UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C. 20460

OFFICE OF THE ADMINISTRATOR

SCIENCE ADVISORY BOARD

June 4, 2013

EPA-CASAC-13-005

The Honorable Bob Perciasepe

Acting Administrator

U.S. Environmental Protection Agency

1200 Pennsylvania Avenue, N.W.

Washington, D.C. 20460

Subject: CASAC Review of the EPA’s Policy Assessment for the Review of the Lead National 

Ambient Air Quality Standards (External Review Draft – January 2013)

Dear Acting Administrator Perciasepe:

The Clean Air Scientific Advisory Committee (CASAC) Lead Review Panel met on February 5 - 6, 

2013, to peer review the EPA’s Policy Assessment for the Review of the Lead National Ambient Air 

Quality Standards (External Review Draft – January 2013), hereafter referred to as the PA. The 

CASAC’s consensus responses to the agency’s charge questions and the individual review comments 

from the CASAC Lead Review Panel are enclosed. The CASAC’s key points are highlighted below.

Overall, the CASAC concurs with the EPA that the current scientific literature does not support a 

revision to the Primary Lead (Pb) National Ambient Air Quality Standard (NAAQS) nor the Secondary 

Pb NAAQS. Although the current review incorporates a substantial body of new scientific literature, the 

new literature does not justify a revision to the standards because it does not significantly reduce 

substantial data gaps and uncertainties (e.g., air-blood Pb relationship at low levels; sources contributing 

to current population blood Pb levels, especially in children; the relationship between Pb and childhood 

neurocognitive function at current population exposure levels; the relationship between ambient air Pb 

and outdoor dust and surface soil Pb concentrations). Further details on these and other research needs 

are provided in the consensus responses. The CASAC recommends that research be performed to 

address these data gaps and uncertainties to inform future Pb NAAQS reviews.

The CASAC has additional comments and recommendations on improving the document. With the 

completion of the recommended revisions outlined below and in the consensus responses, the PA will 

serve its intended purpose. Another CASAC review of the document is not needed.

The PA should include a discussion that Pb is a unique pollutant in many ways. Unlike other criteria air 

pollutants, Pb is of concern from a multimedia perspective. Millions of tons of Pb are present in the 

environment from legacy sources. The distribution of this substantial reservoir of Pb is not known. Thus,

the extent of current human exposure from this legacy cannot be reliably estimated.

The PA generally captures the key aspects of the health effects evidence presented in the Integrated 

Science Assessment, but can be made more concise and clear by providing summary conclusions 
2

regarding the health effects evidence at the beginning of the sections. The risk and exposure information 

from the previous Pb NAAQS review is adequately presented. The CASAC concurs that a new risk and 

exposure assessment (REA) is not needed due the lack of sufficient new scientific information to 

warrant revision of the prior REA data and methods. 

The application of the evidence-based framework and the use of the health risk and exposure 

information from the previous Pb NAAQS review seem appropriate and provide a sufficient rationale to 

support retaining the current primary standard without revision. However, there should be more 

description in the PA of the data and rationale behind the averaging time and form of the current primary 

standard. Additionally, research is needed to address uncertainties and data gaps in the evidence-based 

framework and in the health risk and exposure information for future Pb NAAQS reviews.

Given the existing scientific data, the CASAC concurs with retaining the current secondary standard

without revision. However, the CASAC also notes that important research gaps remain. For example 

questions remain regarding the relevance of the primary standard’s indicator, level, averaging time, and 

form for the secondary standard. Other areas for additional research to address data gaps and uncertainty 

include developing a critical loads approach for U.S. conditions and a multi-media approach to account 

for legacy Pb and contributions from different sources. Addressing these gaps may require 

reconsideration of the secondary standard in future assessments. 

The CASAC also wishes to highlight the importance of a separate but related policy issue. The CASAC 

notes that it has not considered this separate policy issue in providing advice on the NAAQS. The 

decrease in childhood lead poisoning in the United States over the last three decades is a great public 

health success story. Concurrently, there is a trend of increased relocation of Pb production, recycling, 

and recovery to other nations. One example is the export of spent lead acid batteries (SLAB) to Mexico. 

As detailed in a report by the Secretariat of the Commission for Environmental Cooperation (CEC), 

environmental and health protections in the secondary lead industry in other countries are not 

functionally equivalent to those in the United States. The CEC offers recommendations to avoid 

development of pollution havens and for the United States to work with Mexico and Canada to foster 

adoption of best practices throughout North America. The CASAC recognizes the role of the EPA 

Administrator as a member of the CEC Council and strongly urges the EPA to carefully consider the 

recommendations of the CEC report, and to support decisive action that will enable the success of the Pb 

NAAQS in the United States to be a role model for development of best practices internationally that 

avoid adverse public health impacts abroad. For example, the considerable effort by the EPA to develop 

the ISA and the PA could be a valuable starting point for other countries to develop or revise their own 

ambient standards for lead.
3

The CASAC appreciates the opportunity to provide advice and looks forward to receiving the EPA’s 

response.

Sincerely,

/signed/

Dr. H. Christopher Frey, Chair

Clean Air Scientific Advisory Committee

Enclosures
i

NOTICE

This report has been written as part of the activities of the EPA's Clean Air Scientific Advisory 

Committee (CASAC), a federal advisory committee independently chartered to provide extramural 

scientific information and advice to the Administrator and other officials of the EPA. The CASAC 

provides balanced, expert assessment of scientific matters related to issues and problems facing the 

agency. This report has not been reviewed for approval by the agency and, hence, the contents of this 

report do not necessarily represent the views and policies of the EPA, nor of other agencies within the 

Executive Branch of the federal government. In addition, any mention of trade names or commercial 

products does not constitute a recommendation for use. The CASAC reports are posted on the EPA 

website at: http://www.epa.gov/casac.
ii

U.S. Environmental Protection Agency

Clean Air Scientific Advisory Committee

CASAC Lead Review Panel (2010-2013)

CHAIR

Dr. H. Christopher Frey, Distinguished University Professor, Department of Civil, Construction and 

Environmental Engineering, College of Engineering, North Carolina State University, Raleigh, NC

OTHER CASAC MEMBER

Mr. George A. Allen, Senior Scientist, Northeast States for Coordinated Air Use Management 

(NESCAUM), Boston, MA

CONSULTANTS

Dr. Herbert Allen, Professor Emeritus, Department of Civil and Environmental Engineering, 

University of Delaware, Newark, DE

Dr. Richard Canfield, Senior Research Associate, Division of Nutritional Sciences, Cornell University, 

Ithaca, NY

Dr. Deborah Cory-Slechta, Professor, Department of Environmental Medicine, School of Medicine 

and Dentistry, University of Rochester, Rochester, NY

Dr. Cliff Davidson, Professor, Civil and Environmental Engineering, Syracuse University, Syracuse, 

NY

Dr. Philip E. Goodrum, Senior Consultant, Cardno ENTRIX, Syracuse, NY

Dr. Sean Hays, President, Summit Toxicology, Allenspark, CO

Dr. Philip Hopke, Bayard D. Clarkson Distinguished Professor, Department of Chemical and 

Biomolecular Engineering, Clarkson University, Potsdam, NY

Dr. Chris Johnson, Professor, Department of Civil and Environmental Engineering , Syracuse 

University, Syracuse, NY

Dr. Susan Korrick, Assistant Professor of Medicine , Department of Medicine, Brigham and Women's 

Hospital, Channing Laboratory, Harvard Medical School, Boston, MA

Dr. Michael Kosnett, Associate Clinical Professor, Division of Clinical Pharmacology and Toxicology,

Department of Medicine, University of Colorado School of Medicine, Denver, CO
iii

Dr. Roman Lanno, Associate Professor and Associate Chair, Department of Evolution, Ecology, and 

Organismal Biology, Ohio State University, Columbus, OH

Mr. Richard L. Poirot, Environmental Analyst, Air Pollution Control Division, Department of 

Environmental Conservation, Vermont Agency of Natural Resources, Waterbury, VT

Dr. Joel G. Pounds, Laboratory Fellow, Cell Biology & Biochemistry, Biological Sciences Division, 

Pacific Northwest National Laboratory, Richland, WA

Dr. Michael Rabinowitz, Geochemist, Marine Biological Laboratory, Newport, RI

Dr. William Stubblefield, Senior Research Professor, Department of Molecular and Environmental 

Toxicology, Oregon State University, Corvallis, OR

Dr. Ian von Lindern, President, TerraGraphics Environmental Engineering, Inc., Moscow, ID

Dr. Gail Wasserman, Professor of Clinical Psychology in Child Psychiatry, Division of Child and 

Adolescent Psychiatry, College of Physicians and Surgeons, Columbia University, New York, NY

Dr. Michael Weitzman, Professor, Pediatrics; Psychiatry, New York University School of Medicine, 

New York, NY

SCIENCE ADVISORY BOARD STAFF

Mr. Aaron Yeow, Designated Federal Officer, U.S. Environmental Protection Agency, Science 

Advisory Board (1400R), 1200 Pennsylvania Avenue, NW, Washington, DC
iv

U.S. Environmental Protection Agency

Clean Air Scientific Advisory Committee

CASAC

CHAIR

Dr. H. Christopher Frey, Distinguished University Professor, Department of Civil, Construction and 

Environmental Engineering, College of Engineering, North Carolina State University, Raleigh, NC

MEMBERS

Mr. George A. Allen, Senior Scientist, Northeast States for Coordinated Air Use Management 

(NESCAUM), Boston, MA

Dr. Ana Diez-Roux, Professor of Epidemiology, School of Public Health, University of Michigan, Ann 

Arbor, MI

Dr. Jack Harkema, Professor, Department of Pathobiology, College of Veterinary Medicine, Michigan 

State University, East Lansing, MI

Dr. Helen Suh, Associate Professor, Bouve School of Health Sciences, Northeastern University, 

Boston, MA

Dr. Kathleen Weathers, Senior Scientist, Cary Institute of Ecosystem Studies, Millbrook, NY

Dr. Ronald Wyzga, Technical Executive, Air Quality Health and Risk, Electric Power Research 

Institute, Palo Alto, CA

SCIENCE ADVISORY BOARD STAFF

Dr. Holly Stallworth, Designated Federal Officer, U.S. Environmental Protection Agency, Science 

Advisory Board (1400R), 1200 Pennsylvania Avenue, NW, Washington, DC
1

Consensus Responses to Charge Questions on 

EPA’s Policy Assessment for the Review of the Lead National Ambient Air Quality Standards 

(External Review Draft – January 2013)

Chapter 1 – Introduction

This chapter provides context for the review, including the background of past reviews, as well as the 

scope for the current review. This includes discussion of fate and multimedia pathways of ambient air 

Pb and other nonair sources of Pb in the environment.

Does the Panel find the introductory and background material, including that pertaining to previous 

reviews of the Pb standard and the scope of the current review to be appropriately characterized and 

clearly communicated?

Chapter 1 of the Policy Assessment (PA) is reasonably well characterized and for the most part clearly 

communicated, although there are several improvements that should be made (see below). The CASAC

concurs with the EPA that the current scientific evidence does not justify a change to the current Lead 

(Pb) National Ambient Air Quality Standards (NAAQS), with the caveats stated below.

Chapter 1 should emphasize Pb as a unique pollutant in many ways. Historically, anthropogenic

emissions of Pb to the air around the globe exceeded natural emissions by a huge margin, more than any 

other trace metal. Natural emissions come from unpolluted soil, seaspray, and other natural sources. 

Removal of Pb from gasoline, paint, solder, and other anthropogenic sources constitutes what is 

arguably the biggest environmental success story for any pollutant to-date. Unlike other criteria air 

pollutants, Pb is of concern from a multimedia perspective; human exposure to Pb comes from 

inhalation of air and also from ingestion of food, water, and dust. In addition, Pb may be the pollutant 

with the biggest legacy problem: millions of tons of Pb are now present in the environment as a result of 

discharges from years ago. The distribution of this huge reservoir of Pb is not known, and thus current 

human exposure from this legacy cannot reliably be estimated. What is known, however, is that human 

activities have on average substantially elevated the Pb content of soil at numerous locations around the 

United States, more so than other trace metals processed in large quantities. Although air Pb levels are 

much lower because of reduced emissions, soil Pb can be expected to remain elevated for many years. 

