Document ID: EPA-HQ-OAR-2010-0108-0188
Agency: epa
Document Type: Rule
Title: National Ambient Air Quality Standards for Lead; Review
Posted Date: 2016-10-18T04:00Z

[Federal Register Volume 81, Number 201 (Tuesday, October 18, 2016)]
[Rules and Regulations]
[Pages 71906-71943]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2016-23153]

[[Page 71905]]

Vol. 81

Tuesday,

No. 201

October 18, 2016

Part V

Environmental Protection Agency

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40 CFR Part 50

Review of the National Ambient Air Quality Standards for Lead; Final 
Rule

  Federal Register / Vol. 81 , No. 201 / Tuesday, October 18, 2016 / 
Rules and Regulations  

[[Page 71906]]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 50

[EPA-HQ-OAR-2010-0108; FRL-9952-87-OAR]
RIN 2060-AQ44

Review of the National Ambient Air Quality Standards for Lead

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: Based on the Environmental Protection Agency's (EPA's) review 
of the air quality criteria and the national ambient air quality 
standards (NAAQS) for lead (Pb), the EPA is retaining the current 
standards, without revision.

DATES: This final rule is effective on November 17, 2016.

ADDRESSES: The EPA has established a docket for this action under 
Docket ID No. EPA-HQ-OAR-2010-0108. Incorporated into this docket is a 
separate docket established for the Integrated Science Assessment for 
this review (Docket ID No. EPA-HQ-ORD-2011-0051). All documents in 
these dockets are listed on the www.regulations.gov Web site. 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, is not placed on 
the Internet and will be publicly available only in hard copy form. It 
may be viewed, with prior arrangement, at the EPA Docket Center. 
Publicly available docket materials are available either electronically 
in www.regulations.gov or in hard copy at the Air and Radiation Docket 
Information Center, EPA/DC, WJC West Building, 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 
Information Center is (202) 566-1742.

FOR FURTHER INFORMATION CONTACT: Dr. Deirdre L. 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; email: murphy.deirdre@epa.gov.

Availability of Information Related to this Action

    A number of the documents that are relevant to this action are 
available through the 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 documents 
include the Integrated Review Plan for the National Ambient Air Quality 
Standards for Lead (USEPA, 2011a), available at http://www.epa.gov/ttn/naaqs/standards/pb/s_pb_2010_pd.html, the Integrated Science Assessment 
for Lead (USEPA, 2013a), available at http://www.epa.gov/ttn/naaqs/standards/pb/s_pb_2010_isa.html, the Review of the National Ambient Air 
Quality Standards for Lead: Risk and Exposure Assessment Planning 
Document (USEPA, 2011b), available at http://www.epa.gov/ttn/naaqs/standards/pb/s_pb_2010_pd.html, and the Policy Assessment for the 
Review of the Lead National Ambient Air Quality Standards (USEPA, 
2014), available at http://www.epa.gov/ttn/naaqs/standards/pb/s_pb_2010_pa.html. These and other related documents are also available 
for inspection and copying in the EPA docket identified above.

SUPPLEMENTARY INFORMATION: 

Table of Contents

Executive Summary
I. Background
    A. Legislative Requirements
    B. Related Lead Control Programs
    C. Review of the Air Quality Criteria and Standards for Lead
    D. Multimedia, Multipathway Aspects of Lead
    E. Air Quality Monitoring
    F. Summary of Proposed Decisions
    G. Organization and Approach to Final Decisions
II. Rationale for Decision on the Primary Standard
    A. Introduction
    1. Background on the Current Standard
    2. Overview of Health Effects Evidence
    3. Overview of Information on Blood Lead Relationships With Air 
Lead
    4. Overview of Risk and Exposure Assessment Information
    B. Conclusions on the Primary Standard
    1. Basis for the Proposed Decision
    2. CASAC Advice in This Review
    3. Comments on the Proposed Decision
    4. Administrator's Conclusions
    C. Decision on the Primary Standard
III. Rationale for Decision on the Secondary Standard
    A. Introduction
    1. Overview of Welfare Effects Information
    2. Overview of Risk Assessment Information
    B. Conclusions on the Secondary Standard
    1. Basis for the Proposed Decision
    2. CASAC Advice in This Review
    3. Comments on the Proposed Decision
    4. Administrator's Conclusions
    C. Decision on the Secondary Standard
IV. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review and 
Executive Order 13563: Improving Regulation and Regulatory Review
    B. Paperwork Reduction Act (PRA)
    C. Regulatory Flexibility Act (RFA)
    D. Unfunded Mandates Reform Act (UMRA)
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With 
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From 
Environmental Health and Safety Risks
    H. Executive Order 13211: Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution, or Use
    I. National Technology Transfer and Advancement Act
    J. Executive Order 12898: Federal Actions To Address 
Environmental Justice in Minority Populations and Low-Income 
Populations
    K. Determination Under Section 307(d)
    L. Congressional Review Act
References

Executive Summary

    This document describes the completion of our current review of the 
NAAQS for Pb. This review of the standards and the air quality criteria 
(the scientific information upon which the standards are based) is 
required by the Clean Air Act on a periodic basis. In conducting this 
review, the EPA has carefully evaluated the currently available 
scientific literature on the health and welfare effects of Pb, focusing 
particularly on the information newly available since the conclusion of 
the last review in 2008. Between 2008 and 2014, the EPA prepared draft 
and final versions of the Integrated Science Assessment and the Policy 
Assessment, multiple drafts of which were subject to public review and 
comment and were reviewed by the Clean Air Scientific Advisory 
Committee, an independent scientific advisory committee established 
pursuant to the Clean Air Act and charged with providing advice to the 
Administrator. The EPA issued a proposed decision on the standards on 
January 5, 2015 (80 FR 278), and provided a 3-month period for 
submission of comments from the public. After consideration of public 
comments on the proposed decision and advice from the Clean Air 
Scientific Advisory Committee, the EPA has developed this document, 
which is the final step in the review process.
    The prior review of the NAAQS for Pb was completed in 2008. As a 
result of that review, we significantly revised

[[Page 71907]]

both the primary and secondary standards, including a lowering of the 
standard levels by an order of magnitude. The 2008 change to the 
primary standard was focused on providing the requisite protection for 
children and other at-risk populations against an array of adverse 
health effects, most notably including neurological effects in 
children, including neurocognitive effects (e.g., IQ loss) and 
neurobehavioral effects. Although Pb has long been recognized to exert 
an array of adverse health effects, over the three decades from the 
time the standard was initially set in 1978 through its revision with 
the NAAQS review completed in 2008, the evidence base expanded 
considerably in a number of areas, including with regard to effects on 
neurocognitive function in young children at increasingly lower blood 
Pb levels. These effects formed the principal basis for the 2008 
revisions to the primary standard.
    The health effects evidence newly available in this review of the 
2008 standard, as critically assessed in the ISA in conjunction with 
the full body of evidence, reaffirms conclusions on the broad array of 
effects recognized for Pb in the last review. Further, the currently 
available evidence is generally consistent with the evidence available 
in the last review, particularly with regard to key aspects of the 
evidence on which the current standard (set in 2008) is based. These 
key aspects include those regarding the relationships between air Pb 
concentrations and the associated Pb in the blood of young children as 
well as between total blood Pb levels and effects on children's IQ.
    Based on consideration of the currently available health effects 
evidence in the context of this framework, and with support from the 
exposure/risk information, recognizing the uncertainties attendant in 
both, as well as the increasing uncertainty of risk estimates for lower 
air Pb concentrations, the Administrator concludes that the current 
primary standard provides the requisite protection of public health 
with an adequate margin of safety, including protection of at-risk 
populations. With regard to the secondary standard, the EPA has 
considered the currently available welfare effects evidence and 
screening-level risk information, including the general consistency of 
the current evidence with that available in the last review and the 
substantial limitations in the current evidence that complicate 
conclusions regarding the potential for Pb emissions under the current, 
much lower standard to contribute to welfare effects. Based on these 
considerations, the Administrator concludes that the current secondary 
standard is requisite to protect public welfare from known or 
anticipated adverse effects. Thus, based on the EPA's review of the air 
quality criteria and the NAAQS for Pb, the EPA is retaining the current 
standards, without revision.

I. Background

A. Legislative Requirements

    Two sections of the Clean Air Act (CAA or the Act) govern the 
establishment and revision of the NAAQS. Section 108 (42 U.S.C. 7408) 
directs the Administrator to identify and list certain air pollutants 
and then to issue air quality criteria for those pollutants. The 
Administrator is to list those air pollutants that in her ``judgment, 
cause or contribute to air pollution which may reasonably be 
anticipated to endanger public health or welfare;'' ``the presence of 
which in the ambient air results from numerous or diverse mobile or 
stationary sources;'' and ``for which . . . [the Administrator] plans 
to issue air quality criteria . . .'' Air quality criteria are intended 
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 the ambient air . . .'' 42 U.S.C. 7408(b). Section 109 (42 
U.S.C. 7409) directs the Administrator to propose and promulgate 
``primary'' and ``secondary'' NAAQS for pollutants for which air 
quality criteria are issued. Section 109(b)(1) defines a primary 
standard as one ``the attainment and maintenance of which in the 
judgment of the Administrator, based on such 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 such 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.''
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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.'' 
See S. Rep. No. 91-1196, 91st Cong., 2d Sess. 10 (1970).
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    The requirement that primary standards provide 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. See 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); American Farm Bureau Federation v. 
EPA, 559 F. 3d 512, 533 (D.C. Cir. 2009); Association of Battery 
Recyclers v. EPA, 604 F. 3d 613, 617-18 (D.C. Cir. 2010). 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 provide 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 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.
    In addressing the requirement for an adequate margin of safety, the 
EPA considers such factors as the nature and severity of the health 
effects involved, the size of sensitive population(s) at risk,\2\ and 
the kind and degree of the uncertainties that must be addressed. The 
selection of any particular approach to providing an adequate margin of 
safety is a policy choice left specifically to the Administrator's 
judgment. See Lead Industries Association v. EPA, 647 F.2d at 1161-62.
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    \2\ As used here and similarly throughout this document, the 
term population (or group) refers to persons having a quality or 
characteristic in common, such as a specific pre-existing illness or 
a specific age or life stage. As discussed more fully in section 
II.A.2.d below, the identification of sensitive groups (called at-
risk groups or at-risk populations) involves consideration of 
susceptibility and vulnerability.
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    In setting primary and secondary standards that are ``requisite'' 
to protect public health and welfare, respectively, as provided in 
section 109(b), the EPA's task is to establish standards that are 
neither more nor less stringent than necessary for these purposes. In 
so doing, the EPA may not consider the

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costs of implementing the standards. See generally, Whitman v. American 
Trucking Associations, 531 U.S. 457, 465-472, 475-76 (2001). Likewise, 
``[a]ttainability and technological feasibility are not relevant 
considerations in the promulgation of national ambient air quality 
standards.'' American Petroleum Institute v. Costle, 665 F. 2d at 1185.
    Section 109(d)(1) requires that ``not 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 . . . and shall make such 
revisions in such criteria and standards and promulgate such new 
standards as may be appropriate. . . .'' Section 109(d)(2) requires 
that an independent scientific review committee ``shall complete a 
review of the criteria . . . and the national primary and secondary 
ambient air quality standards . . . and shall recommend to the 
Administrator any new . . . standards and revisions of existing 
criteria and standards as may be appropriate . . .'' Since the early 
1980s, this independent review function has been performed by the Clean 
Air Scientific Advisory Committee (CASAC).\3\
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    \3\ Lists of CASAC members and of members of the CASAC Lead 
Review Panel are available at: http://yosemite.epa.gov/sab/sabproduct.nsf/WebCASAC/CommitteesandMembership?OpenDocument.
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B. Related Lead Control Programs

    States are primarily responsible for ensuring attainment and 
maintenance of the NAAQS. Under section 110 of the Act (42 U.S.C. 7410) 
and related provisions, states are to submit, for EPA approval, state 
implementation plans 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 the EPA, also 
administer the Prevention of Significant Deterioration program (42 
U.S.C. 7470-7479) for these pollutants.
    The NAAQS is only one component of the EPA's programs to address Pb 
in the environment. Federal programs additionally provide for 
nationwide reductions in air 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); emissions standards for solid waste 
incineration units and the national emission standards for hazardous 
air pollutants (NESHAP) under sections 129 (42 U.S.C. 7429) and 112 (42 
U.S.C. 7412) of the Act, respectively.
    The EPA has taken a number of actions associated with these air 
pollution control programs since the last review of the Pb NAAQS 
(completed in 2008), including completion of several regulations that 
will result in reduced Pb emissions from stationary sources regulated 
under the CAA sections 112 and 129. For example, in January 2012, the 
EPA updated the NESHAP for the secondary lead smelting source category 
(77 FR 555, January 5, 2012). These amendments to the original maximum 
achievable control technology standards apply to facilities nationwide 
that use furnaces to recover Pb from Pb-bearing scrap, mainly from 
automobile batteries (13 existing facilities). This action was 
estimated to result in a Pb emissions reduction of 13.6 tons per year 
(tpy) across the category (a 68 percent reduction). Somewhat lesser Pb 
emissions reductions are also expected from regulations completed in 
2013 for commercial and industrial solid waste incineration units (78 
FR 9112, February 7, 2013), as well as several other regulations since 
2007 (72 FR 73179, December 26, 2007; 72 FR 74088, December 28, 2007; 
73 FR 225, November 20, 2008; 78 FR 10006, February 12, 2013; 76 FR 
15372, March 21, 2011; 78 FR 7138, January 31, 2013; 74 FR 51368, 
October 6, 2009; Policy Assessment, Appendix 2A).
    The presentation below briefly summarizes additional ongoing 
activities that, although not directly pertinent to the review of the 
NAAQS, are associated with controlling environmental Pb levels and 
human Pb exposures more broadly. Among those identified are the EPA 
programs intended to encourage exposure reduction programs in other 
countries.
    Reducing Pb exposures has long been recognized as a federal 
priority as environmental and public health agencies continue to 
grapple with soil and dust Pb levels from the historical use of Pb in 
paint and gasoline and from other sources (Alliance to End Childhood 
Lead Poisoning, 1991; 62 FR 19885, April 23, 1997; 66 FR 52013, October 
11, 2001; 68 FR 19931, April 23, 2003). A broad range of federal 
programs beyond those that focus on air pollution control provide for 
nationwide reductions in environmental releases and human exposures.
    Pursuant to section 1412 of the Safe Drinking Water Act (SDWA), EPA 
sets public health goals and enforceable standards for drinking water 
quality. The Lead and Copper Rule (LCR) is a treatment technique rule. 
The LCR requires public water systems to treat the water to reduce 
corrosion of Pb and copper from premise plumbing and drinking water 
distribution system components. When corrosion control treatment isn't 
enough, water systems must educate the public about Pb in drinking 
water and replace lead service lines, which are the pipes that connect 
buildings to the drinking water mains (40 CFR 141.80-141.91). The 
importance of corrosion control treatment was illustrated by the recent 
events in Flint, MI, when Pb levels in drinking water increased after 
the water system did not maintain corrosion control treatment when the 
system changed its water supply. Section 1417 of the SDWA additionally 
prohibits the use of any pipe, any pipe or plumbing fitting or fixture, 
any solder, or any flux in the installation or repair of any public 
water system or any plumbing in a residential or non-residential 
facility providing water for human consumption, that is not lead free 
as defined by the Act.\4\
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    \4\ Effective in January 2014, the amount of Pb permitted in 
pipes, fittings, and fixtures was lowered (see ``Section 1417 of the 
Safe Drinking Water Act: Prohibition on Use of Lead Pipes, Solder, 
and Flux'' at http://www.epa.gov/dwstandardsregulations/section-1417-safe-drinking-water-act-prohibition-use-lead-pipes-solder-and).
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    Additionally, federal Pb 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 (68 FR 36487, June 18, 2003).
    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 (codified as Title IV of the Toxic Substances 
Control Act [TSCA]), the EPA has established regulations and associated 
programs in six categories: (1) Training, certification and work 
practice requirements for persons engaged in Pb-based paint activities 
(abatement, inspection and risk assessment); accreditation of training 
providers; and authorization of state and tribal Pb-based paint 
programs; (2) training, certification, and work practice requirements 
for persons engaged in home renovation, repair and painting (RRP) 
activities; accreditation of RRP training providers; and authorization 
of

[[Page 71909]]

state and tribal RRP programs; (3) ensuring that, for most housing 
constructed before 1978, information about Pb-based paint and Pb-based 
paint hazards flows from sellers to purchasers, from landlords to 
tenants, and from renovators to owners and occupants; (4) establishing 
standards for identifying dangerous levels of Pb in paint, dust and 
soil; (5) providing grant funding to establish and maintain state and 
tribal Pb-based paint programs; and (6) providing information on Pb 
hazards to the public, including steps that people can take to protect 
themselves and their families from Pb-based paint hazards. The most 
recent rule issued under Title IV of TSCA is for the Lead Renovation, 
Repair and Painting Program (73 FR 21692, April 22, 2008), which became 
fully effective in April 2010 and which applies to compensated 
renovators and maintenance professionals who perform RRP activities in 
housing and child-care facilities built prior to 1978. To foster 
adoption of the rule's measures, the EPA has been conducting an 
extensive education and outreach campaign to promote awareness of these 
new requirements among both the regulated entities and the consumers 
who hire them (http://www2.epa.gov/lead/renovation-repair-and-painting-program). In addition, the EPA is investigating whether Pb hazards are 
also created by RRP activities in public and commercial buildings, in 
which case the EPA plans to issue RRP requirements, where appropriate, 
for this class of buildings (79 FR 31072, May 30, 2014).
    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, the 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 (e.g., 66 FR 58258, 
November 20, 2001). Federal regulations concerning batteries in 
municipal solid waste facilitate the collection and recycling or proper 
disposal of batteries containing Pb.\5\ 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/).
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    \5\ See, e.g., ``Implementation of the Mercury-Containing and 
Rechargeable Battery Management Act'' available from https://www.epa.gov/hw and facts and figures on recycling and disposal in 
the U.S. at https://www.epa.gov/smm/advancing-sustainable-materials-management-facts-and-figures.
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    A variety of federal nonregulatory programs also provide for 
reduced environmental release of Pb-containing materials by encouraging 
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 ``National Waste Minimization 
Program'' (https://archive.epa.gov/epawaste/hazard/wastemin/web/html/tools.html), ``Sustainable Management of Electronics'' (https://www.epa.gov/smm-electronics), and the ``Sustainable Materials 
Management (SMM) Electronics Challenge'' (https://www.epa.gov/smm-electronics/sustainable-materials-management-smm-electronics-challenge).
    The EPA's research program identifies, encourages and conducts 
research needed to develop methods and tools to characterize and help 
reduce risks related to Pb exposure. An example of one such effort is 
the EPA's Integrated Exposure Uptake Biokinetic Model for Lead in 
Children (IEUBK model), which is widely used and accepted as a tool 
that informs the evaluation of site-specific data. More recently, in 
recognition of the need for a single model that predicts Pb 
concentrations in tissues for children and adults, the EPA has been 
developing the All Ages Lead Model (AALM) to provide researchers and 
risk assessors with a pharmacokinetic model capable of estimating 
blood, tissue, and bone concentrations of Pb based on estimates of 
exposure over the lifetime of the individual (USEPA, 2006a, sections 
4.4.5 and 4.4.8; USEPA, 2013a, section 3.6). The EPA's research 
activities on substances including Pb, such as those identified here, 
focus on improving our characterization of health and environmental 
effects, exposure, and control or management of environmental releases 
(see http://www.epa.gov/research/).
    Other federal agencies also participate in programs intended to 
reduce Pb exposures. For example, programs of the Centers for Disease 
Control and Prevention (CDC) provide for the tracking of children's 
blood Pb levels in the U.S. and provide guidance on levels at which 
medical and environmental case management activities should be 
implemented (CDC, 2012; ACCLPP, 2012). As a result of coordinated, 
intensive efforts at the national, state and local levels, including 
those programs described above, blood Pb levels in all segments of the 
population have continued to decline from levels observed in the past. 
For example, blood Pb levels for the general population of children 1 
to 5 years of age have dropped to a geometric mean level of 1.17 [mu]g/
dL in the 2009-2010 National Health and Nutrition Examination Survey 
(NHANES) \6\ as compared to the geometric mean in 1999-2000 of 2.23 
[micro]g/dL and in 1988-1991 of 3.6 [mu]g/dL (USEPA, 2013a, section 
3.4.1; USEPA, 2006a, AX4-2). Similarly, statistics for the distribution 
of blood Pb levels in non-Hispanic black and lower socioeconomic groups 
of young children, which are generally higher than those for that 
population as a whole, have also declined, as have the differences in 
these statistics between non-Hispanic black and other groups, as well 
as between lower and higher socioeconomic groups (USEPA, 2013a, 
sections 3.4.1, 5.2.3 and 5.2.4; Jones et al., 2009).
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    \6\ Since the completion of the ISA, more recent NHANES data 
indicate the geometric mean blood Pb concentration for children in 
the U.S. population, aged one to five, to have declined to 0.97 
[mu]g/dL in the 2011-2012 survey (CDC, 2015).
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    The EPA also participates in a broad range of international 
programs focused on reducing environmental releases and human exposures 
in other countries. For example, the Partnership for Clean Fuels and 
Vehicles program engages governments and stakeholders in developing 
countries to eliminate Pb in gasoline globally.\7\ From 2007 to 2011, 
the number of countries known to still be using leaded gasoline was 
reduced from just over 20 to six (USEPA, 2011c). As of January, leaded 
gasoline for on-road use is known to be available (along with unleaded 
gasoline) in three countries.\8\
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    \7\ International programs in which the U.S. participates, 
including those identified here, are described at: https://www.epa.gov/international-cooperation, http://www.unep.org/transport/pcfv/, http://www.unep.org/hazardoussubstances/Home/tabid/197/hazardoussubstances/LeadCadmium/PrioritiesforAction/GAELP/tabid/6176/Default.aspx.
    \8\ UNEP. ``Leaded Petrol Phase-out: Global Status as at January 
2016'' map downloaded from http://www.unep.org/transport/new/pcfv/.
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    The EPA is a contributor to the Global Alliance to Eliminate Lead 
Paint, a voluntary public-private partnership jointly led by the World 
Health Organization and the United Nations Environment Programme (UNEP) 
to prevent children's exposure to Pb from paints containing Pb and to 
minimize occupational exposures to Pb paint. The objective of this 
alliance is to promote a phase-out of the manufacture and sale of 
paints containing Pb and eventually to eliminate the risks that such 
paints

[[Page 71910]]

pose. The UNEP is also engaged on the problem of managing wastes 
containing Pb, including Pb-containing batteries. The Governing Council 
of the UNEP, of which the U.S. is a member, has adopted decisions 
focused on promoting the environmentally sound management of products, 
wastes and contaminated sites containing Pb and reducing risks to human 
health and the environment from Pb and cadmium throughout the life 
cycles of those substances (UNEP Governing Council, 2011, 2013). The 
EPA is also engaged in the issue of environmental impacts of spent Pb-
acid batteries internationally through the Commission for Environmental 
Cooperation (CEC), where the EPA Administrator along with the cabinet-
level or equivalent representatives of Mexico and Canada comprise the 
CEC's senior governing body (CEC Council).\9\
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    \9\ The CEC was established to support cooperation among the 
North American Free Trade Agreement partners to address 
environmental issues of continental concern, including the 
environmental challenges and opportunities presented by continent-
wide free trade.
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C. Review of the Air Quality Criteria and Standards for Lead

    Unlike pollutants such as particulate matter and carbon monoxide, 
air quality criteria had not been issued for Pb as of the enactment of 
the CAA of 1970, which first set forth the requirement to set NAAQS 
based on air quality criteria. In the years just after enactment of the 
CAA, the EPA did not list Pb under section 108 of the Act, having 
determined to control Pb air pollution through regulations to phase out 
the use of Pb additives in gasoline (see 41 FR 14921, April 8, 1976). 
However, the decision not to list Pb under section 108 was challenged 
by environmental and public health groups, and the U.S. District Court 
for the Southern District of New York concluded that the EPA was 
required to list Pb under section 108. Natural Resources Defense 
Council v. EPA, 411 F. Supp. 864 21 (S.D. N.Y. 1976), affirmed, 545 
F.2d 320 (2d Cir. 1978). Accordingly, on April 8, 1976, the EPA 
published a notice in the Federal Register that Pb had been listed 
under section 108 as a criteria pollutant (41 FR 14921, April 8, 1976), 
and on October 5, 1978, the EPA promulgated primary and secondary NAAQS 
for Pb under section 109 of the Act (43 FR 46246, October 5, 1978). 
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 particles (Pb-TSP), not to be exceeded by the maximum 
arithmetic mean concentration averaged over a calendar quarter. These 
standards were based on the 1977 Air Quality Criteria for Lead (USEPA, 
1977).
    The first 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; henceforth referred 
to as the 1986 CD), 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 recommendations 
for consideration by the Administrator (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). The EPA continues 
this broad, multi-program, multimedia approach to reducing Pb exposures 
today, as described in section I.B above.
    The last review of the air quality criteria and standards for Pb 
was initiated in November 2004 (69 FR 64926, November 9, 2004); the 
agency's plans for preparation of the Air Quality Criteria Document 
(AQCD) and conduct of the NAAQS review were presented in documents 
completed in 2005 and early 2006 (USEPA, 2005a; USEPA 2006b).\10\ The 
schedule for completion of the review was governed by a judicial order 
in Missouri Coalition for the Environment v. EPA (No. 4:04CV00660 ERW, 
September 14, 2005; and amended on April 29, 2008 and July 1, 2008).
---------------------------------------------------------------------------

    \10\ In the current review, these two documents have been 
combined in the Integrated Review Plan for the National Ambient Air 
Quality Standards for Lead (USEPA, 2011a).
---------------------------------------------------------------------------

    The scientific assessment for the review is described in the 2006 
Air Quality Criteria for Lead (USEPA, 2006a; henceforth referred to as 
the 2006 CD), multiple drafts of which received review by CASAC and the 
public. The EPA also conducted human exposure and health risk 
assessments and a pilot ecological risk assessment for the review after 
consultation with the CASAC and receiving public comment on a draft 
analysis plan (USEPA, 2006c). Drafts of these quantitative assessments 
were reviewed by CASAC and the public. The pilot ecological risk 
assessment was released in December 2006 (ICF International, 2006), and 
the final health risk assessment report was released in November 2007 
(USEPA, 2007a). The policy assessment, based on both of these 
assessments, air quality analyses and key evidence from the 2006 CD, 
was presented in the Staff Paper (USEPA, 2007b), a draft of which also 
received CASAC and public review. The final Staff Paper presented OAQPS 
staff's evaluation of the public health and welfare policy implications 
of the key studies and scientific information contained in the 2006 CD 
and presented and interpreted results from the quantitative risk/
exposure analyses conducted for this review. Based on this evaluation, 
the Staff Paper presented OAQPS staff recommendations that the 
Administrator give consideration to substantially revising the primary 
and secondary standards to a range of levels at or below 0.2 [micro]g/
m\3\.
    Immediately subsequent to completion of the Staff Paper, the EPA 
issued an advance notice of proposed rulemaking (ANPR) that was signed 
by the Administrator on December 5, 2007 (72 FR 71488, December 17, 
2007).\11\ The CASAC provided advice and recommendations to the 
Administrator with regard to the Pb NAAQS based on its review of the 
ANPR and the previously released final Staff Paper and risk assessment 
reports. In 2008, the proposed decision on revisions to the Pb NAAQS 
was signed on May 1, and published in the Federal Register on May 20 
(73 FR 29184, May 20, 2008). Members of the public provided comments, 
and the CASAC Pb Panel also provided advice and recommendations to the 
Administrator based on its review of the proposal. The decision on 
revisions to the Pb NAAQS was signed on October 15, 2008, and published 
in the Federal Register on November 12, 2008 (73 FR 66964, November 12, 
2008).
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    \11\ The ANPR, one of the features of the revised NAAQS review 
process that EPA instituted in 2006, was replaced by reinstatement 
of the Policy Assessment prepared by OAQPS staff (previously termed 
the OAQPS Staff Paper) in 2009 (Jackson, 2009).

