to modifications to this limited dataset lead the PA to conclude that
the currently available evidence continues to support consideration of
-1.75 IQ points per [mu]g/dL blood Pb as a well-founded and stable
estimate for purposes of describing the neurocognitive impact
quantitatively on this age group of U.S. children.
    In summary, in considering the evidence and information available
in this review pertaining to the level of the current Pb standard, the
PA notes that the evidence available in this review, as summarized in
the ISA, continues to support the air-related IQ loss evidence-based
framework, with the inputs that were used in the last review. These
include estimates of air-to-blood ratios ranging from 1:5 to 1:10, with
a generally central estimate of 1:7. Additionally, the C-R functions
most relevant to blood Pb levels in U.S. children today continue to be
provided by the set of four analyses considered in the last review for
which the median estimate is -1.75 IQ points per [mu]g/dL Pb in young
children's blood. Thus, the PA observed that the evidence available in
this review has changed little if at all with regard to the aspects
given weight in the conclusion on level for the new standard in the
last review and would not appear to call into question any of the basic
elements of the standard. In so doing, the PA additionally recognizes
that the overall decision on adequacy of the current standard is a
public health policy judgment by the Administrator.
2. Exposure/Risk-Based Considerations in the Policy Assessment
    In consideration of the issue of adequacy of public health
protection provided by the current standard, the PA also considered the
quantitative exposure/risk assessment completed in the last review,
augmented as described in section II.C above. The PA recognizes
substantial uncertainty inherent in the REA estimates of air-related
risk associated with localized conditions just meeting the current
standard, which we have characterized as approximate and falling within
rough bounds.\66\ This approximate estimate of risk for children living
in such areas is generally overlapping with and consistent with the
evidence-based air-related IQ loss estimates described in section
II.A.1 above. The PA discussion with regard to interpretation of the
exposure/risk information for air quality conditions associated with
just meeting the current standard is organized around two questions, as
summarized here (PA, section 4.2.2).
---------------------------------------------------------------------------

    \66\ 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
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).
---------------------------------------------------------------------------

    In considering the level of confidence associated with estimates of
air-related risk generated for simulations just meeting the current Pb
standard, the PA recognizes, as an initial matter, the significant
limitations and complexity associated with the risk and exposure
assessments for Pb that are far beyond those associated with similar
assessments typically performed for other criteria pollutants. In
completing the assessment, we were constrained by significant
limitations with regard to data and tools particular to the problem at
hand. Further, the multimedia and persistent nature of Pb and the role
of multiple exposure pathways contribute significant additional
complexity to the assessment as compared to other assessments that
focus only on the inhalation pathway. As a result, the estimates of
air-related exposure and risk are approximate, presented as upper and
lower bounds within which we consider air-related risk likely to fall.
The description of overall confidence in this characterization of air-
related risk is based on consideration of the overall design of the
analysis (summarized in section II.D), the degree to which key sources
of variability are reflected in the design of the analysis (summarized
in section II.D.3), and our characterization of key sources of
uncertainty (summarized in section II.D.3).
    With regard to key sources of uncertainty, the PA notes
particularly those affecting the precision of the air-related risk
estimates. Associated sources of uncertainty include the inability to
simulate changes in air-related Pb as a function of changes in ambient
air Pb in exposure pathways other than those involving inhalation of
ambient air and ingestion of indoor dust. This contributes to the
positive bias of the upper bound for the air-related risk estimates.
The PA additionally recognizes the significant uncertainty associated
with estimating upper percentiles of the distribution of air-related
blood Pb concentration estimates (and associated IQ loss estimates) due
to limitations in available information. Lastly, the PA recognizes the
uncertainty associated with application of the C-R function at the
lower blood Pb levels in the distribution; this relates to the limited
representation of blood Pb levels of this magnitude in the dataset from
which the C-R function is derived (PA, section 4.2.2).
    In the quantitative risk information available in this review, we
have air-related risk estimates for simulations just meeting the
current standard from one of the location-specific urban case studies
(Chicago) and from the generalized (local) urban case study. With
regard to the latter, the PA notes its simplified design that does not
include multiple exposure zones; thus reducing the dimensions
simulated. The PA concludes a reasonable degree of confidence in
aspects of the generalized (local) urban case study for the specific
situation we consider it to represent (i.e., a temporal pattern of air
Pb concentrations that just meets the level of the standard), and when
the associated estimates are characterized as approximate, within upper
and lower bounds (as described above), while also recognizing
considerable associated uncertainty.
    In considering the extent to which the estimated air-related risks
remaining upon just meeting the current Pb standard are important from
a public health perspective, the PA considers the nature and magnitude
of such estimated risks (and attendant uncertainties), including such
impacts on the affected

population, and additionally considers the size of the affected
population. In considering the quantitative risk estimates for
decrements in IQ, we recognize that although some neurocognitive
effects may be transient, some effects may persist into adulthood,
affecting success later in life (ISA, sections 1.9.5 and 4.3.14). The
PA additionally recognizes the potential population impacts of small
changes in population mean values of metrics such as IQ, presuming a
uniform manifestation of Pb-related decrement across the range of
population IQ (ISA, section 1.9.1; PA, section 3.3).
    As summarized in sections II.D above, limitations in modeling tools
and data affected our ability to develop precise risk estimates for
air-related Pb exposure pathways and contributed uncertainties to the
risk estimates. The results are approximate estimates which we describe
through the use of rough upper and lower bounds within which we
estimate air-related risk to fall. We have recognized a number of
uncertainties in the underlying risk estimates from the 2007 REA and in
the interpolation approach employed in the new analyses for this
review. We have characterized the magnitude of air-related risk
associated with the current standard with a focus on median estimates,
for which we have appreciably greater confidence than estimates for
outer ends of risk distribution (see section 3.4.7 of the PA) and on
risks derived using the C-R function in which we have greatest
confidence (see sections <IP_ADDRESS>.1 and 3.4.7 of the PA). These risk
estimates include estimates from the last review for one of the
location-specific urban study area populations as well as estimates
newly derived in this review based on interpolation from 2007 REA
results for the generalized (local) urban case study, which is
recognized to reflect a generalized high end of air-related exposure
for localized populations. Taken together, these results for just
meeting the current standard include a high-end localized risk estimate
for air-related Pb of a magnitude falling within general rough bounds
of 1 and 3 points IQ loss, with attendant uncertainties, and with
appreciably lower risks with increasing distance from the highest
exposure locations.
    In considering the importance of such risk from a public health
perspective, the PA also considers the size of at-risk populations
represented by the REA case studies. As summarized in section II.D.1
above (and described more fully in the PA, section 3.4), the
generalized (local) urban case study is considered to represent a
localized urban population exposed near the level of the standard, such
as a very small, compact neighborhood near a source contributing to air
Pb concentrations just meeting the standard. This case study provides
representation in the risk assessment for such small populations at the
upper end of the gradient in ambient air concentrations expected to
occur near sources; thus estimates for this case study reflect
exposures nearest the standard being evaluated. While we do not have
precise estimates of the number of young children living in such areas
of the U.S. today, we have information that informs our understanding
of their magnitude. For example, as summarized in section II.B.5 above,
the PA estimates some 2,700 children, aged 5 years and younger, to be
living in localized areas with elevated air Pb concentrations that are
above or near the current standard. Based on the 2010 census estimates
of approximately 24.3 million children in the U.S. aged 5 years or
younger, this indicates the size of the population of young children of
this age living in areas in close proximity to areas where air Pb
concentrations may be above or near the current standard to be
generally on the order of a hundredth of a percent of the full
population of correspondingly aged children.67 68 While
these estimates pertain to the age group of children aged 5 years and
younger, the PA additionally notes that a focus on an alternative age
range (e.g., through age 7), while increasing the number for children
living in such locations, would not be expected to appreciably change
the percentage of the full U.S. age group that the subset represents.
---------------------------------------------------------------------------

    \67\ The areas included in this estimate where the standard is
currently exceeded are treated, for present purposes, as areas with
air Pb concentrations just meeting the current standard and are
included for purposes of this analysis (PA, pp. 3-36 to 3-38). This
is in light of the requirement for areas not in attainment with the
standard to attain the standard as expeditiously as practicable, but
no later than 5 years after designation.
    \68\ A second PA analysis, performed in recognition of the
potential for the first analysis to under-represent sites with
elevated Pb concentrations, but with its own attendant
uncertainties, indicates the potential for the population group in
such areas to be only slightly larger, in terms of hundredths of a
percent of the full population of children in this age group (PA,
pp. 3-36 to 3-38, 4-25, 4-32).
---------------------------------------------------------------------------

3. CASAC Advice
    In the current review of the primary standard for Pb, the CASAC has
provided advice and recommendations in their review of drafts of the
ISA, of the REA Planning Document, and of the draft PA. We have
additionally received comments from the public on drafts of these
documents.\69\
---------------------------------------------------------------------------

    \69\ As noted in section II.E.3 above, written comments
submitted to the agency, as well as transcripts and minutes of the
public meetings held in conjunction with CASAC's reviews of
documents for the review will be available in the docket for this
rulemaking.
---------------------------------------------------------------------------

    In their comments on the draft PA, the CASAC concurred with staff's
overall preliminary conclusions that it is appropriate to consider
retaining the current primary standard without revision, stating that
``the current scientific literature does not support a revision to the
Primary Lead (Pb) National Ambient Air Quality Standard (NAAQS)''
(Frey, 2013b). They further noted that ``[a]lthough the current review
incorporates a substantial body of new scientific literature, the new
literature does not justify a revision to the standards 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).'' In
recognition of these limitations in the available information, the
CASAC provided recommendations on research to address these data gaps
and uncertainties so as to inform future Pb NAAQS reviews (Frey,
2013b).
    The CASAC comments indicated agreements with key aspects of staff's
consideration of the exposure/risk information and currently available
evidence in this review (Frey, 2013b, Consensus Response to Charge
Questions, p. 7).

