used by air monitoring 
laboratories, as evidence by the fact that data obtained from AQS 
includes reported locally determined MDL values for the AA FRM that are 
well below 0.07 [mu]g/m\3\ (typically 0.01 (g/m\3\ or below).
    One estimate of the method detection limit (MDL) for AA analysis of 
a low-volume sample of either Pb-PM10 or Pb-TSP, taking into 
account the nominal LDL of 0.07 [mu]g/m\3\ (or 140 [mu]g/L), and the 
smaller sample volume, extraction volume, and filter size for low-
volume sampling, is about 0.12 [mu]g/m\3\ (see Table 10). Assuming an 
LDL of 0.01 (g/m\3\ for TSP sampling, the MDL for low-volume sampling 
would be about 0.02 (g/m\3\. Other Pb-TSP FEM analysis methods 
currently used with the high-volume sampling method, such as XRF, 
inductively coupled plasma mass spectrometry (ICP/MS) and graphite 
furnace atomic absorption (GFAA) are more sensitive than AA analysis, 
and are clearly sensitive enough to support low-volume sampling and a 
reduced NAAQS level.
2. Proposed Changes
    As discussed in Section II.E.3 of this preamble, after considering 
the CASAC and public comments on monitoring issues, we are proposing to 
retain Pb-TSP, as measured by the FRM method specified in 40 CFR part 
50, appendix G (which cross references appendix B, the specification of 
the TSP FRM) as the indicator for the Pb standard, and to invite 
comment on a second option which would instead make Pb-PM10 
measured by a low-volume monitor the indicator. We further propose that 
monitoring agencies should be given the option to use adjusted or 
scaled low-volume Pb-PM10 monitoring data as a surrogate for 
Pb-TSP data. Details on how this option would work are discussed in the 
data handling section of this preamble (section IV). Also, in section 
IV.B we are inviting comment on whether, if low-volume Pb-
PM10 is selected as the indicator, Pb-TSP data with an 
adjustment should be useable as a surrogate for Pb-PM10 data 
for the specific purpose of initial designations under the revised 
standard. In this section, we discuss the Pb-TSP and Pb-PM10 
sampling and analysis issues themselves and propose approaches for 
these issues, as these issues are relevant to the use of data from each 
method directly or as surrogates for the other.
a. TSP Sampling Method
    If the final standard is based on Pb-TSP we believe it is 
appropriate to continue to allow, although perhaps not to encourage, 
the use of the current high-volume FRM for measuring Pb-TSP. The 
selection of Pb-TSP as the NAAQS indicator would depend on a conclusion 
that the precision, bias, and MDL (discussed above) of the TSP sampler 
is adequate for continued use in the Pb monitoring network, including a 
conclusion that although the TSP sampler's size selection performance 
is affected by wind speed and wind direction, we do not believe that 
this effect is so significant as to prevent the continued use of this 
sampler in the Pb network. EPA proposes to make several minor 
clarifying changes in Appendix G to correct long-standing errors in 
reference citations. We are not proposing any other substantive changes 
to Appendix G.
    However, we also believe that low-volume Pb-TSP samplers might be 
superior to high-volume TSP samplers. Presently, a low-volume TSP 
sampler cannot obtain FRM status, because the FRM is specified in 
design terms that preclude designation of a low-volume sampler as a 
FRM. A low-volume Pb-TSP monitoring system (including an analytical 
method for Pb) can in principle be designated as a FEM Pb-TSP monitor, 
if side-by-side testing is performed as prescribed by 40 CFR 53.33. We 
are proposing amendments to this CFR section, described below, to make 
such testing more practical and to clarify that both high-volume and 
low-volume TSP methods may use this route to FEM status. Note that the 
terms of the revised FEM procedures can also be used to obtain FEM 
status for Pb-PM10 samplers.

[[Page 29260]]

b. PM10 Sampling Method
    If the final standard is based on Pb-PM10, or if the 
final rule for a standard based on Pb-TSP includes an option to monitor 
Pb-PM10 instead of Pb-TSP, we will need to promulgate both 
an FRM for measuring Pb-PM10 and an appropriate set of FEM 
criteria. Accordingly, we are proposing new FRM and FEM criteria for 
measuring Pb-PM10. The proposed FRM for Pb-PM10 
can be broken down into two parts: (1) the sampling method (i.e., the 
procedures and apparatus used for collecting PM10 on a 
filter) and (2) the analysis method (i.e., the procedures and apparatus 
used to analyze the collected particulate matter for Pb content).
    Currently, the FRM specification for PM10 monitoring, 
Appendix J to 40 CFR Part 50, is based on a performance test and does 
not specify whether a sampler is high-volume or low-volume. Early 
commercialized samplers were high-volume, but more recently a number of 
low-volume PM10 samplers have received FRM approvals. To be 
certain that Pb-PM10 monitoring is conducted with low-volume 
samplers without specifying the use of particular sampler brands or 
models, it is necessary to establish a new FRM specification for low-
volume PM10 samplers. There is a recently promulgated FRM 
for particulate matter with aerodynamic diameter between 2.5 and 10 
microns (PM10-2.5) (Appendix O to 40 CFR part 50) that is 
based on a pair of low-volume samplers for PM2.5 and 
PM10 to provide a PM10-2.5 concentration by 
difference. We are proposing to create a FRM for Pb-PM10 
sampling by cross-referencing to the specification for the 
PM10 sampler in this paired FRM (referred to as the 
PM10C sampler, where the ``C'' refers to the use of this 
PM10 sampler as part of a pair for measuring coarse PM). We 
are proposing to use the low-volume PM10C sampler for the 
FRM for Pb-PM10 rather than the existing PM10 FRM 
specified by appendix J, for several reasons. Appendix J to part 50 has 
resulted in the designation of both high-volume and low-volume 
PM10 samplers as FRM for PM10. We believe high-
volume PM10 sampling should not be used to measure Pb-
PM10 under a revised Pb standard. A low-volume 
PM10C FRM sampler must meet more demanding performance 
criteria than is required for PM10 samplers in general in 
Appendix J. We note the current availability of samplers that meet 
these more demanding performance criteria (already in use for 
PM2.5 and PM10-2.5 sampling) that are equipped 
with sequential sampling capabilities (i.e., the ability to schedule 
multiple samples between operator visits, which is desirable if the 
proposed sampling frequency requirements are increased to support a 
monthly averaging form of Pb NAAQS). The geometry of commercial high-
volume PM10 samplers makes sequential sampling with a single 
sampler impossible. The low-volume sampler also precisely maintains a 
constant sample flow rate corrected to actual conditions by actively 
sensing changes in temperature and pressure and regulating sampling 
flow rate. Use of a low-volume sampler for the Pb-PM10 FRM 
would also provide network efficiencies and operational consistencies 
with the samplers that are in widespread use for the PM2.5 
FRM network, and that are seeing growing use in the PM10 and 
PM10-2.5 networks. Finally, the use of a low-volume sampler 
is consistent with the comments and recommendations from CASAC and 
members of CASAC's AAMM (Henderson 2007a, Henderson 2008, Russell 
2008).
    Low-volume Pb-PM10 samplers and the data systems that 
they connect to can be configured to report concentrations corrected to 
standard conditions of temperature and pressure or based on local 
conditions of temperature and pressure. We are proposing that the FRM 
for samplers used to collect Pb data specify reporting of 
concentrations based on local conditions, for a few reasons. The actual 
concentration of Pb in the atmosphere is a better indicator of the 
potential for deposition than the concentration based on standard 
pressure and temperature. In addition, there are practical advantages 
to moving to local conditions since the FRM for both PM2.5 
and PM10-2.5 are also based on local conditions.
c. Analysis Method
    There are several potential analysis methods for a Pb-
PM10 FRM. Atomic absorption (AA) is the analysis method for 
the current Pb-TSP FRM. In addition, there are several other analysis 
methods (e.g., XRF, ICP/MS) approved as FEMs for the measurement of Pb-
TSP. Table 10 summarizes the estimated MDLs for the analysis methods 
considered in developing the proposed FRM for Pb-PM10. The 
estimated MDLs are based on published instrument detection limits and 
LDLs, which typically take into account only instrument signal-to-noise 
ratios and laboratory-related variability but not variability related 
to sample collection and handling. It is important to note that the 
MDLs in Table 10 are estimates and these values will vary as a function 
of the specific instrument used, detector age, instrument signal-to-
noise level, etc., and therefore, MDLs must be determined for the 
specific instrument used.

Table 10.--Summary of Candidate Analysis Method Detection Limits for a Pb-PM10 FRM or FEM With Low-Volume Sample
                                                   Collection
----------------------------------------------------------------------------------------------------------------
                                                                                                  Estimated MDL
                 Analysis method                                Estimated DLs \a\                 \b\  ([mu]g/
                                                                                                      m\3\)
----------------------------------------------------------------------------------------------------------------
Atomic Absorption (AA)..........................  0.07 [mu]g/m\3\ \c\.........................         0.12 \f\
                                                  0.01 [mu]g/m\3\ \d\.........................         0.02 \f\
X-Ray Fluorescence (XRF)........................  1.5 ng/cm\2\ \e\............................         0.001 \g\
Graphite Furnace Atomic Absorption (GFAA).......  0.05 [mu]g/L \h\............................         0.00004 \f\
Inductively Coupled Plasma/Mass Spectrometry      0.08 [mu]g/L \e\............................         0.00006 \f\ 
 (ICP/MS).
----------------------------------------------------------------------------------------------------------------
\a\ Detection limits (DLs) found in available literature as provided in footnotes below.
\b\ Estimated MDLs determined using estimated DL, extraction volume, and sample volume as noted in footnotes
  provided.
\c\ The lower detectable limit (LDL) for Pb-TSP taken from Appendix G to Part 50 based on 2400m\3\ sample
  volume, 0.10L extraction volume, and 12 strips per filter.
\d\ Based on MDLs reported in AQS.
\e\ DL expressed as nanogram per square centimeter of filter surface is taken from the Compendium of Methods for
  the Determination of Inorganic Compounds in Ambient Air (USEPA, 1999).
\f\ Based on 46.2-mm filter extraction volume of 0.020 L and sample volume of 24 m\3\ of air.
\g\ Based on 46.2-mm filter area of 11.86 cm\2\ and sample volume of 24 m\3\ of air.
\h\ Taken from the Perkin Elmer Guide to Atomic Spectroscopy Techniques and Applications (Perkin Elmer, 2000).

[[Page 29261]]

    One disadvantage of the low-volume sampler is that the total mass 
of the PM10 sample collected is significantly lower than 
that of the high-volume sampler due to the lower volume of air sampled 
(24 m\3\ per 24 hours for the low-volume sampler versus. over 1500 m\3\ 
per 24 hours for a high-volume sampler). The lower mass of sample 
collected results in higher MDLs for any given analysis method when 
coupled with the low-volume sampler. As can be seen in Table 10, even 
assuming the smaller LDL reported to AQS for recent sampling, the 
estimated MDL for atomic absorption (the current FRM analysis method 
for Pb-TSP) when coupled with low-volume sampling is the highest (least 
sensitive) of all potential methods for use as an FRM/FEM method for 
Pb-PM10.
    AA, GFAA, and ICP/MS are destructive methods and require solvent 
extractions that possibly involve the use of strong acids to adequately 
extract Pb from the collected PM for analysis. The specific extraction 
solutions and methods are selected and optimized in order to meet the 
required extraction efficiency for a measurement program. Both methods 
are destructive, meaning that the sample collected on the filter is 
destroyed during analysis. These methods also have higher analysis 
costs relative to XRF.
    While XRF, GFAA, and ICP/MS all have more than adequate MDLs to 
support a reduced NAAQS level, we believe that the XRF analysis method 
has several advantages which make it a desirable analysis method to 
specify as the FRM. XRF does not require sample preparation or 
extraction with acids prior to analysis. It is a non-destructive 
method; therefore, the sample is not destroyed during analysis and can 
be archived for future analysis or re-analysis if needed. XRF analysis 
is a cost-effective approach that could be used at the option of the 
monitoring agency to simultaneously analyze for many additional metals 
(e.g., arsenic, antimony, and iron) which may be useful in source 
apportionment. XRF is also the method used for the urban 
PM2.5 speciation monitoring networks and for the mostly 
rural visibility monitoring program in Class I visibility areas, and is 
being considered for the PM10-2.5 coarse speciation 
monitoring network that will be implemented by monitoring agencies as 
part of the NCore multi-pollutant network. The XRF analysis method 
should have acceptable precision, bias, and MDL for use as the FRM for 
Pb-PM10 when coupled with the low-volume PM10 
sampler. Finally, CASAC recommended the use of XRF as a low-cost and 
sensitive analysis method for the FRM (Henderson 2007a, Henderson 
2008). For these reasons, we are proposing to base the analysis method 
for the proposed Pb-PM10 FRM on XRF.
d. FEM Criteria
    The FEM criteria provide for approval of candidate methods that 
employ an alternative analysis method for Pb, an alternative sampler, 
or both.
    The proposed Pb-PM10 FRM is based on the low-volume 
PM10c sampler and XRF analysis. Under the proposed revisions 
to 40 CFR 53.33, Pb-PM10 data from any candidate FEM using 
an alternative sampler would be compared to side-by-side data from the 
low-volume PM10c FRM sampler. An FEM candidate using only an 
alternative analysis method would be evaluated by collecting paired 
filters from paired low-volume PM10c FRM samplers, and 
analyzing one filter of each pair with XRF and the other filter with 
the candidate method.
    As mentioned above, there are other analysis methods commonly used 
which are also expected to meet the precision, bias, and MDLs necessary 
to be used in the Pb surveillance monitoring network (e.g., GFAA and 
ICP/MS). These analysis methods would be compared to the proposed XRF 
method and would be approvable as FEMs through the performance testing 
requirements outlined in regulation Sec.  53.33 of 40 CFR part 53, 
subpart C. Several of these requirements need revisions for consistency 
with a potentially lowered Pb NAAQS and for the potential addition of a 
Pb-PM10 FRM. The following paragraphs describe the aspects 
of the FEM criteria that we are proposing to revise.
    The current FEM requirements state that the ambient Pb 
concentration range at which the FEM comparability testing must be 
conducted to be valid is 0.5 to 4.0 [mu]g/m\3\. Currently there are few 
locations in the United States where FEM testing can be conducted with 
assurance that the ambient concentrations during the time of the 
testing would exceed 0.5 [mu]g/m\3\. In addition, the Agency is 
proposing to lower the Pb NAAQS level to between 0.10 and 0.30 [mu]g/
m\3\. As such, we are proposing to revise the Pb concentration 
requirements for candidate FEM testing to a range of 30% of the NAAQS 
to 250% of the NAAQS in [mu]g/m\3\. For example, if the level of the Pb 
NAAQS is finalized at 0.20 [mu]g/m\3\, the ambient concentrations that 
would be required for FEM testing would have to range between 0.06 
[mu]g/m\3\ to 0.50 [mu]g/m\3\. The requirements were changed from 
actual concentration values to percentages of the NAAQS to allow the 
FEM text to remain appropriate if subsequent changes to NAAQS levels 
occur in the future.
    The current FEM requirements state that the maximum precision and 
accuracy for candidate analytical methods must be 15% and 5% 
respectively. No changes are proposed for these requirements. Based on 
the results for the current high-volume Pb-TSP precision and bias 
(Camalier and Rice, 2007), these requirement seem reasonable for the 
proposed FEM requirements. The current FEM does not have a requirement 
for a maximum MDL. In order to ensure that candidate analytical methods 
have adequate sensitivity or MDLs, we are proposing to add a 
requirement that as part of the testing of a candidate FEM, the 
applicant must demonstrate that the MDL of the method is less than 1% 
of the level of Pb NAAQS. We believe this MDL requirement will ensure 
that FEM methods will have enough sensitivity to detect Pb 
concentrations much less than the proposed NAAQS level, but will not 
unnecessarily restrict methods which could be used to provide data 
sufficient for the purpose of determining compliance with the NAAQS. 
Subsequent users of a previously approved FEM would not be required to 
demonstrate the MDL of the method as implemented in their laboratories, 
but EPA plans to encourage them to do so periodically as a good quality 
assurance practice.
    The existing FEM requirements require that audit samples (the known 
concentration or reference samples provided on request by EPA used to 
verify the accuracy with which a laboratory conducts the FRM analytical 
procedure before it may begin comparing the FRM to the candidate FEM) 
be analyzed at levels that are equal to 100, 300, and 750 [mu]g per 
spiked filter strip (equivalent to 0.5, 1.5, and 3.75 [mu]g/m\3\ of 
sampled air). We are proposing to revise the levels of the audit 
concentrations to percentages (30%, 100% and 250%) of the Pb NAAQS to 
provide for reduced audit concentrations for a lowered NAAQS. These 
percentages are roughly equivalent to the percentages of the current 
NAAQS level (1.5 [mu]g/m\3\) used to set the spiked filter strip audit 
concentrations provided above in the original FEM regulation.
    The existing FEM requirements are based on the high-volume TSP 
sampler, and as such, refer to \3/4\ x 8-inch glass fiber strips. In 
order to also accommodate the use of low-volume sample filters, we are 
proposing to add references to 46.2-mm sample filters

[[Page 29262]]

where appropriate. Pairs of these filters will be collected by a pair 
of FRM samplers, so that there is no need to cut the 46.2 mm filters 
into two parts before analysis.
e. Quality Assurance
    Modifications are needed to the quality assurance (QA) requirements 
for Pb in 40 CFR part 58, Appendix A paragraph 3.3.4 in order to 
accommodate Pb-PM10 monitoring. Paragraph 3.3.4 specifies 
requirements for annual flow rate audits for TSP samplers used in Pb 
monitoring and Pb strip audits for laboratories performing analysis of 
TSP filters for Pb. Other QA requirements specified in paragraph 3.3.1 
for all TSP samplers are also applicable to Pb-TSP samplers. As part of 
the overall Pb NAAQS review, it is appropriate to revise these 
requirements to consolidate all the QA requirements for Pb monitoring 
in paragraph 3.3.4, to add provisions specific for Pb-PM10 
measurements and to eliminate cross references to the general TSP 
provisions. The following paragraphs detail the QA requirements we are 
proposing to change.
    The collocation requirement for all TSP samplers (paragraph 3.3.1) 
applies to TSP samplers used for Pb-TSP monitoring. These requirements 
are the same for PM10 (paragraph 3.3.1); as such, no changes 
are needed to accommodate low-volume Pb-PM10. However, to 
clarify that this requirement also applies to Pb monitoring we are 
proposing to add a reference to this requirement in paragraph 3.3.4.
    The sampler flow rate verifications requirement (paragraph 3.3.2) 
for low-volume PM10 and for TSP are at different intervals. 
While this appears appropriate and no change is needed, to clarify that 
this requirement also applies to Pb monitoring we are proposing to add 
a reference to this requirement in paragraph 3.3.4.
    Paragraph 3.3.4.1 has an error in the text that suggests an annual 
flow rate audit for Pb, but then includes reference in the text to 
semi-annual audits. The correct flow rate audit frequency is semi-
annual. We are proposing to correct this error. Also, we are proposing 
to change the references to the Pb FRM to include the proposed Pb-
PM10 FRM.
    Paragraph 3.3.4.2 discusses the audit procedures for the lead 
analysis method. This section assumes the use of a high-volume TSP 
sampler, and we are proposing edits to account for the proposed Pb-
PM10 FRM. In addition, the audit concentration ranges will 
not be appropriate if the NAAQS is lowered. We are proposing to lower 
the audit ranges for Pb-TSP from the current range of 0.5-1.5 [mu]g/
m\3\ to a range from 30-100% of the proposed Pb NAAQS level for the low 
concentration audit and from 3.0-5.0 [mu]g/m\3\ to 200-300% of the 
proposed NAAQS for the higher concentration audit standard. The 
requirements would also be changed from specific concentration value-
based ranges to ranges based on the percentages of the NAAQS to allow 
these QA requirements to remain appropriate if changes to NAAQS levels 
occur during future reviews.
    Unlike the PM2.5 and PM10-2.5 Performance 
Evaluation Program (PEP), the existing QA program requirements for Pb 
monitoring do not include a requirement for the collection of data 
appropriate for making an independent estimate of the overall sampling 
and analysis bias. We are proposing to require one PEP-like audit at 
one site within each primary quality assurance organization (PQAO) once 
per year. We are also proposing that, for each quarter, one filter of a 
collocated sample filter pair from one site within each PQAO be sent to 
an independent laboratory for analysis. The independent measurement on 
one filter from each pair would be compared to the monitoring agency's 
regular laboratory's measurement on the other filter of the pair, to 
allow estimation of any bias in the regular laboratory's measurements. 
EPA believes that the combination of the PEP data and the independent 
collocation data will be enough to provide a reasonable assessment of 
overall bias and data comparability on a PQAO basis over the 
designation period. As currently is the case for PEP auditing of 
PM2.5 and PM10-2.5 monitoring sites, it would be 
the responsibility of each State to ensure that Pb PEP testing and 
collocation testing as described here is performed as required. EPA 
plans to consult with monitoring agencies after completion of this 
rulemaking as to whether a centrally run program managed by EPA and 
funded with State and Tribal Assistance Grant funds would be a more 
efficient and preferred alternative than individual State-managed 
programs.