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[[Page 71911]]

    The November 2008 preamble to the final rule described the EPA's 
decision to revise the primary and secondary standards for Pb, as 
discussed more fully in sections II.A.1 and III.A below. In 
consideration of the much-expanded health effects evidence on 
neurocognitive effects of Pb in children, the EPA substantially revised 
the primary standard level from 1.5 [micro]g/m\3\ to a level of 0.15 
[micro]g/m\3\. The averaging time was revised to a rolling 3-month 
period with a maximum (not-to-be-exceeded) form, evaluated over a 3-
year period. The indicator of Pb-TSP was retained, reflecting the 
evidence that Pb particles of all sizes pose health risks. The 
secondary standard was revised to be identical in all respects to the 
revised primary standard (40 CFR 50.16). Revisions to the NAAQS were 
accompanied by revisions to the data handling procedures, the treatment 
of exceptional events and the ambient air monitoring and reporting 
requirements, as well as emissions inventory reporting requirements. 
One aspect of the revised data handling requirements is the allowance 
for the use of monitoring for particulate matter with mean diameter 
below 10 microns (Pb-PM10) for Pb NAAQS attainment purposes 
in certain limited circumstances at non-source-oriented sites. 
Subsequent to the 2008 rulemaking, additional revisions were made to 
the monitoring network requirements (75 FR 81126, December 27, 2010). 
Guidance on the approach for implementation of the new standards was 
described in the preambles for the proposed and final rules (73 FR 
29184, May 20, 2008; 73 FR 66964, November 12, 2008).
    On February 26, 2010, the EPA formally initiated its current review 
of the air quality criteria and standards for Pb, requesting the 
submission of recent scientific information on specified topics (75 FR 
8934, February 26, 2010). Soon after this, the EPA held a workshop to 
discuss the policy-relevant science, which informed identification of 
key policy issues and questions to frame the review (75 FR 20843, April 
21, 2010). Drawing from the workshop discussions, the EPA developed the 
draft Integrated Review Plan (draft IRP, USEPA, 2011d). The draft IRP 
was made available in late March 2011 for consultation with the CASAC 
Pb Review Panel and for public comment (76 FR 20347, April 12, 2011). 
This document was discussed by the Panel via a publicly accessible 
teleconference consultation on May 5, 2011 (76 FR 21346, April 15, 
2011; Frey, 2011a). The final Integrated Review Plan for the National 
Ambient Air Quality Standards for Lead (IRP), developed in 
consideration of the CASAC consultation and public comment, was 
released in November 2011 (USEPA, 2011a; 76 FR 76972, December 9, 
2011).
    In developing the Integrated Science Assessment (ISA) \12\ for this 
review, the EPA held a workshop in December 2010 to discuss with 
invited scientific experts preliminary draft materials and released the 
first external review draft of the document for CASAC review and public 
comment in May 2011 (USEPA, 2011e; 76 FR 26284, May 6, 2011; 76 FR 
36120, June 21, 2011). The CASAC Pb Review Panel met at a public 
meeting on July 20, 2011, to review the draft ISA (76 FR 36120, June 
21, 2011). The CASAC provided comments in a December 9, 2011, letter to 
the EPA Administrator (Frey and Samet, 2011). The second external 
review draft ISA was released for CASAC review and public comment in 
February 2012 (USEPA, 2012a; 77 FR 5247, February 2, 2012) and was the 
subject of a public meeting on April 10-11, 2012 (77 FR 14783, March 
13, 2012). The CASAC provided comments in a July 20, 2012, letter 
(Samet and Frey, 2012). The third external review draft was released 
for CASAC review and public comment in November 2012 (USEPA, 2012b; 77 
FR 70776, November 27, 2012) and was the subject of a public meeting on 
February 5-6, 2013 (78 FR 938, January 7, 2013). The CASAC provided 
comments in a June 4, 2013, letter (Frey, 2013a). The final ISA was 
released in late June 2013 (USEPA, 2013a, henceforth referred to as the 
ISA; 78 FR 38318, June 26, 2013).
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    \12\ As of this review, the document developed in NAAQS reviews 
in which the air quality criteria are assessed, previously the AQCD, 
is the ISA, and the document describing the OAQPS staff evaluation, 
previously the Staff Paper, is the PA. These documents are described 
in the IRP.
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    In June 2011, the EPA developed and released the Risk and Exposure 
Assessment Planning Document (REA Planning Document) for consultation 
with the CASAC and public comment (USEPA, 2011b; 76 FR 58509). This 
document presented a critical evaluation of the information related to 
Pb human and ecological exposure and risk (e.g., data, modeling 
approaches) newly available in this review, with a focus on 
consideration of the extent to which new or substantially revised REAs 
for health and ecological risk might be warranted by the newly 
available evidence. Evaluation of the newly available information with 
regard to designing and implementing health and ecological REAs for 
this review led us to conclude that the currently available information 
did not provide a basis for developing new quantitative risk and 
exposure assessments that would have substantially improved utility for 
informing the agency's consideration of health and welfare effects and 
evaluation of the adequacy of the current primary and secondary 
standards, respectively (REA Planning Document, sections 2.3 and 3.3, 
respectively). The CASAC Pb Review Panel provided consultative advice 
on that document and its conclusions at a public meeting on July 21, 
2011 (76 FR 36120, June 21, 2011; Frey, 2011b). Based on its 
consideration of the REA Planning Document analysis, the CASAC Pb 
Review Panel generally concurred with the conclusion that a new REA was 
not warranted in this review (Frey, 2011b; Frey, 2013b). In 
consideration of the conclusions reached in the REA Planning Document 
and CASAC's consultative advice, the EPA has not developed REAs for 
health and ecological risk for this review. We have considered the 
findings from the last review for human exposure and health risk 
(USEPA, 2007a, henceforth referred to as the 2007 REA) and ecological 
risk (ICF International, 2006; henceforth referred to as the 2006 REA) 
with regard to any appropriate further interpretation in light of the 
evidence newly available in this review, as described in the Policy 
Assessment (PA) and proposal.
    A draft of the PA was released for public comment and review by 
CASAC in January 2013 (USEPA, 2013b; 77 FR 70776, November 27, 2012) 
and was the subject of a public meeting on February 5-6, 2013 (78 FR 
938, January 7, 2013). Comments provided by the CASAC in a June 4, 
2013, letter (Frey, 2013b), as well as public comments received on the 
draft PA were considered in preparing the final PA, which was released 
in May 2014 (USEPA, 2014; 79 FR 26751, May 9, 2014). The proposed 
decision (henceforth ``proposal'') on this review of the NAAQS for Pb 
was signed on December 19, 2014, and published in the Federal Register 
on January 5, 2015. Written comments were received from twelve 
commenters during the public comment period on the proposal. 
Significant issues raised in the public comments and the EPA's 
responses to those comments are discussed in the preamble of this final 
action.
    As in prior NAAQS reviews, the EPA is basing its decision in this 
review on studies and related information included in the ISA and 
PA,\13\ which

[[Page 71912]]

have undergone CASAC and public review. The studies assessed in the ISA 
\14\ and PA, and the integration of the scientific evidence presented 
in them, have undergone extensive critical review by the EPA, the 
CASAC, and the public. The rigor of that review makes these studies, 
and their integrative assessment, the most reliable source of 
scientific information on which to base decisions on the NAAQS, 
decisions that all parties recognize as of great import. Decisions on 
the NAAQS can have profound impacts on public health and welfare, and 
NAAQS decisions should be based on studies that have been rigorously 
assessed in an integrative manner not only by the EPA but also by the 
statutorily mandated independent scientific advisory committee, as well 
as the public review that accompanies this process. Some commenters 
have referred to and discussed individual scientific studies on the 
health effects of Pb that were not included in the ISA (`` `new' 
studies''). In considering and responding to comments for which such 
``new'' studies were cited in support, the EPA has provisionally 
considered the cited studies in the context of the findings of the ISA. 
The EPA's provisional consideration of these studies did not and could 
not provide the kind of in-depth critical review described above.
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    \13\ As a new REA was not warranted in this review, the exposure 
and risk information from the last review (2007 REA; 2006 REA) is 
summarized in the PA in the context of the currently available 
health and welfare effects evidence.
    \14\ Studies were identified for the Pb ISA based on the 
review's opening ``call for information'' (75 FR 8934), as well as 
literature searches conducted routinely ``to identify studies 
published since the last review, focusing on studies published from 
2006 (close of the previous scientific assessment) through September 
2011'' (ISA, p. 1-2). In a subsequent step, ``[s]tudies that have 
undergone scientific peer review and have been published or accepted 
for publication and reports that have undergone review are 
considered for inclusion in the ISA'' and ``[a]nalyses conducted by 
EPA using publicly available data are also considered for inclusion 
in the ISA'' (ISA, p. xlv). References ``that were considered for 
inclusion or actually cited in this ISA can be found at http://hero.epa.gov/lead'' (ISA, p. 1-2).
---------------------------------------------------------------------------

    The decision to rely on studies and related information included in 
the ISA, REAs and PA, which have undergone CASAC and public review, is 
consistent with the EPA's practice in prior NAAQS reviews and its 
interpretation of the requirements of the CAA. Since the 1970 
amendments, the EPA has taken the view that NAAQS decisions are to be 
based on scientific studies and related information that have been 
assessed as a part of the pertinent air quality criteria, and the EPA 
has consistently followed this approach. This longstanding 
interpretation was strengthened by new legislative requirements enacted 
in 1977, which added section 109(d)(2) of the Act concerning CASAC 
review of air quality criteria. See 71 FR 61144, 61148 (October 17, 
2006, final decision on review of NAAQS for particulate matter) for a 
detailed discussion of this issue and the EPA's past practice.
    As discussed in the EPA's 1993 decision not to revise the NAAQS for 
ozone, ``new'' studies may sometimes be of such significance that it is 
appropriate to delay a decision on revision of a NAAQS and to 
supplement the pertinent air quality criteria so the studies can be 
taken into account (58 FR at 13013-13014, March 9, 1993). In the 
present case, the EPA's provisional consideration of ``new'' studies 
concludes that, taken in context, the ``new'' information and findings 
do not materially change any of the broad scientific conclusions 
regarding the health and welfare effects and exposure pathways of Pb in 
ambient air made in the air quality criteria. For this reason, 
reopening the air quality criteria review would not be warranted.
    Accordingly, the EPA is basing the final decisions in this review 
on the studies and related information included in the Pb air quality 
criteria that have undergone CASAC and public review. The EPA will 
consider the ``new'' studies for purposes of decision making in the 
next periodic review of the NAAQS for Pb, which the EPA expects to 
begin soon after the conclusion of this review and which will provide 
the opportunity to fully assess these studies through a more rigorous 
review process involving the EPA, CASAC, and the public.

D. Multimedia, Multipathway Aspects of Lead

    Since Pb is distributed from air to other media and is persistent, 
our review of the NAAQS for Pb considers the protection provided 
against effects associated both with exposures to Pb in ambient air and 
with exposures to Pb that makes its way into other media from ambient 
air. Additionally, in assessing the adequacy of protection afforded by 
the current NAAQS, we are mindful of the long history of greater and 
more widespread atmospheric emissions that occurred in previous years 
(both before and after establishment of the 1978 NAAQS) and that 
contributed to the Pb that is in human populations and ecosystems 
today. Likewise, we also recognize the role of other, nonair sources of 
Pb now and in the past that also contribute to the Pb that is in human 
populations and ecosystems today.
    Lead emitted to ambient air is transported through the air and is 
also distributed from air to other media. This multimedia distribution 
of Pb emitted into ambient air (air-related Pb) contributes to multiple 
air-related pathways of human and ecosystem exposure (ISA, sections 
3.1.1 and 3.7.1). Air-related pathways may also involve media other 
than air, including indoor and outdoor dust, soil, surface water and 
sediments, vegetation and biota. Air-related Pb exposure pathways for 
humans include inhalation of ambient air or ingestion of food, water or 
other materials, including dust and soil, that have been contaminated 
through a pathway involving Pb deposition from ambient air (ISA, 
section 3.1.1.1). Ambient air inhalation pathways include both 
inhalation of air outdoors and inhalation of ambient air that has 
infiltrated into indoor environments. The air-related ingestion 
pathways occur as a result of Pb passing through the ambient air, being 
distributed to other environmental media and contributing to human 
exposures via contact with and ingestion of indoor and outdoor dusts, 
outdoor soil, food and drinking water.
    Lead currently occurring in nonair media may also derive from 
sources other than ambient air (nonair Pb sources) (ISA, sections 2.3 
and 3.7.1). For example, Pb in dust inside some houses or outdoors in 
some urban areas may derive from the common past usage of leaded paint, 
while Pb in drinking water may derive from the use of leaded pipe or 
solder in drinking water distribution systems (ISA, section 3.1.3.3). 
We also recognize the history of much greater air emissions of Pb in 
the past, such as that associated with leaded gasoline usage and higher 
industrial emissions which have left a legacy of Pb in other (nonair) 
media.
    The relative importance of different pathways of human exposure to 
Pb, as well as the relative contributions from Pb resulting from recent 
and historic air emissions and from nonair sources, vary across the 
U.S. population as a result of both extrinsic factors, such as a home's 
proximity to industrial Pb sources or its history of leaded paint 
usage, and intrinsic factors, such as a person's age and nutritional 
status (ISA, sections 5.1, 5.2, 5.2.1, 5.2.5 and 5.2.6). Thus, the 
relative contributions from specific pathways are situation specific 
(ISA, p. 1-11), although a predominant Pb exposure pathway for very 
young children is the incidental ingestion of indoor dust by hand-to-
mouth activity (ISA, section 3.1.1.1). For adults, however, diet may be 
the primary Pb exposure pathway (2006 CD, section 3.4). Similarly, the 
relative importance of air-related and nonair-related Pb also varies 
with the relative magnitudes of

[[Page 71913]]

exposure by those pathways, which may vary with different 
circumstances.
    The distribution of Pb from ambient air to other environmental 
media also influences the exposure pathways for organisms in 
terrestrial and aquatic ecosystems. Exposure of terrestrial animals and 
vegetation to air-related Pb can occur by contact with ambient air or 
by contact with soil, water or food items that have been contaminated 
by Pb from ambient air (ISA, section 6.2). Transport of Pb into aquatic 
systems similarly provides for exposure of biota in those systems, and 
exposures may vary among systems as a result of differences in sources 
and levels of contamination, as well as characteristics of the systems 
themselves, such as salinity, pH and turbidity (ISA, section 2.3.2). In 
addition to Pb contributed by current atmospheric deposition, Pb may 
occur in aquatic systems as a result of nonair sources such as 
industrial discharges or mine-related drainage, of historical air Pb 
emissions (e.g., contributing to deposition to a water body or via 
runoff from soils near historical air sources) or combinations of 
different types of sources (e.g., resuspension of sediments 
contaminated by urban runoff and surface water discharges).
    The persistence of Pb contributes an important temporal aspect to 
lead's environmental pathways, and the time (or lag) associated with 
realization of the impact of air Pb concentrations on concentrations in 
other media can vary with the media (e.g., ISA, section 6.2.2). For 
example, exposure pathways most directly involving Pb in ambient air or 
surface waters can respond more quickly to changes in ambient air Pb 
concentrations, while pathways involving exposure to Pb in soil or 
sediments generally respond more slowly.\15\ An additional influence on 
the response time for nonair media is the environmental presence of Pb 
associated with past, generally higher, air concentrations. For 
example, after a reduction in air Pb concentrations, the time needed 
for sediment or surface soil concentrations to indicate a response to 
reduced air Pb concentrations might be expected to be longer in areas 
of more substantial past contamination than in areas with lesser past 
contamination. Thus, considering the Pb concentrations occurring in 
nonair environmental media as a result of air quality conditions that 
meet the current NAAQS is a complexity of this review, as it also was, 
although to a lesser degree, with regard to the prior standard in the 
last review.
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    \15\ The time it takes for exposures to be reduced in response 
to reductions in air Pb concentrations varies with the various 
inhalation and ingestion exposure pathways. For example, exposures 
resulting from human exposure pathways most directly involving Pb in 
ambient air and exchanges of ambient air with indoor air (e.g., 
inhalation) can respond most quickly, while those for pathways 
involving exposure to Pb deposited from ambient air into the 
environment (e.g., diet) may be expected to respond more slowly. The 
extent of this will be influenced by the magnitude of change, as 
well as--for deposition-related pathways--the extent of prior 
deposition and environment characteristics influencing availability 
of prior deposited Pb.
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E. Air Quality Monitoring

    Lead emitted to the air is predominantly in particulate form. Once 
emitted, particle-bound Pb can be transported long or short distances 
depending on particle size, which influences the amount of time spent 
in the aerosol phase. In general, larger particles tend to deposit more 
quickly, within shorter distances from emissions points, compared with 
smaller particles that remain in the aerosol phase and travel longer 
distances before depositing (ISA, section 1.2.1). Accordingly, airborne 
concentrations of Pb near sources are much higher (and the 
representation of larger particles generally greater) than at sites not 
directly influenced by sources (PA, Figure 2-11; ISA sections 2.3.1 and 
2.5.3).
    Ambient air monitoring data for Pb, in terms of Pb-TSP, Pb-
PM10 or Pb in particulate matter with mean aerodynamic 
diameter less than or equal to 2.5 microns (Pb-PM2.5), are 
currently collected in several national networks. Monitoring conducted 
for purposes of Pb NAAQS surveillance is regulated to ensure accurate 
and comparable data for determining compliance with the NAAQS. In order 
to be used in NAAQS attainment designations, ambient Pb concentration 
data must be obtained using either the federal reference method (FRM) 
or a federal equivalent method (FEM). The FRMs for sample collection 
and analysis are specified in 40 CFR part 50. The procedures for 
approval of FRMs and FEMs are specified in 40 CFR part 53. In 2013, 
after consultation with the CASAC's Ambient Air Monitoring and Methods 
Subcommittee, the EPA adopted a new FRM for Pb-TSP, based on 
inductively coupled plasma-mass spectrometry (78 FR 40000, July 3, 
2013). The previous FRM was retained as an FEM, and existing FEMs were 
retained as well.
    The Pb NAAQS surveillance network regulations (40 CFR part 58, 
appendix D, paragraph 4.5) require source-oriented monitoring sites, 
and also the collection of one year of Pb-TSP measurements at 15 
specific airports. The indicator for the current Pb NAAQS is Pb-TSP, 
although in some situations,\16\ Pb-PM10 concentrations may 
be used in judging nonattainment. Currently, more than 200 Pb-TSP 
monitors are in operation; these are a mixture of source- and non-
source-oriented monitors (PA, p. 2-14).
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    \16\ The Pb-PM10 measurements may be used for NAAQS 
monitoring as an alternative to Pb-TSP measurements in certain 
conditions defined in 40 CFR part 58, appendix C, section 2.10.1.2. 
These conditions include where Pb concentrations are not expected to 
equal or exceed 0.10 [mu]g/m\3\ as an arithmetic 3-month mean and 
where the source of Pb emissions is expected to emit a substantial 
majority of its Pb in the size fraction captured by PM10 
monitors.
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    Since the phase-out of Pb in on-road gasoline, Pb is widely 
recognized as a near-source air pollutant, the ambient air 
concentrations of which generally fall off quickly with distance from 
sources. Variability in ambient air Pb concentrations is highest in 
areas including a Pb source, ``with high concentrations downwind of the 
sources and low concentration at areas far from sources'' (ISA, p. 2-
92). The current requirements for source-oriented monitoring include 
placement of monitor sites near sources of air Pb emissions that are 
expected to or have been shown to contribute to ambient air Pb 
concentrations in excess of the NAAQS. At a minimum, there must be one 
source-oriented site located to measure the maximum Pb concentration in 
ambient air resulting from each non-airport Pb source that emits 0.50 
or more tons of Pb per year and from each airport that emits 1.0 or 
more tons of Pb per year.\17\ The EPA Regional Administrators may 
require additional monitoring beyond the minimum requirements where the 
likelihood of Pb air quality violations is significant or where the 
emissions density, topography, or population locations are complex and 
varied. Such locations may include those near additional industrial Pb 
sources, recently closed industrial sources and other sources of re-
entrained Pb dust, as well as airports where piston-engine aircraft 
emit Pb associated with combustion of leaded aviation fuel (40 CFR part 
58, appendix D, section 4.5(c)). A single year of monitoring was also 
required near 15 specific airports\18\ in order to gather

[[Page 71914]]

additional information on ambient air Pb concentrations near airports, 
including specifically on the likelihood of NAAQS exceedances due to 
the combustion of leaded aviation gasoline (75 FR 81126, December 27, 
2010; 40 CFR part 58, appendix D, 4.5(a)(iii)). These airport 
monitoring data along with other data gathering and analyses will 
inform the EPA's ongoing investigation under section 231(a)(2)(A) of 
the CAA of whether Pb emissions from piston-engine aircraft cause or 
contribute to air pollution which may reasonably be anticipated to 
endanger public health or welfare (see for example, EPA's Advance 
Notice of Proposed Rulemaking on Lead Emissions From Piston-Engine 
Aircraft Using Leaded Aviation Gasoline, 75 FR 22439, April 28, 2010). 
The EPA is conducting this investigation separate from the Pb NAAQS 
review. As a whole, the various data gathering efforts and analyses are 
expected to improve our understanding of Pb concentrations in ambient 
air near airports and conditions influencing these concentrations.
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    \17\ The Regional Administrator may waive this requirement for 
monitoring near Pb sources if the state or, where appropriate, local 
agency can demonstrate the Pb source will not contribute to a 
maximum 3-month average Pb concentration in ambient air in excess of 
50 percent of the NAAQS level based on historical monitoring data, 
modeling, or other means (40 CFR part 58, appendix D, section 
4.5(a)(ii)).
    \18\ These airports were selected based on three criteria: 
annual Pb inventory between 0.5 ton/year and 1.0 ton/year, ambient 
air within 150 meters of the location of maximum emissions (e.g., 
the end of the runway or run-up location), and airport configuration 
and meteorological scenario that leads to a greater frequency of 
operations from one runway. These criteria or characteristics were 
selected as they were expected, ``collectively, to identify airports 
with the highest potential to have ambient air Pb concentrations 
approaching or exceeding the Pb NAAQS'' (75 FR 81132, December 27, 
2010).
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    Monitoring agencies may also conduct non-source-oriented Pb 
monitoring at the NCore monitoring sites.\19\ In 2015, all NCore sites 
with a population of 500,000 or more (as defined by the U.S. Census 
Bureau) \20\ were measuring Pb concentrations, with a 2014 analysis 
indicating generally similar numbers of sites measuring Pb in TSP and 
Pb in PM10 (Cavender, 2014). These numbers may change in the 
future as the requirement for Pb monitoring at these sites was recently 
eliminated in consideration of current information indicating 
concentrations at these sites to be well below the Pb NAAQS and of the 
existence of other monitoring networks that provide information on Pb 
concentrations at similar types of sites (81 FR 17248, March 28, 2016). 
The data available for the NCore sites indicate maximum 3-month average 
concentrations (of Pb-PM10 or Pb-TSP) well below the level 
of the Pb NAAQS, with the large majority of these sites indicating 
maximum 3-month average concentrations at or below 0.01 [micro]g/m\3\ 
(Cavender, 2014). Other monitoring networks that provide data on Pb in 
PM10 or PM2.5 at non-source-oriented urban, and 
some rural, sites include the National Air Toxics Trends Stations for 
PM10 and the Chemical Speciation Network for 
PM2.5. Data on Pb in PM2.5 are also provided at 
the rural sites of the Interagency Monitoring of Protected Visual 
Environments network (also known as the IMPROVE network).
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    \19\ The NCore network that formally began in January 2011, is a 
subset of the state and local air monitoring stations network that 
is intended to meet multiple monitoring objectives (e.g., long-term 
trends analysis, model evaluation, health and ecosystem studies, as 
well as NAAQS compliance). The complete NCore network consists of 63 
urban and 15 rural stations, with each state containing at least one 
NCore station; 46 of the states plus Washington, DC and Puerto Rico 
have at least one urban station.
    \20\ Metropolitan area population size information is available 
at the Census Bureau Web site (http://www.census.gov/population/www/metroareas/metroarea.htm).
---------------------------------------------------------------------------

    The long-term record of Pb monitoring data documents the dramatic 
decline in atmospheric Pb concentrations that has occurred since the 
1970s in response to reduced emissions (PA, Figures 2-1 and 2-7). 
Currently, the highest concentrations occur near some metals industries 
where some individual locations have concentrations that exceed the 
NAAQS (PA, Figure 2-10). Concentrations at non-source-oriented 
monitoring sites are much lower than those at source-oriented sites and 
well below the standard (PA, Figure 2-11).

F. Summary of Proposed Decisions

    For reasons discussed in the proposal and summarized in sections 
II.B.1 and III.B.1 below, the Administrator proposed to retain the 
current primary and secondary standards for Pb, without revision.

G. Organization and Approach to Final Decisions

    This action presents the Administrator's final decisions in the 
current review of the primary and secondary Pb standards. The final 
decisions addressing standards for Pb are based on a thorough review in 
the ISA of scientific information on known and potential human health 
and welfare effects associated with exposure to Pb associated with 
levels typically found in the ambient air. These final decisions also 
take into account the following: (1) Staff assessments in the PA of the 
most policy-relevant information in the ISA as well as quantitative 
health and welfare exposure and risk information; (2) CASAC advice and 
recommendations, as reflected in its letters to the Administrator and 
its discussions of drafts of the ISA and PA at public meetings; (3) 
public comments received during the development of these documents, 
both in connection with CASAC meetings and separately; and (4) public 
comments received on the proposal.
    The primary standard is addressed in section II and the secondary 
standard is addressed in section III. Section IV addresses applicable 
statutory and executive order reviews.

II. Rationale for Decision on the Primary Standard

    This section presents the rationale for the Administrator's 
decision to retain the existing primary Pb standard. This rationale is 
based on a thorough review in the ISA of the latest scientific 
information, generally published through September 2011, on human 
health effects associated with Pb and pertaining to the presence of Pb 
in the ambient air. This decision also takes into account: (1) The PA's 
staff assessments of the most policy-relevant information in the ISA 
and staff analyses of air quality, human exposure and health risks, 
upon which staff conclusions regarding appropriate considerations in 
this review are based; (2) CASAC advice and recommendations, as 
reflected in discussions of drafts of the ISA and PA at public 
meetings, in separate written comments, and in the CASAC's letters to 
the Administrator; (3) public comments received during the development 
of these documents, either in connection with CASAC meetings or 
separately, and (4) public comments received on the proposal.
    Section II.A provides background on the general approach for review 
of the primary standard for Pb and brief summaries of key aspects of 
the currently available health effects and exposure/risk information. 
Section II.B presents the Administrator's conclusions on adequacy of 
the current standard, drawing on consideration of this information, 
advice from the CASAC, and comments from the public. Section II.C 
summarizes the Administrator's decision on the primary standard.

