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> **UNITED STATES ENVIRONMENTAL PROTECTION AGENCY**

**WASHINGTON D.C. 20460**

> **OFFICE OF THE ADMINISTRATOR**
>
> **SCIENCE ADVISORY BOARD**

July 18, 2008

EPA-CASAC-08-016

The Honorable Stephen L. Johnson

Administrator

U.S. Environmental Protection Agency

1200 Pennsylvania Avenue, NW

Washington, DC 20460

> Subject: Clean Air Scientific Advisory Committee (CASAC) Comments and
> Recommendations Concerning the Proposed Rule for the Revision of the
> National Ambient Air Quality Standards (NAAQS) for Lead

Dear Administrator Johnson:

The Clean Air Scientific Advisory Committee (CASAC), augmented by
subject-matter-expert Panelists --- collectively referred to as the
CASAC Lead Review Panel (CASAC Panel) --- met via a public
teleconference on June 9, 2008. The purpose of this conference call
meeting was to hold discussions and provide comments concerning the
Environmental Protection Agency's (EPA) Proposed Rule for the Revision
of the National Ambient Air Quality Standards (NAAQS) for Lead (40 CFR
Parts 50, 51, 53 & 58), which the Agency released on May 1, 2008, and
which was published in the *Federal Register* on May 20, 2008 (73 FR
29184--29291). The CASAC Panel held a subsequent public teleconference
meeting on July 8, 2008 to discuss, and for the chartered CASAC to
approve, the draft letter (dated June 30, 2008) containing our comments
and recommendations. The CASAC Panel roster is enclosed.

While the CASAC is pleased that the Agency has recommended substantially
lowering the allowable air concentration (*i.e.*, the level of the
NAAQS) for lead in ambient air --- which has not been revised since 1978
--- the CASAC has several critical concerns vis-à-vis the Notice of
Proposed Rulemaking (NPR), including:

-   ongoing problems with respect to the implementation of EPA's revised
    NAAQS review process;

-   the last-minute introduction of a new analytical framework ---
    *i.e.*, the "Air-related IQ Loss Evidence-based Framework" --- as
    the *basis* for setting the primary (human-health based) Lead NAAQS
    --- a framework that was not previously presented for review by the
    CASAC or the public and also apparently excludes other analyses that
    had been produced to date by the Agency and subject to such external
    review;

-   the Agency's consideration of values for certain critical parameters
    (*e.g.*, the air-to-blood ratio and the slope of the
    concentration-response function curve) in this analytical framework
    that are contrary to those recommended by the CASAC, and that would
    justify a significantly-higher level for the primary Lead NAAQS than
    the CASAC recommended --- at the expense of the values for those
    selfsame parameters that the CASAC documented as being most relevant
    for the low levels of blood lead (Pb) found in U.S. children today;

-   the misrepresentation of the CASAC's statement that "the primary
    lead standard should be set so as to protect 99.5 % of the
    population from exceeding an IQ loss of 1-2 points" to wrongfully
    suggest that CASAC declared that an *average* loss of one to two IQ
    points in the population was an acceptable public-health endpoint;
    and

-   the Agency's proposal of a range for the level of the primary
    standard that includes an upper bound (*i.e.*, 0.3 μg/m^3^) which is
    higher --- and therefore less health-protective --- than that
    recommended in the final EPA Staff Paper and by the CASAC in any of
    its previous letters to you on this subject.

The following paragraphs describe in detail these and other concerns
that the CASAC identified in the Agency's proposed rule for the revision
of Lead NAAQS and, where applicable, reiterate the scientific basis for
the CASAC's previous recommendations.

**Implementation of Agency's Revised NAAQS Review Process**

Before commenting on the substance of the NPR, the members of the
chartered (statutory) CASAC wish to note that they are extremely, and
increasingly, concerned about the lack of a reliable, standard "roadmap"
for the implementation of the new NAAQS review process, as starkly
illustrated by the content of this NPR. With the introduction of any new
process, of course, it is essential that such a "path forward" be
clearly delineated and followed from the outset. However, CASAC members
cannot overstate how dissatisfying it has been to observe the
introduction of the Agency's revised process for reviewing the NAAQS ---
especially in the middle of the current review of the Lead NAAQS ---
without any discernible, well-organized plan.