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

    The CASAC concurred with the appropriateness of the application of
the evidence-based framework from the last Pb NAAQS review. With regard
to the key inputs to that framework, CASAC concluded that ``[t]he new
literature published since the previous review provides further support
for the health effect conclusions presented in that review'' and that
the studies newly available in this review ``do not fundamentally alter
the uncertainties for air-to-blood ratios or C-R functions for IQ
decrements in young children'' (Frey, 2013b, Consensus Response to
Charge Questions, p. 6).
    The comments from CASAC also took note of the uncertainties that
remain in this review, which contribute to the uncertainties associated
with drawing conclusions regarding air-related exposures and associated
health risk at or below the level of the current standard, stating
their agreement with ``the EPA conclusion that `there is appreciable
uncertainty associated with drawing conclusions regarding whether there
would be reductions in blood Pb levels from alternative lower levels as
compared to the level of the current standard' '' (Frey, 2013b,
Consensus Response to Charge Questions, p. 6).
    Of the limited public comments received on this review to date that
have addressed adequacy of the current primary Pb standard, all but one
state support for retaining the current standard without revision,
citing uncertainties in the available evidence and risk information.
The other commenter expressed the view that the standard should be
revised to be more restrictive given the evidence of Pb effects in
populations with mean blood Pb levels below 10 [micro]g/dL.
4. Administrator's Proposed Conclusions on the Adequacy of the Current
Primary Standard
    Based on the large body of evidence concerning the health effects
and potential public health impacts of exposure to Pb emitted into
ambient air, and taking into consideration the attendant uncertainties
and limitations of the evidence, the Administrator proposes to conclude
that the current primary standard provides the requisite protection of
public health, with an adequate margin of safety and should be
retained.
    In considering the adequacy of the current standard, the
Administrator has carefully considered the assessment of the available
evidence and conclusions contained in the ISA; the technical
information, including exposure/risk information, staff conclusions,
and associated rationale, presented in the PA; the advice and
recommendations from CASAC; and public comments to date in this review.
In the discussion below, the Administrator gives weight to the PA
conclusions, with which CASAC has concurred, and takes note of key
aspects of the rationale presented for those conclusions which
contribute to her proposed decision.
    As an initial matter, the Administrator takes note of the PA
discussion with regard to the complexity involved in considering the
adequacy of protection in the case of the primary Pb standard, which
differs substantially from that involved in consideration of the
primary NAAQS for other pollutants, for which the limited focus on the
inhalation pathway is a relatively simpler context. Additionally, while
an important component of the evidence base for most other NAAQS
pollutants is the availability of studies that have investigated an
association between current concentrations of the pollutant in ambient
air and the occurrence of health effects plausibly related to ambient
air exposure to that pollutant, the evidence base that supports
conclusions in this review of the Pb NAAQS includes most prominently
epidemiological studies focused on associations of blood Pb levels in
U.S. populations with health effects plausibly related to Pb exposures.
Support for conclusions regarding the plausibility for ambient air Pb
to play a role in such findings derives, in part, from studies linking
Pb in ambient air with the occurrence of health effects. However, such
studies (dating from the past or from other countries) involve ambient
air Pb concentrations many times greater than those that would meet the
current standard. Thus, in considering the adequacy of the current Pb
standard, rather than considering studies that have directly
investigated current concentrations of Pb in ambient air (including in
locations where the current standard is met) and the occurrence of
health effects, we primarily consider the evidence for, and risk
estimated from, models, based upon key relationships, such as those
among ambient air Pb, Pb exposure, blood Pb and health effects. This
evidence, with its associated limitations and uncertainties,
contributes to the EPA's conclusions regarding a relationship between
ambient air Pb conditions under the current standard and health
effects.
    With regard to the current evidence, the Administrator first takes
note of the well-established body of evidence on the health effects of
Pb, augmented in some aspects since the last review, which continues to
support identification of neurocognitive effects in young children as
the most sensitive endpoint associated with Pb exposure. The evidence,
as summarized in the PA and discussed in detail in the ISA, continues
to indicate that a standard that provides protection from
neurocognitive effects in young children additionally provides
protection for other health effects of Pb, such as those reported in
adult populations. The Administrator takes note of the PA finding that
application of the evidence-based, air-related IQ loss framework,
developed in the last review, continues to provide a useful approach
for considering and integrating the evidence on relationships between
Pb in ambient air and Pb in children's blood and risks of
neurocognitive effects (for which IQ loss is used as an indicator). She
additionally takes note of the PA finding (described in section II.E.1
above) that the currently available evidence base, while somewhat
expanded since the last review, is not appreciably expanded or
supportive of appreciably different conclusions with regard to air-to-
blood ratios or C-R functions for neurocognitive decrements in young
children. She concurs with the PA findings, summarized in section
II.E.1 above, that application of this framework, in light of the
current evidence and exposure/risk information, continues to support a
standard as protective as the current standard.
    In considering the nature and magnitude of the array of
uncertainties that are inherent in the scientific evidence and
analyses, the Administrator recognizes that our understanding of the
relationships between the presence of a pollutant in ambient air and
associated health effects is based on a broad body of information
encompassing not only more established aspects of the evidence, but
also aspects in which there may be substantial uncertainty. In the case
of the Pb NAAQS review, she takes note of the recognition in the PA of
increased uncertainty in characterizing the relationship of effects on
IQ with blood Pb levels below those represented in the evidence base
and in projecting the magnitude of blood Pb response to ambient air Pb
concentrations at and below the level of the current standard. The PA
recognizes this increased uncertainty, particularly in light of the
multiple factors that play a role in such a projection (e.g.,
meteorology, atmospheric dispersion and deposition, human physiology
and behavior), each of which carry attendant uncertainties. The
Administrator recognizes that collectively, these aspects of the

