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# CHAPTER 2 INTEGRATIVE SUMMARY

2.1 ISA Development and Scope

This chapter su mmarizes and synthesizes the recent ly available scientific evidence and is 1



### intended to provide a concise synopsis of the ISA conclusions and findings that best 2



### inform the review of the NAAQS. The Integrated Review Plan (IRP) for the National 3



### Ambient Air Quality Standards for Lead ( U.S. EPA, 2011c ) identifies a series of 4



### policy

- relevant questions (in Chapter 3 ) that provide the framework for this assessment, 5



### and which frame the entire review of the NAAQS for Pb, and thus are informed by both 6



### scien ce and policy considerations. The plans and underlying questions for the ISA are 7



### included in the IRP. The ISA organizes, presents, and integrates the scientific evidence, 8



### which is considered along with findings from any risk analyses and policy considerati ons, 9



### to help the U.S. Environmental Protection Agency (EPA) address these questions during 10



### the NAAQS review for Pb. The ISA includes: 11



###  An integration of the evidence on the human health effects associated with Pb 12



### exposure, discussion of important uncertaint ies identified in the interpretation of 13



### the scientific evidence, and an integration across different scientific disciplines 14



### and across individual endpoints within major outcome categories. 15



###  An integration of the evidence on the ecological effects of Pb in a quatic and 16



### terrestrial ecosystems, discussion of endpoints common to plants, invertebrates 17



### and vertebrates and consideration of uncertainties in relating atmospheric Pb 18



### concentrations to ecological effects. 19



###  An integration of the effects associated with exp osure to Pb across the scientific 20



### disciplines for health and ecology, focusing on common modes of action. 21



###  Discussion of policy relevant considerations, such as potentially at

- risk 22



### populations and concentration

- response relationships. 23



### EPA has developed a process for evaluating the scientific evidence; and drawing 24



### conclusions and causal judgments regarding air pollution

- related health and 25



### environmental effects. The ISA development process includes literature search strategies, 26



### criteria for selecting and eva luating studies, approaches for evaluating weight of the 27



### evidence, and a framework for making causality determinations. The process and 28



### causality framework are described in more detail in the Preamble to the ISA. This section 29



### provides a brief overview of t he process for development of this ISA. 30February 2012 2

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### EPA initiated the current review of the NAAQS in April 2010 with a call for information 1



### from the public ( 75 FR 20843 ). Literature searches were conducted routinely to identify 2



### studies published since the last review, focusing on studies published from 2006 (close of 3



### previous scientific assessmen t) through September 2011. References that were considered 4



### for inclusion or cited in this ISA can be found at http://hero.epa.gov/lead

. 5



### This ISA evaluates relevant epidemiologic, animal toxicological, and ecological a nd 6



### welfare effects studies, including those related to concentration

- response relationships, 7



### mode(s) of action (MOA), and susceptible populations. Additionally, air quality and 8



### emissions data, studies on environmental fate and transport, and issues related to Pb 9



### toxicokinetics and exposure were considered for inclusion in the document. Previous 10



### AQCDs ( U.S. EPA, 2006b

, 1986b

, 1977 ) have included an extensive body of evidence on 11



### these topi cs. In this ISA, the conclusions and key findings from previous reviews are 12



### summarized at the beginning of each section, to provide the foundation for consideration 13



### of evidence from recent studies. Results of key studies from previous reviews are 14



### included in discussions or tables and figures, as appropriate, and conclusions are drawn 15



### based on the synthesis of evidence from recent studies with the extensive literature 16



### summarized in previous reviews. 17



### The Preamble discusses the general framework for conductin g the science assessment 18



### and developing an ISA, including criteria for selecting studies for inclusion in the ISA, 19



### evaluating and integrating the scientific evidence and developing scientific conclusions. 20



### In selecting the studies for inclusion in the Pb IS A, particular emphasis is placed on those 21



### studies most relevant to the review of the NAAQS. 22



### In drawing judgments regarding causality for the criteria air pollutants, evidence of health 23



### effects in the range of relevant pollutant exposures or doses is consi dered. With regard to 24



### the causal determinations drawn for human health effects of Pb , population

- based 25



### epidemiology studies were emphasized over occupational studies. Recent occupational 26



### studies were considered insofar as they added to the evidence base fo r an outcome for 27



### which sufficient numbers of population

- based studies were unavailable or, to the extent 28



### that they addressed a topic area that was of particular relevance to the NAAQS review 29



### ( e.g., longitudinal studies designed to examine recent versus his torical Pb exposure). 30



### Evidence from toxicological studies of effects observed in experimental animals at doses 31



### that were relevant to, or somewhat above, those currently experienced by the U.S. general 32



### population were emphasized. The extent to which studies of higher concentrations were 33



### considered varied by major outcome category, but generally studies with blood Pb levels 34



### within one order of magnitude above the upper end of the distribution of U.S. blood Pb 35



### levels were considered ( i.e., toxicological studie s reporting blood Pb levels less than 36February 2012 2

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### about 100 μ g/dL). 1 

### The majority of these studies reported blood Pb levels below 1



### approximately 30

- 40 μ g/dL, however. Studies with higher blood Pb levels were 2



### considered to the extent that they provided useful informatio n to inform modes of action 3



### or mechanisms or kinetics. For toxicological studies where blood Pb levels were not 4



### measured, judgments regarding how to distinguish high from the more relevant low doses 5



### were made considering the range of doses across the avail able body of evidence and 6



### emphasizing studies at the lower end of the range. 7



### Relevant concentrations for drawing causality judgments for ecological effects of Pb 8



### were determined considering the range of Pb concentrations in the environment and the 9



### availab le evidence for concentrations at which effects were observed in biota. Effects 10



### observed at or near ambient levels of Pb were emphasized and studies generally within 11



### one to two orders of magnitude above current conditions were considered in the body of 12



### evi dence for terrestrial and aquatic ecosystems. Studies at higher concentrations were 13



### used to the extent that they informed modes of action and illustrated the wide range of 14



### sensitivity to Pb across taxa. For aquatic biota, generally, the number of studies a vailable 15



### on freshwater organisms is greater than on saltwater organisms, covering more taxa as 16



### well as more endpoints. The causal determinations for aquatic biota are, therefore, based 17



### primarily on evidence from freshwater species. When available, data fro m saltwater 18



### ecosystems are discussed separately under the appropriate causal endpoint. For most of 19



### the endpoints under consideration, evidence is inadequate to establish causality in 20



### saltwater species. When sufficient evidence is available for marine organ isms, data on 21



### concentrations at which effects are observed are presented in Section 7.4.2

. 22



### The causal statements for terrestrial and aquatic effect s are arranged according to 23



### ecologically meaningful levels of biological organization (organism, population, 24



### community, ecosystem). As recognized in EPA's Framework for Ecological Risk 25



### Assessment ( U.S. EPA, 1992 )

, and in the adverse outcome pathway (AOP) framework 26



### ( Ankley et al., 2010 ) endpoints that are measured at one level of ecological organization 27



### may b e related to an endpoint at a higher level. The AOP conceptual framework was 28



### proposed to link mechanistic data from initiating events at the molecular level through a 29



### series of higher order biological responses to survival and to developmental and 30



### reproduc tive endpoints that can be used in ecological risk assessment, i.e., at the 31



### population level and higher. Fecundity, growth, and survival are organism

- level attributes 32



### that lead to population

- level ( e.g., abundance, production, extirpation), community

- level 33



### (taxa richness, relative abundance) and ecosystem

- level responses ( Ankley et al., 2010 ; 34

1 Studies considered were generally within an order of magnitude above 10 μg/dL (i.e., 100 μg/dL) , which was used to indicate the upper end of the blood Pb distribution in the U.S. population. Currently approximately 1.4% of U.S. children overall have blood Pb levels that exceed 10 μg/dL ( Jones et al., 2009a ) ; however, the proportion of individuals with blood Pb levels that exceed this concentration varies depending on factors including age and/or residence near a source of Pb exposure ( Section 4.1 )

.February 2012 2

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### Suter et al., 2005 )

. In the case of Pb, physiological stress, hematological effects and 1



### neurobehavioral alterations may decrease the overall fitness of an organism, even though 2



### their connection to effects at higher levels of biological organization may not have been 3



### characterized. Furthermore, the effects of Pb on ecosystems necessarily begin with some 4



### initial effects at the molecular level of specific organisms within the ecosystem ( U.S. 5



### EPA, 1986b )

. There are many different molecular and cellular level effects, and toxicity 6



### of Pb in ecosystems may be attained through multiple modes of action. 7



### The ISA considers evidence of health effects for both short

- and long

- term pollutant 8



### exposures. Biomarkers are typically used in epidemiologic studies of the health effects 9



### associated with Pb as an index of exposure or dose. Consequently, the timing, frequency, 10



### level, and duration of P b exposure(s) associated with the observed health effects are 11



### uncertain. Evidence from animal toxicological studies is also drawn upon to understand 12



### and interpret Pb exposures in epidemiologic studies. Animal toxicological studies that are 13



### relied upon to i nform our understanding of the exposures needed to induce health effects 14



### in humans include chronic exposure studies ( i.e., over 10% of the lifespan of the animal ), 15



### long

- term exposure studies ( e.g., greater than 4 weeks in rodents ) as well as acute or 16



### short

- term exposure studies ( e.g., less than 4 weeks in rodents ). In this ISA, short

- term 17



### human exposures are generally defined to include exposures of months ( e.g., < one year ) 18



### while long

- term human exposures include those greater than one year in duration. In 19



### addition, information including the age of the population studied, study period and study 20



### location can be used to aid in the interpretation of findings from epidemiologic studies 21



### because Pb exposures have declined over time and exposures vary depending on 22



### proximity to Pb sources. 23



### This ISA uses a five

- level hierarchy that classifies the weight of evidence for causation: 24



###  Causal relationship 25



###  Likely to be a causal relationship 26



###  Suggestive of a causal relationship 27



###  Inadequate to infer a causal relationship 28



###  Not likely to be a causal relationship 29



### Beyond judgments regarding causality are questions relevant to quantifying health or 30



### environmental risks based on the understanding of the quantitative relationships between 31



### pollutant exposures and health or ecologic al effects. Once a determination is made 32



### regarding the causal relationship between the pollutant and outcome category, important 33



### questions regarding quantitative relationships include: 34February 2012 2

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###  What is the concentration

- response, exposure

- response, or dose

- respons e 1



### relationship in the human population? 2



###  What exposure conditions (dose or exposure, exposure pathways, duration and 3



### pattern) are important? 4



###  What populations and lifestages appear to be differentially affected i.e., at 5



### greater risk of Pb

- related health effe cts? 6



###  What elements of the ecosystem ( e.g., types, regions, taxonomic groups, 7



### populations, functions, etc.) appear to be affected or are more sensitive to 8



### effects? 9



### This chapter summarizes and integrates the newly available scientific evidence that best 10



### info rms consideration of the policy

- relevant questions that frame this assessment. The 11



### organization of this chapter generally follows the organization of the document as a 12



### whole, with several additional sections including: (Section 2.1 ) a discussion of the 13



### assessment development and scope; (Section 2.8 ) an integration of the evidence across 14



### the disciplines of health and ecology; (Section 2.9 ) a discussion of policy

- relevant 15



### considerations; and, (Section 2.10 ) an overall summary. This ISA itself is composed of 16



### six chapters including this integrative summary. Chapter 3 highlights key concepts or 17



### issues relevant to understanding the sources, ambient concentrations, and fate and 18



### transport of Pb in the environment. 0 summarizes key concepts and recent findings on Pb 19



### exposures, toxicokinetics, and biomarkers reflecting Pb exposure and body burden. 20



### C hapter 5 presents a discussion of the MOA of Pb and evaluates and integrates 21



### epidemiologic and animal toxicological information on health effects related to Pb 22



### exposures, including nervous system, cardiovascular, renal, immunological, reproductive 23



### and developmental, and cancer outcomes. Chapter 6 summarizes the evidence on 24



### po tentially susceptible populations. Chapter 7 evaluates ecological effects evidence that 25



### is relevant to the review of the secondary NAAQS for Pb. 26



## 2.2 Am bient Lead: Source to Concentration

2.2.1 Sources, Fate and Transport of Ambient Lead

The findings of this review with respect to sources of atmospheric Pb build upon those 27



### from the 2006 Pb AQCD ( U.S. EPA, 2006b )

, which documented the decline in ambient 28



### air Pb emissions following the ban on alkyl

- Pb additives for on

- road gasoline. Pb 29



### emissions declined by 98% from 1970 to 1995 and then by an additional 76% from 1995 30February 2012 2

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### to 2008, at which time emissions were estimated a t 970 tons per year . As was the case at 1



### the time of the last Pb NAAQS review, data from the 2008 National Emissions Inventory 2



### (NEI) ( U.S. EPA, 2011a ) illustrate that piston

- engine aircraft emissions comprise the 3



### largest share (56%) of total atmospheric Pb emissions; the 2008 NEI estimated that 550 4



### tons of Pb were emitted from this source. Other sources of ambient air Pb, beginning with 5



### the largest, include metals processing, fossil fuel combustion, other industrial sources, 6



### roadway related sources, and historic Pb. Globa l atmospheric Pb deposition peaked in the 7



### 1970s, followed by a decline. See Section 3.2 for additional information. 8



### The atmosphere is the main envi ronmental transport pathway for Pb. On a local scale 9



### atmospheric Pb is primarily associated with coarse particulate matter (PM), and on a 10



### global scale atmospheric Pb is primarily associated with fine PM. Both wet and dry 11



### deposition are important removal me chanisms for atmospheric Pb. Because Pb in fine 12



### particles is typically fairly soluble, wet deposition is more important for fine Pb. In 13



### contrast, Pb associated with coarse particles is usually insoluble and removed by dry 14



### deposition. Pb associated with coa rse PM deposits to a great extent near local industrial 15



### sources, contributing to soil Pb concentrations in those locations, while fine Pb

- bearing 16



### PM can be transported long distances, contributing Pb to remote areas. Depending on 17



### local conditions, once dep osited particles may be resuspended and redeposited before 18



### reaching a site where further transport is unlikely, especially for dry deposition. See 19



### Section 3.3 for additional information. 20



### Environmental distribution of Pb occurs mainly through the atmosphere, from which it is 21



### deposited into surface waters and soil. Surface waters act as an important reservoir, with 22



### Pb lifetimes in the water column large ly controlled by deposition and resuspension of Pb 23



### in sediments. Substantial amounts of Pb from vehicle wear and building materials can 24



### also be transported by runoff waters to surface waters and sediments without becoming 25



### airborne. Pb containing sediment p articles can be remobilized into the water column, and 26



### sediment concentrations tend to follow those in overlying waters. See Section 3.3 for 27



### additio nal information. 28



### 2.2.2 Monitoring and Concentrations of Ambient Air Lead

The indicator for the Pb NAAQS is Pb in total suspended particles (Pb

- TSP). The 29



### Pb

- TSP indicator was retained in 2008 in recognition of the role of all PM sizes in 30



### ambient air Pb exposures . The Federal Reference Method (FRM) for Pb

- TSP specifies 31



### that ambient air is drawn through a high

- volume TSP sampler onto a glass fiber filter. 32



### The Pb

- TSP sampler’s size selective performance is known to be affected by wind speed 33



### and direction, and collection efficiency has been demonstrated to decline with particle 34February 2012 2

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### size with an uncertain upper size limit ( Wedding et al., 1977 )

. In recognition of the steep 1



### spatial gradients associated with sources of ultra

- coarse particles, ambient Pb sampled 2



### using the FRM for Pb

- PM 10 

### is allowed in certain instances where the expected Pb 3



### concentration does not approach the NAAQS and no sources of ultra

- coarse Pb are 4



### ne arby. A new FRM for Pb

- PM 10 

### has been implemented in which ambient air is drawn 5



### through an inertial particle size separator for collection on a polytetrafluoroethylene 6



### (PTFE) filter. The Pb

- PM 10 

### FRM is free of wind direction bias. Several FEMs have also 7



### bee n approved. The Pb

- TSP FRM is based on flame atomic absorption spectroscopy 8



### (AAS), while the Pb

- PM 10 

### FRM is based on x

- ray fluorescense spectroscopy (XRF). 9



### Inductively

- coupled plasma mass spectrometry (ICPMS) is under consideration as a new 10



### FRM for Pb

- TSP. See Section 3.4.1 for additional information. 11



### Pb monitoring requirements have experienced several changes since publication of the 12



### 2006 Pb AQCD ( U.S. EPA, 2006b )

. The current Pb monitoring network design 13



### requirements include two types of FRM monitoring sites: source

- oriented and 14



### non

- source

- oriented. Source

- oriented FRM Pb

- TSP monitoring sites are required near 15



### sources of air Pb emissions which are expected to or have been shown to contribute to 16



### ambient air Pb concentrations in excess of the NAAQS. At a minimum, monitoring is 17



### required near sources that emit 0.50 tons/year or more of Pb unless it can be determined 18



### that the s ource will not contribute to an ambient concentration exceeding 50% of the Pb 19



### NAAQS. With the December 2010 completion of action on regulatory requirement of Pb 20



### monitoring, one

- year of Pb

- TSP FRM monitoring is also required near 15 specific 21



### airports to gat her additional information on the likelihood of NAAQS exceedances near 22



### airports due to combustion of leaded aviation gasoline. Non

- source

- oriented monitoring 23



### is also required at national core multipollutant monitoring network (NCore) sites in Core 24



### Based St atistical Areas (CBSA) with a population of at least 500,000. In addition to FRM 25



### monitoring, Pb is also routinely measured in smaller particle fractions in the chemical 26



### speciation network (CSN), interagency monitoring of protected visual environment 27



### (IMPRO VE), and the national air toxics trends station (NATTS) networks. While 28



### monitoring in multiple networks provides extensive geographic coverage, measurements 29



### between networks are not directly comparable in all cases because there are differences in 30



### the meth ods, including the different particle size ranges sampled in the different 31



### networks. Depending on monitoring network, Pb is monitored in TSP, PM 10 

### , or PM 2.5



### . 32



### For the purpose of analyzing data for the ISA, monitors reporting to the AQS were 33



### considered to be source

- oriented if they were designated in AQS as source

- oriented, or 34



### they were located within 1 mile of a 0.5 ton per year or greater source, as noted in the 35



### 2005 NEI ( U.S. EPA, 2008a ) or the 2008 NEI ( U.S. EPA, 2011a )

. See Section 3.4 for 36



### additional information. 37February 2012 2

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### Ambient air Pb concentrations have declined drastically over the period 1980

- 2010. The 1


### median annual concentrations have dropped by 97% from 0.87 μg/m 3 

### in 1980 to 0.03 2


### μg/m 3 

### in 2010. While the sharpest drop in Pb concentration occurred during 1980

- 1990, a 3



### declining trend was observed between 1990 and 2010. There was an 8 4 % reduction in the 4



### median annual source

- oriented Pb concentration and a 85 % reductio n in the median 5



### annual non

- source

- oriented Pb concentration for 1990

- 2010. Recent estimates for the 6



### natural contribution to background Pb are ~0.3 to 1 ng/m 3 

### . These estimates exceed 7



### estimates of natural background presented in the 1986 Pb AQCD by a factor of 2 to 20. 8



### The more recent estimate still indicates that background airborne Pb concentrations are 9



### well below current ambient concentrations. See Section 3.5 for additional information. 10



### AQS data for source

- oriented and non

- source

- oriented FRM monitoring were analyzed 11



### for 2008

- 2010. For source

- oriented monitors, the three

- month rolling average was above 12



### the level of the NAAQS in twenty counties acros s the U.S. The three

- month rolling 13



### average was never above the level of the NAAQS for any of the non

- source

- oriented 14



### FRM monitors. Pb concentrations, seasonal variations, inter

- monitor correlations, and 15



### wind data were analyzed for six counties: Los Angeles County, CA; 16



### Hillsborough/Pinellas Counties, FL; Cook County, IL; Jefferson County, MO; Cuyahoga 17



### County, OH; and Sullivan County, TN. Spatial and temporal variability of Pb 18



### concentrations in each county were commonly high. Meteorology, distance from source s, 19



### and positioning of sources with respect to the monitors all appeared to influence the level 20



### of concentration variability across time and space. See Section 3.5 for additional 21



### information. 22



### Size distribution of Pb

- bearing PM varied substantially depending on the nature of Pb 23



### sources and proximity of the monitors to the Pb sources. Variation in the correlation of 24



### size fractionated Pb samples among dif ferent land use types may be related to differences 25



### in sources across land use types; for example, ultra

- coarse Pb

- PM has been observed near 26



### industrial sites. Additionally, Pb concentrations exhibited varying degrees of association 27



### with other criteria poll utant concentrations. Overall, Pb was moderately associated with 28



### PM 2.5 

### , PM 10 

### and NO 2 

### . Pb was moderately associated with CO in fall and winter only. The 29



### poorest associations were observed between Pb and O 3 

### . Among trace metals, the 30



### strongest association was with Zn. Moderate associations with Pb concentrations were 31



### observed for Br, Cu, and K. Such correlations may suggest some common sources 32



### affecting the concentrations of various pollutants. See Section 3.5 for additional 33



### information. 34February 2012 2

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### 2.2.3 Ambient Lead Concentrations in Non