As a significant example of the root cause of the CASAC's frustration,
we noted in our January 23, 2008 letter on this subject
(EPA-CASAC-08-008) that, in the memorandum from EPA Deputy Administrator
Marcus Peacock dated December 7, 2006, the Agency stated the new process
would include a true *policy assessment* that reflects the views of EPA
management --- to be published in the *Federal Register* as an advance
notice of proposed rulemaking (ANPR) --- that would "describe a range of
options for standard setting, in terms of indicators, averaging times,
\[statistical\] form, and ranges of levels for any alternative
standards," along with the underlying scientific justification and
supporting data and analyses for each of these." The Deputy
Administrator's memo goes on to state that such a policy assessment
would "help ... 'bridge the gap' between the Agency's scientific
assessment and the judgments required of the Administrator in
determining whether it is appropriate to retain or revise the
standards." Therefore, the CASAC was surprised to read in the NPR that,
"in analyses *subsequent to* the Staff Paper and ANPR, the Agency has
*primarily* considered the evidence in the context of an *alternative*
evidence-based framework'' (73 FR 29238, italics not in original) ---
that is, the aforementioned "air-related IQ loss framework." While it is
entirely reasonable to expect that the policy assessment contemplated by
the Deputy Administrator's December 2006 memo would *include* such an
"evidence-based" analytical framework, the CASAC notes with dismay that
*this alternative framework is not found in the Lead Staff Paper, the
Lead Risk Assessment or the ANPR for the Lead NAAQS*.

Therefore, the CASAC is led to conclude that the ostensible scientific
basis for standard-setting that had been previously presented for
rigorous review by the CASAC and the public was substituted at the last
minute for an "alternative" analytical framework that EPA plainly notes
was their *primary consideration* as the basis for the proposed rule for
the Lead NAAQS. At a minimum, the manner in which this process is being
implemented suggests that the Agency is "winging it" in an *ad hoc*,
rather than a systematic, manner. This is not what the public expects of
their EPA.

Finally, the CASAC notes with disappointment that, to date, there has
been no response from the Agency to our January 23, 2008 letter. In that
letter, the CASAC complimented certain features of the new NAAQS process
(*e.g.*, the "kick-off" science workshop and the integrated science
assessment. However, the CASAC also requested a modification of other
aspects of the revised process (such as the absence of a meaningful
policy assessment discussed above) that appear to be ever-shifting and
that tend to conceal the Agency's underlying scientific analyses from
its own, statutorily-mandated scientific advisory body.

**Introduction of New Air-Related IQ Loss Evidence-based Framework**

By the Agency's own acknowledgment, as noted above, the analyses that
led to the proposed range for the standard, especially the upper bound
of 0.3 μg/m^3^ (and possibly extending as high as 0.5 μg/m^3^), are
based primarily on consideration of the evidence found "in the context
of an alternative evidence-based framework" resulting from analyses
conducted subsequent to the release of the Final Lead Staff Paper
(November 1, 2007) and the ANPR for the Lead NAAQS (December 17, 2007)
--- that is, the evidence in a single new meta-analysis, entitled the
"Air-related IQ Loss Evidence-based Framework." The following comments
are focused primarily on this new analytical framework:

1.  **Timing:** In the professional judgment of the CASAC, *the issuance
    of the NPR is far too late a point in the regulatory process to
    introduce a set of new and apparently determinative risk
    calculations.* The CASAC notes that the Agency's stated intent is
    that this evidence-based framework "builds on a recommendation by
    the CASAC Pb Panel" (73 FR 29237). The CASAC infers that this
    recommendation stems from the information contained in Appendix D of
    the CASAC's letter of March 27, 2007 (EPA-CASAC-07-003) concerning
    its review of the [1^st^ Draft Lead Staff Paper]{.mark}
    (December 2006) and the Draft Lead Exposure and Risk Assessments
    (December 2006). The CASAC included Appendix D in its letter in
    order to provide the Agency with several population-based risk
    assessment analyses for the primary Lead NAAQS. However, the CASAC
    questions why EPA's analyses reflected in this "Air-related IQ Loss
    Evidence-based Framework" were not explicitly presented to the CASAC
    much sooner, either as part of the Agency's 2^nd^ Draft Lead Human
    Exposure and Health Risk Assessments (July 2007), the Final Lead
    Risk Assessment (November 2007), or the Final Lead Staff Paper
    (November 2007) --- or, at the very least, aired for open review by
    the CASAC and the public in the ANPR (December 2007). Instead, at
    this very late stage in the rulemaking process, we are presented
    with a set of heretofore unseen quantitative analyses --- an
    unfortunate scenario that, by definition, precludes an in-depth,
    thoughtful deliberation by the CASAC. Our objections to these
    analyses are noted in detail below. Moreover, there is considerable
    concern that this might be an example of EPA's "standard operating
    procedures" under the new NAAQS review process.