evidence and associated uncertainties contribute to a recognition that
for Pb, as for other pollutants, the available health effects evidence
generally reflects a continuum, consisting of levels at which
scientists generally agree that health effects are likely to occur,
through lower levels at which the likelihood and magnitude of the
response become increasingly uncertain.
    In making a judgment on the point at which health effects
associated with Pb become important from a public health perspective,
the Administrator has considered the public health significance of a
decrement of a very small number of IQ points in the at-risk population
of young children, in light of associated uncertainties. She notes that
her judgment on this matter relates to her consideration of the IQ loss
estimates yielded by the air-related IQ loss evidence-based framework
for specific combinations of standard level, air-to-blood ratio and C-R
function. In considering the public health significance of IQ loss
estimates in young children, the Administrator gives weight to the
comments of CASAC and some public commenters in the last review which
recognized a population mean IQ loss of 1 to 2 points to be of public
health significance and recommended that a very high percentage of the
population be protected from such a magnitude of IQ loss (73 FR 67000,
November 12, 2008). In so doing, the Administrator additionally notes
that the EPA is aware of no new information or new commonly accepted
guidelines or criteria within the public health community for
interpreting public health significance of neurocognitive effects in
the context of a decision on adequacy of the current Pb standard (PA,
pp. 4-33 to 4-34).
    With the objective identified by CASAC in the 2008 review in mind,
the Administrator considers the role of the air-related IQ loss
evidence-based framework in informing consideration of standards that
might be concluded to provide such a level of protection. In so doing,
she first recognizes, like the Administrator at the time of the last
review, that the IQ loss estimates produced with the evidence-based
framework do not correspond to a specific quantitative public health
policy goal for air-related IQ loss that would be acceptable or
unacceptable for the entire population of children in the U.S. Rather,
the conceptual context for the evidence-based framework is that it
provides estimates for the mean air-related IQ loss of a subset of the
population of U.S. children (i.e., the subset living in close proximity
to air Pb sources that contributed to elevated air Pb concentrations
that equal the current level of the standard). This is the subset
expected to experience air-related Pb exposures at the high end of the
national distribution of such exposures. The associated mean IQ loss
estimate is the average for this highly exposed subset and is not the
average air-related IQ loss projected for the entire U.S. population of
children. Further, the Administrator recognizes uncertainties
associated with those estimates, and notes the PA conclusion that the
uncertainties increase with estimates associated with successively
lower standard levels. The Administrator additionally takes note of the
PA estimates for the size of such a population, drawn from information
on numbers of young children (aged 5 years or younger) living near
monitors registering ambient Pb concentrations above or within 10
percent of the NAAQS, which indicate it to be on the order of one
hundredth of one percent of the U.S. population of children of this
age, with an upper bound of approximately four hundredths of one
percent, drawn from similar demographic information based on proximity
to large Pb sources, as identified using the NEI (PA, pp. 3-36 to 3-
38). In summary, the current evidence, as considered within the
conceptual and quantitative context of the evidence-based framework,
and current air monitoring information indicates that the current
standard would be expected to satisfy the public health policy goal
recommended by CASAC in the last Pb NAAQS review, and CASAC did not
provide a different goal in the present review. Thus, the evidence
indicates that the current standard provides protection for young
children from neurocognitive impacts, including IQ loss, consistent
with advice from CASAC regarding IQ loss of public health significance.
    In drawing conclusions from application of the evidence-based
framework with regard to adequacy of the current standard, the
Administrator further recognizes the degree to which IQ loss estimates
drawn from the air-related IQ loss evidence-based framework reflect
mean blood Pb levels that are below those represented in the currently
available evidence for young children. For example, in the case of the
current standard level of 0.15 [micro]g/m\3\, multiplication by the
air-to-blood ratio of 1:7, the value that was the focus of the last
review and which the evidence continues to support in this review,
yields a mean air-related blood Pb level of 1.05 [micro]g/dL. This
blood Pb level is half the level of the lowest blood Pb subgroup of
pre-school children in which neurocognitive effects have been observed
(PA, Table 3-2; Miranda et al., 2009) and well below the means of
subgroups for which continuous C-R functions have been estimated (Table
1 above). The Administrator views such an extension below the lowest
studied levels to be reasonable given the lack of identified blood Pb
level threshold in the current evidence base for neurocognitive effects
and the need for the NAAQS to provide a margin of safety. She takes
note, however, of the PA finding that the framework IQ loss estimates
for standard levels lower than the current standard level represent
still greater extrapolations from the current evidence base with
corresponding increased uncertainty (PA, section 3.2, pp. 4-32 to 4-
33).
    In considering application of the evidence-based framework in this
review with regard to the extent there is support within the evidence
for a standard with greater protection, the Administrator additionally
takes note of the uncertainties that remain in our understanding of
important aspects of ambient air Pb exposure and associated health
effects, as discussed in the PA (PA, Chapter 3) and summarized in
sections II.B and II.C above. With regard to the air-to-blood ratios
that reflect the relationship between concentrations of Pb in ambient
air and air-related Pb in children's blood, she particularly notes the
limitations and uncertainties identified in the ISA and PA with regard
to the available studies and the gaps and uncertainties in the evidence
base. These include gaps and uncertainties with regard to studies that
have investigated such quantitative relationships under conditions
pertaining to the current standard (e.g., in localized areas near air
Pb sources where the standard is just met in the U.S. today), as well
as with regard to evidence to inform our understanding of the
quantitative aspects of relationships between ambient air Pb and
outdoor soil/dust Pb and indoor dust Pb. These critical exposure
pathways are also represented in the evidence-based air-related IQ loss
framework within the estimates of air-to-blood ratios. In light of
these uncertainties and limitations in the evidence base, the
Administrator gives weight to the PA conclusion of greater uncertainty
with regard to relationships between concentrations of Pb in ambient
air and air-related Pb in children's blood, and with regard to
estimates of the slope of the C-R function of neurocognitive impacts
(IQ loss) for application of the framework to

levels below the current standard, given the weaker linkage with
existing evidence as discussed in the PA (PA, sections 3.1, 3.2 and
4.2.1).
    With respect to exposure/risk-based considerations, as in the last
review, the Administrator notes the complexity of the REA modeling
analyses and the associated limitations and uncertainties. Based on
consideration of the risk-related information for conditions just
meeting the current standard, the Administrator takes note of the
attendant uncertainties, discussed in detail in the PA (PA, sections
3.4 and 4.2.2), while finding that the quantitative risk estimates,
with a focus on those for the generalized (local) urban case study, are
``roughly consistent with and generally supportive'' of estimates from
the evidence-based air-related IQ loss framework. She further takes
note of the PA finding of increasing uncertainty for air quality
scenarios involving air Pb concentrations increasingly below the
current conditions for each case study, due in part to modeling
limitations that derive from uncertainty regarding relationships
between ambient air Pb and outdoor soil/dust Pb and indoor dust Pb (PA,
sections <IP_ADDRESS> and 3.4.7).
    Based on the above considerations and with consideration of advice
from CASAC, the Administrator reaches the conclusion that the current
body of evidence, in combination with the exposure/risk information,
supports a primary standard as protective as the current standard.
Based on consideration of the evidence and exposure/risk information
available in this review with its attendant uncertainties and
limitations and information that might inform public health policy
judgments, as well as advice from CASAC, including their concurrence
with the PA conclusions that revision of the primary Pb standard is not
warranted at this time, the Administrator further concludes that it is
appropriate to consider retaining the current standard without
revision.
    The Administrator bases these proposed conclusions on consideration
of the health effects evidence, including consideration of this
evidence in the context of the evidence-based, air-related IQ loss
framework, and with support from the exposure/risk information,
recognizing the uncertainties attendant with both. In so doing, she
takes note of the PA description of the complexities and limitations in
the evidence base associated with reaching conclusions regarding the
magnitude of risk associated with the current standard, as well as the
increasing uncertainty of risk estimates for lower air Pb
concentrations. Inherent in the Administrator's conclusions are public
health policy judgments on the public health implications of the blood
Pb levels and risk estimated for air-related Pb under the current
standard, including the public health significance of the Pb effects
being considered, as well as aspects of the use of the evidence-based
framework that may be considered to contribute to the margin of safety.
These public health policy judgments include judgments related to the
appropriate degree of public health protection that should be afforded
to protect against risk of neurocognitive effects in at-risk
populations, such as IQ loss in young children, as well as with regard
to the appropriate weight to be given to differing aspects of the
evidence and exposure/risk information, and how to consider their
associated uncertainties. Based on these considerations and the
judgments identified here, the Administrator concludes that the current
standard provides the requisite protection of public health with an
adequate margin of safety, including protection of at-risk populations,
such as young children living near Pb emissions sources where ambient
concentrations just meet the standard.
    In reaching this conclusion with regard to the adequacy of public
health protection afforded by the existing primary standard, the
Administrator recognizes that in establishing primary standards under
the Act that are requisite to protect public health with an adequate
margin of safety, she is seeking to establish standards that are
neither more nor less stringent than necessary for this purpose. The
Act does not require that primary standards be set at a zero-risk
level, but rather at a level that avoids unacceptable risks to public
health, even if the risk is not precisely identified as to nature or
degree. The CAA requirement that primary standards provide an adequate
margin of safety was intended to address uncertainties associated with
inconclusive scientific and technical information available at the time
of standard setting, as described in section I.A above. This
requirement was also intended to provide a reasonable degree of
protection from hazards that research has not yet identified.
    In this context, the Administrator's proposed conclusion that the
current standard provides the requisite protection and that a more
restrictive standard would not be requisite additionally recognizes
that the uncertainties and limitations associated with the many aspects
of the estimated relationships between air Pb concentrations and blood
Pb levels and associated health effects are amplified with
consideration of increasingly lower air concentrations. In so doing,
she takes note of the PA conclusion, with which CASAC has agreed, that
based on the current evidence, there is appreciable uncertainty
associated with drawing conclusions regarding whether there would be
reductions in blood Pb levels and risk to public health from
alternative lower levels of the standard as compared to the level of
the current standard (PA, pp. 4-35 to 4-36; Frey, 2013b, p. 6). The
Administrator judges this uncertainty to be too great for the current
evidence and exposure/risk information to provide a basis for revising
the current standard. Thus, based on the public health policy judgments
described above, including the weight given to uncertainties in the
evidence, the Administrator proposes to conclude that the current
standard should be retained, without revision. The Administrator
solicits comment on this conclusion.

III. Rationale for Proposed Decision on the Secondary Standard

    This section presents information relevant to the rationale for the
Administrator's proposed decision to retain the existing secondary Pb
standard, which as discussed more fully below, is based on a thorough
review in the ISA of the latest scientific information, generally
published through September 2011,\70\ on ecological or welfare effects
associated with Pb and pertaining to the presence of Pb in the ambient
air. This proposal also takes into account: (1) The PA's staff
assessments of the most policy-relevant information in the ISA and
staff analyses of potential ecological exposures and risk, upon which
staff conclusions regarding appropriate considerations in this review
are based; (2) CASAC advice and recommendations, as reflected in
discussions of drafts of the ISA and PA at public meetings, in separate
written comments, and in CASAC's letters to the Administrator; and (3)
public comments received during the development of these documents,
either in connection with CASAC meetings or separately.
---------------------------------------------------------------------------

    \70\ In addition to the review's opening ``call for
information'' (75 FR 8934), ``literature searches were conducted
routinely to identify studies published since the last review,
focusing on studies published from 2006 (close of the previous
scientific assessment) through September 2011'' and references
``that were considered for inclusion or actually cited in this ISA
can be found at http://hero.epa.gov/lead'' (ISA, p. 1-2).

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

    Section III.A provides background on the general approach for
review of the secondary NAAQS for Pb, including a summary of the
approach used in the last review (section III.A.1) and the general
approach for the current review (section III.A.2). Section III.B
summarizes the body of evidence on ecological or welfare effects
associated with Pb exposures, focusing on consideration of key policy-
relevant questions, and section III.C summarizes the exposure/risk
information in this review. Section III.D presents the Administrator's
proposed conclusions on adequacy of the current standard, drawing on
both evidence-based and exposure/risk-based considerations (sections
III.D.1), and advice from CASAC (section III.D.2).