- Air Media and Biota

Atmospheric deposition has led to measurable Pb concentrations observed in rain, 1



### snowpack, soil, surface waters, sed iments, agricultural plants, livestock, and wildlife 2



### across the world, with highest concentrations near Pb sources, such as metal smelters. 3



### After the phase

- out of Pb from on

- road gasoline, Pb concentrations have decreased 4



### considerably in rain, snowpack, an d surface waters. Declining Pb concentrations in tree 5



### foliage, trunk sections, and grasses, as well as surface sediments and soils in some 6



### locations, have also been observed ( U.S. EPA, 2006b )

. In contrast, Pb is retained in soils 7



### and sediments, where it provides a historical record of deposition and associated 8



### concentrations. In remote lakes, sediment profiles indicate higher Pb concentrations in 9



### near surface sediment as compared to pre

- industrial era sediment from greater depth a nd 10



### indicate peak concentrations between 1960 and 1980 (when leaded on

- road gasoline was 11



### at peak use). Concentrations of Pb in moss, lichens, peat, and aquatic bivalves have been 12



### used to understand spatial and temporal distribution patterns of air Pb concen trations. 13



### Ingestion and water intake are the major routes of Pb exposure for aquatic organisms, and 14



### food, drinking water, and inhalation are major routes of exposure for livestock and 15



### terrestrial wildlife. Overall, Pb concentrations have decreased substant ially in media 16



### through which Pb is rapidly transported, such as air and water. Substantial Pb remains in 17



### soil and sediment sinks. Although in areas less affected by major local sources, the 18



### highest concentrations are below the surface layers and reflect th e phase

- out of Pb from 19



### on

- road gasoline and emissions reductions from other sources. 20



### Information on ambient Pb concentrations in non

- air media and biota is reported in 21



### Section 3.6 , and concentrations considered in the interpretation of the ecological evidence 22



### are tabulated in Table 2

- 1 . As noted in the preamble, the ecological causal determinations 23



### focus on studies where effects of Pb exposure are observed at or near ambient levels of 24



### Pb and studies generally within the ran ge of one to two orders of magnitude above 25



### current or ambient conditions were also considered in the body of evidence. 26February 2012 2

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### Table 2

- 1 Ambient Pb Concentrations in Non

- Air Media and Biota Considered for Ecological Assessment

Media Pb Concentration Years Data Obtained References

Soil National Average: 18.9 mg Pb/kg
Range of state averages: 5

- 38.6 mg Pb/Kg 1961

- 1976 U.S. EPA ( 2007d

, 2006b

, 2003b )

Sediment 1 Median: 28 mg Pb/kg (dry weight) 1996

- 2001 Mahler et al. ( 2006 )

, U.S. EPA ( 2006b )

Fresh Surface Water (Dissolved Pb) a Median: 0.5 μ g Pb/L; Max: 30 μ g Pb/L
Range: 0.0003

- 0.075 μg Pb/L 2001

- 20 03

2002

- 2007 U.S. EPA ( 2006b )

Field and Sherrell ( 2003 )

, Landers et al. ( 2008 )

Saltwater b Range: 0.01

– 27 μg Pb/L
Range: 0.005

- 0.04 μg Pb/L Dates not available Sadiq ( 1992 )

Leland and Kuwabara ( 1985 )

Vegetation Lichens: 0.3

- 5 mg Pb/kg
Grasses: 31% (percent of soil Pb in grass) 2002

- 2007

1980s

- 2000s Landers et al. ( 2008 )

Vandenhove et al. ( 2009 )

Vertebrate Fish: Geometric Mean:

0.54 mg Pb/kg (dry weight)

Maximum:
23 mg Pb/kg (dry weight)

Fish: 0.0033

- 0.97 mg Pb/kg

Moose: 0.021

- 0.23 mg Pb/kg 2001

- 2003

2002

- 2007 U.S. EPA ( 2006b )

Landers et al. ( 2008 )

a Based on synthesis of NAWQA data reported in 2006 Pb AQCD ( U.S. EPA, 2006b )

b Data from a combination of brackish and marine saltwater samples. In general, Pb in seawater is higher in coastal areas and e stuarie s since these locations are closer to sources of Pb contamination and loading from terrestrial systems.



## 2.3 Exposure to Ambient Lead

Exposure data considered in this assessment build upon the conclusions of the 2006 Pb 1



### AQCD ( 2006 b )

, which found air Pb concentrations in the U.S. and associated biomarkers 2



### of exposure to have decreased substantially following the ban on Pb in on

- road gasoline 3



### as well as an earlier ban on Pb in house

- hold paints. Pb exposure is difficult to assess 4



### because Pb has multiple sources in the environment and passes through various media. 5



### The atmosphere is the main environmental transport pathway for Pb, and, on a global 6



### scale, atmospheric Pb is primarily associated with fine particulate matter, which can 7



### d eposit to soil and water. In addition to primary emission of particle

- bearing or gaseous 8



### Pb to the atmosphere, Pb can be suspended to the air from soil or dust. Air

- related 9



### pathways of Pb exposure are the focus of this assessment. In addition to inhalation of Pb 10



### from ambient air, air

- related Pb exposure pathways include inhalation and ingestion of Pb 11



### from indoor dust and/or outdoor soil that originated from recent or historic ambient air 12



### ( e.g., air Pb that has penetrated into the residence either via the ai r or tracking of soil). 13



### Non

- air

- related exposures include occupational exposures, hand

- to

- mouth contact with t 14



### with dust or chips of peeling Pb

- containing paint, or ingestion of Pb in drinking water 15



### conveyed through Pb pipes. Several study results indicate that exposure to Pb

- containing 16February 2012 2

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### paint and home age (often a surrogate for the presence of Pb paint) are important 1



### residential factors that increase risk of elevated blood Pb (Sections 2.9.6.7 and 6.2.6 ). 2



### Most Pb biomarker studies do not indicate species or isotopic signature, and so non

- air 3



### exposures are reviewed in this section because they can also contribute to Pb body 4



### burden. See Section 4.1 for additional information on exposure to ambient Pb. 5



### A number of monitoring and modeling techniques have been employed for ambient Pb 6



### exposure assessment. Environmental Pb concentration data can be collected from 7



### ambient air Pb monitors, soil Pb samples, dust Pb samples, and dietary Pb samples t o 8



### estimate human exposure. Exposure estimation error depends in part on the collection 9



### efficiency of these methods; collection efficiency for ambient air Pb FRM samplers is 10



### described in Section 3.4 . Additionally, high spatial variability of the Pb concentrations in 11



### various media also can contribute to exposure error, as described in the 2009 PM ISA 12



### ( U.S. EPA, 2009 )

. Models, such as the Integra ted Exposure Uptake Biokinetic (IEUBK) 13



### model, simulate human exposure to Pb from multiple sources and through various routes 14



### including inhalation, ingestion, and dermal exposure. IEUBK model inputs include soil 15



### Pb concentration, air Pb concentration, dieta ry Pb intake including drinking water, Pb 16



### dust ingestion, human activity, and biokinetic factors. Measurements and/or assumptions 17



### can be utilized when formulating the model inputs; error in measurements and 18



### assumptions thus have the potential to propagate through the exposure models. 19



### Section 4.1 presents data illustrating potential exposure pathways. Soil can act as a 20



### reservoir for deposited Pb emissions and exposure to soil contaminated with deposited Pb 21



### can occur through resuspende d PM as well as shoe tracking and hand

- to

- mouth contact, 22



### which is the main pathway of childhood exposure to Pb. Recent data by Yamamoto et al. 23



### ( 2006 ) have shown that the size distribution of particles collected on children’s hands 24



### have a mode around 40 μ m with the upper tail of the distribution extending to 25



### 200

- 300 μ m. Infiltration of Pb dust into indoor environments has been suggested, and Pb 26



### dust has been shown to persist in indoor environments even after repeated cleanings. 27



### Measurements of particle

- bound Pb exposures reported in this assessment have shown 28



### that persona l exposure measurements of Pb concentration are typically higher than indoor 29



### or outdoor ambient Pb concentrations. These findings regarding personal exposure to Pb 30



### dust may be related to the personal cloud effect. 31



## 2.4 Toxicokinetics

The majority of Pb in the body is found in bone (roughly 90% in adults, 70% in children); 32



### only about 1% of Pb is found in the blood. Pb in blood is primarily (~99%) bound to red 33



### blood cells (RBCs). It has been suggested that the small fraction of Pb in plasma (<1%) 34February 2012 2

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– Do Not Cite or Quote 

### may be the more biologically labile and toxicologically active fraction of the circulating 1



### Pb. The relationship between Pb in blood and plasma is pseudo

- linear at relatively low 2



### daily Pb intakes ( i.e., <10 μg/day

– kg) and at blood Pb concentrations <25 μg/dL, and 3



### becomes c urvilinear at higher blood Pb concentrations due to saturable binding to RBC 4



### proteins. As blood Pb level increases and the higher affinity binding sites for Pb in RBCs 5



### become saturated, a larger fraction of the blood Pb is available in plasma to distribute to 6



### brain and other Pb

- responsive tissues. See Section 4.2 for additional details. 7



### The burden of Pb in the body may be viewed as divided between a d ominant slow 8



### ( i.e., uptake and elimination) compartment (bone) and smaller fast compartment(s) (soft 9



### tissues). Pb uptake and elimination in soft tissues is much faster than in bone. Pb 10



### accumulates in bone regions undergoing the most active calcification at the time of 11



### exposure. During infancy and childhood, bone calcification is most active in trabecular 12



### bone ( e.g., patella); whereas, in adulthood, calcification occurs at sites of remodeling in 13



### cortical ( e.g., tibia) and trabecular bone ( Aufderheide and Wittmers, 1 992 )

. A high bone 14



### formation rate in early childhood results in the rapid uptake of circulating Pb into 15



### mineralizing bone; however, in early childhood bone Pb is also recycled to other tissue 16



### compartments or excreted in accordance with a high bone resorp tion rate ( O'Flaherty, 17



### 1995 )

. Thus, much of the Pb acquired early in life is not permanently fixed in the bone. 18



### The exchange of Pb from plasma to the bone surface is a relatively rapi d process. Pb in 19



### bone becomes distributed in trabecular and the more dense cortical bone. The proportion 20



### of cortical to trabecular bone in the human body varies by age, but on average is about 21



### 80% cortical to 20% trabecular. Of the bone types, trabecular b one is more reflective of 22



### recent exposures than is cortical bone due to the slow turnover rate and lower blood 23



### perfusion of cortical bone. Some Pb diffuses to deeper bone regions where it is relatively 24



### inert, particularly in adults. These bone compartments are much more labile in infants 25



### and children than in adults as reflected by half

- times for movement of Pb from bone into 26



### the plasma ( e.g., cortical half

- time = 0.23 year s at birth, 3.7 year s at 15 year s of age, and 27



### 23 year s in adults; trabecular half

- time = 0.23 year s at birth, 2.0 year s at 15 year s of age, 28



### and 3.8 year s in adults) ( Leggett, 1993 )

. See Section 4.2 for additional details. 29



### Evidence for maternal

- to

- fetal transfer of Pb in humans is derived from cord blood to 30



### maternal blood Pb ratios. Group mean ratios range from about 0.7 to 1.0 at the ti me of 31



### delivery for mean maternal blood Pb levels ranging from 1.7 to 8.6 μ g/dL. Transplacental 32



### transfer of Pb may be facilitated by an increase in the plasma/blood Pb concentration 33



### ratio during pregnancy. Maternal

- to

- fetal transfer of Pb appears to be rela ted partly to the 34



### mobilization of Pb from the maternal skeleton. See Section 4.2 for additional details. 35



### The dominant elimination phase of Pb kineti cs in the blood, exhibited shortly after a 36



### change in exposure occurs, has a half

- life of ~20

- 30 day s. An abrupt change in Pb uptake 37February 2012 2

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### gives rise to a relatively rapid change in blood Pb, to a new quasi

- steady state, achieved 1



### in ~75

- 100 day s ( i.e., 3

- 4 times the blood elimination half

- life). A slower phase of Pb 2



### clearance from the blood may become evident with longer observation periods following 3



### a decrease in exposure due to the gradual redistribution of Pb among bone and other 4



### compartments. See Section 4.3 for additional details. 5



## 2.5 Lead Biomarkers

Overall, trends in blood Pb levels have been decreasing among U.S. children and adults 6



### over the past 20 y ears (Section 4.4 ). The median blood Pb level for the entire U.S. 7


### population is 1.2 μg/dL and the 95th percentile blood Pb level was 3.7 μg/dL, bas ed on 8



### the 2007

- 2008 NHANES data ( NCHS, 2010 )

. Among children aged 1

- 5 year s, the 9



### median and 95th percentiles were slightly high er at 1.4 μg/dL and 4.1 μg/dL, 10



### respectively. 11



### Blood Pb is dependent on both the recent exposure history of the individual, as well as 12



### the long

- term exposure history that determines body burden and Pb in bone. The 13



### contribution of bone Pb to blood Pb changes depending on the duration and intensity of 14



### the exposure, age, and various other physiological stressors that may affect bone 15



### remodeling ( e.g., nutritional status, pregnancy, menopause, extended bed rest, 16



### hyperparathyroidism) beyond that which normally and continuously occurs . In children, 17



### largely due to faster exchange of Pb to and from bone, blood Pb is both an index of recent 18



### exposure and potentially an index of body burden. In adults and children, where exposure 19



### to Pb has effectively ceased or greatly d ecreased, a slow decline in blood Pb 20



### concentrations over the period of years is most likely due to the gradual release of Pb 21



### from bone. Bone Pb is an index of cumulative exposure and body burden. Even bone 22



### compartments should be recognized as reflective of differing exposure periods with Pb in 23



### trabecular bone exchanging more rapidly than Pb in cortical bone with the blood. This 24



### difference in the compartments making Pb in cortical bone a better marker of cumulative 25



### exposure and Pb in trabecular bone more lik ely to be correlated with blood Pb, even in 26



### adults. See Section 4.3 for additional details. 27



### Sampling frequency is an important consideration when evaluating blood Pb and bone Pb 28



### levels in epidemiologic studies, particularly when the exposure is not well characterized. 29



### It is difficult to determine what blood Pb is reflecting in cross

- sectional studies that 30



### sample blood Pb once, whether recent exposur e or movement of Pb from bone into blood 31



### from historical exposures. In contrast, cross

- sectional studies of bone Pb and longitudinal 32



### samples of blood Pb concentrations over time provide more of an index of cumulative 33



### exposure and are more reflective of ave rage Pb body burdens over time. The degree to 34February 2012 2

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### which repeated sampling will reflect the actual long

- term time

- weighted average blood 1



### Pb concentration depends on the sampling frequency in relation to variability in 2



### exposure. High variability in Pb exposures can produce episodic (or periodic) oscillations 3



### in blood Pb concentration that may not be captured with low sampling frequencies. 4



### Furthermore, similar blood Pb concentrations in two individuals (or populations), 5



### regardless of their age, do not necessarily translate to similar body burdens or similar 6



### exposure histories. 7



### The concentration of Pb in urine follows blood Pb concentration, in that it mainly reflects 8



### the exposure history of the previous few months and therefore, is likely a relatively poor 9



### index o f Pb body burden. There is added complexity with Pb in urine because 10



### concentration is also dependent upon urine flow rate, which requires timed urine samples 11



### that is often not feasible in epidemiologic studies. Other biomarkers have been utilized to 12



### a less er extent ( e.g., Pb in teeth). See Section 4.3

. 13



## 2.6 Health Effects

This section evaluates the evidence from toxicological and epidemiologic studies that 14



### examined the health effects associated with exposure to Pb and integrates that evidence 15



### across these disciplines. The results from the health studies are also considered in 16



### combination with the evidence from other disciplines ( e.g., toxicokinetics) for th e causal 17



### determinations (Section 2.1 ) made for the health outcomes discussed in this assessment. 18



### In the following sections a discussion of the causa l determinations will be presented for 19



### the health effects for which sufficient evidence was available to conclude a causal or 20



### likely to be causal relationship ( Table 2

- 2 ). A more detailed discussion of the underlying 21



### evidence used to formulate each causal determination can be found in Chapter 5 of this 22



### document. 23February 2012 2

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### Table 2

- 2 Summary of causal determinations a 

### between exposure to Pb and

health outcomes

Outcome Causality Determination a

Nervous System Effects (Section 5.3.13 ) Causal Relationship

Cardiovascular Effects (Section 5.4.7 ) Causal Relationship

Renal Effects (Section 5.5.6 ) Causal Relationship

Immune System Effects (Section 5.6.8 ) Causal Relationship

E ffects on Heme Synthesis and Red Blood Cell Function (Section 5.7.7 ) Causal Relationship

Reproductive and Developmental Effects (Section 5.8.10 ) Causal Relationship

Cancer (Section 5.10.6 ) Likely Causal Relationship

a Based upon the framework described in the Preamble, a determination of causality was made for a broad outcome category ( i.e., nervous system effects) by evaluating the coherence of evidence across disciplines and across a spectrum of related endpoints. However, the evidence on which the causal judgment is based, including the strength of evidence for the individual endpoints within the ma jor outcome category, is characterized within the discussion. Causal determinations we re made within approximately 1

- 2 orders of magnitude of

current levels.



### 2.6.1 Nervous System Effects

Recent epidemiologic and toxicological studies substantiated the strong body of evidence 1



### presented in the 2006 Pb AQCD that Pb exposure is associated with nervo us system 2



### effects. The weight of epidemiologic and toxicological evidence clearly supports 3



### associations of higher blood Pb levels with decrements in cognitive function in children, 4



### i.e., full

- scale IQ and various measures of learning and memory. In epidemi ologic 5



### studies, these associations were substantiated in children ages 1 to 11 year s and in 6



### populations with mean blood Pb levels between 2 and 7 μ g/dL. Observation of a 7



### supralinear concentration

- response relationship and associations with mean (or quantil e) 8



### blood Pb levels < 2 μ g/dL do not provide evidence for a threshold for effects of Pb 9



### exposure on the developing nervous systems of children. Epidemiologic and 10



### toxicological evidence clearly demonstrates Pb

- associated increases in behavioral 11



### problems, in particular, inattention and impulsivity (prior symptoms of ADHD). 12



### Associations are substantiated in children ages 1 to 12 year s with mean concurrent blood 13



### Pb levels of 2 to 5 μ g/dL. In epidemiologic studies, associations with cognitive func tion 14



### and behavio r were observed after adjustment for a range of potential confounding 15



### variables, but most commonly, parental IQ, parental education, and other SES

- related 16



### variables. 17February 2012 2

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### In animals, the weight of evidence demonstrates effects on cognition and behavior with 1