B. Network Design

    As a result of this Pb NAAQS review and the proposed tightening of 
the standards, EPA recognizes that the current network design 
requirements are inadequate to assess compliance and determine the 
extent of all the areas that may violate the revised NAAQS. As such, we 
are proposing new network design requirements for the Pb NAAQS 
surveillance network. The following sections provide background, 
rationale, and details for the proposed changes to the Pb network 
design requirements.
1. Background
    The once large Pb surveillance network of FRM samplers for Pb-TSP 
has decreased substantially over the last few decades. In 1980 there 
were over 900 Pb surveillance sites. This number has been reduced to 
approximately 200 sites today. These reductions were made because of 
substantially reduced ambient Pb concentrations causing monitoring 
agencies to shift priorities to other criteria pollutants including 
PM2.5 and ozone which were believed to pose a greater health 
risk. As a result of these reductions, many states currently have no 
ambient air Pb monitors resulting in large portions of the country with 
no data on current ambient Pb air concentrations. In addition, many of 
the largest Pb emitting sources in the country do not have nearby 
ambient Pb air monitors.
    There is also a smaller network, the National Air Toxics Trends 
Stations network, of 27 monitoring sites measuring Pb-PM10. 
Some of these use a high-volume PM10 sampler to collect the 
particulate matter and some use a low-volume PM10 sampler. 
Most are in urban areas.
    The current network design requirements for Pb monitoring are given 
in 40 CFR part 58 appendix D section 4.5. The current minimum network 
design requirements are for two Federal Reference Method (FRM) or 
Federal Equivalent Method (FEM) sites in any area where Pb 
concentrations exceed or have exceeded the NAAQS in the most recent two 
years. These current minimum monitoring requirements cannot be relied 
upon to cause monitoring agencies to fill the existing gaps in the 
current network, and if they are not revised it will be difficult to 
develop the necessary network to properly evaluate ambient air 
concentrations during the designation process, especially if the NAAQS 
is finalized at a significantly lower level than the current standard.
    For these reasons, EPA indicated in the Advanced Notice of Proposed 
Rulemaking (72 FR 71488) that the existing Pb NAAQS surveillance 
network may not be adequate for a lowered Pb NAAQS, and that if the 
NAAQS is substantially lowered as proposed additional monitoring sites 
would be needed to provide estimates of ambient Pb air concentrations 
near Pb emission sources and for characterizing ambient air 
concentrations in large urban areas. Comments received from CASAC and 
other public commenters

[[Page 29263]]

on the ANPR stated that the Pb surveillance network should be expanded 
in order to provide better coverage of Pb emission sources and to 
better understand population exposures to Pb from ambient air. After 
considering these comments and evaluating the existing network, EPA is 
proposing changes to the network as described below.
2. Proposed Changes
    We are proposing to modify the existing network design requirements 
for the Pb surveillance monitoring network to achieve better 
understanding of ambient Pb air concentrations near Pb emission sources 
and to provide better information on population exposure to Pb in large 
urban areas. The following paragraphs provide the rationale and details 
for the proposed changes.
    The primary objective of the Pb monitoring network is to provide 
data on the ambient Pb air concentrations in areas where there is the 
potential for a violation of the NAAQS. Ambient Pb concentrations have 
dropped dramatically in most urban areas due to the elimination of Pb 
in gasoline. However, based on our analysis of the ambient Pb data, 
relatively large sources of Pb continue to have the potential to cause 
ambient air concentrations in excess of the proposed NAAQS (EPA, 
2007c). Furthermore, it appears, based on the limited network still 
operating, that violations of the proposed range for the revised NAAQS 
levels are likely to exist only near such sources of Pb emissions, with 
lower levels of Pb away from such sources. Accordingly, we are 
proposing to require monitoring near Pb emission sources such as Pb 
smelters, metallurgical operations, battery manufacturing, and other 
source categories that emit Pb. By implementing the NAAQS through a 
source-oriented monitoring network, Pb concentrations will be kept 
below the NAAQS level for those living near these sources and for those 
living farther away.
    The 2002 National Emissions Inventory (NEI) lists over 13,000 
sources of Pb, with emission rates from as low as 1 pound to nearly 60 
tons per year (according to the NEI 90% of lead sources emit less than 
0.1 tpy). It is not practical to conduct monitoring at every Pb 
emission source, nor is it likely that very small Pb emission sources 
will cause ambient concentrations to exceed the proposed NAAQS. 
Therefore, it is appropriate to limit the source oriented monitoring 
requirement to emission sources that may have the potential to result 
in ambient air concentrations in excess of the proposed NAAQS.
    We are proposing that monitoring be presumptively required at 
sources that have Pb emissions (as identified in the latest NEI or by 
other scientifically justifiable methods and data) that exceed a Pb 
``emissions threshold.'' This monitoring requirement would apply not 
only to existing industrial sources of lead, but also to fugitive 
sources of lead (e.g., mine tailing piles, closed industrial 
facilities) and airports where leaded aviation gas is used. In this 
context, the emissions threshold is the Pb emission rate for a source 
that may reasonably be expected to result in ambient air concentrations 
in excess of the proposed Pb NAAQS. We conducted an analysis to 
estimate the appropriate emission threshold (Cavender 2008b) which is 
available in the docket for this rulemaking. In this analysis, four 
different methods were used for calculating an appropriate threshold 
emissions rate based on the candidate NAAQS level. The arithmetic mean 
of the four methods suggests a maximum emission impact of 0.5 [mu]g/
m\3\ per 1,000 kg Pb emitted per year. Using the results from this 
analysis, we propose that the emission threshold be set in the range of 
200 kg-600 kg per year total Pb emissions (including point, area, and 
fugitive emissions and including Pb in all sizes of PM). We are 
proposing a range for the emission threshold since we are proposing a 
range for the level of the standard. If the final NAAQS is set at 0.10 
[mu]g/m\3\, we would set the emission threshold at 200 kg per year. 
Conversely, if the final NAAQS is set at 0.30 [mu]g/m\3\, we would set 
the emission threshold at 600 kg per year. We solicit comments on the 
various methods for calculating emission rate thresholds, as well as 
using the arithmetic mean of these results in choosing the appropriate 
threshold for designing the monitoring network.
    We recognize that a number of factors influence the actual impact a 
source of Pb has on ambient Pb concentrations (e.g., local meteorology, 
emission release characteristics, and terrain). As such, we are also 
proposing to allow monitoring agencies to petition the EPA Regional 
Administrator to waive this requirement for a source that emits less 
than 1 ton per year where it can be shown (by demonstrating actual 
emissions are less than the threshold, through modeling, historical 
monitoring data, or other means) that a source will not cause ambient 
air concentrations to exceed 50% of the NAAQS during a three year 
period. We are proposing that for facilities identified as emitting 
more than 1 tpy in the NEI, a waiver is possible only by demonstrating 
that actual emissions are less than the emissions threshold. By 
requiring every source actually emitting more than 1 tpy to be 
monitored, we will avoid the possibility that faulty or uncertain 
modeling demonstrations or past monitoring programs would be the basis 
for not monitoring sources that are the most likely to cause NAAQS 
violations.
    We seek comments on the appropriateness of requiring monitoring 
near Pb emissions sources and the proposed emission rate threshold. We 
also seek comments on the appropriateness of allowing monitoring 
agencies to seek waivers from this requirement and the upper emission 
threshold level at which waivers should no longer be allowed.
    The required source-oriented monitors shall be located at sites of 
maximum impact and will be classified primarily as microscale monitors 
representative of small hot-spot areas adjacent or nearly adjacent to 
facility fence-lines. EPA takes comment on this monitoring requirement 
and whether monitors should only be placed in areas which are 
population-oriented. In some cases, source-oriented monitors may be 
representative of somewhat bigger areas due to the orientation of 
sources with respect to areas with locations appropriate for ambient 
monitoring. In these cases, the source-oriented monitors may be 
classified as middle-scale, but should still represent the locations 
where maximum Pb concentrations around a facility are expected to 
occur, consistent with applicable siting regulations and the outputs of 
quantitative tools (e.g., dispersion modeling) used to determine 
maximum impacts.
    We are proposing to require a small network of nonsource-oriented 
monitors in urban areas in addition to the source oriented monitors 
discussed above, in order to gather information on the general 
population exposure to Pb in ambient air. While it is expected that 
these nonsource-oriented monitors will show lower concentrations than 
source oriented monitors, data from these nonsource-oriented monitors 
will be helpful in understanding the risk posed by Pb to the general 
population. Data from these monitors will also be useful in determining 
impacts on Pb concentrations from re-entrained roadway dust, 
construction and demolition projects, other nonpoint area sources; and 
in determining the spatial variation in Pb concentrations between areas 
that are and are not source impacted. Such data on spatial variations 
within an urban area could assist with the determination of non-
attainment boundaries.

[[Page 29264]]

    We are proposing to require one nonsource-oriented monitor in each 
Core Base Statistical Area (CBSA, as defined by the Office of 
Management and Budget)\164\ with a population of 1,000,000 people or 
more as determined in the most recent census estimates. Based on the 
most current census estimates, 50 CBSAs would be required to have 
nonsource-oriented population monitors. We request comments on the 
appropriateness of requiring nonsource-oriented monitors and the 
proposed population threshold of 1,000,000 people for this requirement.
---------------------------------------------------------------------------

    \164\ For the complete definition of CBSA refer to: http://
www.census.gov/population/www/estimates/aboutmetro.html.
---------------------------------------------------------------------------

    Lead concentrations near roadways are not well understood at this 
time. The Pb critieria document discussed data for the South Coast Air 
Quality Management District where a modeling effort suggested that Pb 
deposited during the years when leaded gasoline was used could be a 
significant portion of their ambient Pb inventory. However, this work 
was conducted in an area of the country where quarterly average Pb-TSP 
concentrations are considerably less than 0.1 [mu]g/m\3\. We analyzed 
ambient air Pb concentrations near a number of large roadways (Cavender 
2008). Based on this analysis it appears unlikely that roadways will 
result in ambient Pb air concentrations in excess of the lowest Pb 
NAAQS level being proposed in this action. In addition, members of the 
CASAC AAMM Subcommittee agreed that a separate monitoring requirement 
for roadways was unnecessary based on the results of this analysis. As 
such, the proposed regulatory text does not include a requirement for 
Pb monitoring near roadways. We do, however, propose to allow 
monitoring near roadways to satisfy the requirements of the nonsource-
oriented monitoring requirement discussed above. For example, a 
monitoring agency could place a monitor in a CBSA with a population 
greater than one million and locate that monitor nearly adjacent to a 
major roadway in a populated area. That monitor would satisfy the 
nonsource-oriented requirements while also gathering data on possible 
roadway exposure. We request comments on the need for monitoring near 
roadways and the appropriateness of allowing near roadway monitoring to 
be used to satisfy the requirement for nonsource-oriented monitoring.
    Monitoring agencies would need to install new Pb monitoring sites 
as a result of these proposed revisions to the Pb monitoring 
requirements. We are estimating that the size of the required Pb 
network will range from between approximately 160 and 500 sites, 
depending on the level of the final standard. If the size of the final 
network is on the order of 500 sites, we are proposing to allow 
monitoring agencies to stagger the installation of newly required sites 
over two years, with at least half the newly required Pb monitoring 
sites being installed and operating by January 1, 2010 (16 months after 
the court-ordered deadline for promulgation of the final Pb NAAQS 
revision) and the remaining newly required monitoring sites installed 
and operating by January 1, 2011. As proposed, monitors near the 
highest Pb emitting sources would need to be installed in the first 
year, with monitors near the lower Pb emitting sources and nonsource-
oriented monitors being installed in the second year. The annual 
network plan due on July 1, 2009 would need to include the plan and 
schedule for installation and operation of the newly required Pb 
monitoring sites necessary to comply with these proposed requirements. 
We are also proposing to allow monitoring agencies one year following 
the release of updates to the NEI or an update to the census to add new 
monitors if these updates would trigger new monitoring requirements. 
Monitoring agencies would be required to identify and propose new Pb 
monitoring sites as part of their annual network plan required under 40 
CFR 58.10. We invite comments on the need for a staggered network 
deployment.
    The type of monitor that must be used at these required monitoring 
sites will depend on whether for a final revised NAAQS based on Pb-TSP 
scaled monitoring data for Pb-PM10 may be used as a 
surrogate. If cross-use of data is permitted, then either type of 
monitor could be used at a required monitoring site. EPA intends to 
encourage a relatively small number of sites to operate both types of 
monitors. The proposed appendix R (see section IV) explains how data 
would be selected for purposes of NAAQS compliance determinations if 
both types of monitors operate in the same month or quarter. One 
approach on which EPA is seeking comment would be to change the Pb 
indicator to Pb-PM10 and allow the use of Pb-TSP data only 
for the purpose of initial designations. If this approach is adopted, a 
Pb-TSP monitor could not be used in lieu of a Pb-PM10 
sampler at a required monitoring site after the area containing the 
monitoring site had received its initial designation (see section VI 
for an explanation of the anticipated designation schedule).
    If the final Pb standard is based on Pb-TSP, the July 1, 2009 
monitoring plan would be required to designate which Pb-PM10 
monitoring sites, if any, are source-oriented, so that this designation 
can be available for public comment and can be reviewed by the EPA 
Regional Administrator. This site designation information is needed to 
determine scaling factors for the Pb concentration data from these Pb-
PM10 monitoring sites (see section IV). Sites that are 
counted towards meeting the required number of source-oriented 
monitoring sites should of course be designated as source-oriented. It 
may be appropriate to designate other sites as source-oriented also. 
Because sources may come and go, or be newly discovered, the revised 40 
CFR 58.10 requires the monitoring agency to consider whether revisions 
in site designations are needed as part of the preparation of each 
year's monitoring plan.

C. Sampling Schedule

    We are proposing to increase the sampling frequency if the final Pb 
NAAQS is based on a monthly averaging form. Specifically, we are 
proposing to increase the sampling frequency to require one 24-hour 
sample taken every 3 days (referred to as ``1 in 3 day sampling'') if 
the final Pb NAAQS is based on a monthly average. The remainder of this 
section provides background, rationale, and details for the proposed 
changes to the Pb sampling frequency.
1. Background
    The current required sampling frequency requirement for Pb is one 
24-hour sample every six days (40 CFR 58.12(b)). For the current form 
of the NAAQS that is based on a quarterly average, the 1-in-6 day 
sampling schedule yields 15 samples per quarter on average with 100% 
completeness, or 12 samples with 75% completeness. A change to a 
monthly averaging period would result in between 4 and 6 samples per 
month at the current sampling frequency with 100% completeness, or 
between 3 and 5 samples with 75% completeness.
    In the ANPR, we indicated that if we changed the averaging time to 
a monthly average, we would need to consider increasing the required 
sampling frequency from 1-in-6 days since 3 to 5 samples would likely 
not result in a reasonably confident estimate of the actual air quality 
for the period. We suggested several alternatives which included 
increasing the sampling frequency to 1-in-3 day, or increasing

[[Page 29265]]

the sampling frequency to 1-in-1 day sampling (i.e., every day 
sampling). In addition, we suggested an option that relates sampling 
frequency to recent ambient Pb-TSP concentrations, such that an 
increased sampling frequency is required as the recent ambient Pb-TSP 
concentration approaches the NAAQS level. In addition, we sought 
comments on several practices that would help to reduce the burden 
associated with more frequent sampling including:
     Increasing sampling time duration (e.g., changing from a 
24-hour sampling time duration to a 48-hour or 72-hour sampling time 
duration),
     Allowing for compositing of samples (i.e., extracting and 
analyzing several sequential samples together), and
     Allowing for multiple samplers at one site.
    In CASAC's comments on the ANPR, they recommended increasing the 
sampling frequency to 1-in-3 day sampling, or higher. They discouraged 
increasing the sample duration and the allowance for compositing of 
samples, as these practices would reduce the ability to use the samples 
in source apportionment techniques that may be useful in identifying 
what sources contributed to the ambient air Pb concentrations.
2. Proposed Changes
    We propose increasing the sampling frequency to 1-in-3 day sampling 
if we change the form of the revised NAAQS to a monthly average in the 
final rule. A 1-in-3 day sampling frequency would yield 9 or 10 samples 
per month on average at 100% completeness. At 75% completeness, a 1-in-
3 day sampling frequency would yield 7 or 8 samples per month at a 
minimum.
    We recognize that at concentrations considerably below the level of 
the NAAQS there is less potential to misclassify an area due to the 
error resulting from less than complete sampling. We believe it is 
appropriate to allow for less frequent sampling in areas with low 
ambient air Pb concentrations relative to the level of the NAAQS. As 
such, we are proposing to allow monitoring agencies to request a 
reduction in the sampling frequency to 1-in-6 day sampling if the most 
recent 3-year design value is less than 70% of the NAAQS.
    We request comment on the proposed change to 1-in-3 day sampling 
and the proposed option to reduce sampling to 1-in-6 day sampling in 
areas with low ambient Pb concentrations. We also seek comments on the 
need to increase sampling frequency further to 1-in-1 day sampling in 
areas with ambient air Pb concentrations near the level of the final 
NAAQS.
    We are currently assessing how different sampling schedules could 
affect the confidence in the estimate of a mean monthly Pb 
concentration as part of developing Data Quality Objectives (DQOs) for 
Pb monitoring. This assessment will include evaluating temporal 
variability at current Pb monitoring sites (both Pb-TSP and Pb-
PM10) in order to provide uncertainty estimates associated 
with various sampling frequency scenarios. We will evaluate 1-in-1 day, 
1-in-3 day, and 1-in-6 day sampling frequencies, at varying degrees of 
completion between 50% and 100%, and for each we plan to estimate the 
margin of error about a mean monthly estimate, focusing on sites 
assumed to be close to the proposed NAAQS. Based upon this assessment, 
expected to be complete in June of 2008, we will be able to better 
understand the uncertainties around a monthly estimate. We will use 
this better understanding and information provided in public comment to 
choose the final sampling frequency requirements.

D. Monitoring for the Secondary NAAQS

    We are not proposing additional monitoring requirements for the 
secondary NAAQS because the proposed monitoring requirements for the 
primary NAAQS will be sufficient to demonstrate compliance with the 
secondary NAAQS. The remainder of this section provides background and 
rationale on our decision to not propose additional monitoring 
requirements for the secondary NAAQS.
1. Background
    CASAC has recommended additional monitoring to gather information 
to better inform consideration of the secondary NAAQS in the next and 
future reviews. Specifically, CASAC stated that ``the EPA needs to 
initiate new measurement activities in rural areas--which quantify and 
track changes in lead concentrations in the ambient air, soils, 
deposition, surface waters, sediments and biota, along with other 
information as may be needed to calculate and apply a critical loads 
approach for assessing environmental lead exposures and risks in the 
next review cycle'' (Henderson, 2007b).
    We currently monitor ambient Pb in PM2.5 (Pb-
PM2.5) as part of the Interagency Monitoring of Protected 
Visual Environments (IMPROVE) network. There are 110 formally 
designated IMPROVE sites located in or near national parks and other 
Class I visibility areas, virtually all of these being rural. 
Approximately 80 additional sites at various urban and rural locations, 
requested and funded by various parties, are also informally treated as 
part of the IMPROVE network. While we believe it is not appropriate to 
rely on Pb-PM2.5 monitoring to demonstrate compliance with a 
Pb-TSP NAAQS, we believe the Pb-PM2.5 measurements provided 
by the IMPROVE network can be used as a useful indicator to temporal 
and spatial patterns in ambient Pb concentrations and resulting Pb 
deposition in rural areas that are not directly impacted by a nearby Pb 
emission source. In the ANPR, we suggested it might be desirable to 
augment the IMPROVE network with a small ``sentinel'' network of 
collocated Pb-TSP monitors for a period of time in order to develop a 
better understanding of how Pb-PM2.5 and Pb-TSP relate in 
these rural areas. Alternatively, since it is likely that at rural 
locations nearly all ambient Pb is in the less than 10 [mu]m size 
range, we suggested it might be possible to analyze the IMPROVE 
PM10 mass samples (which are already being collected) for Pb 
for a period of time to develop a better understanding of how Pb-
PM2.5 and Pb-PM10 relate in these rural areas.
    The National Water-Quality Assessment (NAWQA), conducted by the 
United States Geological Survey, contains data on Pb concentrations in 
surface water, bed sediment, and animal tissue for more than 50 river 
basins and aquifers throughout the country (CD, AX7.2.2.2). NAWQA data 
are collected during long-term, cyclical investigations wherein study 
units undergo intensive sampling for 3 to 4 years, followed by low-
intensity monitoring and assessment of trends every 10 years. 
Similarly, the USGS is collaborating with Canadian and Mexican 
government agencies on a multi-national project called ``Geochemical 
Landscapes'' that has as its long-term goal a soil geochemical survey 
of North America (http://minerals.cr.usgs.gov/projects/geochemical--
landscapes/index.html). The Geochemical Landscapes project has the 
potential to fill the need for periodic Pb soil sampling. We note the 
value of the NAWQA and Geochemical Landscapes data in the assessment of 
trends in Pb concentrations in both soil and aquatic systems, and 
support the continued collection of this data by the USGS.
2. Proposed Changes
    As discussed in Section III of this preamble, we are proposing to 
set the secondary NAAQS equal to the primary NAAQS. Based on our 
analysis of the

[[Page 29266]]

existing ambient Pb monitoring data (EPA 2007c), we do not expect there 
to be ambient air concentrations in excess of the proposed secondary 
NAAQS in rural areas that are not associated with a Pb emission source. 
As noted earlier in this section, we are proposing Pb surveillance 
monitoring requirements for Pb sources to demonstrate compliance with 
the primary NAAQS that will also be sufficient to determine compliance 
with the secondary NAAQS.
    The Pb-PM2.5 data collected as part of the IMPROVE 
program provides useful information on Pb concentrations in rural areas 
that can be used to track trends in ambient air Pb concentrations in 
rural areas and important ecosystems. These data are available through 
the VIEWS Web portal (http://vista.cira.colostate.edu/views/) and are 
also reported to AQS. While collection of a limited amount of 
collocated Pb-TSP or Pb-PM10 would be useful in 
understanding the relationship between Pb-PM2.5 and Pb-TSP 
(or Pb-PM10) in rural areas, we do not believe it is 
appropriate to establish a regulatory requirement for the collection of 
these data. Rather, we believe it is more appropriate to work with the 
monitoring agencies responsible for IMPROVE monitoring to encourage the 
collection of a limited amount of collocated Pb data from 
PM10 or TSP samplers. We seek comments on our decision to 
not require additional monitoring requirements for the proposed 
secondary Pb NAAQS.

E. Other Monitoring Regulation Changes

    We are proposing to make two other minor changes to various aspects 
of the Pb monitoring regulations to make them consistent with the 
proposed NAAQS. The remainder of this section discusses the proposed 
changes.
1. Reporting of Average Pressure and Temperature
    The high-volume FRM for Pb-TSP monitoring is based on standard 
pressure and temperature (25 degrees C, and 760 mmHg). We are not 
proposing to change this. As discussed in section II.E of this 
preamble, we are proposing to adopt a new FRM for low-volume Pb-
PM10 monitoring with concentration reporting based on local 
temperature and pressure. We are proposing to specify reporting based 
on local temperature and pressure because the actual concentration of 
Pb in the atmosphere is a better indicator of the potential for 
deposition than the concentration based on standard pressure and 
temperature. In addition, there are practical advantages to moving to 
local conditions since both PM2.5 and PM10-2.5 
are also based on local conditions. We are proposing to revise 40 CFR 
58.16(a) to add a requirement that the monitoring agency report the 
average pressure and temperature during the time of sampling for both 
Pb-TSP monitoring and Pb-PM10 monitoring, consistent with 
the requirements for such reporting contained in the PM2.5 
and PM10-2.5 FRMs. For low-volume Pb-PM10 
monitors, this requirement is easily met because the monitors 
incorporate temperature and pressure sensors and the monitor software 
makes reporting these parameters automatic. High-volume TSP samplers do 
not incorporate these sensors, so more effort may be needed to report 
the data. We note that sampler-generated average daily temperature and 
pressure are already required to be reported to AQS from filter-based 
PM2.5 FRM/FEM samplers, and that the current submission of 
these data would fulfill the temperature and pressure reporting 
requirements for any Pb-TSP sampling at the same site. Relevant 
measurements could also be obtained from nearby National Weather System 
(NWS) monitoring sites, nearby low-volume PM2.5 or 
PM10 samplers, and other nearby meteorological measurements 
that undergo routine quality control checks and quality assurance; 
relying on one of these sources would mean that a separate data 
submission action would be needed to associate the data with the Pb-TSP 
monitoring site. The reporting of average pressure and temperature data 
would support the ability to investigate data quality and other data 
analysis questions that may be arise with regard to the Pb-TSP or Pb-
PM10 monitors.
    We seek comment on the requirement to report the average 
temperature and pressure recorded during Pb measurements and the 
usefulness of such data in supporting data analysis purposes.
2. Special Purpose Monitoring Exemption
    According to 40 CFR 58.20(e) ``If an SPM using an FRM, FEM, or ARM 
is discontinued within 24 months of start-up, the Administrator will 
not designate an area as nonattainment for the CO, SO2, 
NO2, Pb, or 24-hour PM10 NAAQS solely on the 
basis of data from the SPM. Such data are eligible for use in 
determinations of whether a nonattainment area has attained one of 
these NAAQS.'' When this provision was added in the October 2006 
revisions to the ambient monitoring regulations, we stated that the 
basis for finalizing a prohibition on the use of SPM data to designate 
an area as nonattainment for Pb (as well as CO, SO2, 
NO2, and PM10) was EPA's discretion to not make a 
finding of nonattainment even though a SPM indicated a violation of the 
relevant NAAQS (see 71 FR 61252). We stated that even though the NAAQS 
for these pollutants have forms that allow a nonattainment finding 
based on less than 24 months of data, EPA does not have a mandatory 
duty to make nonattainment redesignations until such time as the NAAQS 
are revised. Since EPA is proposing to revise the Pb NAAQS, and the 
form of the proposed NAAQS would allow a nonattainment finding to be 
based on only 1 or 2 years of data, and such a NAAQS revision must be 
followed by a mandatory round of designations, we are proposing to 
revise 40 CFR Section 58.20(e) by removing the specific reference to Pb 
in the rule language.