A. General Approach

    The past and current approaches described below are all based most
fundamentally on using the EPA's assessment of the current scientific
evidence and previous quantitative analyses to inform the
Administrator's judgment with regard to the secondary standard for Pb.
In drawing conclusions for the Administrator's consideration with
regard to the secondary standard, we note that the final decision on
the adequacy of the current secondary Pb standard is largely a public
welfare policy judgment to be made by the Administrator. The
Administrator's final decision must draw upon scientific information
and analyses about welfare effects, exposure and risks, as well as
judgments about the appropriate response to the range of uncertainties
that are inherent in the scientific evidence and analyses. This
approach is consistent with the requirements of the NAAQS provisions of
the Act. These provisions require the Administrator to establish a
secondary standard that, in the judgment of the Administrator, is
``requisite to protect the public welfare from any known or anticipated
adverse effects associated with the presence of the pollutant in the
ambient air.'' In so doing, the Administrator seeks to establish
standards that are neither more nor less stringent than necessary for
this purpose.
1. Approach in the Last Review
    In the last review, completed in 2008, the current secondary
standard for Pb was set equal to the primary standard (73 FR 66964,
November 12, 2008). As summarized in sections I.C and II.A.1 above, the
primary standard was substantially revised in the last review. The 2008
decision considered the body of evidence as assessed in the 2006 CD
(USEPA, 2006a) as well as the 2007 Staff Paper assessment of the
policy-relevant information contained in the 2006 CD and the screening-
level ecological risk assessment (2006 REA; USEPA, 2007b), the advice
and recommendations of CASAC (Henderson 2007a, 2007b, 2008a, 2008b),
and public comment.
    In the previous review, the Staff Paper concluded, based on
laboratory studies and current media concentrations in a wide range of
locations, that it seemed likely that adverse effects were occurring
from ambient air-related Pb, particularly near point sources, under the
then-current standard (73 FR 67010, November 12, 2008). Given the
limited data on Pb effects in ecosystems, and associated uncertainties,
such as those with regard to factors such as the presence of multiple
metals and historic environmental burdens, it was at the time, as it is
now, necessary to look at evidence of Pb effects on organisms and
extrapolate to ecosystem effects. Taking into account the available
evidence and current media concentrations in a wide range of locations,
the Administrator concluded that there was potential for adverse
effects occurring under the then-current standard; however there were
insufficient data to provide a quantitative basis for setting a
secondary standard different from the primary (73 FR 67011, November
12, 2008). Therefore, citing a general lack of data that would indicate
the appropriate level of Pb in environmental media that may be
associated with adverse effects, as well as the comments of the CASAC
Pb panel that a significant change to current air concentrations (e.g.,
via a significant change to the standard) was likely to have
significant beneficial effects on the magnitude of Pb exposures in the
environment, the secondary standard was revised to be consistent with
the revised primary standard (73 FR 67011, November 12, 2008).
2. Approach for the Current Review
    Our approach for reviewing the current secondary standard takes
into consideration the approaches used in the last Pb NAAQS review and
involves addressing key policy-relevant questions in light of currently
available scientific and technical information. In evaluating whether
it is appropriate to consider retaining the current secondary Pb
standard, or whether consideration of revision is appropriate, we have
adopted an approach in this review that builds on the general approach
from the last review and reflects the body of evidence and information
now available. As summarized above, the Administrator's decisions in
the previous review were based on the conclusion that there was the
potential for adverse ecological effects under the previous standard.
    In our approach here, we focus on consideration of the extent to
which a broader body of scientific evidence is now available that would
inform decisions on either the potential for adverse effects to
ecosystems under the current standard or the ability to set a more
ecologically relevant secondary standard than was feasible in the
previous review. In considering the scientific and technical
information in sections II.B and II.C below, as in the PA, we draw on
the ecological effects evidence presented in detail in the ISA and
aspects summarized in the PA, along with the information associated
with the screening-level risk assessment also in the PA. In section
III.D below, we have taken into account both evidence-based and risk-
based considerations framed by a series of policy-relevant questions
presented in the PA. These questions generally discuss the extent to
which we are able to better characterize effects and the likelihood of
adverse effects in the environment under the current standard. Our
approach to considering these issues recognizes that the available
welfare effects evidence generally reflects laboratory-based evidence
of toxicological effects on specific organisms exposed to
concentrations of Pb. It is widely recognized, however, that
environmental exposures from atmospherically derived Pb are likely to
be lower than those commonly assessed in laboratory studies and that
studies of exposures similar to those in the environment are often
accompanied by significant confounding and modifying factors (e.g.,
other metals, acidification), increasing our uncertainty about the
likelihood and magnitude of organism and ecosystem responses.

B. Welfare Effects Information

    Welfare effects addressed by the secondary NAAQS include, but are
not limited to, effects on soils, water, crops, vegetation, manmade
materials, animals, wildlife, weather, visibility and climate, damage
to and deterioration of property, and hazards to transportation, as
well as effects on economic values and on personal comfort and
wellbeing. This discussion presents key aspects of the current evidence
of Pb-related welfare effects that are assessed in the ISA and the 2006
CD, drawing from the summary of policy-relevant aspects in the PA (PA,
section 5.1).
    Lead has been demonstrated to have harmful effects on reproduction
and development, growth, and survival in

many species as described in the assessment of the evidence available
in this review and consistent with the conclusions drawn in the last
review (ISA, section 1.7; 2006 CD, sections 7.1.5 and 7.2.5). A number
of studies on ecological effects of Pb are newly available in this
review and are critically assessed in the ISA as part of the full body
of evidence. The full body of currently available evidence reaffirms
conclusions on the array of effects recognized for Pb in the last
review (ISA, section 1.7). In so doing, in the context of pollutant
exposures considered relevant the ISA determines \71\ that causal \72\
or likely causal \73\ relationships exist in both freshwater and
terrestrial ecosystems for Pb with effects on reproduction and
development in vertebrates and invertebrates; growth in plants and
invertebrates; and survival in vertebrates and invertebrates (ISA,
Table 1-3). In drawing judgments regarding causality for the criteria
air pollutants, the ISA places emphasis on ``evidence of effects at
doses (e.g., blood Pb concentration) or exposures (e.g., air
concentrations) that are relevant to, or somewhat above, those
currently experienced by the population.'' The ISA notes that the
``extent to which studies of higher concentrations are considered
varies . . . but generally includes those with doses or exposures in
the range of one to two orders of magnitude above current or ambient
conditions.'' Studies ``that use higher doses or exposures may also be
considered . . . [t]hus, a causality determination is based on weight
of evidence evaluation for health, ecological or welfare effects,
focusing on the evidence from exposures or doses generally ranging from
current levels to one or two orders of magnitude above current levels''
(ISA, pp. lx to lxi).
---------------------------------------------------------------------------

    \71\ Since the last Pb NAAQS review, the ISAs, which have
replaced CDs in documenting each review of the scientific evidence
(or air quality criteria), employ a systematic framework for
weighing the evidence and describing associated conclusions with
regard to causality, using established descriptors: ``causal''
relationship with relevant exposure, ``likely'' to be a causal
relationship, evidence is ``suggestive'' of a causal relationship,
``inadequate'' evidence to infer a causal relationship, and ``not
likely'' to be a causal relationship (ISA, Preamble).
    \72\ In determining that a causal relationship exists for Pb
with specific ecological or welfare effects, the EPA has concluded
that ``[e]vidence is sufficient to conclude that there is a causal
relationship with relevant pollutant exposures (i.e., doses or
exposures generally within one to two orders of magnitude of current
levels)'' (ISA, p. lxii).
    \73\ In determining a likely causal relationship exists for Pb
with specific ecological or welfare effects, the EPA has concluded
that ``[e]vidence is sufficient to conclude that there is a likely
causal association with relevant pollutant exposures . . . but
uncertainties remain'' (ISA, p. lxii).
---------------------------------------------------------------------------