### pre natal and early postnatal Pb exposures that resulted in blood Pb levels of 10 to 2



### 40 μ g/dL. In children, the weight of evidence supports cognitive function decrements and 3



### behavioral problems in association with concurrent blood Pb levels. Associations also are 4



### observed with prenatal, early childhood, and childhood average blood Pb levels, thus 5



### uncertainty remains regarding the lifestage of exposure within childhood that is 6



### associated with the greatest risk. The uncertainty regarding the frequency, timing 7



### dur ation and level of exposure contributing to the observed associations is greater in 8



### studies of older children compared to younger children. The weight of toxicological 9



### evidence demonstrates neurodevelopmental effects on cognition and behavior with 10



### prenatal and early postnatal Pb exposures that can have effects persisting to adulthood. 11



### The biological plausibility for epidemiologic and toxicological findings for effects on 12



### cognitive function and behavior is provided by evidence characterizing underlying 13



### mecha nisms, including Pb

- induced changes in neurogenesis, synaptogenesis and synaptic 14



### pruning, long term potentiation, and neurotransmitter function. Based most heavily on 15



### cognitive function decrements and inattention in children, the collective body of evidenc e 16



### integrated across epidemiologic and toxicological studies is sufficient to conclude that 17



### there is a causal relationship between Pb exposures and nervous system effects 18



### (Section 5.3.13 ). 19



### New evidence demonstrates associations of blood Pb level with Attention Deficit 20



### Hyperactivity Disorder (ADHD) in children (8

- 17 year s old) and this evidence is 21



### consistent with findings demonstrating the effect of Pb on inattention and impulsivity in 22



### children. Several new epidemiologic studies indicate associations between higher 23



### concurrent blood Pb level and higher prevalence or incidence of ADHD diagnosis and its 24



### contributing diagnostic indices, whereas previous evi dence was inconsistent. The 25



### biological plausibility for associations with ADHD is strongly supported by the large 26



### epidemiologic and toxicological evidence base demonstrating Pb

- associated increases in 27



### inattention and impulsivity, both of which are primary symptoms of ADHD. 28



### The evidence for Pb

- associated effects on other nervous system endpoints was also 29



### evaluated. Compared to the body of evidence on behavior and inattention, a smaller but 30



### equally consistent evidence base indicated associations of concurrent and early childhood 31



### blood Pb levels with social misconduct in children and delinquent behaviors in 32



### adolescents and young adults ( Table 5

- 11 ). Associations of blood Pb levels with ADHD, 33



### misconduct, and delinquency were observed in populations of children with a wide range 34



### of blood Pb levels, 1 to 11 μ g/dL, all similar in the strength of evidence. While the 35



### different behavioral indices are examine d, Pb exposure also was found to affect behavior 36



### (decreased ability to escape predators or capture prey) in aquatic and terrestrial species 37



### (Section 7.2 and Section 7.3 ). 38February 2012 2

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– Do Not Cite or Quote 

### A few new toxicological studies augmented the evidence for Pb

- related effects to the 1



### visual system by demonstrating retinal c hanges in male rodent offspring in association 2



### with lower blood Pb levels (<15 μ g/dL) than previously examined (20 to > 100 μ g/dL) 3



### (Section 5.3.4.3 ). A small body of epidemiologic evidence together with a large historical 4



### base of toxicological evidence indicated associations of Pb biomarkers or exposure with 5



### impaired auditory function. Associations were found in children ranging from 4 to 6



### 19 year s in age and with mean concurrent blood Pb levels of 7

- 12 μ g/dL 7



### (Section 5.3.4.1 ). While mood and emotional state have been examined less frequently 8



### compared with inattention and misconduct, several studies found associations of 9



### biomarkers of cumulative Pb exposure ( i.e., tooth or childhood average blood Pb) and 10



### concurrent blood Pb levels with parental or teacher reports of withdrawn behavior or 11



### depressio n in children with mean blood Pb levels 8

- 28 μ g/dL (Section 5.3.3.3 ). These 12



### findings in children are supported by a small body of toxicological studies in which 13



### prenatal plus lactational Pb exposure resulted in depression

- like behavior in rodent 14



### models. Studies also reported associations of early childhood average and concurrent 15



### blood Pb levels with lower fine and gross motor function in children ages 3 to 17 year s 16



### (Section 5.3.5 ). A common observation across studies was finding that biomarkers of Pb 17



### exposure were associated with decrements in multiple neurodevelopmental outcomes, 18



### including cognitive function, externalizing behaviors, internalizing behaviors, and motor 19



### function, within the same population. These findings in combination with previously 20



### discussed cognitive and behavioral effect s indicate that Pb exposure affects a broad 21



### spectrum of neurodevelopmental effects in children. 22



### In adults, the frequency, duration, timing and level of Pb exposure implicated in nervous 23



### system effects remain uncertain. Among occupationally

- exposed adults, a spectrum of 24


### nervous system effects is associated with concurrent blood Pb level (≥ 14 μ g/dL), which 25



### reflects both current and cumulative exposure. However, in adults without occupational 26



### exposure, cognitive performance is more strongly associated with ti bia Pb levels than 27



### blood Pb levels, which indicates an effect of long

- term, cumulative Pb exposures. Based 28



### on a smaller body of epidemiologic studies, blood and bone Pb levels were associated 29



### with essential tremor and PD, respectively, in adults (Section 5.3.7.1 ). However, in these 30



### case

- control studies, it is difficult to establish temporality between Pb exposure and 31



### disease. Support for epidemiologic findings for PD is provided by toxicological evidence 32



### for Pb

- induced decreased dopaminergic cell activity in the substantia nigra, which 33



### contributes to the primary symptoms of Parkinson’s disease. Whereas evidence for 34



### association with Alzheimer's disease in adults is weak, developmental Pb exposures of 35



### monkeys (early postnatal, PND 1

- 400) and rats (lactational) has been shown to induce 36



### formation of amyloid plaques, pathology that underlies Alzheimer's disease 37



### (Section 5.3.7.2 ). A small body of studies of behavior in adults examined and found 38February 2012 2

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– Do Not Cite or Quote 

### associations of blood and tibia Pb levels with depression and anxiety symptoms 1



### (Section 5.3.3.6 ). 2



### 2.6.2 Cardiovascular Effects

The 2006 Pb AQCD concluded that there was a relationship between higher blood Pb and 3



### bone Pb and cardiovascular effects in adults, in particular increased blood pressure ( BP ) 4



### and increased incidence of hypertension ( U.S. EPA, 2006b )

. Building on this strong body 5



### of evidence, recent epidemiologic and to xicological studies substantiated the evidence 6



### that long

- term Pb exposure is associated with cardiovascular effects in adults with the 7



### largest body of evidence demonstrating associat ions of Pb with increased BP and 8



### hypertension. The epidemiologic evidence is strengthened by several recent prospective 9



### studies that find associations between biomarkers of Pb and BP and hypertension and by 10



### eff ect estimates that are observed after adjustme nt for multiple potential confounding 11



### factors. The weight of epidemiologic evidence supported associations in adults with mean 12



### concurrent blood Pb levels less than 5 μ g/dL. As these outcomes in epidemiologic studies 13



### were most often observed in adults with likely higher past than current Pb exposures, 14



### uncertainty exists as to the Pb exposure level, timing, frequency, and duration 15



### contributing to the observed associations. Recent epidemiologic studies found that bone 16



### Pb level, a metric of cumulative exposure, is strongly related to hypertension risk in 17



### adults with mean bone Pb levels greater than 20 μ g/g. However, uncertainties also exist 18



### as to the specific Pb exposure conditions that contributed to the associations. The weight 19



### of animal evidence also demonstr ates an increase in BP after long

- term ( i.e., greater than 20



### 4 week s in rodents) exposure to Pb. Whereas the majority of studies examined and found 21



### increases in BP in animals with mean blood Pb levels greater than 10 μ g/dL ( Table 5

- 18 ), 22



### a recent study found elevated BP in animals with a mean blood Pb level of 2 μ g/dL (Tsao 23



### et al. 2000). Also, animal toxicological studies provided mechanistic evidence to s upport 24



### the biological plausibility of Pb

- induced hypertension, including Pb

- induced oxidative 25



### stress, activation of RAAS (renin

- angiotensin

- aldosterone system) , altered sympathetic 26



### activity, and vasomodulator imbalance. Collectively, the evidence integrate d across 27



### epidemiologic and toxicological studies as well as across the spectrum of other 28



### cardiovascular endpoints examined is sufficient to conclude that there is a causal 29



### relationship between Pb exposures and cardiovascular health effects (Section 5.4.7 )

. 30



### Studies in the 2006 Pb AQCD ( U.S. EPA, 2006b ) also found associations between Pb 31



### biomarkers of exposure and other cardiovascular diseases such as IHD, cerebrovas cular 32



### disease, peripheral vascular disease, and cardiovascular disease related mortality; 33



### however, the available evidence was limited. Recent epidemiologic and toxicological 34



### studies continue to provide evidence in adults for blood Pb

- associated increased 35February 2012 2

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– Do Not Cite or Quote 

### a therosclerosis, thrombosis, IHD, PAD, arrhythmia, and cardiac contractility in 1



### populations with mean blood Pb levels >2.5 μ g/dL ( Table 5

- 19 ). Further, animal 2



### toxicological evidence continued to build on the evidence supporting the mechanisms 3



### leading to these cardiovascular system responses, as well as Pb

- induced changes in BP 4



### and hypertension. Enhanced understanding of Pb

- induced oxidative stress includi ng  ̇NO 5



### inactivation, endothelial dysfunction leading to altered vascular reactivity, activation of 6



### the RAAS, and vasomodulator imbalance provides biological plausibility for the 7



### consistent associations observed between higher blood and bone Pb levels and g reater 8



### cardiovascular effects. 9



### Recent epidemiologic studies of adults also investigated the interaction of Pb biomarkers 10



### with genetic variants in associations with cardiovascular effects. Evidence was presented 11



### for a larger blood Pb

- associated increase in BP in carriers of the ALAD2 allele, which is 12



### associated with greater binding affinity for Pb in the bloodstream ( Figure 5

- 26 ). 13



### Additionally, bone Pb concentration was associated with larger increases in PP, which is 14



### a good predictor of cardiovascular morbidity and mortality and an indicator of arterial 15



### stiffness, among adults with the HFE H63D and/or C282Y variant and there was 16



### evidence of HFE and tran sferrin gene variants, related to iron metabolism, impacting the 17



### associations of bone Pb levels with cardiovascular effects, evaluated by QT interval 18



### changes ( Figure 5

- 26 ). The evidence for genetic factors to potentially increase the risk of 19



### Pb related health effects was limited ( Table 6

- 4 ). New evi dence extended the potential 20



### continuum of Pb

- related cardiovascular effects by demonstrating associations of blood Pb 21



### and bone Pb with both cardiovascular and all

- cause mortality with follow

- up periods 22



### ranging between 8 and 12 year s. The associations of Pb with cardiovascular morbidity 23



### observed in both epidemiologic and toxicological studies support recent epidemiologic 24



### findings of increased Pb

- associated cardiovascular mortality. Since the populations 25



### enrolled in the epidemiologic studies were largely comp osed of adults with likely higher 26



### past than current Pb exposures, uncertainty exists as to the Pb exposure level, timing, 27



### frequency, and duration contributing to the observed associations. 28



### 2.6.3 Renal Effects

The 2006 Pb AQCD concluded that “in the general popul ation, both circulating and 29



### cumulative Pb was found to be associated with a longitudinal decline in renal function,” 30



### evidenced by increased serum creatinine and decreased creatinine clearance or eGFR 31



### over follow

- up of 4 to 15 year s in association with high er baseline blood and bone Pb 32



### levels ( U.S. EPA, 2006b )

. Uncertainty remained on the contribution of past Pb exposures 33



### to associations observed in adults, the renal effects of Pb in children, and the implication 34



### of hyperfiltration . Because blood Pb level in nonoccupationally

- exposed adults reflects 35February 2012 2

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– Do Not Cite or Quote 

### both recent and past Pb exposures, the magnitude, timing, frequency, and duration of Pb 1



### exposure contributing to the observed associations remains uncertain. 2



### New epidemiologic and toxic ological studies evaluated in the current review support or 3



### expand upon the strong body of evidence presented in the 2006 Pb AQCD ( U.S. EPA, 4



### 2006b )

. The weight of epidemiologic evidence demonstrates consistently a relationship 5



### between higher blood Pb level and kidney dysfunction ( e.g., lower creatinine clearance, 6



### higher serum creatinine, and lower GFR [glomerular filtration rate] ) in 7



### nonoccupationally

- exposed adults with mean concurrent or baseline blood Pb levels of 8



### 2

- 10 μ g/dL. A few analyses find higher blood Pb levels to be associated with a greater 9



### longitudinal decrease in kidney function over time (4

- 15 year s), suggesting that past Pb 10



### exposures ma y contribute to ongoing renal effects. The epidemiologic evidence is 11



### strengthened by associations between Pb biomarker levels and r enal function that are 12



### observed after adjustment for multiple potential confounding factors such as age, sex, 13



### comorbid cardio vascular conditions, BMI (body mass index) , smoking, and alcohol use. 14



### Coherence for epidemiologic findings is provided by observations in animal models that 15



### Pb exposure for greater than 6 months decreases GFR and increases serum creatinine. 16



### The weight of e vidence in animal studies indicates that Pb induces histopathological 17



### changes, including tubular atrophy and sclerosis. Overall, reduced renal function and 18



### increased kidney damage in animals are observed with chronic Pb (> 4 week s) exposure 19



### that results in blood Pb levels > 20 μ g/dL. By demonstrating Pb

- induced renal oxidative 20



### stress, inflammation, mitochondrial dysfunction, apoptosis, and glomerular hypertrophy, 21



### toxicological studies provide biological plausibility for the associations observed in 22



### epidemio logic studies between blood Pb levels and kidney dysfunction. Collectively, the 23



### evidence integrated across epidemiologic and toxicological studies as well as across the 24



### spectrum of renal outcomes is sufficient to conclude that there is a causal relationshi p 25



### between Pb exposures and renal health effects ( Section 5.5.6 ). 26



### In addition, data on the effects of Pb on the kidney in children were reported in a recent 27



### NHANES analysis of adolescents, ages 12

- 20 year s, which observed an association 28


### between higher concurrent blood Pb (mean: 1.5 μg/dL) and lower cystatin C

- based eGFR 29



### (Section 5.5.6 ). These findings are consistent with results from a rodent model study in 30



### which a low dose of Pb (50 ppm ) administered from birth resulted in renal impairment 31



### (elevated serum creatinine as compared to control rats), but these observations require 32



### confirmation by measurement of GFR and renal pathology. This recent epidemiologic 33



### study along with several previo us studies that included children with higher Pb exposures 34



### (due to residence near sources, Pb poisoning, or parental occupational exposure) provide 35



### evidence that renal function in children may be affected by Pb exposure. The NHANES 36



### adolescents, however, li kely had higher Pb exposures earlier in childhood, thus, the 37



### magnitude, timing, frequency, and duration of Pb exposure contributing to the observed 38February 2012 2

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– Do Not Cite or Quote 

### association is uncertain. Research on the association of Pb with kidney function in the 1



### occupational setting is less consistent than that in environmentally exposed populations 2



### ( Section 5.5.2. 2 5.5.2.2 ). The observation of paradoxical or inverse associations (higher 3



### Pb dose with lower serum creatinine, and/or higher eGFR or calculated or measured 4



### creatinine clearance) in several of these studies refl ects limitations of the study design. 5



### 2.6.4 Immune System Effects

The 2006 Pb AQCD presented consistent evidence for immune system effects associated 6



### with Pb exposure ( U.S. EPA, 2006b )

. Rather than producing overt cytotoxicity or 7



### patho logy, Pb exposure was found to be associated with alterations in several subclinical 8



### parameters related to cellular and humoral immunity ( Figure 5

- 42 ). Recent toxicological 9



### and epidemiologic studies support the strong body of evidence presented in the 2006 Pb 10



### AQCD that Pb exposure may be associated with a broad spectrum of changes in both 11



### cell

- mediated and humoral immunity that cumulatively promote a Th2 phenotype and 12



### hyperinflammatory state ( U.S. EPA, 2006b )

. The principal findings are Pb

- induced 13



### increased production of Th2 cytokines, suppressed production of Th1 cytokines, 14



### increased inflammation, and elevated IgE, with the weight of evidence provided by 15



### toxicological studies. Collectively, these findings are coherent with the observed effects 16



### of Pb exposure on decreasing responses to antigens ( e.g., DTH, bacterial resistance) in 17



### animals. Both toxicological studies in animals and epidemiologic studies in children 18



### provide evidence for Pb

- associated increases in IgE. The toxicological and epidemiologic 19



### findings for Th2 cytokines, IgE, and inflammation provide biological plausibility for the 20



### associations observed for blood Pb lev els with asthma and allergic conditions in children. 21



### Associations with asthma and allergy were observed after considering potential 22



### confounding by several factors, including, SES and allergen exposure. Animal studies 23



### found a range of immune effects with pr enatal exposure in juvenile animals and 24



### long

- term postnatal (> 4 week s) Pb exposures in adult animals. The blood Pb levels and 25



### Pb exposure lifestage, magnitude, frequency, and duration associated with immune 26



### effects are not well characterized in children o r adults. Epidemiologic studies of children 27



### and adults primarily examined concurrent blood Pb levels. Little information was 28



### provided on concentration

- response functions. In epidemiologic studies, higher IgE and 29



### higher asthma prevalence were examined and f ound in children with blood Pb levels > 30



### 10 μ g/dL. The consistency and coherence of findings across the continuum of related 31



### immune parameters that demonstrate a stimulation of Th2 responses in toxicological 32



### studies combined with the supporting epidemiologi c evidence in children are sufficient to 33



### conclude that there is a causal relationship between Pb exposures and immune system 34



### effects ( Section 5.6.8 ). 35February 2012 2

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– Do Not Cite or Quote 

### The toxicological evidence for Pb

- induced production of Th2 cytokines provides 1



### biological plausibility for the evidence linking Pb exposure with elevated IgE levels 2



### (Section 5.6.8 ). An increase in IL

- 4 from activated Th2 cells induces differentiation of B 3



### cells into antibody

- producing cells, thereby amplifying B cell expansion to secrete IgE, 4



### IgA, and IgG. However, epidemiologic studies did not fin d blood Pb level to be 5



### associated consistently with B cell abundance. In addition to T cell responses, a 6



### prominent effect of Pb exposure, as demonstrated in an extensive historical toxicological 7



### evidence base, was the induction of macrophages into a hyperi nflammatory state as 8



### characterized by enhanced production of ROS, suppressed production of NO, enhanced 9



### production of TNF

- α, and excessive metabolism of arachidonic acid into 10



### immunosuppressive metabolites ( e.g., PGE 2 

### ). Consistent with these observations, a 11



### previous epidemiologic study examined and found greater release of ROS and lower 12



### release of NO from macrophages, primarily in children with concurrent blood Pb levels 13



### 10.31

- 47.49 μ g/dL ( Pineda

- Zavaleta et al., 200 4 )

. Misregulated inflammation represents 14



### one of the major modes of action for Pb

- induced immune effects. Toxicological studies 15



### provide evidence for the modulation of inflammatory cell function, production of 16



### pro

- inflammatory cytokines and metabolites, enhanced inflammatory chemical 17



### messengers, and pro

- inflammatory signaling cascades. In addition to the associations 18



### reported with IL

- 4, epidemiologic evidence for Pb effects on inflammation is limited to a 19



### few recent studies in nonoccupationally

- exposed ad ults in which concurrent blood Pb 20



### level was associated with other indicators of inflammation such as CRP and IL

- 6 21



### (Section 5.6.5.1 ). The studies com monly adjusted for potential confounding by age, sex, 22



### BMI, and smoking status. However, because only concurrent blood Pb levels in adults 23



### were examined, there is uncertainty regarding the magnitude, timing, frequency, and 24



### duration of Pb exposures that cont ributed to the observed associations. 25



### The effects of Pb exposure on macrophages also suggest a role for the immune system in 26



### mediating Pb

- associated effects in multiple other physiological systems. A small body of 27



### new toxicological studies indicated Pb

- in duced changes in specialized macrophages in 28



### nonlymphoid tissue such as alveolar macrophages, testicular macrophages, and brain 29



### microglia (Section 5.6.4.5 ); however, these studies primarily used the i.p. route to 30



### administer Pb. Thus, the relevancy of observations to those expected from typical routes 31



### of human exposure is not clear. 32



### In the large body of studies of adults (mostly males) with occupationa l Pb exposures 33



### (Section 5.6.2.5 ), the most consistent findings were decreased neutrophil functionality in 34



### workers with mean blood Pb levels 21

- 71 μ g/dL. Recent epidemiologic studies provided 35



### new evidence in adults without occupational Pb exposures; however, each examined a 36



### different immune endpoint, for example, IgE, eNO, IL

- 6. These endpoints were 37



### associated with concurrent blood Pb levels in popula tions of adults with mean blood Pb 38February 2012 2

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### levels of 1.9 μ g/dL to 7 μ g/dL; however, there is uncertainty regarding the contributions 1



### of current Pb exposures and cumulative Pb stores in bone. The small body of 2



### epidemiologic studies of nonoccupationally

- exposed adul ts examined different endpoints 3



### and found associations with concurrent blood Pb levels, which are influenced by current 4



### Pb exposures as well as cumulative Pb stores in bone ( Section 5.6 ). 5



### 2.6.5 Heme Synthesis and R ed B lood C ell Function

The 2006 Pb AQCD reported that Pb affects developing red blood cells (RBCs) in 6



### children and occupationally exposed adults as noted by anemia observed with blood Pb 7



### > 40 μ g/dL. Pb

- induced anemia is thought to occur due to decreased RBC life span and 8



### effects on hemoglobin (Hb) synthesis. The exact mechanism for these effects was not 9



### known, although Pb

- induced changes on iron uptake or inhibition of enzymes in the heme 10



### synthe tic pathway may be responsible. Pb was also observed to exert effects on heme 11



### synthesis through the inhibition of multiple key enzymes, most notably ALAD 12



### (aminolevulinic acid dehydratase) , the enzyme that catalyzes the second, rate

- limiting 13



### step in heme bi osynthesis ( Figure 5

- 45 presents a schematic representation of the heme 14



### biosynthetic pathway). Decreased RBC ALAD activity was concluded to be the most 15



### sensitive measure of human Pb exposure, in that measurement of ALAD activity is 16



### correlated with blood Pb levels. Oxidative stress was identified as an important potential 17



### mechanism of action by which Pb exposure induced effects on RBCs ( U.S. EPA, 2006b )

. 18



### Recent epidemiologic and toxicological studies support f indings from the 2006 Pb 19



### AQCD . The principal finding regarding RBC survival and function are consistent 20



### Pb

- induced alterations in several inter

- connected hematological param eters such as Hb 21



### (hemoglobin) , Hct (hematocrit) , and MCV (mean corpuscular volume) across multiple 22



### studies, with the weight of evidence provided by epidemiological studies in 23



### occupationally

- exposed adult populations and children. In occupationally

- exposed adults, 24



### these findings are most substantiated in populations with current blood Pb levels 25



### > 20 μ g/dL, although effects on hematological parameters were observed in some 26



### occupationally

- exposed populations at concurrent blood Pb levels in the range of 27



### 5

- 7 μ g/dL. The weight of evidence in adult rodents exposed long

- term to Pb 28



### ( i.e., ≥ 4 week s) is coherent with epidemiologic studies regarding decrements in 29



### hematological parameters at blood Pb levels as low as 6.6

- 7.1 μ g/dL in rats and mice. 30



### Regarding alteratio ns in heme synthesis, the largest body of evidence again is provided 31



### by decreased ALAD activity in association with Pb exposure or blood Pb levels in 32



### occupationally

- exposed adult s or in children (3

- 12 year s old) , respectively . In the 33



### occupationally

- exposed adult populations, the observation of decreased ALAD activity 34



### was most often observed in populations with concurrent blood Pb levels >15 μ g/dL. 35February 2012 2

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### Animal toxicological studies also provide to the weight of evidence regarding altered 1