VI. Implementation Considerations

    This section of the proposal discusses the specific CAA 
requirements that must be addressed when implementing any new or 
revised Pb NAAQS based on the structure outlined in the CAA, existing 
rules, existing guidance, and in some cases proposed revised guidance. 
We intend the preamble to the final rule revising the Pb NAAQS to 
provide EPA's final implementation guidance.
    The CAA assigns important roles to EPA, states, and Tribal 
governments in implementing NAAQS. States have the primary 
responsibility for developing and implementing State Implementation 
Plans (SIPs) that contain state measures necessary to achieve the air 
quality standards in each area. EPA provides assistance to states and 
Tribes by providing technical tools, assistance, and guidance, 
including information on the potential control measures.
    A SIP is the compilation of regulations and control programs that a 
state uses to carry out its responsibilities under the CAA, including 
the attainment, maintenance, and enforcement of the NAAQS. States use 
the SIP development process to identify the emissions sources that 
contribute to the nonattainment problem in a particular area, and to 
select the emissions reduction measures most appropriate for the 
particular area in question. Under the CAA, SIPs must ensure that areas 
reach attainment as expeditiously as practicable.
    Currently only two areas in the United States are designated as 
nonattainment and eleven areas are designated as maintenance areas for 
the current Pb NAAQS. If the Pb NAAQS is lowered to the range proposed, 
it is likely (based on a review of the current air quality monitoring 
data) that

[[Page 29267]]

additional areas would be designated as nonattainment. States 
determined to have lead nonattainment areas would be required to submit 
SIPs that identify and implement specific air pollution control 
measures to reduce the ambient concentrations of lead to meet the 
NAAQS.
    The EPA's analysis of the available Pb monitoring data suggests 
that a large majority of recent exceedances of Pb levels in the range 
of 0.10 to [mu]g/m\3\ have occurred in locations with active or retired 
industrial sources of Pb. Accordingly, if this pattern also prevails 
for concentrations observed from new monitoring sites, many states may 
be able to attain the revised NAAQS by implementing air pollution 
control measures on lead emitting industrial sources only. These 
controls could include measures such as fabric filter particulate 
matter control measures and industrial fugitive dust control measures 
applied in plant buildings and on plant grounds. However, it may become 
necessary in some areas to also implement controls on non-industrial 
sources. Based on these considerations, EPA believes that some of the 
regulations and guidance being used to implement the current Pb NAAQS 
is still appropriate to implement any of the options being proposed in 
this rulemaking for a new or revised Pb NAAQS.
    The regulations and guidance for implementing the current NAAQS for 
Pb are mainly provided in the following documents: (1) ``State 
Implementation Plans; General Preamble for the Implementation of Title 
I of the Clean Air Act Amendments of 1990'', 57 FR 13549, April 16, 
1992, (2) ``State Implementation Plans for Lead Nonattainment Areas; 
Addendum to the General Preamble for the Implementation of Title I of 
the Clean Air Act Amendments of 1990'', 58 FR 67748, December 22, 1993, 
and (3) regulations at 40 CFR 51.117. The aforementioned documents 
address requirements such as designating areas, setting nonattainment 
area boundaries, promulgating area classifications, nonattainment area 
SIP requirements such as Reasonably Available Control Measures (RACM), 
Reasonably Available Control Technology (RACT), New Source Review 
(NSR), Prevention of Significant Deterioration (PSD), and emissions 
inventory requirements. We have summarized the most relevant 
information from these documents below for your convenience. The EPA 
believes that there is sufficient guidance and regulations to fully 
implement the proposed revised Pb NAAQS, although EPA may review and 
revise or update as necessary, policies, guidance, and regulations for 
implementing the Pb NAAQS in the future. The EPA solicits comment on 
whether additional guidance is necessary for implementation of the 
revised Pb NAAQS.

A. Designations for the Lead NAAQS

    After EPA establishes or revises a NAAQS, the CAA requires EPA and 
the states to begin taking steps to ensure that the new or revised 
NAAQS are met. The first step is to identify areas of the country that 
do not meet the new or revised NAAQS. The CAA defines EPA's authority 
to designate areas that do not meet a new or revised NAAQS. Section 
107(d)(1) provides that ``By such date as the Administrator may 
reasonably require, but not later than 1 year after promulgation of a 
new or revised NAAQS for any pollutant under section 109, the Governor 
of each state shall * * * submit to the Administrator a list of all 
areas (or portions thereof) in the state'' that designates those areas 
as nonattainment, attainment, or unclassifiable. Section 
107(d)(1)(B)(i) further provides, ``Upon promulgation or revision of a 
NAAQS, the Administrator shall promulgate the designations of all areas 
(or portions thereof) * * * as expeditiously as practicable, but in no 
case later than 2 years from the date of promulgation. Such period may 
be extended for up to one year in the event the Administrator has 
insufficient information to promulgate the designations.'' The term 
``promulgation'' has been interpreted by the courts to be signature and 
dissemination of a rule.\165\ By no later than 120 days prior to 
promulgating final designations, EPA is required to notify states or 
Tribes of any intended modifications to their boundaries as EPA may 
deem necessary. States and Tribes then have an opportunity to comment 
on EPA's tentative decision. Whether or not a state or a Tribe provides 
a recommendation, EPA must promulgate the designation that it deems 
appropriate.
---------------------------------------------------------------------------

    \165\ American Petroleum Institute v. Costle, 609 F.2d 20 (D.C. 
Cir. 1979).
---------------------------------------------------------------------------

    Accordingly, Governors of states and Tribal leaders will be 
required to submit their initial designation recommendations to EPA no 
later than September 2009. The initial designation of areas for any new 
or revised NAAQS for lead must occur no later than September 2010, 
although that date may be extended by up to one year under the CAA (or 
no later than September 2011) if EPA has insufficient information to 
promulgate the designations. As discussed below, EPA is anticipating a 
designations schedule that provides the full 3 years allowed under the 
CAA, and is taking comment on issues related to the anticipated 
designation schedule.
1. Potential Schedule for Initial Designations of a Revised Lead NAAQS
    As stated previously, section 107(d)(1)(B)(i) requires EPA to 
promulgate initial designations for all areas of the country for any 
new or revised NAAQS, as expeditiously as practicable, but in no case 
later than 3 years from the date of promulgation of the new or revised 
NAAQS. Two key considerations in establishing a schedule for 
designating areas are: (1) The advantages of promulgating all 
designations at the same time; and (2) the availability of a monitoring 
network and sufficient monitoring data to identify areas that may be 
violating the NAAQS.
    EPA continues to believe, consistent with its past practice, that 
there are important advantages to promulgating designations for all 
areas at the same time. This practice provides helpful uniformity for 
the deadlines for SIP submissions and attainment. Moreover, since a key 
question for the designation process is delineating the boundaries of 
nonattainment areas, establishing appropriate nonattainment boundaries 
in a two-stage process is likely to generate significant issues. Thus, 
EPA intends to promulgate designations for all areas at the same time.
    As discussed in section V.B, the existing Pb monitoring network is 
not adequate to evaluate attainment of the proposed revised Pb NAAQS at 
locations consistent with EPA's proposed new network siting criteria 
and data collection requirements. These new requirements would result 
in a more strategically targeted network that would begin to be in 
operation by January 1, 2010. Thus, taking the additional year provided 
under section 107(d)(1)(B)(1) of the CAA (which would allow up to 3 
years to promulgate designations following the promulgate of a new 
NAAQS) would allow the first year of data from this network to be 
available. The EPA believes that, due to the updated network design 
requirements, this additional data would be of significant benefit for 
designating areas for a new NAAQS. If EPA completes the initial 
designations within 2 years of new NAAQS promulgation, it is likely 
that large areas of the country will be designated ``unclassifiable'' 
because the monitoring network will not be sufficient to make clear 
decisions. Even if EPA takes an extra year for final initial 
designation

[[Page 29268]]

decisions we recognize that some areas may still have to be designated 
as unclassifiable or attainment/unclassifiable because of the lack of a 
sufficient record of FRM (FEM) monitoring data.\166\ If sufficient 
monitoring data become available for ``unclassifiable'' areas 
subsequent to the time EPA finalizes initial designations, EPA may use 
the discretion provided to the Administrator under the CAA pursuant to 
section 107(d)(3) to revise the initial designations for these areas.
---------------------------------------------------------------------------

    \166\ As discussed in Section IV of this notice, EPA is 
soliciting comment on the use of Pb-TSP monitoring data, with or 
without a scaling factor, as a surrogate for Pb-PM10 data 
where Pb-PM10 data are not available, particularly for 
initial designations.
---------------------------------------------------------------------------

    Under the initial designation schedule described above, states (and 
Tribes) would be required to submit designation recommendations to EPA 
no later than September 2009 (i.e., one year following promulgation of 
a new NAAQS). States will be able to consider ambient data collected 
with FRM (FEM) samplers through the end of 2008 and part way through 
2009 when formulating their recommendations. As stated previously, by 
no later than 120 days prior to promulgating designations, EPA is 
required to notify states or Tribes of any intended modifications to 
their recommended boundaries as EPA may deem necessary. This would 
occur no later than in May 2011. If EPA promulgates designations in 
September 2011, EPA will have access to Pb air quality data from 2010 
which state monitoring officials have certified is complete and 
accurate, since the deadline for such certification is May 1, 2011. 
Under this schedule, EPA would consider data from calendar years 2008-
2010 in formulating its proposed revisions, if any, to the designations 
recommended by states and Tribes. States and Tribes will then have an 
opportunity to comment on EPA's proposed modifications
    As described above, EPA is currently anticipating that there will 
be insufficient information to promulgate designations in 2010. The EPA 
is soliciting comment on whether we have the authority to determine in 
the final rule that three years are necessary to promulgate 
designations based on the availability of appropriate information. EPA 
is also soliciting comment on whether designations should be made 
within the 2 year period provided under section 107(d)(1)(B)(i) 
utilizing all data available by that time.
2. Ambient Data For Designations
    The proposed alternative forms of the NAAQS, maximum quarterly 
average concentration over three years and second maximum monthly 
concentration over three years, would both allow a nonattainment 
determination based on less than three years of data, if the monitoring 
data in a more limited time period includes a quarterly average above 
the level of the NAAQS or if it includes two monthly averages above the 
level of the NAAQS. In such a case, EPA intends to designate the 
affected area nonattainment even though less than three years of data 
are available. EPA would designate an area attainment only if three 
calendar years of data indicate the absence of a violation. As stated 
above, EPA anticipates that some areas will have to be designated as 
unclassifiable. If sufficient monitoring data become available for 
``unclassifiable'' areas subsequent to the time EPA finalizes initial 
designations, EPA may use the discretion provided to the Administrator 
under the CAA pursuant to section 107(d)(3) to revise the initial 
designations for these areas.

B. Lead Nonattainment Area Boundaries

    As stated previously, the process for initially designating areas 
following the promulgation of a new NAAQS is prescribed in section 
107(d)(1) of the CAA. This section of the CAA provides each state 
Governor an opportunity to recommend initial designations of 
attainment, nonattainment, or unclassifiable for each area in the 
state. Section 107(d)(1) of the CAA also directs the state to provide 
the appropriate boundaries to EPA for each area of the state, and 
provides that EPA may make modifications to the boundaries submitted by 
the state as it deems necessary. A lead nonattainment area must consist 
of that area that does not meet (or contributes to ambient air quality 
in a nearby area that does not meet) the Pb NAAQS. Thus, a key factor 
in setting boundaries for nonattainment areas is determining the 
geographic extent of nearby source areas contributing to the 
nonattainment problem. For each monitor or group of monitors that 
exceed a standard, nonattainment boundaries must be set that include a 
sufficiently large enough area to include both the area judged to be 
violating the standard as well as the source areas that are determined 
to be contributing to these violations.
    Historically, Pb NAAQS violations have been the result of lead 
emissions from large stationary sources and mobile sources that burn 
lead-based fuels. In some locations, a limited number of area sources 
have also contributed to violations. Since lead has been successfully 
phased out of motor vehicle gasoline, mobile sources are no longer a 
significant source of violations of the current Pb NAAQS. At the 
current standard level, EPA expects stationary sources to be the 
primary contributor to violations of the NAAQS. At the lower standard 
levels contemplated in this proposal, it is possible that fugitive dust 
emissions from area sources containing deposited lead will also 
contribute to violations of a revised Pb NAAQS. The location and 
dispersion characteristics of these sources of ambient lead 
concentrations are important factors in determining nonattainment area 
boundaries. The EPA is proposing that the county boundary be the 
presumptive boundary for lead nonattainment areas. However, we are also 
taking comment on whether urban-based Metropolitan Statistical Area 
(MSA) boundaries should be the presumptive boundaries for lead 
nonattainment areas.
    The EPA is proposing to presumptively define the boundary for 
designating a nonattainment area as the perimeter of the county 
associated with the air quality monitor(s) which records a violation of 
the standard. This presumption is the existing EPA recommendation for 
defining the nonattainment boundaries for the current Pb NAAQS, and is 
described in the 1992 General Preamble (57 FR 13549). The EPA is also 
taking comment on an option to presumptively define the nonattainment 
boundary using the OMB-defined Metropolitan Statistical Area (MSA) 
associated with the violating monitor(s). This presumption is used, by 
CAA requirement, for the ozone and CO NAAQS nonattainment boundaries, 
and was recommended by EPA as the appropriate presumption for the 1997 
PM2.5 NAAQS nonattainment boundaries. Under either option, 
the state and/or EPA may conduct additional area-specific analyses that 
could lead EPA to depart from the presumptive boundary. Factors 
relevant to such an analysis are described below.
1. County-Based Boundaries
    The option being proposed by EPA is that lead nonattainment 
boundaries would be presumptively defined by the perimeter of the 
county in which the ambient lead monitor(s) recording a violation of 
the NAAQS is located, unless area-specific information indicates that 
some other boundary is more appropriate. In addition, if the relevant 
air quality monitor measuring a violation(s) is located near another 
county, then EPA would presume that the contributing county should also 
be designated as nonattainment for the Pb NAAQS. In some instances, a 
boundary other than the county perimeter, that

[[Page 29269]]

addresses areas impacted by specific sources of lead, may also be 
appropriate.
    For the new proposed Pb NAAQS, EPA is recommending that 
nonattainment area boundaries that deviate from presumptive county 
boundaries should be supported by an assessment of several factors, 
which are discussed below. The factors for determining nonattainment 
area boundaries for the Pb NAAQS under this recommendation closely 
resemble the factors identified in recent EPA guidance for the 1997 8-
hour ozone NAAQS, the 1997 PM2.5 NAAQS, and the 2006 
PM2.5 NAAQS nonattainment area boundaries. EPA intends to 
apply these factors in evaluating boundary modifications. For this 
particular option, EPA would consider the following factors in 
assessing whether to exclude portions of a county and whether to 
include additional nearby areas outside the county as part of the 
designated nonattainment area:
     Emissions in areas potentially included versus excluded 
from the nonattainment area,
     Air quality in potentially included versus excluded areas,
     Population density and degree of urbanization including 
commercial development in included versus excluded areas,
     Expected growth (including extent, pattern and rate of 
growth),
     Meteorology (weather/transport patterns),
     Geography/topography (mountain ranges or other air basin 
boundaries),
     Jurisdictional boundaries (e.g., counties, air districts, 
Reservations, etc.),
     Level of control of emission sources.
    Analyses of these factors may suggest nonattainment boundaries that 
are either larger or smaller than the county. A demonstration 
supporting the designation of boundaries that are less than the full 
county must show both that violation(s) are not occurring in the 
excluded portions of the county and that the excluded portions are not 
source areas that contribute to the observed violations. 
Recommendations to designate a nonattainment area larger than the 
county should also be based on an analysis of these factors. EPA will 
consider these factors in evaluating state and tribal recommendations 
and assessing whether any modifications are appropriate.
    Under previous Pb implementation guidance, EPA advised that 
Governors could choose to recommend lead nonattainment boundaries by 
using any one, or a combination of the following techniques, the 
results of which EPA would consider when making a decision as to 
whether and how to modify the Governors' recommendations: (1) 
Qualitative analysis, (2) spatial interpolation of air quality 
monitoring data, or (3) air quality simulation by dispersion modeling. 
These techniques are more fully described in ``Procedures for 
Estimating Probability of Nonattainment of a PM10 NAAQS 
Using Total Suspended Particulate or PM10 Data,'' December 
1986 (see 57 FR 13549).
    EPA solicits comments on the use of these factors and modeling 
techniques, and other approaches, for adjusting county boundaries in 
designating nonattainment areas.
2. MSA-Based Boundaries
    The EPA is also taking comment on the alternative that lead 
nonattainment boundaries should be presumptively defined by the 
perimeter of a metropolitan area as defined by OMB's Metropolitan 
Statistical Areas (MSAs), or appropriate divisions thereof, within 
which a violating monitor(s) is located. The Metropolitan Statistical 
Area, as delineated by the Office of Management and Budget (OMB), 
provides a presumptive definition of the populated area associated with 
a core urban area. Accordingly, EPA is taking comment on the 
alternative option that the Metropolitan Statistical Area would provide 
the presumptive definition of the source area that contributes to a 
lead nonattainment problem. This presumption would take the view that, 
in the absence of evidence to the contrary, violations of the Pb NAAQS 
in urban-oriented areas may be presumed attributable, at least in part, 
to contributions from large sources of lead emissions distributed 
throughout the Metropolitan Area. The last revision to the OMB listing 
of MSAs was published November 20, 2007. As in the EPA's preferred 
proposed option, EPA would consider state, local, and tribal 
recommendations of nonattainment area boundaries based on the same set 
of factors listed in the previous subsection.
    As stated previously, EPA is proposing that the county boundaries 
be used as the presumptive boundaries for any new or revised Pb NAAQS, 
but is also requesting comments the MSA boundaries being used as the 
presumptive boundaries for any new or revised Pb NAAQS.

C. Classifications

    Section 172(a)(1)(A) of the CAA authorizes EPA to classify areas 
designated as nonattainment for the purposes of applying an attainment 
date pursuant to section 172(a)(2), or for other reasons. In 
determining the appropriate classification, EPA may consider such 
factors as the severity of the nonattainment problem and the 
availability and feasibility of pollution control measures (see section 
172(a)(1)(A) of the CAA). The EPA may classify lead nonattainment 
areas, but is not required to do so.
    While section 172(a)(1)(A) provides a mechanism to classify 
nonattainment areas, section 172(a)(2)(D) provides that the attainment 
date extensions described in section 172(a)(2)(A) do not apply to 
nonatainment areas having specific attainment dates that are addressed 
under other provisions of the part D of the CAA. Section 192(a), of 
part D, specifically provides an attainment date for areas designated 
as nonattainment for the Pb NAAQS. Therefore, EPA has legal authority 
to classify lead nonattainment areas, but the 5 year attainment date 
under section 192(a) cannot be extended pursuant to section 
172(a)(2)(D).
    Based on this limitation, EPA is proposing not to establish 
classifications within the 5 year interval for attaining any new or 
revised NAAQS. This approach is consistent with EPA's previous 
classification decision in the 1992 General Preamble (See 57 FR 13549, 
April 16, 1992).

D. Section 110(a)(2) Lead NAAQS Infrastructure Requirements

    Under section 110(a)(1) and (2) of the CAA, all states are required 
to submit plans to provide for the implementation, maintenance, and 
enforcement of any new or revised NAAQS. Section 110(a)(1) and (2) 
require states to address basic program elements, including 
requirements for emissions inventories, monitoring, and modeling, among 
other things. States are required to submit SIPs to EPA demonstrating 
these basic program elements within 3 years of the promulgation of any 
new or revised NAAQS. Subsections (A) through (M), of section 
110(a)(2), set forth the elements that a state's program must contain 
in their SIP. The list below identifies the required program elements 
contained in section 110(a)(2).\167\ The list of section 110(a)(2)

[[Page 29270]]

NAAQS implementation requirements are the following:
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    \167\ Two elements identified in section 110(a)(2) are not 
listed below because, as EPA interprets the CAA, SIPs incorporating 
any necessary local nonattainment area controls would not be due 
within 3 years, but rather are due at the time the nonattainment 
area planning requirements are due. The elements are: (1) Emission 
limits and other control measures, section 110(a)(2)(A), and (2) 
Provisions for meeting part D, section 110(a)(2)(I), which requires 
areas designated as nonattainment to meet the applicable 
nonattainment planning requirements of part D, title I of the CAA.
---------------------------------------------------------------------------

     Ambient air quality monitoring/data system: Section 
110(a)(2)(B) requires SIPs to provide for setting up and operating 
ambient air quality monitors, collecting and analyzing data and making 
these data available to EPA upon request.
     Program for enforcement of control measures: Section 
110(a)(2)(C) requires SIPs to include a program providing for 
enforcement of measures and regulation of new/modified (permitted) 
sources.
     Interstate transport: Section 110(a)(2)(D) requires SIPs 
to include provisions prohibiting any source or other type of emissions 
activity in one State from contributing significantly to nonattainment 
in another State or from interfering with measures required to prevent 
significant deterioration of air quality or to protect visibility.
     Adequate resources: Section 110(a)(2)(E) requires States 
to provide adequate funding, personnel and legal authority for 
implementation of their SIPs.
     Stationary source monitoring system: Section 110(a)(2)(F) 
requires States to establish a system to monitor emissions from 
stationary sources and to submit periodic emissions reports to EPA.
     Emergency power: Section 110(a)(2)(G) requires States to 
provide for authority to implement the emergency episode provisions in 
their SIPs.
     Provisions for SIP revision due to NAAQS changes or 
findings of inadequacies: Section 110(a)(2)(H) requires States to 
revise their SIPs in response to changes in the NAAQS, availability of 
improved methods for attaining the NAAQS, or in response to an EPA 
finding that the SIP is inadequate.
     Section 121 consultation with local and Federal government 
officials: Section 110(a)(2)(J) requires States to meet applicable 
local and Federal government consultation requirements of section 121.
     Section 127 public notification of NAAQS exceedances: 
Section 110(a)(2)(J) requires States to meet applicable requirements of 
section 127 relating to public notification of violating NAAQS.
     PSD and visibility protection: Section 110(a)(2)(J) also 
requires States to meet applicable requirements of title I part C 
related to prevention of significant deterioration and visibility 
protection.
     Air quality modeling/data: Section 110(a)(2)(K) requires 
that SIPs provide for performing air quality modeling for predicting 
effects on air quality of emissions from any NAAQS pollutant and 
submission of data to EPA upon request.
     Permitting fees: Section 110(a)(2)(L) requires the SIP to 
include requirements for each major stationary source to pay permitting 
fees to cover the cost of reviewing, approving, implementing and 
enforcing a permit.
     Consultation/participation by affected local government: 
Section 110(a)(2)(M) requires States to provide for consultation and 
participation by local political subdivisions affected by the SIP.

E. Attainment Dates

    Generally, the date by which an area is required to attain the Pb 
NAAQS is determined by the effective date of the nonattainment 
designation for the area. For areas designated nonattainment for any 
new or revised primary Pb NAAQS, SIPs must provide for attainment of 
the NAAQS as expeditiously as practicable, but no later than 5 years 
from the date of the nonattainment designation for the area (see 
section 192(a) of the CAA). So, for example, if final designations are 
effective in Fall 2011, then nonattainment areas must plan to attain 
the NAAQS by no later than Fall 2016. For an area with an attainment 
date of September 2016, EPA would determine whether it had attained the 
Pb NAAQS by evaluating air quality monitoring data from the 1, 2, or 3 
previous calendar years (i.e., 2013, 2014, and 2015) as available.