These unique aspects of Pb, especially the problem of not knowing the distribution of legacy Pb, should 

be clearly discussed in the PA.

This chapter concludes that there is no information published in the last five years justifying 

reconsideration of the current NAAQS. Although that is true, this conclusion should be conveyed with 

an assessment of the adequacy of the old information. In particular, there were significant unknowns and 

uncertainties associated with a lack of information five years ago; those unknowns and uncertainties still 

remain.

There are no statements in the PA that the Integrated Science Assessment (ISA) is limited only to 

exposures and data sources considered currently relevant to the U.S. population, as opposed to 

populations outside of the United States. Furthermore, the literature is considered only to assess how 

new studies relate to conclusions drawn in the past review, and then only to studies in the peer-reviewed 

literature. This has resulted in an ISA that is dedicated predominately to toxicology, health effects, 
2

biokinetics, and causal determinations. These are areas that were data rich in the last review, and 

continue to produce volumes of new peer-reviewed information. In contrast, in areas where the least is 

known and EPA relies on past findings, uncertainty is becoming greater as the existing information 

becomes outdated. Additionally, the current assessment excludes consideration of impacts on 

populations outside of the United States. 

There is considerable discussion dedicated to the reduction of Pb in air and other media in the United 

States over the last four decades. Most of the reduction was achieved through the elimination of tetraethyl Pb gasoline additives. Another major component of the reduction was substantial decreases in 

emissions from primary and secondary smelters, and metals processing industries. In the case of motor 

vehicle gasoline-related emissions, these ceased and other non-Pb products were substituted in 

commerce. This resulted in decreased Pb emissions and health and environmental effects in both the 

United States and globally. Within the United States, Pb continues to be used as an octane boosting fuel 

additive for very high octane fuels used in general aviation for piston engine aircraft. In the case of Pb

production and secondary recovery, however, this production and recovery were exported overseas.

There is no mention of the impact of the “avoided emissions” in their new locales.

Thus, overall, there is no reason to change the current airborne Pb standard. However, although airborne 

Pb is far more limited as a problem within the United States, potential exposure to Pb in other 

environmental media in the United States is likely to be more significant. Furthermore, there may be 

increasing Pb exposures overseas (e.g., as described in CEC, 2013).

There are a few areas that need revision for clarity and accuracy. On page ES-1, line 25, the following 

sentence should be added to the end of the paragraph: “This approach was taken to aid in the decision to 

retain or revise the current standards.” On page 1-13 line 35, it states: “And we recognize that past Pb

emissions in many situations were well in excess of the current Pb standard.” One cannot compare 

emissions to an airborne standard. This sentence can be revised to state: “We recognize that past Pb

emissions in many situations caused airborne Pb concentrations far in excess of the current Pb standard.”

Chapter 2 – Ambient Air Lead

This chapter provides an overview of current information on air Pb emissions and monitoring data, 

consideration of the current air Pb monitoring requirements and an overview of current information on 

Pb in nonair media.

To what extent does the Panel agree that the most relevant information on emissions (section 2.1), air 

quality (section 2.2.2), and Pb concentrations in other media (section 2.3) is presented, and to what 

extent is the information presented appropriately characterized and clearly communicated?

With a few minor exceptions (see specific individual panel member comments), the information on Pb 

emissions, air quality and concentrations in other media is appropriately characterized and clearly 

presented. Historical and recent (2008) emissions data are summarized quantitatively in clear charts and 

tables, with additional detail on the 2008 National Emissions Inventory (NEI) data sources and 

limitations provided in Appendix 2A. There are also qualitative discussions and an informative 

Appendix 2B on recent regulatory actions, indicating that current emissions have declined since 2008, 

with additional reductions pending. However, quantitative estimates of emissions reductions would be
3

informative. To the extent that these or other historical controls of U.S. Pb source categories have 

shifted Pb emissions to other countries, it would be informative to include discussion of those displaced 

emissions.

The information on ambient air concentrations is clearly presented (for sites with 1 to 3 years of valid 

data for 2009 to 2011) in maps, charts and in a detailed appendix (Appendix 2D). More recent 

measurements from sites (including near airports) initiated since the previous Pb NAAQS review would 

help inform the current Pb NAAQS review, as well as the separate Section 231 aviation gasoline 

(“avgas”) review.

Given the “not to be exceeded” 3-month rolling average form of the Pb NAAQS, an exceedance could 

be determined with as few as 3 months of new data. Therefore, it would be useful if more recent data are

summarized in the next Pb PA, without being limited to sites with multiple years of valid data.

The information on Pb concentrations in other media is clearly presented. The sections (2.3.2.1 and 

2.3.2.2) on indoor and outdoor dust are highly relevant to exposure assessments and would benefit from 

some added discussion of how dust Pb concentration, loading, and loading rates are measured. In 

particular, information relating to the differences in particle sizes in dust samples and ambient air 

samples would be helpful. More information on changes, if any, over time in the availability of 

historically deposited soil Pb for resuspension to the air or for direct uptake through ingestion could help 

clarify the significance of this potentially important source category.

With regard to information on ambient Pb monitoring (section 2.2.1), to what extent is this information 

appropriately characterized and clearly communicated?

The information on ambient Pb monitoring is appropriately characterized and clearly communicated. It

is understood that the high-volume (Hi-Vol) Total Suspended Particulates (TSP) sampler is an imperfect 

historical artifact, and that there is not time for this review cycle of the Pb NAAQS to develop, fully test, 

and deploy alternative samplers that would consistently capture particles (less than and) greater than 10 

microns with appropriate collection efficiencies and size ranges under varying wind speeds and 

directions. The draft PA notes that the EPA expects a new, improved sampler to be “available for 

consideration in a future review.” Toward this goal, discussion is needed regarding the desirable cut size 

characteristics of, and practical constraints on, an alternative sampler. Information from the ISA could 

be cited here, such as material currently on page 3-67 of the 3rd external draft of the ISA that may be 

revised for the final ISA regarding discussion of the desirable cut size. 

If an alternative low-volume sampler could be developed with an upper 50% particle cut size in the 

range of 15 to 20 microns, and without the wind speed and direction biases of the Hi-Vol TSP sampler, 

it seems likely that such a sampler would typically capture as much (or occasionally more) Pb as the HiVol TSP sampler. The CASAC has previously recommended the development of a new air Pb sampler 

that collects larger particle sizes, that could improve the quality of sampling in the National Air Toxics 

Trends Station (NATTS) network, and that could serve as an Federal Reference Method (FRM) or 

Federal Equivalent Method (FEM) for Pb. Filters collected by this sampler also would be amenable to 

multi-elemental analyses by lower-cost analytical methods and could be useful for more accurate and 

precise assessments of other particulate pollutants with significant coarse mode concentrations, 

including chemical contaminants (like hexavalent chromium, silica, and cadmium) and biological 

components like pollen, fungi, and endotoxins.
4

Chapter 3 – Health Effects and Exposure/Risk Information

This chapter discusses key policy relevant aspects of the health effects evidence and exposure/risk 

information.

To what extent does the information in sections 3.1 (Internal Disposition and Biomarkers of Exposure 

and Dose), 3.2 (Nature of Effects) and 3.3 (Public Health Implications and At-Risk Populations) capture 

and appropriately characterize the key aspects of the evidence assessed and integrated in the ISA?

Chapter 3 of the draft PA generally captures the key aspects of the evidence presented in the ISA;

therefore, concerns about content stem from the content of the ISA and not its condensation in the PA.

Recognizing the degree of condensation needed to summarize the ISA in only a few pages, this format 

presents a great writing challenge, and the writing in the chapter lacks clarity. Wordiness should be 

reduced to directly and efficiently convey the meaning. For example, sentences such as the following 

could be shortened and recast in a more active voice: “The results from the various case studies 

assessed, with consideration of the context in which they were derived (e.g., the extent to which the 

range of air-related pathways were simulated, and limitations associated with those simulations), and the 

multiple sources of uncertainty (see section 3.4.7 below) are also informative to our understanding of 

air-to-blood ratios.” (Please refer to Dr. Canfield’s individual comments for details on the sentences in 

need of streamlining and clarification.)

In addition, there are a few places where legacy text from the previous PA remains, so extraneous words 

need to be deleted and tenses updated. What needs the most attention is the length and complexity of 

some sentences.

To what extent is the newly available evidence on air-to-blood ratios appropriately characterized and 

considered in light of information previously available in past reviews?

The new information on air-to-blood ratios is presented in context of previous information and no 

change in the estimate is justified at this time. 

When revising this section (3.1) it would be helpful to first read the last (summary paragraph) on page 3-

14. Those conclusions should be included in the first paragraph of the section and then restated at the 

end of the section when the reader will be in a position to understand the context.

To what extent is the newly available evidence on concentration-response functions for IQ decrements 

in young children appropriately characterized and considered in light of information previously 

available in past reviews?

The newly available evidence is appropriately characterized. Parametric information could be extracted 

from these data to produce quantitative results for blood Pb subgroups, but the quality of the data would

not likely provide a useful basis for altering the conclusions reached from the data available prior to 

2008.

There is a critical need for more information about effects of Pb at levels in the 0-5 μg/dL range. Studies 

about effects of Pb at these low levels are a future research need.
5

With regard to the exposure and risk information, to what extent is the information drawn from the 

human exposure and health risk assessment in the last review sufficiently characterized and clearly 

communicated? To what extent is the information appropriately interpreted in light of the currently 

available information and for the purpose of assessing the adequacy of the now current standard?

Information from the last review is well-characterized and appropriately interpreted, but the clarity of 

communication should be improved. Putting the conclusion in the first paragraph of the section was very 

helpful. The CASAC concurs that a new risk and exposure assessment (REA) is not warranted at this 

time.

Are the limitations and uncertainties in the exposure/risk information appropriately characterized and 

considered in our interpretation of the information in the context of this current review?

The limitations and uncertainties in the exposure/risk information are well characterized.

Epidemiological data are inherently limited; there is a lack of data on the effects of Pb exposure at the 

levels that are common today and thus concentration-response (C-R) estimates require extrapolation.

Parameter choices for biokinetic models typically require restrictive assumptions. No single air quality 

scenario is adequate.

There are specific areas of the chapter that should be revised for clarity:

• Page 3-2, Line 15, referring to distribution of Pb from bone to blood, includes the sentence: 

“Changes in Pb exposure circumstances also can influence these exchanges, e.g., substantial 

reductions in exposure levels contribute to increased release of Pb from the bone into the blood 

(ISA, section 4.3.5).” This sentence should be revised, as it appears to incorrectly characterize 

the information in section 4.3.5 of the ISA. A reduction in external Pb exposure does not, from a 

pharmacodynamic standpoint, induce an increase in the release of Pb from bone. In the context 

of the paragraph, the intended point could be expressed as follows: “When there are substantial 

reductions in external Pb exposure, the relative contribution of Pb from bone to the concentration 

of Pb in blood increases.”

• Page 3-5, line 29 to Page 3-6, line 9: The italicized sentence in this paragraph, reproduced 

below, should be revised to improve clarity:

“The response of adult blood Pb levels to appreciable changes in exposure circumstances is 

generally slower than that of blood Pb levels in young children. For example, simulations using 

biokinetic models indicate that blood Pb levels in adults achieve a new quasi-steady state within 

75-100 days (approximately 3-4 times the blood elimination half-life) subsequent to abrupt 

increases in Pb intake (ISA, section 4.3.5.2); similar models indicate a much quicker response of 

blood Pb levels in children both with regard to abrupt increases and reductions in Pb exposure 

(ISA, section 4.3.5.1). The response in young children may reflect their much more labile bone 

pool associated with the rapid turnover of bone mineral in response to their rapid growth rates 

(ISA, section 4.3.5). As a result of these physiological processes in young children, their blood 

Pb levels tend to more quickly reflect changes in their total body burden (associated with their 

shorter exposure history), and also can reflect changes in recent exposures (ISA, section 4.3.5).”
6

Instead of the italicized sentence above, substitution of a sentence such as the following might 

enhance clarity: “Because the skeletal compartment of Pb is relatively smaller and subject to 

more rapid turnover in children compared to adults, the blood Pb concentration of children is 

more reflective of their recent external exposure.” 