### ALAD activity, with effec ts seen in adult animals exposed for 3

- 4 week s with blood Pb 2



### levels as low as 6.5 μ g/dL. The weight of evidence for oxidative stress ( i.e., increased 3



### lipid peroxidation or alterations in antioxidant enzyme levels) primarily comes from 4



### epidemiological studi es in occupationally

- exposed adults and children. The majority of 5



### evidence for increased oxidative stress in Pb

- exposed adults comes from occupational 6



### cohorts with concurrent blood Pb levels >15 μ g/dL. In children, concurrent blood Pb 7



### levels of 7

- 22 μ g/dL were associated with measures of oxidative stress. The frequency, 8



### timing and duration of exposure necessary to alter RBC survival and function, heme 9



### synthesis, or the state of oxidative stress in RBCs is uncertain in both adults and children. 10



### The consisten cy of findings in epidemiologic studies investigating effects in 11



### occupationally

- exposed adults and in children, and the coherence of findings in the 12



### toxicological literature and coherence across the disciplines, is sufficient to conclude that 13



### there is a ca usal relationship between Pb exposures and heme synthesis and RBC 14



### function ( Section 5.7.7 ). 15



### 2.6.6 Reproductive and Developmental Effects

Recent toxicol ogical and epidemiologic literature provides strong evidence that Pb 16



### exposure is associated with effects on reproduction and development supporting 17



### conclusion s of the 2006 Pb AQCD and expanding evidence for additional endpoints. The 18



### weight of the evidence supports the association of Pb exposure with delayed onset of 19



### puberty in both males and females and detrimental effects on sperm and semen quality in 20



### occupationally

- exposed males and in laboratory animals. In cross

- sectional 21



### epidemiologic studies of girls (ages 6

- 18 year s) with mean and/or median concurrent 22



### blood Pb levels less than 5 μ g/dL consistent associations with delayed pubertal 23



### development (measured by age at menarche, pubic hair development, and breast 24



### development) were observed. Toxicological studies of rodents indicate that prenatal and 25



### lactational exposures to Pb can cause a delay in the onset of female puberty at blood Pb 26



### levels as low as 8 μ g/dL. Recent studies show that pubertal onset is one of the more 27



### sensitive markers of Pb exposure wit h effects observed after maternal exposures leading 28



### to blood Pb levels in the pup of 3.5

- 13 μ g/dL. In boys (ages 8

- 15 year s), fewer studies 29



### were conducted but associations were observed in most. Male animal toxicology studies 30



### have reported delayed sexual m aturity as measured with prostate weight, among other 31



### outcomes, seeing significant decrements at blood Pb levels of 34 μ g/dL. There is 32



### uncertainty with regard to the exposure frequency, timing, duration and level that 33



### contributed to these observed associat ion in these studies of adolescents. Multiple studies 34



### were performed in areas, which were contaminated with other chemicals as well as Pb. 35February 2012 2

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### Additionally, Pb exposure has been shown to have detrimental effects on sperm. These 1



### were observed in epidemiologic s tudies at population mean blood Pb levels of 30 μ g/dL 2



### and greater among men occupationally exposed (mean blood Pb levels in study controls 3



### around 10 μ g/dL) and in animal toxicological studies with rabbits exposed to 4



### subcutaneous Pb 3 times per week for 15 week s with blood Pb levels of 20 μ g/dL. The 5



### collective body of evidence integrated across epidemiologic and toxicological studies 6



### with a focus on the strong rel ationship observed with detrimental effects on sperm and 7



### delayed pubertal onset is sufficient to conclude that there is a causal relationship between 8



### Pb exposures and reproductive and developmental effects ( Section 5.8.10 ). 9



### The evidence on ho rmonal influences and fecundity are less consistent (Section 5.8.1

, 10



### Section 5.8.2 ). Pb

- mediated changes in levels or function of reproductive and growth 11



### hormones have been demonstrated in past and more recent toxicological studies; however 12



### the findings are inconsistent. Recent toxicological studies suggest that oxidative stress is 13



### a major contributor to the toxic effects of Pb on male a nd female reproductive systems

. 14



### The effects of ROS may involve interference with cellular defense systems leading to 15



### increased lipid peroxidation and free radi cal attack on lipids, proteins, and DNA. Several 16



### recent studies showed an association between increased generation of ROS and germ cell 17



### injury as evidenced by destruction of germ cell structure and function. Co

- administration 18



### of Pb with various antioxidant compounds either eliminated Pb

- induced injury or greatly 19



### attenuated its effects. In addition, many studies that observed increased oxidative stress 20



### also observed increased apoptosis which is likely a critical underlying mechanism in 21



### Pb

- induced germ cell D NA damage and dysfunction. 22



### Consistent conclusions in the 2006 Pb ISA recent studies of pregnancy outcomes were 23



### reported mixed results. Inconsistent evidence of a relationship with Pb was available for 24



### preterm birth and little evidence was available to stu dy the associations with spontaneous 25



### abortions (Section 5.8.6 , Section 5.8.3 ). The 2006 Pb AQCD included a few studies that 26



### reported potential associations between Pb and neural tube defects, but the recent 27



### epidemiologic studies found no association. Some associations were observed between 28



### Pb and low birth weight (Section 5.8.7 ) when epidemiologic studies used measures of 29



### maternal bone Pb or air exposures, but the associations were less consistent when using 30



### maternal blood Pb or umbilical cord and placenta Pb (maternal blood Pb or umbilical 31



### cord and placenta Pb were the biomarkers most commonly used in studies of low birth 32



### weight). Effects of Pb exposure during early development on toxico logical studies 33



### included reduction in litter size, implantation, birth weight and postnatal growth 34



### (Section 5.8.4 ). Findings from epidemiologic stu dies of postnatal growth are inconsistent 35



### (Section 5.8.8 ). Toxicological studies demonstrated that the effects of Pb exposure during 36



### early developme nt include impairment of retinal development and alterations in the 37February 2012 2

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### developing hematopoietic and hepatic systems (Section 5.8.9 ). Negative developm ental 1



### outcomes were also noted including effects on the eyes and teeth (Section 5.8.9 ). 2



### 2.6.7 Cancer

The previous epidemiologic studies included in the 2006 Pb AQCD ( U.S. EPA, 2006b ) 3



### “provide[d] only very limited evidence suggestive of Pb exposure associa tions with 4



### carcinogenic or genotoxic effects in humans” and the studies were summarized as 5



### follows: 6

“The epidemiologic data ...suggest a relationship between Pb exposure and cancers of the lung and the stomach... Studies of genotoxicity consistently link Pb

- ex posed populations with DNA damage and micronuclei formation, although less consistently with

chromosomal aberrations.”



### The International Agency for Research on Cancer (IARC) classified inorganic Pb 7



### compounds as probable human carcinogens (Group 2A of IARC classifications) based on 8



### stronger evidence in animal studies than human studies, and organic Pb compounds as 9



### not classifiable (Group 3 of IARC classifications) ( IARC, 2006a ; Rousseau et al., 2005 )

. 10



### Additionally, the National Toxicology Program has listed Pb and Pb compounds as 11



### “reasonably a nticipated to be human carcinogens” ( NTP, 2004 )

. The typical cancer 12



### bioassays used by IARC or NTP as evidence of Pb

- induced carcinogenicity used rodents 13



### that were continuously exposed to Pb

- acetate in chow or drinking water for 18 months to 14



### two years in duration. These two year cancer bioassays and the doses administered are 15



### typical of cancer bioassays used with other chemicals. 16



### The animal toxicological literature continues to provide the strongest evidence for Pb 17



### exposure and cancer with some supporting evidence provided by the ep idemiologic 18



### literature. E vidence from toxicological studies demonstrates an association between Pb 19



### and cancer, genotoxicity/clastogenicity or epigenetic modification. Carci nogenicity in 20



### historical animal toxicology studies with Pb exposure has been reported in the kidneys, 21



### testes, brain, adrenals, prostate, pituitary, and mammary gland, albeit at high doses of Pb. 22



### Epidemiologic studies of cancer incidence and mortality repor ted inconsistent results; one 23



### large epidemiologic study demonstrated an association between blood Pb and increased 24



### cancer mortality, but the other studies reported weak or no associations. In the 2006 Pb 25



### AQCD, Pb exposure was found to be associated with st omach cancer, but there was only 26



### one recent study on stomach cancer and Pb exposure, which reported mixed findings. 27



### Similarly, some studies in the 2006 Pb AQCD reported associations between Pb exposure 28



### and lung cancer ( U.S. EPA, 200 6b )

. More recent occupational studies of Pb exposure and 29



### lung cancer reported no associations. The majority of epidemiologic studies of brain 30



### cancer had null results overall, but positive associations between Pb exposure and brain 31February 2012 2

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### cancer were observed a mong individuals with certain genotypes (e.g., ALAD2) . In 1



### toxicological studies, chromosomal aberrations after Pb exposure are most often reported 2



### with Pb chromate exposure, which is likely due to toxicity of the chromate moiety. 3



### Mechanistic understanding of Pb and its effect on cancer and genotoxicity is expanding 4



### through toxicological work focusing on antioxidants and other proteins that sequester Pb 5



### or reduce its bioavailability. The collective body of evidence integrated across 6



### toxicological and epidemi ologic studies is sufficient to conclude that there is a likely 7



### causal relationship between Pb exposure and cancer (Section 5.10.6 ). 8



## 2.7 Ecological Eff ects of Lead

This section evaluates the evidence from studies of ecological effects associated with 9



### exposure to Pb. Causal determinations are developed for the ecological outcomes 10



### discussed in this assessment, in combination with evidence from other disciplines 11



### ( e.g., fate and transport) where relevant. Pb effects on terrestrial and aquatic systems 12



### (Section 2.7.1 and Section 2.7.2 ) are summarized from Chapter 7 in which the effects on 13



### terrestrial and aquatic ecosystems are presented separately. These sections are followed 14



### by a summary of the evidence for the causal determinations (Section 2.7.3 ) and 15



### consideration of atmospheric deposition of Pb as related to ecological effects 16



### (Section 2.9.3 ). The ecological causal determinations are integrated across endpoints 17



### (physiological stress, hematological effects, neurobehavioral effects, development and 18



### reproduction, growth, survival) common to both terrestrial and aquatic biota ( Table 2

- 4 ). 19



### Where the causal determination varies substantially between types of organisms 20



### (typically between pla nts and other organisms or between aquatic and terrestrial biota), 21



### the divergence is noted. 22



### 2.7.1 Summary of Effects on Terrestrial Ecosystems

Historically, Pb poisoning is one of the earliest recognized toxicoses of terrestrial biota, 23



### occurring primarily throu gh ingestion of spent shot by birds (Section 7.4.2.3 ). At the time 24



### of the 1977 Pb AQCD few studies of Pb exposure and effects in wild animals other than 25



### birds were available. A limited number of rodent trapping studies and observations from 26



### grazing animals near smelters provided evidence for differences in Pb sensitivity among 27



### species and these findings were further supported in the 1986 and 2006 Pb A QCDs ( U.S. 28



### EPA, 2006b

, 1986b

, 1977 )

. ALAD was r ecognized as a sensitive indicator of Pb 29



### exposure in rats and waterfowl in the 1977 Pb AQCD and now is regarded as a biomarker 30



### of exposure in many terrestrial organisms. According to the 2006 Pb AQCD and 31



### supported by evidence from previous Pb AQCDs, common ly observed effects of Pb on 32February 2012 2

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### terrestrial organisms include decreased survival, reproduction, and growth, as well as 1



### effects on development and behavior. Furthermore, the toxicity of Pb to terrestrial 2



### vertebrates and invertebrates varies with bioavailabilit y of the metal, species and 3



### lifestage, duration of exposure, form of Pb, and soil characteristics. 4



### In plants, Pb effects have also been studied for several decades. At the time of the 1977 5



### Pb AQCD, it was understood that Pb uptake in plants was influenced by plant species and 6



### by the available Pb pool in the soils ( U.S. EPA, 1977 )

. Furthermore, most of the Pb taken 7



### up by plants from soil, remains in the roots and that distribution to other portions of the 8



### plant is variable among species ( U.S. EPA, 1977 )

. Plant growth wa s recognized as an 9



### endpoint of Pb toxicity in plants in the 1977 Pb AQCD and additional effects of Pb on 10



### growth processes were reported in subsequent Pb AQCDs ( U.S. EPA, 2006b

, 1986b

, 11



### 1977 )

. A study reviewed in the 1977 Pb AQCD provided evidence f or Pb effects on 12



### forest

- nutrient cycling and shifts in arthropod community composition in the vicinity of a 13



### smelting complex. A number of ecosystem

- level effects, including decreased species 14



### diversity, changes in floral and faunal community composition, an d decreasing vigor of 15



### terrestrial vegetation have subsequently been reported near Pb

- point sources ( U.S. EPA, 16



### 2006b

, 1986b

, 1977 ; Watson et al., 1976 )

. 17



### Pb in terrestrial ecosystems is either deposited directly onto plant surfaces, or 18



### incorporated into soil where it can bind with organic matter or dissolve in pore w ater. The 19



### amount of Pb dissolved in soil pore water determines the impact of soil Pb on terrestrial 20



### ecosystems to a much greater extent than the total amount present. It has long been 21



### established that the amount of Pb dissolved in soil solution is controll ed by at least six 22



### variables: (1) solubility equilibria; (2) adsorption

- desorption relationship of total Pb with 23



### inorganic compounds; (3) adsorption

- desorption reactions of dissolved Pb phases on soil 24



### organic matter; (4) pH; (5) cation exchange capacity (C EC); and (6) aging. Since 2006, 25



### further details have been contributed to the understanding of the role of pH, CEC, organic 26



### matter, and aging. Smolders et al. ( 2009 ) demonstrated that the two most important 27



### determinants of both Pb solubility and toxicity in soils are pH and CEC. However, they 28



### had previously shown that experimental aging, primarily in the form of initial leaching 29



### following addition of Pb, decreases soluble metal fraction by approximately one order of 30



### magnitude ( Smolders et al., 2009 )

. Since 2006, organic matter has b een confirmed as an 31



### important influence on Pb sequestration, leading to longer

- term retention in soils with 32



### higher organic matter content, and also creating the potential for later release of deposited 33



### Pb. Aging, both under natural conditions and simulated through leaching, was shown to 34



### substantially decrease bioavailability to plants, microbes, and vertebrates. 35



### There is evidence over several decades of research previously reviewed in Pb AQCDs 36



### and in recent studies reviewed in this ISA that Pb accumulates i n terrestrial plants, 37February 2012 2

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### invertebrates and vertebrates. Studies with herbaceous plant species growing at various 1



### distances from smelters added to the existing strong evidence that atmospherically 2



### transported Pb is taken up by plants. These studies did not est ablish the relative 3



### proportion that originated from atmospheric Pb deposited in the soil, as opposed to that 4



### taken up directly from the atmosphere through the leaves. Multiple new studies showed 5



### that in trees, the latter is likely to be very substantial. O ne study attempted to quantify the 6



### proportion of atmospheric Pb up directly from the atmosphere, and suggested it amounts 7



### to 50% of the Pb contained in Scots Pine in Sweden ( Klaminder et al., 2005 )

. Studies 8



### with herbaceous plants found that in most species tested, soil Pb taken up by the roots is 9



### not translocated into the stem and leaves. Studies with trees found that soil Pb generally 10



### is translocated to other parts. 11



### Since the 2006 Pb AQCD, various species of terrestrial sn ails have been found to 12



### accumulate Pb from both diet and soil ( U.S. EPA, 2006b )

. New studies with earthworms 13



### have found that both internal concentration of Pb and mortality increase with decreasing 14



### soil pH and CEC. In addition, t issue concentration differences have been found between 15



### species of earthworms that burrow in different soil layers. The rate of accumulation in 16



### each of these species may result from differences in interacting factors such as pH and 17



### CEC between layers. Beca use earthworms often sequester Pb in granules, some authors 18



### have suggested that earthworm Pb is not bioavailable to their predators. There is some 19



### evidence that earthworm activity increases Pb availability in soil, but it is inconsistent. In 20



### various arthro pods collected at contaminated sites, recent studies found gradients in 21



### accumulated Pb that corresponded to gradients in soil with increasing distance from point 22



### sources. 23



### There are a few new studies of Pb bioavailability and uptake in birds since the 2006 Pb 24



### AQCD ( U.S. EPA, 2006b )

. Several found tissue levels in birds that indicated exposure to 25



### Pb, but none of the locations for these studies was in proximity to point sources, and the 26



### origin of the Pb could not be identified. A stu dy at the Anaconda Smelter Superfund site 27



### found increasing Pb accumulation in gophers with increasing soil Pb around the location 28



### of capture. A study of swine fed various Pb

- contaminated soils showed that the form of 29



### Pb determined accumulation. New studies were able to measure Pb in the components of 30



### various food chains that included soil, plants, invertebrates, arthropods and vertebrates. 31



### They confirmed that trophic transfer of Pb is pervasive, but no consistent evidence of 32



### trophic magnification was found. 33



### Evidence in this review further supports the findings of the previous Pb AQCDs that 34



### biological effects of Pb on terrestrial organisms vary with species and lifestage, duration 35



### of exposure, form of Pb, and soil characteristics. In photosynthetic organisms, 36



### experimental studies have added to the existing evidence of photosynthesis impairment in 37February 2012 2

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### plants exposed to Pb, and have found damage to photosystem II due to alteration of 1



### chlorophyll structure, as well as decreases in chlorophyll content in diverse taxa, 2



### including lichens and mosses. Evidence of oxidative stress in response to Pb exposure has 3



### also been observed in plants. Reactive oxygen species were found to increase in broad 4



### bean and tomato plants exposed to increasing concentrations of soil Pb, and a 5



### c oncomitant increase in superoxide dismutase, glutathione, peroxidases, and lipid 6



### peroxidation, as well as decreases in catalase were observed in the same plants. Monocot, 7



### dicot, and bryophytic taxa grown in Pb

- contaminated soil or in experimentally spiked soil 8



### all responded to increasing exposure with increased antioxidant activity. In addition, 9



### reduced growth was observed in some experiments, as well as genotoxicity, decreased 10



### germination, and pollen sterility. 11



### In terrestrial invertebrates, evidence for Pb effects has included neurological and 12



### reproductive endpoints. Recently published studies have shown neuronal damage in 13


### nematodes exposed to low concentrations of Pb (2.5 μM), accompanied by behavioral 14



### abnormalities. Reproductive adverse effects were found at lower exposure in younger 15



### nematodes, and effects on longevity and fecundity were shown to persist for several 16



### generations. Increased mortality was found in earthworms, but was strongly dependent on 17



### soil characteristics including pH, CEC, and aging. Sna ils exposed to Pb through either 18



### topical application or through consumption of Pb

- exposed plants had increased 19



### antioxidant activity, and decreased food consumption, growth, and shell thickness. 20



### Effects on arthropods exposed through soil or diet varied with species and exposure 21



### conditions, and included diminished growth and fecundity, endocrine and reproductive 22



### anomalies, and body malformations. Within each study, increasing concentration of Pb in 23



### the exposure medium generally resulted in increased effects, but the relationship between 24



### concentration and effects varied between studies, even when the same medium, e.g., soil, 25



### was used. Evidence suggested that aging and pH are important modifiers. 26



### Effects on amphibian and reptiles included decreased white blood cell counts, decreased 27



### testis weight, and behavioral anomalies. However, large differences in effects were 28



### observed at the same concentration of Pb in soil, depending on whether the soil was 29



### freshly amended or field

- collected from contaminated areas. As in most studies where the 30



### comparison was made, effects were smaller when field

- collected soils were used. In some 31



### birds, maternal elevated blood Pb level was associated in recent studies with decreased 32



### hatching success, smaller clutch size, high corticostero id level, and abnormal behavior. 33



### Some species evidenced little or no effect of elevated blood Pb level. Effects of dietary 34



### exposure were studied in several mammalian species, and cognitive, endocrine, 35



### immunological, and growth effects were observed. 36February 2012 2

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### New e vidence reviewed in Section 7.2.3 and Section 7.2.4 demonstrates that exposure to 1