F. Attainment Planning Requirements

    Any state containing an area designated as nonattainment with 
respect to the Pb NAAQS must develop for submission, a SIP meeting the 
requirements of part D, Title I, of the CAA, providing for attainment 
(see sections 191(a) and 192(a) of the CAA). As indicated in section 
191(a) all components of the lead part D SIP must be submitted within 
18 months of an areas nonattainment designation. So, for example, if 
final designations are effective in Fall 2011, the part D SIPs must be 
submitted by Spring 2013. Additional specific plan requirements for 
lead nonattainment areas are outlined in 40 CFR 51.117.
    The general part D nonattainment plan requirements are set forth in 
section 172 of the CAA. Section 172(c) specifies that SIPs submitted to 
meet the part D requirements must, among other things, include 
Reasonably Available Control Measures (RACM) (which includes Reasonably 
Available Control Technology (RACT)), provide for Reasonable Further 
Progress (RFP), include an emissions inventory, require permits for the 
construction and operation of major new or modified stationary sources 
(see also section 173), contain contingency measures, and meet the 
applicable provisions of section 110(a)(2) of the CAA related to the 
general implementation of a new or revised NAAQS. It is important to 
note that lead nonattainment SIPs must meet all of the requirements 
related to part D of the CAA, including those specified in section 
172(c), even if EPA does not provide separate specific guidance for 
each provision (e.g., applicable provisions of section 110(a)(2)).
1. RACM for Lead Nonattainment Areas
    Lead nonattainment area SIPs must contain RACM (including RACT) 
that addresses sources of ambient lead concentrations. In general, as 
stated previously, EPA believes that lead nonattainment area issues are 
usually attributed to emissions from stationary sources, but some 
emissions may also be attributed to smaller area sources. As a general 
rule, the stationary sources in lead nonattainment areas tend to emit a 
relatively large amount of particulate matter containing lead. In EPA's 
2002 National Emissions Inventory (NEI), there were 29 stationary 
sources in the country with lead emissions over 5 tons per year, and 
239 sources over 1 ton of lead emissions per year.
    At primary lead smelters, for example, the process of reducing 
concentrated ore to lead involves a series of steps, some of which are 
completed outside of buildings, or inside of buildings which are not 
totally enclosed. Over a period of time, emissions from these sources 
have been deposited in neighboring communities (e.g., on roadways, 
parking lots, yards, and off-plant property). This historically 
deposited lead, when disturbed, may be re-entrained into the ambient 
air and re-entrained fugitive lead bearing dust may contribute to 
violations of the Pb NAAQS in the affected area. There are also 
potential sources of lead that are under federal control. As a part of 
the Regulatory Impact Analysis for this rule, the EPA is reviewing the 
impact of these and other sources of lead emissions to assess their 
impact on any new or revised Pb NAAQS. States must also meet the 
requirements outlined in 40 CFR 51.117(a) related to control strategy 
demonstrations.
    The first step in addressing RACM for lead is identifying potential 
control measures for sources of lead in the nonattainment area. A 
suggested starting point for specifying RACM in lead nonattainment area 
SIPs is outlined in appendix 1 of the guidance entitled

[[Page 29271]]

``State Implementation Plans for Lead Nonattainment Areas; Addendum to 
the General Preamble for the Implementation of Title I of the Clean Air 
Act Amendments of 1990, 58 FR 67752, December 22, 1993. If a state 
receives substantive public comments that demonstrate through 
appropriate documentation, that additional control measures may be 
reasonably available in a particular circumstance for an area, those 
measures should be added to the list of available measures for 
consideration in that particular area.
    While EPA does not presume that these control measures are 
reasonably available in all areas, a reasoned justification for 
rejection of any available control measure should be prepared. If it 
can be shown that measures, considered both individually and as a 
group, are unreasonable because emissions from the affected sources are 
insignificant, those measures may be excluded from further 
consideration as they would not be representative of RACM for an area. 
The resulting control measures should then be evaluated for 
reasonableness, considering their technological feasibility and the 
cost of control in the area for which the SIP applies. In the case of 
public sector sources and control measures, this evaluation should 
consider the impact and reasonableness of the measures on the 
municipal, or other governmental entity that must assume the 
responsibility for their implementation. It is important to note that a 
state should consider the feasibility of implementing measures in part 
when full implementation would be infeasible. A reasoned justification 
for partial or full rejection of any available control measure, 
including those considered or presented during the state's public 
hearing process, should be prepared. The justification should contain 
an explanation, with appropriate documentation, as to why each rejected 
control measure is deemed infeasible or otherwise unreasonable for 
implementation.
    Economic feasibility considers the cost of reducing emissions and 
the difference between the cost of the emissions reduction approach at 
the particular source in question and the costs of emissions reduction 
approaches that have been implemented at other similar sources. Absent 
other indications, EPA presumes that it is reasonable for similar 
sources to bear similar costs of emissions reduction. Economic 
feasibility for RACT purposes is largely determined by evidence that 
other sources in a source category have in fact applied the control 
technology or process change in question. EPA also encourages the 
development of innovative measures not previously employed which may 
also be technically and economically feasible.
    The capital costs, annualized costs, and cost effectiveness of an 
emissions reduction technology should be considered in determining 
whether a potential control measure is reasonable for an area or state. 
One available reference for calculating costs is the EPA Air Pollution 
Control Cost Manual,\168\ which describes the procedures EPA uses for 
determining these costs for stationary sources. The above costs should 
be determined for all technologically feasible emission reduction 
options. States may give substantial weight to cost effectiveness in 
evaluating the economic feasibility of an emission reduction 
technology. The cost effectiveness of a technology is its annualized 
cost ($/year) divided by the emissions reduced (i.e., tons/year) which 
yields a cost per amount of emission reduction ($/ton). Cost 
effectiveness provides a value for each emission reduction option that 
is comparable with other options and other facilities. With respect to 
a given pollutant, a measure is likely to be reasonable if it has a 
cost per ton similar to other measures previously employed for that 
pollutant. In addition, a measure is likely to be reasonable from a 
cost effectiveness standpoint if it has a cost per ton similar to that 
of other measures needed to achieve expeditious attainment in the area 
within the CAA's time frames.
---------------------------------------------------------------------------

    \168\ EPA Air Pollution Control Cost Manual--Sixth Edition (EPA 
452/B-02-001), EPA Office of Air Quality Planning and Standards, 
Research Triangle Park, NC, Jan 2002.
---------------------------------------------------------------------------

    The fact that a measure has been adopted or is in the process of 
being adopted by other states is an indicator (though not a definitive 
one) that the measure may be technically and economically feasible for 
another state. We anticipate that states may decide upon RACT and RACM 
controls that differ from state to state, based on the state's 
determination of the most effective strategies given the relevant 
mixture of sources and potential controls in the relevant nonattainment 
areas, and differences in difficulty of attaining expeditiously. 
Nevertheless, states should consider and address RACT and RACM measures 
developed for other areas or other states as part of a well reasoned 
RACT and RACM analysis. The EPA's own evaluation of SIPs for compliance 
with the RACT and RACM requirements will include comparison of measures 
considered or adopted by other states.
    In considering what level of control is reasonable, EPA is not 
proposing a specific dollar per ton cost threshold for RACT. Areas with 
more serious air quality problems typically will need to obtain greater 
levels of emissions reductions from local sources than areas with less 
serious problems, and it would be expected that their residents could 
realize greater public health benefits from attaining the standard. For 
these reasons, we believe that it will be reasonable and appropriate 
for areas with more serious air quality problems and higher design 
values to impose emission reduction requirements with generally higher 
costs per ton of reduced emissions than the cost of emissions 
reductions in areas with lower design values. In addition, where 
essential reductions are more difficult to achieve (e.g., because many 
sources are already controlled), the cost per ton of control may 
necessarily be higher.
    The EPA believes that in determining appropriate emission control 
levels, the state should consider the collective public health benefits 
that can be realized in the area due to projected improvements in air 
quality. Because EPA believes that RACT requirements will be met where 
the state demonstrates timely attainment, and areas with more severe 
air quality problems typically will need to adopt more stringent 
controls, RACT level controls in such areas will require controls at 
higher cost effectiveness levels ($/ton) than areas with less severe 
air quality problems.
    In identifying the range of costs per ton that are reasonable, 
information on benefits per ton of emission reduction can be useful as 
one factor to consider. The Pb NAAQS RIA will provide information on 
the estimated benefits per ton of reducing Pb emissions from various 
emissions sources. It should be noted that such benefits estimates are 
subject to significant uncertainty, and that benefits per ton vary in 
different areas. Nonetheless this information could be used in a way 
that recognizes these uncertainties. If a per ton cost of implementing 
a measure is significantly less than the anticipated benefits per ton, 
this would be an indicator that the cost per ton is reasonable. If a 
source contends that a source-specific RACT level should be established 
because it cannot afford the technology that appears to be RACT for 
other sources in its source category, the source should support its 
claim by providing detailed and verified information regarding the 
impact of imposing RACT on:
     Fixed and variable production costs ($/unit),

[[Page 29272]]

     Product supply and demand elasticity,
     Product prices (cost absorption vs. cost pass-through),
     Expected costs incurred by competitors,
     Company profits, and
     Employment costs.
    The technical guidance entitled ``Fugitive Dust Background Document 
and Technical Information Document for Best Available Control 
Measures'' (EPA-450/2-92-004, September 1992) provides an example for 
states on how to analyze control costs for a given area.
    Once the process of determining RACM for an area is completed, the 
individual measures should then be converted into a legally enforceable 
vehicle (e.g., a regulation or permit program) (see section 172(c)(6) 
and section 110(a)(2)(A) of the CAA). The regulations or other measures 
submitted should meet EPA's criteria regarding the enforceability of 
SIPs and SIP revisions. These criteria were stated in a September 23, 
1987 memorandum (with attachments) from J. Craig Potter, Assistant 
Administrator for Air and Radiation; Thomas L. Adams, Jr. Assistant 
Administrator for Enforcement and Compliance Monitoring; and S. Blake, 
General Counsel, Office of the General Counsel; entitled ``Review of 
State Implementation Plans and Revisions of Enforceability and Legal 
Sufficiency.'' As stated in this memorandum, SIPs and SIP revisions 
that fail to satisfy the enforceability criteria should not be 
forwarded for approval. If they are submitted, they will be disapproved 
if, in EPA's judgment, they fail to satisfy applicable statutory and 
regulatory requirements.
    The EPA's historic definition of RACT is the lowest emissions 
limitation that a particular source is capable of meeting by the 
application of control technology that is reasonably available 
considering technological and economic feasibility.\169\ RACT applies 
to the ``existing sources'' of lead including stack emissions, 
industrial process fugitive emissions, and industrial fugitive dust 
emissions (e.g., on-site haul roads, unpaved staging areas at the 
facility, etc) (see section 172(c)(1)). EPA's most recent guidance for 
implementing the current Pb NAAQS recommends that stationary sources 
which actually emit a total of 5 tons per year of lead or lead 
compounds, measured as elemental lead, be the minimum starting point 
for RACT analysis (see 58 FR 67750, December 22, 1993). Further, EPA 
recommends that available control technology be applied to those 
existing sources in the nonattainment area that are reasonable to 
control in light of the attainment needs of the area and the 
feasibility of such controls. Thus a state's control technology 
analysis may need to include sources which actually emit less than 5 
tons per year of lead or lead compounds in the area, or other sources 
in the area that are reasonable to control, in light of the attainment 
needs and feasibility of control for the area.
---------------------------------------------------------------------------

    \169\ See for example, 44 FR 53762 (September 17, 1979) and 
footnote 3 of that notice. Note that EPA's emissions trading policy 
statement has clarified that the RACT requirement may be satisfied 
by achieving ``RACT equivalent'' emission reductions in the 
aggregate from the full set of existing stationary sources in the 
area. See also EPA's economic incentive proposal which reflects the 
Agency's policy guidance with respect to emissions trading 58 FR 
11110, February 23, 1993.
---------------------------------------------------------------------------

    Given the proposal for promulgating a new or revised Pb NAAQS 
significantly lower than the current standard, EPA is seeking comment 
on an appropriate threshold for the minimum starting point for future 
Pb RACT analyses for stationary lead sources in nonattainment areas. In 
the monitoring section of today's proposal, EPA is taking comment on 
minimum network monitoring requirements based on emissions source sizes 
ranging from 200 kg/yr to 600 kg/yr. One possible approach for RACT is 
to recommend that RACT analyses for Pb sources be consistent with the 
monitoring requirements, such that all stationary sources above from 
200 kg/yr to 600 kg/yr should undergo a RACT review. EPA is also taking 
comment on source monitoring for stationary sources that emit Pb 
emissions in amounts that have potential to cause ambient levels at 
least one-half the selected NAAQS level. This suggests another 
potential recommended starting point for RACT analysis. EPA is seeking 
comment on these ideas as well as any information commenters can 
provide that would help inform EPA recommendations on an appropriate 
emissions threshold for initiating RACT analyses.
2. Demonstration of Attainment for Lead Nonattainment Areas
    The SIPs for lead nonattainment areas should provide for the 
implementation of control measures for point and area stationary 
sources of lead emissions which demonstrate attainment of the Pb NAAQS 
as expeditiously as practicable, but no later than the applicable 
statutory attainment date for the area (See also 40 CFR 51.117(a) for 
additional control strategy requirements). Therefore, if a state adopts 
less than all available measures in an area but demonstrates, 
adequately, that reasonable further progress (RFP), and attainment of 
the Pb NAAQS are assured, and application of all such available 
measures would not result in attainment any faster, then a plan which 
requires implementation of less than all technologically and 
economically available measures may be approved (see 44 FR 20375 (April 
4, 1979) and 56 FR 5460 (February 11, 1991)). The EPA believes that it 
would be unreasonable to require that a plan which demonstrates 
attainment include all technologically and economically available 
control measures even though such measures would not expedite 
attainment. Thus, for some sources in areas which demonstrate 
attainment, it is possible that some available control measures may not 
be ``reasonably'' available because their implementation would not 
expedite attainment.
3. Reasonable Further Progress (RFP)
    Part D SIPs must provide for RFP (see section 172(c)(2) of the 
CAA). Section 171 of the CAA defines RFP as ``such annual incremental 
reductions in emissions of the relevant air pollution as are required 
by part D, or may reasonably be required by the Administrator for the 
purpose of ensuring attainment of the applicable NAAQS by the 
applicable attainment date.'' Historically, for some pollutants, RFP 
has been met by showing annual incremental emission reductions 
generally sufficient to maintain linear progress toward attainment by 
the applicable attainment date. Requiring linear emission reduction 
progress to maintain RFP may be appropriate where:
     Pollutants are emitted by numerous and diverse sources;
     The relationship between any individual source and the 
overall air quality is not explicitly quantified;
     There is a chemical transformation involved; and
     The emission control system utilized (e.g., at major point 
sources) will result in swift and significant emission reductions.
    The EPA believes that it may not be reasonable to require linear 
reductions in emissions in SIPs for lead nonattainment areas because 
the air quality problem is not usually due to a vast inventory of 
sources. However, this is not to suggest that generally it would be 
unreasonable for EPA to require annual incremental reductions in 
emissions in lead nonattainment areas. RFP for lead nonattainment areas 
should be met, at least in part, by ``adherence to an ambitious 
compliance schedule'' which is expected to periodically yield 
significant emission reductions, and as appropriate, linear

[[Page 29273]]

progress.\170\ The EPA recommends that SIPs for lead nonattainment 
areas provide a detailed schedule for compliance of RACM (including 
RACT) in the areas and accurately indicate the corresponding annual 
emission reductions to be achieved. In reviewing the SIP, EPA believes 
that it is appropriate to expect early implementation of less 
technology-intensive control measures (e.g., controlling fugitive dust 
emissions at the stationary source, as well as required controls on 
area sources) while phasing in the more technology-intensive control 
measures, such as those involving the installation of new hardware. 
Finally, it should be noted that failure to implement the SIP 
provisions required to meet annual incremental reductions in emissions 
(i.e., RFP) in a particular area could result in the application of 
sanctions as described in sections 110(m) and 179(b) of the CAA 
(pursuant to a finding under section 179(a)(4)), and the implementation 
of contingency measures required by section 172(c)(9) of the CAA.
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    \170\ As previously stated most of the lead nonattainment 
problems are caused by point sources. For this reason EPA believes 
that the RFP for Pb should parallel the RFP policy for SO2 (see 
General Preamble, 57 FR 13545, April 16, 1992).
---------------------------------------------------------------------------

4. Contingency Measures
    Section 172(c)(9) of the CAA defines contingency measures as 
measures in a SIP that are to be implemented if an area fails to 
achieve and maintain RFP, or fails to attain the NAAQS by the 
applicable attainment date. Contingency measures must be designed to 
become effective without further action by the state or the 
Administrator, upon determination by EPA that the area has failed to 
achieve or maintain reasonable further progress, or attain the Pb NAAQS 
by the applicable statutory attainment date. Contingency measures 
should consist of available control measures that are not already 
included in the primary control strategy for the affected area.
    Contingency measures are important for lead nonattainment areas, 
which is generally due to emissions from stationary sources, for 
several reasons. First, process and fugitive emissions from these 
stationary sources, and the possible re-entrainment of historically 
deposited emissions, have historically been difficult to quantify. 
Therefore, the analytical tools for determining the relationship 
between reductions in emissions, and resulting air quality 
improvements, can be subject to some uncertainties. Second, emission 
estimates and attainment analysis can be influenced by overly-
optimistic assumptions about fugitive emission control efficiency.
    Examples of contingency measures for controlling area fugitive 
emissions may include stabilizing additional storage piles, etc. 
Examples of contingency measures for processed-related fugitive 
emissions include increasing the enclosure of buildings, increasing air 
flow in hoods, increasing operation and maintenance procedures, etc. 
Examples for contingency measures for stack sources include reducing 
hours of operation, changing the feed material to lower lead content, 
and reducing the occurrence of malfunctions by increasing operation and 
maintenance procedures, etc.
    Section 172(c)(9) provides that contingency measures should be 
included in the SIP for a lead nonattainment area and shall ``take 
effect without further action by the state or the Administrator.'' The 
EPA interprets this requirement to mean that no further rulemaking 
actions by the state, or EPA, would be needed to implement the 
contingency measures (see generally 57 FR 12512 and 13543-13544). The 
EPA recognizes that certain actions, such as the notification of 
sources, modification of permits, etc., may be needed before a measure 
could be implemented. However, states must show that their contingency 
measures can be implemented with minimal further action on their part 
and with no additional rulemaking actions such as public hearings or 
legislative review. After EPA determines that a lead nonattainment area 
has failed to maintain RFP or timely attain the Pb NAAQS, EPA generally 
expects all actions needed to affect full implementation of the 
measures to occur within 60 days after EPA notifies the state of such 
failure. The state should ensure that the measures are fully 
implemented as expeditiously as practicable after the requirement takes 
effect.
5. Nonattainment New Source Review (NSR) and Prevention of Significant 
Deterioration (PSD) Requirements
    The PSD and nonattainment NSR programs contained in parts C and D 
of title I of the CAA govern preconstruction review and permitting 
programs for any new or modified major stationary sources of air 
pollutants regulated under the CAA as well as any precursors to the 
formation of that pollutant when identified for regulation by the 
Administrator. EPA rules addressing these regulations can be found at 
40 CFR 51.165, 51.166, 52.21, 52.24, and part 51, appendix S.
    Areas designated as nonattainment for the Pb NAAQS must submit SIPs 
that address the requirements of nonattainment area NSR. Specifically, 
section 172(c)(5) of the CAA requires that States which have areas 
designated as nonattainment for the Pb NAAQS must submit, as a part of 
the nonattainment area SIP, provisions requiring permits for the 
construction and operation of new or modified stationary sources 
anywhere in the nonattainment area, in accordance with the permit 
requirements pursuant to section 173 of the CAA.
    Stationary sources that emit lead are currently subject to 
regulation under existing requirements for the preconstruction review 
and approval of new and modified stationary sources. The existing 
requirements, referred to collectively as the New Source Review (NSR) 
program, require any major and minor stationary sources of any air 
pollutant for which there is a NAAQS to undergo review and approval 
prior to the commencement of construction.\171\ The NSR program is 
composed of three different permit programs:
---------------------------------------------------------------------------

    \171\ The terms ``major'' and ``minor'' define the size of a 
stationary source, for applicability purposes, in terms of an annual 
emissions rate (tons per year, tpy) for a pollutant. Generally, a 
minor source is any source that is not ``major.'' ``Major'' is 
defined by the applicable regulations--PSD or nonattainment NSR.
---------------------------------------------------------------------------

    The NSR program is composed of three different permit programs:
     Prevention of Significant Deterioration (PSD);
     Nonattainment NSR (NA NSR); and,
     Minor NSR.
    The PSD program and nonattainment NSR programs, contained in parts 
C and D, respectively, of Title I of the CAA, are often referred to as 
the major NSR program because these programs regulate only major 
sources.
    The PSD program applies when a major source, that is located in an 
area that is designated as attainment or unclassifiable for any 
criteria pollutant, is constructed, or undergoes a major 
modification.\172\ The NA NSR program applies when a major source that 
is located in an area that is designated as nonattainment for any 
criteria pollutant is constructed or undergoes a major modification. 
The minor NSR program addresses both major and minor sources that 
underground construction or modification activities that do not qualify 
as major, and it applies regardless of the designation of the area in 
which a source is located.
---------------------------------------------------------------------------

    \172\ In addition, the PSD program applies to most non-criteria 
regulated pollutants.
---------------------------------------------------------------------------

    The national regulations that apply to each of these programs are 
located in the CFR as shown below:

[[Page 29274]]

------------------------------------------------------------------------
                                                    Applications
------------------------------------------------------------------------
PSD.......................................  40 CFR 52.21, 40 CFR 51.166,
                                             40 CFR 51.165(b).
NA NSR....................................  40 CFR 52.24, 40 CFR 51.165,
                                             40 CFR part 51, Appendix S.
Minor NSR.................................  40 CFR 51.160-164.
------------------------------------------------------------------------

    The PSD requirements include but are not limited to the following:
     Installation of Best Available Control Technology (BACT);
     Air quality monitoring and modeling analyses to ensure 
that a project's emissions will not cause or contribute to a violation 
of any NAAQS or maximum allowable pollutant increase (PSD increment);
     Notification of Federal Land Manager of nearby Class I 
areas; and
     Public comment on permit.
    Nonattainment NSR requirements include but are not limited to:
     Installation of Lowest Achievable Emissions Rate (LAER) 
control technology;
     Offsetting new emissions with creditable emissions 
reductions;
     A certification that all major sources owned and operated 
in the state by the same owner are in compliance with all applicable 
requirements under the CAA;
     An alternative citing analysis demonstrating that the 
benefits of proposed source significantly outweigh the environmental 
and social costs imposed as a result of its location, construction, or 
modification; and
     Public comment on the permit.

Minor NSR programs must meet the statutory requirements in section 
110(a)(2)(C) of the CAA which requires ``* * * regulation of the 
modification and construction of any stationary source * * * as 
necessary to assure that the [NAAQS] are achieved.''