A. Introduction

    As in prior reviews, the general approach to reviewing the current 
primary standard is based, most fundamentally, on using the EPA's 
assessment of the current scientific evidence and associated 
quantitative analyses to inform the Administrator's judgment regarding 
a primary standard for Pb that protects public health with an adequate 
margin of safety. In drawing conclusions with regard to the primary 
standard, the final decision on the adequacy of the current standard is 
largely a public health policy judgment to be made by the 
Administrator. The

[[Page 71915]]

Administrator's final decision must draw upon scientific information 
and analyses about health effects, population exposure and risks, as 
well as judgments about how to consider the range and magnitude of 
uncertainties that are inherent in the scientific evidence and 
analyses. The approach to informing these judgments, discussed more 
fully below, is based on the recognition that the available health 
effects evidence generally reflects a continuum, consisting of levels 
at which scientists generally agree that health effects are likely to 
occur, through lower levels at which the likelihood and magnitude of 
the response become increasingly uncertain. This approach is consistent 
with the requirements of the NAAQS provisions of the Act and with how 
the EPA and the courts have historically interpreted the Act. These 
provisions require the Administrator to establish primary standards 
that, in the judgment of the Administrator, 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 four basic elements of the NAAQS 
(indicator, averaging time, level, and form) are considered 
collectively in evaluating the health protection afforded by the 
current standard.
    To evaluate whether it is appropriate to consider retaining the 
current primary Pb standard, or whether consideration of revision is 
appropriate, the EPA has adopted an approach in this review that builds 
upon the general approach used in the last review and reflects the 
broader body of evidence and information now available. As summarized 
in section II.A.1 below, the Administrator's decisions in the prior 
review were based on an integration of information on health effects 
associated with exposure to Pb with that on relationships between 
ambient air Pb and blood Pb; expert judgments on the adversity and 
public health significance of key health effects; and policy judgments 
as to when the standard is requisite to protect public health with an 
adequate margin of safety. These considerations were informed by air 
quality and related analyses, quantitative exposure and risk 
assessments, and qualitative assessment of impacts that could not be 
quantified.
    Similarly in this review, as described in the PA, we draw on the 
current evidence and quantitative assessments of exposure pertaining to 
the public health risk of Pb in ambient air. In considering the 
scientific and technical information here as in the PA, we consider 
both the information available at the time of the last review and 
information newly available since the last review, including most 
particularly that which has been critically analyzed and characterized 
in the current ISA. We additionally consider the quantitative exposure/
risk assessments from the last review that estimated Pb-related IQ 
decrements associated with different air quality conditions in 
simulated at-risk populations in multiple case studies (PA, section 
3.4; 2007 REA). The evidence-based discussions presented below draw 
upon evidence from epidemiological studies and experimental animal 
studies evaluating health effects related to exposures to Pb, as 
discussed in the ISA. The exposure/risk-based discussions have drawn 
from the quantitative health risk analyses for Pb performed in the last 
Pb NAAQS review in light of the currently available evidence (PA, 
section 3.4; 2007 REA; REA Planning Document). Sections II.A.2 through 
II.A.4 below provide an overview of the current health effects and 
quantitative exposure and risk information with a focus on the specific 
policy-relevant questions identified for these categories of 
information in the PA (PA, chapter 3).
1. Background on the Current Standard
    The current primary standard was established in the last review, 
which was completed in 2008 (73 FR 66964, November 12, 2008), and is 
set at a level that is one-tenth the level of the prior standard. The 
2008 decision to substantially revise the primary standard was based on 
the extensive body of scientific evidence published over almost three 
decades, from the time the standard was originally set in 1978 through 
2005-2006. While recognizing that Pb has been demonstrated to exert ``a 
broad array of deleterious effects on multiple organ systems,'' the 
2008 review focused on the effects most pertinent to recent ambient air 
exposures, which are those associated with relatively lower exposures 
and associated blood Pb levels (73 FR 66975, November 12, 2008). Given 
the general scientific consensus that the developing nervous system in 
children is among the most sensitive health endpoints associated with 
Pb exposure, if not the most sensitive one, primary attention was given 
to consideration of nervous system effects, including neurocognitive 
and neurobehavioral effects, in children (73 FR 66976, November 12, 
2008). The body of evidence included associations of such effects in 
study populations of variously aged children with mean blood Pb levels 
below 10 [micro]g/dL, extending from 8 down to 2 [micro]g/dL (73 FR 
66976, November 12, 2008). Particular focus was given to the public 
health implications of effects of air-related Pb on cognitive function 
(e.g., IQ).
    The conclusions reached by the Administrator in the 2008 review 
were based primarily on the scientific evidence, with the risk- and 
exposure-based information providing support for various aspects of the 
decision. In reaching his conclusion on the adequacy of the then-
current standard, which was set in 1978, the Administrator placed 
primary consideration on the large body of scientific evidence 
available in the review including significant new evidence concerning 
effects at blood Pb concentrations substantially below those identified 
when the standard was initially set (73 FR 66987, November 12, 2008; 43 
FR 46246, October 5, 1978). He gave particular attention to the robust 
evidence of neurotoxic effects of Pb exposure in children, recognizing: 
(1) That while blood Pb levels in U.S. children had decreased notably 
since the late 1970s, newer epidemiological studies had investigated 
and reported associations of effects on the neurodevelopment of 
children with those more recent lower blood Pb levels and (2) that the 
toxicological evidence included extensive experimental laboratory 
animal evidence substantiating well the plausibility of the 
epidemiological findings observed in human children and expanding our 
understanding of likely mechanisms underlying the neurotoxic effects 
(73 FR 66987, November 12, 2008). Additionally, within the range of 
blood Pb levels investigated in the available evidence base, a 
threshold level for neurocognitive effects was not identified (73 FR 
66984, November 12, 2008; 2006 CD, p. 8-67). Further, the evidence 
indicated a steeper concentration-response (C-R) relationship for 
effects on cognitive function at those lower blood Pb levels than at 
higher blood Pb levels that were more common in the past, ``indicating 
the potential for greater incremental impact associated with exposure 
at these lower levels'' (73 FR 66987, November 12, 2008).
    Based on consideration of the health effects evidence, supported by 
the quantitative risk analyses, the Administrator concluded that, for 
exposures projected for air Pb concentrations at the level of the 1978

[[Page 71916]]

standard, the quantitative estimates of IQ loss associated with air-
related Pb indicated risk of a magnitude that, in his judgment, was 
significant from a public health perspective, and that the 1978 
standard did not protect public health with an adequate margin of 
safety (73 FR 66987, November 12, 2008). The Administrator further 
concluded that the evidence indicated the need for a substantially 
lower standard level to provide increased public health protection, 
especially for sensitive or at-risk groups (most notably children), 
against an array of effects, most importantly including effects on the 
developing nervous system (73 FR 66987, November 12, 2008). In 
identifying the appropriate revised standard, revisions to each of the 
four basic elements of the NAAQS (indicator, averaging time, form and 
level) were considered.
    With regard to indicator, the Administrator decided to retain Pb-
TSP as the indicator. The EPA recognized that the difference in 
particulate Pb captured by TSP and PM10 monitors may be on 
the order of a factor of two in some areas, and that ultra-coarse Pb 
particles may have a greater presence in areas near sources where Pb 
concentrations are highest, contributing uncertainty with regard to 
whether a Pb-PM10-based standard would also effectively 
control ultra-coarse Pb particles (73 FR 66991, November 12, 2008). 
Accordingly, Pb-TSP was retained as the indicator in order to provide 
sufficient public health protection from the broad range of particle 
sizes of ambient air Pb, including ultra-coarse particles, given the 
recognition that Pb in all particle sizes contributes to Pb in blood 
and associated health effects (73 FR 66991, November 12, 2008).\21\
---------------------------------------------------------------------------

    \21\ However, in order to take advantage of the increased 
precision of Pb-PM10 measurements and decreased spatial 
variation of Pb-PM10 concentrations without raising the 
same concerns over a lack of protection against health risks from 
all particulate Pb emitted to the ambient air that support retention 
of Pb-TSP as the indicator (versus revision to Pb-PM10), 
a role was provided for Pb-PM10 measurements in the 
monitoring required for a Pb-TSP standard (73 FR 66991, November 12, 
2008) at sites not influenced by sources of ultra-coarse Pb, and 
where Pb concentrations are well below the standard (73 FR 66991, 
November 12, 2008).
---------------------------------------------------------------------------

    With regard to averaging time and form for the revised standard, 
after giving consideration to a monthly averaging time, with a form of 
second maximum, and to 3-month and calendar quarter averaging times, 
with not-to-be exceeded forms, two changes were made. These were to a 
rolling 3-month average, thus giving equal weight to all 3-month 
periods, and to the method for deriving the 3-month average to provide 
equal weighting to each month. Both of these changes afford greater 
weight to each individual month than did the calendar quarter form of 
the 1978 standard, thus tending to control both the likelihood that any 
month will exceed the level of the standard and the magnitude of any 
such exceedance. The Administrator decided on these changes in 
recognition of the complexity inherent in this aspect of the standard 
which is greater for Pb than in the case of other criteria pollutants 
due to the multimedia nature of Pb and its multiple pathways of human 
exposure. In this situation for Pb, the Administrator emphasized the 
importance of considering in an integrated manner all of the relevant 
factors, both those pertaining to the human physiological response to 
changes in Pb exposures and those pertaining to the response of air-
related Pb exposure pathways to changes in airborne Pb, recognizing 
that some factors might imply support for a period as short as a month 
for averaging time, and others supporting use of a longer time, with 
all having associated uncertainty. Based on such an integrated 
consideration of the range of relevant factors, the averaging time was 
revised to a rolling 3-month period with a maximum (not-to-be-exceeded) 
form, evaluated over a 3-year period (73 FR 66996, November 12, 2008).
    In reaching the decision on level for the revised standard, that, 
in combination with the specified choice of indicator, averaging time, 
and form, the Administrator judged requisite to protect public health, 
including the health of sensitive groups, with an adequate margin of 
safety, he considered the evidence using a very specifically defined 
framework, referred to as an air-related IQ loss evidence-based 
framework (73 FR 67004, November 12, 2008). This framework integrates 
evidence for the relationship between Pb in air and Pb in young 
children's blood with evidence for the relationship between Pb in young 
children's blood and IQ loss (73 FR 66987, November 12, 2008). This 
evidence-based approach considers air-related effects on neurocognitive 
function (using the quantitative metric of IQ loss) associated with 
exposure in those areas with elevated air concentrations equal to 
potential alternative levels for the Pb standard. In simplest terms, 
the framework focuses on children exposed to air-related Pb in those 
areas with elevated air Pb concentrations equal to specific potential 
standard levels, providing for estimation of a mean air-related IQ 
decrement for young children with air-related exposures that are in the 
high end of the national distribution of such exposures. Thus, the 
conceptual context for the framework is that it provides estimates of 
air-related IQ loss for the subset of U.S. children living in close 
proximity to air Pb sources that contribute to such elevated air Pb 
concentrations. Consideration of this framework additionally recognizes 
that in such cases when a standard of a particular level is just met at 
a monitor sited to record the highest source-oriented concentration in 
an area, the large majority of children in the larger surrounding area 
would likely experience exposures to concentrations well below that 
level.
    The two primary inputs to the air-related IQ loss evidence-based 
framework are air-to-blood ratios \22\ and C-R functions for the 
relationship between blood Pb concentration and IQ response in young 
children (73 FR 67004, November 12, 2008). In applying and drawing 
conclusions from the framework, the Administrator additionally took 
into consideration the uncertainties inherent in these two inputs. 
Application of the framework also entailed consideration of an 
appropriate level of protection from air-related IQ loss to be used in 
conjunction with the framework. The framework estimates of mean air-
related IQ loss are derived through multiplication of the following 
factors: standard level ([micro]g/m\3\), air-to-blood ratio (albeit in 
terms of [micro]g/dL blood Pb per [micro]g/m\3\ air concentration), and 
slope for the C-R function in terms of points of IQ decrement per 
[micro]g/dL blood Pb. In light of the uncertainties and limitations 
associated with the evidence on these relationships, and other 
considerations, application of the air-related IQ loss evidence-based 
framework was recognized to provide ``no evidence- or risk-based bright 
line that indicates a single appropriate level'' for the standard (73 
FR 67005-67006, November 12, 2008). Rather, the framework was seen as a 
useful guide, in the context of the specified averaging time and form, 
for consideration of health risks from exposure to levels of Pb in the 
ambient air to inform the Administrator's decision on a level for

[[Page 71917]]

a revised NAAQS that provides public health protection that is 
sufficient but not more than necessary under the Act (73 FR 67004, 
November 12, 2008).
---------------------------------------------------------------------------

    \22\ The term ``air-to-blood ratio'' describes the increase in 
blood Pb (in [micro]g/dL) estimated to be associated with each unit 
increase of air Pb (in [micro]g/m\3\). Ratios are presented in the 
form of 1:x, with the 1 representing air Pb (in [micro]g/m\3\) and x 
representing blood Pb (in [micro]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).
---------------------------------------------------------------------------

    Use of the air-related IQ loss evidence-based framework to inform 
selection of the standard level involved consideration of the evidence 
for the two primary input parameters mentioned above. With regard to 
air-to-blood ratio estimates, the evidence in the 2008 review indicated 
a broad range of estimates, each with limitations and associated 
uncertainties. Based on this evidence, the Administrator concluded that 
1:5 to 1:10 represented a reasonable range to consider and focused on 
1:7 as a generally central value (73 FR 67004, November 12, 2008). With 
regard to C-R functions, in light of the evidence of nonlinearity and 
of steeper slopes at lower blood Pb levels, the Administrator concluded 
it was appropriate to focus on C-R analyses based on blood Pb levels 
that most closely reflected the then-current population of young 
children in the U.S.,\23\ recognizing the EPA's identification of four 
such analyses and giving weight to the central estimate or median of 
the resultant linear C-R functions (73 FR 67003, November 12, 2008, 
Table 3; 73 FR 67004, November 12, 2008). The median estimate for the 
four C-R slopes of -1.75 IQ points decrement per [micro]g/dL blood Pb 
was selected for use with the framework. With the framework, potential 
alternative standard levels ([micro]g/m\3\) are multiplied by estimates 
of air-to-blood ratio ([micro]g/dL blood Pb per [micro]g/m\3\ air Pb) 
and the median slope for the C-R function (points IQ decrement per 
[micro]g/dL blood Pb), yielding estimates of a mean air-related IQ 
decrement for a specific subset of young children (i.e., those children 
exposed to air-related Pb in areas with elevated air Pb concentrations 
equal to specified alternative levels). As such, the application of the 
framework yields estimates for the mean air-related IQ decrements of 
the subset of children expected to experience air-related Pb exposures 
at the high end of the distribution of such exposures. The associated 
mean IQ loss estimate is the average for this highly exposed subset and 
is not the average air-related IQ loss projected for the entire U.S. 
population of children. Uncertainties and limitations were recognized 
in the use of the framework and in the resultant estimates (73 FR 
67000, November 12, 2008).
---------------------------------------------------------------------------

    \23\ The geometric mean blood Pb level for U.S. children aged 5 
years and below, reported for NHANES in 2003-04 (the most recent 
years for which such an estimate was available at the time of the 
2008 decision) was 1.8 [micro]g/dL and the 5th and 95th percentiles 
were 0.7 [micro]g/dL and 5.1 [micro]g/dL, respectively (73 FR 
67002). Using the air-to-blood ratio 1:7, the estimated air-related 
blood Pb level associated with the final standard level is 
approximately 1 [micro]g/dL. In the 2008 decision, the EPA noted 
that even if it assumed, as an extreme hypothetical example, that 
the mean for the general population of U.S. children included zero 
contribution from air-related sources and added that to the estimate 
of air-related Pb, the result would still be below the lowest mean 
blood Pb level among the set of C-R analyses (73 FR 67002).
---------------------------------------------------------------------------

    In considering the use of the air-related IQ loss evidence-based 
framework to inform his judgment as to the appropriate degree of public 
health protection that should be afforded by the NAAQS to provide 
requisite protection against risk of neurocognitive effects in 
sensitive populations, such as IQ loss in children, the Administrator 
recognized in the 2008 review that there were no commonly accepted 
guidelines or criteria within the public health community that would 
provide a clear basis for such a judgment. During the 2008 review, 
CASAC commented regarding the significance from a public health 
perspective of a 1-2 point IQ loss in the entire population of children 
and, along with some commenters, emphasized that the NAAQS should 
prevent air-related IQ loss of a significant magnitude, such as on the 
order of 1-2 IQ points, in all but a small percentile of the 
population. Similarly, the Administrator stated 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'' (73 FR 
66998, November 12, 2008). The Administrator further recognized that, 
in the case of setting a national ambient air quality standard, he was 
required to make a judgment as to what degree of protection is 
requisite to protect public health with an adequate margin of safety 
(73 FR 66998, November 12, 2008). The NAAQS must be sufficient but not 
more stringent than necessary to achieve that result, and the Act does 
not require a zero-risk standard (73 FR 66998, November 12, 2008). The 
Administrator additionally recognized that the air-related IQ loss 
evidence-based framework did not provide estimates pertaining to the 
U.S. population of children as a whole. Rather, the framework provided 
estimates (with associated uncertainties and limitations) for the mean 
of a subset of that population, the subset of children assumed to be 
exposed to the level of the standard. As described in the final 
decision ``[t]he framework in effect focuses on the sensitive 
subpopulation that is the group of children living near sources and 
more likely to be exposed at the level of the standard'' (73 FR 67000, 
November 12, 2008). Further description of the EPA's consideration of 
this issue is provided in the preamble to the final decision rule (73 
FR 67000, November 12, 2008):

    EPA is unable to quantify the percentile of the U.S. population 
of children that corresponds to the mean of this sensitive 
subpopulation. Nor is EPA confident in its ability to develop 
quantified estimates of air-related IQ loss for higher percentiles 
than the mean of this subpopulation. EPA expects that the mean of 
this subpopulation represents a high, but not quantifiable, 
percentile of the U.S. population of children. As a result, EPA 
expects that a standard based on consideration of this framework 
would provide the same or greater protection from estimated air-
related IQ loss for a high, albeit unquantifiable, percentage of the 
entire population of U.S. children.

    In reaching a judgment as to the appropriate degree of protection, 
the Administrator considered advice and recommendations from CASAC and 
public comments and recognized the uncertainties in the health effects 
evidence and related information as well as the role of, and context 
for, a selected air-related IQ loss in the application of the 
framework, as described above. Based on these considerations, the 
Administrator identified an air-related IQ loss of 2 points for use 
with the framework, as a tool for considering the evidence with regard 
to the level for the standard (73 FR 67005, November 12, 2008). In so 
doing, the Administrator was not determining that such an IQ decrement 
value was appropriate in other contexts (73 FR 67005, November 12, 
2008). Given the various uncertainties associated with the framework 
and the scientific evidence base, and the focus of the framework on the 
sensitive subpopulation of children that are more highly exposed to 
air-related Pb, a standard level selected in this way, in combination 
with the selected averaging time and form, was expected to 
significantly reduce and limit for a high percentage of U.S. children 
the risk of experiencing an air-related IQ loss of that magnitude (73 
FR 67005, November 12, 2008). At the standard level of 0.15 [micro]g/
m\3\, with the combination of the generally central estimate of air-to-
blood ratio of 1:7 and the median of the four C-R functions (-1.75 IQ 
point decrement per [micro]g/dL blood Pb), the framework estimates of 
air-related IQ loss were below 2 IQ points (73 FR 67005, November 12, 
2008, Table 4).
    In reaching the decision in 2008 on a level for the revised 
standard, the Administrator also considered the results of the 
quantitative risk assessment to provide a useful

[[Page 71918]]

perspective on risk from air-related Pb. In light of important 
uncertainties and limitations for purposes of evaluating potential 
standard levels, however, the Administrator placed less weight on the 
risk estimates than on the evidence-based assessment. Nevertheless, in 
recognition of the general comparability of quantitative risk estimates 
for the case studies considered most conceptually similar to the 
scenario represented by the evidence-based framework, he judged the 
quantitative risk estimates to be ``roughly consistent with and 
generally supportive'' of the evidence-based framework estimates (73 FR 
67006, November 12, 2008).
    Based on consideration of the entire body of evidence and 
information available in the review, as well as the recommendations of 
CASAC and public comments, the Administrator decided that a level for 
the primary Pb standard of 0.15 [micro]g/m\3\, in combination with the 
specified choice of indicator, averaging time and form, was requisite 
to protect public health, including the health of sensitive groups, 
with an adequate margin of safety (73 FR 67006, November 12, 2008). In 
reaching decisions on level as well as the other elements of the 
revised standard, the Administrator took note of the complexity 
associated with consideration of health effects caused by different 
ambient air concentrations of Pb and with uncertainties with regard to 
the relationships between air concentrations, exposures, and health 
effects. For example, selection of a maximum, not to be exceeded, form 
in conjunction with a rolling 3-month averaging time over a 3-year span 
was expected to have the effect that the at-risk population of children 
would be exposed below the standard most of the time (73 FR 67005, 
November 12, 2008). The Administrator additionally considered the 
provision of an adequate margin of safety in making decisions on each 
of the elements of the standard, including, for example ``selection of 
TSP as the indicator and the rejection of the use of PM10 
scaling factors; selection of a maximum, not to be exceeded form, in 
conjunction with a 3-month averaging time that employs a rolling 
average, with the requirement that each month in the 3-month period be 
weighted equally (rather than being averaged by individual data) and 
that a 3-year span be used for comparison to the standard; and the use 
of a range of inputs for the evidence-based framework, that includes a 
focus on higher air-to-blood ratios than the lowest ratio considered to 
be supportable, and steeper rather than shallower C-R functions, and 
the consideration of these inputs in selection of 0.15 [mu]g/m\3\ as 
the level of the standard'' (73 FR 67007, November 12, 2008).
    The Administrator additionally noted that a standard with this 
level would reduce the risk of a variety of health effects associated 
with exposure to Pb, including effects indicated in the epidemiological 
studies at lower blood Pb levels, particularly including neurological 
effects in children, and the potential for cardiovascular and renal 
effects in adults (73 FR 67006, November 12, 2008). The Administrator 
additionally considered higher and lower levels for the standard, 
concluding that a level of 0.15 [micro]g/m\3\ provided for a standard 
that was neither more or less stringent than necessary for this 
purpose, recognizing that the Act does not require that primary 
standards be set 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 (73 FR 67007, November 12, 2008). For 
example, the Administrator additionally considered potential public 
health protection provided by standard levels above 0.15 [micro]g/m\3\, 
which he concluded were insufficient to protect public health with an 
adequate margin of safety. The Administrator also noted that in light 
of all of the evidence, including the evidence-based framework, the 
degree of public health protection likely afforded by standard levels 
below 0.15 [micro]g/m\3\ would be greater than what is necessary to 
protect public safety with an adequate margin of safety.
    The Administrator concluded, based on review of all of the evidence 
(including the evidence-based framework), that when taken as a whole 
the selected standard, including the indicator, averaging time, form, 
and level, would be ``sufficient but not more than necessary to protect 
public health, including the health of sensitive subpopulations, with 
an adequate margin of safety'' (73 FR 67007, November 12, 2008).
2. Overview of Health Effects Evidence
    In this section, we provide an overview of the information 
presented in section II.B of the proposal on policy-relevant aspects of 
the health effects evidence available for consideration in this review. 
Section II.B of the proposal provides a detailed summary of key 
information contained in the ISA and in the PA on health and public 
health effects of Pb, focusing particularly on the information most 
relevant to consideration of effects associated with the presence of Pb 
in ambient air (80 FR 290-297, January 5, 2015). The subsections below 
briefly outline this information in the five topic areas addressed in 
section II.B of the proposal.
a. Array of Effects
    Lead has been demonstrated to exert a broad array of deleterious 
effects on multiple organ systems as described in the assessment of the 
evidence available in this review and consistent with conclusions of 
past CDs (ISA, section 1.6; 2006 CD, section 8.4.1). A sizeable number 
of studies on Pb health effects are newly available in this review and 
are critically assessed in the ISA as part of the full body of 
evidence. The newly available evidence reaffirms conclusions on the 
broad array of effects recognized for Pb in the last review (see ISA, 
section 1.10).\24\ Consistent with those conclusions, in the context of 
pollutant exposures considered relevant to the Pb NAAQS review,\25\ the 
ISA determines that causal relationships \26\ exist for Pb with effects 
on the nervous system in children (cognitive function decrements and 
the group of externalizing behaviors comprising attention, impulsivity 
and hyperactivity), the hematological system (altered heme synthesis 
and decreased red blood cell survival and function), and the 
cardiovascular system (hypertension and coronary heart disease), and on 
reproduction and development (postnatal development and male 
reproductive function) (ISA, Table 1-2). Additionally, the ISA

[[Page 71919]]

describes relationships between Pb and certain types of effects on the 
nervous system in adults, and on immune system function, as well as 
with cancer,\27\ as likely to be causal \28\ (ISA, Table 1-2, sections 
1.6.4 and 1.6.7).
---------------------------------------------------------------------------

    \24\ Since the last Pb NAAQS review, the ISAs, which have 
replaced CDs in documenting each review of the scientific evidence 
(or air quality criteria), employ a systematic framework for 
weighing the evidence and describing associated conclusions with 
regard to causality using established descriptors: ``causal'' 
relationship with relevant exposure, ``likely'' to be a causal 
relationship, evidence is ``suggestive'' of a causal relationship, 
``inadequate'' evidence to infer a causal relationship, and ``not 
likely'' to be a causal relationship (ISA, Preamble).
    \25\ In drawing judgments regarding causality for the criteria 
air pollutants, the ISA places emphasis ``on evidence of effects at 
doses (e.g., blood Pb concentration) or exposures (e.g., air 
concentrations) that are relevant to, or somewhat above, those 
currently experienced by the population. The extent to which studies 
of higher concentrations are considered varies . . . but generally 
includes those with doses or exposures in the range of one to two 
orders of magnitude above current or ambient conditions. Studies 
that use higher doses or exposures may also be considered . . 
.[t]hus, a causality determination is based on weight of evidence 
evaluation . . ., focusing on the evidence from exposures or doses 
generally ranging from current levels to one or two orders of 
magnitude above current levels'' (ISA, pp. lx-lxi).
    \26\ In determining a causal relationship to exist for Pb with 
specific health effects, the EPA concludes that ``[e]vidence is 
sufficient to conclude that there is a causal relationship with 
relevant pollutant exposures (i.e., doses or exposures generally 
within one to two orders of magnitude of current levels)'' (ISA, p. 
lxii).
    \27\ The EPA concludes that a causal relationship is likely to 
exist between Pb exposure and cancer, based primarily on consistent, 
strong evidence from experimental animal studies, but inconsistent 
epidemiological evidence (ISA, section 4.10.5). Lead has also 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 (ISA, section 4.10).
    \28\ In determining that there is likely to be a causal 
relationship for Pb with specific health effects, the EPA has 
concluded that ``[e]vidence is sufficient to conclude that a causal 
relationship is likely to exist with relevant pollutant exposures, 
but important uncertainties remain'' (ISA, p. lxii).
---------------------------------------------------------------------------

    Among the nervous system effects of Pb, the newly available 
evidence is consistent with conclusions in the previous review which 
recognized that ``[t]he neurotoxic effects of Pb exposure are among 
those most studied and most extensively documented among human 
population groups'' (2006 CD, p. 8-25) and took note of the diversity 
of studies in which such effects of Pb exposure early in development 
(from fetal to postnatal childhood periods) have been observed (2006 
CD, p. E-9). While some studies are newly available of other effects in 
children with somewhat lower blood Pb levels than previously available 
for these effects, nervous system effects continue to receive 
prominence in the current review, as in previous reviews, with 
particular emphasis on those affecting cognitive function and behavior 
in children (ISA, section 4.3), with conclusions that are consistent 
with findings of the last review. For example, based on the extensive 
assessment of the full body of evidence available in this review, the 
major conclusions drawn by the ISA regarding health effects of Pb in 
children include the following (ISA, p. lxxxvii).

    Multiple epidemiologic studies conducted in diverse populations 
of children consistently demonstrate the harmful effects of Pb 
exposure on cognitive function (as measured by IQ decrements, 
decreased academic performance and poorer performance on tests of 
executive function). . . . Evidence suggests that some Pb-related 
cognitive effects may be irreversible and that the 
neurodevelopmental effects of Pb exposure may persist into adulthood 
(Section 1.9.4). Epidemiologic studies also demonstrate that Pb 
exposure is associated with decreased attention, and increased 
impulsivity and hyperactivity in children (externalizing behaviors). 
This is supported by findings in animal studies demonstrating both 
analogous effects and biological plausibility at relevant exposure 
levels. Pb exposure can also exert harmful effects on blood cells 
and blood producing organs, and is likely to cause an increased risk 
of symptoms of depression and anxiety and withdrawn behavior 
(internalizing behaviors), decreases in auditory and motor function, 
asthma and allergy, as well as conduct disorders in children and 
young adults. There is some uncertainty about the Pb exposures 
contributing to the effects and blood Pb levels observed in 
epidemiologic studies; however, these uncertainties are greater in 
studies of older children and adults than in studies of young 
children (Section 1.9.5).