2.  **Exclusivity:** All other previous analyses, risk/exposure
    assessments, staff, CASAC and public recommendations appear to have
    been set aside, with this single new meta-analysis used as the
    exclusive basis for the proposed NAAQS level. The range of proposed
    standards appears to be predominantly driven by alternative --- and,
    in the CASAC's judgment, unwarranted --- assumptions of the
    appropriate concentration-response (C-R) functions to relate IQ
    score point reductions to blood Pb concentrations, combined with a
    policy judgment that a mean population loss of up to two IQ points
    is the desired health outcome of a revised Lead NAAQS.
    *Significantly, the CASAC notes that, aside from this new
    "air-related IQ loss evidence-based framework," no other analyses
    are presented that support a level as high as 0.3 (or 0.5) μg/m^3^.*

3.  **Air Pb-to-blood Pb ratios:** The analytical results are
    constrained to an assumed range of air-to-blood ratios of 1:3 to
    1:7, which is described as being consistent "with the results and
    observations drawn from the exposure assessment, including related
    uncertainties" (73 FR 29197). But this is only true if one: (1)
    discards the many estimated ratios that fall above this range; (2)
    ignores the clear indications that the air Pb to blood Pb ratio
    *increases* as both air Pb and blood Pb *decrease*; and (3) assumes
    that the related "uncertainties" are directionally-biased and
    somehow justify the use of lower ratios that are more representative
    of the much *higher* air Pb and blood Pb levels found in the U.S. in
    the 1970s and 80s. By contrast, EPA's Final Lead Staff Paper noted
    that, while "there is uncertainty and variability in the absolute
    value of an air-to-blood relationship, the current evidence
    indicates a notably greater ratio... *e.g.*, on the order of 1:3 to
    1:10" (p. 5-17) --- that is, *not* 1:3 to 1:7.

> Even from EPA's 1986 Air Quality Criteria Document (AQCD) for Lead,
> the analysis cited as Brunekreef *et al.* (*J. Air Pollut. Control
> Assoc.* 1983; 33: 872-876) indicated an air-to-blood ratio of 1:8.5.
> The Schwartz and Pitcher analyses (Schwartz, J., Pitcher, H., *J.
> Official Stat.* 1989; 5(4): 421-431) suggest a ratio of 1:9 or 1:10.
> Additionally, results from Hayes *et al.* (*Pediatrics* 1994;
> 93:195--200) suggested a range from about 1:6 (at high air Pb levels
> near 1 μg/m^3^) to 1:16 (at ambient air Pb of about 0.25 μg/m^3^ ---
> which are within the range currently being considered for the Lead
> NAAQS). In EPA's Final Lead Risk Assessment, estimated ratios ranged
> from 1:2 to 1:9 across the range of alternative standards considered
> for the urban case study and from 1:10 to 1:19 across the range of
> alternative standards considered for the primary smelter. The NPR
> discredits these risk assessment calculations by noting (without
> attribution of authorship) that "some have suggested, however, that
> the regression modeling ... could produce air-to-blood Pb ratios that
> are biased high" (73 FR 29197), although it later notes (73 FR 29215)
> that the ratios used in the risk assessment "reflect a subset of
> air-related pathways related to inhalation and ingestion of indoor
> dust \[and that\] inclusion of the remaining pathways would be
> expected to yield higher ratios." The lower end of the proposed range
> (1:3) reflects the much higher air and blood levels encountered
> decades ago, while the upper end of the range (1:7) fails to account
> for the higher ratios expected at lower current and future air and
> blood Pb levels, especially when multiple air-related lead exposure
> pathways are considered.
>
> The NPR states (73 FR 29197), "For the general urban case study,
> air-to-blood ratios ranged from 1:2 to 1:9.... \[and\] this pattern of
> model-derived ratios generally support the range of ratios obtained
> from the literature and also supports the observation that lower
> ambient air Pb levels are associated with \[a\] higher air-to-blood
> ratio." As several CASAC Panel members noted in their individual
> written comments attached to the CASAC's March 27, 2007 letter
> (EPA-CASAC-07-003), the best documented evidence for the blood-to-air
> ratio under current conditions is based on actual epidemiology data
> showing that declines in U.S. national blood Pb levels from the
> National Health and Nutrition Examination Survey (NHANES) surveys
> tracked declines in EPA- and state-monitored air Pb levels over the
> same time period and the air-to-blood ratio was 1:10. Given that there
> is agreement that the *lower* the current air Pb levels the *higher*
> the air-to-blood ratio, *the CASAC recommends that the Agency use an
> air-to-blood ratio closer to 1:9 or 1:10 as being most reflective of
> current conditions*.