    Areas which are newly designated as nonattainment for the Pb NAAQS 
as a result of any changes made to the NAAQS will be required to adopt 
the NA NSR program to address major sources of lead where the program 
does not currently exist for the Pb NAAQS. Prior to adoption of the SIP 
revision addressing NSR for lead nonattainment areas, the requirements 
of 40 CFR part 51, appendix S will apply.
6. Emissions Inventories
    States must develop and periodically update a comprehensive, 
accurate, current inventory of actual emissions affecting ambient lead 
concentrations. The emissions inventory is used by states and EPA to 
determine the nature and extent of the specific control strategy 
necessary to help bring an area into attainment of the NAAQS. Emissions 
inventories should be based on measured emissions or documented 
emissions factors. Generally, the more comprehensive and accurate the 
inventory, the more effective the evaluation of possible control 
measures can be for the affected area (see section 172(c)(3) of the 
CAA).
    Pursuant to its authority under section 110 of Title I of the CAA, 
EPA has long required states to submit emission inventories containing 
information regarding the emissions of criteria pollutants as well as 
their precursors. The EPA codified these requirements in 40 CFR part 
51, subpart Q in 1979 and amended them in 1987. The 1990 Clean Air Act 
Amendments (CAAA) revised many of the provisions of the CAA related to 
attainment of the NAAQS. These revisions established new emission 
inventory requirements applicable to certain areas that were designated 
as nonattainment for certain pollutants. In the case of lead, the 
emission inventory provisions are in the general provisions pursuant to 
section 173(c)(3) of the CAA.
    In June 2002, EPA promulgated the Consolidated Emissions Reporting 
Rule (CERR) (67 FR 39602, June 10, 2002). The CERR consolidates the 
various emissions reporting requirements that already exist into one 
place in the CFR, and establishes new requirements for the state wide 
reporting of area source and mobile source emissions. States should 
follow the requirements under the CERR as well as any new or revised 
guidance related to emissions inventories for criteria pollutants. The 
CERR establishes two types of required emissions inventories: (1) 
Annual inventories, and (2) 3-year cycle inventories. The annual 
inventory requirement is limited to reporting statewide emissions data 
from the larger point sources. For the 3-year cycle inventory, states 
will need to report data from all of their point sources plus all of 
the area and mobile sources on a statewide basis.
    By merging emissions information from relevant point sources, area 
sources and mobile sources into a comprehensive emission inventory, the 
CERR allows state, local and tribal agencies to do the following:
     Set a baseline for SIP development.
     Measure their progress in reducing emissions.
     Answer the public's request for information.
    The EPA uses the data submitted by the states to develop the 
National Emission Inventory (NEI). The NEI is used by EPA to show 
national emission trends, as modeling input for analysis of potential 
regulations, and other purposes.
    Most importantly, states need these inventories to help in the 
development of control strategies and demonstrations to attain the Pb 
NAAQS. While the CERR sets forth requirements for data elements, EPA 
guidance complements these requirements and indicates how the data 
should be prepared for SIP submissions. Our regulations at 40 CFR 
51.117(e) require states to include in the inventory all point sources 
that emit 5 or more tons of lead emissions per year. EPA is also 
considering whether revision to the recommended threshold for RACT 
analysis is appropriate in light of the proposed revision to the Pb 
NAAQS. In this proposed rulemaking we are taking comment on whether the 
recommended threshold for RACT analysis should be less than the current 
5 tons/yr (see section VI.F.1). If EPA lowers the recommended threshold 
for RACT at the time of the final rulemaking, we propose also to 
revise, to be consistent, the emissions threshold for including sources 
in the inventory pursuant to 40 CFR 51.117. We solicit comment on the 
appropriate threshold for Pb point source inventory reporting 
requirements.
    The SIP inventory must be approved by EPA as a SIP element and is 
subject to public hearing requirements, whereas the CERR is not. 
Because of the regulatory significance of the SIP inventory, EPA will 
need more documentation on how the SIP inventory was developed by the 
State as opposed to the documentation required for the CERR inventory. 
In addition, the geographic area encompassed by some aspects of the SIP 
submission inventory will be different from the statewide area covered 
by the CERR emissions inventory.
    The EPA has proposed the Air Emissions Reporting Rule (AERR) at 71 
FR 69 (Jan. 3, 2006). When finalized, the AERR would update the CERR 
reporting requirements by consolidating and harmonizing new emissions 
reporting requirements with pre-existing sets of reporting requirements 
under the Clean Air Interstate Rule (CAIR) and the NOX SIP 
Call. At this time, EPA expects to finalize the AERR rulemaking in the 
Fall of calendar year 2008. The AERR is expected to be a means by which 
the Agency will implement additional data reporting requirements for 
the Pb NAAQS SIP emission inventories.
7. Modeling
    The lead SIP regulations found at 40 CFR 51.117 require states to 
employ atmospheric dispersion modeling for the demonstration of 
attainment for areas in

[[Page 29275]]

the vicinity of point sources listed in 40 CFR 51.117(a)(1). To 
complete the necessary dispersion modeling, meteorological, and other 
data are necessary. Dispersion modeling should follow the procedures 
outlined in EPA's latest guidance document entitled ``Guideline on Air 
Quality Models''. This guideline indicates the types and historical 
records for data necessary for modeling demonstrations (e.g., on-site 
meteorological stations are used, 12 months of data are required in 
order to demonstrate attainment for the affected area).

G. General Conformity

    Section 176(c) of the CAA, as amended (42 U.S.C. 7401 et seq.), 
requires that all Federal actions conform to an applicable 
implementation plan developed pursuant to section 110 and part D of the 
CAA. Section 176(c) of the CAA requires EPA to promulgate criteria and 
procedures for demonstrating and assuring conformity of Federal actions 
to a SIP. For the purpose of summarizing the general conformity rule, 
it can be viewed as containing three major parts: applicability, 
procedure, and analysis. These are briefly described below.
    The general conformity rule covers direct and indirect emissions of 
criteria pollutants or their precursors that are caused by a Federal 
action, are reasonably foreseeable, and can practicably be controlled 
by the Federal agency through its continuing program responsibility. 
The general conformity rule generally applies to Federal actions 
except: (1) Actions covered by the transportation conformity rule; (2) 
Actions with respect to associated emissions below specified de minimis 
levels; and (3) Certain other actions that are exempt or presumed to 
conform.
    The general conformity rule also establishes procedural 
requirements. Federal agencies must make their conformity 
determinations available for public review. Notice of draft and final 
general conformity determinations must be provided directly to air 
quality regulatory agencies and to the public by publication in a local 
newspaper.
    The general conformity determination examines the impacts of direct 
and indirect emissions related to Federal actions. The general 
conformity rule provides several options to satisfy air quality 
criteria and requires the Federal action to also meet any applicable 
SIP requirements and emissions milestones. Each Federal agency must 
determine that any actions covered by the general conformity rule 
conform to the applicable SIP before the action is taken. The criteria 
and procedures for conformity apply only in nonattainment and 
maintenance areas with respect to the criteria pollutants under the 
CAA: \173\ carbon monoxide (CO), lead (Pb), nitrogen dioxide 
(NO2), ozone (O3), particulate matter 
(PM-2.5 and PM10), and sulfur dioxide 
(SO2). The general conformity rule establishes procedural 
requirements for Federal agencies for actions related to all NAAQS 
pollutants, both nonattainment and maintenance areas and will apply one 
year following the promulgation of designations for any new or revised 
Pb NAAQS.\174\
---------------------------------------------------------------------------

    \173\ Criteria pollutants are those pollutants for which EPA has 
established a NAAQS under section 109 of the CAA.
    \174\ Transportation conformity is required under CAA section 
176(c) (42 U.S.C. 7506(c)) to ensure that federally supported 
highway and transit project activities are consistent with 
(``conform to'') the purpose of the SIP. Transportation conformity 
applies to areas that are designated nonattainment, and those areas 
redesignated to attainment after 1990 (``maintenance areas'' with 
plans developed under CAA section 175A) for transportation-related 
criteria pollutants. In light of the elimination of Pb additives 
from gasoline transportation conformity does not apply to the Pb 
NAAQS.
---------------------------------------------------------------------------

H. Transition From the Current NAAQS to a Revised NAAQS for Lead

    EPA is proposing to revise the level of the Pb NAAQS significantly, 
as well as changing the indicator and averaging time. The EPA believes 
that Congress's intent, as evidenced by section 110(l), 193, and 
section 172(e) of the CAA, was to ensure that continuous progress, in 
terms of public health protection, takes place in transitioning from a 
current NAAQS for a pollutant to a new or revised NAAQS. Therefore, in 
this section, EPA is proposing that the existing NAAQS will be revoked 
one year following the promulgation of designations for any new NAAQS, 
except that the existing NAAQS will not be revoked for any current 
nonattainment area until the affected area submits, and EPA approves, 
an attainment demonstration which addresses the attainment of the new 
Pb NAAQS.
    The CAA contains a number of provisions that indicate Congress's 
intent to not allow states to alter or remove provisions from 
implementation plans if the plan revision would jeopardize the air 
quality protection being provided by the plan. For example, section 
110(l) provides that EPA may not approve a SIP revision if it 
interferes with any applicable requirement concerning attainment and 
RFP, or any other applicable requirement under the CAA. In addition 
section 193 of the CAA prohibits the modification of a control, or a 
control requirement, in effect or required to be adopted as of November 
15, 1990 (i.e., following the promulgation of the Clean Air Act 
Amendments (CAAA) of 1990), unless such a modification would ensure 
equivalent or greater emissions reductions. One other provision of the 
CAA provides additional insight into Congress's intent related to the 
need to continue progress towards meeting air quality standards during 
periods of transition from one standard to another. Section 172(e) of 
the CAA, related to future modifications of a standard, applies when 
EPA promulgates a new or revised NAAQS and makes it less stringent than 
the previous NAAQS. This provision of the CAA specifies that in such 
circumstances, States may not relax control obligations that apply in 
nonattainment area SIPs, or avoid adopting those controls that have not 
yet been adopted as required.
    Because it is EPA's belief that Congress did not intend to permit 
states to remove control measures when EPA revises a standard until the 
new or revised standard is implemented, we believe that controls that 
are required under the current Pb NAAQS, or that are currently in place 
under the current Pb NAAQS, should remain in place until designations 
are promulgated and, for current nonattainment areas, attainment SIPs 
are approved for any new or revised standard. As a result, EPA is 
proposing that the current Pb NAAQS should stay in place for one year 
following the effective date of designations for any new or revised 
NAAQS before being revoked, except in current nonattainment areas, 
where the existing NAAQS will not be revoked until the affected area 
submits, and EPA approves, an attainment demonstration for the revised 
Pb NAAQS. Pursuant to CAA section 110(l), any proposed SIP revision 
being considered by EPA after the effective date of the revised Pb 
NAAQs would be evaluated for its potential to interfere with attainment 
or maintenance of the new standard. Unlike the transition from the 1-
hour ozone standard to the 8-hour ozone standard, EPA believes that any 
area attaining the revised Pb NAAQS would also attain the existing Pb 
NAAQS, and thus reviewing proposed SIP revisions for interference with 
the new standard will be sufficient to prevent backsliding. 
Consequently, in light of the nature of the proposed revision of the Pb 
NAAQS, the lack of classifications (and mandatory controls associated 
with such classifications pursuant to the CAA), and the small number of 
nonattainment areas, EPA believes that retaining the current standard 
for a limited period of time until attainment SIPs are approved for the 
new standard

[[Page 29276]]

in current nonattainment areas, or one year after designations in other 
areas, will adequately serve the anti-backsliding goals of the CAA. The 
EPA requests comment on this proposed approach for transitioning to the 
proposed revised Pb NAAQS.

VII. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review

    Under section 3(f)(1) of Executive Order 12866 (58 FR 51735, 
October 4, 1993), this action is an ``economically significant 
regulatory action'' because it is likely to have an annual effect on 
the economy of $100 million or more. Accordingly, EPA submitted this 
action to the Office of Management and Budget (OMB) for review under EO 
12866 and any changes made in response to OMB recommendations have been 
documented in the docket for this action (EPA-HQ-OAR-2006-0735). In 
addition, EPA prepared a Regulatory Impact Analysis (RIA) of the 
potential costs and benefits associated with this action. A copy of the 
analysis is available in the RIA docket (EPA-HQ-OAR-2008-0253) and the 
analysis is briefly summarized here. The RIA estimates the costs and 
monetized human health and welfare benefits of attaining four 
alternative Pb NAAQS nationwide. Specifically, the RIA examines the 
alternatives of 0.30 [mu]g/m\3\, 0.20 [mu]g/m\3\, 0.10 [mu]g/m\3\ and 
0.05 [mu]g/m\3\. The RIA contains illustrative analyses that consider a 
limited number of emissions control scenarios that States and Regional 
Planning Organizations might implement to achieve these alternative Pb 
NAAQS. However, the CAA and judicial decisions make clear that the 
economic and technical feasibility of attaining ambient standards are 
not to be considered in setting or revising NAAQS, although such 
factors may be considered in the development of State plans to 
implement the standards. Accordingly, although an RIA has been 
prepared, the results of the RIA have not been considered in issuing 
this proposed rule.

B. Paperwork Reduction Act

    The information collection requirements in this proposed rule have 
been submitted for approval to the Office of Management and Budget 
(OMB) under the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. The 
Information Collection Request (ICR) document prepared by EPA for these 
proposed revisions to part 58 has been assigned EPA ICR numbers 
0940.21.
    The information collected under 40 CFR part 53 (e.g., test results, 
monitoring records, instruction manual, and other associated 
information) is needed to determine whether a candidate method intended 
for use in determining attainment of the National Ambient Air Quality 
Standards (NAAQS) in 40 CFR part 50 will meet the design, performance, 
and/or comparability requirements for designation as a Federal 
reference method (FRM) or Federal equivalent method (FEM). While this 
proposed rule amends the requirements for Pb FRM and FEM 
determinations, they merely provide additional flexibility in meeting 
the FRM/FEM determination requirements. Furthermore, we do not expect 
the number of FRM or FEM determinations to increase over the number 
that is currently used to estimate burden associated with Pb FRM/FEM 
determinations provided in the current ICR for 40 CFR part 53 (EPA ICR 
numbers 0559.12). As such, no change in the burden estimate for 40 CFR 
part 53 has been made as part of this rulemaking.
    The information collected and reported under 40 CFR part 58 is 
needed to determine compliance with the NAAQS, to characterize air 
quality and associated health and ecosystem impacts, to develop 
emissions control strategies, and to measure progress for the air 
pollution program. The proposed amendments would revise the technical 
requirements for Pb monitoring sites, require the siting and operation 
of additional Pb ambient air monitors, and the reporting of the 
collected ambient Pb monitoring data to EPA's Air Quality System (AQS). 
Because this rulemaking includes a range of proposals for the level and 
averaging time, it is not possible accurately predict the size of the 
final network, and its associated burden. Rather we have estimated the 
upper range of burden possible based on the regulatory options being 
proposed which would result in a higher reporting burden (i.e., a final 
level for the standard of 0.1 [mu]g/m\3\ with a 2nd maximum monthly 
averaging form). Based on these assumptions, the annual average 
reporting burden for the collection under 40 CFR part 58 (averaged over 
the first 3 years of this ICR) for 150 respondents is estimated to 
increase by a total of 90,434 labor hours per year with an increase of 
$6,599,653 per year. Burden is defined at 5 CFR 1320.3(b). State, 
local, and tribal entities are eligible for State assistance grants 
provided by the Federal government under the CAA which can be used for 
monitors and related activities.
    An agency may not conduct or sponsor, and a person is not required 
to respond to, a collection of information unless it displays a 
currently valid OMB control number. The OMB control numbers for EPA's 
regulations in 40 CFR are listed in 40 CFR part 9.
    To comment on the Agency's need for this information, the accuracy 
of the provided burden estimates, and any suggested methods for 
minimizing respondent burden, EPA has established a public docket for 
this rule, which includes this ICR, under Docket ID number EPA-HQ-OAR-
2006-0735. Submit any comments related to the ICR to EPA and OMB. See 
ADDRESSES section at the beginning of this notice for where to submit 
comments to EPA. Send comments to OMB at the Office of Information and 
Regulatory Affairs, Office of Management and Budget, 725 17th Street, 
NW., Washington, DC 20503, Attention: Desk Office for EPA. Since OMB is 
required to make a decision concerning the ICR between 30 and 60 days 
after May 20, 2008, a comment to OMB is best assured of having its full 
effect if OMB receives it by June 19, 2008. The final rule will respond 
to any OMB or public comments on the information collection 
requirements contained in this proposal.

C. Regulatory Flexibility Act

    The Regulatory Flexibility Act (RFA) generally requires an agency 
to prepare a regulatory flexibility analysis of any rule subject to 
notice and comment rulemaking requirements under the Administrative 
Procedure Act or any other statute unless the agency certifies that the 
rule will not have a significant economic impact on a substantial 
number of small entities. Small entities include small businesses, 
small organizations, and small governmental jurisdictions.
    For purposes of assessing the impacts of this rule on small 
entities, small entity is defined as: (1) A small business that is a 
small industrial entity as defined by the Small Business 
Administration's (SBA) regulations at 13 CFR 121.201; (2) a small 
governmental jurisdiction that is a government of a city, county, town, 
school district or special district with a population of less than 
50,000; and (3) a small organization that is any not-for-profit 
enterprise which is independently owned and operated and is not 
dominant in its field.
    After considering the economic impacts of this proposed rule on 
small entities, I certify that this action will not have a significant 
economic impact on a substantial number of small entities. This 
proposed rule will not impose any

[[Page 29277]]

requirements on small entities. Rather, this rule establishes national 
standards for allowable concentrations of Pb in ambient air as required 
by section 109 of the CAA. American Trucking Ass'ns v. EPA, 175 F. 3d 
1027, 1044-45 (D.C. cir. 1999) (NAAQS do not have significant impacts 
upon small entities because NAAQS themselves impose no regulations upon 
small entities). Similarly, the proposed amendments to 40 CFR part 58 
address the requirements for States to collect information and report 
compliance with the NAAQS and will not impose any requirements on small 
entities. We continue to be interested in the potential impacts of the 
proposed rule on small entities and welcome comments on issues related 
to such impacts.

D. Unfunded Mandates Reform Act

    Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Public 
Law 104-4, establishes requirements for Federal agencies to assess the 
effects of their regulatory actions on State, local, and tribal 
governments and the private sector. Unless otherwise prohibited by law, 
under section 202 of the UMRA, EPA generally must prepare a written 
statement, including a cost-benefit analysis, for proposed and final 
rules with ``Federal mandates'' that may result in expenditures to 
State, local, and tribal governments, in the aggregate, or to the 
private sector, of $100 million or more in any one year. Before 
promulgating an EPA rule for which a written statement is required 
under section 202, section 205 of the UMRA generally requires EPA to 
identify and consider a reasonable number of regulatory alternatives 
and to adopt the least costly, most cost-effective or least burdensome 
alternative that achieves the objectives of the rule. The provisions of 
section 205 do not apply when they are inconsistent with applicable 
law. Moreover, section 205 allows EPA to adopt an alternative other 
than the least costly, most cost-effective or least burdensome 
alternative if the Administrator publishes with the final rule an 
explanation why that alternative was not adopted. Before EPA 
establishes any regulatory requirements that may significantly or 
uniquely affect small governments, including tribal governments, it 
must have developed under section 203 of the UMRA a small government 
agency plan. The plan must provide for notifying potentially affected 
small governments, enabling officials of affected small governments to 
have meaningful and timely input in the development of EPA regulatory 
proposals with significant Federal intergovernmental mandates, and 
informing, educating, and advising small governments on compliance with 
the regulatory requirements.
    This action is not subject to the requirements of sections 202 and 
205 of the UMRA. EPA has determined that this proposed rule does not 
contain a Federal mandate that may result in expenditures of $100 
million or more for State, local, and tribal governments, in the 
aggregate, or the private sector in any one year. The revisions to the 
Pb NAAQS impose no enforceable duty on any State, local or Tribal 
governments or the private sector. The expected costs associated with 
the increased monitoring requirements are described in EPA's ICR 
document, but those costs are not expected to exceed $100 million in 
the aggregate for any year. Furthermore, as indicated previously, in 
setting a NAAQS EPA cannot consider the economic or technological 
feasibility of attaining ambient air quality standards. Because the 
Clean Air Act prohibits EPA from considering the types of estimates and 
assessments described in section 202 when setting the NAAQS, the UMRA 
does not require EPA to prepare a written statement under section 202 
for the revisions to the Pb NAAQS.
    With regard to implementation guidance, the CAA imposes the 
obligation for States to submit SIPs to implement the Pb NAAQS. In this 
proposed rule, EPA is merely providing an interpretation of those 
requirements. However, even if this rule did establish an independent 
obligation for States to submit SIPs, it is questionable whether an 
obligation to submit a SIP revision would constitute a Federal mandate 
in any case. The obligation for a State to submit a SIP that arises out 
of section 110 and section 191 of the CAA is not legally enforceable by 
a court of law, and at most is a condition for continued receipt of 
highway funds. Therefore, it is possible to view an action requiring 
such a submittal as not creating any enforceable duty within the 
meaning of 2 U.S.C. 658 for purposes of the UMRA. Even if it did, the 
duty could be viewed as falling within the exception for a condition of 
Federal assistance under 2 U.S.C. 658.
    EPA has determined that this proposed rule contains no regulatory 
requirements that might significantly or uniquely affect small 
governments because it imposes no enforceable duty on any small 
governments. Therefore, this rule is not subject to the requirements of 
section 203 of the UMRA.

E. Executive Order 13132: Federalism

    Executive Order 13132, entitled ``Federalism'' (64 FR 43255, August 
10, 1999), requires EPA to develop an accountable process to ensure 
``meaningful and timely input by State and local officials in the 
development of regulatory policies that have federalism implications.'' 
``Policies that have federalism implications'' is defined in the 
Executive Order to include regulations that have ``substantial direct 
effects on the States, on the relationship between the national 
government and the States, or on the distribution of power and 
responsibilities among the various levels of government.''
    This proposed rule does not have federalism implications. It will 
not have substantial direct effects on the States, on the relationship 
between the national government and the States, or on the distribution 
of power and responsibilities among the various levels of government, 
as specified in Executive Order 13132. The rule does not alter the 
relationship between the Federal government and the States regarding 
the establishment and implementation of air quality improvement 
programs as codified in the CAA. Under section 109 of the CAA, EPA is 
mandated to establish NAAQS; however, CAA section 116 preserves the 
rights of States to establish more stringent requirements if deemed 
necessary by a State. Furthermore, this rule does not impact CAA 
section 107 which establishes that the States have primary 
responsibility for implementation of the NAAQS. Finally, as noted in 
section E (above) on UMRA, this rule does not impose significant costs 
on State, local, or tribal governments or the private sector. Thus, 
Executive Order 13132 does not apply to this rule.
    However, EPA recognizes that States will have a substantial 
interest in this rule and any corresponding revisions to associated air 
quality surveillance requirements, 40 CFR part 58. Therefore, in the 
spirit of Executive Order 13132, and consistent with EPA policy to 
promote communications between EPA and State and local governments, EPA 
specifically solicits comment on this proposed rule from State and 
local officials.

F. Executive Order 13175: Consultation and Coordination With Indian 
Tribal Governments

    Executive Order 13175, entitled ``Consultation and Coordination 
with Indian Tribal Governments'' (65 FR 67249, November 9, 2000), 
requires EPA to develop an accountable process to

[[Page 29278]]

ensure ``meaningful and timely input by tribal officials in the 
development of regulatory policies that have tribal implications.'' 
This proposed rule does not have tribal implications, as specified in 
Executive Order 13175. It does not have a substantial direct effect on 
one or more Indian Tribes, since Tribes are not obligated to adopt or 
implement any NAAQS. Thus, Executive Order 13175 does not apply to this 
rule. However, EPA specifically solicits additional comment on this 
proposed rule from tribal officials.

G. Executive Order 13045: Protection of Children From Environmental 
Health & Safety Risks

    This action is subject to Executive Order (62 FR 19885, April 23, 
1997) because it is an economically significant regulatory action as 
defined by Executive Order 12866, and we believe that the environmental 
health risk addressed by this action has a disproportionate effect on 
children. The proposed rule will establish uniform national ambient air 
quality standards for Pb; these standards are designed to protect 
public health with an adequate margin of safety, as required by CAA 
section 109. However, the protection offered by these standards may be 
especially important for children because neurological effects in 
children are among if not the most sensitive health endpoints for Pb 
exposure. Because children are considered a sensitive population, we 
have carefully evaluated the environmental health effects of exposure 
to Pb pollution among children. These effects and the size of the 
population affected are summarized in chapters 6 and 8 of the Criteria 
Document and sections 3.3 and 3.4 of the Staff Paper, and the results 
of our evaluation of the effects of Pb pollution on children are 
discussed in sections II.B and II.C of this preamble.

H. Executive Order 13211: Actions That Significantly Affect Energy 
Supply, Distribution or Use

    This rule is not a ``significant energy action'' as defined in 
Executive Order 13211, ``Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution, or Use'' (66 FR 28355 
(May 22, 2001)) because it is not likely to have a significant adverse 
effect on the supply, distribution, or use of energy. The purpose of 
this rule is to establish revised NAAQS for Pb. The rule does not 
prescribe specific control strategies by which these ambient standards 
will be met. Such strategies will be developed by States on a case-by-
case basis, and EPA cannot predict whether the control options selected 
by States will include regulations on energy suppliers, distributors, 
or users. Thus, EPA concludes that this rule is not likely to have any 
adverse energy effects.