    As in prior reviews of the Pb NAAQS, this review is focused on 
those effects most pertinent to ambient air Pb exposures. Given the 
reductions in ambient air Pb concentrations over the past decades, 
these effects are generally those associated with the lowest levels of 
Pb exposure that have been evaluated. Additionally, we recognize the 
limitations on our ability to draw conclusions regarding the exposure 
conditions contributing to the findings from epidemiological analyses 
of blood Pb levels in populations of older children and adults, 
particularly in light of their history of higher Pb exposures. For 
example, the evidence newly available for Pb relationships with 
cardiovascular effects in adults includes some studies with somewhat 
lower blood Pb levels than in the last review. However, the long 
exposure histories of these cohorts, as well as the generally higher Pb 
exposures of the past, complicate conclusions regarding exposure levels 
that may be eliciting observed effects (ISA, sections 4.4.2.4 and 
4.4.7).\29\ Evidence available in future reviews may better inform this 
issue. Recognizing this, the extensive assessment of the full body of 
evidence available in this review contributed to the following major 
conclusions drawn by the ISA regarding health effects of Pb in adults 
(ISA, p. lxxxviii).

    \29\ Studies from the late 1960s and 1970s suggest that adult 
blood Pb levels during that period ranged from roughly 13 to 16 
[mu]g/dL and from 15 to 30 [micro]g/dL in children aged 6 and 
younger (ISA, section 4.4.1).
---------------------------------------------------------------------------

    A large body of evidence from both epidemiologic studies of 
adults and experimental studies in animals demonstrates the effect 
of long-term Pb exposure on increased blood pressure (BP) and 
hypertension (Section 1.6.2). In addition to its effect on BP, Pb 
exposure can also lead to coronary heart disease and death from 
cardiovascular causes and is associated with cognitive function 
decrements, symptoms of depression and anxiety, and immune effects 
in adult humans. The extent to which the effects of Pb on the 
cardiovascular system are reversible is not well-characterized. 
Additionally, the frequency, timing, level, and duration of Pb 
exposure causing the effects observed in adults has not been 
pinpointed, and higher past exposures may contribute to the 
development of health effects measured later in life.

    In the last review, while recognizing the range of health effects 
in variously aged populations related to Pb exposure, we focused on the 
health effects for which the evidence was strongest with regard to 
relationships with the lowest exposure levels, neurocognitive effects 
in young children. Similarly, given the strength of the evidence, 
including the greater confidence in conclusions regarding the exposures 
contributing to the observed effects, we focus in this review, as in 
the last, on neurocognitive effects in young children.
b. Critical Periods of Exposure
    As in the last review, we base our current understanding of health 
effects associated with different Pb exposure circumstances at various 
stages of life or in different populations on the full body of 
available evidence and primarily on epidemiological studies of health 
effects associated with population Pb biomarker levels (as discussed 
further in section II.B.3 of the proposal). The epidemiological 
evidence is overwhelmingly composed of studies that rely on blood Pb 
for the exposure metric, with the remainder largely including a focus 
on bone Pb. Because these metrics reflect Pb in the body (e.g., as 
compared to Pb exposure concentrations) and, in the case of blood Pb, 
reflect Pb available for distribution to target sites, they strengthen 
the evidence base for purposes of drawing causal conclusions with 
regard to Pb generally. The complexity of Pb exposure pathways and 
internal dosimetry, however, tends to limit the extent to which these 
types of studies inform our more specific understanding of the Pb 
exposure circumstances (e.g., timing within lifetime, duration, 
frequency and magnitude) eliciting the various effects.
    A critical aspect of much of the epidemiological evidence, 
particularly studies focused on adults (and older children) in the U.S. 
today, is the backdrop of generally declining environmental Pb exposure 
(from higher exposures during their younger years) that is common 
across many study populations (ISA, p. 4-2).\30\ An additional factor 
complicating the interpretation of health effect

[[Page 71920]]

associations with blood Pb measurements in older children and younger 
adults is the common behaviors of younger children (e.g., hand-to-mouth 
contact) that generally contribute to relatively greater exposures 
earlier in life (ISA, sections 3.1.1, 5.2.1). Such exposure histories 
for adults and older children complicate our ability to draw 
conclusions regarding critical time periods and lifestages for Pb 
exposures eliciting the effects for which associations with Pb 
biomarkers have been observed in these populations (e.g., ISA, section 
1.9.6).\31\ Thus, our confidence is greatest in the role of early 
childhood exposure in contributing to Pb-related neurocognitive effects 
that have been associated with blood Pb levels in young children. This 
is due, in part, to the relatively short exposure histories of young 
children (ISA, sections 1.9.4, 1.9.6 and 4.3.11).
---------------------------------------------------------------------------

    \30\ The declines in Pb exposure concentrations occurring from 
the 1970s through the early 1990s (and experienced by middle aged 
and older adults of today), as indicated by NHANES blood Pb 
information, were particularly dramatic (ISA, section 3.4.1).
    \31\ The evidence from experimental animal studies can be 
informative with regard to key aspects of exposure circumstances in 
eliciting specific effects, thus informing our interpretation of 
epidemiological evidence. For example, the animal evidence base with 
regard to Pb effects on blood pressure demonstrates the 
etiologically-relevant role of long-term exposure (ISA, section 
4.4.1). This finding then informs consideration of epidemiological 
studies of adult populations for whom historical exposures were 
likely more substantial than concurrent ones, suggesting that the 
observed effects may be related to the past exposure (ISA, section 
4.4.1). For other health effects, the animal evidence base may or 
may not be informative in this manner.
---------------------------------------------------------------------------

    Epidemiological analyses evaluating risk of neurocognitive impacts 
(e.g., reduced IQ) associated with different blood Pb metrics in 
cohorts with differing exposure patterns (including those for which 
blood Pb levels at different ages were not highly correlated) also 
indicate associations with blood Pb measurements concurrent with full 
scale IQ (FSIQ) tests at ages of approximately 6-7 years. The analyses 
did not, however, conclusively demonstrate stronger findings for early 
(e.g., at age 2 years) or concurrent blood Pb levels (ISA, section 
4.3.11).\32\ The experimental animal evidence additionally indicates 
early life susceptibility (ISA, section 4.3.15 and p. 5-21). Thus, 
while uncertainties remain with regard to the role of Pb exposures 
during a particular age of life in eliciting nervous system effects, 
such as cognitive function decrements, the full evidence base continues 
to indicate prenatal and early childhood lifestages as periods of 
increased Pb-related risk (ISA, sections 4.3.11 and 4.3.15). We 
recognize increasing uncertainty, however, in our understanding of the 
relative impact on neurocognitive function of additional Pb exposure of 
children by school age or later that is associated with limitations of 
the currently available evidence, including epidemiological cohorts 
with generally similar temporal patterns of exposure.
---------------------------------------------------------------------------

    \32\ In the collective body of evidence of nervous system 
effects in children, it is difficult to distinguish exposure in 
later lifestages (e.g., school age) and its associated risk from 
risks resulting from exposure in prenatal and early childhood (ISA, 
section 4.3.11). While early childhood is recognized as a time of 
increased susceptibility, a difficulty in identifying a discrete 
period of susceptibility from epidemiological studies has been that 
the period of peak exposure, reflected in peak blood Pb levels, is 
around 18-27 months when hand-to-mouth activity is at its maximum 
(ISA, section 3.4.1 and 5.2.1.1; 2006 CD, p. 6-60). The task is 
additionally complicated by the role of maternal exposure history in 
contributing Pb to the developing fetus (ISA, section 3.2.2.4.).
---------------------------------------------------------------------------

    In summary, as in the last review, we continue to recognize a 
number of uncertainties regarding the circumstances of Pb exposure, 
including timing or lifestages, eliciting specific health effects. 
Consideration of the evidence newly available in this review has not 
appreciably changed our understanding on this topic. The relationship 
of long-term exposure to Pb with hypertension and increased blood 
pressure in adults is substantiated despite some uncertainty regarding 
the exposure circumstances contributing to blood Pb levels measured in 
epidemiological studies. For example, the evidence does not indicate 
the exposure magnitude and timing that are eliciting such effects. 
Across the full evidence base, the effects for which our understanding 
of relevant exposure circumstances is greatest are neurocognitive 
effects in young children. Moreover, available evidence does not 
suggest a more sensitive endpoint. Thus, we continue to recognize and 
give particular attention to the role of Pb exposures relatively early 
in childhood in contributing to neurocognitive effects, some of which 
may persist into adulthood.
c. Nervous System Effects in Children
    The evidence currently available with regard to the magnitude of 
blood Pb levels associated with neurocognitive effects in children is 
generally consistent with that available in the review completed in 
2008. Nervous system effects in children, specifically effects on 
cognitive function, continue to be the effects that are best 
substantiated as occurring at the lowest blood Pb concentrations (ISA, 
pp. lxxxvii-lxxxviii). Associations of blood Pb with effects on 
cognitive function measures in children have been reported in many 
studies across a range of childhood blood Pb levels, including study 
group (mean/median) levels ranging down to 2 [micro]g/dL (e.g., ISA, p. 
lxxxvii and section 4.3.2).\33\
---------------------------------------------------------------------------

    \33\ The value of 2 [mu]g/dL refers to the regression analysis 
of blood Pb and end-of-grade test scores, in which blood Pb was 
represented by categories for integer values of blood Pb from 1 
[mu]g/dL to 9 and >10 [mu]g/dL from large statewide database. A 
significant effect estimate was reported for test scores with all 
blood Pb categories in comparison to the reference category (1 
[mu]g/dL), which included results at and below the limit of 
detection. Mean levels are not provided for any of the categories 
(Miranda et al., 2009).
---------------------------------------------------------------------------

    Among the analyses of lowest study group blood Pb levels at the 
youngest ages are analyses available in the last review of Pb 
associations with neurocognitive function decrement in study groups 
with mean levels on the order of 3-4 [mu]g/dL in children aged 24 
months or ranging from 5 to 7 years (73 FR 66978-66979, November 12, 
2008; ISA, sections 4.3.2.1 and 4.3.2.2; Bellinger and Needleman, 2003; 
Canfield et al., 2003; Lanphear et al., 2005; Tellez-Rojo et al., 2006; 
Bellinger, 2008; Canfield, 2008; Tellez-Rojo, 2008; Kirrane and Patel, 
2014).\34\ Newly available in this review are two studies reporting 
association of blood Pb levels prior to 3 years of age with academic 
performance on standardized tests in primary school; mean blood Pb 
levels in these studies were 4.2 and 4.8 [mu]g/dL (ISA, section 
4.3.2.5; Chandramouli et al., 2009; Miranda et al., 2009). One of these 
two studies, which represented integer blood Pb levels as categorical 
variables, indicated a small effect on end-of-grade reading score of 
blood Pb levels as low as 2 [mu]g/dL, after adjustment for age of 
measurement, race, sex, enrollment in free or reduced lunch program, 
parental education, and school type (Miranda et al., 2009).
---------------------------------------------------------------------------

    \34\ The tests for cognitive function in these studies include 
age-appropriate Wechsler intelligence tests (Lanphear et al., 2005; 
Bellinger and Needleman, 2003), the Stanford-Binet intelligence test 
(Canfield et al., 2003), and the Bayley Scales of Infant Development 
(Tellez-Rojo et al., 2006). The Wechsler and Stanford-Binet tests 
are widely used to assess neurocognitive function in children and 
adults. These tests, however, are not appropriate for children under 
age 3. For such children, studies generally use the age-appropriate 
Bayley Scales of Infant Development as a measure of cognitive 
development.
---------------------------------------------------------------------------

    Newly available in this review are also several studies in older 
children on neurocognitive effects and other nervous system effects. As 
described in section II.B.3 of the proposal, however, these studies are 
focused on population groups of ages for which the available 
information indicates exposure levels were higher earlier in childhood. 
Thus, in light of this information, although the blood Pb levels in the 
studies in older child population groups are lower (at the time of the 
study) than the younger child study levels, the studies of older

[[Page 71921]]

children do not provide a basis for concluding a role for lower Pb 
exposure levels than those experienced by the younger study groups. 
Rather, this information makes these studies relatively uninformative 
with regard to evidence of effects associated with lower exposure 
levels than provided by evidence previously available.
    Recognizing the complexity associated with interpretation of 
studies involving older cohorts,\35\ as well as the potential role of 
higher exposure levels in the past, we continue to focus our 
consideration of this question on the evidence of effects in young 
children for which our understanding of exposure history is less 
uncertain.\36\ Within this evidence base, we recognize the lowest study 
group blood Pb levels to be associated with effects on cognitive 
function measures, indicating that to be the most sensitive endpoint. 
As described above, the evidence available in this review is generally 
consistent with that available in the last review with regard to blood 
Pb levels at which such effects had been reported (ISA, section 4.3.2; 
2006 CD, section 8.4.2.1; 73 FR 66976-66979, November 12, 2008). As 
blood Pb levels are a reflection of exposure history, particularly in 
early childhood (ISA, section 3.3.2), we conclude, by extension, that 
the currently available evidence does not indicate Pb effects at 
exposure levels appreciably lower than recognized in the last review.
---------------------------------------------------------------------------

    \35\ Our conclusions regarding exposure levels at which Pb 
health effects occur, particularly with regard to such levels that 
might be common in the U.S. today, are complicated now, as in the 
last review, by several factors. These factors include the scarcity 
of information in epidemiological studies on cohort exposure 
histories, as well as by the backdrop of higher past exposure levels 
which frame the history of most, if not all, older study cohorts.
    \36\ In focusing on effects associated with blood Pb levels in 
early childhood, however, we additionally recognize the evidence 
across categories of effects that relate to blood Pb levels in older 
child study groups (for which early childhood exposure may have had 
an influence) which provides additional support to an emphasis on 
nervous system effects (ISA, sections 4.3, 4.4, 4.5, 4.6, 4.7, 4.8).
---------------------------------------------------------------------------

    We additionally note that, as in the last review, a threshold blood 
Pb level with which nervous system effects, and specifically cognitive 
effects, occur in young children cannot be discerned from the currently 
available studies (ISA, sections 1.9.3 and 4.3.12). Epidemiological 
analyses have reported blood Pb associations with cognitive effects 
(FSIQ or BSID MDI \37\) for young child population subgroups (age 5 
years or younger) with individual blood Pb measurements as low as 
approximately 1 [mu]g/dL and mean concentrations as low as 2.9 to 3.8 
[mu]g/dL (ISA, section 4.3.12; Bellinger and Needleman, 2003; 
Bellinger, 2008; Canfield el al., 2003; Canfield, 2008; Tellez-Rojo et 
al., 2006; Tellez-Rojo, 2008). As concluded in the ISA, however, ``the 
current evidence does not preclude the possibility of a threshold for 
neurodevelopmental effects in children existing with lower blood levels 
than those currently examined'' (ISA, p. 4-274).
---------------------------------------------------------------------------

    \37\ The Bayley Scales of Infant Development, Mental Development 
Index (BSID MDI) is a well-standardized and widely used assessment 
measure of infant cognitive development. Scores earlier than 24 
months are not necessarily strongly correlated with later FSIQ 
scores in children with normal development (ISA, section 4.3.15.1).
---------------------------------------------------------------------------

    Important uncertainties associated with the evidence of effects at 
low exposure levels are similar to those recognized in the last review, 
including the shape of the concentration-response relationship for 
effects on neurocognitive function at low blood Pb levels in today's 
young children. Also of note is our interpretation of associations 
between blood Pb levels and effects in epidemiological studies, with 
which we recognize uncertainty with regard to the specific exposure 
circumstances (timing, duration, magnitude and frequency) that have 
elicited the observed effects, as well as uncertainties in relating 
ambient air concentrations (and associated air-related exposures) to 
blood Pb levels in early childhood, as recognized in section II.A.2.b 
above. We additionally recognize uncertainties associated with 
conclusions drawn with regard to the nature of the epidemiological 
associations with blood Pb (e.g., ISA, section 4.3.13) but note that, 
based on consideration of the full body of evidence for neurocognitive 
effects, the EPA has determined a causal relationship to exist between 
relevant blood Pb levels and neurocognitive impacts in children (ISA, 
section 4.3.15.1).
    Based primarily on studies of FSIQ, the assessment of the currently 
available studies, as was the case in the last review, continues to 
recognize a nonlinear relationship between blood Pb levels and effects 
on cognitive function, with a greater incremental effect (greater 
slope) at lower relative to higher blood Pb levels within the range 
thus far studied, extending from well above 10 [mu]g/dL to below 5 
[mu]g/dL (ISA, section 4.3.12). This was supported by the evidence 
available in the last review, including the analysis of the large 
pooled international dataset comprised of blood Pb measurements and IQ 
test results from seven prospective cohorts (Lanphear et al., 2005; 
Rothenberg and Rothenberg, 2005; ISA, section 4.3.12). The blood Pb 
measurements in this pooled dataset that were concurrent with the IQ 
tests ranged from 2.5 [mu]g/dL to 33.2 [mu]g/dL.
    The study by Lanphear et al. (2005) additionally presented analyses 
that stratified the dataset based on peak blood Pb levels (e.g., with 
cutpoints of 7.5 [mu]g/dL and 10 [mu]g/dL peak blood Pb) and found that 
the coefficients from linear models of the association for IQ with 
concurrent blood Pb levels were higher in the lower peak blood Pb level 
subsets than the higher groups (ISA, section 4.3.12; Lanphear et al., 
2005).\38\ In other publications, stratified analyses of several 
individual cohorts also observed higher coefficients for blood Pb 
relationships with measures of neurocognitive function in lower as 
compared to higher blood Pb subgroups (ISA, section 4.3.12; Canfield et 
al., 2003; Bellinger and Needleman, 2003; Kordas et al., 2006; Tellez-
Rojo et al., 2006). Of these subgroup analyses, those involving the 
lowest mean blood Pb levels and closest to the current mean for U.S. 
preschool children are listed in Table 1 of the proposal (drawn from 
Table 3 of the 2008 preamble to the final rule [73 FR 67003, November 
12, 2008], and Kirrane and Patel, 2014).\39\ These analyses were 
important inputs for the air-related IQ loss evidence-based framework 
which informed decisions on a revised standard in the last review (73 
FR 67005, November 12, 2008), discussed in section II.A.1 above. 
Specifically, the framework focused on the median of the four average 
linear slope estimates from the studies recognized in Table 3 of the 
2008 decision (73 FR 67003, November 12, 2008). As shown in Table 1 of 
the proposal, the median is unchanged by

[[Page 71922]]

consideration of the information newly available in this review.\40\
---------------------------------------------------------------------------

    \38\ As described in the PA and noted in the proposal, since the 
completion of the ISA, two errors have been identified with the 
pooled dataset analyzed by Lanphear et al. (2005) (Kirrane and 
Patel, 2014). A recent publication and the EPA have separately 
recalculated the statistics and mathematical model parameters of 
Lanphear et al. (2005) using the corrected pooled dataset (see 
Kirrane and Patel, 2014). While the magnitude of the loglinear and 
linear regression coefficients are modified slightly based on the 
corrections, the conclusions drawn from these coefficients, 
including the finding of a steeper slope at lower (as compared to 
higher) blood Pb concentrations, are not affected (Kirrane and 
Patel, 2014).
    \39\ One of these four subgroup analyses is the analysis of the 
lowest blood Pb subset of the pooled international study by Lanphear 
et al. (2005). The nonlinear model developed from the full pooled 
dataset is the basis of the C-R functions used in the 2007 REA, in 
which risk was estimated over a large range of blood Pb levels (PA, 
section 3.4.3.3). Given the narrower focus of the evidence-based 
framework on IQ response at the end of studied blood Pb levels 
(closer to U.S. mean level), the C-R functions in Table 1 are from 
linear analyses (each from separate publications) for the study 
group subsets with blood Pb levels closest to mean for children in 
the U.S. today.
    \40\ As the framework focused on the median of the four slopes 
in Table 1, the change to the one from Lanphear et al. (2005) based 
on the recalculation described above has no impact on conclusions 
drawn from the framework.
---------------------------------------------------------------------------

    Several studies newly available in the current review have, in all 
but one instance, also found a nonlinear blood Pb-cognitive function 
relationship in nonparametric regression analyses of the cohort blood 
Pb levels analyzed (ISA, section 4.3.12). These studies, however, used 
statistical approaches that did not produce quantitative results for 
each blood Pb group (ISA, section 4.3.12). Thus, newly available 
studies have not extended the range of observation for quantitative 
estimates of this relationship to lower blood Pb levels than those of 
the previous review. The ISA further notes that the potential for 
nonlinearity has not been examined in detail within a lower, narrower 
range of blood Pb levels than those of the full cohorts thus far 
studied in the currently available evidence base (ISA, section 4.3.12). 
Such an observation in the last review supported the consideration of 
linear slopes with regard to blood Pb levels at and below those 
represented in Table 1 of the proposal. In summary, the newly available 
evidence does not substantively alter our understanding of the C-R 
relationship (including quantitative aspects) for neurocognitive 
impact, such as IQ, with blood Pb in young children.
d. At-Risk Populations
    In this section, as elsewhere, we use the term ``at-risk 
populations'' \41\ to recognize populations that have a greater 
likelihood of experiencing Pb-related health effects, i.e., groups with 
characteristics that contribute to an increased risk of Pb-related 
health effects. These populations are also referred to as sensitive 
groups (as in section I.A above). In identifying factors that increase 
risk of Pb-related health effects, we have considered evidence 
regarding factors contributing to increased susceptibility, generally 
including physiological or intrinsic factors contributing to a greater 
response for the same exposure and those contributing to increased 
exposure, including that resulting from behavior leading to increased 
contact with contaminated media (ISA, Chapter 5). Physiological risk 
factors include both conditions contributing to a group'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 (e.g., ISA, sections 5.3 and 5.1, respectively).
---------------------------------------------------------------------------

    \41\ In the context of ``at-risk populations,'' the term 
``population'' refers to persons having one or more qualities or 
characteristics including, for example, a specific pre-existing 
illness or a specific age or lifestage, with lifestage referring to 
a distinguishable time frame in an individual's life characterized 
by unique and relatively stable behavioral and/or physiological 
characteristics that are associated with development and growth.
---------------------------------------------------------------------------

    In considering factors that increase risk by contributing to 
increased exposure or to increased blood Pb levels over those otherwise 
associated with a given Pb exposure, we note that the currently 
available evidence continues to support a nonlinear relationship 
between neurocognitive effects and blood Pb that indicates 
incrementally greater impacts at lower as compared to higher blood Pb 
levels (ISA, section 4.3.12), as described in section II.B.3 of the 
proposal and briefly noted in section II.A.2.c above. An important 
implication of this finding is that while children with higher blood Pb 
levels are at greater risk of Pb-related effects than children with 
lower blood Pb levels, on an incremental basis (e.g., per [mu]g/dL) the 
risk is greater for children at lower blood Pb levels. This was given 
particular attention in the last review of the Pb NAAQS, in which the 
standard was revised with consideration of the incremental impact of 
air-related Pb on young children in the U.S. and the recognition of 
greater incremental impact for those children with lower absolute blood 
Pb levels (73 FR 67002, November 12, 2008). Such consideration included 
a focus on those C-R studies involving the lowest blood Pb levels, as 
described in section II.A.1 above.
    The information newly available in this review has not appreciably 
altered our previous understanding of at-risk populations for Pb in 
ambient air. As in the last review, the factor most prominently 
recognized to contribute to increased risk of Pb effects is childhood 
(ISA, section 1.9.6). As discussed in section II.B.2 of the proposal 
and briefly noted in section II.A.2.b above, while uncertainties remain 
with regard to the role of Pb exposures during a particular age of life 
in eliciting nervous system effects, such as cognitive function 
decrements, the full evidence base continues to indicate prenatal and 
early childhood lifestages as periods of increased Pb-related risk 
(ISA, sections 4.3.11 and 4.3.15). Thus, in the current review, as at 
the time of the last review of the Pb NAAQS, we recognize young 
children as an important at-risk population, with sensitivity extending 
to prenatal exposures and into childhood development.
    An additional physiological risk factor that contributes to 
increased blood Pb levels is nutritional status, which can play a role 
in Pb absorption from the gastrointestinal tract, with iron-, calcium- 
and zinc-deficient diets contributing to increased Pb absorption and 
associated blood Pb levels (ISA, sections 3.2.1.2, 5.1, 5.3.10 and 
5.4). Risk factors based on increased exposure include spending time in 
proximity to sources of Pb to ambient air or other environmental media, 
such as large active metals industries or locations of historical Pb 
contamination (ISA, sections 1.9.6, 3.7.1, 5.2.5 and 5.4). Residential 
factors associated with other sources of Pb exposure (e.g., leaded 
paint or plumbing with Pb pipes or solder) are another exposure-related 
risk factor (ISA, sections 3.7.1, 5.2.6 and 5.4). Additionally, some 
races or ethnicities have been associated with higher blood Pb levels, 
with differential exposure indicated in some cases as the cause (ISA, 
sections 5.2.3 and 5.4).
    Lower socioeconomic status (SES) has been associated with higher Pb 
exposure and higher blood Pb concentration in some study groups, 
leading the ISA to conclude the evidence is suggestive for low SES as a 
risk factor (ISA, sections 5.3.16, 5.2.4 and 5.4).\42\ Although the 
differences in blood Pb levels, nationally, between children of lower 
and higher income levels (as well as among some races or ethnicities) 
have lessened, blood Pb levels continue to be higher among lower-income 
children indicating higher exposure and/or greater influence of factors 
independent of exposure, such as nutritional factors (ISA, sections 
1.9.6, 5.2.1.1 and 5.4).\43\ The evidence is also suggestive of 
increased risk associated with several other factors: older 
adulthood,\44\ pre-

[[Page 71923]]

existing disease (e.g., hypertension), variants for certain genes and 
increased stress (ISA, section 5.3.4).
---------------------------------------------------------------------------

    \42\ The approach used by the EPA in evaluating the evidence 
regarding factors that may influence the risk of Pb-related health 
effects is described in chapter 5 of the ISA.
    \43\ Although the evidence for SES continues to indicate 
increased blood Pb levels in lower income children, its role with 
regard to an increased health risk for the same blood Pb level is 
unclear and its role generally with regard to Pb-related risk is 
somewhat complicated. SES often serves as a marker term for one or a 
combination of unspecified or unknown environmental or behavioral 
variables. Further, it is independently associated with an adverse 
impact on neurocognitive development, and a few studies have 
examined SES as a potential modifier of the association of childhood 
Pb exposure with cognitive function with inconsistent findings 
regarding low SES as a potential risk factor.
    \44\ The ISA identifies older adulthood as a lifestage of 
potentially greater risk of Pb-related health effects based 
primarily on the evidence of increases in blood Pb levels during 
this lifestage (ISA, sections 5.2.1.2, 5.3.1.2, and 5.4), as well as 
observed associations of some cardiovascular and nervous system 
effects with bone and blood Pb in older populations, with biological 
plausibility for the role of Pb provided by experimental animal 
studies (ISA, sections 4.3.5, 4.3.7 and 4.4). Exposure histories of 
older adult study populations, which included younger years during 
the time of leaded gasoline usage and other sources of Pb exposures 
which were more prevalent in the past than today, are likely 
contributors to their blood Pb levels (ISA, pp. lx-lxi; Figure 2-1 
and sections 2.5.2, 3.3.5 and 5.2.1.2).
---------------------------------------------------------------------------