    Although considerable uncertainties are recognized in generalizing
effects observed under particular, small-scale conditions, up to the
ecosystem level of biological organization, the ISA determines that the
cumulative evidence reported for Pb effects at such higher levels of
biological organization and for endpoints in single species with direct
relevance to population and ecosystem level effects (i.e., development
and reproduction, growth, survival) is sufficient to conclude that a
causal relationship is likely to exist between Pb exposures and
community and ecosystem-level effects in freshwater and terrestrial
systems (ISA, section <IP_ADDRESS>).
    The ISA also presents evidence for saltwater ecosystems, concluding
that current evidence is inadequate to make causality determinations
for most population-level responses, as well as community and ecosystem
effects, while finding the evidence to be suggestive linking Pb and
effects on reproduction and development in marine invertebrates (ISA,
Table 1-3, sections 6.3.12 and 6.4.21).
    As in prior reviews of the Pb NAAQS, this review is focused on
those effects most pertinent to ambient air Pb exposures. Given the
reductions in ambient air Pb concentrations over the past decades,
these effects are generally those associated with the lowest levels of
Pb exposure that have been evaluated. Additionally, we recognize the
limitations on our ability to draw conclusions about environmental
exposures from ecological studies of organism-level effects, as most
studies were conducted in laboratory settings which may not accurately
represent field conditions or the multiple variables that govern
exposure.
    The relationship between ambient air Pb and ecosystem response is
important in making the connection between current emissions of Pb and
the potential for adverse ecological effects. The limitations in the
data available on this subject for the last review were significant.
There is no new evidence since the last review that substantially
improves our understanding of the relationship between ambient air Pb
and measurable ecological effects. As stated in the last review, the
role of ambient air Pb in contributing to ecosystem Pb has been
declining over the past several decades. It remains difficult to
apportion exposure between air and other sources to inform our
understanding of the potential for ecosystem effects that might be
associated with air emissions. As noted in the ISA, ``[t]he amount of
Pb in ecosystems is a result of a number of inputs and it is not
currently possible to determine the contribution of atmospherically-
derived Pb from total Pb in terrestrial, freshwater or saltwater
systems'' (ISA, section 6.5). Further, considerable uncertainties also
remain in drawing conclusions from effects evidence observed under
laboratory conditions with regard to effects expected at the ecosystem
level in the environment. In many cases it is difficult to characterize
the nature and magnitude of effects and to quantify relationships
between ambient concentrations of Pb and ecosystem response due to the
existence of multiple stressors, variability in field conditions, and
differences in Pb bioavailability at that level of organization (ISA,
section 6.5). In summary, the ISA concludes that ``[r]ecent information
available since the 2006 Pb AQCD, includes additional field studies in
both terrestrial and aquatic ecosystems, but the connection between air
concentration and ecosystem exposure continues to be poorly
characterized for Pb and the contribution of atmospheric Pb to specific
sites is not clear'' (ISA, section 6.5).
    It is also important to consider the fate and transport of both
current Pb and Pb emitted in the past. It is this past legacy of Pb
that was cited as a significant source of uncertainty in the last
review. The extensive history of Pb uses in developed countries coupled
with atmospheric transport processes has left a legacy of Pb in
ecosystems globally (e.g., 2006 CD, sections 2.3.1 and 7.1; 1977 CD,
section 6.3.1). Records of U.S. atmospheric emissions of Pb in the
twentieth and late nineteenth centuries have been documented in
sediment cores (PA, section 2.3; ISA, section 2.6.2; Landers et al.,
2010). Once deposited, Pb can be transported by stormwater runoff or
resuspension to catchments and nearby water bodies or stored in soil
layers in forested areas, its further movement influenced by soil or
sediment composition and chemistry and physical processes. Some new
studies are available that provide additional information, briefly
summarized below, on Pb cycling, flux and retention within terrestrial
and aquatic systems. This new information does not fundamentally change
our understanding from the last review of Pb movement through or
accumulation in ecosystems over time but rather improves our
understanding of some of the underlying processes and

mechanisms in soil, water and sediment. There is little new
information, however, on fate and transport in ecosystems specifically
related to air-derived Pb (ISA, section 2.3). There is limited newly
available information with regard to the timing of ecosystem recovery
from historic atmospheric deposition of Pb (ISA, sections <IP_ADDRESS> and
<IP_ADDRESS>).
    Overall, recent studies in terrestrial ecosystems provide
deposition data consistent with deposition fluxes reported in the 2006
CD and demonstrate consistently that atmospheric deposition of Pb has
decreased since the phase-out of leaded on-road gasoline (PA, section
<IP_ADDRESS>; ISA, section 2.3.3). Follow-up studies in several locations at
high elevation sites indicate little change in soil Pb concentrations
since the phase-out of leaded onroad gasoline in surface soils,
consistent with the high retention reportedly associated with reduced
microbial activity at lower temperatures associated with high elevation
sites. However, amounts of Pb in the surface soils at some lower
altitude sites were reduced over the same time period in the same study
(ISA, section 2.3.3). New studies in the ISA also enhance our
understanding of Pb sequestration in forest soils by providing
additional information on the role of leaf litter as a Pb reservoir in
some situations and the effect of litter decomposition on Pb
distribution (ISA, section 2.3.3).
    Recent research on Pb transport in aquatic systems has provided a
large body of observations confirming that such transport is dominated
by colloids rich in iron and organic material (ISA, section 2.3.2).
Recent research on Pb flux in sediments provides greater detail on
resuspension processes than was available in the 2006 CD, including
research on resuspended Pb largely associated with organic material or
iron and manganese particles and research on the important role played
by anoxic or depleted oxygen environments in Pb cycling in aquatic
systems. This newer research is consistent with prior evidence in
indicating that appreciable resuspension and release from sediments
largely occurs during discrete events related to storms. It has also
confirmed that resuspension is an important process that strongly
influences the lifetime of Pb in bodies of water. Finally, there have
been advances in understanding and modeling of Pb partitioning between
organic material and sediment in aquatic environments (ISA, section
2.7.2).
    The bioavailability of Pb is also an important component of
understanding the effects Pb is likely to have on organisms and
ecosystems (ISA, section 6.3.3). It is the amount of Pb that can
interact within the organism that leads to toxicity, and there are many
factors which govern this interaction (ISA, sections 6.2.1 and 6.3.3).
The bioavailability of metals varies widely depending on the physical,
chemical, and biological conditions under which an organism is exposed
(ISA, section 6.3.3). Studies newly available since the last Pb NAAQS
review provide additional insight into factors that influence the
bioavailability of Pb to specific organisms (ISA, section 6.3.3). In
general, this evidence is supportive of previous conclusions and does
not identify significant new variables from those identified
previously. Section 6.3.3 of the ISA provides a detailed discussion of
bioavailability in terrestrial systems. With regard to aquatic systems,
a detailed discussion of bioavailability in freshwater systems is
provided in sections 6.4.3 and 6.4.4 of the ISA, and section 6.4.14 of
the ISA discusses bioavailability in saltwater systems.
    In terrestrial systems, the amount of bioavailable Pb present
determines the impact of soil Pb to a much greater extent than does the
total amount present (ISA, section 6.3.11). In such ecosystems, Pb is
deposited either directly onto plant surfaces or onto soil where it can
bind with organic matter or dissolve in pore water. The Pb dissolved in
pore water is particularly bioavailable to organisms in the soil and,
therefore, the impact of this Pb on the ecosystem is potentially
greater than soil Pb that is not in pore water (ISA, section 6.3.11).
    In aquatic systems as in terrestrial systems, the amount of Pb
bioavailable to organisms is a better predictor of effect on organisms
than the overall amount of Pb in the system. Once atmospherically
derived Pb enters surface water bodies through deposition or runoff,
its fate and bioavailability are influenced by many water quality
characteristics, such as pH, suspended solids levels and organic
content (ISA, section 6.4.2). In sediments, bioavailability of Pb to
sediment-dwelling organisms may be influenced by the presence of other
metals, sulfides, iron oxides and manganese oxides and also by physical
disturbance (ISA, section 2.6.2). For many aquatic organisms, Pb
dissolved in the water column can be the primary exposure route, while
for others sediment ingestion is significant (ISA, section 2.6.2). As
recognized in the 2006 CD and further supported in the ISA, there is a
body of evidence showing that uptake and elimination of Pb vary widely
among aquatic species.
    There is a substantial amount of new evidence in this review
regarding the ecological effects of Pb on individual terrestrial and
aquatic species with less new information available on marine species
and ecosystems. On the whole, this evidence supports previous
conclusions that Pb has effects on growth, reproduction and survival,
and that under some conditions these effects can be adverse to
organisms and ecosystems. The ISA provides evidence of effects in
additional species and in a few cases at lower exposures than reported
in the previous review, but does not substantially alter our
understanding of the ecological endpoints affected by Pb from the
previous review. Looking beyond organism-level evidence, the evidence
of adversity in natural systems remains sparse due to the difficulty in
determining the effects of confounding factors such as co-occurring
metals or system characteristics that influence bioavailability of Pb
in field studies. The following paragraphs summarize the information
presented in this review for terrestrial, aquatic and marine systems.
    With regard to terrestrial ecosystems, recent studies cited in this
review support previous conclusions about the effects of Pb, namely
that increasing soil Pb concentrations in areas of Pb contamination
(e.g., mining sites and industrial sites) can cause decreases in
microorganism abundance, diversity, and function. Previous reviews have
also reported on effects on bird and plant communities (2006 CD,
section AX7.1.3). The shifts in bacterial species and fungal diversity
have been observed near long-established sources of Pb contamination
(ISA, section <IP_ADDRESS>). Most recent evidence for Pb toxicity to
terrestrial plants, invertebrates and vertebrates is from single-
species assays in laboratory studies which do not capture the
complexity of bioavailability and other modifiers of effect in natural
systems (ISA, section <IP_ADDRESS>). Further, models that might account for
modifiers of bioavailability have proven difficult to develop (ISA, p.
6-16).
    Evidence presented in the ISA and prior CDs demonstrates the
toxicity of Pb in aquatic ecosystems and the role of many factors,
including Pb speciation and various water chemistry properties, in
modifying toxicity (ISA, section 1.7.2). Since the 2006 CD, additional
evidence for community and ecosystem level effects of Pb is available,
primarily in microcosm studies or field studies with other metals
present (ISA, section 6.4.11). Such evidence described in