 I. National Technology Transfer and Advancement Act

    Section 12(d) of the National Technology Transfer and Advancement 
Act of 1995 (NTTAA), Public Law 104-113, section 12(d) (15 U.S.C. 272 
note) directs EPA to use voluntary consensus standards in its 
regulatory activities unless to do so would be inconsistent with 
applicable law or otherwise impractical. Voluntary consensus standards 
are technical standards (e.g., materials specifications, test methods, 
sampling procedures, and business practices) that are developed or 
adopted by voluntary consensus standards bodies. The NTTAA directs EPA 
to provide Congress, through OMB, explanations when the Agency decides 
not to use available and applicable voluntary consensus standards.
    This proposed rulemaking involves technical standards. EPA proposes 
to use low-volume PM10 samplers coupled with XRF analysis as 
the FRM for Pb-PM10 measurement. While EPA identified the 
ISO standard ``Determination of the particulate lead content of 
aerosols collected on filters'' (ISO 9855: 1993) as being potentially 
applicable, we do not propose to use it in this rule. The use of this 
voluntary consensus standard would be impractical because the analysis 
method does not provide for the method detection limits necessary to 
adequately characterize ambient Pb concentrations for the purpose of 
determining compliance with the proposed revisions to the Pb NAAQS.
    EPA welcomes comments on this aspect of the proposed rule, and 
specifically invites the public to identify potentially applicable 
voluntary consensus standards and to explain why such standards should 
be used in the regulation.

J. Executive Order 12898: Federal Actions To Address Environmental 
Justice in Minority Populations and Low-Income Populations

    Executive Order 12898 (59 FR 7629; Feb. 16, 1994) establishes 
federal executive policy on environmental justice. Its main provision 
directs federal agencies, to the greatest extent practicable and 
permitted by law, to make environmental justice part of their mission 
by identifying and addressing, as appropriate, disproportionately high 
and adverse human health or environmental effects of their programs, 
policies, and activities on minority populations and low-income 
populations in the United States.
    EPA has determined that this proposed rule will not have 
disproportionately high and adverse human health or environmental 
effects on minority or low-income populations because it increases the 
level of environmental protection for all affected populations without 
having any disproportionately high and adverse human health or 
environmental effects on any population, including any minority or low-
income population. The proposed rule will establish uniform national 
standards for Pb in ambient air.
    EPA is continuing to assess the impact of Pb air pollution on 
minority and low-income populations, and plans to prepare a technical 
memo as part of its assessment to be placed in the docket by the date 
of publication of this proposed rule in the Federal Register. EPA 
solicits comment on environmental justice issues related to the 
proposed revision of the Pb NAAQS.

References

    Adgate, J. L.; Willis, R.D.; Buckley, T.J.; Chow, J.C.; Watson, 
J.G.; Rhoads, G.G.; Lioy, P.J. (1998) Chemical mass balance source 
apportionment of lead in house dust. Environ. Sci. Technol. 32: 108-
114.
    Advisory Committee on Childhood Lead Poisoning Prevention 
(ACCLPP) (2007) Interpreting and managing blood lead levels <10 ug/
dL in children and reducing childhood exposures to lead: 
Recommendations of CDC's Advisory Committee on Childhood Lead 
Poisoning Prevention. Morbidity and Mortality Weekly Report. 56(RR-
8). November 2, 2007.
    Alliance to End Childhood Lead Poisoning. 1991. The First 
Comprehensive National Conference; Final Report. October 6, 7, 8, 
1991.
    American Academy of Pediatrics. 2008. Letter to Stephen Johnson 
from Renee R. Jenkins. January 16, 2008. Available in docket number 
EPA-HQ-OAR-2006-0735.
    Auinger, 2008. E-mail message to Jee-Young Kim, U.S. EPA. 
February 10, 2008. Docket number EPA-HQ-OAR-2006-0735.
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A.A.E.; Salle, H.J.A. (1979) Concentrations of lead and other metals 
in blood of two and three year-old children living near a secondary 
smelter. Int. Arch. Occup. Environ. Health 42: 231-239.

List of Subjects

40 CFR Part 50

    Environmental protection, Air pollution control, Carbon monoxide, 
Lead, Nitrogen dioxide, Ozone, Particulate matter, Sulfur oxides.

40 CFR Part 51

    Environmental protection, Administrative practice and procedure, 
Air pollution control, Carbon monoxide, Intergovernmental relations, 
Lead, Nitrogen dioxide, Ozone, Particulate matter, Reporting and 
recordkeeping requirements.

40 CFR Part 53

    Environmental protection, Administrative practice and procedure, 
Air pollution control, Intergovernmental relations, Reporting and 
recordkeeping requirements.

40 CFR Part 58

    Environmental protection, Administrative practice and procedure, 
Air pollution control, Intergovernmental relations, Reporting and 
recordkeeping requirements.

    Dated: May 1, 2008.
Stephen L. Johnson,
Administrator.
    For the reasons stated in the preamble, title 40, chapter I of the 
Code of Federal Regulations is proposed to be amended as follows:

PART 50--NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY 
STANDARDS

    1. The authority citation for part 50 continues to read as follows:

    Authority: 42 U.S.C. 7401 et seq.

    2. Section 50.3 is revised to read as follows:

[[Page 29282]]

Sec.  50.3  Reference conditions.

    All measurements of air quality that are expressed as mass per unit 
volume (e.g., micrograms per cubic meter) other than for particulate 
matter (PM2.5) standards contained in Sec. Sec.  50.7 and 50.13 and 
lead standards contained in Sec.  50.16 shall be corrected to a 
reference temperature of 25 (deg) C and a reference pressure of 760 
millimeters of mercury (1,013.2 millibars). Measurements of 
PM2.5 for purposes of comparison to the standards contained 
in Sec. Sec.  50.7 and 50.13 and of lead for purposes of comparison to 
the standards contained in Sec.  50.16 shall be reported based on 
actual ambient air volume measured at the actual ambient temperature 
and pressure at the monitoring site during the measurement period.
    3. Section 50.12 is amended by designating the existing text as 
paragraph (a) and adding paragraph (b) to read as follows:

Sec.  50.12  National primary and secondary ambient air quality 
standards for lead.

* * * * *
    (b) The standards set forth in this section will remain applicable 
to all areas notwithstanding the promulgation of lead national ambient 
air quality standards (NAAQS) in Sec.  50.16. The lead NAAQS set forth 
in this section will no longer apply to an area one year after the 
effective date of the designation of that area, pursuant to section 107 
of the Clean Air Act, for the lead NAAQS set forth in Sec.  50.16; 
except that for areas designated nonattainment for the lead NAAQS set 
forth in this section as of the effective date of Sec.  50.16, the lead 
NAAQS set forth in this section will apply until that area submits, 
pursuant to section 191 of the Clean Air Act, and EPA approves, an 
implementation plan providing for attainment of the lead NAAQS set 
forth in Sec.  50.16.
    4. Section 50.14 is amended by:
    (a) Revising paragraph (a)(2);
    (b) Revising paragraph (c)(2)(iii);
    (c) Redesignating paragraph (c)(2)(v) as paragraph (c)(2)(vi) and 
adding a new paragraph (c)(2)(v); and
    (d) Redesignating existing paragraphs (c)(3)(iii) and (c)(3)(iv) as 
paragraphs (c)(3)(iv) and (c)(3)(v), respectively, and adding paragraph 
(c)(3)(iii).
    The additions and revisions read as follows:

Sec.  50.14  Treatment of air quality monitoring data influenced by 
exceptional events.

* * * * *
    (a) * * *
* * * * *
    (2) Demonstration to justify data exclusion may include any 
reliable and accurate data, but must demonstrate a clear causal 
relationship between the measured exceedance or violation of such 
standard and the event in accordance with paragraph (c)(3)(iv) of this 
section.
    (c) * * *
    (2) * * *
    (iii) Flags placed on data as being due to an exceptional event 
together with an initial description of the event shall be submitted to 
EPA not later than July 1st of the calendar year following the year in 
which the flagged measurement occurred, except as allowed under 
paragraph (c)(2)(iv) or (c)(2)(v) of this section.
* * * * *
    (v) For lead (Pb) data collected during calendar years 2006-2008, 
that the State identifies as resulting from an exceptional event, the 
State must notify EPA of the flag and submit an initial description of 
the event no later than July 1, 2009. For Pb data collected during 
calendar year 2009, that the State identifies as resulting from an 
exceptional event, the State must notify EPA of the flag and submit an 
initial description of the event no later than July 1, 2010. For Pb 
data collected during calendar year 2010, that the State identifies as 
resulting from an exceptional event, the State must notify EPA of the 
flag and submit an initial description of the event no later than May 
1, 2011.
* * * * *
    (3) * * *
    (iii) A State that flags Pb data collected during calendar years 
2006-2009, pursuant to paragraph (c)(2)(v) of this section shall, after 
notice and opportunity for public comment, submit to EPA a 
demonstration to justify exclusion of the data not later than September 
15, 2010. A State that flags Pb data collected during calendar year 
2010 shall, after notice and opportunity for public comment, submit to 
EPA a demonstration to justify the exclusion of the data not later than 
May 1, 2011. A state must submit the public comments it received along 
with its demonstration to EPA.
* * * * *
    5. Section 50.16 is added to read as follows:

Sec.  50.16  National primary and secondary ambient air quality 
standards for lead.

    (a) The national primary and secondary ambient air quality 
standards for lead (Pb) and its compounds is [0.10-0.30] micrograms per 
cubic meter ([mu]/m\3\), [arithmetic mean concentration averaged over a 
calendar quarter or second highest arithmetic mean concentration 
averaged over a calendar month] measured in the ambient air as Pb 
either by:
    (1) A reference method based on (Appendix G or Appendix Q of this 
part) and designated in accordance with part 53 of this chapter; or
    (2) An equivalent method designated in accordance with part 53 of 
this chapter.
    (b) The national primary and secondary ambient air quality 
standards for Pb are met when the [quarterly or second highest monthly] 
arithmetic mean concentration, as determined in accordance with 
Appendix R of this part, is less than or equal to [0.10-0.30] 
micrograms per cubic meter.
    6. Appendix G is amended as follows:
    a. In section 10.2 the definition of the term ``VSTP'' 
in the equation is revised; and
    b. In section 14 reference 10 is added and reference 15 is revised.

Appendix G to Part 50--Reference Method for the Determination of Lead 
in Suspended Particulate Matter Collected From Ambient Air

* * * * *
    10.2 * * *
    VSTP= Air volume from section 10.1.
* * * * *
    14. * * *
    10. Intersociety Committee (1972). Methods of Air Sampling and 
Analysis. 1015 Eighteenth Street, NW., Washington, DC: American 
Public Health Association. 365-372.
    * * *
    15. Sharon J. Long, et. al., ``Lead Analysis of Ambient Air 
Particulates: Interlaboratory Evaluation of EPA Lead Reference 
Method,'' APCA Journal, 29, 28-31 (1979).
* * * * *
    7. Appendix Q is added to read as follows:

Appendix Q to Part 50--Reference Method for the Determination of Lead 
in Particulate Matter as PM10 Collected From Ambient Air

    This Federal Reference Method (FRM) draws heavily from the 
specific analytical protocols used by the U.S. EPA.
    1. Applicability and Principle
    1.1 This method provides for the measurement of the lead (Pb) 
concentration in particulate matter that is 10 micrometers or less 
(PM10) in ambient air. PM10 is collected on a 
46.2 mm diameter polytetrafluoroethylene (PTFE) filter for 24 hours 
using active sampling at local conditions with a low-volume air 
sampler. The low-volume sampler has an average flow rate of 16.7 
liters per minute (Lpm) and total sampled volume of 24 cubic meters 
(m\3\) of air. The analysis of Pb in PM10 is performed on 
each individual 24-hour sample. For the purpose of this method, 
PM10 is defined as particulate matter having an 
aerodynamic

[[Continued on page 29283]]

From the Federal Register Online via GPO Access [wais.access.gpo.gov]
]                         
 
[[pp. 29283-29291]] National Ambient Air Quality Standards for Lead

[[Continued from page 29282]]

[[Page 29283]]

diameter in the nominal range of 10 micrometers (10 [mu]m) or less.
    1.2 For this reference method, PM10 shall be 
collected with the PM10c federal reference method (FRM) 
sampler as described in Appendix O to Part 50 using the same sample 
period, measurement procedures, and requirements specified in 
Appendix L of Part 50. The PM10c sampler is also being 
used for measurement PM10-2.5 mass by difference and as 
such, the PM10c sampler must also meet all of the 
performance requirements specified for PM2.5 in Appendix 
L. The concentration of Pb in the atmosphere is determined in the 
total volume of air sampled and expressed in micrograms per cubic 
meter ([mu]g/m\3\) at local temperature and pressure conditions.
    1.3 The FRM will serve as the basis for approving Federal 
Equivalent Methods (FEMs) as specified in 40 CFR part 53 (Reference 
and Equivalent Methods).
    1.4 An electrically powered air sampler for PM10c 
draws ambient air at a constant volumetric flow rate into a 
specially shaped inlet and through an inertial particle size 
separator, where the suspended particulate matter in the 
PM10 size range is separated for collection on a PTFE 
filter over the specified sampling period. The lead content of the 
PM10c sample is analyzed by energy-dispersive X-ray 
fluorescence spectrometry (EDXRF). Energy-dispersive X-ray 
fluorescence spectrometry provides a means for identification of an 
element by measurement of its characteristic X-ray emission energy. 
The method allows for quantification of the element by measuring the 
emitted characteristic line intensity and then relating this 
intensity to the elemental concentration. The number or intensity of 
X-rays produced at a given energy provides a measure of the amount 
of the element present by comparisons with calibration standards. 
The X-rays are detected and the spectral signals are acquired and 
processed with a personal computer. EDXRF is commonly used as a non-
destructive method for quantifying trace elements in PM. An EPA 
method for the EDXRF analysis of ambient particulate matter is 
described in reference 1 of section 8. A detailed explanation of 
quantitative X-ray spectrometry is described in references 2 and 3.
    1.5 Quality assurance (QA) procedures for the collection of 
monitoring data are contained in Part 58, Appendix A.
    2. PM10c Lead Measurement Range and Method Detection Limit. The 
values given below in section 2.1 and 2.2 are typical of the method 
capabilities. Absolute values will vary for individual situations 
depending on the instrument, detector age, and operating conditions 
used. Data are typically reported in ng/m\3\ for ambient air 
samples; however, for this reference method, data will be reported 
in [mu]g/m\3\ at local temperature and pressure conditions.
    2.1 EDXRF Measurement Range. The typical ambient air measurement 
range is 0.001 to 30 [mu]g Pb/m\3\, assuming an upper range 
calibration standard of about 60 [mu]g Pb per square centimeter 
(cm\2\), a filter deposit area of 11.86 cm\2\, and an air volume of 
24-m\3\. The top range of the EDXRF instrument is much greater than 
what is stated here. The top measurement range of quantification is 
defined by the level of the high concentration calibration standard 
used and can be increased to expand the measurement range as needed.
    2.2 Method Detection Limit (MDL). A typical one-sigma estimate 
of the method detection limit (MDL) is about 1.5 ng Pb/cm\2\ or 
0.001 [mu]g Pb/m\3\, assuming a filter size of 46.2-mm (filter 
deposit area of 11.86 cm\2\) and a sample air volume of 24-m\3\. The 
MDL is an estimate of the lowest amount of lead that can be detected 
by the analytical instrument. The one-sigma detection limit for Pb 
is calculated as the average overall uncertainty or propagated error 
for Pb, determined from measurements on a series of blank filters. 
The sources of random error which are considered are calibration 
uncertainty; system stability; peak and background counting 
statistics; uncertainty in attenuation corrections; uncertainty in 
peak overlap corrections; and uncertainty in flow rate, but the 
dominating source is by far peak and background counting statistics. 
Laboratories are to estimate the MDLs using 40 CFR Part 136, 
Appendix B, ``Definition and Procedure for the Determination of the 
Method Detection Limit.'' (Reference 4).
    3. Factors Affecting Bias and Precision of Lead Determination by 
EDXRF
    3.1 Filter Deposit. Too much deposit material can be problematic 
because XRF analysis and data processing programs for aerosol 
samples are designed specifically for a thin film or thin layer of 
material to be analyzed. The X-ray spectra are subject to distortion 
if unusually heavy deposits are analyzed. This is the result of 
internal absorption of both primary and secondary X-rays within the 
sample. The optimum filter loading is about 150 [mu]g/cm\2\ or 1.6 
mg/filter for a 46.2-mm filter. Too little deposit material can also 
be problematic due to low counting statistics and signal noise. The 
particle mass deposit should minimally be 15 [mu]g/cm\2\. A properly 
collected sample will have a uniform deposit over the entire 
collection area. Sample heterogeneity can lead to very large 
systematic errors. Samples with physical deformities (including a 
visually non-uniform deposit area) should not be quantitatively 
analyzed.
    3.2 Spectral Interferences and Spectral Overlap. Spectral 
interference occurs when the entirety of the analyte spectral lines 
of two species are nearly 100% overlapped. There are only a few 
cases where this may occur and they are instrument specific: Si/Rb, 
Si/Ta, S/Mo, S/Tl, Al/Br, Al/Tm. These interferences are determined 
during instrument calibration and automatically corrected for by the 
XRF instrument software. Interferences need to be addressed when 
multi-elemental analysis is performed. The presence of arsenic (As) 
is a problematic interference for EDXRF systems which use the Pb 
L[alpha] line exclusively to quantify the Pb 
concentration. This is because the Pb L[alpha] line and 
the As K[alpha] lines severely overlap. However, if the 
instrument software is able to use multiple Pb lines, including the 
L[beta] and/or the L[gamma] lines for 
quantification, then the uncertainty in the Pb determination in the 
presence of As can be significantly reduced. There can be instances 
when lines partially overlap the Pb spectral lines, but with the 
energy resolution of most detectors, these overlaps are typically 
de-convoluted using standard spectral de-convolution software 
provided by the instrument vendor. An EDXRF protocol for Pb must 
define which Pb lines are used for quantification and where spectral 
overlaps occur. Some of the overlaps may be very small and some 
severe. A de-convolution protocol must be used to separate all the 
lines which overlap with Pb.
    3.3 Particle Size Effects and Attenuation Correction Factors. X-
ray attenuation is dependent on the X-ray energy, mass sample 
loading, composition, and particle size. In some cases, the 
excitation and fluorescent X-rays are attenuated as they pass 
through the sample. In order to relate the measured intensity of the 
X-rays to the thin-film calibration standards used, the magnitude of 
any attenuation present must be corrected for. The effect is 
especially significant and more complex for PM10 
measurements, especially for the lighter elements that may also be 
measured. An average attenuation and uncertainty for each coarse 
particle element is based on a broad range of mineral compositions 
and is a one-time calculation that gives an attenuation factor for 
use in all subsequent particle analyses. See references 6, 7, and 8 
of section 8 for more discussion on addressing this issue. 
Essentially no attenuation corrections are necessary for Pb in 
PM10: both the incoming excitation X-rays used for 
analyzing lead and the fluoresced Pb X-rays are sufficiently 
energetic that for particles in this size range and for normal 
filter loadings, the Pb x-ray yield is not significantly impacted by 
attenuation. However, this issue must be addressed when doing multi-
element analyses.
    4. Precision
    4.1 Measurement system precision is assessed according to the 
procedures set forth in Appendix A to part 58. Measurement method 
precision is assessed from collocated sampling and analysis. The 
goal for acceptable measurement uncertainty, as precision, is 
defined as an upper 90 percent confidence limit for the coefficient 
of variation (CV) of 15 percent.
    5. Bias
    5.1 Measurement system bias for monitoring data is assessed 
according to the procedures set forth in Appendix A of part 58. The 
bias is assessed through an audit using spiked filters. The goal for 
measurement bias is defined as an upper 95 percent confidence limit 
for the absolute bias of 10 percent.
    6. Measurement of PTFE Filters by EDXRF
    6.1 Sampling
    6.1.1 Low-Volume PM10c Sampler. The low-volume PM10c 
sampler shall be used for sample collection and operated in 
accordance with the performance specifications described in Part 50, 
Appendix L.
    6.1.2 PTFE Filters and Filter Acceptance Testing. The PTFE 
filters used for PM10c sample collection shall meet the 
specifications provided in Part 50, Appendix L. The following 
requirements are similar to those currently specified for the 
acceptance of PM2.5 filters that are tested for trace

[[Page 29284]]

elements by EDXRF. For large batches of filters (greater than 500 
filters) randomly select 50 filters from a given batch. For small 
batches (less than 500 filters) a lesser number of filters may be 
taken. Analyze each filter separately and calculate the average lead 
concentration in ng/cm\2\. Ninety percent, or 45 of the 50 filters, 
must have an average lead concentration that is less than 4.8 ng Pb/
cm\2\.
    6.2 Analysis. The four main categories of random and systematic 
error encountered in X-ray fluorescence analysis include errors from 
sample collection, the X-ray source, the counting process, and 
inter-element effects. These errors are addressed through the 
calibration process and mathematical corrections in the instrument 
software.
    6.2.1 EDXRF Analysis Instrument. An energy-dispersive XRF system 
is used. Energy-dispersive XRF systems are available from a number 
of commercial vendors including Thermo (www.thermo.com) and 
PANalytical (www.panalytical.com). Note the mention of commercial 
products does not imply endorsement by the U.S. Environmental 
Protection Agency. The analysis is performed at room temperature in 
either vacuum or in a helium atmosphere. The specific details of the 
corrections and calibration algorithms are typically included in 
commercial analytical instrument software routines for automated 
spectral acquisition and processing and vary by manufacturer. It is 
important for the analyst to understand the correction procedures 
and algorithms of the particular system used, to ensure that the 
necessary corrections are applied.
    6.2.2 Thin film standards. Thin film standards are used for 
calibration because they most closely resemble the layer of 
particles on a filter. Thin films standards are typically deposited 
on Nuclepore substrates. The preparation of thin film standards is 
discussed in reference 6, and 9. Thin film standards are 
commercially available from MicroMatter Inc. (Arlington, WA).\1\
    6.2.3 Filter Preparation. Filters used for sample collection are 
46.2-mm PTFE filters with a pore size of 2 microns and filter 
deposit area 11.86 cm\2\. Filters are typically archived in cold 
storage prior to analysis. Filters that are scheduled for XRF 
analysis are removed from storage and allowed to reach room 
temperature. All filter samples received for analysis are checked 
for any holes, tears, or a non-uniform deposit which would prevent 
quantitative analysis. A properly collected sample will have a 
uniform deposit over the entire collection area. Samples with 
physical deformities are not quantitatively analyzable. The filters 
are carefully removed with tweezers from the Petri dish and securely 
placed into the instrument-specific sampler holder for analysis. 
Care must be taken to protect filters to avoid contamination prior 
to analysis. Filters must be kept covered when not being analyzed. 
No other preparation of the samples is required.
    6.2.4 Calibration. In general, calibration determines each 
element's sensitivity, i.e., its response in X-ray counts/sec to 
each [mu]g/cm\2\ of a standard and an interference coefficient for 
each element that causes interference with another one (See section 
3.2 above). The sensitivity can be determined by a linear plot of 
count rate versus concentration ([mu]g/cm\2\) in which the slope is 
the instrument's sensitivity for that element. A more precise way, 
which requires fewer standards, is to fit sensitivity versus atomic 
number. Calibration is a complex task in the operation of an XRF 
system. Two major functions accomplished by calibration are the 
production of reference spectra which are used for fitting and the 
determination of the elemental sensitivities. Included in the 
reference spectra (referred to as ``shapes'') are background-
subtracted peak shapes of the elements to be analyzed, as well as 
peak shapes for interfering element energies and spectral 
backgrounds. Pure element thin film standards are used for the 
element peak shapes and clean filter blanks from the same lot as 
unknowns are used for the background. The analysis of PM filter 
deposits is based on the assumption that the thickness of the 
deposit is small with respect to the characteristic lead X-ray 
transmission thickness. Therefore, the concentration of lead in a 
sample is determined by first calibrating the spectrometer with thin 
film standards to determine sensitivity factors and then analyzing 
the unknown samples under identical excitation conditions as used to 
determine the calibration factors. Calibration is performed only 
when significant repairs occur or when a change in fluorescers, X-
ray tubes, or detector is made. Calibration establishes the 
elemental sensitivity factors and the magnitude of interference or 
overlap coefficients. See reference 7 for more detailed discussion 
of calibration and analysis of shapes standards for background 
correction, coarse particle absorption corrections, and spectral 
overlap.
    6.2.4.1 Spectral Peak Fitting. The EPA uses a library of pure 
element peak shapes (shape standards) to extract the elemental 
background-free peak areas from an unknown spectrum. It is also 
possible to fit spectra using peak stripping or analytically defined 
functions such as modified Gaussian functions. The EPA shape 
standards are generated from pure, mono-elemental thin film 
standards. The shape standards are acquired for sufficiently long 
times to provide a large number of counts in the peaks of interest. 
It is not necessary for the concentration of the standard to be 
known. A slight contaminant in the region of interest in a shape 
standard can have a significant and serious effect on the ability of 
the least squares fitting algorithm to fit the shapes to the unknown 
spectrum. It is these elemental shapes, that are fitted to the peaks 
in an unknown sample during spectral processing by the analyzer. In 
addition to this library of elemental shapes, there is also a 
background shape spectrum for the filter type used as discussed 
below in section 6.2.4.2 of this section.
    6.2.4.2 Background Measurement and Correction. A background 
spectrum generated by the filter itself must be subtracted from the 
X-ray spectrum prior to extracting peak areas. The background shape 
standards which are used for background fitting are created at the 
time of calibration. About 20-30 clean blank filters are kept in a 
sealed container and are used exclusively for background measurement 
and correction. The spectra acquired on individual blank filters are 
added together to produce a single spectrum for each of the 
secondary targets or fluorescers used in the analysis of lead. 
Individual blank filter spectra which show contamination are 
excluded from the summed spectra. The summed spectra are fitted to 
the appropriate background during spectral processing. Background 
correction is automatically included during spectral processing of 
each sample.
    7. Calculation.
    7.1 The PM10 lead concentration in the atmosphere 
([mu]g/m\3\) is calculated using the following equation:
[GRAPHIC] [TIFF OMITTED] TP20MY08.006

Where,

MPb is the mass per unit volume for lead in [mu]g/m\3\;
CPb is the mass per unit area for lead in [mu]g/cm\2\ as provided by 
the XRF instrument software;
A is the filter deposit area in cm\2\;
VLC is the total volume of air sampled by the PM10c 
sampler in actual volume units measured at local conditions of 
temperature and pressure, as provided by the sampler in m\3\.