    In summary, we recognize the sensitivity of the prenatal period and 
several stages of childhood to an array of neurocognitive and 
behavioral effects, and we particularly recognize young children as an 
important at-risk population in light of current environmental exposure 
levels. Age or lifestage was used to distinguish potential groups on 
which to focus in the last review in recognition of its role in 
exposure and susceptibility, and young children were the focus of the 
REA in consideration of the health effects evidence regarding endpoints 
of greatest public health concern and in recognition of effects on the 
developing nervous system as a sentinel endpoint for public health 
impacts of Pb. This identification continues to be supported by the 
evidence available in the current review.
e. Potential Impacts on Public Health
    There are several potential public health impacts associated with 
Pb exposure in the current U.S. population. In recognition of effects 
causally related to blood Pb levels somewhat near those most recently 
reported for today's population and for which the weight of the 
evidence is greatest, the potential public health impacts most 
prominently recognized in the ISA are population IQ impacts associated 
with childhood Pb exposure and prevalence of cardiovascular effects in 
adults (ISA, section 1.9.1). With regard to the latter category, as 
discussed above, the full body of evidence indicates a role of long-
term cumulative exposure, with uncertainty regarding the specific 
exposure circumstances contributing to the effects in the 
epidemiological studies of adult populations, for whom historical Pb 
exposures were likely much higher than exposures that commonly occur 
today (ISA, section 4.4). There is less uncertainty regarding the 
exposure patterns contributing to the blood Pb levels reported in 
studies of younger populations (ISA, sections 1.9.4 and 1.10). 
Accordingly, the discussion of public health implications relevant to 
this review is focused predominantly on nervous system effects, 
including IQ decrements, in children.
    The magnitude of a public health impact is dependent upon the type 
or severity of the effect, as well as the size of populations affected. 
Intelligence quotient is a well-established, widely recognized and 
rigorously standardized measure of neurocognitive function, as well as 
a global measure reflecting the integration of numerous processes (ISA, 
section 4.3.2; 2006 CD, sections 6.2.2 and 8.4.2). In considering 
population risk, the distribution of effects across members of the 
population is important. For example, if Pb-related decrements are 
manifested uniformly across the range of IQ scores in a population, ``a 
small shift in the population mean IQ may be significant from a public 
health perspective because such a shift could yield a larger proportion 
of individuals functioning in the low range of the IQ distribution, 
which is associated with increased risk of educational, vocational, and 
social failure'' as well as a decrease in the proportion with high IQ 
scores (ISA, section 1.9.1). Examples of other measures of cognitive 
function negatively associated with Pb exposure include other measures 
of intelligence and cognitive development and measures of other 
cognitive abilities, such as learning, memory, and executive functions, 
as well as academic performance and achievement (ISA, section 4.3.2). 
Although some neurocognitive effects of Pb in children may be 
transient, some may persist into adulthood (ISA, section 1.9.5).\45\ We 
also note that deficits in neurodevelopment early in life may have 
lifetime consequences as ``[n]eurodevelopmental deficits measured in 
childhood may set affected children on trajectories more prone toward 
lower educational attainment and financial well-being'' (ISA, section 
4.3.14). Thus, population groups for which neurodevelopment is affected 
by Pb exposure in early childhood are at risk of related impacts on 
their success later in life.
---------------------------------------------------------------------------

    \45\ The ISA states that the ``persistence of effects appears to 
depend on the duration and window of exposure as well as other 
factors that may affect an individual's ability to recover from an 
insult,'' with some evidence of greater recovery in children reared 
in households with more optimal caregiving characteristics and low 
concurrent blood Pb levels (ISA, p. 1-77; Bellinger et al., 1990).
---------------------------------------------------------------------------

    As indicated above, young children are the at-risk population that 
may be most at risk of health effects associated with exposure to Pb, 
and children at greatest risk from air-related Pb are those children 
with highest air-related Pb exposure, which we consider to be those 
living in areas of higher ambient air Pb concentrations (e.g., 
concentrations near or above the current standard). Analyses in the PA 
indicate this group to be a very small subset of all young children in 
the U.S. Together the analyses indicate that well below one-tenth of 
one percent of the full population of children aged 5 years or younger 
in the U.S. today live in areas with air Pb concentrations near or 
above the current standard, with the current monitoring data indicating 
the size of this population to be approximately one-hundredth of a 
percent of the full population of children aged 5 or younger (PA, pp. 
3-36 to 3-38, 4-25, 4-32). It is these children that were the 
Administrator's focus in revising the primary standard in 2008.
3. Overview of Information on Blood Lead Relationships With Air Lead
    This section provides a brief overview of the information 
summarized in section II.C of the proposal on key aspects of the 
information available in this review on blood Pb as a biomarker and on 
relationships of blood Pb with air Pb (80 FR 298-300, January 5, 2015). 
Blood Pb is well established as a biomarker of Pb exposure and of 
internal dose, with relationships between air Pb concentrations and 
blood Pb concentrations informing consideration of the NAAQS for Pb 
since its initial establishment in 1978. The blood Pb concentration in 
childhood (particularly early childhood) can more quickly (than in 
adulthood) reflect changes in total body burden (associated with the 
shorter exposure history) and can also reflect changes in recent 
exposures (ISA, section 3.3.5). The relationship of children's blood Pb 
to recent exposure may reflect their labile bone pool, with their rapid 
bone turnover in response to rapid childhood growth rates (ISA, section 
3.3.5). The relatively smaller skeletal compartment of Pb in children 
(particularly very young children) compared to adults is subject to 
more rapid turnover. Multiple studies have demonstrated young 
children's blood Pb levels to reflect Pb exposures, including exposures 
to Pb in surface dust (e.g., Lanphear and Roghmann, 1997; Lanphear et 
al., 1998). These and studies of child populations near sources of air 
Pb emissions, such as metal smelters, have further demonstrated the 
effect of airborne Pb on interior dust and on blood Pb (ISA, sections 
3.4.1, 3.5.1 and 3.5.3; Hilts, 2003; Gulson et al., 2004).
    As blood Pb is an integrated marker of aggregate Pb exposure across 
all pathways, the blood Pb C-R relationships described in 
epidemiological studies of Pb-exposed populations do not distinguish 
among different sources of Pb or pathways of

[[Page 71924]]

Pb exposure (e.g., inhalation, ingestion of indoor dust, ingestion of 
dust containing leaded paint). Thus, our interpretation of the health 
effects evidence for purposes of this review necessitates 
characterization of the relationships between Pb from those sources and 
pathways of interest in this review (i.e., those related to Pb emitted 
into the air) and blood Pb.
    The evidence for air-to-blood relationships derives from analyses 
of datasets for populations residing in areas with differing air Pb 
concentrations, including datasets for circumstances in which blood Pb 
levels have changed in response to changes in air Pb. The control for 
variables other than air Pb that can affect blood Pb varies across 
these analyses. At the conclusion of the last review in 2008, the EPA 
interpreted the evidence as providing support for use (in informing the 
Administrator's decision on standard level) of a range of air-to-blood 
ratios \46\ ``inclusive at the upper end of estimates on the order of 
1:10 and at the lower end on the order of 1:5'' (73 FR 67002, November 
12, 2008). This conclusion reflected consideration of the air-to-blood 
ratios presented in the 1986 CD \47\ and associated observations 
regarding factors contributing to variation in such ratios, ratios 
reported subsequently and ratios estimated based on modeling performed 
in the REA, as well as advice from CASAC (73 FR 66973-66975, 67001-
67002, November 12, 2008). The information available in this review, 
which is assessed in the ISA and largely, although not completely, 
comprises studies that were available in the last review, does not 
alter the primary scientific conclusions drawn in the last review 
regarding the relationships between Pb in ambient air and Pb in 
children's blood. The ratios summarized in the ISA in this review span 
a range generally consistent with the range concluded in 2008 (ISA, 
section 3.5.1).
---------------------------------------------------------------------------

    \46\ The quantitative relationship between ambient air Pb and 
blood Pb, often termed a slope or ratio, describes the increase in 
blood Pb (in [mu]g/dL) estimated to be associated with each unit 
increase of air Pb (in [mu]g/m\3\). 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.
    \47\ The 2006 CD did not include an assessment of then-current 
evidence on air-to-blood ratios.
---------------------------------------------------------------------------

    The evidence on the quantitative relationship between air Pb and 
air-related Pb in blood is now, as in the past, limited by the 
circumstances (such as those related to Pb exposure) in which the data 
were collected. Previous reviews have recognized the significant 
variability in air-to-blood ratios for different populations exposed to 
Pb through different air-related exposure pathways and at different air 
and blood levels, with the 1986 CD noting that ratios derived from 
studies involving the higher blood and air Pb levels pertaining to 
occupationally exposed workers are generally smaller than ratios from 
studies involving lower blood and air Pb levels (ISA, p. 3-132; 1986 
CD, p. 11-99). Consistent with this observation, slopes in the range of 
3 to 5 were estimated for child population datasets assessed in the 
1986 CD (ISA, p. 3-132; 1986 CD p. 11-100; Brunekreef, 1984). 
Additional studies considered in the last review and those assessed in 
the ISA provide evidence of ratios above this older range (ISA, p. 3-
133). For example, a ratio of 1:6.5 to 1:7 is indicated by the study by 
Hilts (2003), one of the few studies that evaluate the air Pb-blood Pb 
relationship in conditions that are closer to the current state in the 
U.S. (ISA, p. 3-132). We additionally note the variety of factors 
identified in the ISA that may potentially affect estimates of various 
ratios (including potentially coincident reductions in nonair Pb 
sources during the course of the studies) and for which a lack of 
complete information may preclude any adjustment of estimates to 
account for their role (ISA, section 3.5).
    In summary, as at the time of the last review of the NAAQS for Pb, 
the currently available evidence includes estimates of air-to-blood 
ratios, both empirical and model-derived, with associated limitations 
and related uncertainties. These limitations and uncertainties, which 
are summarized here and also noted in the ISA, usually include 
uncertainty associated with reductions in other Pb sources during the 
study period. The limited amount of new information available in this 
review has not appreciably altered the scientific conclusions reached 
in the last review regarding relationships between Pb in ambient air 
and Pb in children's blood or with regard to the range of ratios. The 
currently available evidence continues to indicate ratios relevant to 
the population of young children in the U.S. today, reflecting multiple 
air-related pathways in addition to inhalation, to be generally 
consistent with the approximate range of 1:5 to 1:10 given particular 
attention in the 2008 NAAQS decision, including the ``generally central 
estimate'' of 1:7 (73 FR 67002, 67004, November 12, 2008; ISA, pp. 3-
132 to 3-133).
4. Overview of Risk and Exposure Assessment Information
    This section provides a brief overview of key aspects of the risk 
and exposure assessment information available in this review, which is 
based primarily on the exposure and risk assessment developed in the 
last review of the Pb NAAQS.\48\ This overview is drawn from the 
summary presented in the proposal (80 FR 300-305, January 5, 2015). As 
described in the REA Planning Document, careful consideration of the 
information newly available in this review, with regard to designing 
and implementing a full REA for this review, led to the conclusion that 
performance of a new REA for this review was not warranted. We did not 
find the information newly available in this review to provide the 
means by which to develop an updated or enhanced risk model that would 
substantially improve the utility of risk estimates in informing the 
current Pb NAAQS review (REA Planning Document, section 2.3). Based on 
its consideration of the REA Planning Document analysis, the CASAC Pb 
Review Panel generally concurred with the conclusion that a new REA was 
not warranted in this review (Frey, 2011b).\49\ Accordingly, the 
exposure/risk information considered in this review is drawn primarily 
from the 2007 REA, augmented by a limited new computation for one case 
study focused on risk associated with the current standard, as 
described in section II.D of the proposal and in section 3.4 and 
Appendix 3A of the PA.
---------------------------------------------------------------------------

    \48\ The information in this review is based on the assessment 
from the last review, described in the 2007 REA, the 2007 Staff 
Paper and the 2008 notice of final decision (USEPA, 2007a; USEPA, 
2007b; 73 FR 66964, November 12, 2008), as considered in the context 
of the evidence newly available in this review (PA, section 3.4; 
proposal, section II.D).
    \49\ In its review of the draft PA, the CASAC Pb Review Panel 
reinforced its concurrence with the EPA's decision not to develop a 
new REA (Frey, 2013).
---------------------------------------------------------------------------

    The focus for the risk assessment and associated estimates is on Pb 
derived from sources emitting Pb to ambient air. In order to 
characterize exposure and risk from these pathways, however, the 
assessment also recognized the role of Pb exposure pathways unrelated 
to Pb in ambient air (2007 REA, section 2.1). Sources of human Pb 
exposure include current and historical air emissions sources, as well 
as miscellaneous nonair sources, which can contribute to multiple 
exposure media and associated pathways, such as inhalation of ambient 
air, ingestion of indoor dust, outdoor soil/dust and diet or drinking 
water (as recognized in section I.D above). In addition to airborne 
emissions (recent or

[[Page 71925]]

those in the past), sources of Pb to these pathways also include old 
leaded paint, including Pb mobilized indoors during renovation/repair 
activities, and contaminated soils. Lead in diet and drinking water may 
have air pathway-related contributions as well as contributions from 
nonair sources (e.g., Pb solder on older water distribution pipes and 
Pb in materials used in food processing).
    Limitations in our data and modeling tools handicapped our ability 
to address the various complexities associated with exposure to ambient 
air Pb and to fully separate the nonair contributions to Pb exposure 
from estimates of air-related Pb exposure and risk. As a result, the 
assessment included a number of simplifying assumptions in a number of 
areas, and the estimates of air-related Pb risk produced are 
approximate, characterized by bounds within which air-related Pb risk 
is estimated to fall. The lower bound is based on a combination of 
pathway-specific estimates that do not completely represent all air-
related pathways, while the upper bound is based on a combination of 
pathway-specific estimates that includes pathways that are not air-
related but the separating out of which is precluded by modeling and 
data limitations (PA, section 3.4).
    Key aspects of the 2007 REA, such as the exposure populations, 
exposure or dose metric, health effects endpoint and risk metric were 
based on consideration of the then-currently available evidence as 
assessed in detail in the 2006 CD. As discussed in the REA Planning 
Document (USEPA, 2011b), these selections continue to be supported by 
the evidence now available in this review as described in the ISA. The 
REA focused on risk to the central nervous system in childhood as the 
most sensitive effect that could be quantitatively assessed, with 
decrement in IQ used as the risk metric. Exposure and biokinetic 
modeling was used to estimate blood Pb concentrations in children 
exposed to Pb up to age 7 years.\50\ This focus reflected the evidence 
for young children with regard to air-related exposure pathways and 
susceptibility to Pb health impacts (e.g., ISA, sections 3.1.1, 4.3, 
5.2.1.1, 5.3.1.1, and 5.4). For example, the hand-to-mouth activity of 
young children contributes to their Pb exposure (i.e., incidental soil 
and indoor dust ingestion), and ambient air-related Pb has been shown 
to contribute to Pb in outdoor soil and indoor house dust (ISA, 
sections 3.1.1 and 3.4.1; 2006 CD, section 3.2.3).
---------------------------------------------------------------------------

    \50\ The pathways represented in this modeling included 
childhood inhalation and ingestion pathways, as well as maternal 
contributions to newborn body burden (2007 REA, Appendix H, Exhibit 
H-6).
---------------------------------------------------------------------------

    The 2007 REA relied on a case study approach to provide estimates 
that inform our understanding of air-related exposure and risk in 
different types of air Pb exposure situations. Lead exposure and 
associated risk were estimated for multiple case studies that generally 
represent two types of residential population exposures to air-related 
Pb: (1) Location-specific urban populations of children with a broad 
range of air-related exposures, reflecting existence of urban 
concentration gradients; and (2) children residing in localized areas 
with air-related exposures representing air concentrations specifically 
reflecting the standard level being evaluated (see PA, Table 3-6). 
Thus, the two types of case studies differed with regard to the extent 
to which they represented population variability in air-related Pb 
exposure.
    In drawing on the 2007 REA for our purposes in this review, we 
focused on two case studies, one from each of these two categories: (1) 
The location-specific urban case study for Chicago and (2) the 
generalized (local) urban case study (PA, Table 3-6). The generalized 
(local) urban case study (also referred to as general urban case study) 
was not based on a specific geographic location and reflected several 
simplifying assumptions 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. Based on 
the nature of the population exposures represented by the two 
categories of case study, the generalized (local) urban case study 
includes populations that are relatively more highly exposed by way of 
air pathways to air Pb concentrations near the standard level 
evaluated, compared with the populations in the location-specific urban 
case. The location-specific urban case studies provided representations 
of urban populations with a broad range of air-related exposures due to 
spatial gradients in both ambient air Pb levels and population density. 
For example, the highest air concentrations in these case studies 
(i.e., those closest to the standard being assessed) were found in very 
small parts of the study areas, while a large majority of the case 
study populations resided in areas with much lower air concentrations.
    Air-related risk estimates for the two case studies are accompanied 
by a number of uncertainties (summarized in section II.D.3 of the 
proposal and described in detail in section 3.4 of the PA). Exposure 
and risk modeling conducted for this analysis was complex and subject 
to significant uncertainties due to limitations in the data and models, 
among other aspects, as recognized at the time of the last review.\51\ 
The multimedia and persistent nature of Pb, the role of multiple 
exposure pathways, and the contributions of nonair sources of Pb to 
human exposure media all present challenges and contribute significant 
additional complexity to the health risk assessment that goes far 
beyond the situation for similar assessments typically performed for 
other NAAQS pollutants (e.g., that focus only on the inhalation 
pathway). Of particular note among the assessment limitations are 
limitations in the assessment design, data and modeling tools that 
handicapped us from sharply separating Pb linked to ambient air from Pb 
that is not air related. The resultant, approximate, air-related risk 
bounds, however, encompass estimates drawn from the air-related IQ loss 
evidence-based framework, providing a rough consistency and general 
support, as was the case in the last review (73 FR 67004, November 12, 
2008).
---------------------------------------------------------------------------

    \51\ As summarized in section II.D.3 of the proposal, a range of 
limitations and areas of uncertainty were associated with the 
information available in the last review (PA, sections 3.4.4, 3.4.6 
and 3.4.7), and the newly available information in this review did 
not substantially reduce any of the primary sources of uncertainty 
identified to have the greatest impact on risk estimates (USEPA, 
2011b). Thus, the key observations regarding air-related Pb risk 
modeled for the set of standard levels assessed in the 2007 REA, as 
well as the risk estimates interpolated for the current standard, 
are not significantly affected by the new information. Nor is our 
overall characterization of uncertainty and variability associated 
with those estimates (as summarized above and in sections 3.4.6 and 
3.4.7 of the PA).
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B. Conclusions on the Primary Standard

    In drawing conclusions on the adequacy of the current primary Pb 
standard, in view of the advances in scientific knowledge and 
additional information now available, the Administrator considers the 
evidence base, information and policy judgments that were the 
foundation of the last review and reflects upon the body of evidence 
and information newly available in this review. The Administrator has 
taken into account both evidence-based and exposure- and risk-based 
considerations, advice from CASAC and public comment. Evidence-based 
considerations draw upon the EPA's assessment and integrated synthesis 
of the scientific evidence from epidemiological studies and 
experimental animal studies evaluating health effects related to 
exposures to Pb,

[[Page 71926]]

with a focus on policy-relevant considerations as discussed in the PA. 
The exposure- and risk-based considerations draw from the results of 
the quantitative analyses presented in the 2007 REA (augmented as 
described in the PA and summarized in section II.D of the proposal) and 
consideration of those results in the PA.
    As described in section II.A.2 of the proposal, consideration of 
the evidence and exposure/risk information in the PA and by the 
Administrator is framed by consideration of a series of key policy-
relevant questions. Section II.B.1 below summarizes the rationale for 
the Administrator's proposed decision, drawing from section II.E.4 of 
the proposal. A fuller presentation of PA considerations and 
conclusions, and advice from the CASAC, which were taken into account 
by the Administrator, is provided in sections II.E.1 through II.E.3 of 
the proposal. Advice received from CASAC in this review is briefly 
summarized in section II.B.2 below, and public comments on the proposed 
decision are addressed in section II.B.3. The Administrator's 
conclusions in this review regarding the adequacy of the current 
primary standard are described in section II.B.4.
1. Basis for the Proposed Decision
    At the time of the proposal, the Administrator carefully considered 
the assessment of the current evidence and conclusions reached in the 
ISA; the currently available exposure/risk information, including 
associated limitations and uncertainties; considerations and staff 
conclusions and associated rationales presented in the PA; the advice 
and recommendations from CASAC; and public comments that had been 
offered up to that point. In reaching her proposed conclusion on the 
primary standard, the Administrator first took note of the PA 
discussion with regard to the complexity and associated uncertainties 
involved in considering the adequacy of protection in the case of the 
primary Pb standard, which differs substantially from that involved in 
consideration of the primary standard in other NAAQS reviews. For the 
pollutants in the other reviews, the focus is on inhalation as the 
single route of exposures, which provides a relatively simpler context 
than the multiple exposure pathways that are relevant to Pb. 
Additionally, an important component of the evidence base for most 
other NAAQS pollutants is the availability of studies that have 
investigated an association between concentrations of the pollutant in 
ambient air and the occurrence of health effects plausibly related to 
ambient air exposure to that pollutant. Such studies of associations 
with air concentrations do not figure prominently in the review of the 
NAAQS for Pb. Rather, the evidence base in this review includes most 
prominently epidemiological studies focused on associations of blood Pb 
levels in U.S. populations with health effects plausibly related to Pb 
exposures occurring by multiple pathways. Support for conclusions 
regarding the plausibility for ambient air Pb to play a role in such 
findings derives, in part, from studies linking Pb in ambient air with 
the occurrence of health effects. However, such studies (dating from 
the past or from other countries) involve ambient air Pb concentrations 
many times greater than those that would meet the current standard. 
Thus, in considering the adequacy of the current Pb standard, rather 
than considering studies that have directly investigated current 
concentrations of Pb in ambient air (including in locations where the 
current standard is met) and the occurrence of health effects, we 
primarily consider the evidence for, and risk estimated from, models 
based upon key relationships, such as those among ambient air Pb, Pb 
exposure, blood Pb and health effects. This evidence, with its 
associated limitations and uncertainties, contributes to the EPA's 
conclusions regarding a relationship between ambient air Pb conditions 
under the current standard and health effects.
    In considering the nature and magnitude of the array of 
uncertainties that are inherent in the scientific evidence and 
analyses, the Administrator recognized that the current understanding 
of the relationships between the presence of a pollutant in ambient air 
and associated health effects is based on a broad body of information 
encompassing not only more established aspects of the evidence, but 
also aspects in which there may be substantial uncertainty. In her 
considerations for the proposal, she took into account both the well-
established body of evidence on the health effects of Pb, which 
continues to support identification of neurocognitive effects in young 
children as the most sensitive endpoint associated with Pb exposure, 
and of the recognition in the PA, with which the CASAC concurred, of 
increased uncertainty in characterizing the relationship of effects on 
IQ with blood Pb levels below those represented in the evidence base 
and also in projecting the magnitude of blood Pb response to ambient 
air Pb concentrations at and below the level of the current standard. 
In this light, she based her proposed decision on her consideration of 
the current evidence within the conceptual and quantitative context of 
the air-related IQ evidence-based loss framework; the available 
information and advice from CASAC regarding the public health 
significance of neurocognitive effects; and the limitations and 
uncertainties inherent in the evidence and its consideration within 
this framework. The Administrator additionally recognized support from 
the exposure/risk information, with its attendant uncertainties.
    In her consideration of the air-related IQ loss evidence-based 
framework, the Administrator took note of the PA finding, with which 
the CASAC concurred, that application of the air-related IQ loss 
evidence-based framework, developed in the last review, continues to 
provide a useful approach for considering and integrating the evidence 
on relationships between Pb in ambient air and Pb in children's blood 
and risks of neurocognitive effects (for which IQ loss is used as an 
indicator). She additionally took note of the PA finding (described in 
section II.E.1 of the proposal, and with which the CASAC concurred) 
that the currently available evidence base, while somewhat expanded 
since the last review, is not supportive of appreciably different 
conclusions with regard to air-to-blood ratios or C-R functions for 
neurocognitive decrements in young children.
    In the Administrator's consideration of the level of public health 
protection provided by the current standard, she gave weight to CASAC 
advice in the last review (and similar views expressed in the last 
review by public health experts, such as the American Academy of 
Pediatrics), which recognized a population mean IQ loss of 1 to 2 
points to be of public health significance and recommended that a very 
high percentage of the population be protected from such a magnitude of 
IQ loss (73 FR 67000, November 12, 2008). In so doing, she additionally 
noted that the EPA is aware of no new information or new commonly 
accepted guidelines or criteria within the public health community for 
interpreting public health significance of neurocognitive effects in 
the context of a decision on adequacy of the current Pb standard, and 
CASAC provided no alternate advice in this area in the current review 
(PA, pp. 4-33 to 4-34). Accordingly, with the objective identified in 
the CASAC advice from the 2008 review in

[[Page 71927]]

mind, the Administrator considered the role of the air-related IQ loss 
evidence-based framework in reviewing the level of protection provided 
by the current standard. In so doing, the Administrator recognized 
distinctions between estimates produced by the framework, for which the 
conceptual context is a subset of U.S. children, and specific 
quantitative public health policy goals for air-related IQ loss for the 
entire U.S. population of children. She additionally took note of the 
PA conclusion on the size of the population subset that might pertain 
to the situation represented by the framework (areas with elevated air 
Pb concentrations equal to the standard level), as well as 
uncertainties associated with the framework estimates, particularly at 
successively lower standard levels. In summary, the Administrator 
concluded in the proposal that the current evidence, as considered 
within the conceptual and quantitative context of the evidence-based 
framework, and current air monitoring information indicate that the 
current standard provides protection for young children from 
neurocognitive impacts, including IQ loss, consistent with advice from 
CASAC regarding IQ loss of public health significance.
    The Administrator based her proposed conclusions on consideration 
of the health effects evidence, including consideration of this 
evidence in the context of the air-related IQ loss evidence-based 
framework, and with support from the exposure/risk information, 
recognizing the uncertainties attendant with both. In so doing, she 
took note of the PA description of the complexities and limitations in 
the evidence base associated with reaching conclusions regarding the 
magnitude of risk associated with the current standard, as well as the 
increasing uncertainty of risk estimates for lower air Pb 
concentrations. Inherent in the Administrator's proposed conclusions 
are public health policy judgments on the public health implications of 
the blood Pb levels and risk estimated for air-related Pb under the 
current standard, including the public health significance of the Pb 
effects being considered, as well as aspects of the use of the 
evidence-based framework that may be considered to contribute to the 
margin of safety. These public health policy judgments include 
judgments related to the appropriate degree of public health protection 
that should be afforded to protect against risk of neurocognitive 
effects in at-risk populations, such as IQ loss in young children, as 
well as with regard to the appropriate weight to be given to differing 
aspects of the evidence and the exposure/risk information, and how to 
consider their associated uncertainties. Based on these considerations 
and the judgments summarized here, the Administrator proposed to 
conclude that the current standard provides the requisite protection of 
public health with an adequate margin of safety, including protection 
of at-risk populations, such as young children living near Pb emissions 
sources where ambient concentrations just meet the standard.
    The Administrator's proposed conclusion that the current standard 
provides the requisite protection and that a more restrictive standard 
would not be requisite additionally recognized that the uncertainties 
and limitations associated with many aspects of the estimated 
relationship between air Pb concentrations and blood Pb levels and 
associated health effects are amplified with consideration of 
increasingly lower air concentrations. In reaching her proposed 
conclusion, she took note of the PA conclusion, with which CASAC has 
agreed, that based on the current evidence, there is appreciable 
uncertainty associated with drawing conclusions regarding whether there 
would be reductions in blood Pb levels and risk to public health from 
alternative lower levels of the standard as compared to the level of 
the current standard (PA, pp. 4-35 to 4-36; Frey, 2013b, p. 6). The 
Administrator judged this uncertainty to be too great for the current 
evidence and exposure/risk information to provide a basis for revising 
the current standard. Thus, based on the public health policy judgments 
described above, including the weight given to uncertainties in the 
evidence, the Administrator proposed to conclude that the current 
standard should be retained, without revision.
2. CASAC Advice in This Review
    In comments on the draft PA, the CASAC concurred with staff's 
overall preliminary conclusions that it is appropriate to consider 
retaining the current primary standard without revision, stating that 
``the current scientific literature does not support a revision to the 
Primary Lead (Pb) National Ambient Air Quality Standard (NAAQS)'' 
(Frey, 2013b, p. 1). The CASAC further noted that ``[a]lthough the 
current review incorporates a substantial body of new scientific 
literature, the new literature does not justify a revision to the 
standards'' (Frey, 2013b, p. 1).
    The CASAC comments additionally indicated agreement with key 
aspects of staff's consideration of the exposure/risk information and 
currently available evidence in this review (Frey, 2013b, Consensus 
Response to Charge Questions, p. 7).