• Page 3-19 lines 23-24: It might be clearer to use the phrase “qualitatively change” rather than 

“appreciably change” to allow for appreciable strengthening of the previous conclusion but no 

change of consequence.

• Page 3-22 lines 17-23: This is a helpful discussion of the problem with unknown earlier 

exposures in adults and older children. The topic comes up multiple times throughout this 

document and becomes redundant. Maybe this should be covered fully (including this as a 

general critique of cross-sectional studies), early in the chapter and then simply referred back to 

when the context warrants.

Chapter 4 – Review of the Primary Standard for Lead

This chapter describes the basis for the current primary standard and consideration of the current 

evidence and exposure/risk-based information with regard to reaching preliminary staff conclusions 

about the adequacy of the current standard.

In this chapter, staff applies the same evidence-based air-related IQ loss framework as developed and 

used in the last review, which has fundamentally two key inputs: an air-to-blood ratio and the slope of a 

concentration-response (C-R) function for IQ decrements in young children.

This draft PA is constrained by the absence of new observational and experimental data that address, at 

least in part, limitations and uncertainties in the evidence that was present at the time of the last update 

of the Pb NAAQS. Until evidence is available to assess Pb exposure and health risks related to air Pb 

levels reflecting the current standard, a substantive refinement and update of the PA will not be possible. 

The obvious uncertainty underlying evaluation of this PA is whether lowering the standard would (or 

would not) impact exposure and thus risk. The CASAC agrees 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.” If lowering the primary standard would lower blood Pb levels amongst the U.S. population, 

then there would be potential public health benefits from a lower standard. Research priorities discussed 

below are designed to help inform these uncertainties.

To what extent does the Panel agree with application of the evidence-based framework from the last 

review, particularly with regard to consideration of the currently available information, and related 

limitations and uncertainties, for air-to-blood ratios and C-R functions for IQ decrements in young 

children?

The application of the evidence-based framework from the previous Pb NAAQS review seems 

appropriate. The new literature published since the previous review provides further support for the 

health effect conclusions presented in that review. Additionally, the new studies do not fundamentally 

alter the uncertainties for air-to-blood ratios or C-R functions for IQ decrements in young children.
7

As previously discussed with CASAC, staff concluded that the current information does not warrant 

development of a new REA in this review. Thus, exposure/risk information was drawn from the REA 

conducted in the last review.

What are the Panel’s views on staff’s interpretation of the exposure/risk information, and on staff’s 

conclusions that the information is generally supportive of conclusions drawn from the evidence-based 

framework as to the adequacy of the current standard?

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.

In reaching preliminary staff conclusions, staff notes that, like any NAAQS review, this Pb NAAQS 

review requires public health policy judgments. The public health policy judgments for this review 

include the public health significance of a given magnitude of IQ loss in a small subset of highly exposed 

children (i.e., those likely to experience air-related Pb exposures at the level of the standard), as well as 

how to consider the nature and magnitude of the array of uncertainties that are inherent in the evidence 

and in the application of this specific framework.

What are the Panel’s views on public health policy judgments that inform staff’s preliminary

conclusions with regard to the adequacy of current standard and a lack of support for consideration of 

potential alternative standards?

The PA states repeatedly that no threshold for Pb effects on IQ can be identified. In some respects, the 

ability to define a threshold may already be a moot issue. Reductions in IQ in children are being 

reported at blood Pb values as low as 2 μg/dL. In essence, these effects are being reported at the lowest 

levels of Pb in blood that can be reliably measured by most laboratories doing such analyses. 

Child IQ is the Pb-sensitive health endpoint on which this PA (and the previous one) is based. Thus, the 

discussion of health policy judgment needs to be carefully considered in light of the far-reaching public 

health value of childhood cognitive and neurobehavioral health. For example, the 2012 Centers for 

Disease Control and Prevention (CDC) update of recommendations regarding childhood Pb poisoning 

acknowledges that there is no blood Pb level in childhood that has been shown to be without deleterious 

effects. In this context, defining the threshold for "unacceptable risks to public health" or "sufficient 

public health protection" is difficult. Indeed, such language - with its implicit use of a threshold 

approach to a process that presumably has no threshold - may no longer be appropriate. Although 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 
8

current standard (as opposed to other sources of Pb in the environment) has not been established. 

Therefore there is not justification for modifying the current standard based on these data at this point in 

time. However additional research on air to blood Pb at low levels may require reconsideration of this 

decision in the future.

In the Panel’s view, does the discussion in section 4.3 provide an appropriate and sufficient rationale to 

support staff’s preliminary conclusion that it is appropriate to consider retaining the current standard 

(including the indicator, level, averaging time, and form) without revision?

Given the evidence-based framework, the discussion in section 4.3 provides an appropriate and 

sufficient rationale to support retaining the current standard without revision. For example, there is 

discussion in the PA regarding the choice of indicator level. However, there should be more description 

of supporting data and rationale behind the recommendation for the averaging time and form of the 

current standard.

The CASAC concurs that the new science does not support lowering the Pb NAAQS from its current 

level (0.15 μg/m3

). Additionally, the CASAC concurs with the caveats provided about the uncertainty in 

the science behind the NAAQS for Pb. In particular it appreciates and affirms a key point on page 4-28, 

lines 2-3: “We also recognize increased uncertainty in projecting the magnitude of blood Pb response to 

ambient air Pb concentrations at and below the level of the current standard.” Likewise, the key idea on 

page 4-32, lines 32-35 is important, but a clarifying revision is recommended as follows:

Page 4-32, lines 32-35, current text: “In staff’s view, based on current evidence there is 

appreciable uncertainty associated with drawing conclusions regarding whether there would be 

reductions in risk to public health from alternative lower levels as compared to the level of the 

current standard.” This should be re-written to read “In staff’s view, based on current evidence 

there is appreciable uncertainty associated with drawing conclusions regarding whether there 

would be reductions in blood lead levels from alternative lower levels as compared to the level of 

the current standard.”

Does the Panel have any recommendations regarding additional interpretations and conclusions based 

on the available information that would be appropriate for consideration beyond those discussed in this 

chapter?

As noted above, repeated statements about a threshold do not seem warranted given that IQ reductions 

now occur at the lowest blood Pb levels that can be reliably measured in most laboratories. It is for this 

reason that the Advisory Committee on Childhood Lead Poisoning Prevention recommended to CDC a 

complete elimination of the phrase ‘level of concern’ and stated that no blood Pb level in children has 

been shown to be without deleterious effects.

The EPA should encourage development of research programs to address those limitations and 

uncertainties in currently available evidence (and exposure/risk information) that are critical to the 

identification of "sufficiently health protective" air Pb standards in the future.
9

There are some areas that need revision for clarity:

• Page 4-34, line 13: The statement should be edited to: “Factors affecting relationships between 

Pb in ambient air and Pb in blood at low exposures experienced in the general population 

today”

• Page 4-34, lines 19-21: This research need is profound, but as written is too vague to be 

appreciated by the average reader. This research need should be revised to: “Apportionment of 

blood Pb levels with regard to exposure pathways, with particular focus on understanding 

exposure pathways and sources that cause the more elevated blood Pb levels among children 

today.”

Research Needs

Several areas of research that could assist in further refinement of the Pb NAAQS include:

1. For the purposes of policy and decision making, key research priorities should be studies that

elucidate: (1) the air-blood Pb relationship at low levels; (2) sources (exposure pathways) 

contributing to current population blood Pb levels, especially in children; (3) the relationship 

between Pb and childhood neurocognitive function at current population exposure levels; and (4) 

the relationship between ambient air Pb and outdoor dust and surface soil Pb concentrations, 

including the temporal dynamics of that relationship. These research priorities are of particular 

interest because of the prominent contribution of past (as opposed to recent) Pb emissions to Pb

in soil and dust, and the significant contribution of dust and soil matrices to the Pb exposure of 

children. 

2. For the typical American adult not subject to current or past point sources or occupational Pb

exposure, Pb in the diet is likely to constitute the largest fraction of daily Pb exposure. Therefore, 

another research need of considerable interest is to determine the source of contemporary dietary 

Pb, including the indirect contribution of historical air Pb emissions (i.e. “legacy Pb”). Further, 

there remains a need to determine how much of dietary Pb is from legacy and how much can be 

amenable to interventions. 

3. The shape of the C-R curve for IQ reductions at extremely low levels requires further 

clarification. In addition, studies on more sensitive endpoints in the domain of emotion and 

behavior regulation are warranted, given that they may yield specific and sensitive measures and 

thereby assist in defining appropriate intervention strategies for children. 

4. There has been a long-term reliance on the Integrated Exposure Uptake Biokinetic (IEUBK)

model. However, greater understanding of inter-individual variability, as quantified in the 

Geometric Standard Deviation (GSD) input parameter, is needed. Information about 

toxicokinetics during adolescence remains limited. The All Ages Lead Model could be utilized to 

improve this understanding. There is also the need to know more about gene-environment 

interactions, particularly in driving inter-individual susceptibility and vulnerability.

5. Characterization and better understanding of Pb exposure hotspots/sources will give better 

representation of significant exposure risks.
10

6. Understanding of the impacts of Pb exposures during critical developmental windows and their 

contribution to adverse outcomes; e.g., little is known about the specific effects of prenatal 

exposure.

7. The effect of contemporary Pb exposure (i.e., that resulting in blood Pb concentrations on the 

order of 5 μg/dL or lower) on the future risk of hypertension and cardiovascular morbidity and 

mortality, and on age-related neurodegeneration, as these could lead to additional information 

related to most sensitive health outcomes.

8. A further understanding of the role of “reverse causation” in the inverse association observed in 

some studies between low blood Pb concentration and renal function (e.g., glomerular filtration 

rate).

9. The extent to which product substitution, i.e., replacement of Pb with less hazardous alternative 

substances in contemporary commerce, may result in reduction of human Pb exposure. The EPA 

might consider supporting studies on Pb potentially undertaken by programs such as the Toxic 

Use Reduction Program in Massachusetts, and the Green Chemistry Initiative in California.

10. As yet, the extent to which global warming will influence exposure to Pb (e.g., through soil 

erosion, resuspension) has not been evaluated.

Chapter 5 – Welfare Effects and Exposure/Risk Information

This chapter discusses key policy relevant aspects of the environmental evidence and exposure/risk 

information.

Chapter 5 of the PA is a well-written synthesis of the findings related to ecological effects in the ISA. 

The ISA supports the conclusion that recent research has not changed our fundamental understanding of 

Pb fate, transport and toxicity in the environment.

To what extent does the information in section 5.1 (Welfare Effects Information) capture and 

appropriately characterize the key aspects of the evidence assessed and integrated in the ISA?

Section 5.1 does a good job of summarizing the evidence for ecological effects from the ISA. The 

general conclusion is that recent research has added depth and nuance to the understanding of the fate 

and transport of Pb in ecological systems, and to the understanding of effects on organisms in terrestrial 

and aquatic ecosystems, but has not changed the understanding in a way that merits reconsideration of 

the relationships used to assess risk. 

A persistent theme in the ecological effects sections of the ISA and this PA document is that it is 

difficult to isolate the effects of air Pb on ecosystems from other Pb sources, including “legacy” Pb 

accumulated in soils and sediments. The threat of release of legacy Pb in soils and sediments, whatever 

the original source, may necessitate a lower secondary air quality standard than would be warranted in 

the absence of the legacy Pb. With respect to critical loads, it is recommended that Chapter 5 

acknowledge the impact on raptors and water fowl of Pb in spent ammunition; these are the ecological 
11

receptors most heavily exposed to Pb, and thus potentially the most susceptible to the incremental 

contribution of Pb in air.

With regard to the exposure and risk information in section 5.2 (Exposure and Risk Information), to 

what extent is the information drawn from the screening-level risk assessment in the last review 

sufficiently characterized and clearly communicated? To what extent is the information appropriately 

interpreted in light of the currently available information and for the purpose of assessing the adequacy 

of the current standard?

The results of the 2006 REA are summarized in section 5.2. The summary is concise and clear, both in 

the explanation of the model employed and in the descriptions of the case studies used in the assessment.