    8. References
    1. Inorganic Compendium Method IO-3.3; Determination of Metals 
in Ambient Particulate Matter Using X-Ray Fluorescence (XRF) 
Spectroscopy; U.S. Environmental Protection Agency, Cincinnati, OH 
45268. EPA/625/R-96/010a. June 1999.
    2. Jenkins, R., Gould, R.W., and Gedcke, D. Quantitative X-ray 
Spectrometry: Second Edition. Marcel Dekker, Inc., New York, NY. 
1995.
    3. Jenkins, R. X-Ray Fluorescence Spectrometry: Second Edition 
in Chemical Analysis, a Series of Monographs on Analytical Chemistry 
and Its Applications, Volume 152. Editor J.D.Winefordner; John Wiley 
& Sons, Inc. New York, NY. 1999.
    4. Code of Federal Regulations (CFR) 40 part 136, Appendix B; 
Definition and Procedure for the Determination of the Method 
Detection Limit--Revision 1.11
    5. Dzubay, T.G. X-ray Fluorescence Analysis of Environmental 
Samples, Ann Arbor Science Publishers Inc., 1977.
    6. Drane, E.A, Rickel, D.G., and Courtney, W.J., ``Computer Code 
for Analysis X-Ray Fluorescence Spectra of Airborne Particulate 
Matter,'' in Advances in X-Ray Analysis, J.R. Rhodes, Ed., Plenum 
Publishing Corporation, New York, NY, p. 23 (1980).
    7. Analysis of Energy-Dispersive X-ray Spectra of ambient 
Aerosols with Shapes Optimization, Guidance Document; TR-WDE-06-02; 
prepared under contract EP-D-05-065 for the U.S. Environmental 
Protection Agency, National Exposure Research Laboratory. March 
2006.
    8. Billiet, J., Dams, R., and Hoste, J. (1980) Multielement Thin 
Film Standards for XRF Analysis, X-Ray Spectrometry, 9(4): 206-211.
    8. Appendix R is added to read as follows:

[[Page 29285]]

Appendix R to Part 50--Interpretation of the National Ambient Air 
Quality Standards for Lead

1. General

    (a) This appendix explains the data handling conventions and 
computations necessary for determining when the primary and 
secondary national ambient air quality standards (NAAQS) for lead 
(Pb) specified in Sec.  50.16 are met. The NAAQS indicator for Pb is 
defined as: lead and its compounds, measured as elemental lead in 
total suspended particulate (Pb-TSP), sampled and analyzed by a 
Federal reference method (FRM) based on appendix G to this part or 
by a Federal equivalent method (FEM) designated in accordance with 
part 53 of this chapter. Although Pb-TSP is the lead NAAQS 
indicator, surrogate Pb-TSP concentrations shall also be used for 
NAAQS comparisons; specifically, valid surrogate Pb-TSP data are 
concentration data for lead and its compounds, measured as elemental 
lead, in particles with an aerodynamic size of 10 microns or less 
(Pb-PM10), sampled and analyzed by an FRM based on 
appendix Q to this part or by an FEM designated in accordance with 
part 53 of this chapter, the resulting concentrations then 
multiplied by an appropriate site-specific scaling factor to 
represent Pb-TSP. Data handling and computation procedures to be 
used in making comparisons between reported and/or surrogate Pb-TSP 
concentrations and the level of the Pb NAAQS, including Pb-
PM10 to Pb-TSP scaling instructions, are specified in the 
following sections.
    (b) Whether to exclude, retain, or make adjustments to the data 
affected by exceptional events, including natural events, is 
determined by the requirements and process deadlines specified in 
Sec. Sec.  50.1, 50.14, and 51.930 of this chapter.
    (c) The terms used in this appendix are defined as follows:
    Annual monitoring plan refers to the plan required by section 
58.10 of this chapter.
    Creditable samples are samples that are given credit for data 
completeness. They include valid samples collected on required 
sampling days and valid ``make-up'' samples taken for missed or 
invalidated samples on required sampling days.
    Daily values for Pb refers to the 24-hour mean concentrations of 
Pb (Pb-TSP or Pb-PM10) measured from midnight to midnight 
(local standard time) that are used in NAAQS computations.
    Design value is the site-level metric (i.e., statistic) that is 
compared to the NAAQS level to determine compliance; the design 
value for the Pb NAAQS is the second highest monthly mean Pb-TSP or 
surrogate Pb-TSP concentration for the most recent valid 3-year 
calendar period.
    Extra samples are non-creditable samples. They are daily values 
that do not occur on scheduled sampling days and that can not be 
used as make-ups for missed or invalidated scheduled samples. Extra 
samples are used in mean calculations. For purposes of determining 
whether a sample must be treated as a make-up sample or an extra 
sample, Pb-TSP and Pb-PM10 data collected before January 
1, 2009 will be treated with an assumed scheduled sampling frequency 
of every sixth day.
    Make-up samples are samples taken to supplant missed or 
invalidated required scheduled samples. Make-ups can be made by 
either the primary or collocated (same size cut) instruments. Make-
up samples are either taken before the next required sampling day or 
exactly one week after the missed (or voided) sampling day. Make-up 
samples can not span years; that is, if a scheduled sample for 
December is missed (or voided), it can not be made up in January. 
Make-up samples, however, may span months, for example a missed 
sample on January 31 may be made up on February 1, 2, or 6. Section 
3(e) explains how such month-spanning make-up samples are to be 
treated for purposes of data completeness and monthly means. Only 
two make-up samples are permitted each calendar month; these are 
counted according to the month in which the miss and not the makeup 
occurred Also, to be considered a valid make-up, the sampling must 
be conducted with equipment and procedures that meet the 
requirements for scheduled sampling. For purposes of determining 
whether a sample must be treated as a make-up sample or an extra 
sample, Pb-TSP and Pb-PM10 data collected before January 
1, 2009 will be treated with an assumed scheduled sampling frequency 
of every sixth day.
    Monthly mean refers to an arithmetic mean, as defined in section 
4.3 of this appendix. Monthly means are one of two specific types, 
``monthly parameter means'' or ``monthly site means''. Monthly means 
are computed at each monitoring site separately for Pb-TSP and Pb-
PM10 (i.e., by site-parameter-year-month); these 
parameter-specific means are referred to as monthly parameter means. 
Monthly parameter means are validated according to the criteria 
stated in section 4 of this appendix. A ``monthly site mean'' (i.e., 
one for a site-year-month level) will be the valid monthly Pb-TSP 
mean if available, or the valid Pb-PM10 (scaled) monthly 
mean when it is available and a valid Pb-TSP monthly mean is not. If 
neither a valid Pb-TSP nor a valid Pb-PM10 monthly 
(parameter) mean exists for a particular site-year-month then there 
will be no corresponding valid monthly site mean.
    Parameter refers either to Pb-TSP or to Pb-PM10.
    Scheduled sampling day means a day on which sampling is 
scheduled based on the required sampling frequency for the 
monitoring site, as provided in section 58.12 of this chapter.
    Year refers to a calendar year.

2. Monitoring Considerations for Use of Scaled Pb-PM10 Data as 
Surrogate Pb-TSP Data

    (a) Monitoring agencies are permitted to monitor for Pb-
PM10 at a required Pb monitoring site rather than 
monitoring for Pb-TSP, but only after the monitoring agency 
develops, and the Regional Administrator approves, a site-specific 
scaling factor to be used to adjust Pb-PM10 data before 
comparison to the standard. The development of such a factor must 
meet the criteria stated below (in sections 2(b)(i) through 
2(b)(iv)), and the factor and associated analysis must be documented 
in the monitoring agency's Annual Monitoring Network Plan. The site-
specific scaling factor meeting all of these requirements shall take 
effect on January 1 following Regional Administrator approval of the 
Plan. The data criteria for establishing a site-specific alternative 
Pb-PM10 to Pb-TSP scaling factor are:
    (i) A scaling factor shall be based on a minimum of 12 
consecutive months of collocated Pb-TSP and Pb-PM10 FRM/
FEM monitoring which produces at least 6 pairs of valid collocated 
measurements for each of at least 10 months of each period of 12 
months.
    (ii) Calculated Pearson correlation coefficients for the paired 
data shall equal or exceed 0.60 for each individual month of the 
evaluation period (for months containing at least 6 pairs), and a 
calculated overall (using all 10 or more months with at least 6 
pairs of valid collocated measurements) Pearson correlation 
coefficient shall equal or exceed 0.80.
    (iii) The site-specific scaling factor shall be equal to the 
mean of the ratios of monthly mean Pb-TSP concentration to monthly 
mean Pb-PM10 concentration, using all 10 or more months 
with at least 6 pairs of valid collocated measurements and only 
using the days with valid collocated measurements. The scaling 
factor shall be rounded to two decimal places.
    (iv) Each monthly ratio of Pb-TSP to Pb-PM10 shall be 
within twenty percent of the 10-month (or more) mean ratio. Ratios 
shall be computed from unrounded means but monthly ratios shall be 
rounded to two decimal places before making the comparison.

3. Requirements for Data Used for Comparisons With the Pb NAAQS and 
Data Reporting Considerations

    (a) All valid FRM/FEM Pb-TSP data and all valid FRM/FEM Pb-
PM10 data submitted to EPA's Air Quality System (AQS), or 
otherwise available to EPA, meeting the requirements of part 58 of 
this chapter including appendices A, C, and E shall be used in 
design value calculations. Pb-TSP and Pb-PM10 data 
representing sample collection periods prior to January 1, 2009 
(i.e., ``pre-rule'' data) will also be considered valid for NAAQS 
comparisons and related attainment/nonattainment determinations if 
the sampling and analysis methods that were utilized to collect that 
data were consistent with previous or newly designated FRMs or FEMs 
and with either the provisions of part 58 of this chapter including 
appendices A, C, and E that were in effect at the time of original 
sampling or that are in effect at the time of the attainment/
nonattainment determination, and if such data are submitted to AQS 
prior to September 1, 2009.
    (b) Pb-TSP and Pb-PM10 measurement data shall be 
reported to AQS in units of micrograms per cubic meter ([mu]g/m\3\) 
at local conditions (local temperature and pressure, LC) to three 
decimal places, with additional digits to the right being truncated. 
Pb-PM10 data shall be reported without application of a 
scaling factor. Pre-rule Pb-TSP and Pb-PM10 concentration 
data that were reported in standard conditions (standard temperature

[[Page 29286]]

and standard pressure, STP) will not require a conversion to local 
conditions but rather, after truncating to three decimal places and 
processing as stated in this appendix, shall compared ``as is'' to 
the NAAQS (i.e., the LC to STP conversion factor will be assumed to 
be one). However, if the monitoring agency has retroactively 
resubmitted Pb-TSP or Pb-PM10 pre-rule data converted 
from STP to LC based on suitable meteorological data, only the LC 
data will be used.
    (c) At each monitoring location (site), Pb-TSP and Pb-
PM10 data are to be processed separately when selecting 
daily data by day (as specified in 3(d) below) and when aggregating 
daily data by month (per 4(2)(a) below), however, when deriving the 
design value for the three-year period, monthly means for the two 
data types may be combined; see section 4(e) below.
    (d) Daily values for sites will be selected for a site on a size 
cut (Pb-TSP or Pb-PM10, i.e., ``parameter'') basis; Pb-
TSP concentrations and Pb-PM10 concentrations shall not 
be commingled in these determinations. Site level, parameter-
specific daily values will be selected as follows:
    (i) The starting dataset for a site-parameter shall consist of 
the measured daily concentrations recorded from the designated 
primary FRM/FEM monitor for that parameter. The primary monitor for 
each parameter shall be designated in the appropriate State or local 
agency annual Monitoring Network Plan. If no primary monitor is 
designated, the Administrator will select which monitor to treat as 
primary. All daily values produced by the primary sampler are 
considered part of the site-parameter composite record (i.e., that 
site-parameter's set of daily values); this includes all creditable 
samples and all extra samples.
    (ii) Data for the primary monitor for each parameter shall be 
augmented as much as possible with data from collocated (same 
parameter) FRM/FEM monitors. If a valid 24-hour measurement is not 
produced from the primary monitor for a particular day (scheduled or 
otherwise), but a valid sample is generated by a collocated (same 
parameter) FRM/FEM instrument, then that collocated value shall be 
considered part of the site-parameter data record (i.e., that site-
parameter's monthly set of daily values). If more than one valid 
collocated FRM/FEM value is available, the mean of those valid 
collocated values shall be used as the daily value.
    (e) All daily values in the composite site-parameter record are 
used in monthly mean calculations. However, not all daily values are 
given credit towards data completeness requirements. Only 
``creditable'' samples are given credit for data completeness. 
Creditable samples include valid samples on scheduled sampling days 
and valid make-up samples. All other types of daily values are 
referred to as ``extra'' samples. Make-up samples taken in the 
(first week of the) month after the one in which the miss/void 
occurred will be credited for data capture in the month of the miss/
void but will be included in the month actually taken when computing 
monthly means.

4. Comparisons With the Pb NAAQS

    (a) The Pb NAAQS is met at a monitoring site when the identified 
design value is valid and less than or equal to 0.20 [0.10, 0.30] 
micrograms per cubic meter ([mu]g/m\3\). A Pb design value of 0.20 
[0.10, 0.30] [mu]g/m\3\ or less is valid if it encompasses 3 
consecutive calendar years of valid monthly means (i.e., 36 valid 
monthly means). See 4(c) below for the definition of a valid monthly 
mean and 6(c) below for the definition of the design value. A Pb 
design value of 0.20 [0.10, 0.30] [mu]g/m\3\ or less will also be 
considered valid if it encompasses 35 valid monthly means (out of 36 
possible over 3 consecutive calendar years) and the highest of the 
35 is equal to or less than 0.20 [0.10, 0.30] [mu]g/m\3\.
    (b) The Pb NAAQS is violated at a monitoring site when the 
identified design value is valid and is greater than 0.20 [0.10, 
0.30] micrograms per cubic meter ([mu]g/m\3\). A Pb design value 
greater than 0.20 [0.10, 0.30] [mu]g/m\3\ is valid if it encompasses 
at least two valid monthly means. A site does not have to have valid 
monitoring data for three full calendar years in order to have a 
valid violating design value. For example, a site could start 
monitoring in November of a given calendar year and violate the 
NAAQS for any three-year period that includes that given calendar 
year, if the November and December means are valid and greater than 
0.20 [0.10, 0.30] [mu]g/m\3\.
    (c) (i) A monthly mean is considered valid (i.e., meets data 
completeness requirements) if for one or both of the Pb parameters 
measured at the site, the data capture rate is greater than or equal 
to 75 percent. Monthly data capture rates (expressed as a 
percentage) are specifically calculated as the number of creditable 
samples for the month (including any make-up samples taken the 
subsequent month for missed samples in the (previous) month in 
question) divided by the number of scheduled samples for the month, 
the result then multiplied by 100 and rounded to the nearest 
integer. As noted above, Pb-TSP and Pb-PM10 daily values 
are processed separately when calculating monthly means and data 
capture rates; a Pb-TSP value cannot be used as a make-up for a 
missing Pb-PM10 value or vice versa. For purposes of 
assessing data capture, Pb-TSP and Pb-PM10 data collected 
before January 1, 2009 will be treated with an assumed scheduled 
sampling frequency of every sixth day.
    (ii) A monthly parameter mean that does not have at least 75 
percent data capture and thus cannot be considered valid under 
4(c)(1) shall still be considered valid (and complete) if it passes 
either of the two following ``data substitution'' tests, one such 
test for validating an above NAAQS-level mean (using actual ``low'' 
reported values from the site), and the second test for validating a 
below-NAAQS level mean (using actual ``high'' values reported for 
the site). Note that both tests are merely diagnostic in nature, 
intending to confirm that there is a very high likelihood if not 
certainty that that original mean (the one with less than 75% data 
capture) reflects the true over/under NAAQS-level status for that 
month; the result of these data substitution tests (i.e., the test 
means, as described below) is never considered the actual monthly 
parameter mean and shall not be used to determine the design value. 
For both types of data substitution, substitution is permitted only 
if there are a sufficient number of available data points from which 
to identify the high or low 3-year month-specific values, 
specifically if there are at least 10 data points total from at 
least two of the three possible year-months. Data substitution may 
only use data of the same parameter type. For Pb-PM10 
data, the ``test'' monthly mean after data substitution shall be 
scaled using Equation 2 of section 6(b) before being compared to the 
level of the standard.
    (A) The ``above NAAQS level'' test is as follows: If by 
substituting the lowest reported daily value for that month over the 
3-year design value period in question (year non-specific; e.g., for 
January) for missing scheduled data in the deficient months 
(substituting only enough to meet the 75 percent data capture 
minimum), the computation yields a recalculated test monthly 
parameter mean concentration above the level of the standard, then 
the month is deemed to have passed the diagnostic test and the level 
of the standard is deemed to have been exceeded in that month. As 
noted above, in such a case, the monthly parameter mean of the data 
actually reported, not the recalculated (``test'') result including 
the low values, shall be used to determine the design value.
    (B) The ``below NAAQS level'' test is as follows: A monthly 
parameter mean that does not have at least 75 percent data capture 
but does have at least 50 percent data capture shall still be 
considered valid (and complete) if, by substituting the highest 
reported daily value for that month over the 3-year design value 
period in question, for all missing scheduled data in the deficient 
months (i.e., bringing the data capture rate up to 100%), the 
computation yields a recalculated monthly parameter mean 
concentration equal or less than the level of the standard, then the 
month is deemed to have passed the diagnostic test and the level of 
the standard is deemed not to have been exceeded in that month. As 
noted above, in such a case, the monthly parameter mean of the data 
actually reported, not the recalculated (``test'') result including 
the high values, shall be used to determine the design value.
    (d) Months that do not meet the completeness criteria stated in 
4(c)(i) or 4(c)(ii) above, and design values that do not meet the 
completeness criteria stated in 4(a) or 4(b) above, may also be 
considered valid (and complete) with the approval of, or at the 
initiative of, the Administrator, who may consider factors such as 
monitoring site closures/moves, monitoring diligence, the 
consistency and levels of the valid concentration measurements that 
are available, and nearby concentrations in determining whether to 
use such data.
    (e) The site-level design value for a three calendar year period 
is identified from the available valid monthly parameter means. In a 
situation where there are valid monthly means for both parameters 
(Pb-TSP and Pb-PM10), the mean originating from the 
reported Pb-TSP data will be the one deemed the site-level monthly 
mean and used in design value identifications. A monitoring site 
will have only one site-level monthly

[[Page 29287]]

mean per month; however, the set of site-level monthly means 
considered for design value identification (i.e., two to 36 site-
level monthly means) can be a combination of Pb-TSP and scaled Pb-
PM10 data.
    (f) The procedures for calculating monthly means, scaling Pb-
PM10 monthly means to a surrogate Pb-TSP basis, and 
identifying Pb design values are given in section 6 of this 
appendix.

5. Rounding Conventions

    (a) Monthly means shall be rounded to the nearest hundredth 
[mu]g/m\3\ (0.xx). Decimals 0.xx5 and greater are rounded up, and 
any decimal lower than 0.xx5 is rounded down; e.g., a monthly mean 
of 0.104925 rounds to 0.10, and a monthly mean of .10500 rounds to 
0.11.
    (b) Because a Pb design value is simply a (second highest) 
monthly mean and because the NAAQS level is stated to two decimal 
places, no additional rounding beyond what is specified for monthly 
means is required before a design value is compared to the NAAQS.

6. Procedures and Equations for the Pb NAAQS.

    (a) A monthly mean value for Pb-TSP (or Pb-PM10) is 
determined by averaging the daily values of a calendar month using 
equation 1 of this appendix:
[GRAPHIC] [TIFF OMITTED] TP20MY08.007

Where:

Xm,y,s = the mean for quarter q of the year y for site s; 
and
nm = the number of daily values in the month; and
Xi,m,y,s = the ith value in month m for year y 
for site s.
    (b) Monthly means for reported Pb-PM10 data are 
scaled to a surrogate Pb-TSP basis using Equation 2 of this 
appendix.
[GRAPHIC] [TIFF OMITTED] TP20MY08.008

Where:

Zm,y,s = the surrogate Pb-TSP mean for month m of the 
year y for site s; and
Xm,y,s = the Pb-PM10 mean for month m of the 
year y for site s; and
Fm,y,s = the scaling factor for year y and for site s 
determined through collocated testing in accordance with section 
2.0(b).

    (c) The site-level identified Pb design value is the second 
highest valid site-level monthly mean over the most recent 3-year 
period. Section 4 above explains when the identified design value is 
itself considered valid for purposes of determining that the NAAQS 
is met or violated at a site.

PART 53--AMBIENT AIR MONITORING REFERENCE AND EQUIVALENT METHODS

    9. The authority citation for part 53 continues to read as follows:

    Authority: Sec. 301(a) of the Clean Air Act (42 U.S.C. sec. 
1857g(a)), as amended by sec. 15(c)(2) of Pub. L. 91-604, 84 Stat. 
1713, unless otherwise noted.

Subpart C--[Amended]

    10. Section 53.33 is revised to read as follows:

Sec.  53.33  Test Procedure for Methods for Lead (Pb).