4.  **C-R Functions:** The critical concentration-response functions
    used in this meta-analysis represent the estimated slope of the
    relationship between IQ point decrements and blood Pb concentration.
    As summarized in Table 1 of the NPR (73 FR 29203), the analysis
    identifies two groups of C-R functions --- one with *steeper* slopes
    (ranging from -1.71 to -2.94 IQ points per μg/dl blood Pb) and one
    with *shallower* slopes (ranging from -0.4 to -1.79 IQ points per
    μg/dl blood Pb). The median value of the shallow-sloped group
    (-0.90) is subsequently used (as the "2^nd^ group of C-R functions")
    in the summary Table 7 "Estimates of Air-Related Population Mean IQ
    Loss for Children Exposed at the Level of the Standard" (73 FR
    29239). *Like the lowest air-to-blood Pb ratio (1:3), the
    shallow-slope C-R function (-0.9) is based on analyses of
    populations exposed to much higher air Pb concentrations and
    exhibiting much higher* *blood Pb levels than is appropriate for
    current U.S. populations and the levels under consideration for a
    revised Lead NAAQS.*

> For example, the median blood Pb level for children one to five (1-5)
> years of age from the NHANES survey dropped from 3.5 μg/dl in 1988--91
> to 1.9 μg/dl in 2003--04 (at which time the 90^th^ percentile blood Pb
> level was 3.5 μg/dl. However, all eight of the "shallow slope" C-R
> functions presented in Table 1 had geometric mean blood Pb levels
> (indicated as "BLL" in Table 1) greater than 3.3 μg/dl, and the four
> studies with slopes below the median value of -0.9 IQ points/μg/dl BLL
> had geometric mean blood levels ranging between 4.3 and 9.7 μg/dl.
> Within the shallow-slope group, the only studies with geometric mean
> BLLs less than 4 μg/dl (which were the only studies in that group
> based entirely on U.S. population groups) had slopes of -1.6 and -1.8
> respectively. *It is only the combination of the lowest C-R slopes and
> lowest air Pb to blood Pb ratios --- both representative of much
> higher exposure conditions of 30 years ago --- that provides any basis
> for considering a standard as high as 0.3 μg/m^3^.*
>
> In questioning the validity of the higher slope C-R functions
> (typically based on lower blood Pb level population subsets of larger
> population studies), the NPR (73 FR 29209) first notes that "these
> analyses are quite suitable for the purpose of investigating whether
> the slope at lower concentration levels is greater compared to higher
> concentration levels" *---* but then cautions that the "use of such
> coefficients as the primary C-R function in a risk analysis such as
> this may be inappropriate." The NPR further notes that, while a subset
> of children with maximal blood Pb levels below 7.5 μg/dl "may better
> represent current blood Pb levels, not fitting a single model using
> all available data may lead to bias" (73 FR 29209). Therefore, the NPR
> admits that the slope of the C-R functions steepens at lower
> concentration and also concedes that this is more reflective of the
> current blood Pb levels. However, the NPR then concludes that limiting
> the C-R analysis to this range of blood Pb levels would introduce
> "bias." This vague statement is not only completely unscientific
> (since any assertion of "bias" should be accompanied by a
> demonstration of why that is the case and include appropriate
> references), it is also *at best a specious argument, since we are
> indeed concerned with current blood Pb levels in the setting of a
> health-protective NAAQS, not with blood Pb levels of the past.*
>
> Furthermore, the CASAC rejects the suggestion that the existence of "a
> larger set of studies" (73 FR 29238) indicating C-R functions with
> shallower slopes is scientifically-relevant for choosing the most
> appropriate C-R functions for risk analyses. Rather, the selection of
> C-R function should be based on determining which studies indicate
> slopes that best reflect the current, lower blood Pb levels for
> children in the U.S. *---* which, in this instance, are those studies
> from which *steeper* slopes are drawn.
>
> In turn, the CASAC notes that three additional studies have recently
> been published that confirm the steep slope at the lowest blood lead
> concentrations (Surkan *et al.*, *NeuroToxicology* 2007;
> 28:1170--1177; Solon *et al.*, *J Pediatr* 2008; 152:237--43; and
> Jusko *et al.*, *Environ Health Perspect* 2008; 116:243--248, the last
> of which is a follow-up of the cohort first described in Canfield *et
> al.*, *New Engl J Med* 2003; 348:1517--26).