The interpretation of the results from the 2006 REA is appropriate insofar as it re-states the conclusions 

from that document, and there have been no fundamental changes to our understanding of key thresholds 

or ecological receptors in the intervening years. Of four terrestrial case studies employed, the results 

from two (the primary and secondary smelter cases) are judged to be “not informative.” The relevance 

of a third case study (non-urban near-roadway conditions) is deemed “highly uncertain” due to the 

presence of legacy Pb in roadside soils. The only terrestrial case study that is deemed relevant is the 

Hubbard Brook case, where ambient Pb concentrations are far below the current (and proposed) 

standard. Results from analysis of surface water and sediment data are judged to be inconclusive 

because of possible non-air sources to waters and legacy Pb in sediments. Therefore, overall, four of the 

five major efforts in the 2006 REA are judged to be of limited or no value for the purposes of this PA. 

Given that there is little field research underway on Pb in U.S. ecosystems that are not impacted by point 

sources, it would appear to be unlikely that data for new REA case studies is forthcoming. A robust 

critical loads approach, which is a research priority to support a future review, is needed to fill this gap.

Are the limitations and uncertainties in the exposure/risk information appropriately characterized and 

considered in our interpretation of the information in the context of this current review?

The discussion of limitations and uncertainties is generally good. Issues such as legacy Pb, multistressor effects, and lab-to-field applicability create considerable uncertainty. The use of conservative 

screening levels in the calculation of hazard quotients is particularly useful because the calculated risks 

are overstated.

Chapter 6 – Review of the Secondary Standard for Lead

This chapter describes the basis for the current secondary standard and consideration of the current 

evidence and exposure/risk-based information with regard to reaching preliminary staff conclusions 

about the adequacy of the current standard.

Does the Panel agree with preliminary staff conclusions about the evidence and previous risk

assessment in light of current standards as presented in section 6.2 (Adequacy of the Current 

Standard)?
12

The preliminary staff conclusions provide a good assessment of the available evidence and the previous 

risk assessment in light of the current secondary standard. The CASAC notes, however, the concerns 

raised in the response to the chapter 5 charge questions regarding the previous risk assessment.

In the Panel’s view, does the discussion in this chapter provide an appropriate and sufficient rationale 

to support preliminary staff conclusions that it is appropriate to consider retaining the current standard 

(including the indicator, level, averaging time, and form) without revision?

The discussion provides appropriate and sufficient rationale to support retaining the current secondary 

standard without revision. A general lack of new data that would indicate the appropriate level of Pb in 

environmental media that may be associated with adverse effects suggests that the secondary standard 

should be retained. Questions remain regarding the relevance of the indicator, level, averaging time and 

form to the secondary standard (ecological context). A multi-media approach may be necessary to 

account for legacy Pb and contributions from different sources for a secondary standard. 

Does the Panel have any recommendations regarding additional interpretations and conclusions based 

on the available information that would be appropriate for consideration beyond those discussed in this

chapter?

The CASAC does not have any recommendations regarding additional interpretations and conclusions 

beyond what is contained in the chapter. Developing a critical loads approach for U.S. conditions would 

be an important area for additional research. The discussion of uncertainties at the end of the chapter is 

excellent. It should include mention of the use and/or relevance of toxicity data that are generated in test 

systems that deploy exposures to media other than soil or water for appropriate organisms (e.g., plants in 

hydroponic systems, soil nematodes in agar or culture medium).

Research Needs

Application of a critical loads approach with sensitivity analysis will help to determine which processes 

are most important in determining Pb exposure to ecological receptors. This would be an integrated, 

holistic, multi-media approach that could be used to examine the contributions of current aerial Pb 

deposition to historical aerial deposition as well as Pb from other sources. Current critical loads models 

are largely qualitative and empirical. Mechanistic sub-models need to be incorporated into the critical 

loads model to provide an adequate means to predict Pb bioavailability, exposure, and toxicity. This 

critical loads approach could be integrated to include other aerial pollutants such as oxides of nitrogen 

and oxides of sulfur.
13

Reference

Secretariat of the Commission for Environmental Cooperation (CEC), (2013), Hazardous Trade? An 

Examination of US-generated Spent Lead-acid Battery Exports and Secondary Lead Recycling in 

Mexico, the United States and Canada, Final Report, 15 April.
A-1

Appendix A

Compendium of Individual Comments by CASAC Lead Review Panel Members on

EPA’s Policy Assessment for the Review of the Lead National Ambient Air Quality Standards 

(External Review Draft – January 2013)

Mr. George A. Allen.............................................................................................................................. A-2

Dr. Herbert Allen.................................................................................................................................. A-3

Dr. Richard Canfield ............................................................................................................................ A-4

Dr. Deborah Cory-Slechta.................................................................................................................... A-6

Dr. Cliff Davidson................................................................................................................................. A-8

Dr. Sean Hays........................................................................................................................................ A-9

Dr. Philip Hopke ................................................................................................................................. A-10

Dr. Chris E. Johnson .......................................................................................................................... A-11

Dr. Susan Korrick............................................................................................................................... A-13

Dr. Michael Kosnett............................................................................................................................ A-15

Dr. Roman Lanno ............................................................................................................................... A-18

Mr. Richard L. Poirot......................................................................................................................... A-20

Dr. Michael Rabinowitz...................................................................................................................... A-25

Dr. Ian von Lindern............................................................................................................................ A-26

Dr. Gail Wasserman ........................................................................................................................... A-29

Dr. Michael Weitzman........................................................................................................................ A-30
A-2

Mr. George A. Allen

Comments on Chapter 2

Response to specific Charge Questions:

1. To what extent does the Panel agree that the most relevant information on emissions (section

2.1), air quality (section 2.2.2), and Pb concentrations in other media (section 2.3) is presented,

and to what extent is the information presented appropriately characterized and clearly

communicated?

Overall, Chapter 2 provides a concise and well-organized summary of the relevant material from the 

ISA. Minor note: the boxplots in section 2.2.2 need to have the whisker defined - is it 95th percentile?

2. With regard to information on ambient Pb monitoring (section 2.2.1), to what extent is this

information appropriately characterized and clearly communicated?

2.2.1.3.1, pg 2-20, lines 4-9: this paragraph is a well written description of the process being taken 

towards a better FRM sampler. It states that known limitations in wind-tunnel aerosol generation and 

particle sampling of ultra-coarse particles will limit the upper range of any new FRM to 18-20 microns. I 

would suggest that EPA consider the practical aspects of sampler design and testing, and (at least 

initially) constrain the project goals to an upper limit of 15 microns, a size noted in the ISA as being 

appropriate (sufficiently large enough) for exposure assessment in a NAAQS context.

2.2.1.3.3, Pg. 2-22, lines 17-18: The Pb NAAQS form is “never to be exceeded” – a unique form. How 

is the Pb design value calculated - is it the highest 3-month running average over the 3-year period?
A-3

Dr. Herbert Allen

Comments on Chapter 5

Generally this Chapter is well-written and follows the important information in the ISA. There are 

several places that need attention.

Page 5-5 lines 27-30. This sentence references section 7.4.24 of the ISA. However, the ISA does not 

contain a section 7.4.24. The statement that “dissolved organic carbon and DOM [i.e., dissolved organic 

matter] do not have the same effect on free lead ions” is very misleading. Dissolved organic carbon is 

not a substance. It is means of expressing the concentration of the carbon contained dissolved organic 

matter and is typically used to express the results of instrumental carbon analysis.

Page 5-6 line 35 – page 5.7 line 2. The lead concentration of 2.5 μM is not a concentration in soil, but 

the concentration in a solution to which the nematodes were exposed.

Page 5-19 line 15. Rather than “from 5 ppb to about 5 ppt” it would be more appropriate to write “from 

5 μg/L to 5 ng/L”.

Comments on Chapter 6

I believe this Chapter is acceptable as written. The conclusions are clearly stated and justified.
A-4

Dr. Richard Canfield

Comments on Chapter 3: Health Effects and Exposure/Risk Information

1. To what extent does the information in sections 3.1 (Internal Disposition and Biomarkers of 

Exposure and Dose), 3.2 (Nature of Effects) and 3.3 (Public Health Implications and At-Risk 

Populations) capture and appropriately characterize the key aspects of the evidence assessed 

and integrated in the ISA?

a. This draft PA generally captures the key aspects of the evidence presented in the ISA and 

so any concerns about content are related to the content of the ISA and not its 

condensation in the PA.

b. Recognizing the degree of condensation needed to summarize the ISA in only a few 

pages, this format presents a great writing challenge, and the clarity of writing in this 

chapter betrays its status as a “draft.” During revision it will be important to reduce 

wordiness in order to convey the meaning more directly and efficiently. For example, 

sentences such as the following could be shortened and recast in a more active voice: 

“The results from the various case studies assessed, with consideration of the context in 

which they were derived (e.g., the extent to which the range of air-related pathways were 

simulated, and limitations associated with those simulations), and the multiple sources of 

uncertainty (see section 3.4.7 below) are also informative to our understanding of air-toblood ratios.” I will note in my specific comments below the sentences I found most in 

need of streamlining and clarification.

c. In addition, there are a few places where legacy text from the previous PA remains and so 

extraneous words need to be deleted and tenses updated. What needs the most attention is 

the length and complexity of some sentences

2. To what extent is the newly available evidence on air-to-blood ratios appropriately 

characterized and considered in light of information previously available in past reviews?

a. The new information on air-to-blood ratios is presented in context of previous 

information and it is evident why no change in the estimate is justified at this time.

b. When revising this section (3.1) it would be helpful to first read the last (summary 

paragraph) on page 3-14. Those conclusions should be included in the first paragraph of 

the section and then restated at the end of the section when the reader will be in a position 

to understand the context.

3. To what extent is the newly available evidence on concentration-response functions for IQ 

decrements in young children appropriately characterized and considered in light of information 

previously available in past reviews?

a. The newly-available evidence is appropriately characterized. Parametric information 

could be extracted from these data to produce quantitative results for blood Pb subgroups, 
A-5

but I do not believe the quality of the data would provide a useful basis for altering the 

conclusions reached from the data available prior to 2008.

b. EPA has correctly identified the lack of information about effects of Pb at levels in the 0-

5 ug/dL range. Such a study should be done.

4. With regard to the exposure and risk information, to what extent is the information drawn from 

the human exposure and health risk assessment in the last review sufficiently characterized and 

clearly communicated? To what extent is the information appropriately interpreted in light of the 

currently available information and for the purpose of assessing the adequacy of the now current 

standard?

a. Information from the last review is well-characterized and appropriately interpreted.

Clarity of communication can be improved.

b. Putting the conclusion in the first paragraph of the section was very helpful. I concur that 

a new REA is not warranted at this time.

5. Are the limitations and uncertainties in the exposure/risk information appropriately 

characterized and considered in our interpretation of the information in the context of this 

current review?

a. Limitations and uncertainties are well characterized.

i. Epidemiological data are inherently limited; viz., there is a lack of data on the 

effects of Pb exposure at the levels that are common today and thus C-R estimates 

require excessive extrapolation.

ii. Parameter choices for biokinetic models typically require restrictive assumption.

iii. No single air quality scenario is adequate.

Other comments:

3-19 lines 23-24: It might be clearer to use the phrase “qualitatively change” rather than “appreciably 

change” to allow for appreciable strengthening of the previous conclusion but no change of 

consequence.

3-21 Table 3-2 and elsewhere: I suggest reconsidering whether 24-month Bayley data are sufficiently 

strong to mention in this high-level review. [note that the table includes lots of measures besides IQ

3-22 lines 17-23: This is a nice discussion of the problem with unknown earlier exposures in adults and 

older children. It comes up multiple times throughout this document and becomes redundant. Maybe this

should be covered fully (including this as a general critique of cross-sectional studies), early in the 

chapter and then simply referred back to when the context warrants.
A-6

Dr. Deborah Cory-Slechta

Comments on Chapter 4 – Primary Standard for Lead

To what extent does the Panel agree with the application of the evidence-based framework from the last 

review, particularly with regard to consideration of the currently available information, and related 

limitations with uncertainties, for air-to-blood ratios and C-R functions for IQ decrements in young 

children?