### Pb is generally associated with negative effects in terrestrial ecosystems. It also 2



### demonstrates that many factors, including species and various soil physiochemical 3



### properties, interact strongly with Pb concentra tion to modify those effects. In these 4



### ecosystems, where soil is generally the main component of the exposure route, Pb aging 5



### is a particularly important factor, and one that may be difficult to reproduce 6



### experimentally. Without quantitative characterizati on of those interactions, 7



### characterizations of exposure

- response relationships would likely not be transferable 8



### outside of experimental settings. Since the 2006 Pb AQCD, a few studies of 9



### exposure

- response have been conducted with earthworms, and results ha ve been 10



### inconsistent ( U.S. EPA, 2006b )

. 11



### New evidence of effects of Pb at the community and ecosystem levels of biological 12



### organization include several studies of the ameliorative effects of mycorrhizal fungi on 13



### plant growth in th e presence of Pb, attributed to decreased uptake of Pb by plants, 14



### although both mycorrhizal fungus and plant were negatively affected. Most recently 15



### published research on community and ecosystem

- level effects of Pb has focused on soil 16



### microbial communities , which have been shown to be impacted in both composition and 17



### activity. Many recent studies have been conducted using mixtures of metals, but have 18



### tried to separate the effects of individual metals when possible. Soil microbial activity 19



### was generally dimi nished, but in some cases recovered over time. Species and genotype 20



### composition were consistently altered, and those changes were long

- lasting or permanent. 21



### Recent studies have addressed differences in sensitivity between species explicitly, and 22



### have clear ly demonstrated high variability between related species, as well as within 23



### larger taxonomic groupings. Mammalian no observed effect concentration (NOEC) 24



### values expressed as blood Pb levels were shown to vary by a factor of 8, while avian 25



### blood NOECs varie d by a factor of 50 ( Buekers et al., 2009 )

. Protective effects of dietary 26



### Ca have been found in plants, birds, and invertebrates. 27



### 2.7.2 Summary of Effects on Aquatic Ecosystems

Pb effects on aquatic biota were previously assessed in the 1977 Pb AQCD, the 1986 Pb 28



### AQCD and the 2006 Pb AQCD ( U.S. EPA, 2006b

, 1986a

, 1977 )

. Evidence of toxicity of 29



### Pb and other metals to freshwater organisms goes back to early observations of 30



### contamination of natural areas by Pb mining leading to extirpation of fish from streams 31



### ( U.S. EPA, 1977 )

. Observed responses of fish to Pb reported in the 1986 Pb AQCD and 32



### the 2006 Pb AQCD include inhibition of heme formation, alterations in brain receptors, 33



### effects on blood chemistry a nd hormonal systems, and decreases in some enzyme 34



### activities ( U.S. EPA, 2006b

, 1986a )

. In the 1986 Pb AQCD and 2006 Pb AQCD, 35February 2012 2

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### additional evidence for Pb toxicity was available for aquatic invertebrates. Inhibition of 1



### ALAD, and reduced reproduction, growth, and survival were reported . Few studies of Pb 2



### toxicity to saltwater organisms are reported in previous Pb AQCDs. The toxicity of Pb to 3



### saltwater and freshwater organisms varies with bioavailability of the metal, species and 4



### lifestage, duration of exposure, form of Pb, and water qua lity parameters ( U.S. EPA, 5



### 2006b

, 1986a )

. As reviewed in the 2006 Pb AQCD, the biotic ligand model (BLM) 6



### constitutes an attractive means of quantifying factors that affect bioavailability, such as 7



### pH, disso lved organic carbon (DOC), and alkalinity ( U.S. EPA, 2006b )

. 8



### The toxicity of Pb to aquatic algae and plants has been recognized in earlier agency 9



### reviews of this metal. In the 1977 Pb AQCD, differences in sensitivity to Pb among 10



### different species of algae were reported and concentrations of Pb varied among genera 11



### and within a genus, an observation subsequently found across aquatic taxa ( U.S. EPA, 12



### 1977 )

. At the time of the 1977 Pb AQCD, the information available on effects of Pb on 13



### aquat ic plants was limited. For plants in general, Pb was recognized to affect 14



### photosynthesis, mitosis, and growth, but at concentrations higher than typically found in 15



### the environment ( U.S. EPA, 1977 )

. Findings from field studies of aquatic communities in 16



### the vicini ty of Pb point sources include changes in species composition and species 17



### richness, predator/prey interactions, nutrient cycling and energy flow; however, Pb is 18



### often found coexisting with other metals and other stressors, which risk confounding the 19



### observ ed effects. 20



### Effects of Pb observed in aquatic organisms are tied to terrestrial systems via watershed 21



### processes (Section 3.3 ). Atmospherically

- der ived Pb can enter aquatic systems through 22



### runoff from terrestrial systems or via direct deposition over a water surface. Once Pb 23



### enters surface waters, its fate and bioavailability are influenced by Ca 2+ 

### concentration, 24



### pH, alkalinity, total suspended solids, and dissolved organic carbon (DOC, including 25



### humic acids). In sediments, Pb bioavailability may be influenced by the presence of other 26



### metals, sulfides, Fe and Mn oxides and physical disturbance. In m any, but not all aquatic 27



### organisms, Pb dissolved in the water can be the primary exposure route to gills or other 28



### biotic ligands. As recognized in the 2006 Pb AQCD and further supported in this review, 29



### chronic exposures to Pb may also include dietary uptak e, and there is an increasing body 30



### of evidence showing that differences in uptake and elimination of Pb vary with species. 31



### Currently available models for predicting bioavailability focus on acute toxicity and do 32



### not consider all possible routes of uptake. They are therefore of limited applicability, 33



### especially when considering species

- dependent differences in uptake and 34



### bioaccumulation of Pb. 35



### Recent evidence supports the 2006 Pb AQCD conclusion that processes such as Pb 36



### adsorption, complexation, and chelat ion alter bioavailability to aquatic biota. Given the 37February 2012 2

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### low solubility of Pb in water, bioaccumulation by aquatic organisms may preferentially 1



### occur via exposure routes other than direct absorption from the water column; which 2



### include ingestion of contaminat ed food and water, uptake from sediment pore waters, or 3



### incidental ingestion of sediment ( U.S. EPA, 2006b )

. 4



### There are considerable differences between species in both the amount of Pb taken up 5



### from the environment and in the amo unt retained in the organism. Closely related species 6



### can vary greatly in bioaccumulation of Pb and other non

- essential metals. Recent studies 7



### on uptake of Pb by aquatic plants and algae support the findings of previous Pb AQCDs 8



### that all plants tend to seq uester larger amounts of Pb in their roots than in their shoots, 9



### and provide additional evidence for species differences in compartmentalization of 10



### sequestered Pb and in responses to Pb in water and sediments. In invertebrates, Pb can be 11



### accumulated from m ultiple sources, including the water column, sediment, and dietary 12



### exposure. Since the last review, new studies using stable isotopes have enabled 13



### simultaneous measurement of uptake and elimination in several aquatic organisms to 14



### assess the relative import ance of water versus dietary uptake. In uptake studies of various 15



### invertebrates, Pb was mainly found in the gills and digestive gland/hepatopancreas. There 16



### is more information now on the cellular and subcellular distribution of Pb in invertebrates 17



### than the re was at the time of writing the 2006 Pb AQCD. Specifically, localization of Pb 18



### at the ultrastructural level has been assessed in several species. 19



### Recent evidence also supports the 2006 conclusions that the gill is a major site of Pb 20



### uptake in fish, and t hat there are species differences in the rate of Pb accumulation and 21



### distribution of Pb within the organism are supported in this review. The anterior intestine 22



### has been newly identified as a site of uptake of Pb through dietary exposure studies. 23



### There are few new studies on Pb uptake by amphibians and mammals. At the time of the 24



### publication of the 2006 Pb AQCD, trophic transfer of Pb through aquatic food chains was 25



### considered to be negligible. Measured concentrations of Pb in the tissues of aquatic 26



### organis ms were generally higher in algae and benthic organisms than in consumers at 27



### higher trophic levels, indicating that Pb was bioconcentrated but not biomagnified. Some 28



### studies published since the 2006 Pb AQCD support the potential for transfer of Pb in 29



### aquat ic food webs, while other studies indicate that Pb concentration decreases with 30



### increasing trophic level ( U.S. EPA, 2006b )

. 31



### Evidence in this ISA further supports the findings of the previous Pb AQCDs that 32



### waterborne Pb is highly toxic to aquatic organisms, with toxicity varying with species 33



### and lifestage, duration of exposure, form of Pb, and water quality characteristics. Effects 34



### of Pb on algae reported in the 2006 Pb AQCD are further supported by evidence from 35



### additional specie s. They include decreased growth, deformation and disintegration of 36



### cells, and blocking of the pathways that lead to pigment synthesis, thus affecting 37February 2012 2

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### photosynthesis. Effects on plants supported by additional evidence in this review include 1



### oxidative damag e, decreased photosynthesis and reduced growth. Elevated levels of 2



### antioxidant enzymes are commonly observed in aquatic plant, algae, and moss species 3



### exposed to Pb. 4



### Since the 2006 Pb AQCD, there is additional evidence for Pb effects on antioxidant 5



### enzyme s, lipid peroxidation, stress response and osmoregulation in aquatic invertebrates. 6



### Studies of reproductive and developmental effects of Pb in this review provide further 7



### support for findings in the 2006 Pb AQCD. These new studies include reproductive 8



### endp oints for rotifers and freshwater snails as well as multigenerational effects of Pb in 9



### mosquito larvae and marine amphipods. As reviewed below, growth effects are observed 10



### at lower concentrations in some aquatic invertebrates since the 2006 Pb AQCD, 11



### especi ally in juvenile organisms. Behavioral effects of Pb in aquatic invertebrates 12



### reviewed in this ISA include decreased valve closing speed in scallops and slower 13



### feeding rate in blackworms. 14



### Evidence in this ISA supports the findings of reproductive, behavior al, and growth effects 15



### in previous Pb AQCDs, as well as effects on blood parameters in aquatic vertebrates. 16



### Since the 2006 Pb AQCD, possible molecular targets for Pb neurotoxicity have been 17



### identified in fish and additional mechanisms of Pb toxicity have b een elucidated in the 18



### fish gill and the fish renal system. In the 2006 Pb AQCD, amphibians were considered to 19



### be relatively tolerant to Pb. Observed responses to Pb exposure included decreased 20



### enzyme activity ( e.g., ALAD reduction) and changes in behavior. Since the 2006 Pb 21



### AQCD, studies conducted at concentrations approaching environmental levels of Pb have 22



### indicated sublethal effects on tadpole endpoints including growth, deformity, and 23



### swimming ability. In fish, several recent studies on behavioral effec ts of Pb indicate 24



### decreased prey capture rate, slower swim speed and decline in startle response and visual 25



### contrast with Pb exposure. 26



### Concentration

- response data from plants, invertebrates and vertebrates are consistent with 27



### findings in previous AQCDs of species differences in sensitivity to Pb in aquatic systems 28



### (Section 7.3.17.4 ). In this ISA, as in previous AQCDs, aquatic plant growth was shown t o 29



### be adversely affected by Pb exposure. The lowest EC 50 

### for growth observed in marine 30



### microalgae and freshwater microalgae was in the range of 100 μ g Pb/L. In the 2006 Pb 31



### AQCD, concentrations at which effects were observed in aquatic invertebrates ranged 32



### f rom 5 to 8,000 μ g Pb/L. Several studies in this review have provided evidence of effects 33



### at lower concentrations. Among the most sensitive species, growth of juvenile freshwater 34



### snails ( L. stagnalis ) was inhibited at an EC 20 

### of <4 μ g Pb/L ( Grosell and Brix, 2009 ; 35



### Grosell et al., 2006a )

. A chronic value of 10 μ g Pb/L obtained in 28

- day exposures of 36



### 2

- month

- old Lampsilis siliquoidea ju veniles was the lowest genus mean chronic value 37February 2012 2

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### ever reported for Pb ( Wang et al., 2010e )

. In a series of 48 hour acute toxicity tests using 1



### a variety of natural waters across North America, LC 50 

### values ranged from 29 to 180 μ g 2



### Pb/L tests with the c ladoceran Ceriodaphnia dubia ( Esbaugh et al., 2011 )

. 3



### In the 2006 Pb AQCD, adverse effects were found in freshwater fish at concentrations 4



### ranging from 10 to >5,400 μ g Pb/L, generally depending on water quality variables 5



### ( e.g., pH, hardness, salinity). Additional testing of Pb toxicity under conditions of varied 6



### alkalinity, DOC, and pH has been conducted since the last review. However, adverse 7



### effects in fish observed i n recent studies fall within the range of concentrations observed 8



### in the previous Pb AQCD. 9



### Since the 2006 Pb AQCD, additional evidence for community and ecosystem level 10



### effects of Pb have been observed primarily in microcosm studies or field studies near 11



### p oint sources (mining, effluent) with other metals present. Ecological effects associated 12



### with Pb, reported in previous Pb AQCDs, include alteration of predator

- prey dynamics, 13



### species richness, species composition, and biodiversity. New studies in this ISA provide 14



### evidence in additional habitats for these community and ecological

- level effects, 15



### specifically in aquatic macrophyte communities and sediment

- associated communities. 16



### Different species may exhibit different responses to Pb

- impacted ecosystems depend ent 17



### not only upon other environmental factors ( e.g., temperature, pH), but also on the species 18



### sensitivity, lifestage, or seasonally

- affected physiological state. Aquatic ecosystems with 19



### low pH and low DOM are likely to be the most sensitive to the effects of 20



### atmospherically

- deposited Pb. 21February 2012 2

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### 2.7.3 Determinations of Causality for Effects on Ecosystems

Table 2

- 3 Summary of Pb causal determinations for plants, invertebrates and

vertebrates

Effect Terrestrial Aquatic a

Physiological Stress

- All organisms Causal Causal

Hematological Effects

- Invertebrates Inadequate Causal

Hematological Effects

- Vertebrates Causal Causal

Neurobehavioral Effects

- Invertebrates and Vertebrates Likely Causal Likely Causal

Developmental and Reproductive Effects

- Plants Inadequate Inadequate

Developmental and Reproductive Effects

- Invertebrates and Vertebrates Causal Causal

Growth

- Plants Causal Causal

Growth

- Invertebrates Inadequate Causal

Growth

- Vertebrates Inadequate Inadequate

Survival

- Plants Inadequate Inadequate

Survival

- Invertebrates and Vertebrates Causal Causal

Community and Ecosystem Level Effects Likely Causal Likely Causal

a Causal determinations for aquatic biota are based primarily on evidence from freshwater organisms.



### 2.7.3.1 Effects on Physiological Stress

Evidence is sufficient to conclude that there is a causal relationship between Pb 1



### exposures and physiological stress in terrestrial and aquatic plants, invertebrates and 2



### vertebrates (Section s 7.4.1.1 and 7.4.2.1 ). 3



### Endpoints associated with physiological stress received no consideration prior to the 4



### 2006 Pb AQCD and this ISA. Studies published since the 2006 Pb AQCD support 5



### previous associations of Pb exposure with physiological stress. New evidence includes 6



### upregulation of an tioxidant enzymes, production of reactive oxygen species and 7



### increased lipid peroxidation associated with Pb exposure in additional species of 8



### terrestrial and aquatic plants, invertebrates and vertebrates that support, and expand upon 9



### findings in the previ ous Pb AQCD ( U.S. EPA, 2006b )

. 10



### In this ISA and the 2006 Pb AQCD, there is strong evidence of upregulation of 11



### antioxidant enzymes and increased lipid peroxidation associated with Pb exposure in 12



### many species of plants, invertebrat es and vertebrates. In plants, increases of antioxidant 13February 2012 2

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### enzymes with Pb exposure occur in algae, aquatic mosses, floating and rooted aquatic 1



### macrophytes, and terrestrial species. Most observations of antioxidant responses in plants 2



### typically occur at conce ntrations of Pb higher than found in the environment. However, 3



### in a few terrestrial plant species, increases of antioxidant enzymes occur at concentrations 4



### approaching the average Pb concentrations in U.S. soils and limited transplantation 5



### studies with aqu atic plants indicate elevated antioxidant enzyme activity associated with 6



### Pb levels measured in sediments at polluted sites. There is considerable evidence for 7



### antioxidant activity in invertebrates, including gastropods, mussels, and crustaceans, in 8



### respon se to Pb exposure. Some recent evidence for invertebrate antioxidant responses in 9



### aquatic species indicates effects at Pb concentrations associated with polluted sites. 10



### Markers of oxidative damage are also observed in fish, amphibians and mammals, both in 11



### the laboratory and in exposed natural environments. Across all biota, there are differences 12



### in the induction of antioxidant enzymes that appear to be species

- dependent. 13



### Additional stress responses observed in terrestrial and aquatic invertebrates include 14



### e levated heat shock proteins, osmotic stress and decreased glycogen levels. Heat shock 15



### protein induction by Pb exposure has been observed in zebra mussels and mites. Tissue 16



### volume regulation is adversely affected in freshwater crabs. Glycogen levels in the 17



### freshwater snail Biomphalaria glabrata were significantly decreased following 96

- hour 18



### exposures at near environmentally

- relevant concentrations (50 μ g Pb/L and higher) 19



### ( Ansaldo et al., 2006 )

. 20



### Upregulation of antio xidant enzymes and increased lipid peroxidation are considered to 21



### be reliable biomarkers of stress, and suggest that Pb exposure induces a stress response in 22



### those organisms, which may increase susceptibility to other stressors and reduce 23



### individual fitnes s. The oxidative stress responses associated with Pb exposure are 24



### consistent in terrestrial biota and in aquatic organisms. Furthermore, these responses are 25



### also observed in experimental animal studies, and in humans. 26



### 2.7.3.2 Hematological Effects

Based on observa tions in both terrestrial and aquatic organisms and additionally 27



### supported by toxicological and epidemiological findings in laboratory animals and 28



### humans, evidence is sufficient to conclude that there is a causal relationship between Pb 29



### exposures and hemat ological effects in aquatic invertebrates and terrestrial and aquatic 30



### vertebrates (Section 7.4.1.2 , Section 7.4.2.2 ). The evidence is inadequate to conclude that 31



### there is a causal r elationship between Pb exposures and hematological effects in 32



### terrestrial invertebrates. 33February 2012 2

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### Recent studies add support to the strong body of evidence presented in previous Pb 1



### AQCDs that Pb exposure is associated with hematological responses in aquatic 2



### inverte brates and terrestrial and aquatic vertebrates. In environmental assessments of 3



### metal

- impacted habitats, ALAD is a recognized biomarker of Pb exposure ( U.S. EPA, 4



### 2006b )

. ALAD activity is negatively correlated with total Pb concen tration in bivalves. 5



### Lower ALAD activity has been significantly correlated with elevated blood Pb levels in 6



### fish and mammals as well. In the 1986 Pb AQCD, decreases in RBC ALAD activity 7



### following Pb exposure were well documented in birds and mammals ( U.S. EPA, 1986a )

. 8



### Further evidence from the 2006 Pb AQCD and this review suggests this enzyme is an 9



### indicator for Pb exposure across a wide range of taxa. Since the 2006 Pb AQCD, 10



### evidence of Pb effects on ALAD activity has been found in additional species of 11



### amphibians and fish, and has been identified in bacteria. New field studies of ALAD 12



### activity include observations in songbirds and owls near historical mining areas. In 13



### addition to consideration of ALAD activity, there is new evidence for deceased white 14



### blood cell count s in amphibians affected by Pb exposure. The consistency and coherence 15



### of these findings of effects on ALAD activity are also supported by some evidence of 16



### Pb

- induced alterations of blood chemistry in fish reported in the 2006 Pb AQCD ( U.S. 17



### EPA, 2006b )

. This evidence is strongly coherent with observations from human 18



### epidemiologic and animal toxicology studies where a causal relationship was identified 19



### between exposure to Pb and hematological effects in humans and laboratory animal s 20



### (Section 2.6.5 and Section 5.7 ). 21



### 2.7.3.3 Neur obehavioral E ffects

Overall, the evidence from terrestrial and aquatic systems is sufficient to conclude that 22



### there is a likely causal relationship between Pb exposures and neurobehavioral effects in 23



### terrestrial and aquatic invertebrates and vertebrates (Section 7.4.1.3 , Section 7.4.2.3 ). 24



### Evi dence from laboratory studies reviewed in Chapter 7 and previous Pb AQCDs have 25



### shown adverse effects of Pb on neurological endpoints in both aquati c and terrestrial 26



### animal taxa. Studies that consider mode

- of

- action and molecular targets of Pb toxicity in 27



### biota are now available for a few species. New studies have continued adding to the 28



### evidence from both invertebrate and vertebrate studies that Pb a dversely affects behaviors 29



### such as food consumption, avoidance and escape from predators, behavioral 30



### thermoregulation, and prey capture. These changes are likely to decrease the overall 31



### fitness of the organism. New evidence in this ISA includes reports of behavioral 32



### responses across a larger variety of organisms including reptiles and fish larvae born 33



### from Pb

- exposed adults, while some impairments in feeding and escaping behaviors were 34



### reported for the first time. More evidence has become available for mari ne organisms. 35February 2012 2

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### Central nervous system effects in fish recognized in previous Pb AQCDs include effects 1