    The use of exposure/risk information from the previous Pb NAAQS 
review appears appropriate given the absence of significant new 
information that could fundamentally change the interpretation of 
the exposure/risk information. This interpretation is reasonable 
given that information supporting the current standard is largely 
unchanged since the current standard was issued.
    The CASAC agrees that the adverse impact of low levels of Pb 
exposure on neurocognitive function and development in children 
remains the most sensitive health endpoint, and that a primary Pb 
NAAQS designed to protect against that effect will offer 
satisfactory protection against the many other health impacts 
associated with Pb exposure.
    The CASAC concurs with the draft PA that the scientific findings 
pertaining to air-to-blood Pb ratios and the C-R relationships 
between blood Pb and childhood IQ decrements that formed the basis 
of the current Pb NAAQS remain valid and are consistent with current 
data.

    The CASAC concurred with the appropriateness of the application of 
the evidence-based framework from the last Pb NAAQS review. With regard 
to the key inputs to that framework, the CASAC concluded that ``[t]he 
new literature published since the previous review provides further 
support for the health effect conclusions presented in that review'' 
and that the studies newly available in this review ``do not 
fundamentally alter the uncertainties for air-to-blood ratios or C-R 
functions for IQ decrements in young children'' (Frey, 2013b, Consensus 
Response to Charge Questions, p. 6). The comments from the CASAC also 
took note of the uncertainties that remain in this review which 
contribute to the uncertainties associated with drawing conclusions 
regarding air-related exposures and associated health risk at or below 
the level of the current standard, stating agreement with ``the EPA 
conclusion that `there is appreciable uncertainty associated with 
drawing conclusions regarding whether there would be reductions in 
blood Pb levels from alternative lower levels as compared to the level 
of the current standard''' (Frey, 2013b, Consensus Response to Charge 
Questions, p. 6).
3. Comments on the Proposed Decision
    The majority of public comments on the proposal supported the 
Administrator's proposed decision to retain the current primary 
standard, without revision. This group includes the National 
Association of Clean Air

[[Page 71928]]

Agencies (NACAA), both of the state agencies that submitted comments 
and nearly all of the industry organizations that submitted comments. 
All of these commenters generally noted their agreement with the 
rationale provided in the proposal and noted the CASAC's concurrence 
with the EPA conclusion that the current evidence does not support 
revision to the standard. Most also cited the EPA and CASAC statements 
that information newly available in this review has not substantially 
altered our previous understanding of at-risk populations, C-R 
relationships or effects from exposures lower than what was previously 
examined and does not call into question the adequacy of the current 
standard. Some commenters stated that multimedia or multipathway 
aspects of Pb make the review of the primary standard for Pb subject to 
greater uncertainty than reviews of primary NAAQS for other pollutants 
and/or noted greater uncertainty with consideration of lower blood Pb 
and standard levels. Some also noted that EPA's task in setting NAAQS 
is not to reduce risk to zero but to identify a standard that is 
neither more nor less stringent than necessary. The EPA generally 
agrees with these commenters and with the CASAC regarding the adequacy 
of the current primary standard and the lack of support for revision of 
the standard.
    Four submissions recommending revision of the standard were 
received; all four advocated a tightening of the standard. These 
commenters include two individuals, a secondary Pb smelting company, 
and the Children's Health Protection Advisory Committee to the EPA 
(CHPAC).\52\ In support of their view that the standard should be 
revised, all four commenters generally stated that there is no safe 
level of Pb exposure.\53\ The CHPAC submission, to which the smelting 
company submission repeatedly cited, asserted that a lower standard is 
needed to protect children from impacts related to neurodevelopmental 
and low birthweight effects, stating that studies it cited that have 
been published since the cut-off for the ISA indicate effects on 
children's IQ at ``appreciably lower'' Pb exposures than those 
recognized in the last review and raise concerns regarding cumulative 
effects of multiple chemical exposures. These commenters additionally 
cited the PA's presentation of the 2007 REA results that included lower 
risk estimates for alternative more stringent standards, stating that 
minority and low-income groups are more greatly impacted by Pb, and 
that for these reasons the standard should be lowered. The CHPAC 
submission also suggests consideration of some transient sources to 
provide support for a more stringent standard. Among the reasons given 
for their recommendations to substantially lower the standard level, 
the individual commenters variously stated that not revising or 
lowering the standard will allow increases in air Pb in locations near 
some sources of Pb emissions, such as airports, and that the 
persistence of Pb indicated the need for a more stringent standard.
---------------------------------------------------------------------------

    \52\ As described in its charter, the CHPAC is a policy-oriented 
committee providing policy advice to EPA related to the development 
of regulations, guidance and policies to address children's 
environmental health, consistent with provisions of the Federal 
Advisory Committee Act (http://www.epa.gov/faca/childrens-health-protection-advisory-committee-charter-september-11-2015). The role 
and scope of activities for the CHPAC differs from those of the 
CASAC, which is the independent scientific review committee 
fulfilling the function described in the CAA of reviewing the air 
quality criteria and the NAAQS for protection of public health and 
welfare and making recommendations to the Administrator concerning 
revisions as may be appropriate (as described in section 109(d)(2) 
of the Act and summarized in section I.A above).
    \53\ In expressing this view, some commenters cited statements 
by various government agencies regarding their interpretation of 
children's blood Pb levels with regard to risk management decisions 
based on consideration of the available information in those risk 
management contexts (e.g., CDC, 2005; Cal EPA, 2007; NYDHMH, 2010). 
The scientific information on health effects of Pb considered by 
these agencies was also available and, to the extent relevant to 
consideration of the adequacy of the NAAQS, was assessed in the 
current and, in some cases, also the prior review. As discussed 
below, the conclusion that a threshold level for neurocognitive 
effects has not been identified was a consideration of the EPA in 
the last review, and the current one.
---------------------------------------------------------------------------

    The four commenters that supported revision of the standard 
suggested a wide array of alternatives. The CHPAC repeated the view it 
expressed in the 2008 review that the standard should be revised to the 
most stringent alternative analyzed in the 2007 REA (a potential 
standard with an averaging time of one month and a level of 0.02 
[micro]g/m\3\). One individual commenter expressed a preference for a 
standard level of 0.0005 [micro]g/m\3\. Another individual commenter 
urged revision to the lowest feasible standard, and the smelting 
company recommended that EPA adopt an approach similar to a local air 
quality management district's emissions standards regulation \54\ that 
requires air monitoring at large Pb acid battery recycling metal 
melting facilities to meet, by a future date, a 30-day average Pb 
concentration of 0.1 [micro]g/m\3\, which the company indicated its 
technology can address.
---------------------------------------------------------------------------

    \54\ This commenter referred to a March 2015 amendment of a 
California South Coast Air Quality Management District rule on 
emission standards for lead and other toxic air contaminants from 
large lead-acid battery recycling facilities in that state air 
quality district.
---------------------------------------------------------------------------

    We agree with commenters that a threshold level for neurocognitive 
effects has not been identified in the current evidence, as stated in 
section II.A.2.c above, and described in more detail in the ISA. We 
additionally note that the lack of an established threshold of effects 
is not uncommon among the criteria pollutant evidence bases. For 
example, in past reviews of the primary standards for ozone and 
particulate matter, the EPA has 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 lack of a discernible threshold of exposure associated with 
health effects does not of itself provide support for revision of an 
existing standard or for revision to the most stringent standard one 
might identify. As recognized in section I.A above, the CAA does not 
require the Administrator to establish a primary national ambient air 
quality standard at a zero-risk level or at background concentrations 
(Lead Industries v. EPA, 647 F.2d at 1156 n.51; Mississippi v. EPA, 744 
F. 3d at 1351), but rather at a level that reduces risk sufficiently so 
as to protect public health with an adequate margin of safety, and the 
selection of any particular approach for 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; 
Mississippi, 744 F. 3d at 1353). The CAA requirement in establishing a 
standard is that it be set at a level of air quality that is requisite, 
meaning ``sufficient, but not more than necessary'' (Whitman v. 
American Trucking Ass'ns, 531 U.S. 457, 473 [2001]).
    In the setting of the current standard in 2008, a key consideration 
of the Administrator was the recognition of the lack of a discernible 
threshold level in the evidence with respect to neurocognitive effects 
associated with Pb exposure. This recognition, which differed from the 
scientific consensus at the time the previous standard was set in 1978, 
led the Administrator in 2008 to depart from the threshold-based 
approach used in setting the 1978 standard and to focus on 
consideration of air-related Pb in the context of the air-related IQ 
loss evidence-based framework (described in section II.A.1

[[Page 71929]]

above). In the current review of the 2008 standard, while recognizing 
the continued lack of a discernible threshold of exposure associated 
with neurocognitive effects, the CASAC commented regarding effects at 
very low Pb levels when expressing its view that the scientific 
evidence does not support revision to the Pb NAAQS. It stated that 
``[a]lthough there is evidence that even very low Pb levels are related 
to measurable reductions in IQ in children, the extent to which the 
blood Pb levels observed in children are linked to ambient air Pb 
levels below the current standard (as opposed to other sources of Pb in 
the environment) has not been established'' (Frey, 2013b, Consensus 
Response to Charge Questions, pp. 7-8).\55\
---------------------------------------------------------------------------

    \55\ The CASAC recognized the multimedia and legacy aspects of 
Pb that, unlike the case for other criteria air pollutants, 
complicate consideration of the risks of Pb concentrations in 
ambient air (Frey, 2013b, p. 1).
---------------------------------------------------------------------------

    The four submissions recommending a revised standard variously cite 
a number of studies as providing support for their view. Some of these 
studies have been reviewed in the ISA, some were published too late to 
be included in the ISA, and a few others were of a type that are not 
generally included in the ISA (e.g., review articles).\56\ As discussed 
in section I.C above, we have provisionally considered studies that 
were not in the ISA or in previous AQCDs (``new'' studies) \57\ which 
some of these commenters cite in statements about evidence of effects 
at low exposures and in the presence of other pollutants. We conclude 
that these studies are consistent with the scientific conclusions 
reached in the ISA, including those related to blood Pb levels in 
studies from which effects on IQ have been reported and related to co-
exposure with other metals. Taken in context, the information from 
these studies and these findings do not materially change any of the 
broad scientific conclusions of the ISA regarding the health effects 
and exposure pathways of Pb in ambient air on which the Administrator 
based her proposed conclusions as well as her final conclusions in this 
review, as described in section II.B.4 below. We additionally note that 
with regard to the inputs for the air-related IQ loss evidence-based 
framework, a key aspect of the Administrator's rationale for her 
proposed decision to retain the current primary standard (as described 
in section II.E.4 of the proposal), none of the cited studies indicate 
a steeper blood Pb-IQ slope or greater air-to-blood ratio than those 
assessed in the ISA and considered in the PA and the proposal.
---------------------------------------------------------------------------

    \56\ Some studies cited by commenters are review articles or 
government reviews (e.g., Henn et al., 2014; Grandjean and 
Landrigan, 2014; Jakubowski, 2011; NTP, 2011), which are not 
generally cited in the ISA because the ISA considers the original 
studies underlying a review article, rather than a review's 
interpretation of the studies. Further, in the case of government 
reviews, such reports generally review the literature for specific 
purposes of those government agencies (which differ from the focus 
for the ISA). Many of the scientific studies reviewed in these 
reports (as well as the other reviews), however, were considered 
relevant to review of the lead air quality criteria (based on the 
description of study selection for inclusion in the preamble to the 
ISA), and thus were assessed in this review.
    \57\ These studies are listed in a memorandum to the rulemaking 
docket (Kirrane, 2016).
---------------------------------------------------------------------------

    We respectfully disagree with the comment from CHPAC that studies 
available since the cut-off date for the ISA contradict the PA 
conclusions regarding blood Pb levels in children and effects on 
cognitive function measures, such as IQ.\58\ Of the studies cited in 
the comment that were published subsequent to the date for publication 
in the ISA, one is an analysis that relies on data from studies that 
were published prior to 2008 and assessed in the last review (Budtz-
Jorgensen et al., 2013). These data were the subject of the pooled 
analysis by Lanphear et al (2005) which we assessed in both the last 
and the current review. As such, this commenter-cited publication does 
not present a new study of children with lower blood Pb levels; rather, 
it reanalyzes existing data using a different approach for a different 
purpose.\59\ The other two of the commenter-cited publications are 
review articles that do not present information on specific blood Pb 
levels associated with IQ effects. Thus, we do not find these 
publications to be contrary to the discussion and associated 
conclusions in the PA or to indicate the current standard to be 
inadequate.
---------------------------------------------------------------------------

    \58\ The PA recognized the complexity associated with 
considering the evidence regarding exposure levels associated with 
health effects, and in particular effects on cognitive function 
measures, including IQ, which the evidence base indicates to be the 
most sensitive endpoint. The PA observed that the evidence available 
in this review is generally consistent with that available in the 
last review with regard to blood Pb levels in young children at 
which such effects have been reported. Noting that blood Pb levels 
are a reflection of exposure history, particularly in early 
childhood, the PA concludes by extension that the currently 
available evidence does not indicate Pb effects at exposure levels 
appreciably lower than recognized in the last review. In so doing, 
the PA continued to focus in this review (as in the last review) on 
the evidence of effects in young children for which our 
understanding of exposure history is less uncertain (PA, pp. 3-21 to 
3-26).
    \59\ This analysis uses the data from the same studies analyzed 
by Lanphear et al (2005) to extrapolate below the blood Pb 
concentrations measured in the studies and estimate a 95 percent 
lower confidence bound on the estimated blood Pb concentration 
associated with a 1 point decrement in IQ (Budtz-Jorgensen et al., 
2013). Unlike the prior study by Lanphear et al (2005) and similar 
epidemiological analyses of IQ and blood Pb, which are intended to 
produce a quantitative description of the change in IQ associated 
with blood Pb concentrations in the studied children, this analysis 
is focused on estimating a lower bound confidence limit on the 
incremental concentration in blood Pb, as compared to zero, 
associated with a single point IQ decrement. Even if we were to 
interpret the results of the Budtz-Jorgensen et al (2013) analysis 
as providing another estimate of C-R function for IQ decrement based 
on the pooled dataset from Lanphear et al (2005), we note that that 
dataset is already represented among the four low blood Pb analyses 
on which we focused in identifying a slope estimate for use with the 
air-related IQ loss evidence-based framework, and as noted in 
section II.B.3 of the proposal, revision or replacement of the 
estimate for the pooled dataset has no impact on conclusions drawn 
from the framework (80 FR 29295, January 5, 2015).
---------------------------------------------------------------------------

    We further disagree with the suggestion in the CHPAC submission 
that the evidence related to co-exposures to other pollutants, such as 
metals, provides a basis for concluding that the current standard is 
not requisite. The ISA assessment of the strength of the evidence for 
co-exposures to other pollutants, such as other metals, to contribute 
to increased risk of a Pb-related health effects concluded the evidence 
to be suggestive, ``but overall the evidence was limited'' (ISA, 
sections 1.9.6 and 5.4). With regard to the articles cited by the CHPAC 
that have been published subsequent to the ISA, the general conclusions 
of these review articles (Henn et al., 2014; Grandjean and Landrigan, 
2014) are consistent with conclusions of the ISA. As stated in the ISA, 
``interactions between Pb and co-exposure with other metals were 
evaluated in recent epidemiologic and toxicological studies of health 
effects'' and ``[h]igh levels of other metals, such as Cd and Mn, were 
observed to result in greater effects for the associations between Pb 
and various health endpoints but evidence was limited due to the small 
number of studies'' (ISA, p. 5-43). We note that even in raising co-
exposure as a concern, the comments recognize that the potential for 
such impacts is not well understood. Further, the comments do not 
explain how the limited information regarding this factor supports 
their conclusion that the current standard does not provide the 
requisite protection or leads to the specific revisions the comments 
suggest, and we find no such support in the current evidence.
    We additionally disagree with the comment that the currently 
available evidence indicates that the current standard is not 
protective of effects such as low birth weight. For example, the

[[Page 71930]]

CHPAC cites epidemiological studies reporting associations of maternal 
or cord blood Pb concentrations with reduced fetal growth (Xie et al., 
2013; Nishioka et al., 2014), stating that these studies strengthen the 
association of decreased birth weight and maternal blood Pb levels. 
Although we would agree that these studies present an addition to the 
evidence base overall, they do not provide a basis for change in the 
conclusion of the ISA, which states, ``Some well-conducted 
epidemiologic studies report associations of maternal Pb biomarkers or 
cord blood Pb with preterm birth and low birth weight/fetal growth; 
however, the epidemiologic evidence is inconsistent overall and 
findings from experimental animal studies are mixed'' (ISA, p. 1-18). 
In citing these studies, in fact, the CHPAC also stated its view that 
the findings of these studies are consistent with a larger study that 
was assessed in the ISA; it did not explain how these studies support 
its view that the current standard provides inadequate protection from 
such effects, and we find no such support.
    With regard to information related to Pb impacts in minority and 
low-income populations, which some comments suggested provided a basis 
for a more stringent standard, we note that we have considered the 
available information on such impacts, as recognized in section 
II.A.2.d above and summarized more fully in section II.B.4 of the 
proposal and in section 3.3 of the PA. As all of these documents have 
recognized, the ISA identifies non-white populations as at-risk 
populations, with this conclusion based primarily on findings of higher 
blood Pb levels in black compared to white populations (ISA, section 
5.4).\60\ Blood Pb levels have also been found to be higher in low SES 
groups as compared to higher SES \61\ (ISA, sections 5.3.6, 5.2.4 and 
5.4). However, as noted in the ISA, the number of studies examining the 
relationship of SES with Pb-related health effects is limited, and the 
results have differed with regard to finding increased risk with higher 
or lower SES (ISA, Table 5-1, p. 5-42). The comments generally identify 
impacts in minority and low income groups as a reason EPA should revise 
the standard, although they provide no explanation for how the 
currently available information leads to that conclusion or provides a 
basis for the alternative standards the comments suggest. \62\ While 
our assessment of the health effects evidence in this review concluded 
there was adequate evidence for race or ethnicity (and suggestive 
evidence for SES) to contribute to increased risk of Pb-related health 
effects, we do not find this information to call into question the 
adequacy of protection provided by the current primary standard. Nor 
did the CASAC find this to be the case, based on its review of the 
scientific materials in this review, including three drafts of the ISA 
in which the evidence for these factors was presented. Further, to the 
extent such differences may be related to exposure contributions from 
air Pb and proximity to air sources,\63\ we note that children that are 
exposed to air-related Pb in areas with elevated air Pb concentrations 
near or equal to the level of the standard are among those that were 
the focus of the 2008 decision, as recognized in sections II.A.1 and 
II.A.2.e above, and are the focus of the decision described in section 
II.B.4 below to retain the standard set in 2008.\64\
---------------------------------------------------------------------------

    \60\ Recent data suggest that differences in blood Pb levels 
between young black and white children is decreasing over time (ISA, 
section 5.2.3, 5.4). Although more recent data are not available by 
age group, the CDC data through 2011-2012 indicate little or no 
difference between non-Hispanic blacks, Mexican Americans or all 
Hispanics and non-Hispanic whites at the central tendencies of the 
populations and reduced differences at the 95th percentile (CDC, 
2015). Findings of some studies indicate that non-white populations 
may be at greater risk of Pb-related health effects although, as 
described in the ISA, this could be related to confounding by other 
factors (ISA, sections 5.3.7 and 5.4).
    \61\ As with differences among groups of different races and 
ethnicities, ``[t]he gap between SES groups with respect to Pb body 
burden appears to be diminishing,'' although blood Pb levels 
continue to be higher among lower-income children (ISA, p. 1-80, 
sections 1.9.6, 5.1, 5.2.1.1, 5.2.4 and 5.4), leading the ISA to 
conclude that the evidence is suggestive of SES as a risk factor for 
Pb-related health effects (as summarized in section II.A.2.d above).
    \62\ In making this statement, these commenters cite a 1988 
study on blood Pb and early childhood scores on the BSID MDI infant 
cognitive development test (Bellinger et al., 1988). The study found 
that 18 and 24 month BSID MDI scores of the ``lower'' SES children 
were adversely affected at lower cord blood Pb levels than were 
scores of the ``higher'' SES children, finding significantly lower 
scores of the lower SES children with cord blood Pb levels of 6-7 
[micro]g/dL as compared to children of this SES group with cord 
blood Pb levels less than 3 [micro]g/dL (Bellinger et al., 1988; 
USEPA, 1990a; USEPA, 2006). As the study cohort was mostly middle to 
upper-middle class, the ``lower'' SES group ``refers to [families of 
SES] less than the highest SES levels and is probably in fact [of 
SES levels] much closer to the median of the U.S. population than 
the term suggests'' (USEPA, 1990a, p. 53). The ISA considered these 
study findings in the context of considering available evidence on 
this issue in the current review (ISA, section 5.3.6; Bellinger et 
al., 1990). The ISA found that the available study results are 
limited, have differed with regard to finding increased risk with 
higher or lower SES and that ``they do not clearly indicate whether 
groups with different socioeconomic status differ in Pb-related 
changes for cognitive function'' (ISA, p. 5-34, Table 5-1, p. 5-42).
    \63\ As noted in section I.D above and described in more detail 
in the PA and ISA, sources of Pb to which children are exposed also 
include consumer goods, dust or chips of peeling Pb-containing paint 
and ingestion of Pb in drinking water conveyed through Pb pipes, as 
well as historically deposited Pb in urban soils (ISA, pp. pp. lxxix 
to lxxx).
    \64\ Additionally, the focus of the air-related IQ loss 
evidence-based framework on C-R functions observed for children with 
low blood Pb levels closer to those observed in U.S. children today 
reflects evidence-based conclusions from the last review, affirmed 
in this review, of a steeper slope for the C-R relationship at lower 
as compared to higher blood Pb levels. As noted in section II.A.2.d 
above, while children with higher blood Pb levels are at greater 
risk of Pb-related effects than children with lower blood Pb levels, 
on an incremental basis (e.g., per [micro]g/dL) the risk is greater 
for children at lower blood Pb levels. The 2008 revision of the 
primary Pb standard focused on the incremental impact of air-related 
Pb on young children and in so doing, recognized the greater 
incremental impact for those children with lower absolute blood Pb 
levels. Accordingly, the decision focused on those C-R studies 
involving the lowest blood Pb levels (as summarized in II.A.1 
above). Although the comment did not indicate how information that 
some groups may be generally more highly exposed to Pb should be 
used, we note that for the Administrator to rely on C-R functions 
from analyses for higher blood Pb study groups (with a less steep 
slope) would lead to consideration of a higher standard level, and 
would not provide the desired protection for the sensitive group of 
children with lower blood Pb levels that are exposed to air-related 
Pb in areas with air Pb concentrations at the level of the standard 
(73 FR 67002-07, November 12, 2008; 80 FR 311-313, January 5, 2015).
---------------------------------------------------------------------------

    With regard to consideration of the potential for risk reduction 
from lower air concentrations, the PA stated that ``the uncertainties 
and limitations associated with many aspects of the estimated 
relationships between air Pb concentrations and blood Pb levels and 
associated health effects are amplified with consideration of 
increasingly lower air concentrations'' (PA, p. 4-35). Contrary to the 
suggestion by the CHPAC and the smelter company, the PA did not 
conclude that there would be public health benefits from a lower 
standard and that such benefits were not large enough to warrant 
revising the standard. Rather, the PA notes that ``[a]s recognized at 
the time of the last review, exposure and risk modeling conducted for 
[the REA] was complex and subject to significant uncertainties'' (PA, 
p. 3-67) and recognizes ``increasing uncertainty of risk estimates'' 
for air Pb concentrations below those associated with the current 
standard (PA, p. 4-35). The PA further stated that that ``there is 
appreciable uncertainty associated with drawing conclusions regarding 
whether there would be reductions in blood Pb levels and risk to public 
health from alternative lower levels of the standard as compared to the 
level of the current standard'' (PA, pp. 4-35 to 4-36). The CASAC 
stated that it agreed with this conclusion regarding ``[t]he obvious 
uncertainty'' articulated in the PA, additionally stating, as noted 
above, that ``[a]lthough there is evidence that even

[[Page 71931]]

very low Pb levels are related to measurable reductions in IQ in 
children, the extent to which the blood Pb levels observed in children 
are linked to ambient air Pb levels below the current standard (as 
opposed to other sources of Pb in the environment) has not been 
established'' and, accordingly (as noted below), that the current 
information does not provide support for lowering the primary standard 
(Frey, 2013b, Consensus Response to Charge Questions, pp. 6-8). These 
conclusions from the CASAC and the PA findings were among the 
considerations that led to the Administrator's proposed decision 
(summarized in section II.B.1 above) and her final decision in this 
review, as described in section II.B.4 below, that, based on the 
current scientific information, including information regarding at-risk 
populations, as well as uncertainties and limitations associated with 
the current information, the current primary standard provides the 
requisite protection of public health with an adequate margin of 
safety, including the health of at-risk populations.
    The comment regarding a potential for increases in air Pb near 
sources of Pb emissions if the standard is not revised does not explain 
how such a potential provides support for revising the standard. The 
comment also suggests that EPA consider two alternative standard levels 
well below the current standard level while providing no explanation of 
why a revised standard with either of the suggested levels would be 
requisite. With regard to the potential for increases in air Pb near 
sources of Pb emissions if the standard is not revised, we note that 
such a concern, to the extent it applies to the current standard, would 
also pertain to any more stringent Pb standard except in the extreme 
case in which the standard is set such that there is no location with 
air quality conditions better than those that just meet the standard. 
As discussed in sections II.B.1 above and II.B.4 below, the 
Administrator has considered the current evidence and exposure/risk 
information with regard to the potential for a revised standard to 
offer additional protection, found there to be substantial uncertainty 
associated with such a potential, and concluded that the current 
standard is requisite. Regarding the possibility that air Pb 
concentrations could increase in some locations, we additionally note 
that the Clean Air Act and associated EPA permitting regulations 
restrict increases in air Pb concentrations (and in other pollutants 
for which there are NAAQS) in various circumstances, both in areas 
already meeting the NAAQS as well as those in nonattainment (e.g., New 
Source Review regulations at 40 CFR part 51, subpart I, applicable in 
attainment and nonattainment areas; General Conformity regulations at 
40 CFR 93.150-165, applicable in nonattainment and maintenance areas; 
and, the general anti-backsliding requirements under Section 110(l) of 
the Clean Air Act).
    Regarding the view expressed by some commenters that the most 
restrictive standard assessed in the 2007 REA should be adopted, \65\ 
or that the standard level should be revised to a concentration 
described in one comment as the average air Pb concentration in 
pristine locations, we note the greater uncertainty in risk estimates 
associated with air quality scenarios for air Pb concentrations 
increasingly below those of current conditions. Additionally, the PA 
described the ``increasing uncertainty recognized for air quality 
scenarios involving air Pb concentrations increasingly below the 
current conditions for each case study, recognizing that such 
uncertainty is due in part to modeling limitations deriving from 
uncertainty regarding relationships between ambient air Pb and outdoor 
soil/dust Pb and indoor dust Pb'' (PA, 4-34). Further, the PA 
concluded, and the CASAC agreed, that ``there is appreciable 
uncertainty associated with drawing conclusions regarding whether there 
would be reductions in blood Pb levels from alternative lower levels as 
compared to the level of the current standard' (Frey, 2013b, Consensus 
Response to Charge Questions, p. 6; PA, p.4-35 to 4-36). The CASAC 
further stated that ``there is not justification for modifying the 
current standard based on these data at this time'' (Frey, 2013b, 
Consensus Response to Charge Questions, p. 8). In reaching her proposed 
decision to retain the current standard, the Administrator took note of 
the PA conclusion and associated CASAC agreement and additionally 
recognized that ``the uncertainties and limitations associated with the 
many aspects of the estimated relationships between air Pb 
concentrations and blood Pb levels and associated health effects are 
amplified with consideration of increasingly lower air concentrations'' 
(80 FR 313). Finally, in the proposal, as in the final decision 
described in section II.B.3 below, the Administrator judges this 
uncertainty to be too great for the current evidence and exposure/risk 
information to provide a basis for revising the current standard. With 
regard to comments recommending consideration of technological 
feasibility in judging the requisiteness of the primary standard, we 
note, as we have described in section I.A above, the EPA may not 
consider technological feasibility or attainability in determining what 
standard is requisite to protect public health with an adequate margin 
of safety.
---------------------------------------------------------------------------