previous CDs includes alteration of predator-prey dynamics, species
richness, species composition, and biodiversity. New studies available
in this review provide evidence in additional habitats for these
community and ecological-scale effects, specifically in aquatic plant
communities and sediment-associated communities at both acute and
chronic exposures involving concentrations similar to those previously
reported (ISA, section 6.4.7). In many cases, it is difficult to
characterize the nature and magnitude of effects and to quantify
relationships between ambient concentrations of Pb and ecosystem
response due to existence of multiple ecosystem-level stressors,
variability in field conditions, and differences in Pb bioavailability
(ISA, sections <IP_ADDRESS> and 6.4.7). Additionally, the degree to which
air concentrations have contributed to such effects in freshwater
ecosystems is largely unknown.
    With regard to evidence in marine ecosystems, recently available
evidence on the toxicity of Pb to marine algae augments the 2006 CD
findings of variation in sensitivity across marine species. Recent
studies on Pb exposure include reports of growth inhibition and
oxidative stress in a few additional species of marine algae (ISA,
section 6.4.15). Recent literature provides little new evidence of
endpoints or effects in marine invertebrates beyond those reported in
the 2006 CD. For example, some recent studies strengthen the evidence
presented in the 2006 CD regarding negative effects of Pb exposure on
marine invertebrates (ISA, section <IP_ADDRESS>). Recent studies also
identify several species exhibiting particularly low sensitivity to
high acute exposures (ISA, section <IP_ADDRESS>). Little new evidence is
available of Pb effects on marine fish and mammals for reproductive,
growth and survival endpoints that are particularly relevant to the
population level of biological organization and higher (ISA, section
6.4.15). New studies on organism-level effects from Pb in saltwater
ecosystems (ISA, section 6.4.15) provide little evidence to inform our
understanding of linkages among atmospheric concentrations, ambient
exposures in saltwater systems and such effects or to inform our
conclusions regarding the likelihood of adverse effects under
conditions associated with the current NAAQS for Pb. Nor does the
currently available evidence indicate significantly different exposure
levels from the previous review at which ecological systems or
receptors are expected to experience effects.
    During the last review, the 2006 CD assessed the available
information on critical loads for Pb (2006 CD, section 7.3). This
information included publications on methods and example applications,
primarily in Europe, specific to the bedrock geology, soil types,
vegetation, and historical deposition trends in each European country
(2006 CD, p. E-24), with no analyses available for U.S. locations (2006
CD, sections 7.3.4-7.3.6). As a result, the 2006 CD concluded that
``[c]onsiderable research is necessary before critical load estimates
can be formulated for ecosystems extant in the United States'' (2006
CD, p. E-24).
    For this current review, newly available evidence pertaining to
critical loads analysis includes limited recent research on
consideration of bioavailability in characterizing Pb effect
concentrations or indices and on modeling approaches to incorporate
chemistry effects on Pb speciation and bioavailability (ISA, sections
6.3.7 and 6.4.8). With consideration of this information and the four
critical load analysis studies newly available in this review (none of
which are for U.S. ecosystems), the ISA does not modify the conclusions
noted above from the 2006 CD (ISA, sections 6.1.3, 6.3.7 and 6.4.8). In
summary, the new information in this review does not appreciably change
our evidence base or further inform our understanding of critical loads
of Pb, including critical loads in sensitive U.S. ecosystems.
    There is no new evidence since the last review that substantially
improves our understanding of the relationship between ambient air Pb
and measurable ecological effects. As stated in the last review, the
role of ambient air Pb in contributing to ecosystem Pb has been
declining over the past several decades. It remains difficult to
apportion exposure between air and other sources to better inform our
understanding of the potential for ecosystem effects that might be
associated with air emissions. As noted in the ISA, ``[t]he amount of
Pb in ecosystems is a result of a number of inputs and it is not
currently possible to determine the contribution of atmospherically-
derived Pb from total Pb in terrestrial, freshwater or saltwater
systems'' (ISA, section 6.5). Further, considerable uncertainties also
remain in drawing conclusions from evidence of effects observed under
laboratory conditions with regard to effects expected at the ecosystem
level in the environment. In many cases it is difficult to characterize
the nature and magnitude of effects and to quantify relationships
between ambient concentrations of Pb and ecosystem response due to the
existence of multiple stressors, variability in field conditions, and
differences in Pb bioavailability at that level of organization (ISA,
section 6.5). In summary, the ISA concludes that ``[r]ecent information
available since the 2006 Pb AQCD, includes additional field studies in
both terrestrial and aquatic ecosystems, but the connection between air
concentration and ecosystem exposure continues to be poorly
characterized for Pb and the contribution of atmospheric Pb to specific
sites is not clear'' (ISA, section 6.5).

C. Summary of Risk Assessment Information

    The risk assessment information available in this review and
summarized here is based on the screening-level risk assessment
performed for the last review, described in the 2006 REA, 2007 Staff
Paper and 2008 notice of final decision (73 FR 66964, November 12,
2008), as considered in the context of the evidence newly available in
this review (PA, section 5.2). As described in the REA Planning
Document, careful consideration of the information newly available in
this review, with regard to designing and implementing a full REA for
this review, led us to conclude that performance of a new REA for this
review was not warranted (REA Planning Document, section 3.3). Based on
their consideration of the REA Planning Document analysis, the CASAC Pb
Review Panel generally concurred with the conclusion that a new REA was
not warranted in this review (Frey, 2011b). Accordingly, the risk/
exposure information considered in this review is drawn primarily from
the 2006 REA as summarized below (PA, section 5.2 and Appendix 5A; REA
Planning Document, section 3.1).
    The 2006 screening-level assessment focused on estimating the
potential for ecological risks associated with ecosystem exposures to
Pb emitted into ambient air (PA, section 5.2; 2006 REA, section 7). A
national-scale screen was used to evaluate surface water and sediment
monitoring locations across the U.S. for the potential for ecological
impacts that might be associated with atmospheric deposition of Pb
(2006 REA, section 7.1.2). In addition to the national-scale screen
(2006 REA, section 3.6), the assessment involved a case study approach,
with case studies for areas surrounding a primary Pb smelter (2006 REA,
section 3.1) and a secondary Pb smelter (2006 REA, section 3.2), as
well as a location near a non-urban roadway (2006 REA, section 3.4). An
additional case study, focused on

consideration of atmospherically derived Pb effects on an ecologically
vulnerable ecosystem (Hubbard Brook Experimental Forest), was
identified (2006 REA, section 3.5). The Hubbard Brook Experimental
Forest (HBEF), in the White Mountain National Forest, near North
Woodstock, New Hampshire, was selected as a fourth case study because
of its location and its long record of available data on concentration
trends of Pb in three media (air or deposition from air, soil, and
surface water). The HBEF case study was a qualitative analysis focusing
on a summary review of the literature, without new quantitative
analyses (2006 REA, Appendix E). For the other three case studies,
exposure concentrations of Pb in soil, surface water, and/or sediment
concentrations were estimated from available monitoring data or
modeling analysis and then compared to ecological screening benchmarks
(2006 REA, section 7.1).
    In interpreting the results from the 2006 REA, the PA considers
newly available evidence that may inform interpretation of risk under
the now current standard (PA, section 5.2). Factors that could alter
our interpretation of risk would include new evidence of harm at lower
concentrations of Pb, new linkages that enable us to draw more explicit
conclusions as to the air contribution of environmental exposures, and
new methods of interpreting confounding factors that were largely
uncontrolled in the previous risk assessment. In general, however, the
key uncertainties identified in the last review remain today.
    The results for the ecological screening assessment for the three
case studies and the national-scale screen for surface water and for
sediment in the last review indicated a potential for adverse effects
from ambient Pb to multiple ecological receptor groups in terrestrial
and aquatic locations. Detailed descriptions of the location-specific
case studies and the national screening assessment, key findings of the
risk assessment for each, and an interpretation of the results with
regard to past air conditions can be found in the 2006 REA. In
considering the potential for adverse welfare effects to result from
levels of air-related Pb that would meet the current standard, the
findings of the 2006 REA, as summarized in the PA, are discussed below.
    While the contribution to Pb concentrations from air as compared to
nonair sources is not quantified, air emissions from the primary Pb
smelter case study facility were substantial (2006 REA, Appendix B). In
addition, this facility, which closed in 2013, had been emitting Pb for
many decades, including some seven decades prior to establishment of
any Pb NAAQS, such that it is likely air concentrations associated with
the facility were substantial relative to the 1978 NAAQS, which it
exceeded at the time of the last review. At the time of the last review
and also since the adoption of the current standard, concentrations
monitored near this facility have exceeded the level of the applicable
NAAQS (2007 Staff Paper, Appendix 2B-1; PA, Appendices 2D and 5A).
Accordingly, this case study is not informative for considering the
likelihood of adverse welfare effects related to Pb from air sources
under air quality conditions associated with meeting the current Pb
standard.
    The secondary Pb smelter case study location continues to emit Pb,
and the county where this facility is located does not meet the current
Pb standard (PA, Appendices 2D and 5A). Given the exceedances of the
current standard, which likely extend back over 4 to 5 decades, this
case study also is not informative for considering the likelihood of
adverse welfare effects related to Pb from air sources under air
quality conditions associated with meeting the current Pb standard.
    The locations for the near-roadway non-urban case study are highly
impacted by past deposition of gasoline Pb. It is unknown whether
current conditions at these sites exceed the current Pb standard, but,
given evidence from the past of Pb concentrations near highways that
ranged above the previous (1978) Pb standard (1986 CD, section 7.2.1),
conditions at these locations during the time of leaded gasoline very
likely exceeded the current standard. Similarly, those conditions
likely resulted in Pb deposition associated with leaded gasoline that
exceeds that being deposited under air quality conditions that would
meet the current Pb standard. Given this legacy, consideration of the
potential for environmental risks from levels of air-related Pb
associated with meeting the current Pb standard in these locations is
highly uncertain.
    The extent to which past air emissions of Pb have contributed to
surface water or sediment Pb concentrations at the locations identified
in the national scale surface water and sediment screen is unclear. For
some of the surface water locations, nonair sources likely contributed
significantly to the surface water Pb concentrations. For other
locations, a lack of nearby nonair sources indicated a potential role
for air sources to contribute to observed surface water Pb
concentrations. Additionally, these concentrations may have been
influenced by Pb in resuspended sediments and may reflect contribution
of Pb from erosion of soils with Pb derived from historic as well as
current air emissions.
    The most useful case study to the current review is that of the
Vulnerable Ecosystem Case Study located in the HBEF. This case study
was focused on consideration of information which included a long
record (from 1976 through 2000) of available data on concentration
trends of Pb in three media (air or deposition from air, soil, and
surface water). While no quantitative analyses were performed, a
summary review of literature published on HBEF was developed. This
review indicated: (1) Atmospheric Pb inputs do not directly affect
stream Pb levels at HBEF because deposited Pb is almost entirely
retained in the soil profile; and (2) soil horizon analysis results
showed Pb to have become more concentrated at lower soil depths over
time, with the soil serving as a Pb sink, appreciably reducing Pb in
pore water as it moves through the soil layers to streams (dissolved Pb
concentrations were reduced from 5 [mu]g/L to about 5 ng/L from surface
soil to streams). As a result, the HBEF studies concluded that the
contribution of dissolved Pb from soils to streams was insignificant
(2006 REA, Appendix E). Further, atmospheric input of Pb, based on bulk
precipitation data, was estimated to decline substantially from the
mid-1970s to 1989; forest floor soil Pb concentrations between 1976 and
2000 were also estimated to decline appreciably (2006 REA, sections E.1
and E.2). In considering HBEF and other terrestrial sites with Pb
burdens derived primarily from long-range atmospheric transport, the
2006 CD found that ``[d]espite years of elevated atmospheric Pb inputs
and elevated concentrations in soils, there is little evidence that
sites affected primarily by long-range Pb transport have experienced
significant effects on ecosystem structure or function'' (2006 CD, p.
AX7-98). The explanation suggested by the 2006 CD for this finding is
``[l]ow concentrations of Pb in soil solutions, the result of strong
complexation of Pb by soil organic matter'' (2006 CD, p. AZX7-98).
While more recent soil or stream data on Pb concentrations are not
available, we find it unlikely, given the general evidence for air Pb
emissions and concentration