### on spinal neurons and brain receptors. New evidence from this review identifies the 2



### MAPKs ERK1/2 and p38 MAPK 

### as possible molecular targets for Pb neurotoxi city in 3



### catfish ( Leal et al., 2006 )

. Additionally, there is new evidence for neurotoxic action of Pb 4



### in invertebrates with exposure to Pb observed to cause changes in the morphology of 5



### GABA motor neurons in nematodes ( Caenorhabditis elegans ) ( Du and Wang, 2009 )

. 6



### Decreased food consumption of Pb

- contaminated diet has been demonstrated in some 7



### invertebrates (snails) and vertebrates (lizards, pigs, fish). Behavioral effects in grunt fish 8



### Haemulon scudderi , occupying the top level of a simulated marine food chain included 9



### lethargy and decreased food intake in a 42

- day feeding study ( Soto

- Jiménez et al., 10



### 2011a )

. These fish were fed white shrimp exposed to Pb via brine shrimp that were 11



### initially fed microalgae cultured at 20 μ g Pb/L. In the same study, surfacing, reduction of 12



### motility, and erratic swimming were observed in the white shrimp after 30 day s of 13



### exposure to Pb via diet. Pb may also decrease the ability of an organism to capture prey 14



### or escape predation. For example, Pb exposure has been demonstrated to adversely affect 15



### prey capture ability of certain fungal and fish species, and the motility of nematodes was 16



### adversely affected in Pb

- contaminated soils ( Wang and Xing, 2008 )

. Prey captu re ability 17



### was decreased in 10 day old fathead minnows born from adult fish exposed to 120 μ g 18



### Pb/L for 300 day s, then subsequently tested in a 21

- day breeding assay ( Mager et al., 19



### 2010 )

. In a laboratory study, Pb

- exposed gull chicks exhibited abnormal behaviors such 20



### as decreased walking, erratic behavioral thermoregulation and food begging that could 21



### make them more vulnerable in the wild ( Burger and Gochfeld, 2005 )

. The chicks were 22



### exposed to Pb via injection to produce feather Pb concentration approximately equivalent 23



### to those observed in wild gulls. Lizards ex posed to Pb through diet in the laboratory 24



### exhibited abnormal coloration and posturing behaviors. Other behavioral effects affected 25



### by Pb exposure include increased hyperactivity in fish and hypoxia

- like behavior in 26



### frogs. 27



### These findings show strong coher ence with findings from studies in laboratory animals 28



### described in Section 2.6.1 and Section 5.3 of the ISA that show that Pb induces changes 29



### in attention, increased response rates and motor function. The evidence presented in those 30



### sections is sufficient to conclude that there is a causal relat ionship between Pb exposure 31



### and neurobehavioral effects (Section 5.3 ). 32



### 2.7.3.4 Effects on Development and Reproduction

Evidence in this review and the previous Pb AQCDs from invertebrate and vertebrate 33



### studies indicate that Pb is affecting reproductive performance in multiple species. Various 34February 2012 2

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### endpoints have been measured in multiple taxa of terrestrial and aquatic organism s to 1



### assess the effect of Pb on development, fecundity and hormone homeostasis, and they 2



### have demonstrated the presence of adverse effects. Reproductive effects are important 3



### when considering effects of Pb because impaired fecundity at the organismal level can 4



### result in a decline in abundance and/or extirpation of populations, decreased taxa 5



### richness, and decreased relative or absolute abundance at the community level ( Suter et 6



### al. , 2005 ; U.S. EPA, 2003a )

. The evidence is sufficient to conclude that there is a causal 7



### relationship between Pb exposures and developmental and reproductive effects in 8



### terrestrial and aquatic invertebrates and vert ebrates (Section 7.4.1.4 , Section 7.4.2.4 ). The 9



### evidence is inadequate to conclude that there is a causal relationship between Pb 10



### exposures and developmental and reproductive effects i n plants (Section 7.4 .2.4 )

. 11



### In terrestrial invertebrates, new developmental and reproductive endpoints shown to be 12



### affected by Pb include hatching success in collembolans, increased development time in 13



### fruit flies and aphids, and disrupted hormone homeostasis in moths; however, these 14



### studies have been conducted at Pb concentrations that exceed Pb soil concentrations 15



### found in most U.S. locations. In terrestrial vertebrates, new evidence for decreased sperm 16



### count and qua lity in deer at a location contaminated by mining, and for decreased testis 17



### weight in lizards, support previous associations between Pb exposure and reproductive 18



### and developmental effects. Recent studies in freshwater rotifers and cladocerans provide 19



### addit ional evidence for reproductive and developmental effects of Pb at concentrations at 20



### or near ambient Pb levels in some aquatic species. New evidence in frogs and fish 21



### continue to support developmental and reproductive effects of Pb in aquatic vertebrates 22



### r eported in earlier Pb AQCDs. Few studies are available that specifically address 23



### reproductive effects of Pb exposure in plants. 24



### In terrestrial invertebrates, Pb can alter developmental timing, hatching success, sperm 25



### morphology, and hormone homeostasis. I n fruit flies, Pb exposure increased time to 26



### pupation and decreased pre

- adult development. Sperm morphology was altered in 27



### earthworms exposed to Pb

- contaminated soils. Pb may also disrupt hormonal 28



### homeostasis in invertebrates as studies with moths have sug gested. Evidence of 29



### multi

- generational toxicity of Pb is also present in terrestrial invertebrates, specifically 30



### springtails, mosquitoes, carabid beetles, and nematodes where decreased fecundity in 31



### progeny of Pb

- exposed individuals was observed. However, e ffects have only been 32



### studied in a small number of species and at concentrations that typically exceed Pb levels 33



### in U.S. soils. 34



### For aquatic invertebrates, reproductive effects were reported to begin at 19 μ g Pb/L for 35



### the freshwater snail Lymnea palustris and 27 μ g Pb/L for Daphnia sp. as reported in the 36



### 1986 Pb AQCD ( U.S. EPA, 1986b )

. Several new studies of snails, clams, and rotifers 37February 2012 2

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### support previous findings of adverse impacts to embryonic development. Reproductive 1



### effects have also been observed in multi

- generational studies with aquatic invertebrates. 2



### Larval settlement rate and rate of population increase was decreased in rotifers and 3



### marine amphipods. Rotifers have a reduced fertilization rate associated with Pb exposure 4



### that appears to be due to decreased viability of sperm and eggs. 5



### In aquatic vertebrates there is evidence for reproductive and developmental effects of Pb. 6



### Pb

- exposure in tadpoles has been demonstrated to delay metamorphosis, decrease larval 7



### size, produce sub tle skeletal malformations, and to result in slower swimming speed. 8



### Previous Pb AQCDs have reported developmental effects in fish, specifically spinal 9



### deformities in larvae at a concentration of 120 μ g Pb/L. In the 2006 Pb AQCD, decreased 10



### spermatocyte deve lopment in rainbow trout was observed at 10 μ g Pb/L and in fathead 11



### minnow testicular damage occurred at 500 μ g Pb/L. In fish, there is new evidence in this 12



### ISA of Pb effects on steroid profiles. Reproduction in fathead minnows was affected in 13



### breeding expo sures following 300

- day chronic toxicity testing. However, reproductive 14



### performance was unaffected in zebrafish Danio rerio exposed to Pb

- contaminated prey. 15



### Additional observed impacts of Pb on reproductive endpoints in fish include decreased 16



### oocyte diamet er and density in toadfish, associated with elevated Pb levels in gonad. 17



### In terrestrial vertebrates, evidence from Chapter 7 and in previous Pb AQCDs indicates 18



### an association between Pb exposure and observed adverse reproductive effects. In 19



### mammals, few studies in the field have addressed Pb specifically: most available data in 20



### wild or grazing animals are from near smelters, wh ere animals are co

- exposed to other 21



### metals. Evidence obtained using mammals in the context of human health research 22



### demonstrates adverse effects of Pb on sperm, and on onset of puberty in males and 23



### females ( Chapter 5 ), which is coherent with the partial evidence from mammals in the 24



### wild. Other reproductive endpoints including spontaneous abortions, pre

- term birth, 25



### embryo development, placental develop ment, low birth weight, subfecundity, hormonal 26



### changes, and teratology were also affected, but less consistently. New toxicological data 27



### support trans

- generational effects, a finding that is also an area of emerging interest in 28



### ecology. The evidence presen ted in Section 5.8 is sufficient to conclude that there is a 29



### causal relationship between Pb exposure and reproductive effects in humans and 30



### laborato ry animals. 31



### Many studies of effects on reproductive and developmental endpoints in terrestrial 32



### invertebrates and vertebrates have been conducted with soil Pb concentrations exceeding 33



### those found in most U.S. locations. Studies in this ISA include exposure

- response 34



### experiments showing exposure

- dependent responses with exposure increasing from 35



### background level to levels greater than near point sources. For some aquatic species, 36February 2012 2

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### recent evidence supports previous findings of reproductive and developmental effe cts of 1



### Pb and differential lifestage response at near ambient concentrations of Pb. 2



### 2.7.3.5 Effects on Growth

Evidence is sufficient to conclude that there is a causal relationship between Pb 3



### exposures and effects on growth in aquatic and terrestrial plants and a quatic invertebrates 4



### (Section 7.4.1.5 , Section 7.4.2.5 ). Evidence is inadequate to establish a causal 5



### relationship between Pb exposures and effects on growth in terrestrial invertebrates and 6



### in terrestrial and aquatic vertebrates (Section 7.4.2.5 ). 7



### Alterations in the growth of an organism can impact population, community and 8



### ecosystem level variables. Evidence for effects of Pb on growth is strongest in aquatic 9



### and terrestrial plants. In invertebrates, evidence for effects of Pb on growth has been 10



### observed most extensively in aquatic taxa, with inhibition in sensitive species occurring 11



### near the current range of Pb concentrations in surface waters. Vertebrates, particularly 12



### terrestrial, have been the object of a comparatively much smaller number of studies of the 13



### effects of Pb on growth. Growth effects observed in both invertebrates and vertebrates, 14



### however, underscore the importance of lifestage to overall Pb susceptibility. In general, 15



### juvenile organisms are more sensitive than adults. Evidence for growth effects of Pb in 16



### freshwater and terrestrial plant species is primarily supported by earlier Pb AQCDs. In 17



### aquatic invertebrates, the weight of the evidence continues to support growth e ffects of 18


### Pb with several new studies reporting effects at ≤ 10 μ g Pb/L, specifically in snails and 19



### mussels. Also, growth effects in frogs are reported at lower concentrations in this ISA 20



### than in earlier reviews. 21



### There is evidence over several decades of r esearch that Pb inhibits photosynthesis and 22



### respiration in plants, both of which reduce growth ( U.S. EPA, 2006b

, 1977 )

. Many 23



### laboratory and greenhouse toxicity studies have reported effects on plants. These effects 24



### are typically observed in laboratory studies with high exposure concentrations or in field 25



### stu dies near point sources. Pb has been shown to affect photosystem II with the 26



### hypothesized mechanism being that Pb may replace either Mg or Ca in chlorophyll, 27



### altering the pigment structure and decreasing the efficiency of visible light absorption by 28



### affect ed plants. Decreases in chlorophyll a and b content have been observed in various 29



### algal and plant species. Most primary producers experience EC 50 

### values for growth in the 30



### range of 1,000 to 100,000 μ g Pb/L with minimal inhibition of growth observed as low a s 31



### 100 μ g Pb/L ( U.S. EPA, 2006b )

. 32



### Growth effects of Pb on aquatic invertebrates are reviewed in the draft Ambient Aquatic 33



### Life Water Quality Criteria for Pb ( U.S. EPA, 2008b ) and the 2006 Pb AQCD. In the 34February 2012 2

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### 2006 Pb AQCD, the LOEC for growth of freshwater amphipods Hyalella azteca in 1



### 42

- day chr onic exposure to Pb was 16 μ g Pb/L ( Besser et al., 2005 )

. Recent studies 2


### provide additional evidence for effects on growth of aquatic invertebrates at ≤ 10 μ g 3



### Pb/L. Growth of juven ile freshwater snails L. stagnalis was inhibited below the lowest 4



### concentration tested resulting in an EC 20 

### <4 μ g Pb/L ( Grosell and Brix, 2009 ; Grosell et 5



### al., 2006a )

. In the same study, the NOEC was 12 μ g Pb/L and the LOEC was 16 μ g Pb/L. 6



### The authors indicated that the observed effect level for Pb was very close to the current 7



### U.S. EPA water quality criteria for Pb (3.3 μ g Pb/L normalized to test water hardness) 8



### ( Grosell and Brix, 2009 )

. In the freshwater mussel, fatmucket ( L. siliquoidea ) juven iles 9



### were the most sensitive Lifestage ( Wang et al., 2010e )

. A chronic value of 10 μ g Pb/L in 10



### a 28 day exposure of 2

- month

- old fatmucket juveniles was the lowest genus mean 11



### chronic value ever reported for Pb. Growth effects are also reported in mari ne 12



### invertebrates at higher concentrations of Pb than sensitive freshwater invertebrates. 13



### In previous Pb AQCDs, a few studies have reported growth effects of Pb on vertebrates 14



### including fish (growth inhibition), birds (changes in juvenile weight gain), and frogs 15



### (delayed metamorphosis, smaller larvae). A new study reviewed in this ISA supports 16



### findings of growth effects in frogs and suggests that these effects may be occurring at 17



### lower concentrations: the growth rate of tadpoles of the northern leopard frog exposed to 18



### 100 μ g Pb/L from embryo to metamorphosis was slower than the growth rate of the 19



### controls ( Chen et al., 2006b )

. In this study, Pb concentrations in the tissues of tadpoles 20



### were quantified and the authors reported that they were within the range of reported 21



### tissue concentrations reported in wild

- caught populations. Reports of Pb

- associated 22



### growth effects in fish are inconsistent. 23



### 2.7.3.6 Effects on Survival

The evidence is sufficient to conclude that there is a causal relationship between Pb 24



### exposures and survival in terrestrial and aquatic invertebrates and vertebrates 25



### (Section 7.4.1.6 , Section 7.4.2.6 ). The evidence is inadequate to conclude that there is a 26



### causal relationship between Pb exposure and survival in terrestrial and aquatic plants 27



### (Sect ion 7.4.1.6 , Section 7.4.2.6 ). In terr estrial vertebrates and invertebrates, evidence for 28



### Pb effects on survival is primarily supported by previous Pb AQCDs with no new studies 29



### reporting effects on survival at lower concentrations. For aquatic invertebrates recent 30



### studies support previous asso ciations between Pb exposure and mortality at 31



### concentrations near the range of Pb measured in U.S. surface waters in cladocerans, 32



### amphipods and rotifers. In aquatic vertebrates, there is new evidence for effects in fish at 33



### <100 μ g Pb/L. Pb is generally not phytotoxic to aquatic or terrestrial plants at 34



### concentrations found in the environment away from point sources, probably due to the 35February 2012 2

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### fact that plants often sequester large amounts of Pb in roots, and that translocation to 1



### other parts of the plant is limited. 2



### The relationship between Pb exposure and decreased survival rate has been well 3



### demonstrated in terrestrial and aquatic species, as presented in Section 7.2.5

, 4



### Section 7.3.6 , and Section 7.3.17.4 of this ISA (and in the previous Pb AQCDs). 5



### Toxicological studies have established LC 50 

### values for some species of plants, 6



### invertebrates and vertebrates. From the LC 50 

### data on Pb in this review and previous Pb 7



### AQCDs, a wide r ange of sensitivity to Pb is evident across taxa. LC 50 

### values are usually 8



### much higher than Pb concentrations near point

- sources, although physiological 9



### dysfunction that adversely impacts the fitness of an organism often occurs well below 10



### concentrations tha t result in mortality. 11



### Freshwater aquatic invertebrates are generally more sensitive to Pb exposure than other 12



### taxa, with survival adversely impacted in a few species at concentrations occurring near 13



### point

- sources, or at concentrations near ambient levels . These impacted species may 14



### include endangered species or candidates for the endangered species list, such as the 15



### freshwater mussel Lampsilis rafinesqueana (Neosho mucket), The EC 50 

### for foot 16



### movement (a measure of viability) for newly transformed juvenile s of this species was 17



### 188 μ g Pb/L. Freshwater biota that exhibit sensitivity to Pb in the range of Pb 18



### concentrations measured in U.S. waters [median 0.50 μ g Pb/L, range 0.04 to 30 μ g Pb/L 19



### ( U.S. EPA, 2006b ) ] , include some species of gastropods, amphipods, cladocerans, and 20



### rotifers although the toxicity of Pb is highly dependent upon water quality variables such 21



### as DOC, hardness, and pH. Other aquatic invertebrates such as odonates may be tolerant 22



### of Pb concen trations that greatly exceed environmental levels. 23



### Terrestrial invertebrates typically tolerate higher concentrations of Pb. In the 1986 Pb 24



### AQCD it was reported that Pb at environmental concentrations occasionally found near 25



### roadsides and smelters (10,000 to 40,000 μ g Pb/g dry weight [mg Pb/kg]) can eliminate 26



### populations of bacteria and fungi on leaf surfaces and in soil. LC 50 

### values for soil 27



### nematodes vary from 10

- 1,550 mg Pb/kg dry weight dependent upon soil OM content 28



### and soil pH ( U.S. EPA, 2006b )

. In earthworms, 14 and 28 day LC 50 

### values typically fall 29



### in the range of 2,400

- 5,800 mg Pb/kg depending upon the species tested. 30



### Data on mortality of saltwater species associated with exposure to Pb is limited; however, 31



### in general, ma rine organisms are less sensitive to this metal than freshwater organisms 32



### and the highest toxicity is observed in juveniles. In one study, effects of Pb on survival at 33



### environmentally relevant concentrations of Pb in diet have been demonstrated though a 34



### si mulated marine food chain in which the primary producer, the microalgae T. suecica

, 35



### was exposed to 20 μ g Pb/L and subsequently fed to brine shrimp Artemia franciscana

, 36



### (mean Pb content 12 to 15 μ g Pb/g) which were consumed by white

- leg shrimp 37February 2012 2

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– Do Not Cite or Quote 

### Litopenaeus v annamei, itself consumed by grunt fish H. scudderi representing the top of 1



### the marine food chain ( Soto

- Jiménez et al., 2011a )

. Survival of brine shrimp was 25 to 35 2



### % lower than the control and both white shrimp and grunt fish had significantly hi gher 3



### mortalities than controls. 4



### In terrestrial avian and mammalian species, toxicity is observed in laboratory studies over 5



### a wide range of doses (<1 to >1,000 mg Pb/kg body weight

- day) as reviewed for the 6



### development of Eco

- SSL’s ( U.S. EPA, 2005b )

. The NOAELs for survival ranged from 7



### 3.5 to 3,200 mg Pb/kg • day

. 8



### In aquatic vertebrates there is co nsiderable historic information on Pb toxicity to 9



### freshwater fish. New studies support findings in previous AQCDs of Pb effects on fish 10



### survival and indicate effects at lower concentrations in testing with juvenile lifestages. In 11



### a series of 96

- hour acute toxicity tests with fathead minnow conducted in a variety of 12



### natural waters across North America, LC 50 

### values ranged from 41 to 3,598 μ g Pb/L and 13



### no Pb toxicity occurred in three highly alkaline waters ( Esbaugh et al., 2011 )

. Thirty day 14



### LC 50 

### values for larval fathead minnows ranged from 39 to 1,903 μ g Pb/L in varying 15



### concentrations of DOC, CaSO 4 

### and pH ( Grosell et al., 2006a )

. In a recent study of 16



### rainbow trout fry at 2

- 4 week s post

- swim up, the 96

- hour LC 50 

### was 120 μ g Pb/L at a 17



### hardness of 29 mg /L as CaCO 3 

### , a value much lower than in testing with older fish 18



### ( Mebane et al., 2008 )

. 19



### 2.7.3.7 Community and Ecosystem Effects

More evidence for Pb toxicity to terrestrial and aquatic biota has been reported from 20



### single

- species assays in laboratory studies than from whole ecosystem studies. The 21



### ev idence is strong for effects of Pb on growth, reproduction and survival in very diverse 22



### species, but considerable uncertainties exist in generalizing effects observed under 23



### particular, small

- scale conditions, up to the ecosystem level of biological organiz ation. At 24



### the ecosystem level, the presence of multiple stressors, variability in field conditions, and 25



### differences in bioavailability of Pb make it difficult to measure the magnitude of effects, 26



### and to quantify relationships between ambient concentrations of Pb and ecosystem 27



### response. However, the cumulative evidence that has been reported for Pb effects at 28



### higher levels of ecological organization and for endpoints in single species with direct 29



### relevance to population and ecosystem level effects ( i.e., dev elopment and reproduction, 30



### growth, survival) is sufficient to conclude that there is a likely causal relationship 31



### between Pb exposures and the alteration of species richness, species composition and 32



### biodiversity in terrestrial and aquatic ecosystems (Secti on 7.4.1.7 , Section 7.4.2.7 ). 33February 2012 2

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### Ecosystem

- level studies are complicated by the confounding of Pb exposure with other 1



### factors such as the presence of other trace metals and acidic deposition. In natural 2



### systems, Pb is often found co

- existing with other stressors, and observed effects may be 3



### due to cumulative toxicity. In laboratory studies and simul ated ecosystems, where it is 4



### possible to isolate the effect of Pb, this metal has been shown to alter competitive 5



### behavior of species, predator

- prey interactions and contaminant avoidance. At higher 6



### levels of ecological organization, these effects may chan ge species abundance and 7



### community structure. Uptake of Pb into aquatic and terrestrial organisms and its effects 8



### on survival, growth, physiological stress, blood, neurobehavior, and developmental and 9



### reproductive endpoints at the organism level are expect ed to have ecosystem

- level 10



### consequences. Where evidence of effects is observed at the ecosystem level of 11



### organization, evidence from lower levels brings consistency and plausibility for causality. 12



### Most direct evidence of community and ecosystem level effec ts is from near point 13



### sources where Pb concentrations are higher than typically observed in the environment. 14



### For terrestrial systems, evidence of impacts on natural ecosystems near smelters, mines, 15



### and other industrial sources of Pb has been assembled in p revious decades. Those impacts 16



### include decreases in species diversity and changes in floral and faunal community 17



### composition. For aquatic systems, the literature focuses on evaluating ecological stress 18



### from Pb originating from urban and mining effluents ra ther than atmospheric deposition. 19



### In simulated ecosystems, where it is possible to isolate the effect of Pb, this metal has 20



### been shown to alter competitive behavior of species, predator

- prey interactions and 21



### contaminant avoidance. For example, frogs and to ads lack avoidance response while 22



### snails and fish avoid higher concentrations of Pb. New evidence, published since the 23



### 2006 Pb AQCD indicates that some species of worms will avoid Pb

- contaminated soils 24



### ( Langdon et al., 2005 )

. These dynamics are likely to change species abundance and 25



### community structure at higher levels of ecological organization. 26



### Recent studies continue to demonstrate associations between Pb exposures and e ffects at 27



### higher levels of biological organization that were shown in field and microcosm studies 28



### in previous Pb AQCDs. New studies on plant and soil microbial communities and 29



### sediment

- associated and aquatic plant communities increase the total number of t ypes of 30