    \65\ The alternative more stringent primary standard suggested 
by the CHPAC was the most stringent assessed in the 2007 REA and 
included both a lower level and a shorter averaging time than those 
for the current standard. In establishing the current standard in 
2008, the EPA considered these suggestions regarding level and 
averaging time, which were also made by the CHPAC at that time. The 
EPA's considerations with regard to averaging time in establishing 
the current standard in 2008 are summarized in section II.E.1 of the 
proposal and section 4.1.1.2 of the PA. The comments from the CHPAC 
repeat its recommendation from the last review and do not provide 
any additional information or explanation in support of its view on 
a revised averaging time. The EPA response to substantive comments 
on averaging time in the last review from the CASAC and the public, 
including the CHPAC, is described in the notice of final decision 
(73 FR 66991-996, November 12, 2008).
---------------------------------------------------------------------------

    Comments on topics less directly related to consideration of the 
primary standard included recommendations for addressing data gaps and 
uncertainties to inform future reviews. Additionally, one comment 
focused on pathways by which Pb may be further distributed in the 
environment, recommending use of a ``more robust [monitoring] network 
to adequately estimate children's lead exposures from transient and 
other sources,'' emphasizing building demolition and Pb wheel weights. 
This comment also states that the PA overlooks the contribution from 
these and other sources and therefore may underestimate the number of 
children exposed to Pb from transient sources. Another comment 
described leaded aviation gasoline and airports as a source of Pb 
emissions but did not explain how such information was relevant to the 
Administrator's proposed decision that the current standard provided 
the requisite protection and should be retained without revision.
    With regard to the need for research, the PA highlighted key 
uncertainties associated with reviewing and establishing NAAQS for Pb 
and areas for future health-related research, model development, and 
data gathering. The topic areas of key uncertainties, research 
questions and data gaps that were highlighted in the PA with regard to 
review of the health-based primary standard overlap with many raised by 
commenters. We encourage research in these areas, although we note that 
research planning and priority setting are beyond the scope of this 
action.
    With regard to the monitoring network in place for Pb NAAQS

[[Page 71932]]

surveillance, the current regulations require air monitors in areas 
that are expected to or have been shown to experience or contribute to 
exceedance of the standards. As described in section I.E above, this 
includes requirements for monitors in areas with non-airport sources 
emitting 0.5 tpy or where an airport emits 1.0 or more tpy, based on 
either the most recent National Emissions Inventory or other 
scientifically justifiable methods and data (40 CFR part 58, appendix 
D, section 4.5). The establishment of the source-oriented monitoring 
requirement reflects our conclusion that monitoring should be 
presumptively required at sites near sources that have estimated Pb 
emissions in exceedance of a Pb ``emissions threshold'' (73 FR 67025). 
This monitoring requirement applies not only to existing industrial 
sources of Pb, but also to fugitive sources of Pb (e.g., mine tailing 
piles, closed industrial facilities) and airports where leaded aviation 
gasoline is used. Additionally, as noted in section I.E above, to 
account for other sources that may contribute to a maximum Pb 
concentration in ambient air in excess of the Pb NAAQS, the monitoring 
regulations also grant the EPA Regional Administrator the authority to 
require additional monitoring ``where the likelihood of Pb air quality 
violations is significant or where the emissions density, topography, 
or population locations are complex and varied'' (40 CFR part 58, 
appendix D, section 4.5(c)).
    In addition to this monitoring required for Pb NAAQS surveillance, 
state or local agencies may site additional monitors and there are also 
particulate matter monitoring networks that collect Pb data in specific 
particle size fractions in many urban areas (40 CFR part 58, appendix 
D, section 4.5). Further, as described in section I.E above,\66\ 
monitoring data collected at NCore sites in large population areas, in 
combination with the data for all other non-source-oriented sites, 
including those in urban areas, indicate air Pb concentrations well 
below the Pb NAAQS (as summarized in section I.E above). Accordingly, 
we believe that the current Pb monitoring requirements are consistent 
with the currently available information regarding sources of Pb to the 
ambient air and areas with the potential for exceedance of the Pb 
standards. Further, as described below, the information available 
regarding the transient sources mentioned by the commenters does not 
indicate the potential for such transient sources to result in 
exceedances of the NAAQS.
---------------------------------------------------------------------------

    \66\ The various air Pb monitoring networks are summarized in 
section I.E above and described in more detail in section 2.2.1 of 
the PA.
---------------------------------------------------------------------------

    As to the comment on the significance of building demolition or Pb 
wheel weights in contributing to environmental Pb exposure pathways, 
the ISA and PA considered the very limited available data pertaining to 
these issues. With regard to building demolition, for which the data 
are in terms of loading of dust containing Pb on alleys and sidewalks 
immediately following an event, the ISA concludes that the limited data 
``suggest that building demolition may be a short-term source of Pb in 
the environment,'' and that ``it is unclear if demolition is related to 
long-term Pb persistence in the environment'' (ISA, p. 2-21).\67\ 
Accordingly, we do not interpret the limited available information, 
which does not include measurements of air Pb concentrations, to 
indicate a potential for such occasional activities as demolition of 
buildings containing leaded paint to result in air Pb concentrations 
near or in exceedance of the NAAQS. \68\ With regard to the comment on 
lead wheel weights, we note that the commenter states they are unaware 
of studies that have assessed the impact of Pb wheel weights on 
childhood blood Pb levels, as are we. The ISA examined the very limited 
data on potential contribution of Pb wheel weights to Pb near roadways; 
these data yield widely varying and uncertain estimates of associated 
Pb releases (ISA, section 2.2.2.6). Contrary to the commenter's 
assertion that the PA overlooks these potential Pb exposure pathways, 
the assessment and consideration of policy-relevant information in the 
PA \69\ reflects these ISA findings based on consideration of the 
current information for these potential transient pathways. 
Specifically, the current information does not provide support for 
specific estimates of exposures associated with these pathways. 
Further, data for monitoring sites near roads find Pb concentrations 
well below the NAAQS (e.g., ISA, Figure 2-20). Thus, we conclude that 
the current information does not provide support for changes to the 
current Pb monitoring regulations with regard to roadways or occasional 
activities such as building demolition.
---------------------------------------------------------------------------

    \67\ Characterization of this activity by the study published 
subsequent to the ISA that was cited by the CHPAC (Jacobs et al., 
2013) is consistent with findings from the limited number of studies 
included in the ISA (ISA, p. 2-21).
    \68\ We note that airborne dust release from demolition of large 
buildings in some areas may be regulated under various state and/or 
local programs (e.g., demolition activities in some particulate 
matter non-attainment or maintenance areas may be subject to 
specific state implementation plan requirements on airborne dust 
releases).
    \69\ Consistent with the strength and specificity of information 
described in the ISA, the PA recognizes the loss of Pb wheel weights 
as an additional source of Pb emissions and notes the potential for 
previously deposited Pb to be resuspended into the air, without 
providing detailed consideration (PA, sections 2.1.2.2 and 2.1.2.4). 
Further, the input for air-to-blood ratio in the air-related IQ loss 
evidence-based framework, which the Administrator has used as a 
guide in her consideration of the adequacy of the current standard, 
does not restrict sources of Pb from consideration. Thus, such 
ratios, which are drawn from empirical studies, would be expected to 
reflect all sources contributing to children's blood Pb, including 
the transient sources identified by commenters to the extent they 
provide contributions (ISA, section 3.5; PA, section 3.1; 80 FR 298-
300, January 5, 2015; 73 FR 66973-66975,67004, November 12, 2008).
---------------------------------------------------------------------------

4. Administrator's Conclusions
    Having carefully considered the public comments, as discussed 
above, the Administrator believes that the fundamental scientific 
conclusions on the effects of Pb in ambient air reached in the ISA and 
PA, and summarized in sections II.B and II.C of the proposal, remain 
valid. Additionally, the Administrator believes the judgments she 
reached in the proposal (section II.E.4) with regard to consideration 
of the evidence and quantitative exposure/risk information remain 
appropriate. Thus, as described below, the Administrator concludes that 
the current primary standard provides the requisite protection of 
public health with an adequate margin of safety and should be retained.
    In considering the adequacy of the current primary Pb standard, the 
Administrator has carefully considered the current policy-relevant 
evidence and conclusions contained in the ISA; the evaluation of this 
evidence and the exposure/risk information, rationale and conclusions 
presented in the PA; the advice and recommendations from the CASAC; and 
public comments. In the discussion below, the Administrator gives 
weight to the PA conclusions, with which the CASAC has concurred, as 
summarized in section II of the proposal, and takes note of key aspects 
of the rationale for those conclusions that contribute to her decision 
in this review.
    As an initial matter, the Administrator recognizes the complexity 
involved in considering the adequacy of protection in the case of the 
primary Pb standard, which differs substantially from that involved in 
consideration of the health protection provided by the primary 
standards in other NAAQS reviews. For the pollutants in the other 
reviews, the more limited focus solely on the inhalation pathways of 
exposure is a relatively simpler context. Further, as

[[Page 71933]]

described in the PA and noted in section II.B.1 above, the influence of 
multimedia and historical exposure on the internal biomarkers in Pb 
epidemiological studies contrasts with the epidemiological studies 
considered for other NAAQS pollutants which focus on generally current 
concentrations of those pollutants in ambient air. While the use of an 
internal biomarker strengthens conclusions regarding Pb as the causal 
agent in associations observed in epidemiological studies, the 
persistence of Pb and the role of multimedia and historical exposures 
limit the conclusions that can be drawn regarding the particular 
exposure circumstances eliciting the reported effects. Thus, as we lack 
studies that can directly assess current concentrations of Pb in 
ambient air (including in locations where the current standard is met) 
and the occurrence of health effects, we primarily consider the 
evidence for, and risk estimated from, models, based upon key 
relationships, such as those among ambient air Pb, Pb exposure, blood 
Pb and health effects. This information base, both with its strong, 
long-established evidence of the health effects of Pb in young 
children, and the associated limitations and uncertainties mentioned 
here, contributes to our conclusions regarding relationships between 
ambient air Pb conditions under the current standard and health 
effects.
    The Administrator recognizes that in primary NAAQS reviews, our 
understanding of the relationships between the presence of a pollutant 
in ambient air and associated health effects is based on a broad body 
of information encompassing not only more established aspects of the 
evidence, but also aspects in which there may be substantial 
uncertainty. In the case of this review of the primary standard for Pb, 
she takes note of the increased uncertainty in characterizing the 
relationship of effects on IQ with blood Pb levels below those 
represented in the evidence base and in projecting the magnitude of 
blood Pb response to ambient air Pb concentrations at and below the 
level of the current standard. The PA recognizes this increased 
uncertainty, particularly in light of the multiple factors that play a 
role in such a projection (e.g., meteorology, atmospheric dispersion 
and deposition, human physiology and behavior), each of which carry 
attendant uncertainties. These aspects of the scientific evidence and 
analyses, and the associated uncertainties, collectively contribute to 
the Administrator's recognition that for Pb, as for other pollutants, 
the available health effects evidence and associated information 
generally reflect a continuum, consisting of levels at which scientists 
generally agree that health effects are likely to occur, through lower 
levels at which the likelihood and magnitude of the response become 
increasingly uncertain.
    With regard to the current evidence, as summarized in the PA and 
discussed in detail in the ISA, the Administrator takes note of the 
well-established body of evidence on the health effects of Pb, which 
has been augmented in some aspects since the last review and continues 
to support identification of neurocognitive effects in young children 
as the most sensitive endpoint associated with Pb exposure. For 
example, while the ISA continues to recognize cardiovascular effects in 
adults, in addition to neurodevelopmental effects in children, as being 
associated with the lowest blood Pb levels compared to other health 
effects (ISA, pp. xciii), the ISA also notes uncertainties regarding 
the timing, frequency, duration and level of Pb exposures contributing 
to the effects observed in adult epidemiologic studies and indicates 
that higher exposures in the past (rather than lower current exposures) 
may contribute to the development of health effects measured later in 
life (ISA, p. lxxxviii). Given the evidence-based identification of 
neurocognitive effects in young children as the most sensitive endpoint 
associated with Pb exposure, the Administrator has accordingly focused 
on nervous system effects in young children and particularly 
neurocognitive effects. In so doing, she finds that the evidence, while 
describing a broad array of health effects associated with Pb, 
continues to indicate that a standard that provides protection from 
neurocognitive effects in young children additionally provides 
protection from other health effects of Pb, such as those reported in 
adult populations.
    The Administrator takes note of the PA finding that application of 
the air-related IQ loss evidence-based framework, developed in the last 
review, continues to provide a useful approach for considering and 
integrating the evidence on relationships between Pb in ambient air and 
Pb in young children's blood and risks of neurocognitive effects (for 
which IQ loss is used as an indicator). In so doing, as in the 2008 
review, she notes that the framework, and the IQ loss estimates yielded 
by it for specific combinations of standard level, air-to-blood ratio 
and C-R function, does not provide an evidence- or risk-based bright 
line that indicates a single appropriate level for the standard. 
Further, the Administrator recognizes uncertainties associated with IQ 
estimates produced by the framework, noting the PA conclusion that the 
uncertainties increase with estimates associated with successively 
lower standard levels. She additionally takes note of the PA finding 
(described in section II.E.1 of the proposal) that the currently 
available evidence base, while somewhat expanded since the last review, 
is not appreciably expanded or supportive of appreciably different 
conclusions with regard to air-to-blood ratios or C-R functions for 
neurocognitive decrements in young children. The Administrator further 
notes the concurrence from the CASAC on both of these points and the 
lack of recommendations in public comments for a change to either of 
these inputs to the evidence-based framework. Thus, she judges the 
evidence base and related air-related IQ loss framework to be an 
appropriate tool for informing her decision on the adequacy of the 
current standard.
    In light of the continuum referenced above, the Administrator 
additionally recognizes in this review, as in the 2008 review, the role 
of judgment in reaching conclusions regarding Pb health effects that 
are important from a public health perspective. Most specifically, the 
Administrator has considered the public health significance of a 
decrement of a very small number of IQ points in the at-risk population 
of young children, in light of associated uncertainties. With regard to 
making a public health policy judgment as to the appropriate protection 
against risk of air-related IQ loss and related effects, the 
Administrator believes, as did the Administrator at the time of the 
last review, 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. She recognizes, however, that in the case of 
setting NAAQS, she is required to make a judgment as to what degree of 
protection is requisite (neither more nor less than necessary) to 
protect public health with an adequate margin of safety. As described 
in the proposal with regard to considering the public health 
significance of IQ loss estimates in young children, the Administrator 
gives weight to the comments of the CASAC and some public commenters in 
the last review which recognized a population mean IQ loss of 1 to 2 
points to be of public health significance and recommended that a very 
high

[[Page 71934]]

percentage of the U.S. population be protected from such a magnitude of 
IQ loss (73 FR 67000, November 12, 2008). She additionally notes that 
the CASAC did not provide a different goal in the present review. The 
Administrator additionally notes that the EPA is aware of no new 
information or new commonly accepted guidelines or criteria within the 
public health community for interpreting public health significance of 
neurocognitive effects in the context of a decision on adequacy of the 
current Pb standard (PA, pp. 4-33 to 4-34), and no new information has 
been identified by public commenters.
    With the objective identified by the CASAC in the 2008 review in 
mind, the Administrator recognizes, as was recognized at the time of 
the last review, that her judgment on the degree of protection against 
IQ impacts that should be afforded by the primary standard is 
particularly focused on consideration of impacts in the at-risk 
population and is not addressing a specific quantitative public health 
policy goal for air-related decrements in IQ that would be acceptable 
or unacceptable for the entire population of children in the U.S. As in 
the last review, the at-risk population to which she gives particular 
attention is the small subset of U.S. children living in close 
proximity to air Pb sources that contribute to elevated air Pb 
concentrations that equal the level of the standard). Accordingly, she 
is considering IQ impacts in this small subset of U.S. children that is 
expected to experience air-related Pb exposures at the high end of the 
national distribution of such exposures (as described in section II.E.4 
of the proposal and summarized in section II.B.1 above), and not a 
projection of the average air-related IQ loss for the entire U.S. 
population of children. The evidence-based framework estimates, with 
which there are associated uncertainties and limitations (as described 
in section II.A.1 above), relate to this small subset of children 
exposed at the level of the standard. Based on these considerations, 
the Administrator judges the conceptual evidence-based framework to 
continue to be appropriate for her consideration of the public health 
protection afforded by the current standard. Further, she concurs with 
the PA findings (summarized in section II.E.1 of the proposal and 
briefly outlined in II.B.1 above) that the current evidence, as 
considered within the conceptual and quantitative context of the 
evidence-based framework, and current air monitoring information 
indicate that the current standard would be expected to satisfy the 
public health policy goal recommended by the CASAC in the last Pb NAAQS 
review, from which it did not indicate a departure in the present 
review.
    In the context of the Administrator's use of the framework as a 
tool to inform her decision on the adequacy of the current standard, 
the EPA additionally notes that the maximum, not to be exceeded, form 
of the standard, in conjunction with the rolling 3-month averaging 
time, is expected to result in the at-risk population of children being 
exposed below the level of the standard most of the time (73 FR 67005, 
November 12, 2008). In light of this and the uncertainty in the 
relationship between time period of ambient level, exposure, and 
occurrence of a health effect, the air-related IQ loss considered for 
the current standard in applying the framework should not be 
interpreted to mean that a specific level of air-related IQ loss will 
occur in fact in areas where the standard is just met or that such a 
loss has been determined as acceptable if it were to occur. Instead, 
judgment regarding such an air-related IQ loss is one of the judgments 
that need to be made in using the evidence-based framework to provide 
useful guidance in the context of public health policy judgment on the 
degree of protection from risk to public health that is sufficient but 
not more than necessary, taking into consideration the patterns of air 
quality that would likely occur upon just meeting the standard and 
uncertainties in relating those patterns to exposures and effects.
    In drawing conclusions regarding adequacy of the current standard 
based on considering application of the evidence-based framework, the 
Administrator further recognizes the degree to which IQ loss estimates 
drawn from the air-related IQ loss evidence-based framework reflect 
mean blood Pb levels that are below those represented in the currently 
available evidence for young children, as described in section II.B.4 
of the proposal. The Administrator views such an extension below the 
lowest studied levels to be reasonable given the lack of identified 
blood Pb level threshold in the current evidence base for 
neurocognitive effects and the need for the NAAQS to provide a margin 
of safety. She additionally takes note, however, of the PA finding that 
the framework IQ loss estimates for standard levels lower than the 
current standard level represent still greater extrapolations from the 
current evidence base with corresponding increased uncertainty (PA, 
section 3.2, pp. 4-32 to 4-33). The Administrator also gives weight to 
the PA conclusion of greater uncertainty with regard to relationships 
between concentrations of Pb in ambient air and air-related Pb in 
children's blood, and with regard to estimates of the slope of the C-R 
function of neurocognitive impacts (IQ loss) for application of the 
framework to levels below the current standard, given the weaker 
linkage with existing evidence as discussed in the PA (PA, sections 
3.1, 3.2 and 4.2.1). Thus, consistent with the conceptual continuum 
referenced above, the Administrator recognizes the increasing 
uncertainty with regard to likelihood of response and magnitude of the 
estimates at levels extending below the current standard.
    With respect to exposure/risk-based considerations, as in the last 
review, the Administrator notes the complexity of the REA modeling 
analyses and the associated limitations and uncertainties. Based on 
consideration of the risk-related information for conditions just 
meeting the current standard, the Administrator takes note of the 
attendant uncertainties, discussed in detail in the PA (PA, sections 
3.4 and 4.2.2), while finding that the quantitative risk estimates, 
with a focus on those for the generalized (local) urban case study, are 
roughly consistent with and generally supportive of estimates from the 
air-related IQ loss evidence-based framework. She further takes note of 
the PA finding of increasing uncertainty for air quality scenarios 
involving air Pb concentrations increasingly below the current 
conditions for each case study, due in part to modeling limitations 
that derive from uncertainty regarding relationships between ambient 
air Pb and outdoor soil/dust Pb and indoor dust Pb (PA, sections 
3.4.3.1 and 3.4.7).
    Based on the above evidence- and exposure/risk-based considerations 
and with consideration of advice from CASAC and public comment, the 
Administrator concludes that the current standard provides protection 
for young children from neurocognitive impacts, including IQ loss, that 
is consistent with advice from CASAC regarding IQ loss of public health 
significance. Based on consideration of the evidence and exposure/risk 
information available in this review with its attendant uncertainties 
and limitations, and information that might inform public health policy 
judgments, as well as advice from CASAC, including its concurrence with 
the PA conclusions that revision of the primary Pb standard is not 
warranted at this time, the Administrator further concludes that it is 
appropriate to retain

[[Page 71935]]

the current standard without revision. The Administrator bases these 
conclusions on consideration of the health effects evidence, including 
consideration of this evidence in the context of the air-related IQ 
loss evidence-based framework, and with support from the exposure/risk 
information, recognizing the uncertainties attendant with both. In so 
doing, she takes note of the PA description of the complexities and 
limitations in the evidence base associated with reaching conclusions 
regarding the magnitude of risk associated with the current standard, 
as well as the increasing uncertainty of risk estimates for lower air 
Pb concentrations. Inherent in the Administrator's conclusions are 
public health policy judgments on the public health implications of the 
blood Pb levels and risk estimated for air-related Pb under the current 
standard, including the public health significance of the Pb effects 
being considered, as well as aspects of the use of the evidence-based 
framework that may be considered to contribute to the margin of safety 
(as noted in section II.A.1 above and the 2008 decision preamble to the 
final rule, 73 FR 67007, November 12, 2008). These public health policy 
judgments include judgments related to the appropriate degree of public 
health protection that should be afforded to protect against risk of 
neurocognitive effects in at-risk populations, such as IQ loss in young 
children, as well as the appropriate weight to be given to differing 
aspects of the evidence and exposure/risk information, and how to 
consider their associated uncertainties. Based on these considerations 
and the judgments identified here, the Administrator concludes that the 
current standard provides the requisite protection of public health 
with an adequate margin of safety, including protection of at-risk 
populations, such as, in particular, young children living near Pb 
emissions sources where ambient concentrations just meet the standard.
    In reaching this conclusion with regard to the adequacy of public 
health protection afforded by the existing primary standard, the 
Administrator recognizes that in establishing primary standards under 
the Act that are requisite to protect public health with an adequate 
margin of safety, she is seeking 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, even if the risk is not precisely identified as to nature or 
degree. The CAA requirement that primary standards provide an adequate 
margin of safety was intended to address uncertainties associated with 
inconclusive scientific and technical information available at the time 
of standard setting, as described in section I.A above. This 
requirement was also intended to provide a reasonable degree of 
protection from hazards that research has not yet identified.
    In this context, the Administrator has considered conclusions drawn 
in the ISA and PA with regard to interpretation of the information 
concerning the broader array of health effects of Pb beyond those on 
the nervous system of young children. Based on the body of evidence in 
support of identification of neurocognitive effects in young children 
as the most sensitive endpoint associated with Pb exposure, as noted 
previously in this section and briefly summarized in section II.A.2 
above, she judges that a standard providing protection from such 
effects additionally provides adequate protection against the risk of 
other health effects and she further concludes that consideration of 
the more limited and less certain information concerning Pb exposures 
associated with such other effects does not lead her to identify a need 
for any greater protection.
    Further, the Administrator's conclusion that the current standard 
provides the requisite protection and that a more restrictive standard 
would not be requisite additionally recognizes that the uncertainties 
and limitations associated with the many aspects of the estimated 
relationships between air Pb concentrations and blood Pb levels and 
associated health effects are amplified with consideration of 
increasingly lower air concentrations. In reaching this conclusion, she 
additionally takes note of the PA conclusion, with which the CASAC has 
agreed, that based on the current evidence, there is appreciable 
uncertainty associated with drawing conclusions regarding whether there 
would be reductions in blood Pb levels and risk to public health from 
alternative lower levels of the standard as compared to the level of 
the current standard (PA, pp. 4-35 to 4-36; Frey, 2013b, Consensus 
Response to Charge Questions, p. 6). The Administrator judges this 
uncertainty to be too great for the current evidence and exposure/risk 
information to provide a basis for revising the current standard. Thus, 
based on the public health policy judgments described above, including 
the weight given to uncertainties in the evidence, the Administrator 
concludes that the current standard should be retained, without 
revision.

C. Decision on the Primary Standard

    For the reasons discussed above, and taking into account 
information and assessments presented in the ISA and PA, the advice 
from CASAC, and consideration of public comments, the Administrator 
concludes that the current primary standard for Pb is requisite to 
protect public health with an adequate margin of safety, including the 
health of at-risk populations, and is retaining the standard without 
revision.

III. Rationale for Decision on the Secondary Standard

    This section presents the rationale for the Administrator's 
decision to retain the existing secondary Pb standard, which, as 
discussed more fully below, is based on a thorough review in the ISA of 
the latest scientific information, generally published through 
September 2011, on welfare effects associated with Pb and pertaining to 
the presence of Pb in the ambient air. This decision also takes into 
account (1) the PA's staff assessments of the most policy-relevant 
information in the ISA and staff analyses of potential ecological 
exposures and risk, upon which staff conclusions regarding appropriate 
considerations in this review are based; (2) the CASAC advice and 
recommendations, as reflected in discussions of drafts of the ISA and 
PA at public meetings, in separate written comments, and in the CASAC's 
letters to the Administrator; (3) public comments received during the 
development of these documents, either in connection with CASAC 
meetings or separately; and (4) public comments on the proposal.
    Section III.A provides background on the general approach for the 
review of the secondary NAAQS for Pb and brief summaries of key aspects 
of the current body of evidence on welfare effects associated with Pb 
exposures and the exposure/risk information considered in this review. 
Section III.B summarizes the basis for the proposed decision and advice 
from the CASAC, addresses public comments and presents the conclusions 
the Administrator has drawn from a full consideration of the 
information. Section III.C summarizes the Administrator's decision on 
the secondary standard.