5.  **Target IQ Decrements:** The air-related IQ loss framework proposes
    a target mean IQ decrement of roughly one to two (1-2) points in the
    population as a level of damage that the proposed standard is
    intended to protect against. This target level has been erroneously
    attributed as being the CASAC's recommendation. The use of this
    target level is inappropriate for several reasons. First, in the
    CASAC's letter dated March 27, 2007 (EPA-CASAC-07-003) from its
    review of the Agency's [1^st^ Draft Lead Staff Paper]{.mark} and
    Draft Lead Exposure and Risk Assessments, the CASAC wrote that "*the
    CASAC Lead Review Panel considers that a population loss of 1-2 IQ
    points is highly significant from a public health perspective.
    Therefore, the primary lead standard should be set so as to protect
    99.5% of the population from exceeding that IQ loss*" (italics in
    original).

> The CASAC wishes to emphasize that this comment refers to 1-2 IQ
> points as being a "highly significant" loss to be *prevented* *---
> not* as a desired national damage level goal that a standard should be
> set to assure. The CASAC also notes that the recommendation is that IQ
> decrements as large as this should be prevented in all but a small
> percentile of the population *---* and certainly not accepted as a
> reasonable change in *mean* IQ scores across the entire population.
> *Indeed, if a loss of one IQ point (rather than losses of up to 3.9
> points) in mean IQ levels were considered a significant loss to be
> prevented, this analysis would point to a range of proposed standards
> between 0.05 and 0.2 μg/m^3^, with the lower end of that range being
> more consistent with the higher C-R slopes and higher air-to-blood
> ratios representative of current U.S. ambient air and blood lead
> concentrations.* However, by combining the *lowest* air-to-blood Pb
> ratios (1:3), the *shallowest* C-R slope (-0.9) and a
> *higher-than-acceptable* IQ decrement endpoint (\>1 IQ point), *the
> NPR subsequently, even shockingly, goes on to suggest (73 FR 29244)
> that a standard as high as 0.5 μg/m^3^ would somehow be adequate to
> protect public health --- while failing to point-out that, at the
> higher air-to-blood ratios and steeper C-R slopes more representative
> of current U.S. exposures, this contemplated level of the standard
> would allow mean losses of five (5) IQ points or more.*