### ecological associations impacted by Pb. 31



### In terrestrial ecosystems, most studies show decreases in microorganism abundance, 32



### diversity, and function with increasing soil Pb concentration. Specifically, shifts in 33



### nematode communities, bacterial specie s, and fungal diversity have been observed. 34



### Furthermore, presence of arbuscular mycorrhizal fungi may protect plants growing in 35



### Pb

- contaminated soils. Increased plant diversity ameliorated effects of Pb contamination 36



### on a microbial community. 37February 2012 2

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### In aquatic e cosystems, Pb effects reviewed in the 2006 Pb AQCD included reduced 1



### species abundance, richness and diversity, decreased primary productivity, and altered 2



### predator

- prey interactions. Since the 2006 Pb AQCD, there is further evidence for effects 3



### of Pb in se diment

- associated communities. Exposure to three levels of sediment Pb 4



### contamination in a microcosm experiment significantly reduced nematode diversity and 5



### resulted in profound restructuring of the community structure ( Mahmoudi et al., 2007 )

. 6



### Sediment

- bound Pb contamination appears to differentially affect members of the benthic 7



### invertebrate community, potentially altering ecosystems dynamics in small urban streams 8



### ( Kominkova and Nabelkova, 2005 )

. Although surface water Pb concentrations in 9



### monitored streams were determined to be very low, concentrations of the met al in 10



### sediment were high enough to pose a risk to the benthic community 11



### ( e.g., 34

- 101 mg Pb/kg). These risks were observed to be linked to benthic invertebrate 12



### functional feeding group, with collector

- gatherer species exhibiting larger body burdens 13



### of heav y metals than benthic predators and collector

- filterers. 14



### Changes to aquatic plant community composition have been observed in the presence of 15



### elevated surface water Pb concentrations. A shift toward more Pb

- tolerant species is also 16



### observed in terrestrial plant communities near smelter sites ( U.S. EPA, 2006b )

. Certain 17



### types of plants such as rooted and submerged aquatic plants may be more susceptible to 18



### aerially

- deposited Pb resulting in shifts in Pb community composition. High Pb sediment 19



### concentrations are linked to shifts in amphipod communities inhabiting plant structures. 20



## 2.8 Integration of Health and Ecological Effects

The health and ecological effects considered for causal determination are summarized in 21



### the Table 2

- 4 . The health outcomes were nervous system, cardiovascular, renal, immune, 22



### effects on heme synthesis and RBC function, reproductive effects, and cancer. The 23



### ecol ogical endpoints considered for causal determination were: physiological stress, 24



### hematological effects, neurobehavioral effects, developmental and reproductive effects, 25



### growth, survival, and community and ecosystem level effects. The evidence relating to 26



### s pecific ecological endpoints is also integrated across aquatic and terrestrial habitats. 27



### Further, the substantial overlap between the ecological and health endpoints considered in 28



### the causal determinations allowed the integration of the evidence across the se disciplines. 29February 2012 2

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### Table 2

- 4 Summary of Causal Determinations a 

### for Health and Ecological
Effects

Outcome/Effect Human Health
Causal Determination Ecological Receptors
Causal Determination

Neurological Effects b Causal Relationship Likely Causal Relationship: Invertebrates and Vertebrates

Cardiovascular Effects Causal Relationship N/A e

Renal Effects Causal Relationship N/A e

Immune System Effects Causal Relationship N/A e

Heme Synthesis and

RBC Function c Causal Relationship Causal Relationship: Terrestrial Vertebrates,
Aquatic Invertebrates and Vertebrates

Reproductive Effects and

Birth Outcome d Causal Relationship Causal Relationship: Invertebrates and Vertebrates
Inadequate to Infer Causal Relationship: Plants

Cancer Likely to be a causal relationship N/A e

Mortality N/A e (The strongest evidence of Pb

- induced mortality in humans was observed for
cardiovascular disease related mortality and this
evidence was considered in determining the
causal relationship between Pb exposure and cardiovascular effects.) Causal Relationship: Invertebrates and Vertebrates
Inadequate to Infer Causal Relationship: Plants

Growth N/A e (There is evidence from toxicological and
epidemiologic studies of Pb effects on fetal and

post natal growth, which was considered in
determining the causal association between Pb
exposure and reproductive and developmental effects.) Causal Relationship: Plants and Aquatic Invertebrates
Inadequate to Infer Causal Relationship: Vertebrates and

Terres trial Invertebrates

Physiological Stress N/A e (In Human Health, oxidative stress was
considered as a upstream event in the modes of action of Pb, leading downstream to various effects. Ecological literature commonly uses
oxidative stress as a proxy indicator of overall
fitness, and thus treats it as an effect.) Causal Relationship

Community and
Ecosystem Level Effects N/A e Likely Causal Relationship

a Based upon the framework described in the Preamble, a determination of causality for health effects was made for a broad outc ome category ( i.e., nervous system effects) by evaluating the coherence of evidence across disciplines and across a spectrum of related endpoints. Howeve r, the evidence on which the causal judgment is based, including the strength of evidence for the individual endpoints with in the major outcome category, is characterized within the discussion. Causal determinations were made within approximately 1

- 2 orders of magnitude of current levels.

b In ecological receptors, the causal determination was developed considering neurobehavi oral effects that can be observed in toxicological studies of animal models and studies of ecological effects in vertebrates and invertebrates. The human epidemiologic evidence evaluated included a wider range of health endpoints such as cognition.

c The h ealth hematological effects considered in the determination of causality were primarily heme synthesis and RBC function. The ecological evidence considered for the causal determination included heme synthesis, blood cell count, and altered serum profiles.

d Reproductive health effects, including effects on sperm, as well as birth outcomes such as spontaneous abortion, were conside red in the causal determination. In the ecological literature, a wide range of endpoints, including embryonic development, multig enerational studies, delayed metamorphosis, and altered steroid profiles, was considered.

e N/A, not applicable, i.e., for health effects no causal determination for this specific endpoint, considered within the causal determination for the lar ger
outcome c ategory; for ecological effects there was no comparable endpoint.February 2012 2

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### 2.8.1 Modes of Action Relevant to Downstream Health and Ecological
Effects

The diverse health and ecological effects of Pb are mediated through multiple, 1



### interconnected modes of action. This section summarizes the principal 2



### cellular/subcellular effects contributing to modes of action for human health endpoints 3



### associated with Pb exposure and the concentrations at which those effects are observed. 4



### Then, effects of Pb observed in aquatic and ter restrial species (Section 2.7 ) are evaluated 5



### along with evidence from epidemiological and laboratory animal studies to determine the 6



### extent to whic h common modes of action can be inferred from the observed effects. The 7



### rationale for this approach is that the mechanism of Pb toxicity is likely conserved from 8



### invertebrates to vertebrates to humans in some organ systems. 9



### Each of the modes of action dis cussed in Section 5.2 has the potential to contribute to the 10



### development of a number of Pb

- induced health effects ( Table 2

- 5 ). Evidence for the 11



### majority of these modes of action is observed at low blood Pb levels in humans and 12



### laboratory animals, between 2 and 5 μ g/dL, and at doses as low as the p icomolar range in 13



### animals and cells. The concentrations eliciting the modes of action (reported in Table 14



### 2

- 5 ) are drawn from the available data and do not imply that these modes of action are 15



### not acting at lower exposure levels or that these doses represent the threshold of the 16



### effect. Also, the data in presented this table does not inform regarding the exposure 17



### frequency and duration required to elicit a particular MOA. 18February 2012 2

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### Table 2

- 5 MOAs, their related health effects, and information on concentrations eliciting the MOAs

Mode of Action [Related Health Effects (ISA Section)] Concentrations or doses (Conditions) a

Blood Pb Dose

Altered Ion Status

[All Health Effects of Pb] 3.5 μg/dL
(mean in cord blood; association with cord blood Ca 2+

- ATPase pump activity)

Huel et al. ( 2008 ) 0.00005 μM free Pb 2+

(In vitro; 30 minutes; calmodulin activation assay)

Kern et al. ( 2000 )

Protein Binding

[Renal (5.5), Heme Synthesis and RBC Function (5.7)] 17.0 μg/dL
(concurrent mean in adult workers with wildtype metallothionein expression; increased BP susceptibility)

Chen et al. ( 2010a ) 50 μM Pb glutamate
(In vitro; 24 hours; increased nuclear protein in neurological cell)

Klann and Shelton ( 1989 )

Oxidative Stress

[All Heath Effects of Pb] 5.4 μg/ dL
(concurrent mean in adult male workers; decreased CAT activity in blood)

Conterato et al. ( In Press ) 0.1 μM Pb

- acetate (In vitro; 48 hours; decreased cellular GSH in neuroblastoma cells)
Chetty et al. ( 2005 )

Inflammation

[Nervous Syste m (5.3), Cardiovascular (5.4), Renal (5.5), Immune (5.6), Respiratory (5.6.4), Hepatic (5.9.1)] 2.5 μg/dL
(concurrent minimum in adult males; increased serum
TNF

- α and blood WBC count)

Kim et al. ( 2007 ) 0.01 μM Pb

- acetate (In vitro; 48 hours; increased cellular PGE 2 in neuroblastoma cells)
Chetty et al. ( 2005 )

Endocrine Disruption

[Reproductive and Developmental Effects (5.8), Endocrine System (5.9.3), Bone and Teeth (5.9.4)] 1.7 μg/dL
(concurrent minimum in women with both ovaries removed; increased serum FSH)
Krieg ( 20 07 ) 10 μM Pb nitrate
(In vitro; 30 minutes; displaced GHRH binding to rat pituitary receptors)

Lau et al. ( 1991 )

Cell Death/Genotoxicity

[Cancer (5.10), Reproductive and Developmental Effects (5.8), Bone and Teeth (5.9.4)] 3.3 μg/dL
(concurrent median in adult women; increased rate of HPRT mutation frequency)

Van et al. ( 2004 ) 0.03 μM Pb

- acetate (In vitro; 18 hours; increased formation of micronuclei)

Bonacker et al. ( 2005 )

a This table provides examples of studies that report effects with low doses or concentration; they are not the full body of ev idence used to characterize the weight of the evidence. In addition, the levels cited are reflective of the data and methods avail able and do not imply that these modes of action are not acting at lower Pb exposure or blood Pb levels or that these doses represent the threshold of the effect. Additionally, the blood conce ntrations and doses (indicating Pb exposure concentrations from in vitro systems) refer to the concentrations and doses at which these modes of action were observed. While the individual mo des of action are related back to specific health effects sections ( e.g., Nervous System, Cardiovascular), the concentrations and d oses given should not be interpreted as levels at which those specific health effects occur.



### Ecosystem studies have presented evidence for the occurrence of many of these modes of 1



### action in animals, and to some degree in plants, however the connection to ecological 2



### outcomes must usually be inferred because ecological studies are typically not designed 3



### to address mode of action directly. The level at which Pb elicits a specific effect is more 4



### difficult to establish in terrestrial and aquatic systems due to the influence of 5



### environmental variables on Pb bioavailability and toxicity and substantial species 6



### differences in Pb susceptibility. 7



### The alteration of cellular ion status (including disruption of Ca 2+ 

### homeostasis, altered ion 8



### transport mechanisms, and pe rturbed protein function through displacement of metal 9



### cofactors) appears to be the major unifying mode of action underlying all subsequent 10February 2012 2

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### modes of action in plants, animals, and humans ( Figure 5

- 1 ). Pb can interfere with 1



### endogenous cation homeostasis, necessary as a cell signal carrier mediating normal 2



### cellular functions. Pb is able to displace metal ions, such as Zn, Mg, and Ca 2+ 

### , from 3



### proteins due t o the flexible coordination numbers and multiple ligand binding ability of 4



### Pb, leading to abnormal conformational changes to proteins and altered protein function. 5



### Disruption of ion transport leading to increased intracellular Ca 2+ 

### levels is due in part to 6



### the alteration of the activity of transport channels and proteins, such as Na +



### - K + 

### ATPase 7



### and voltage

- sensitive Ca 2+ 

### channels. Pb can interfere with these proteins through direct 8



### competition between Pb and the native metals present in the protein metal bin ding 9



### domain or through disruption of proteins important in calcium

- dependent cell signaling, 10



### such as PKC or calmodulin. 11



### This competition between metals has been reported not only in human systems, but also 12



### in fish, snails, and plants. Altered Ca 2+ 

### channel activity and binding of Pb with Na +



### - K + 13



### ATPase in the gills of fish disrupts the Na + 

### and Cl

- 

### homeostasis, which may lead to 14



### ionoregulatory failure and death. Ca 2+ 

### influx and ionoregulation has also been shown to 15



### be inhibited by Pb exposure in a sensitive species of snail, leading to a reduction in snail 16



### growth. In plants, substitution of the central atom of chlorophyll, Mg, by Pb prevents 17



### light

- harvesting, resultin g in a breakdown of photosynthesis. Pb

- exposed animals also 18



### have decreased cellular energy production due to perturbation of mitochondrial function. 19



### Disruption of ion transport not only leads to altered Ca 2+ 

### homeostasis, but can also result 20



### in perturbed ne urotransmitter function. Evidence for these effects in Pb

- exposed 21



### experimental animals and cell cultures has been linked to altered neurobehavioral 22



### endpoints and other neurotoxicity. Neurobehavioral changes that may decrease the 23



### overall fitness of the orga nism have also been observed in aquatic and terrestrial 24



### invertebrate and vertebrate studies. There is evidence in tadpoles and fish to suggest Pb 25



### may alter neurotransmitter concentrations, possibly resulting in some of these 26



### neurobehavioral changes. 27



### Altere d cellular ion status following Pb exposure can result in the inhibition of heme 28



### synthesis. Pb exposure is commonly associated with altered hematological responses in 29



### aquatic and terrestrial invertebrates, experimental animals, and human subjects. The 30



### prot eins affected by Pb are highly conserved across species accounting for the common 31



### response seen in human health and ecological studies. This evolutionarily conserved 32



### response to Pb is likely the result of the competition of Pb with the necessary metal 33



### cofa ctors in the proteins involved in heme synthesis. 34



### Although Pb will bind to proteins within cells through interactions with side group 35



### moieties, thus potentially disrupting cellular function, protein binding of Pb may 36



### represent a mechanism by which cells p rotect themselves against the toxic effects of Pb. 37February 2012 2

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### Intranuclear and intracytosolic inclusion body formation has been observed in the kidney, 1



### liver, lung, and brain following Pb exposure in experimental animals. A number of 2



### unique Pb binding proteins have b een detected, constituting the observed inclusion 3



### bodies. The major Pb binding protein in blood is ALAD with carriers of the ALAD

- 2 4



### allele potentially exhibiting higher Pb binding affinity. Inhibition of ALAD activity is a 5



### widely recognized response to Pb in environments where Pb is present and is considered 6



### to be biomarker of Pb exposure in both terrestrial and aquatic biota. Additionally, 7



### metallothionein is an important protein in the formation of inclusion bodies and 8



### mitigation of the toxic effects of Pb . Protein binding of Pb is a recognized mechanism of 9



### Pb detoxification in some terrestrial and aquatic biota. For example, plants can sequester 10



### Pb through binding with phytochelatin and some fish have the ability to store 11



### accumulated Pb in heat

- stable prot eins. 12



### A second major mode of action of Pb is the development of oxidative stress, due in many 13



### instances to the antagonism of normal metal ion functions. Disturbances of the normal 14



### redox state of tissues can cause toxic effects and is involved in the major ity of health and 15



### ecological outcomes observed after Pb exposure. The origin of oxidative stress produced 16



### after Pb exposure is likely a multi

- pathway process. Studies in humans and experimental 17



### animals provide evidence to conclude that oxidative stress res ults from oxidation of 18



### δ

- ALA, NAD(P)H oxidase activation, membrane and lipid peroxidation, and antioxidant 19



### enzyme depletion. Evidence of increased lipid peroxidation associated with Pb exposure 20



### exists for many species of plants, invertebrates, and vertebra tes. Enhanced lipid 21



### peroxidation can also result from Pb potentiation of Fe 2+ 

### initiated lipid peroxidation and 22



### alteration of membrane composition after Pb exposure. Increased Pb

- induced ROS will 23



### also sequester and inactivate biologically active • 

### NO, leadin g to the increased production 24



### of the toxic product nitrotyrosine, increased compensatory NOS, and decreased sGC 25



### protein. Pb

- induced oxidative stress not only results from increased ROS production but 26



### also through the alteration and reduction in activity of the antioxidant defense enzymes. 27



### The biological actions of a number of these enzymes are antagonized due to the 28



### displacement of the protein functional metal ions by Pb. Increased ROS are often 29



### followed by a compensatory and protective upregulation in anti oxidant enzymes, such 30



### that this observation is indicative of oxidative stress conditions. A number of studies in 31



### plants, invertebrates, and vertebrates present evidence of increased antioxidant enzymes 32



### with Pb exposure. Additionally, continuous ROS product ion may overwhelm this 33



### defensive process leading to decreased antioxidant activity and further oxidative stress 34



### and injury. 35



### In a number of organ systems Pb

- induced oxidative stress is accompanied by 36



### misregulated inflammation. Pb exposure will modulate infl ammatory cell function, 37



### production of proinflammatory cytokines and metabolites, inflammatory chemical 38February 2012 2

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### messengers, and proinflammatory signaling cascades. Cytokine production is skewed 1



### toward the production of proinflammatory cytokines like TNF

- α and IL

- 6 as well as 2



### leading to the promotion of Th2 response and suppression of Th1cytokines and 3



### Th1

- related responses. 4



### Pb is a potent endocrine disrupting chemical. Steroid receptors and some endocrine 5



### signaling pathways are known to be highly conserved over a bro ad expanse of animal 6



### phylogeny. Pb will disrupt the HPG axis evidenced in humans, other mammals, and fish, 7



### by a decrease in serum hormone levels, such as FSH, LH, testosterone, and estradiol. Pb 8



### interacts with the hypothalamic

- pituitary level hormone contr ol causing a decrease in 9



### pituitary hormones, altered growth dynamics, inhibition of LH secretion, and reduction in 10



### StAR protein. Pb has also been shown to alter hormone receptor binding likely due to 11



### interference of metal cations in secondary messenger sys tems and receptor ligand binding 12



### and through generation of ROS. Pb disrupts hormonal homeostasis in invertebrates 13



### necessary for reproduction and development. Pb also may disrupt the HPT axis by 14



### alteration of a number of thyroid hormones, possibly due to ox idative stress. These 15



### studies have been conducted in humans and animals, including cattle; however the results 16



### of these studies are mixed and require further investigation. 17



### Genotoxicity and cell death has been investigated after Pb exposure in humans, animals, 18



### plants, and cell models. High level Pb exposure to humans leads to increased DNA 19



### damage, however lower blood Pb levels have caused these effects in experimental 20



### animals and cells. Reports vary on the effect of Pb on DNA repair activity, however a 21



### number of studies report decreased repair processes following Pb exposure. There is 22



### some evidence in plants, earthworms, freshwater mussels and fish for DNA damage 23



### associated with Pb exposure. There is evidence of mutagenesis and clastogenicity in 24



### highly e xposed humans, however weak evidence has been shown in animals and cells 25



### based systems. Human occupational studies provide limited evidence for micronucleus 26



### formation (>10 μ g/dL), supported by Pb

- induced effects in both animal and cell studies. 27



### Micronucleu s formation has also been reported in amphibians. Animal and plant studies 28



### have also provided evidence for Pb

- induced chromosomal aberrations. The observed 29



### increases in clastogenicity may be the result of increased oxidative damage to DNA due 30



### to Pb exposur e, as co

- exposures with antioxidants ameliorate the observed toxicities. 31



### Limited evidence of epigenetic effects is available, including DNA methylation, 32



### mitogenesis, and gene expression. Altered gene expression may come about through Pb 33



### displacing Zn from multiple transcriptional factors, and thus perturbing their normal 34



### cellular activities. Consistently positive results have provided evidence of increased 35



### apoptosis following Pb exposure. 36February 2012 2

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### Overall, Pb

- induced health and ecological effects can occur through a number of 1



### interconnected and evolutionarily well conserved modes of action that generally originate 2



### with the alteration of ion status. 3



## 2.9 Policy Relevant Considerations

2.9.1 Public Health Significance

The weight of the epidemiologic and toxicological evidence c learly supports the causal 4



### relationship of Pb with decrements in cognitive function and behavior in young children 5



### (Section 5.3.2 and Section 5.3.13 ). Associations of blood Pb level with higher IgE, 6



### asthma and allergy (Section 5.6.8 ) and delays in the pubertal development in children 7



### (Section 5.8.10 ), as well as associations of blood and bone Pb with increased blood 8



### pressure, hypertension (Section 5.4.7 ), and kidney function (Section 5.5.6 ) in adults are 9



### also well

- substantiated in the evidence base. These endpoints were among those 10



### comprising the weight of the evidence for determining causal relationships for the organ 11



### system effects. 12



### The rationale for establishing the public health significance of the various health 13



### endpoints associated with Pb exposure is multifaceted. The 2006 Pb AQCD concluded 14



### that neurological effects in children and cardiovascular effects in adults were among the 15



### effects best substantiated as occurring at blood Pb levels as low as 5

- 10μg/dL (or possibly 16



### lower), and that these categories of effects were c learly of the greatest public health 17



### concern. Evidence of newly demonstrated immune and renal system effects in the general 18



### population was also noted to be of potential public health concern during the previous 19



### review ( U.S. EPA, 200 6b )

. 