The application of the evidence-based framework from the last review seems appropriate, particularly 

given that new literature since the prior 2006 review provides further support for the health effect 

conclusions presented in the prior review. Additionally, new studies do not fundamentally alter the 

uncertainties for air-to-blood ratios or C-R functions for IQ decrements in young children.

What are the Panel’s views on staff’s interpretation of the exposure/risk information, and on staff’s 

conclusions that the information is generally supportive of conclusions drawn from the evidence-based 

framework as to the adequacy of the current standard?

The use of exposure-risk information from the prior review appears appropriate given the absence of 

significant new information that could fundamentally change the interpretation.

What are the Panel’s views on public health policy judgments that inform staffs’ preliminary 

conclusions with regard to the adequacy of the current standard and a lack of support for consideration 

of potential alternative standards?

The document states repeatedly that no threshold for lead effects on IQ can be identified. In some 

respects, the ability to define a threshold may already be a moot issue. Reductions in IQ in children are 

being reported at blood lead values as low as 2 ug/dl. In essence, these effects are being reported at the 

lowest levels of lead in blood that can be reliably measured by most laboratories doing such analyses. 

While the regulations do not require that zero risk be achieved, neither does it prevent it. Given the 

above statement, and the fact that the supra-linear C-R curve has now been demonstrated in several 

studies, it becomes increasingly difficult to support a standard based on 1-2 IQ point loss. From a 

biological perspective, a standard based on some degeneration of function does not seem appropriate. 

From a public health perspective, communicating to the public that a regulatory standard is based on 

exposures that provide no more than a 1-3 point IQ reduction would seem less than ideal and 

contradictory to their expectations.

In the Panel’s view, does the discussion in section 4.3 provide an appropriate and sufficient rationale to 

support staff’s preliminary conclusion that it is appropriate to consider retaining the current standard 

(including the indicator, level, averaging time, and form) without revision?
A-7

Yes, given the evidence-based framework. However, given that we are now down to the lowest blood 

lead levels that can be reliably measured, it is not clear that all of these arguments are in fact requisite. 

Does the Panel have any recommendations regarding additional interpretations and conclusions based 

on the available information that would be appropriate for consideration beyond those discussed in this 

chapter?

As noted above, statements about the threshold do not seem warranted given that IQ reductions now 

occur at the lowest blood lead levels that can be reliably measured in most laboratories. It was for this 

reason that the ACCLPP committee recommended to CDC a complete elimination of the phrase ‘level 

of concern’ and stated that no safe level of blood lead can be identified.
A-8

Dr. Cliff Davidson

Comments on Chapter 1

Chapter 1 of the PA is generally well written and easy to follow. It is a reasonable introduction to the 

rest of the PA document. 

Page 1-2, lines 21-24 state that a new Risk and Exposure Assessment was found to be unnecessary at 

this time, and hence the health and welfare REAs developed for the 2006 review are adequate for use 

with current environmental concentration and exposure data. This is clearly presented and is justified 

based on our prior committee reviews.

Section 1.3.2 discusses considerations related to the history of Pb emissions during the days of leaded 

gasoline and high stationary source emissions. The section correctly points out that the current task is to 

assess the adequacy of the current airborne Pb standard, while recognizing that there is a history of high 

Pb emissions. But what is missing from this section is an appreciation for the magnitude of the past Pb 

emissions.

A simple calculation illustrates the point. Figure 3-1 in the ISA (page 3-3) which is repeated as Figure 2-

1 in the PA (page 2-3) shows that total Pb emissions in the year 1970 were over 200,000 tons of Pb. The 

PA should put this value into perspective. If we conservatively pick 10 years of emissions at this level, 

we obtain about 2 million tons of Pb emitted. Clearly, the total Pb emissions are more than this value. 

But some of this Pb was carried out of the U.S., where it eventually deposited in the oceans or 

elsewhere. It is not unreasonable to assume that about 2 million tons of Pb deposited within the 

boundaries of the U.S. as a very rough value. If this Pb deposited uniformly over the entire land area of 

continental U.S., around 25 micrograms of Pb would have deposited per cm2 of surface. This is roughly 

equal to the natural amount of Pb in the top 1 cm of soil (12.5 ppm = 12.5 micrograms of Pb per gram of 

soil, or about 25 micrograms per cm3 assuming a soil density of 2 grams per cm3). We have thus 

approximately doubled the amount of Pb in the top cm of soil throughout the continental U.S. It is 

apparent that soil in some areas, especially urban areas, will contain much more than this, while larger 

remote areas will contain less.

The point of this calculation is that we do not know the ultimate fate of roughly 2 million tons of Pb 

deposited during the days of leaded gasoline, a value that dwarfs current emissions. We suspect that 

most of this huge amount of Pb is now stored in the environment, with significant amounts in U.S. urban 

areas where population densities are greatest. The fact that we cannot account for this lead constitutes a 

major uncertainty in our understanding, and it merits a discussion to that effect in the PA.

There is one sentence in need of revision for accuracy, namely on page 1-13 line 35:

“And we recognize that past lead emissions in many situations were well in excess of the current Pb 

standard.” One cannot compare emissions to an airborne standard. One way to fix this sentence is to 

write: “And we recognize that past lead emissions in many situations caused airborne lead 

concentrations far in excess of the current Pb standard.”
A-9

Dr. Sean Hays

General Comments on Chapter 4

• I agree with the caveats provided about the uncertainty in the science behind the NAAQS for 

lead. In particular I agree with, and appreciate EPA adding, the following statements.

o Page 4-28, line 2-3: “We also recognize increased uncertainty in projecting the 

magnitude of blood Pb response to ambient air Pb concentrations at and below the level 

of the current standard”

o Page 4-32, lines 33-35: “In staff’s view, based on current evidence there is appreciable 

uncertainty associated with drawing conclusions regarding whether there would be 

reductions in risk to public health from alternative lower levels as compared to the level 

of the current standard”. This should perhaps be re-written to read “In staff’s view, based 

on current evidence there is appreciable uncertainty associated with drawing conclusions 

regarding whether there would be reductions in blood lead levels from alternative lower 

levels as compared to the level of the current standard

• I agree that the new science does not support lowering the NAAQS any lower than its current 

level (0.15 ug/m3

).

Specific comments on Chapter 4

• Page 4-34, line 13: The following statement should be edited to; “Factors affecting relationships 

between Pb in ambient air and Pb in blood at low exposures experienced in the general 

population today”

• Page 4-34, lines 19-21: This statement is profound, but as written is too vague to be appreciated 

by the average reader. I would recommend editing to be something along the lines of; 

“Apportionment of blood Pb levels with regard to exposure pathways, with particular focus on 

understanding exposure pathways and sources that cause the more elevated blood lead levels 

among children today. “
A-10

Dr. Philip Hopke

I would like to start with a broad comment. I would hope we could see the United States moving to 

eliminate a NAAQS for airborne lead. Now is not yet the time, but this should be part of the discussion 

in the next round of review. If we eliminate lead in aviation gas and in wheel weights, we will have 

removed the remaining major dispersed sources of lead other than resuspended soil. All of the remaining 

point sources whether lead or other metal processing could be handled under HAPs rules. We will need 

to eliminate these final sources (aviation gasoline in particular), but then it is time for a serious 

discussion of the further need for a lead NAAQS or whether the resources that currently go into this 

process would be better used to address other widely dispersed pollutants from multiple sources such as 

benzene or mercury.

Comments on Chapter 2

1. To what extent does the Panel agree that the most relevant information on emissions (section 2.1), air 

quality (section 2.2.2), and Pb concentrations in other media (section 2.3) is presented, and to what 

extent is the information presented appropriately characterized and clearly communicated?

Staff has done a good job of summarizing the information from the ISA. The chapter provides a good 

background to the discussions in the following chapters. 

2. With regard to information on ambient Pb monitoring (section 2.2.1), to what extent is this 

information appropriately characterized and clearly communicated?

The statistical justification for a never to be exceeded standard has never been presented. It is a hangover 

from prior standards that does not seem to have been adequately considered and reviewed. Given the 

natural variability of the environment, this form of the standard represents a poor coupling of science to 

reality and it would be much better if the form of the standard better reflected that control should be 

based on the distribution of lead concentrations. Other forms of the standard can be set to be highly 

restrictive on the range of concentrations so as to provide the requisite protection of public health while 

still recognizing the variable nature of the system. It would be useful to see an adequate statistical 

discussion of the standard form and a justification that this form is appropriate to provide the protection 

required. 
A-11

Dr. Chris E. Johnson

Comments on Chapter 5: Welfare Effects and Exposure/Risk Information

To what extent does the information in section 5.1 (Welfare Effects Information) capture and 

appropriately characterize the key aspects of the evidence assessed and integrated in the ISA?

Section 5.1 does a good job of summarizing the evidence for ecological effects from the Third Draft 

ISA. Each sub-section includes a brief description of our understanding in the 2006 Air Quality Control 

Document, and commentary on how research undertaken since then has (or has not) changed our 

understanding. The general conclusion is that recent research has added depth and nuance to our 

understanding of the fate and transport of Pb in ecological systems, and to our understanding of effects 

on organisms in terrestrial and aquatic ecosystems, but has not changed our understanding in a way that 

merits reconsideration of relationships used to assess risk. 

Two persistent themes in the ecological effects sections of the ISA and this PA document are: (1) it is 

difficult to isolate the effects of air Pb on ecosystems from other sources, including “legacy” Pb 

accumulated in soils and sediments; and (2) it is difficult to isolate the effects of Pb from other metals 

and stressors. It is distressing to see the degree to which these explanations are used to justify no-action 

conclusions. The threat of release of legacy Pb in soils and sediments, for example, whatever the source 

(atmospheric or geologic), may necessitate a lower secondary air quality standard than would be 

warranted in the absence of the legacy Pb.

The overall impression left in reading section 5.1 is that the authors are working very hard to justify a 

no-action conclusion, even if that means forcing some round pegs into square holes.

With regard to the exposure and risk information in section 5.2 (Exposure and Risk Information), to

what extent is the information drawn from the screening-level risk assessment in the last review 

sufficiently characterized and clearly communicated? To what extent is the information appropriately 

interpreted in light of the currently available information and for the purpose of assessing the adequacy 

of the current standard?

The results of the 2006 risk and exposure assessment (REA) are summarized in section 5.2. The 

summary is concise and clear, both in the explanation of the model employed and in the case studies 

used in the assessment.

The interpretation of the results from the 2006 REA is appropriate insofar as it re-states the conclusions 

from that document, and there have been no fundamental changes to our understanding of key thresholds 

or ecological receptors in the intervening years. However, after reading section 5.2 of the draft PA, one 

is left with serious doubts about the value of the original work for the purpose of establishing a 

secondary standard. Of four case studies employed, the results from two (the primary and secondary 

smelter cases) are judged to me “not informative.” The relevance of a third case study (non-urban nearroadway conditions) is deemed “highly uncertain” due to the presence of legacy Pb in roadside soils.

The only case study that is deemed relevant is the Hubbard Brook case, where ambient Pb 

concentrations are far below the current (and proposed) standard. Results from analysis of surface water 
A-12

and sediment data are judged to be inconclusive because of possible non-air sources to waters and 

legacy Pb in sediments.

Overall, four of the five major efforts in the 2006 REA are judged to be of limited or no value for the 

purposes of this policy assessment. Yet the Agency considers another REA unnecessary. Perhaps new 

information since the 2006 REA does not warrant a new REA, but the apparent inadequacy of the 2006 

REA would certainly seem to warrant another try.

Are the limitations and uncertainties in the exposure/risk information appropriately characterized and 

considered in our interpretation of the information in the context of this current review?

As discussed above in my comments to the other charge questions, I believe that the limitations and 

uncertainties presented in chapter 5 of the Draft PA are somewhat overstated. Issues such as legacy Pb, 

multi-stressor effects, and lab-to-field applicability do create uncertainty, but do not make data 

uninformative.
A-13

Dr. Susan Korrick

Comments on Chapter 4

General Comment:

This Draft Policy Assessment (PA) is constrained by the absence of appreciable new observational and 

experimental data that addresses, at least in part, limitations and uncertainties in the evidence that were 

present at the time of the last update of the NAAQS for Pb. Assuming the approach used in the previous 

PA was appropriate at the time, by default, it is reasonable to extend it now. However, this circumstance 

underscores a fundamental dilemma. That is, until evidence is available to assess Pb exposure and health 

risks related to air Pb levels reflecting the current standard, a substantive refinement and update of the 

PA will not be possible. The obvious and most fundamental uncertainty underlying evaluation of this PA 

is whether lowering the standard would (or would not) impact exposure risk. If lowering the standard 

would be beneficial to BPb levels, then there would be potential for additional public health benefit from

a lower standard. However, such information is currently unknown.