    (a) General. The reference method for collection of Pb in TSP 
includes two parts, the reference method for high-volume sampling of 
TSP as specified in 40 CFR part 50, appendix B and the analysis method 
for Pb in TSP as specified in 40 CFR part 50, appendix G. 
Correspondingly, the reference method for Pb in PM10 
includes the reference method for low-volume sampling of 
PM10 in 40 CFR part 50, appendix O and the analysis method 
of Pb in PM10 as specified in 40 CFR part 50, appendix Q. 
This section explains the procedures for demonstrating the equivalence 
of either a candidate method for Pb in TSP to the high-volume reference 
methods, or a candidate method for Pb in PM10 to the low-
volume reference methods.
    (1) Pb in TSP--A candidate method for Pb in TSP specifies reporting 
of Pb concentrations in terms of standard temperature and pressure. 
Comparisons of candidate methods to the reference method in 40 CFR part 
50, appendix G must be made in a consistent manner with regard to 
temperature and pressure.
    (2) Pb in PM10--A candidate method for Pb in 
PM10 must specify reporting of Pb concentrations in terms of 
local conditions of temperature and pressure, which will be compared to 
similarly reported concentrations from the reference method in 40 CFR 
part 50, appendix Q.
    (b) Comparability. Comparability is shown for Pb methods when the 
differences between:
    (1) Measurements made by a candidate method, and
    (2) Measurements made by the reference method on simultaneously 
collected Pb samples (or the same sample, if applicable), are less than 
or equal to the values specified in table C-3 of this subpart.
    (c) Test measurements. Test measurements may be made at any number 
of test sites. Augmentation of pollutant concentrations is not 
permitted, hence an appropriate test site or sites must be selected to 
provide Pb concentrations in the specified range.
    (d) Collocated samplers. The ambient air intake points of all the 
candidate and reference method collocated samplers shall be positioned 
at the same height above the ground level, and between 2 meters (1 
meter for samplers with flow rates less than 200 liters per minute (L/
min)) and 4 meters apart. The samplers shall be oriented in a manner 
that will minimize spatial and wind directional effects on sample 
collection.
    (e) Sample collection. Collect simultaneous 24-hour samples 
(filters) of Pb at the test site or sites with both the reference and 
candidate methods until at least 10 filter pairs have been obtained. A 
candidate method for Pb in TSP which employs a sampler and sample 
collection procedure that are identical to the sampler and sample 
collection procedure specified in the reference method in 40 CFR part 
50, appendix B, but uses a different analytical procedure than 
specified in 40 CFR part 50, appendix G, may be tested by analyzing 
pairs of filter strips taken from a single TSP reference sampler 
operated according to the procedures specified by that reference 
method. A candidate method for Pb in PM10 which employs a 
sampler and sample collection procedure that are identical to the 
sampler and sample collection procedure specified in the reference 
method in 40 CFR part 50, appendix O, but uses a different analytical 
procedure than specified in 40 CFR part 50, appendix Q, requires the 
use of two PM10 reference samplers because a single 46.2-mm 
filter from a reference sampler may not be divided prior to analysis.
    (f) Audit samples. Three audit samples must be obtained from the 
address given in Sec.  53.4(a). For Pb in TSP collected by the high-
volume sampling method, the audit samples are \3/4\ x 8-inch glass 
fiber strips containing known amounts of Pb in micrograms per strip 
([mu]g/strip) equivalent to the following nominal percentages of the 
National Ambient Air Quality Standard (NAAQS): 30%, 100%, and 250%. For 
Pb in PM10 collected by the low-volume sampling method, the 
audit samples are 46.2-mm polytetrafluorethylene (PTFE) filters 
containing known amounts of Pb in micrograms per filter ([mu]g/filter) 
equivalent to the same percentages of the NAAQS: 30%, 100%, and 250%. 
The true amount of Pb (Tqi), in total [mu]g/strip (for TSP) or total 
[mu]g/filter (for PM10), will be provided with each audit 
sample.
    (g) Filter analysis.
    (1) For both the reference method samples and the audit samples, 
analyze each filter or filter extract three times in accordance with 
the reference method analytical procedure. This applies to both the Pb 
in TSP and Pb in PM10 methods. The analysis of replicates

[[Page 29288]]

should not be performed sequentially, i.e., a single sample should not 
be analyzed three times in sequence. Calculate the indicated Pb 
concentrations for the reference method samples in micrograms per cubic 
meter ([mu]g/m\3\) for each analysis of each filter. Calculate the 
indicated total Pb amount for the audit samples in [mu]g/strip for each 
analysis of each strip or [mu]g/filter for each analysis of each audit 
filter. Label these test results as R1A, R1B, 
R1C, R2A, R2B, * * *, Q1A, 
Q1B, Q1C, * * *, where R denotes results from the 
reference method samples; Q denotes results from the audit samples; 1, 
2, 3 indicate the filter number, and A, B, C indicate the first, 
second, and third analysis of each filter, respectively.
    (2) For the candidate method samples, analyze each sample filter or 
filter extract three times and calculate, in accordance with the 
candidate method, the indicated Pb concentration in [mu]g/m\3\ for each 
analysis of each filter. The analysis of replicates should not be 
performed sequentially. Label these test results as C1A, 
C1B, C2C, * * *, where C denotes results from the 
candidate method. For candidate methods which provide a direct 
measurement of Pb concentrations without a separable procedure, 
C1A = C1B = C1C, C2A = 
C2B = C2C, etc.
    (h) Average Pb concentration. For the reference method, calculate 
the average Pb concentration for each filter by averaging the 
concentrations calculated from the three analyses as described in 
paragraph (g)(1) of this section using equation 1 of this section:
[GRAPHIC] [TIFF OMITTED] TP20MY08.009

Where, i is the filter number.

    (i) Accuracy.
    (1)(i) For the audit samples, calculate the average Pb 
concentration for each strip or filter by averaging the concentrations 
calculated from the three analyses as described in (g)(1) using 
equation 2 of this section:
[GRAPHIC] [TIFF OMITTED] TP20MY08.010

Where, i is audit sample number.

    (ii) Calculate the percent difference (Dq) between the 
indicated Pb concentration for each audit sample and the true Pb 
concentration (Tq) using equation 3 of this section:
[GRAPHIC] [TIFF OMITTED] TP20MY08.011

    (2) If any difference value (Dqi) exceeds 5 
percent, the accuracy of the reference method analytical procedure is 
out-of-control. Corrective action must be taken to determine the source 
of the error(s) (e.g., calibration standard discrepancies, extraction 
problems, etc.) and the reference method and audit sample 
determinations must be repeated according to paragraph (g) of this 
section, or the entire test procedure (starting with paragraph (e) of 
this section) must be repeated.
    (j) Acceptable filter pairs. Disregard all filter pairs for which 
the Pb concentration, as determined in paragraph (h) of this section by 
the average of the three reference method determinations, falls outside 
the range of 30% to 250% of the Pb NAAQS level in [mu]g/m\3\ for Pb in 
both TSP and PM10. All remaining filter pairs must be 
subjected to the tests for precision and comparability in paragraphs 
(k) and (l) of this section. At least five filter pairs must be within 
the specified concentration range for the tests to be valid.
    (k) Test for precision.
    (1) Calculate the precision (P) of the analysis (in percent) for 
each filter and for each method, as the maximum minus the minimum 
divided by the average of the three concentration values, using 
equation 4 or equation 5 of this section:
[GRAPHIC] [TIFF OMITTED] TP20MY08.012

    or
    [GRAPHIC] [TIFF OMITTED] TP20MY08.013
    
where, i indicates the filter number.

    (2) If any reference method precision value (PRi) 
exceeds 15 percent, the precision of the reference method analytical 
procedure is out-of-control. Corrective action must be taken to 
determine the source(s) of imprecision, and the reference method 
determinations must be repeated according to paragraph (g) of this 
section, or the entire test procedure (starting with paragraph (e) of 
this section) must be repeated.
    (3) If any candidate method precision value (PCi) 
exceeds 15 percent, the candidate method fails the precision test.
    (4) The candidate method passes this test if all precision values 
(i.e., all PRi's and all PCi's) are less than 15 
percent.
    (l) Test for comparability. (1) For each filter or analytical 
sample pair, calculate all nine possible percent differences (D) 
between the reference and candidate methods, using all nine possible 
combinations of the three determinations (A, B, and C) for each method 
using equation 6 of this section:
[GRAPHIC] [TIFF OMITTED] TP20MY08.014

where, i is the filter number, and n numbers from 1 to 9 for the 
nine possible difference combinations for the three determinations 
for each method (j = A, B, C, candidate; k = A, B, C, reference).

    (2) If none of the percent differences (D) exceeds 20 
percent, the candidate method passes the test for comparability.
    (3) If one or more of the percent differences (D) exceed 20 percent, the candidate method fails the test for 
comparability.
    (4) The candidate method must pass both the precision test 
(paragraph (k) of this section) and the comparability test (paragraph 
(l) of this section) to qualify for designation as an equivalent 
method.
    (m) Method Detection Limit (MDL). Calculate the estimated MDL using 
the guidance provided in 40 CFR Part 136, Appendix B. It is essential 
that all sample processing steps of the analytical method be included 
in the determination of the method detection limit. Take a minimum of 
seven aliquots of the sample to be used to calculate the method 
detection limit and process each through the entire analytical method. 
Make all computations according to the defined method with the final 
results in [mu]g/m\3\. The MDL must be equal to, or less than 1% of the 
level of the Pb NAAQS.
    10a. Revise Table C-3 to Subpart C of Part 53 to read as follows:

  Table C-3 to Subpart C of Part 53.--Test Specifications for Pb in TSP
                         and Pb in PM10 Methods
------------------------------------------------------------------------

------------------------------------------------------------------------
Concentration range equivalent to           30% to 250%.
 percentage of NAAQS in [mu]g/m\3\.
Minimum number of 24-hr measurements......  5.
Maximum precision, PR or PC...............  <=15%.
Maximum analytical accuracy, Dq...........  5%
Maximum difference (D), percent of          20%.
 reference method.

[[Page 29289]]

Estimated Method Detection Limit (MDL),     1% of NAAQS level.
 [mu]g/m\3\.
------------------------------------------------------------------------

PART 58--AMBIENT AIR QUALITY SURVEILLANCE

    11. The authority citation for part 58 continues to read as 
follows:

    Authority: 42 U.S.C. 7403, 7410, 7601(a), 7611, and 7619.

Subpart B--[Amended]

    12. Section 58.10, is amended by adding paragraphs (a)(4) and 
(b)(9) to read as follows:

Sec.  58.10  Annual monitoring network plan and periodic network 
assessment.

    (a) * * *
    (4) A plan for establishing Pb monitoring sites in accordance with 
the requirements of appendix D to this part shall be submitted to the 
EPA Regional Administrator by July 1, 2009. The plan shall provide for 
at least one half of the required Pb monitoring sites to be operational 
by January 1, 2010, and for all required Pb monitoring sites to be 
operational by January 1, 2011. Source oriented Pb monitoring sites for 
the highest emitting half of Pb sources shall be installed by January 
1, 2010.
    (b) * * *
    (9) The designation of any Pb monitors as either source-oriented or 
non-source oriented according to appendix D to this part.
* * * * *
    13. Section 58.12 is amended by revising paragraph (b) to read as 
follows:

Sec.  58.12  Operating schedules.

* * * * *
    (b) For Pb manual methods, at least one 24-hour sample must be 
collected every 3 days except during periods or seasons exempted by the 
Regional Administrator. The Regional Administrator can allow a 
reduction in the sampling schedule to one 24-hour sample every 6 days 
if the Pb design value over the previous 3 years is less than 70% of 
the Pb NAAQS.
    14. Section 58.13 is amended by revising paragraph (b) to read as 
follows:

Sec.  58.13  Monitoring network completion.

* * * * *
    (b) Not withstanding specific dates included in this part, 
beginning January 1, 2008, when existing networks are not in 
conformance with the minimum number of required monitors specified in 
this part, additional required monitors must be identified in the next 
applicable annual monitoring network plan, with monitoring operation 
beginning by January 1 of the following year. To allow sufficient time 
to prepare and comment on Annual Monitoring Network Plans, only 
monitoring requirements effective 120 days prior to the required 
submission date of the plan (i.e., 120 days prior to July 1 of each 
year) shall be included in that year's annual monitoring network plan.
    15. Section 58.16 is amended by revising paragraph (a) to read as 
follows:

Sec.  58.16  Data submittal and archiving requirements.

    (a) The State, or where appropriate, local agency, shall report to 
the Administrator, via AQS all ambient air quality data and associated 
quality assurance data for SO2; CO; O3; 
NO2; NO; NOY; NOX; Pb-TSP mass 
concentration; Pb-PM10 mass concentration; PM10 
mass concentration; PM2.5 mass concentration; for filter-
based PM2.5 FRM/FEM the field blank mass, sampler-generated 
average daily temperature, and sampler-generated average daily 
pressure; chemically speciated PM2.5 mass concentration 
data; PM10-2.5 mass concentration; chemically speciated 
PM10-2.5 mass concentration data; meteorological data from 
NCore and PAMS sites; average daily temperature and average daily 
pressure for Pb sites if not already reported from sampler generated 
records; and metadata records and information specified by the AQS Data 
Coding Manual (http://www.epa.gov/ttn/airs/airsaqs/manuals/
manuals.htm). Such air quality data and information must be submitted 
directly to the AQS via electronic transmission on the specified 
quarterly schedule described in paragraph (b) of this section.
* * * * *

Subpart C--[Amended]

    16. Section 58.20 is amended by revising paragraph (e) to read as 
follows:

Sec.  58.20  Special purpose monitors (SPM).

* * * * *
    (e) If an SPM using an FRM, FEM, or ARM is discontinued within 24 
months of start-up, the Administrator will not designate an area as 
nonattainment for the CO, SO2, NO2, or 24-hour 
PM10 NAAQS solely on the basis of data from the SPM. Such 
data are eligible for use in determinations of whether a nonattainment 
area has attained one of these NAAQS.
* * * * *
    17. Appendix A to part 58 is amended by revising paragraph 3.3.4 
and Table A-2.

Appendix A to Part 58--Quality Assurance Requirements for SLAMS, SPMs 
and PSD Air Monitoring

* * * * *
    3.3.4 Pb Methods.
    3.3.4.1 Flow Rates. For the Pb Reference Methods (40 CFR part 
50, appendix G and appendix Q) and associated FEMs, the flow rates 
of the Pb samplers shall be verified and audited using the same 
procedures described in sections 3.3.2 and 3.3.3 of this appendix.
    3.3.4.2 Pb Analysis Audits. Each calendar quarter or sampling 
quarter (PSD), audit the Pb Reference Method analytical procedure 
using filters containing a known quantity of Pb. These audit filters 
are prepared by depositing a Pb solution on unexposed filters and 
allowing them to dry thoroughly. The audit samples must be prepared 
using batches of reagents different from those used to calibrate the 
Pb analytical equipment being audited. Prepare audit samples in the 
following concentration ranges:

------------------------------------------------------------------------
                                                Equivalent ambient Pb
                   Range                      concentration, [mu]g/m\3\
                                                         \1\
------------------------------------------------------------------------
1.........................................  30-100% of Pb NAAQS.
2.........................................  200-300% of Pb NAAQS.
------------------------------------------------------------------------
\1\ Equivalent ambient Pb concentration in [mu]g/m\3\ is based on
  sampling at 1.7 m\3\/min for 24 hours on a 20.3 cm x 25.4 cm (8 inch x
  10 inch) glass fiber filter.

    (a) Audit samples must be extracted using the same extraction 
procedure used for exposed filters.
    (b) Analyze three audit samples in each of the two ranges each 
quarter samples are analyzed. The audit sample analyses shall be 
distributed as much as possible over the entire calendar quarter.
    (c) Report the audit concentrations (in [mu]g Pb/filter or 
strip) and the corresponding measured concentrations (in [mu]g Pb/
filter or strip) using AQS unit code 077. The relative percent 
differences between the concentrations are used to calculate 
analytical accuracy as described in section 4.4.2 of this appendix.
    (d) The audits of an equivalent Pb method are conducted and 
assessed in the same manner as for the reference method. The flow 
auditing device and Pb analysis audit samples must be compatible 
with the specific requirements of the equivalent method.
    3.3.4.3 Collocated Sampling. The collocated sampling 
requirements for Pb-TSP and Pb-PM10 shall be determined 
using the same procedures described in sections 3.3.1 of this 
appendix.
    3.3.4.4 Pb Performance Evaluation Program (PEP) Procedures. One 
performance evaluation audit, as described in section 3.2.7 of this 
appendix must be performed at one Pb site in each primary quality 
assurance organization each year. The calculations for evaluating 
bias between the primary monitor(s) and the performance evaluation 
monitors for Pb are the same as those for PM10-2.5 which 
are described in section 4.1.3 of this appendix. In addition, for 
each

[[Page 29290]]

quarter, one half of a collocated sample pair (from the designated 
collocated sampler) from one site within each PQAO must sent to an 
independent laboratory for analysis.
* * * * *

            Table A-2 of Appendix A to Part 58.--Minimum Data Assessment Requirements for SLAMS Sites
----------------------------------------------------------------------------------------------------------------
                                                                                                  Parameters
             Method                Assessment method       Coverage       Minimum  frequency       reported
----------------------------------------------------------------------------------------------------------------
                                                Automated Methods
----------------------------------------------------------------------------------------------------------------
1-Point QC for SO2, NO2, O3, CO.  Response check at   Each analyzer.....  Once per 2 weeks..  Audit
                                   concentration                                               concentration\1\
                                   0.01-0.1 ppm SO2,                                           and measured
                                   NO2, O3, and 1-10                                           concentration.\2\
                                   ppm CO.
Annual performance evaluation     See section 3.2.2   Each analyzer.....  Once per year.....  Audit
 for SO2, NO2, O3, CO.             of this appendix.                                           concentration\1\
                                                                                               and measured
                                                                                               concentration\2\
                                                                                               for each level.
Flow rate verification PM10,      Check of sampler    Each sampler......  Once every month..  Audit flow rate
 PM2.5, PM10	2.5.                  flow rate.                                                  and measured flow
                                                                                               rate indicated by
                                                                                               the sampler.
Semi-annual flow rate audit       Check of sampler    Each sampler......  Once every 6......  Audit flow rate
 PM10, PM2.5, PM10	2.5.            flow rate using                                             and measured flow
                                   independent                                                 rate indicated by
                                   standard.                                                   the sampler.
Collocated sampling PM2.5,        Collocated          15%...............  Every 12 days.....  Primary sampler
 PM10	2.5.                         samplers.                                                   concentration and
                                                                                               duplicate sampler
                                                                                               concentration
Performance evaluation program    Collocated          1. 5 valid audits   Over all 4          Primary sampler
 PM2.5, PM10	2.5.                  samplers.           for primary QA      quarters.           concentration and
                                                       orgs, with <= 5                         performance
                                                       sites 2. 8 valid                        evaluation
                                                       audits for                              sampler
                                                       primary QA orgs,                        concentration.
                                                       with > 5 sites 3.
                                                       All samplers in 6
                                                       years.
----------------------------------------------------------------------------------------------------------------
                                                 Manual Methods
----------------------------------------------------------------------------------------------------------------
Collocated sampling PM10, TSP,    Collocated          15%...............  Every 12 days PSD-- Primary sampler
 PM10	2.5, PM2.5, Pb-TSP, Pb-      samplers.                               every 6 days.       concentration and
 PM10.                                                                                         duplicate sampler
                                                                                               concentration.
Flow rate verification PM10 (low  Check of sampler    Each sampler......  Once every month..  Audit flow rate
 Vol), PM10	2.5, PM2.5, Pb-PM10.   flow rate.                                                  and measured flow
                                                                                               rate indicated by
                                                                                               the sampler.
Flow rate verification PM10       Check of sampler    Each sampler......  Once every quarter  Audit flow rate
 (High-Vol), TSP, Pb-TSP.          flow rate.                                                  and measured flow
                                                                                               rate indicated by
                                                                                               the sampler.
Semi-annual flow rate audit       Check of sampler    Each sampler, all   Once every 6        Audit flow rate
 PM10, TSP, PM10	2.5, PM2.5, Pb-   flow rate using     locations.          months.             and measured flow
 TSP, Pb-PM10.                     independent                                                 rate indicated by
                                   standard.                                                   the sampler.
Pb audit strips Pb-TSP, Pb-PM10.  Check of            Analytical........  Each quarter......  Actual
                                   analytical system                                           concentration.
                                   with Pb audit
                                   strips.
Performance evaluation program    Collocated          1. 5 valid audits   Over all 4          Primary sampler
 PM2.5, PM10	2.5.                  samplers.           for primary QA      quarters.           concentration and
                                                       orgs, with <= 5                         performance
                                                       sites 2. 8 valid                        evaluation
                                                       audits for                              sampler
                                                       primary QA orgs,                        concentration.
                                                       with [gteqt] 5
                                                       sites 3. All
                                                       samplers in 6
                                                       years.
Performance evaluation program    Collocated          1 valid audit for   Over all 4          Primary sampler
 Pb-TSP, Pb-PM10.                  samplers.           primary QA orgs.    quarters.           concentration and
                                                                                               performance
                                                                                               evaluation
                                                                                               sampler
                                                                                               concentration.
----------------------------------------------------------------------------------------------------------------
\1\ Effective concentration for open path analyzers.
\2\ Corrected concentration, if applicable, for open path analyzers.

* * * * *
    18. Appendix D to part 58 is amended as by revising paragraph 4.5 
to read as follows:

Appendix D to Part 58--Network Design Criteria for Ambient Air Quality 
Monitoring

* * * * *
    4.5 Lead (Pb) Design Criteria. (a) State and, where appropriate, 
local agencies are required to conduct Pb monitoring near lead 
sources which emit more than [200 to 600] kilograms per year. At a 
minimum, there must be one source-oriented SLAMS site located 
(taking into account logistics and other limitations) to measure the 
maximum Pb concentration in ambient air resulting from the lead 
source.
    (b) The Regional Administrator may waive the requirement in 
paragraph 4.5(a) for monitoring near Pb sources emitting less than 
1000 kilograms if the State or, where appropriate, local agency can 
demonstrate (via historical monitoring data, modeling, or other 
means) that the Pb source will not contribute to a maximum Pb 
concentration in ambient air in excess of 50% of the NAAQS.
    (c) State and, where appropriate, local agencies are required to 
conduct Pb

[[Page 29291]]

monitoring in each CBSA with a population greater than 1,000,000 
people as determined based on the latest available census figures. 
At a minimum, there must be one nonsource-oriented SLAMS site 
located to estimate typical Pb concentrations in the urban area. 
Consideration should be given to locating these monitors in 
neighborhoods near heavily trafficked roadways.
    (d) The most important spatial scales for source-oriented sites 
to effectively characterize the emissions from point sources are 
microscale and middle scale. The most important spatial scale for 
nonsource-oriented sites to characterize typical lead concentrations 
in urban areas is the neighborhood scale.
    (1) Microscale--This scale would typify areas in close proximity 
to lead point sources. Emissions from point sources such as primary 
and secondary lead smelters, and primary copper smelters may under 
fumigation conditions likewise result in high ground level 
concentrations at the microscale. In the latter case, the microscale 
would represent an area impacted by the plume with dimensions 
extending up to approximately 100 meters. Data collected at 
microscale sites provide information for evaluating and developing 
``hot-spot'' control measures.
    (2) Middle scale--This scale generally represents Pb air quality 
levels in areas up to several city blocks in size with dimensions on 
the order of approximately 100 meters to 500 meters. The middle 
scale may for example, include schools and playgrounds in center 
city areas which are close to major Pb point sources. Pb monitors in 
such areas are desirable because of the higher sensitivity of 
children to exposures of elevated Pb concentrations (reference 3 of 
this appendix). Emissions from point sources frequently impact on 
areas at which single sites may be located to measure concentrations 
representing middle spatial scales.
    (3) Neighborhood scale--The neighborhood scale would 
characterize air quality conditions throughout some relatively 
uniform land use areas with dimensions in the 0.5 to 4.0 kilometer 
range. Sites of this scale would provide monitoring data in areas 
representing conditions where children live and play. Monitoring in 
such areas is important since this segment of the population is more 
susceptible to the effects of Pb. Where a neighborhood site is 
located away from immediate Pb sources, the site may be very useful 
in representing typical air quality values for a larger residential 
area, and therefore suitable for population exposure and trends 
analyses.
    (e) Pb monitoring required in paragraphs 4.5(a) and 4.5(c) can 
be conducted with either Pb-TSP or Pb-PM10.
    (f) Technical guidance is found in references 4 and 5 of this 
appendix. These documents provide additional guidance on locating 
sites to meet specific urban area monitoring objectives and should 
be used in locating new sites or evaluating the adequacy of existing 
sites.
* * * * *
[FR Doc. E8-10808 Filed 5-19-08; 8:45 am]

BILLING CODE 6560-50-P