declines over the past several decades (e.g., PA, Figures 2-1, 2-7 and
2-8), that conditions would have worsened from those on which these
conclusions were drawn (e.g., soil data through 2000). Therefore, this
information suggests that the now-lower ambient air concentrations
associated with meeting the current standard would not be expected to
directly impact stream Pb levels.
    With regard to new evidence of Pb effects at lower concentrations,
it is necessary to consider that the evidence of adversity due
specifically to Pb in natural systems is limited, in no small part
because of the difficulty in determining the effects of confounding
factors such as multiple metals and modifying factors influencing
bioavailability in field studies. Modeling of Pb-related exposure and
risk to ecological receptors is subject to a wide array of sources of
both variability and uncertainty. Variability is associated with
geographic location, habitat types, physical and chemical
characteristics of soils and water that influence Pb bioavailability
and terrestrial and aquatic community composition. Lead uptake rates by
invertebrates, fish, and plants may vary by species and season. For
wildlife, variability also is associated with food ingestion rates by
species and season, prey selection, and locations of home ranges for
foraging relative to the Pb contamination levels (USEPA, 2005b).
    There are significant difficulties in quantifying the role of air
emissions under the current standard, which is significantly lower than
the previous standard. As recognized in the PA, Pb deposited before the
standard was enacted remains in soils and sediments, complicating
interpretations regarding the impact of the current standard; historic
Pb emitted from leaded gasoline usage continues to move slowly through
systems along with more recently deposited Pb and Pb derived from
nonair sources (PA, section 1.3.2). The results from the location-
specific case studies and the surface and sediment screen performed in
the last review are difficult to interpret in light of the current
standard and are largely not useful in informing judgments of the
potential for adverse effects at levels of deposition meeting the
current standard.

D. Conclusions on Adequacy of the Current Secondary Standard

1. Evidence- and Risk-Based Considerations in the Policy Assessment
    The current evidence, as discussed more fully in the PA, continues
to support the conclusions from the previous review regarding key
aspects of the ecological effects evidence for Pb and the effects of
exposure associated with levels of Pb occurring in ecological media in
the U.S. The EPA's conclusions in this regard are based on
consideration of the assessment of the currently available evidence in
the ISA, particularly with regard to key aspects summarized in the PA.
    In considering the welfare effects evidence with respect to the
adequacy of the current standard, the PA considers the array of
evidence newly assessed in the ISA with regard to the degree to which
this evidence supports conclusions about the effects of Pb in the
environment that were drawn in the last review and the extent to which
it reduces previously recognized areas of uncertainty. Further, the PA
considers the current evidence and associated conclusions about the
potential for effects to occur as a result of the much lower ambient Pb
concentrations allowed by the current secondary standard (set in 2008)
than those allowed by the prior standard, which was the focus of the
last review. These considerations, as discussed below, inform the
Administrator's conclusions regarding the extent to which the evidence
supports or calls into question the adequacy of protection afforded by
the current standard.
    The range of effects that Pb can exert on terrestrial and aquatic
organisms indicated by information available in the current review is
summarized in the ISA (ISA, sections 1.7, 6.3 and 6.4) and largely
mirrors the findings of the previous review (PA, section 5.1). The
integrated synthesis contained in the ISA conveys how effects of Pb can
vary with species and life stage, duration of exposure, form of Pb, and
media characteristics such as soil and water chemistry. A wide range of
organism effects are recognized, including effects on growth,
development (particularly of the nervous system) and reproductive
success (ISA, sections 6.3 and 6.4). Lead is recognized to distribute
from the air into multiple environmental media, as summarized in
section I.D above, contributing to multiple exposure pathways for
ecological receptors. As discussed in section 5.1 of the PA, many
factors affect the bioavailability of Pb to receptors in terrestrial
and aquatic ecosystems, contributing to differences between laboratory-
assessed toxicity and Pb toxicity in these ecosystems, and challenging
our consideration of environmental impacts of Pb emitted to ambient
air.
    In studies in a variety of ecosystems, adverse ecosystem-level
effects (including decreases in species diversity, loss of vegetation,
changes to community composition, primarily in soil microbes and
plants, decreased growth of vegetation, and increased number of
invasive species) have been demonstrated near smelters, mines and other
industries that have released substantial amounts of Pb, among other
materials, to the environment (ISA, sections 6.3.12 and 6.4.12). As
noted in the PA, however, our ability to characterize the role of air
emissions of Pb in contributing to these effects is complicated because
of coincident releases to other media and of other pollutants. Co-
released pollutants include a variety of other heavy metals, in
addition to sulfur dioxide, which may cause toxic effects in themselves
and may interact with Pb in the environment, contributing uncertainty
to characterization of the role of Pb from ambient air with regard to
the reported effects (PA, section 5.1). These uncertainties limit our
ability to draw conclusions regarding the extent to which Pb-related
effects may be associated with ambient air conditions that would meet
the current standard.
    The role of historically emitted Pb poses additional complications
in addressing this question, as discussed in the PA (PA, section
1.3.2). The vast majority of Pb in the U.S. environment today,
particularly in terrestrial ecosystems, was deposited in the past
during the use of Pb additives in gasoline (2006 CD, pp. 2-82, AX7-36
to AX7-38, AX7-98; Johnson et al., 2004), although contributions from
industrial activities, including metals industries, have also been
documented (ISA, section <IP_ADDRESS>, Jackson et al., 2004). The gasoline-
derived Pb was emitted in very large quantities (2006 CD, p. AX7-98 and
ISA, Figure 2-8) and predominantly in small sized particles which were
widely dispersed and transported across large distances, within and
beyond the U.S. (ISA, section 2.2). As recognized in the PA, historical
records provided by sediment cores in various environments document the
substantially reduced Pb deposition (associated with reduced Pb
emissions) in many locations (PA, sections 2.3.1 and <IP_ADDRESS>; ISA,
section 2.2.1). As Pb is persistent in the environment, these
substantial past environmental releases are expected to generally
dominate current nonair media concentrations.
    There is very limited evidence to relate specific ecosystem effects
with current ambient air concentrations of Pb through deposition to
terrestrial and aquatic ecosystems and subsequent movement of deposited
Pb through the environment (e.g., soil, sediment, water,