1. "To what extent does the Panel agree with application of the evidence-based framework from the last 

review, particularly with regard to consideration of the currently available information, and related 

limitations and uncertainties, for air-to-blood ratios and C-R functions for IQ decrements in young 

children?" 

Application of the evidence-based framework from the last review is reasonable given that there is no 

new information available since the last review that would improve our understanding of air-to-blood 

ratios or C-R functions for IQ at low-level exposures nor that would address previously identified 

limitations and uncertainties in the available evidence. (See my general comment above).

Uncertainties in evidence-based information (and exposure/risk estimates) are emphasized and 

enumerated repeatedly throughout this Chapter. However, there are information sources that could be 

used to address, at least qualitatively, some of these uncertainties. For example, elevated air lead levels 

in the workplace result in relatively rapid increases in blood Pb levels. (Admittedly, extrapolation of the 

occupational setting to low level exposures in pregnant women and children is uncertain and the timing 

of achieving steady state Pb levels may be uncertain). Still, human epidemiologic data, in turn, support 

Pb exposure over a trimester of pregnancy as being a potentially important determinant of subsequent 

neurocognitive development. With such information, one could estimate that exposures occurring over a 

period of months, if not an even shorter period, are likely relevant for certain critical windows of child 

development. 

2. "What are the Panel's views on staff's interpretation of the exposure/risk information, and on staff's 

conclusions that the information is generally supportive of conclusions drawn from the evidence-based 

framework as to the adequacy of the current standard?" (no new REA, use REA from last review)

This interpretation is reasonable given that information supporting the current standard is largely 

unchanged since the current standard was issued. (See my general comment above).
A-14

3. "What are the Panel's views on public health policy judgements that inform staff's preliminary 

conclusions with regard to the adequacy of current standard and a lack of support for consideration of 

potential alternative standards?"

Child IQ is the Pb-sensitive health endpoint on which this PA (and the previous one) is based. Thus, the 

discussion of health policy judgements needs to be carefully considered in light of the fundamental and 

far reaching public health value of childhood cognitive and neurobehavioral health. For example, the 

2012 CDC update of recommendations regarding childhood lead poisoning includes acknowledgement 

that there is no blood Pb level in childhood that is safe from potential neurocognitive toxicity. In this 

context, defining the threshold for "unacceptable risks to public health" or "sufficient public health 

protection" is difficult. Indeed, such language with its implicit use of a threshold approach to a process 

that presumably has no threshold may no longer be appropriate. 

4. "In the Panel's view, does the discussion in section 4.3 provide an appropriate and sufficient rationale 

to support staff's preliminary conclusion that it is appropriate to consider retaining the current standard 

(including the indicator level, averaging time, and form) without revision?" 

The short answer is "yes". However, it would be helpful if there was more description in the PA of the 

data and rationale behind the averaging time and form of the current standard. In contrast, there is some 

discussion in the PA regarding the choice of indicator level. (Also, see my general comment above). 

5. "Does the Panel have any recommendations regarding additional interpretations and conclusions 

based on the available information that would be appropriate for consideration beyond those discussed 

in this chapter?"

I have no recommendations except to encourage development of research programs to address those 

limitations and uncertainties in currently available evidence (and exposure/risk information) that are 

critical to the identification of "sufficiently health protective" air Pb standards in the future. 

For the purposes of policy and decision making, I recommend that key research priorities include studies 

to elucidate: (1) the air-blood Pb relationship at low levels, (2) sources (exposure pathways) contributing 

to current population blood Pb levels, especially in children, and (3) the relationship of Pb with 

childhood neurocognitive function at current population exposure levels.
A-15

Dr. Michael Kosnett

1. I concur with the key finding of draft Policy Assessment (PA) that the currently available information 

supports a primary standard as protective as the current standard, and that it is appropriate to retain the 

current standard without revision at this time. 

2. I agree that the adverse impact of low doses of lead on neurocognitive function and development in 

children remains the most sensitive health endpoint, and that a NAAQS designed to protect against that 

effect will offer satisfactory protection against the many other health impacts associated with lead 

exposure. I agree with the findings in the draft PA that the scientific findings pertaining to air-to-blood 

lead ratios and the concentration-response relationships between blood lead and childhood IQ that 

formed the basis of the current NAAQS remain valid and are consistent with current data. I further agree 

with EPA’s prior assessment that from a public health standpoint, “an IQ loss on the order of one to two 

IQ points [should] be prevented in all but a small percentile of the population.” 

3. I concur with the recommendations suggested in Section 4.4 “Key Uncertainties and Areas for Future 

Research and Data Collection.” I particularly agree with the recommendation in the last bulleted section 

on page 4-35 that reads: 

An important aspect to this review is the relationship between ambient air Pb and outdoor dust 

and surface soil Pb concentrations, including the temporal dynamics of that relationship .... 

[emphasis added]. 

This research point is of particular interest because of the prominent contribution of past (as opposed to 

recent) lead emissions to lead in soil and dust, and the significant contribution of dust and soil matrices 

to the lead exposure of children. 

For the typical American adult not subject to current or past point sources or to occupational lead 

exposure, lead in the diet constitutes the largest fraction of daily lead exposure. Therefore, another 

research question of considerable interest would investigate the source of contemporary dietary lead, 

including the indirect contribution of historical air lead emissions (i.e. “legacy lead”).

Additional research questions of considerable importance include the following: 

• The effect of contemporary lead exposure (i.e. that resulting in blood lead concentrations on the order 

of 5 ug/dL or lower) on the future risk of hypertension and cardiovascular morbidity and mortality, and 

on age-related neurodegeneration.

• The role of “reverse causation” in the inverse association observed in some studies between low blood 

lead concentration and renal function (glomerular filtration rate).

• The extent to which product substitution, i.e. replacement of lead with less hazardous alternative 

substances in contemporary commerce, may result in reduction of human lead exposure. EPA might 

consider supporting studies on lead potentially undertaken by programs such as the Toxic Use Reduction 

Program in Massachusetts, and the Green Chemistry Initiative in California.
A-16

4. The PA, particularly in Chapter 5, should acknowledge the contribution of lead in spent ammunition 

to the critical load of lead in certain ecosystems, and the important contribution that this source has on 

certain ecological receptors such as raptors and other large birds. Recent evidence confirms that these 

species are among the most heavily lead poisoned, sometimes to the point of death (Watson RT, Fuller 

M, Pokras M et al [eds] Ingestion of Lead from Spent Ammunition: Implications for Wildlife and 

Humans. Peregrine Fund: Boise, ID, 2009). The incremental contribution of air Pb to the food chain and 

ecosystem of fauna impacted by spent Pb ammunition therefore takes on considerable importance. 

5. The following statements in the draft PA should be subject to revision: 

Page 3-2, Line 15 referring to distribution of lead from bone to blood, includes the sentence: “Changes 

in Pb exposure circumstances can also influence these exchanges, e.g., substantial reductions in 

exposure levels contribute to increased release of Pb from the bone into the blood (ISA, section 4.3.5).” 

This sentence should be revised, as it appears to incorrectly characterize the information in section 4.3.5 

of the ISA. A reduction in external lead exposure does not, from a pharmacodynamic standpoint, induce 

an increase in the release of lead from bone. In the context of the paragraph, the intended point could be 

expressed as follows: “When there are substantial reductions in external Pb exposure, the relative 

contribution of Pb from bone to the concentration of Pb in blood increases.”

Page 3-5, line 29 to Page 3-6, line 9: The italicized sentence in this paragraph, reproduced below, should 

be revised to improve clarity:

The response of adult blood Pb levels to appreciable changes in exposure circumstances is 

generally slower than that of blood Pb levels in young children. For example, simulations using 

biokinetic models indicate that blood Pb levels in adults achieve a new quasi-steady state within 

75-100 days (approximately 3-4 times the blood elimination half-life) subsequent to abrupt 

increases in Pb intake (ISA, section 4.3.5.2); similar models indicate a much quicker response of 

blood Pb levels in children both with regard to abrupt increases and reductions in Pb exposure 

(ISA, section 4.3.5.1). The response in young children may reflect their much more labile bone 

pool associated with the rapid turnover of bone mineral in response to their rapid growth rates 

(ISA, section 4.3.5). As a result of these physiological processes in young children, their blood 

Pb levels tend to more quickly reflect changes in their total body burden (associated with their 

shorter exposure history), and can also reflect changes in recent exposures (ISA, section 4.3.5). 

Instead of the italicized sentence above, substitution of a sentence such as the following might enhance 

clarity: “Because the skeletal compartment of Pb is relatively smaller and subject to more rapid turnover 

in children compared to adults, the blood Pb concentration of children is more reflective of their recent 

external exposure.” 

Page 3-24, footnote 22. The units for blood lead cited here should be “μg/dL”, not “μg/m3”.

Page 4-24, footnote 9. This footnote, reproduced below in its current form, could be editorially revised 

to improve clarity. This might be accomplished by rewriting it as two shorter sentences, instead of the 

current long sentence:

“We note that the value of the upper bound is influenced by risk associated with exposure 

pathways that were not varied with alternative standard levels, a modeling limitation with the 
A-17

potential to contribute to overestimation of the upper bound with air quality scenarios involving 

air Pb levels below current conditions for the study area (see sections 3.4.4 and 3.4.7 above).”
A-18

Dr. Roman Lanno

The Policy Assessment document (did not read chapters 3 and 4) is well written and summarizes 

evidence justifying retaining the current secondary standard without revision. Retaining the current 

standard is warranted given the lack of significant additional data that has become available since the 

last AQCD. The US EPA nicely describes that the new data adds to an existing database, refines some 

key concepts (e.g., bioavailability, critical loads), but is not yet ready for application in the development 

and revision of a new secondary standard. Additionally, uncertainties in Pb exposure/risk are addressed. 

The magnitude of the contribution of Pb from air to the total environmental Pb load and the fate and 

distribution of airborne Pb to other environmental media is discussed. Figure 1-1 provides a nice 

backdrop for discussing these issues. The confounding effects of other sources of Pb (e.g., surface runoff 

to waters near industries) and the “challenge of disentangling of atmospheric deposition contributions 

from those associated with surface runoff” are discussed. Uncertainties related to screening values used 

in the risk assessment are also discussed.

Page 2-1, line 11 – change “depending on their size” to “depending on particle size”

Page 2-20, lines 26 and 27 – change “adsorption” to “absorption”

Page 2-38, line 5 – What is meant by “substantially”? Is this a statistically significant decrease and if so, 

by how much? Half, ten-fold? Specifics would help here.

Page 2-40, line 7 – remove underscore in 20 ug/kg

Page 2-40, line 12 – Should this be Figure 2-14, not 2-16?

Page 2-41 – Figure 2-14 shows very nicely the drop in environmental Pb due to the phasing out of 

leaded gasoline

Chapter 2 provides an excellent summary of temporal trends in Pb exposure, especially the influence of 

removing Pb from automotive gasoline.

Comments on Chapter 5 - Welfare Effects and Exposure/Risk Information

To what extent does the information in section 5.1 (Welfare Effects Information) capture and 

appropriately characterize the key aspects of the evidence assessed and integrated in the ISA?

Section 5.1 adequately summarizes the key aspects of evidence assessed and integrated in the ISA.

With regard to the exposure and risk information in section 5.2 (Exposure and Risk Information), to 

what extent is the information drawn from the screening-level risk assessment in the last review 

sufficiently characterized and clearly communicated? To what extent is the information appropriately 

interpreted in light of the currently available information and for the purpose of assessing the adequacy 

of the current standard?

The information in section 5.2 adequately integrates and communicates the information from the 

screening-level risk assessment and provides an appropriate interpretation and decision on the adequacy 

of the current secondary standard.
A-19

Are the limitations and uncertainties in the exposure/risk information appropriately characterized and 

considered in our interpretation of the information in the context of this current review?