A. Introduction

    As provided in the Act, the secondary standard is to ``specify a 
level of air quality the attainment and maintenance of which in the 
judgment of the

[[Page 71936]]

Administrator . . . 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'' (CAA, section 109(b)(2)). The 
secondary standard is not meant to protect against all known or 
anticipated Pb-related effects, but rather those that are judged to be 
adverse to the public welfare, and a bright-line determination of 
adversity is not required in judging what is requisite (78 FR 3212, 
January 15, 2013; 80 FR 65376, October 26, 2015). Thus, the level of 
protection from known or anticipated adverse effects to public welfare 
that is requisite for the secondary standard is a public welfare policy 
judgment to be made by the Administrator. In exercising that judgment, 
the Administrator seeks to establish standards that are neither more 
nor less stringent than necessary for this purpose. This section 
presents the rationale for the Administrator's decision to retain the 
existing secondary NAAQS for Pb, without revision. The Administrator's 
decision draws upon scientific information and analyses about welfare 
effects, exposure and risks, as well as judgments about the range of 
uncertainties that are inherent in the scientific evidence and 
analyses. This approach is consistent with the requirements of the 
NAAQS provisions of the Act.
    In the last review, completed in 2008, the current secondary 
standard for Pb was revised substantially, consistent with the revision 
to the primary standard (73 FR 66964, November 12, 2008). The 2008 
decision considered the body of evidence as assessed in the 2006 CD 
(USEPA, 2006a) as well as the 2007 Staff Paper assessment of the 
policy-relevant information contained in the 2006 CD and the screening-
level ecological risk assessment (2006 REA; USEPA, 2007b), the advice 
and recommendations of CASAC (Henderson 2007a, 2007b, 2008a, 2008b), 
and public comment. At that time, the Staff Paper concluded, based on 
laboratory studies and current media concentrations in a wide range of 
locations, that it seemed likely that adverse effects were occurring 
from ambient air-related Pb, particularly near point sources, under the 
then-current standard (73 FR 67010, November 12, 2008). Given the 
limited data on Pb effects in ecosystems, and associated uncertainties, 
such as those with regard to factors such as the presence of multiple 
metals and historic environmental burdens, the EPA also considered the 
evidence of Pb effects on organisms with regard to implications for 
ecosystem effects. Taking into account the available evidence and 
information on media concentrations in a wide range of locations, the 
Administrator concluded that there was potential for adverse effects 
occurring under the then-current standard; however there were 
insufficient data to provide a quantitative basis for setting a 
secondary standard different from the primary (73 FR 67011, November 
12, 2008). Therefore, citing a general lack of data that would indicate 
the appropriate level of Pb in environmental media that may be 
associated with adverse effects, 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) was likely to have 
significant beneficial effects on the magnitude of Pb exposures in the 
environment, the EPA revised the secondary standard substantially, 
consistent with revisions made to the primary standard (73 FR 67011, 
November 12, 2008).
    Building on the approach and findings in the last review, this 
current review of the secondary standard considers the currently 
available scientific and technical information in the context of key 
policy-relevant questions. This review focuses on the consideration of 
the extent to which the body of scientific evidence now available calls 
into question the adequacy of the current standard. In considering the 
scientific and technical information, we draw on the ecological effects 
evidence presented in detail in the ISA and aspects summarized in the 
PA, along with the information associated with the screening-level risk 
assessment also in the PA. Thus, we have taken into account both 
evidence-based and risk-based considerations pertaining to the series 
of policy-relevant questions presented in the PA. These questions 
generally address the extent to which we are able to characterize 
effects and the likelihood of adverse effects in the environment under 
the current standard. Our approach to considering this information 
recognizes that the available welfare effects evidence generally 
reflects laboratory-based evidence of toxicological effects on specific 
organisms exposed to concentrations of Pb (ISA, section 6.5). 
Additionally, it is widely recognized that environmental exposures from 
atmospherically derived Pb are likely to be lower than those commonly 
assessed in laboratory studies and that studies of exposures similar to 
those in the environment are often accompanied by significant 
confounding and modifying factors (e.g., other metals, acidification), 
increasing our uncertainty about the likelihood and magnitude of 
organism and ecosystem responses (ISA, Section 6.5).
1. Overview of Welfare Effects Information
    Welfare effects 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 wellbeing'' (CAA, section 302(h)). 
In this section, we provide an overview of the key aspects of the 
current evidence of Pb-related welfare effects that is assessed in the 
ISA and the 2006 CD, drawing from the summary of policy-relevant 
aspects in the PA (PA, section 5.1) and section III.B of the proposed 
rulemaking (80 FR 314-317, January 5, 2015).
    Lead has been demonstrated to have harmful effects on reproduction 
and development, growth, and survival in many species as described in 
the assessment of the evidence available in this review and consistent 
with the conclusions drawn in the last review (ISA, section 1.7; 2006 
CD, sections 7.1.5 and 7.2.5). A number of studies on ecological 
effects of Pb are newly available in this review and are critically 
assessed in the ISA as part of the full body of evidence. The full body 
of currently available evidence reaffirms conclusions on the array of 
effects recognized for Pb in the last review (ISA, section 1.7). In so 
doing, in the context of pollutant exposures considered relevant the 
ISA determines \70\ that causal \71\ or likely causal \72\ 
relationships exist at the individual and population level in both

[[Page 71937]]

freshwater and terrestrial ecosystems for Pb with effects on 
reproduction and development in vertebrates and invertebrates; growth 
in plants and invertebrates; and survival in vertebrates and 
invertebrates (ISA, Table 1-3). With regard to saltwater ecosystems, 
the ISA concludes that the current evidence is inadequate to make 
causality determinations for most effects, while finding the evidence 
to be suggestive of a linkage between Pb and effects on reproduction 
and development in marine invertebrates (ISA, Table 1-3, sections 
6.3.12 and 6.4.21). In drawing judgments regarding causality for the 
criteria air pollutants, the ISA places emphasis on ``evidence of 
effects at doses (e.g., blood Pb concentration) or exposures (e.g., air 
concentrations) that are relevant to, or somewhat above, those 
currently experienced by the population.'' The ISA notes that the 
``extent to which studies of higher concentrations are considered 
varies . . . but generally includes those with doses or exposures in 
the range of one to two orders of magnitude above current or ambient 
conditions.'' Studies ``that use higher doses or exposures may also be 
considered . . . [t]hus, a causality determination is based on weight 
of evidence evaluation for health, ecological or welfare effects, 
focusing on the evidence from exposures or doses generally ranging from 
current levels to one or two orders of magnitude above current levels'' 
(ISA, pp. lx to lxi). Although considerable uncertainties are 
recognized in generalizing effects observed under particular, small-
scale conditions, up to the ecosystem level of biological organization, 
the ISA also determines that a causal relationship is also likely at 
higher levels of biological organization between Pb exposures and 
community and ecosystem-level effects in freshwater and terrestrial 
systems (ISA, section 1.7.3.7).
---------------------------------------------------------------------------

    \70\ Since the last Pb NAAQS review, the ISAs, which have 
replaced CDs in documenting each review of the scientific evidence 
(or air quality criteria), employ a systematic framework for 
weighing the evidence and describing associated conclusions with 
regard to causality, using established descriptors: ``causal'' 
relationship with relevant exposure, ``likely'' to be a causal 
relationship, evidence is ``suggestive'' of a causal relationship, 
``inadequate'' evidence to infer a causal relationship, and ``not 
likely'' to be a causal relationship (ISA, Preamble).
    \71\ In determining that a causal relationship exists for Pb 
with specific ecological or welfare effects, the EPA has concluded 
that ``[e]vidence is sufficient to conclude that there is a causal 
relationship with relevant pollutant exposures (i.e., doses or 
exposures generally within one to two orders of magnitude of current 
levels)'' (ISA, p. lxii).
    \72\ In determining a likely causal relationship exists for Pb 
with specific ecological or welfare effects, the EPA has concluded 
that ``[e]vidence is sufficient to conclude that there is a likely 
causal association with relevant pollutant exposures . . . but 
uncertainties remain'' (ISA, p. lxii).
---------------------------------------------------------------------------

    As in prior reviews of the Pb NAAQS, this review is focused on 
those effects most pertinent to ambient air Pb exposures. Given the 
reductions in ambient air Pb concentrations over the past decades, 
these effects are generally those associated with the lowest levels of 
Pb exposure that have been evaluated. Additionally, we recognize the 
limitations on our ability to draw conclusions about environmental 
exposures from ecological studies of organism-level effects, as most 
studies were conducted in laboratory settings which may not accurately 
represent field conditions or the multiple variables that govern 
exposure.
    The relationship between ambient air Pb and ecosystem response is 
important in making the connection between current emissions of Pb and 
the potential for adverse ecological effects. The limitations in the 
data available on this subject for the last review were significant. 
There is no new evidence since the last review that substantially 
improves our understanding of the relationship between ambient air Pb 
and measurable ecological effects. As stated in the last review, the 
role of ambient air Pb in contributing to ecosystem Pb has been 
declining over the past several decades. It remains difficult to 
apportion exposure between air and other sources to inform our 
understanding of the potential for ecosystem effects that might be 
associated with air emissions (ISA, section 6.4). Further, considerable 
uncertainties also remain in drawing conclusions from effects evidence 
observed under laboratory conditions with regard to effects expected at 
the ecosystem level in the environment (ISA, section 6.5). In summary, 
the ISA concludes that ``[r]ecent information available since the 2006 
Pb AQCD, includes additional field studies in both terrestrial and 
aquatic ecosystems, but the connection between air concentration and 
ecosystem exposure continues to be poorly characterized for Pb and the 
contribution of atmospheric Pb to specific sites is not clear'' (ISA, 
section 6.5).
    The bioavailability of Pb is also an important component of 
understanding the effects Pb is likely to have on organisms and 
ecosystems (ISA, section 6.3.3, 6.4.4 and 6.4.14). It is the amount of 
Pb that can interact within the organism that can lead to toxicity, and 
there are many factors which govern this interaction (ISA, sections 
6.2.1 and 6.3.3). The bioavailability of metals varies widely depending 
on the physical, chemical, and biological conditions under which an 
organism is exposed (ISA, section 6.3.3). Studies newly available since 
the last Pb NAAQS review provide additional insight into factors that 
influence the bioavailability of Pb to specific organisms (ISA, section 
6.3.3). On the whole, the current evidence, including that newly 
available in this review, supports previous conclusions regarding 
environmental conditions affecting bioavailability and the associated 
potential for adverse effects of Pb on organisms and ecosystems (ISA, 
section 6.3.3). Looking beyond organism-level evidence, the evidence of 
adversity in natural systems remains sparse due to the difficulty in 
determining the effects of confounding factors such as co-occurring 
metals or system characteristics that influence bioavailability of Pb 
in field studies. As summarized in the ISA, ``in natural environments, 
modifying factors affect Pb bioavailability and toxicity and there are 
considerable uncertainties associated with generalizing effects 
observed in controlled studies to effects at higher levels of 
biological organization'' and ``[f]urthermore, available studies on 
community and ecosystem-level effects are usually from contaminated 
areas where Pb concentrations are much higher than typically 
encountered in the environment'' (ISA, p. xcvi).
    There is no new evidence since the last review that substantially 
improves our understanding of the relationship between ambient air Pb 
and measurable ecological effects beyond what was understood in the 
last review. As stated in the last review, the role of ambient air Pb 
in contributing to ecosystem Pb has been declining over the past 
several decades. It remains difficult to apportion exposure between air 
and other sources to better inform our understanding of the potential 
for ecosystem effects that might be associated with air emissions. As 
noted in the ISA, ``[t]he amount of Pb in ecosystems is a result of a 
number of inputs and it is not currently possible to determine the 
contribution of atmospherically-derived Pb from total Pb in 
terrestrial, freshwater or saltwater systems'' (ISA, section 6.5). 
Further, considerable uncertainties also remain in drawing conclusions 
from evidence of effects observed under laboratory conditions with 
regard to effects expected at the ecosystem level in the environment. 
In many cases it is difficult to characterize the nature and magnitude 
of effects and to quantify relationships between ambient concentrations 
of Pb and ecosystem response due to the existence of multiple 
stressors, variability in field conditions, and differences in Pb 
bioavailability at that level of organization (ISA, section 6.5). In 
summary, the ISA concludes that ``[r]ecent information available since 
the 2006 Pb AQCD, includes additional field studies in both terrestrial 
and aquatic ecosystems, but the connection between air concentration 
and ecosystem exposure continues to be poorly characterized for Pb and 
the contribution of atmospheric Pb to specific sites is not clear'' 
(ISA, section 6.5).
2. Overview of Risk Assessment Information
    The risk assessment information available in this review and 
summarized

[[Page 71938]]

here is based on the screening-level risk assessment performed for the 
last review, described in the 2006 REA, 2007 Staff Paper and 2008 
notice of final decision (73 FR 66964, November 12, 2008), as 
considered in the context of the evidence newly available in this 
review (PA, section 5.2). Careful consideration of the information 
newly available in this review, with regard to designing and 
implementing a full REA for this review, led us to conclude that 
performance of a new REA for this review was not warranted (REA 
Planning Document, section 3.3). The CASAC Pb Review Panel generally 
concurred with the conclusion that a new REA was not warranted for the 
secondary standard in this review (Frey, 2011b). Accordingly, the 
exposure/risk information considered in this review is drawn primarily 
from the 2006 REA as summarized in the PA, section 5.2 and Appendix 5A; 
REA Planning Document, section 3.1.
    The 2006 screening-level assessment focused on estimating the 
potential for ecological risks associated with ecosystem exposures to 
Pb emitted into ambient air (PA, section 5.2; 2006 REA, section 7). 
Both a national-scale screen and a case study approach were used to 
evaluate the potential for ecological impacts that might be associated 
with atmospheric deposition of Pb (2006 REA, section 7.1.2). Detailed 
descriptions of the location-specific case studies and the national 
screening assessment, key findings of the risk assessment for each, and 
an interpretation of the results with regard to past air quality 
conditions are presented in the 2006 REA. This information, which is 
outlined below, is summarized more fully in section 5.2 of the PA and 
section III.C of the proposal for this review (80 FR 317-319, January 
5, 2015).
    In interpreting the results from the 2006 REA, the PA considers the 
availability of new evidence that may inform interpretation of risk 
under the now-current standard (PA, section 5.2). Factors that could 
alter our interpretation of risk would include new evidence of harm at 
lower concentrations of Pb, new linkages that enable us to draw more 
explicit conclusions as to the air contribution of environmental 
exposures, and new methods of interpreting confounding factors that 
were largely uncontrolled in the previous risk assessment. In general, 
however, such new evidence is limited, and the key uncertainties 
identified in the last review remain today. For example, with regard to 
new evidence of Pb effects at lower concentrations, it is necessary to 
consider that the evidence of adversity in natural systems due 
specifically to Pb is limited, in no small part because of the 
difficulty in determining the effects of confounding factors such as 
multiple metals and modifying factors influencing bioavailability in 
field studies, as noted in section III.A.1 above. Modeling of Pb-
related exposure and risk to ecological receptors is subject to a wide 
array of sources of both variability and uncertainty resulting in 
differences in Pb bioavailability as well as exposure (USEPA, 2005b). 
Additionally, there are also significant difficulties in quantifying 
the role of air emissions under the current standard, which is 
significantly lower than the previous standard. As recognized in the 
PA, Pb deposited before the standard was enacted remains in soils and 
sediments, complicating interpretations regarding the impact of the 
current standard (PA, section 1.3.2). For example, media in ecosystems 
across the U.S. are still recovering from the past period of greater 
atmospheric emissions and deposition, as well as from Pb derived from 
nonair sources (PA, section 1.3.2).
    As summarized in the PA and proposal, we have considered what the 
risk information from the 2006 REA analyses indicates regarding the 
potential for adverse welfare effects to result from levels of air-
related Pb that would meet the now-current standard. The circumstances 
assessed in all but one of the case study locations, however, likely 
include a history of ambient air Pb concentrations that exceeded the 
NAAQS. Consequently, these analyses are not considered informative for 
predicting effects at the far lower concentrations associated with the 
current NAAQS. The nationwide surface water screen was likewise not 
particularly informative because potential confounding by both nonair 
inputs and resuspension of Pb related to historic sources was not 
easily accounted for. The remaining case study was a site remote from 
Pb sources for which atmospheric deposition was expected to be the 
primary contributor to media Pb concentrations without obvious 
confounding inputs. This case study, based on a summary review of 
published findings for the study site, concluded that atmospheric Pb 
inputs do not directly affect stream Pb levels because deposited Pb is 
almost entirely retained in the soil profile, with the soil serving as 
a Pb sink, appreciably reducing pore water Pb concentrations as it 
moves through the soil layers to streams. As a result, this case study 
(and the publications on which it was based) concluded that the 
contribution of dissolved Pb from soils to streams was insignificant 
(2006 REA, Appendix E). Additionally, we note that the 2006 CD, in 
considering the findings for this site and other terrestrial sites with 
Pb burdens derived primarily from long-range atmospheric transport, 
found that ``[d]espite years of elevated atmospheric Pb inputs and 
elevated concentrations in soils, there is little evidence that sites 
affected primarily by long-range Pb transport have experienced 
significant effects on ecosystem structure or function'' (2006 CD, p. 
AX7-98). The PA and proposal concluded that this information suggests 
that the now-lower ambient air concentrations associated with meeting 
the current standard would not be expected to directly impact stream Pb 
levels (PA, p. 6-10; 80 FR 319, January 5, 2015).

C. Conclusions on the Secondary Standard

1. Basis for the Proposed Decision
    The basis for the proposed decision, which is described in section 
III.D of the proposal, is very briefly summarized here. In considering 
the welfare effects evidence and risk-based information with respect to 
the adequacy of the current secondary standard, the Administrator 
considered the array of evidence newly assessed in the ISA with regard 
to the degree to which this evidence supports conclusions about the 
effects of Pb in the environment that were drawn in the last review and 
the extent to which it reduces previously recognized areas of 
uncertainty. Further, she considered the current evidence and 
associated conclusions about the potential for effects to occur as a 
result of the much lower ambient Pb concentrations allowed by the 
current secondary standard (set in 2008) than those allowed by the 
prior standard, which was the focus of the last review. These 
considerations informed the Administrator's proposed decision to retain 
the current standard.
    With regard to the evidence, the proposal noted there is very 
limited evidence to relate specific ecosystem effects with current 
ambient air concentrations of Pb through deposition to terrestrial and 
aquatic ecosystems and subsequent movement of deposited Pb through the 
environment (e.g., soil, sediment, water, organisms). The potential for 
ecosystem effects of Pb from atmospheric sources under conditions 
meeting the current standard is difficult to assess due to limitations 
on the availability of information to fully characterize the 
distribution of Pb from the atmosphere into ecosystems over the long 
term, as well as limitations

[[Page 71939]]

on information on the bioavailability of atmospherically deposited Pb 
(as affected by the specific characteristics of the receiving 
ecosystem). Therefore, while there are newly available field studies in 
this review, ``the connection between air concentration and ecosystem 
exposure and associated potential for welfare effects continues to be 
poorly characterized for Pb'' (ISA, section 6.4). Such a connection is 
even harder to characterize with respect to the current standard than 
it was in the last review with respect to the previous, much higher 
standard.
    With regard to the currently available risk and exposure 
information, which continues to be sufficient to conclude that the 1978 
standard was not providing adequate protection to ecosystems, the 
proposal concluded that, when considered with regard to air-related 
ecosystem exposures likely to occur with air Pb levels that just meet 
the now-current standard, this current information also does not 
provide evidence of adverse effects under the current standard. 
Accordingly, in consideration of the risk information in combination 
with the current evidence and the associated data gaps and 
uncertainties, the Administrator proposed that the current standards be 
retained, without revision.
2. CASAC Advice in This Review
    In its review of the draft PA, the CASAC agreed with staff's 
preliminary conclusions that the available information since the last 
review is not sufficient to warrant revision to the secondary standard 
(Frey, 2013b). On this subject, the CASAC letter said that ``[o]verall, 
the CASAC concurs with the EPA that the current scientific literature 
does not support a revision to the . . . Secondary Pb NAAQS'' (Frey, 
2013b, p. 1). It additionally stated that ``[g]iven the existing 
scientific data, the CASAC concurs with retaining the current secondary 
standard without revision'' (Frey, 2013b, p. 2). The CASAC additionally 
noted areas for additional research to address data gaps and 
uncertainties (Frey, 2013b, p. 2).
3. Comments on the Proposed Decision
    All of the public comments on the proposed decision to retain the 
current secondary standard, without revision, indicated support. These 
commenters include the NACAA, as well as both of the state agencies and 
nearly all of the industry organizations that submitted comments. Only 
a small subset of this group provided rationales for their concurrence 
with EPA's proposed decision. These commenters emphasized limitations 
and uncertainties in the welfare effects evidence, including 
particularly those with regard to relationships between ambient air Pb 
concentrations, levels of deposition, ecosystem exposures, and adverse 
public welfare effects. One commenter also noted the CASAC's 
concurrence with the EPA conclusion that the current evidence does not 
support revision to the standard, and that information newly available 
in this review does not substantially improve our understanding in the 
identified areas of uncertainty or that would indicate that the current 
standard is inadequate. The EPA generally agrees with these commenters 
and with the CASAC regarding the adequacy of the current secondary 
standard and the lack of support for revision of the standard.
4. Administrator's Conclusions
    Based on the evidence and risk assessment information that is 
available in this review concerning the ecological effects and 
potential public welfare impacts of Pb emitted into ambient air, the 
Administrator concludes that the current secondary standard provides 
the requisite protection of public welfare from adverse effects and 
should be retained. In considering the adequacy of the current 
standard, the Administrator has considered the assessment of the 
available evidence and conclusions contained in the ISA; the staff 
assessment of and conclusions regarding the policy-relevant technical 
information, including screening-level risk information, presented in 
the PA; the advice and recommendations from CASAC; and public comments. 
In reaching her decision, the Administrator gives weight to the PA 
conclusions, with which CASAC has concurred, and takes note of key 
aspects of the rationale presented for those conclusions which 
contribute to her decision.
    As she did in reaching her proposed decision, the Administrator 
notes that the body of evidence on the ecological effects of Pb, 
expanded in some aspects since the last review, continues to support 
identification of ecological effects in organisms relating to growth, 
reproduction, and survival as the most relevant endpoints associated 
with Pb exposure. In consideration of the appreciable influence of 
site-specific environmental characteristics on the bioavailability and 
toxicity of environmental Pb in our assessment, there is a lack of 
studies conducted under conditions closely reflecting the natural 
environment. The currently available evidence, while somewhat expanded 
since the last review, does not include evidence of significant effects 
at lower concentrations or evidence of higher-level ecosystem effects 
beyond those reported in the last review. There continue to be 
significant difficulties in relating effects evidence from laboratory 
studies to the natural environment and linking those effects to ambient 
air Pb concentrations. Further, as the proposal and the PA note, the 
EPA is aware of no new critical loads information that would inform our 
interpretation of the public welfare significance of the effects of Pb 
in various U.S. ecosystems (PA, section 5.1). In summary, while new 
research has added to the understanding of Pb biogeochemistry and 
expanded the list of organisms for which Pb effects have been 
described, there remains a significant lack of knowledge about the 
potential for adverse effects on public welfare from ambient air Pb in 
the environment and the exposures that occur from such air-derived Pb, 
particularly under conditions meeting the current standard (PA, section 
6.2.1). Thus, the scientific evidence presented in detail and assessed 
in the ISA, inclusive of that newly available in this review, is not 
substantively changed, most particularly with regard to the adequacy of 
the now-current standard, from the information that was previously 
available and supported the decision for revision in the last review 
(PA, section 6.2.1).
    With respect to exposure/risk-based considerations identified in 
the PA, the Administrator notes the complexity of interpreting the 
previous risk assessment with regard to the ecological risk of ambient 
air Pb associated with conditions meeting the current standard and the 
associated limitations and uncertainties of such assessments. The 
Administrator additionally takes note that the previous assessment is 
consistent with and generally supportive of the evidence-based 
conclusions about Pb in the environment, yet the limitations on our 
ability to apportion Pb between past and present air contributions and 
between air and nonair sources remain significant.
    In summary, based on the considerations summarized above, the 
Administrator judges that the information available in this review of 
the Pb secondary standard, including the currently available welfare 
effects evidence and exposure/risk information, does not call into 
question the adequacy of the current standard to provide the requisite 
protection for public welfare (PA, section 6.3). In so doing, she also 
notes the advice from CASAC in this review, including that ``[g]iven 
the existing scientific data, the CASAC concurs with retaining the 
current secondary standard without revision.''

[[Page 71940]]

Thus, the Administrator concludes that the current standard is 
requisite and should be retained.

C. Decision on the Secondary Standard

    For the reasons discussed above, and taking into account 
information and assessments presented in the ISA and PA, the advice 
from CASAC, and consideration of public comments, the Administrator 
concludes that the current secondary standard for Pb is requisite to 
protect public welfare from known or anticipated adverse effects and is 
retaining the standard without revision.

IV. Statutory and Executive Order Reviews

    Additional information about these statutes and Executive Orders 
can be found at http://www2.epa.gov/laws-regulations/laws-and-executive-orders.

A. Executive Order 12866: Regulatory Planning and Review and Executive 
Order 13563: Improving Regulation and Regulatory Review

    This action is not a significant regulatory action and was, 
therefore, not submitted to the Office of Management and Budget for 
review.

B. Paperwork Reduction Act (PRA)

    This action does not impose an information collection burden under 
the PRA. There are no information collection requirements directly 
associated with revisions to a NAAQS under section 109 of the CAA and 
this action does not make any revisions to the NAAQS.

C. Regulatory Flexibility Act (RFA)

    I certify that this action will not have a significant economic 
impact on a substantial number of small entities under the RFA. This 
action will not impose any requirements on small entities. Rather, this 
action retains, without revision, existing national standards for 
allowable concentrations of Pb in ambient air as required by section 
109 of the CAA. See also American Trucking Associations v. EPA. 175 
F.3d at 1044-45 (NAAQS do not have significant impacts upon small 
entities because NAAQS themselves impose no regulations upon small 
entities).

D. Unfunded Mandates Reform Act (UMRA)

    This action does not contain any unfunded mandate as described in 
the UMRA, 2 U.S.C. 1531-1538 and does not significantly or uniquely 
affect small governments. This action imposes no enforceable duty on 
any state, local or tribal governments or the private sector.

E. Executive Order 13132: Federalism

    This action 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.

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

    This action 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. This action does not change existing 
regulations; it retains the current NAAQS for Pb, without revision. The 
NAAQS protect public health, including the health of at-risk or 
sensitive groups, with an adequate margin of safety and protect public 
welfare from known or anticipated adverse effects. Executive Order 
13175 does not apply to this action.

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

    This action is not subject to Executive Order 13045 because it is 
not economically significant as defined in Executive Order 12866. We 
note, however, that the primary standard retained with this action 
provides protection for children and other at-risk populations against 
an array of adverse health effects, most notably including nervous 
system effects in children. The health effects evidence and risk 
assessment information for this action, which focuses on children, is 
summarized in sections II.A.2, II.A.3 and II.A.4, and described in the 
ISA and PA, copies of which are in the public docket for this action.

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

    This action is not subject to Executive Order 13211, because it is 
not a significant regulatory action under Executive Order 12866.

I. National Technology Transfer and Advancement Act

    This action does not involve technical standards.

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

    The EPA believes that this action does not have disproportionately 
high and adverse human health or environmental effects on minority 
populations, low-income populations and/or indigenous peoples as 
specified in Executive Order 12898 (59 FR 7629, February 16, 1994). The 
action described in this document is to retain, without revision, the 
existing NAAQS for Pb.
    The NAAQS decisions are based on an explicit and comprehensive 
assessment of the current scientific evidence and associated exposure/
risk analyses. More specifically, the EPA expressly considers the 
available information regarding health effects among at-risk 
populations, including that available for low-income populations and 
minority populations, in decisions on the primary (health-based) NAAQS. 
Where low-income populations or minority populations are among the at-
risk populations, the decision on the standard is based on providing 
protection for these and other at-risk populations and lifestages. 
Where such populations are not identified as at-risk populations, NAAQS 
that are established to provide protection to the at-risk populations 
would also be expected to provide protection to all other populations, 
including low-income populations and minority populations.
    As discussed in sections II.A.2.d and II.B above, and in sections 
II.A and II.B of the proposal, the EPA expressly considered the 
available information regarding health effects among at-risk 
populations in reaching the decision that the existing primary (health-
based) standard for Pb is requisite. The ISA and PA for this review, 
which include identification of populations at risk from Pb health 
effects, are available in the docket, EPA-HQ-OAR-2010-0108. Based on 
consideration of this information and the full evidence base, 
quantitative exposure/risk analyses, advice from the CASAC and 
consideration of public comments, the Administrator concludes that the 
existing NAAQS for Pb protect public health, including the health of 
at-risk or sensitive groups, with an adequate margin of safety and 
protect public welfare from known or anticipated adverse effects (as 
discussed in sections II.B.4 and III.B.4 above).

K. Determination Under Section 307(d)

    Section 307(d)(1)(V) of the CAA provides that the provisions of 
section

[[Page 71941]]

307(d) apply to ``such other actions as the Administrator may 
determine.'' Pursuant to section 307(d)(1)(V), the Administrator 
determines that this action is subject to the provisions of section 
307(d).

L. Congressional Review Act

    The EPA will submit a rule report to each House of the Congress and 
to the Comptroller General of the U.S. This action is not a ``major 
rule'' as defined by 5 U.S.C. 804(2).

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List of Subjects in 40 CFR Part 50

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

    Dated: September 16, 2016.
Gina McCarthy,
Administrator.
[FR Doc. 2016-23153 Filed 10-17-16; 8:45 am]
 BILLING CODE 6560-50-P