organisms). The potential for ecosystem effects of Pb from atmospheric
sources under conditions meeting the current standard is difficult to
assess due to limitations on the availability of information to fully
characterize the distribution of Pb from the atmosphere into ecosystems
over the long term, as well as limitations on information on the
bioavailability of atmospherically deposited Pb (as affected by the
specific characteristics of the receiving ecosystem). Therefore, while
information available since the 2006 CD includes additional terrestrial
and aquatic field studies, ``the connection between air concentration
and ecosystem exposure and associated potential for welfare effects
continues to be poorly characterized for Pb'' (ISA, section 6.5). Such
a connection is even harder to characterize with respect to the current
standard than it was in the last review with respect to the previous,
much higher, standard.
    The current evidence also continues to support conclusions from the
last review with regard to interpreting the risk and exposure results.
These conclusions are based on consideration of the screening-level
ecological risk assessment results from the last review as described in
the 2006 REA and summarized in the notice of final rulemaking (73 FR
67009, November 12, 2008) and in light of the currently available
evidence in the ISA (PA, section 5.2). As noted in section III.C above,
the results from three of the four case studies and from the national
screens are largely not useful in informing judgments of the potential
for adverse effects at levels of deposition associated with conditions
that meet the current standard. The Vulnerable Ecosystem Case Study at
the HBEF is more illustrative with regard to the current review and,
accordingly, is given primary consideration. The EPA concluded that
atmospheric Pb inputs of the past did not directly affect stream Pb
levels at HBEF because deposited Pb is almost entirely retained in the
soil profile and that there was ``little evidence that sites affected
primarily by long-range Pb transport [such as this one] have
experienced significant effects on ecosystem structure or function''
(2006 CD, p. AX-98). We further note here that, as conditions are
unlikely to have worsened since those on which those conclusions were
based, we find it likely that current ambient air concentrations do not
directly impact stream Pb levels under air quality conditions
associated with meeting the now-current standard.
    The available risk and exposure information continues to be
sufficient to conclude that the 1978 standard was not providing
adequate protection to ecosystems and, when considered with regard to
air-related ecosystem exposures likely to occur with air Pb levels that
just meet the now-current standard, additionally does not provide
evidence of adverse effects under the current standard.
2. CASAC Advice
    In the current review of the secondary standard for Pb, the CASAC
has provided advice and recommendations in their review of drafts of
the ISA, of the REA Planning Document, and of the draft PA. We have
additionally received comments from the public on drafts of these
documents.\74\
---------------------------------------------------------------------------

    \74\ All written comments submitted to the agency will be
available in the docket for this rulemaking, as will be transcripts
and minutes of the public meetings held in conjunction with CASAC's
review of drafts of the PA, the REA Planning Document and the ISA.
---------------------------------------------------------------------------

    In their advice and comments conveyed in the context of their
review of the draft PA, the CASAC agreed with staff's preliminary
conclusions that the available information since the last review is not
sufficient to warrant revision to the secondary standard (Frey, 2013b).
On this subject, the CASAC letter said that ``[o]verall, the CASAC
concurs with the EPA that the current scientific literature does not
support a revision to the Primary Lead (Pb) National Ambient Air
quality Standard (NAAQS) nor the Secondary Pb NAAQS'' (Frey, 2013b, p.
1). The CASAC also recognized the many uncertainties and data gaps in
the new scientific literature and recommended that research be
performed in the future to address these limitations (Frey, 2013b, p.
2).

    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 very few public comments received on this review to date that
have addressed adequacy of the current secondary Pb standard indicate
support for retaining the current standard without revision, generally
grouping the secondary standard with their similar view on the primary
standard.
3. Administrator's Proposed Conclusions on the Adequacy of the Current
Standard
    Based on the evidence and risk assessment information that is
available in this review concerning the ecological effects and
potential public welfare impacts of Pb emitted into ambient air, the
Administrator proposes to conclude that the current secondary standard
provides the requisite protection of public welfare from adverse
effects and should be retained.
    In considering the adequacy of the current standard, the
Administrator has considered the assessment of the available evidence
and conclusions contained in the ISA; the staff assessment of and
conclusions regarding the policy-relevant technical information,
including screening-level risk information, presented in the PA; the
advice and recommendations from CASAC; and public comments to date in
this review. In the discussion below, the Administrator gives weight to
the PA conclusions, with which CASAC has concurred, and takes note of
key aspects of the rationale presented for those conclusions which
contribute to her proposed decision.
    The Administrator notes the conclusion in the PA that the body of
evidence on the ecological effects of Pb, expanded in some aspects
since the last review, continues to support identification of
ecological effects in organisms relating to growth, reproduction, and
survival as the most relevant endpoints associated with Pb exposure. In
consideration of the appreciable influence of site-specific
environmental characteristics on the bioavailability and toxicity of
environmental Pb in our assessment here, the PA noted the lack of
studies conducted under conditions closely reflecting the natural
environment. The currently available evidence, while somewhat expanded
since the last review, does not include evidence of significant effects
at lower concentrations or evidence of higher level ecosystem effects
beyond those reported in the last review. There continue to be
significant difficulties in interpreting effects evidence from
laboratory studies to the natural environment and linking those effects
to ambient air Pb concentrations. Further, the PA notes that the EPA is
aware of no new critical loads information that would inform our
interpretation of the public welfare significance of the effects of Pb
in various U.S. ecosystems (PA, section 5.1). In summary, while new
research has added to the understanding of Pb biogeochemistry and
expanded the

list of organisms for which Pb effects have been described, the PA
notes there remains a significant lack of knowledge about the potential
for adverse effects on public welfare from ambient air Pb in the
environment and the exposures that occur from such air-derived Pb,
particularly under conditions meeting the current standard (PA, section
6.2.1). Thus, the scientific evidence presented in detail in the ISA,
inclusive of that newly available in this review, is not substantively
changed, most particularly with regard to the adequacy of the now
current standard, from the information that was available in and
supported the decision for revision in the last review (PA, section
6.2.1).
    With respect to exposure/risk-based considerations, the PA
recognizes the complexity of interpreting the previous risk assessment
with regard to the ecological risk of ambient air Pb associated with
conditions meeting the current standard and the associated limitations
and uncertainties of such assessments. For example, the location-
specific case studies as well as the national screen conducted in the
last review reflect both current air Pb deposition as well as past air
and nonair source contributions (PA, section 6.3). The Administrator
takes note of the PA conclusion that the previous assessment is
consistent with and generally supportive of the evidence-based
conclusions about Pb in the environment, yet the limitations on our
ability to apportion Pb between past and present air contributions and
between air and nonair sources remain significant.
    In the Administrator's consideration of the information available
in this review of the Pb secondary standard, she gives weight to the PA
conclusion that the currently available evidence and exposure/risk
information do not call into question the adequacy of the current
standard to provide the requisite protection for public welfare (PA,
section 6.3). In so doing, she also notes the advice from CASAC in this
review, including that ``[g]iven the existing scientific data, the
CASAC concurs with retaining the current secondary standard without
revision.'' In light of these and the above considerations, the
Administrator finds that the currently available information does not
call into question the adequacy of the current standard to provide the
requisite protection for public welfare and, accordingly, reaches the
conclusion that it is appropriate to retain the current secondary
standard without revision. The Administrator solicits comment on this
conclusion.

IV. Statutory and Executive Order Reviews

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

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

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

B. Paperwork Reduction Act

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

C. Regulatory Flexibility Act

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

D. Unfunded Mandates Reform Act

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

E. Executive Order 13132: Federalism

    This action does not have federalism implications. It will not have
substantial direct effects on the states, on the relationship between
the national government and the states, or on the distribution of power
and responsibilities among the various levels of government.

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

    This action does not have tribal implications, as specified in
Executive Order 13175. This action does not change existing
regulations. It does not have a substantial direct effect on one or
more Indian Tribes, since Tribes are not obligated to adopt or
implement any NAAQS. The Tribal Authority Rule gives Tribes the
opportunity to develop and implement CAA programs such as the Pb NAAQS,
but it leaves to the discretion of the Tribe whether to develop these
programs and which programs, or appropriate elements of a program, they
will adopt. Thus, Executive Order 13175 does not apply to this action.

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

    This action is not subject to Executive Order 13045 because it is
not economically significant as defined in Executive Order 12866. The
health effects evidence and risk assessment information for this
action, which focuses on children in addressing the at-risk population,
is summarized in sections II.B, II.C and II.D, and described in the ISA
and PA, copies of which are in the public docket for this action.

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

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

I. National Technology Transfer and Advancement Act

    This rulemaking does not involve technical standards.

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

    The EPA believes that this action will not have disproportionately
high and adverse human health or environmental effects on minority,
low-income or indigenous populations. The action proposed in this
notice is to retain without revision the existing NAAQS for Pb based on
the Administrator's conclusion that the existing standards protect
public health, including the health of sensitive groups, with an
adequate margin of safety. As discussed earlier in this preamble (see
section II), the EPA expressly considered the available information
regarding health effects among at-risk populations in reaching the
proposed decision that the existing standards are requisite.

K. Determination Under Section 307(d)

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

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List of Subjects in 40 CFR Part 50

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

    Dated: December 19, 2014.
Gina McCarthy,
Administrator.
[FR Doc. 2014-30681 Filed 1-2-15; 8:45 am]
BILLING CODE 6560-50-P