**Level of the Primary Lead Standard**

As noted above, the proposed upper-bound level of 0.3 μg/m^3^ for the
revised Lead NAAQS lies above the upper bound of levels recommended by
both EPA Staff and by the CASAC Panel. The NPR indicates (73 FR 29190)
that three general sets of recommendations were taken into account in
developing this proposal: "(1) staff assessments ...upon which staff
recommendations for revisions to the primary Pb standard are based, (2)
CASAC advice and recommendations...and (3) public comments..."; and
further states that "among the many public comments the Agency has
received in this review regarding the level of the standard, the
overwhelming majority recommended appreciable reductions in the level,
*e.g.*, setting it at 0.2 μg/m^3^ or less..." (73 FR 29241). (For the
CASAC's previous advice to the Agency concerning this CASAC-recommended
level of the Lead NAAQS, see our letters dated March 27, 2007
\[EPA-CASAC-07-003, p. 6 & Appendix D\]; September 27, 2007
\[EPA-CASAC-07-007, p. 2\]; and January 22, 2008 \[EPA-CASAC-08-007, pp.
2, 5\].) Accordingly, since the overwhelming majority of public
comments, the recommendations in the EPA Staff Paper and underlying risk
and exposure analyses, and the CASAC Panel's unanimous recommendations
advocated a maximum level of 0.2 μg/m^3^ or less, it is not clear either
where this proposal for a *higher* (that is, less stringent) level of
0.3 μg/m^3^ level for the primary Lead NAAQS originated (*i.e.*, on what
scientific basis) or why it is necessary at this late stage in the
rulemaking process to seek additional public comment on levels for the
Lead NAAQS ranging as high as 0.5 μg/m^3^.

**Lead NAAQS Indicator**

In several rounds of previous comments, the CASAC Panel recommended that
a revised (and substantially-lowered) Lead NAAQS should be accompanied
by a transition of the sampling indicator from total suspended
particulates (TSP) to a low-volume ambient air monitor for lead in
particulate matter (PM) less than 10 micrometers in diameter (PM~10~) in
ambient air. In the CASAC's advice dated January 22, 2008
(EPA-CASAC-08-007), the CASAC noted that the CASAC Panel "unanimously
supported the selection of an \[PM~10~\] indicator that can be more
robustly measured and thus would be more representative of actual
population exposures," adding that "a more accurate and precise
Pb-PM~10~ indicator would provide a more stable determination of
compliance with the new lower Lead NAAQS." With regard to concerns over
a potential loss of ultra-coarse lead particles by PM~10~ samplers, the
CASAC Panel further noted that "it would be well within EPA's range of
discretionary options to accept a slight loss of ultra-coarse lead at
some monitoring sites by selecting an appropriately conservative level
for the revised Lead NAAQS." In a subsequent teleconference consultation
by the CASAC Ambient Air Monitoring and Methods (AAMM) Subcommittee held
on March 25, 2008, a majority of the subcommittee members also supported
a transition from TSP to low-volume PM~10~ sampling for lead (see
EPA-CASAC-08-010 dated April 14, 2008).

The CASAC needs to call attention to the fact that these recommendations
were based, in part, on an *assumption* that the level of the primary
Lead NAAQS would be "substantially" lowered to the EPA Staff-recommended
range (with an TSP indicator) of between 0.1 to 0.2 μg/m^3^ as an upper
bound and 0.02 to 0.05 μg/m^3^ as a lower bound (with the added
consideration that the selection be made somewhat "conservatively"
within this range to accommodate the potential loss of ultra-coarse lead
with a PM~10~ Pb indicator). For example, at most population-orientated
monitoring sites, levels of PM~10~ Pb are essentially the same as TSP
Pb, but at source-oriented monitoring sites with high coarse mode
particulate lead emissions, TSP Pb was roughly twice as high as PM~10~
Pb. This factor-of-two difference is small compared to the factor of 10
to 100 of the recommended lowering in the level of the standard, and
could be readily accommodated by considering a slightly more
conservative upper bound of 0.1 μg/m^3^ rather than 0.2 μg/m^3^.

However, since with the publication of this proposed rule for the
revision of the Lead NAAQS the Agency now appears to disagree with
previous staff recommendations --- as well as those of the CASAC and the
"overwhelming majority" of the public --- and is considering an upper
bound of 0.3 μg/m^3^ and possibly as high as 0.5 μg/m^3^, a transition
from TSP to PM~10~ at these much less protective upper levels of the
proposed range could represent a critical weakening of the health
protection afforded at the level of the standard that the CASAC
proposed. *Significantly, a particulate (PM~10~) Lead standard at 0.5
μg/m^3^ could potentially allow TSP Pb levels as high as 1 μg/m^3^ at
sites near large sources with coarse-mode particulate lead emissions.*
Therefore, if the level of the standard is set toward the upper end of
the range the Agency is now considering, the CASAC is unanimous in its
recommendation that the current TSP indicator should *not* be changed.
As previously recommended, a transition to a PM~10~ indicator would be
preferable, but only at a level conservatively below an upper bound of
0.2 μg/m^3^ or lower.