The limitations and uncertainties of both the data and the screening levels used in risk assessment of 

case studies are adequately discussed.

Page 5-2, lines 28-31 – another major issue is that Pb rarely occurs alone but in mixtures with other 

metals

Pages 5-8 and 5-9, lines 35 and 1 – in addition to the issue of single species toxicity tests not capturing 

the complexity of bioavailability in natural systems, there is a lack to models that integrate 

bioavailability information that would allow prediction of toxicity among soils varying in physical and 

chemical characteristics

Page 5-10, line 7 – If this data is based only upon nominal concentrations, then it should only be 

considered as secondary data and should be used very cautiously in a PA document. I would suggest 

omitting it, unless there are actual measurements of Pb in the test medium.

Page 5-15, line 5, end of line – change “summarizes” to “summarizing”
A-20

Mr. Richard L. Poirot

Comments on Chapter 2

To what extent does the Panel agree that the most relevant information on emissions (section 2.1), air 

quality (section 2.2.2), and Pb concentrations in other media (section 2.3) is presented, and to what 

extent is the information presented appropriately characterized and clearly communicated?

With a few minor exceptions (see specific comments) the information on Pb emissions, air quality and 

concentrations in other media is appropriately characterized and clearly presented. Historical and recent 

(2008) emissions data are summarized quantitatively in clear charts and tables, with additional detail on 

the 2008 NEI inventory data sources and limitations provided in Appendix 2A. There are also some 

(qualitative) discussions and an informative Appendix (2B) on recent regulatory actions, indicating that 

current emissions have declined since 2008, with additional reductions pending. In a future PAD, it 

would be useful if quantitative estimates of some of these emissions reductions could be presented.

The Information on ambient air concentrations (through 2011) is also clearly presented in maps, charts 

and in a detailed appendix (2D). There are more recent data (including near airports) that were initiated 

following the previous Pb NAAQS review, and which would be informative for the current Pb NAAQS 

review, as well as for the separate Section 231 avgas review. It would be useful if some of these more 

recent data can be presented in (or as a supplement to) the next Pb PAD. While it may take 3-years of 

data to calculate an official design value, an exceedance of the Pb NAAQS and other potentially useful 

information can be provided by as few as 3 months of new data.

The Information on Pb concentrations in other media is clearly presented. The sections (2.3.2.1 and 

2.3.2.2) on indoor and outdoor dust (and air contributions to) are highly relevant to exposure 

assessments and would benefit from some added discussion (also missing in the ISA) of how dust Pb 

concentration, loading, and loading rates are measured. In particular, information relating to the 

differences in particle sizes in dust samples and ambient air samples would be helpful. Information on 

spatial gradients of Pb concentrations in soil, sediments or biota in the vicinity of large (current or 

former) sources could also be informative for conducting exposure assessments or for siting monitors.

With regard to information on ambient Pb monitoring (section 2.2.1), to what extent is this information 

appropriately characterized and clearly communicated?

The information on ambient Pb monitoring is appropriately characterized and clearly communicated. It 

is understood that we are “stuck” with the Hi-Vol TSP sampler as an imperfect historical artifact, and 

that there is not time to develop and fully test alternative samplers that would consistently capture 

particles greater than 10 microns with appropriate collection efficiencies and size ranges under varying 

wind speeds and directions. The draft PAD notes that the Agency expects a new, improved sampler to 

be “available for consideration in a future review”. Given that the Agency had also expressed an interest 

in developing an alternative “TSP” sampler (low-volume TSP FRM) in the previous 2008 NAAQS 

revision, it would be desirable at some point to see a commitment to expend the resources needed to 

have an alternative sampler “available for consideration in the next Pb NAAQS review”.
A-21

Toward this goal, it would also be useful to see some discussion indicating what the desirable cut size 

characteristics of an alternative sampler might be. Information provided in the 3rd draft ISA could be 

cited here, for example (page 3-67) of the ISA: “The relevant particle size distribution for ambient 

sampling is smaller than the size distribution of the settled dust. Particles larger than about 20 μm are 

generally considered too large to be transported for more than a few seconds under typical conditions... 

It follows that 15 to 20 μm may be a practical limit for both good sampling data quality and 

representative sampling in a limited area.”

Along similar lines, the term TSP is used broadly and imprecisely to mean several different things –

including what the Hi-Vol collects, what other currently available so-called TSP samplers collect, and 

what a future alternative TSP sampler might collect (all of which differ from each other). Development 

and usage of more precise terminology could be helpful. No wonder our sampling technology remains 

so imprecise...

Specific Comments

P 2-1, line 11: Change “their” to “particle”, or add “particles” after “Pb” in line 10.

P 2-2, lines 13,14: It might be helpful to provide a few examples here of the recent or pending Pb 

emissions reductions, or at least a pointer to Appendix 2B.

P 2-3, lines 13 and generally in this paragraph: Since you have previously emphasized the considerable 

emissions reductions since the 2008 NEI, why not use the past tense consistently (as in the last sentence 

of this paragraph)., or “...largest source sector emitting Pb into the atmosphere in 2008 was aviation 

gasoline...”, etc.

P 2-3, line 14: A minor point, but combining mining and metal working into a single category seems a 

bit odd, and makes for an awkward following sentence, in which fuel combustion is identified as the 

second largest source category. I wonder if you might instead say something like “Following avgas, 

which accounted for almost 60% of 2008 Pb emissions, the general metal working and mining, fuel 

combustion and miscellaneous source categories each contributed 10% to 15% of the 2008 total.” 

P 2-5, line 13: Would it be possible to provide some indication of how large these pending emissions 

reductions will be?

P 2-6, lines 15-28: This separate CAA Section 231 review process is interesting and unusual, and would 

seem to emphasize the importance of the recently initiated airport Pb monitoring. If any exceedances 

were observed in that monitoring (and/or given the results of the recent Miranda et al. (2011) study), it 

would seem impossible for EPA to conclude that avgas could not be reasonably anticipated to endanger 

public health. Hopefully it will be possible for EPA to report any available results from the recent airport 

monitoring in a subsequent PAD. 

Miranda, M.L., R. Anthopolos, and D. Hastings (2011) A Geospatial Analysis of the Effects of 

Aviation Gasoline on Childhood Blood Lead Levels, Environmental Health Perspectives 119: # 

10, 1513-1516.
A-22

P 2-7: lines 3-8: Could you provide a quantitative indication of the reduction (in tons or %) of NASCAR 

Pb emissions that have resulted from switching to unleaded fuels in the “major” race series? Is there 

some schedule for elimination of Pb fuels for the remaining “minor” race series?

P 2-7, lines 21 and 28: Can you provide averaging times for these concentrations?

P 2-7, line 33: You could add “historical” before “sources”.

P 2-11: There seems to be a slight discrepancy (airport monitoring sites in TX) between the airport 

monitors indicated in Figure 2-2 and in Figure 2.4. Remind me why airport monitoring is not required at 

airports emitting > 1 ton?

P 2-12, line 15: Seeing the words “accessible” and “AQS” in the same sentence always brings a smile.

P 2-13, line 20: Has any such additional monitoring been required by the Regional Administrators?

P 2-16, lines 1-3: But presumably some airport sites were operational on or before 12/27/11 and have 

now collected a year – or at least multiple 3-month periods – of data, which would be of great interest to 

see in the next PAD.

P 2-16, Figure 2-4: As noted previously, the airport monitor in eastern TX in Fig. 2-4 is not indicated in 

Fig. 2-2, and a northern TX airport monitor in Fig 2-2 is not indicated in Fig. 2-4. 

P 2-18, line 3: You could add “currently” before “quantified” since IMPROVE Pb analysis was 

conducted by PIXE prior to 6/1/92.

P 2-18, lines 4-5: The VIEWS reference is currently functional. However VIEWS is no longer funded or 

updated (except for the IMPROVE database). To assure future functionality, you could change “VIEWS 

website” and link to “FED website (http://views.cira.colostate.edu/fed/)”.

P 2-18, line 5: You could add “currently” before “operated” since IMPROVE did not operate on a 1-in-3 

day schedule prior to 2000. 

P 2-18, lines 7-13: To fix several small inaccuracies, I suggest replacing these 3 sentences with: “The 

original IMPROVE network began sampling in 1988, with 36 monitors located in or near “Class I” 

federal areas (including National Parks and Wilderness Areas, which are afforded special visibility 

protection under the Clean Air Act). The network underwent major expansions in in the early 1990s and 

2000s, and currently includes 110 sites located in or near Class I visibility areas, virtually all of these 

being rural. Approximately 60 additional “IMPROVE protocol” sites at various urban and rural 

locations, requested and funded by various parties, have also been included as part of the IMPROVE 

network (Figure 2-6).” 

P 2-19, line 17: As noted in comments on the 3rd draft ISA, I think the term “TSP” is vaguely defined, 

and used to mean many different things. In this case an “alternative TSP” sampler would not collect the 

same TSP as the current “Pb-TSP” FRM sampler. If it did there would be no need for it. To clarify the 

intended meaning, I suggest adding a text box with wording something like: TSP is an acronym for 

Total Suspended Particles, an hypothetical and un-measurable concept. In this document, we use the 
A-23

term TSP to mean “particles with the size characteristics of those collected by the high volume (Hi Vol) 

TSP sampler” and Pb-TSP to mean “Pb in particles collected by the Hi Vol TSP sampler”. When 

referring to alternative existing or future samplers with an upper 50% particle cut size larger than 10 

microns, but not identical to the Hi Vol TSP sampler, we use the term “TSP” in quotes.

P 2-20, line 7, or elsewhere: This might be an appropriate place to add discussion similar to that recently 

added to the ISA suggesting that there is some convergence between the practical limits on largest 

particle cut sizes for size-selective sample technologies and the upper size limits for spatially 

representative sampling of “airborne” particles that remain suspended for more than a few seconds. For 

example on page 3-67 of the ISA: 

The relevant particle size distribution for ambient sampling is smaller than the size distribution 

of the settled dust. Particles larger than about 20 μm are generally considered too large to be 

transported for more than a few seconds under typical conditions... It follows that 15 to 20 μm 

may be a practical limit for both good sampling data quality and representative sampling in a 

limited area.

P 2-22, lines 18-21 and 32-33: Hopefully some of this new data can be presented in the next PAD. 

While 3 years of data may be needed to develop complete design values for the new monitors, 

exceedances of the NAAQS could be observed with as few as 3 months of data – and would be 

informative to see as (or if) they occur.

P 2-24, Figure 2-8: Use of a lower scale (max of 1 μg/m3) would help, if feasible.

P 2-28, lines 6, 7, and Figures 2-11 to 2-13: Could ”previous source-oriented sites” be defined? 

Assuming this means “sites near sources which have shut down”, the implication is that this second 

highest concentration category (where it appears some sites are approaching the NAAQS) would seem 

to be heavily influenced by fugitive emissions of historically deposited Pb. Or is it possible this category 

includes Pb sources that have changed operations or controlled emissions below some threshold level? 

Could the category include sources that were shut down during the 2009-2011 period?

Assuming this category does represent sites where former Pb sources have shut down – and that 

therefore resuspension of historically deposited Pb is a likely cause of the relatively high concentrations 

– it could be informative to report any observed changes over time for sites in this category. It would be 

important to know if the availability of historically deposited Pb remains constant or diminishes over 

time.

P 2-28, line 9: Switch “additional” and “indicate”.

P 2-28, line 15: Change “Pb” to “Pb-TSP”.

P 3-34, line 1: Delete the “0” before “air”.

P 3-34, line 2: Change “at” to “near”. 

P 3-34, line 5: Maybe change “arises” to “originates” to make it clear you’re not necessarily talking 

about dust suspended in the air.
A-24

P 3-35, line 1: I must be missing something, but can’t understand how controls could reduce ambient 

concentrations by 75%, but only reduce outdoor dust concentrations and loading rate by 50% - unless 

maybe dust concentration and loading rate were “measured” by methods that included larger particles 

(from resuspension of historical Pb deposits) than the ambient air sampling measured. 

P 3-36. Line 4: Add “Pb” before “occurring”.