**Lead NAAQS Averaging Time and Form**

The NPR proposes consideration of a monthly averaging time with a
"second highest month in three years" form, but also seeks comment on
retaining the current "calendar" quarter "not to be exceeded" form. The
CASAC wishes to emphasize that there is no logic for averaging only by
"calendar" quarter, as there is nothing unique about effects that may
occur exclusively during the four calendar seasons. A "rolling"
three-month (or 90-day) average would be more logical than a "calendar"
quarter. The CASAC's previous recommendations --- both in the current
review cycle and during the prior review of the Lead NAAQS conducted in
the 1980s --- advocated reducing the averaging time of the Lead NAAQS
from "calendar" quarter to monthly, with the rationale that adverse
effects could result from exposures over as few as 30 days' duration. A
monthly or "rolling" 30-day averaging time with a "not to be exceeded"
form would be more protective against adverse short-term effects than a
form (such as a "second-highest month in three years") that periodically
allows a month of exposures to much higher concentrations.

**Zero Level for the Lead NAAQS**

 The NPR has raised the question of the feasibility of a Lead NAAQS of
"zero."  While it would not be practical to set an enforceable primary
Lead NAAQS of zero, it is both entirely appropriate and indeed very
important that we as a Nation have the goal of reducing exposure of our
children to lead to as close to zero as feasible.  The reasons for this
are numerous, and include: (1) lead is an apparent non-threshold
neurotoxicant that reduces cognitive abilities in children (that is, by
directly affecting children's IQ loss) so that the smaller the amount of
Pb in air and from other sources of lead, the smaller the blood Pb and
associated IQ loss; (2) such neurotoxic effects of lead as IQ loss
appear to be persistent and may be irreversible; and (3) the
environmental reality for childhood lead exposures is that these
exposures often occur concurrently with exposures to mixtures of other
neurotoxicants, with these multiple exposures producing an additive
neurotoxicity over that for lead alone. Nonetheless, consistent with the
CASAC's previous advice in this current review cycle for the Lead NAAQS,
the CASAC continues to believe that the level of the primary Lead
standard unanimously recommended by the CASAC --- *i.e.*, an upper bound
for the primary Lead NAAQS of *no higher than 0.2 μg/m^3^* --- is
necessary to provide an adequate margin of safety for the protection of
human health, including susceptible subpopulations such as children, as
explicitly required by the Clean Air Act for primary NAAQS.

The CASAC stands ready to assist you by advising the Agency concerning
the scientific basis on which to base your scientific policy judgments,
as EPA Administrator, in setting the NAAQS. It is our sincere desire and
goal to work more closely and effectively with the Agency in the future.
As always, the members of the CASAC wish EPA well in our vital --- and,
as previously stated, our mutual --- efforts to protect both human
health and the environment.

Sincerely,

> ***/Signed/***

Dr. Rogene F. Henderson, Chair

> Clean Air Scientific Advisory Committee

Enclosure

**NOTICE**

> This report has been written as part of the activities of the U.S.
> Environmental Protection Agency's (EPA) Clean Air Scientific Advisory
> Committee (CASAC), an independent Federal advisory committee
> administratively-located under the EPA Science Advisory Board (SAB)
> Staff Office that is chartered to provide extramural scientific
> information and advice to the Administrator and other officials of the
> EPA. The CASAC is structured to provide balanced, expert assessment of
> scientific matters related to issue 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 in the Executive
> Branch of the Federal government, nor does mention of trade names or
> commercial products constitute a recommendation for use. CASAC reports
> are posted on the EPA Web site at: <http://www.epa.gov/casac>.

**U.S. Environmental Protection Agency**

**Clean Air Scientific Advisory Committee (CASAC)**

**CASAC Lead Review Panel**

**CASAC** **MEMBERS**

**Dr. Rogene F. Henderson (Chair)**, Scientist Emeritus, Lovelace
Respiratory Research Institute, Albuquerque, NM

**Dr. Ellis Cowling**, University Distinguished Professor At-Large,
Emeritus, Colleges of Natural Resources and Agriculture and Life
Sciences, North Carolina State University, Raleigh, NC

**Dr. James D. Crapo \[M.D.\]**, Professor, Department of Medicine,
National Jewish Medical and Research Center, Denver, CO

**Dr. Douglas Crawford-Brown**, Director, Carolina Environmental
Program; Professor, Environmental Sciences and Engineering; and
Professor, Public Policy, Department of Environmental Sciences and
Engineering, University of North Carolina at Chapel Hill, Chapel Hill,
NC

**Dr. Donna Kenski**, Director of Data Analysis, Lake Michigan Air
Directors Consortium (LADCO), Rosemont, IL

**Dr. Armistead (Ted) Russell**, Georgia Power Distinguished Professor
of Environmental Engineering, Environmental Engineering Group, School of
Civil and Environmental Engineering, Georgia Institute of Technology,
Atlanta, GA

**Dr. Jonathan Samet \[M.D.\]**, Professor and Chairman, Department of
Epidemiology, Bloomberg School of Public Health, Johns Hopkins
University, Baltimore, MD

**PANEL** **MEMBERS**

**Dr. Joshua Cohen**, Research Associate Professor of Medicine, Tufts
University School of Medicine, Institute for Clinical Research and
Health Policy Studies, Center for the Evaluation of Value and Risk,
Tufts New England Medical Center, Boston, MA

**Dr. Deborah Cory-Slechta**, Professor, Department of Environmental
Medicine, University of Rochester School of Medicine and Dentistry,
Rochester, NY

**Dr. Bruce Fowler**, Assistant Director for Science, Division of
Toxicology and Environmental Medicine, Office of the Director, Agency
for Toxic Substances and Disease Registry, U.S. Centers for Disease
Control and Prevention (ATSDR/CDC), Chamblee, GA

**Dr. Andrew Friedland**, Professor and Chair, Environmental Studies
Program, Dartmouth College, Hanover, NH

**Mr. Sean Hays**, President, Summit Toxicology, Allenspark, CO

**Dr. Bruce Lanphear \[M.D.\]**, Sloan Professor of Children's
Environmental Health, and the Director of the Cincinnati Children's
Environmental Health Center at Cincinnati Children's Hospital Medical
Center and the University of Cincinnati, Cincinnati, OH

**Dr. Samuel Luoma**,\* Senior Research Hydrologist, Emeritus, U.S.
Geological Survey (USGS), Menlo Park, CA

**Dr. Frederick J. Miller**, Consultant, Cary, NC

**Dr. Paul Mushak**, Principal, PB Associates, and Visiting Professor,
Albert Einstein College of Medicine (New York, NY), Durham, NC

**Dr. Michael Newman**, Professor of Marine Science, School of Marine
Sciences, Virginia

Institute of Marine Science, College of William & Mary, Gloucester
Point, VA

**Mr. Richard L. Poirot**, Environmental Analyst, Air Pollution Control
Division, Department of Environmental Conservation, Vermont Agency of
Natural Resources, Waterbury, VT

**Dr. Michael Rabinowitz**, Geochemist, Marine Biological Laboratory,
Woods Hole, MA

**Dr. Joel Schwartz**, Professor, Environmental Health, Harvard
University School of Public Health, Boston, MA

**Dr. Frank Speizer \[M.D.\]**, Edward Kass Professor of Medicine,
Channing Laboratory, Harvard Medical School, Boston, MA

**Dr. Ian von Lindern**, Senior Scientist, TerraGraphics Environmental
Engineering, Inc., Moscow, ID

**Dr. Barbara Zielinska**, Research Professor, Division of Atmospheric
Science, Desert Research Institute, Reno, NV

**SCIENCE ADVISORY BOARD STAFF**

**Mr. Fred Butterfield**, CASAC Designated Federal Officer, 1200
Pennsylvania Avenue, N.W., Washington, DC, 20460, Phone: 202-343-9994,
Fax: 202-233-0643 ([butterfield.fred@epa.gov]{.underline})

\*Dr. Luoma did not participate in the June 9, 2008 or the July 8, 2008
public teleconferences or the CASAC's advisory activity to provide
comments on the NPR.