P 2-36, line 9: You could add “spatial patterns and” before “documented reductions”.

P 2-37, lines 5-27: This is a nice summary, but the little bit of discussion of rates of soil Pb decline as a 

function of distance from sources like roadways or smelters reminds me that the general topic of Pb 

gradients (soil, dust, or ambient air concentration) near sources, is not much discussed in the PAD or 

ISA – but could be useful in terms of exposure assessments, monitor siting, etc. This is also a subject 

area where some modeling – evaluating concentration and deposition patterns of different particle sizes 

– could be informative. Maybe next review cycle...

P 2-38, line 12: Can you report how far from the road this “greater distance” was?
A-25

Dr. Michael Rabinowitz

Comments on Executive Summary and Chapter 1 (Introduction)

Does the Panel find the introductory and background material, including that pertaining to previous 

reviews of the Pb standard and the scope of the current review to be appropriately characterized and 

clearly communicated?

Yes, this text adequately provides the reader with a clear, stand-alone basis to make the decision to 

retain or revise the current standard. The regulatory background material and the review of the lead 

pathways in Chapter 1 are satisfactory and sufficient.

Some small additional comments:

On page ES-1 line 25, why not add for emphasis ...This approach was taken to aid in the decision to 

retain or revise the current standards. 

line 31 I concur that retaining the current air standard makes sense, because air lead is 

not the problem now. Even if we were to move the standard to zero, the response in blood lead levels 

would be very small, given the other sources of lead exposure. 

In Chapter 2 page 2-8 line 22 perhaps add....and these are expected to decrease further with the passage 

of time.
A-26

Dr. Ian von Lindern

Comments on the Introduction (Chapter 1)

This chapter provides context for the review, including the background of past reviews, as well as the 

scope for the current review. This includes discussion of fate and multimedia pathways of ambient air 

Pb and other nonair sources of Pb in the environment.

Does the Panel find the introductory and background material, including that pertaining to previous 

reviews of the Pb standard and the scope of the current review to be appropriately characterized and 

clearly communicated?

The Introduction provides a clear and concise description of the new Integrated Science 

Assessment/Risk and Exposure Assessment/Policy Assessment (ISA/REA/PA) process; providing the 

purpose, background, history, and scope of the review and summary of the document’s organization and 

structure. It is well written and does avoid excessive jargon, so as to be readable and understandable to a 

general audience. 

However, I believe it overdoes the conclusion that no information justifying reconsideration of the 

NAAQS has accumulated in the last five years, without caveats to convey the level of uncertainty and 

lack of information in some areas important to consider in the formulation of US lead regulatory policy. 

PURPOSE AND SCOPE: The PA does indicate one purpose is to “bridge the gap” between the 

scientific assessments in the ISA and REA, but a concise description and purpose and scope of the ISA 

and REA would be helpful. With regard to purpose, my understanding in reading the PA, is that analysis 

and synthesis are limited to the question as to whether any information has accumulated in the previous 

5 years that would prompt reconsideration of the primary and secondary NAAQS; and that, in turn, is 

limited to indicator, averaging time, form and level. 

The general conclusion is that no new information has surfaced through the ISA process that would 

prompt reconsideration of the indicator, averaging time, form and level. I would generally agree with 

that conclusion. 

However, this conclusion should be conveyed with an assessment of the adequacy of the old 

information. With respect to health effects, large volumes of new information have come forward to 

supplement an already rich database. However, for other areas there are significant unknowns and 

uncertainties associated with the lack of information available for the last review. Those inadequacies 

and uncertainties should be conveyed to policy makers. A finding that no new data have come forward 

to assist in reviewing the previous decision based on a paucity of information - sends a different 

message to policy evaluators, than stating that the new studies don’t refute the analysis of the existing 

database.

With regard to scope, the PA uses the term to accentuate that lead is a multimedia contaminant and the 

scope of the document goes beyond air. The ISA and REA extend to other media that are impacted by or 

impact air lead, and project and integrate the effect of lead exposures from other media on human and 

ecological receptors. This is appropriate and necessary to effectively evaluate the role and impact of air 
A-27

lead regulation and is accomplished in the context of the other media. Apparently, this is in contrast to 

other priority pollutants as the PA notes.

However, with respect to subject area and geography, the ISA and PA are limited in scope, both in 

contrast to the former CD/ Staff Paper process; and with respect to the potential impacts of policy 

decisions to other components of the environment and beyond the US. These limitations are not 

conveyed in the PA.

With regard to the ISA, it is not clear in the PA that the ISA is limited only to exposures and data 

sources considered currently relevant to the US population. And that the significance of new studies is 

assessed only as to how these relate to conclusions drawn in the past review; and then only to studies in 

the peer reviewed literature. This has resulted in an ISA that is more than 70% dedicated to toxicology, 

health effects, bio-kinetics, and causal determinations. These are areas that were data rich in the last 

review, and continue to produce volumes of new peer reviewed information. In contrast, in areas where 

the least is known and EPA relies on past findings, uncertainty is becoming greater as the existing 

information becomes outdated; and some areas important to policy determinations have been eliminated 

from the review and no information is assessed or conveyed. 

The areas of great uncertainty include any consideration of information relative to the production, use, 

and disposition of lead in the US. The last CD noted that lead use in the US by 2006 was nearing the 

record levels observed during the tetra-ethyl lead gasoline-additive years. Demand for lead for in 

batteries and electronics is ever increasing. Lead prices have been at record highs despite the global 

recession. Where the previous CD contained and acknowledged inadequate data on production, use, and 

disposition of lead in the US – the ISA doesn’t mention it, not even as background discussion.

With regard to the REA, the purpose is not described in the PA; but there is an indication that both the 

staff and CASAC felt a new REA was not warranted. However, the PA fails to note that the 2006-8 

REA was less than ideal. The 2006-8 REA was based on modeling exercises; that necessarily had high 

levels of uncertainty, due to the paucity of production, monitoring and emissions data. As no potentially 

useful new model input data were identified in the staff literature search in 2010-11, attempting a new 

REA would have been superfluous. The policy-makers and evaluators should be informed of this lack of 

data, levels of uncertainty, and decreasing confidence that the REA is reflective of current conditions. 

Failure to distinguish between no data and supportive data in these decisions could perpetuate the use of 

these outdated analyses 5, 10, 15 etc. years in future reviews.

In the previous ISA Draft review, I offered comments regarding the change in procedures from 

developing CDs and Staff Papers to the current ISA/REA/PA. My opinion was, and remains, that this 

results in insular and less comprehensive review process. In that regard, the historic discussion fails to 

note that previous reviews were not so limited, and that EPA policy makers and policy critics were 

provided with scientifically vetted information regarding the role of lead in US commerce, and data 

obtained and analyzed from other EPA Offices to use in effecting more comprehensive and holistic 

policy. A 1990 Staff Paper reviewed by CASAC specifically addressed the consistency and impacts of 

lead regulation across the EPA and other agencies, resulting in a comprehensive inter-agency policy. No 

such communication is evident in the new process. 

The failure to collect and or assess information relative to the production, use and disposition of lead in 

US commerce, and the decision to exclude globally representative exposures, precludes the Agency 
A-28

from considering the effects of policy decisions in media other than air, and beyond the boundaries of 

the US.

As a result, it is inaccurate to indicate that no new information has accrued relevant to the impact of US 

air lead policy on exposures, health effects, and health and economic damage outside the US. It is more 

accurate to say that new ISA/PA process excludes consideration of impacts on populations outside the 

US; that these studies, databases, and other potentially pertinent information was not sought, assessed, 

nor reported on by the Agency; and that this is a significant change from previous NAAQS reviews. 

It would be more comforting to know that information relevant to consideration of the potential harm 

done overseas by US policy with regard to lead in the air, other media and commerce regulated by the 

EPA is being vetted, and used somewhere within the Agency to acknowledge or alleviate global 

suffering. 

Historically Emitted Lead is given special consideration in both the ISA and the PA as a residual 

contaminant in various media, a source of potential emissions, a potential steady-state component of 

different ecosystems, and a continuing exposure to humans. There is considerable discussion dedicated 

to the reduction of lead in air and other media in the US over the last four decades. 

The analysis notes significant reductions and attributes the decline to various factors. Most of the decline 

in emissions and ambient air exposures was achieved through the elimination of tetra-ethyl lead gasoline 

additives. Another major component was substantial decreases in emissions from primary and secondary 

smelters, and metals processing industries. In the case of gasoline-related emissions, these ceased and 

other non-lead products were substituted in commerce. This resulted in decreased lead emissions and 

health and environmental effects in both the US and globally. 

In the case of lead production and secondary recovery, however, this production and recovery were 

exported overseas. The ISA analyses extensively noted the declines in air lead concentrations and past 

accumulations in soils, sediments and other sinks. However, there is no mention, consideration or 

assessment of the impact of the “avoided emissions” in their new locales, much of which may be 

sequestered in repositories in the US, or exported and released in other countries. The ISA and PA did 

note that these excessive emissions in Asia are detectable in the US, and that contaminated cocoa beans 

have been observed from Africa, but not at health significant concentrations.

However, in the developing world, these emissions are of considerable significance and, too often, have 

tragic health consequences. Much of the lead produced in these countries, finds its way to US 

consumers, is eventually disposed of back to the developing countries; setting up a recycling of 

exposure. It seems that EPA policy makers should be made aware that these conditions result from the 

same policy decisions so favorable to US population and the environment, if for no other reason than to 

convey the findings to other regulatory or legislative functionaries.
A-29

Dr. Gail Wasserman

Comments on Chapter 3

How well do sections here map onto conclusions and evidence of ISA?

Sections on both “Public Health Implications and At-Risk Populations” and “Concentration response 

functions for child IQ decrements” are clearly written, and these sections maps well onto the information 

presented in the ISA.

Smaller edits

P3-28 L 22 “behavioral [and] physiological factors”

P 3-31 L 19. Differences between black and white individual betoken racial, and not ethnic 

backgrounds. Differences across subgroups of Hispanics would be “ethnic” differences. The most 

general way to aggregate these comparisons would be to refer to “different racial or ethnic groups” in L 

19.
A-30

Dr. Michael Weitzman

Comments on Chapter 3 - Health Effects and Exposure/Risk Information

In my opinion this is an extremely good chapter, and my comments and suggestions are largely editorial 

or minor in nature.

3-1, line 17 and 18: should the order be changed to “gastrointestinal tract and the respiratory system” as 

most absorption is via the GI tract although the focus of our work is on ambient air lead?

3-1, line 19-21: This sentence, I believe, is unclear.

3-2, line 19: substitute “one” for “a”

3-2, line 28: I suggest changing “current maternal exposure” to “...to exogenous sources of lead during 

pregnancy.”

3-2, line 31: after “umbilical cord” change wording to “which is representative of newborn blood lead 

levels”

3-3, line 16: do we know when blood lead levels begin to rise in infancy...I believe it is usually stated 

that they begin to rise around age 6 months but I am not sure of this.

3-3, line 24: can we cite specific national, i.e. CDC, HUD, EPA, and international health agencies ?

3-4 I have difficulty understanding Figure 3-1

3-5, line 21: I suggest adding “or lead contaminated soil”

3-8, line 14: I suggest adding “their more rapid respiratory rates

3-8, line 27: Mention is made of Table 3-1, I believe the Table should be moved up several pages.

3-14, line 10: Is it possible to estimate the % of blood lead from air by age or to mention that this is not 

possible to do because of multiple variables, including the intensity of exposure to other sources?

3-14, line 27: I suggest adding “strengthens and extends” conclusions.....

3-16, line 13: do we intentionally mean “is associated with” here or should it be “causes?”

3-21 Under Measure some are bolded and others are not bolded—it is unclear to me is this is due to 

footnote C Studies discussed in ISA....

3-23, line 16: I suggest changing “One exception” to “In addition, one...”

3-27, line 5: I suggest adding after population IQ “and neurocognitive and behavioral”
A-31

3-27, line 19: do we mean to say “associated with” or should it be “causes?”

3-29: should we mention very low birth weight, in utero cocaine, heroin, alcohol or tobacco exposure, or 

head trauma as examples of potentially vulnerable populations, or populations for which we currently 

have no data regarding the possibility of heightened vulnerability?