### No safe level of Pb exposure has been identified in current or 20



### previous assessments and any threshold for Pb neurotoxicity would have to exist at 21



### distinctly lower levels than those associated with the lowest blood Pb concentrations 22



### examined in the epidemiolo gic studies included in this assessment. Recent epidemiologic 23



### studies of children continue to find associations with several health endpoints in 24



### populations with lower mean blood Pb levels than previously reported ( Chapter 5

, Table 25



### 2

- 9 ). 26



### The concept of population risk is relevant to the interpreta tion of findings for the 27



### continuously

- distributed subclinical health endpoints frequently studied in association 28



### with Pb biomarkers in the assessment of their public health significance. The World 29



### Health Org anization definition of “health ” is “the state of complete physical, mental and 30



### social well

- being and not merely the absence of disease or infirmity” ( WHO, 1948 )

. By 31February 2012 2

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### this definition, even decrements in health status that are not severe enough to result in the 1



### assignment of a clinical diagnosis might be undesirable if they reflect a decrement in the 2



### well

- being of an individual. Further, deficits in subtle indices of health or well

- being may 3



### not be observable except in aggregate, at the population level, so the critical distinction 4



### between population and individual risk is essential for interpreting the public health 5



### significance of study findings. The American Thoracic Society (ATS) discusses concepts 6



### related to understanding the shift in a population distribution of a health endpoint ( ATS, 7



### 2000 )

. As shown in Figure 2

- 1 , a seemingly small increase in the mean of a continuously 8



### distributed health index may push the most susceptible group in the population above a 9



### critical cut point on the continuum of disease development, such that their condition 10



### meets the clinical definition of a disease. Moreover, small changes at the population level 11



### could translate into large numbers of clinical events if a large population is affected. 12



### Figure 2

- 1 The effect of a small shift in population mean on the proportion of individuals in the population diagnosed with clinical disease ( i.e., the proportion to the right of the “Critical Line .” )

As shown in Table 2

- 6 , the size of the Pb

- associated effects observed in epidemiologic 13



### studies may be small relative to the effect sizes that are considered clinically relevant. 14



### Still, these small shifts in popula tion means are often significant from a public health 15



### perspective. For example, small changes in IQ or inattention are often significant at the 16 

# B Critical

Line Shift in Population MeanPercent of Population



# A

Health OutcomeFebruary 2012 2

- 56 Draft

– Do Not Cite or Quote 

### population level, especially in the two tails of the outcome distribution

. Further, a small 1



### shift in the populat ion mean may result in a substantial increase in the number of 2



### individuals functioning in the low range of the IQ distribution who may fall into the IQ 3



### range associated with increase risk of educational, vocational, and social failure after 4



### experiencing a Pb

- associated decrement in IQ. In cohorts of children where Pb

- associated 5



### decrements in cognition and attention were observed, lower academic performance, 6



### antisocial behavior, or delinquent behavior assessed in adolescence or in early adulthood 7



### were also o bserved in association with blood Pb levels. Studies also find that higher 8



### blood Pb level is associated with measures of inattention and hyperactivity as well as 9



### with ADHD or other diagnostic indices used in a clinical setting (Section 5.3.3.1 ). A 10



### downward shift in the mean IQ value can also reduce the proportion of the population 11



### achieving very high IQ scores. It is shown that interventions that shi ft the population 12



### mean, in a beneficial direction, by an amount that is without clinical consequence for an 13



### individual produce substantial decreases in the proportion of individuals with clinically 14



### significant disorders. This evidence, which informs the pu blic health significance of the 15



### evidence on the nervous system effects of Pb, is summarized in detail in Section 5.3.12

. 16



### It is also important to no te that the change in a population mean observed in an 17



### epidemiologic study may be small compared to its standard error of measurement for the 18



### test. As noted in the 2006 Pb AQCD, statistics that pertain to individual

- level data should 19



### not be used to draw in ferences about group

- level data. Measurement error affects the 20



### likelihood of detecting an association and is not relevant to the size of the association that 21



### is detected. If a study is large enough it will have adequate statistical power to detect 22



### small ch anges. Bias may be introduced if the measurement error of the outcome is highly 23



### correlated with the exposure and there is no evidence indicating that individuals with 24



### higher blood Pb levels test systematically lower than their true IQ. 25



### Pb

- associated chang es in other subclinical indices also increase an individual’s risk for 26



### health effects that are of greater clinical consequence, thus of greater public health 27



### concern. S mall increases in blood pressure or decreases in GFR that are associated with 28



### Pb biomark ers, may shift the population mean resulting in a larger proportion of the 29



### population that is diagnosed with hypertension or CKD, respectively. Results from the 30



### Framingham Heart Study show that higher levels of blood pressure, even within the 31



### nonhypertensi ve range, impose increased rates of cardiovascular disease ( Kannel, 2000a

, 32



### b )

. A continuous graded increase in cardiovascular risk is observed as blood pressure 33



### increases, with no evidence of a threshold value. Most events arise not in the most severe 34



### cases, but mainly in those with high normal blood pressure ( i.e., mild hy pertension). 35



### Kannel ( 2000a ) emphasized that systolic blood pressure exerts a s trong influence on more 36



### serious cardiovascular events, as it is the primary cause of hypertension and its adverse 37



### cardiovascular sequelae. In addition to the small increases in blood pressure associated 38February 2012 2

- 57 Draft

– Do Not Cite or Quote 

### with Pb, Pb

- associated effects on cardiovascular morb idity outcomes such as ischemic 1



### heart disease (Section 5.4.3.5) and mortality (Section 5.4.5 ) have been observed. The 2



### high correlation between blood pressure and clinical cardiovascular outcomes combined 3



### with the high prevalence of cardiovascular disease in the U.S. adult population translate 4



### into a large increase in the prevalence of conditions in the population. In addition to the 5



### small changes in m arkers of kidney function, which are potentially significant from a 6



### public health perspective, Navas

- Acien ( 2009 ) and Munter et al. ( 2003 ) both report 7



### increased risk of clinically significant CKD and albuminuria in association with Pb 8



### among NHANES III participants. CKD results in substantial morbidity and mortality, 9



### and, even at earlier stages than thos e requiring kidney dialysis or transplantation, is an 10



### important risk factor for heart disease. As kidney dysfunction can increase BP and 11



### increased BP can lead to further damage to the kidneys, Pb

- induced damage to either or 12



### both renal or cardiovascular sys tems may result in a cycle of further increased severity of 13



### disease. 14February 2012 2

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– Do Not Cite or Quote 

### Table 2

- 6 Illustrative examples contrasting the effect sizes observed in epidemiologic studies to effect sizes considered significant in a clinical setting. a

Organ System Endpoint and Findings from Epidemiologic
Studies Clinical Significance Context

Nervous IQ: 1 μg/dL increase in blood Pb is typically associated with small decrement in IQ ( e.g., < 3 point decrement in FSIQ score) IQ below 70 is considered a disability by the Social Security Disability

Insurance Administrationb

Cardiovascular Systolic Blood Pressure (SBP): Doubling of blood Pb

is a ssociated with an approximate 1 mmHg increase in blood pressure ( Nawrot et al., 2002 ) Hypertension is defined as systolic over diastolic blood pressure that is greater than 140/90. Pre

- hypertension is blood pressure that is 120 to 139/80 to 89. Hypertension is a risk factor for o ther cardiovascular diseases and mortality.

Renal a Glomerular Filtration Rate (GFR): Increased blood Pb
level is associated with reductions in GFR ( e.g., Akesson et al. ( 2005 ) reports a decrease of

- 2.0 mL/min (95% CI:

- 3.2,

- 0.9) per 1 μg/dL increase in blood Pb) GFR <60mL/min/1.73m2 for ≥ 3 months indicates Chronic Kidney Disease (CKD). Estimated GFR (eGFR) can be calculated using several different equations. An equation using serum cystatin C rather than serum creatinine may be a more sensitive marker of early kidney damage.

Serum Creatinine: Increased blood Pb is assoc iated with increased serum creatinine ( e.g., ( Kim et al.,

1996 ) observed an increase 0.030 mg/g (95% CI: 0.011, 0.049) amo ng those with peak blood Pb levels < 10 μg/dL). Creatinine ≥ 30 mg/g creatinine indicates albuminuria.

Creatinine Clearance: [Increased blood Pb is

associated with decreased creatinine clearance ( e.g., Akesson et al. ( 2005 ) reports a

- 1.8 mL/min (95% CI:

- 3.0, 0.7) per 1 μg/dL increase in blood Pb) Normal value s range from 97 to 137 mL/min (males) and 88 to 128 mL/min (females). Abnormal results indicate poor kidney function.

a Effect sizes based on general population studies

b Information on Adult Mental Disorders can be found at: http://www.socialsecurity.gov/disability/professionals/bluebook/12.00

- MentalDisorders

Adult.htm



### Rather than producing overt cytotoxicity or patholo gy, blood Pb level is associated with 1



### alterations in several subclinical parameters related to cellular and humoral immunity 2



### ( Figure 5

- 42 ). Increases i n IgE may contribute to more consequential health conditions 3



### including allergy and asthma and the small changes observed in epidemiologic studies 4



### may result in a population shift and increased prevalence of these conditions. Several 5



### studies found associati ons between blood Pb levels and asthma and allergy in children 6



### (Section 5.6.4.2 ). Immune changes may also be associated with autoimmune diseases 7



### la ter in life as well as reduced capacity to combat certain viral infections and cancer. 8



### Although the public health significance of a delay in onset of puberty is less clear, there 9



### is some limited evidence that delay in puberty is associated with other healt h outcomes 10



### ( Gilsanz et al., 2011 ; Naves et al., 2005 )

. 11



### There is a new body of literature suggesting there may be relationship between maternal 12



### bone Pb, cord Pb and/or concurrent blood Pb and cardiovascular effects in children 13



### including increased blood pressure, Total Peripheral Resistance (TP R) responses to acute 14



### stress tasks, and acute stress

- induced autonomic and cardiovascular dysregulation 15



### (Section 5.4.4 ). This evidence, however, is difficult to interpret with respect to the risk 16February 2012 2

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– Do Not Cite or Quote 

### for health effects because cardiovascular and renal effects are associated with long

- term 1



### exposures to Pb and ther e is uncertainty regarding the frequency, timing, duration and 2



### level of exposure associated with the effects. There is some evidence that the 3



### pathogenesis of CVD begins in childhood ( Kapuku et al., 2006 )

. Although compensatory 4



### mechanisms may be more active in children compared to adults, t hese early 5



### cardiovascular effects may persist and worsen if Pb exposure persists over the long

- term. 6



### A recent study that strengthens the evidence of an association between blood Pb and 7



### altered renal function in children is included in this review. This NHA NES analysis in 8



### adolescents found that association between higher blood Pb and lower cystatin C

- based 9



### eGFR (Section 5.5.6 ). This association is rep orted in a population with mean blood Pb 10



### levels less than 5 μ g/dL; however, those enrolled in the study were likely to have higher 11



### past than recent Pb exposure and the pattern and level of their exposure was not assessed 12



### in the study. 13



### In addition to the l ong

- term effects of Pb, early life exposure to Pb (postnatally) may 14



### permanently alter normal development of the CNS to increase risk of pathology in adults 15



### (Section 5.3.2.2 ). For example connections between developmental exposure to Pb with 16



### early life programming and the resulting inflammation

- associated DNA damage with 17



### neurodegeneration have been demonstrated in rats. Additionally, there is animal 18



### to xicological evidence for a Pb exposure contribution to Alzheimer’s disease pathology 19



### through the generation of neuronal plaques is in early life (Section 5.3.7.2 ). Early life Pb 20



### exposure is also associated with impaired auditory function (Section 5.3.4.3 ). 21



### 2.9.2 Air Lead

- to

- Blood Lead Relationships

The 1986 Pb AQCD described epidemiological studies of relationships between air Pb 22



### and blood Pb. Much of the pertinent earlier literature described in t he 1986 Pb AQCD 23



### was drawn from a meta

- analysis by Brunekreef ( 1984 )

. Based on the studies available at 24



### that time that considered multiple air

- related Pb exposure pathways in the aggregate, the 25


### 1986 Pb AQCD concluded that “the blood Pb versus air Pb slope β is much smaller at 26



### high b lood and air levels.” This is to say that the slope β was much smaller for 27


### occupational exposures where high blood Pb levels (>40 μg/dL) and high air Pb levels 28


### (much greater than 10 μg/m 3 

### ) prevailed relative to lower environmental exposures which 29



### showed lo wer blood Pb and air Pb concentrations (<30 μg/dL and <3 μg/m 3 

### ). For those 30



### environmental exposures, it was concluded that the relationship between blood Pb and air 31



### Pb “

... for direct inhalation appears to be approximately linear in the range of normal 32



### ambient exposures (0.1

- 2.0 μg/m 3 

### )” (pp 1

– 98 of the 1986 Pb AQCD). In addition to the 33



### meta

- analysis of Brunekreef ( 1984 )

, more recent studies have provided data from which 34



### estimates of the blood Pb

- air Pb slope can be derived for children ( Table 2

- 7

, Table 35February 2012 2

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– Do Not Cite or Quote 

### 4

- 11 ). The ran ge of estimates from these studies is 2

- 9 μ g/dL per μ g/m 3 

### , which 1



### encompasses the estimate from the Brunekreef ( 1984 ) meta

- analysis of (3

- 6 μ g/dL per 2



### μg/m 3 

### ). Most studies have described the blood Pb

- air Pb relationship as either log

- log 3



### ( Schnaas et al., 2004 ; Hayes et al., 1994 ; Brunekreef, 1984 )

, which predicts an increase in 4



### the blood Pb

- air Pb slope with decreasing air Pb concentration or linear ( Hilts, 2003 ; 5



### Tripathi et al., 2001 ; Schwartz and Pitcher, 1989 )

, which predicts a constant blood Pb

- air 6



### Pb slope across all air Pb concentrations. These differences may simply reflect model 7



### selection by the investigators; alternative models are not reported in these studies. 8



### The blood Pb

- air Pb slope may also be affected in some studies by the inclusion of 9



### parameters (e.g., soil Pb) that may account for some of the variance in blood Pb 10



### attributable to a ir Pb. Other factors that likely contribute to the derived blood Pb

- air Pb 11



### slope include differences in the populations examined and Pb sources, which varied 12



### among individual studies. See Section 4.5.1 for a detailed discussion of studies that 13



### inform air Pb

- to blood

- Pb relationships. 14February 2012 2

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– Do Not Cite or Quote 

### Table 2

- 7 Summary of Estimated Slopes for Blood Pb to Air Pb Relationships

in Humans

Reference Study Methods Model Description Blood Pb

– Air Pb Slope a
Children Populations

Brunekreef et al. ( 1984 ) Location: Various countries

Years: 1974

- 1983 Subjects: Children (varying age ranges, n>190,000) Analysis: Meta analysis of 18 studies Model: Log

- Log

Blood Pb: 5

- 41 μg/dL (mean range for studies)

Air Pb: 0.1

- 24 μg/m 3
(mean range for studies) All children: 4.6 (1.5) c

Children <20 μg/dL: 4.8 (0.54) d

Hayes et al. ( 1994 ) Location: Chicago, IL

Years: 1974

- 1988 Subjects: 0.5

- 6 yr (n = 9,604) Analysis: Regression of quarterly median blood Pb and quarterly mean air Pb Model: Log

- Log

Blood Pb: 12

- 30 μg/dL (annual median range)

Air Pb: 0.05

- 1.2 μg/m 3
(annual mean range) 8.2 (0.62) e

Hilts et al. ( 2003 ) Location: Trail, BC

Years: 1989

- 2001 Subjects: 0.5

- 6 yr (Estimated n = 220

- 460, based on 292

- 536 blood Pb measurements/yr with 75

- 85% participation). Analysis: Regression of blood Pb screening and community air

Pb follow ing upgrading of a local smelter Model: Linear

Blood Pb: 4.7

- 11.5 μg/dL (annual geometric mean range)

Air Pb: 0.03

- 1.1 μg/m 3
(annual geometric mean range) 6.5 (0.48) f

Ranft et al. ( 2008 ) Location: Germany

Years: 1983

- 2000 Subjects: 6

- 11 yr (n = 843) Analysis: Pooled regression 5 cross

- sectional studies Model: Multivariate Log

- Linear

Blood Pb: 2.2

- 13.6 μg/dL (5th

- 95th percentile)

Air Pb: 0.03

- 0.47 μg/m 3
(5th

- 95th percentile) 3.2 (0.1) g

Schnaas et al. ( 2004 ) Location: Mexico City

Years: 1987

- 2002 Subjects: 0.5

- 10 yr (n = 321) Analysis: Regression of lifetime blood Pb from longitudinal

blood Pb measurements and annual average air Pb data Model: Log

- Log

Blood Pb : 5

- 12 μg/dL (annual GM range)

Air Pb : 0.07

- 2.8 μg/m 3
(annual mean range in yr of birth) 2.2 (0.4) h

Schwartz and Pitcher ( 1989 )

, U.S. EPA ( 1986a ) Location: Chicago, IL

Years: 1976

- 1980 Subjects : Black children, 0

- 5 yr (n = 5,476) Analysis: Chicago blood Pb screening, gasoline consumption data, and Pb concentrations in gasoline Model: Linear

Blood Pb: 18

- 27 μg/dL (mean range)

Air Pb: 0 .36

- 1.22 μg/m 3
(annual maximum quarterly mean) b 8.6 (0.75) i

Tripathi et al. ( 2001 ) Location: Mumbai, India

Years: 19 84

- 1996 Subjects: 6

- 10 yr (n = 544) Analysis: Regression of blood Pb and air Pb data Model: Linear

Blood Pb: 8.6

- 14.4 μg/dL (regional GM range)

Air Pb: 0.11

- 1.18 μg/m 3
(regional GM range) 3.6 (0.45) jFebruary 2012 2

- 62 Draft

– Do Not Cite or Quote Reference Study Methods Model Description Blood Pb

– Air Pb Slope a

Adult Populations
Rodrigues et al. ( 2010 ) Location: New England, U.S.

Years: 1994

- 1995 Subjects: Adult bridge painters (n=84, 1 female) Analysis: Regression analysis of blood Pb and air Pb data (personal monitors) collected during work performing various job

- related tasks Model: Log

- log

Blood Pb: 16.1 μg/dL (GM, 1,7 GSD)

Air Pb : 58 μg/m 3
(GM, 2.8 G SD) 0.01 (58) k

Mixed Child

- Adult Populations

Schwartz and Pitcher ( 1989 )

, U.S. EPA ( 1986a ) Location: U.S.

Years: 1976

- 1980 Subjects: 0.5

- 74 yr (n = 9,987) Analysis: NHANES blood Pb, gasoline consumption data and

Pb concentrations in gasoline Model: Linear

Blood Pb: 11

- 18 μg/dL (mean range)

Air Pb: 0.36

- 1.22 μg/m 3
(annual maximum quarterly mean) 9.3 (0.75) l

a Slope is predicted change in blood Pb (μg/dL per μg/m3) evaluated at ± 0.01 μg/m3 from central estimate of air Pb for the study (shown in parentheses)

b Based on data for U.S. (1986 Pb AQCD )

. c ln(PbB) = ln(PbA) × 0.3485 + 2.853

d ln(PbB) = ln(PbA) × 0.2159 + 2.620

e ln( Pb B) = ln(PbA) × 0.24 +3.17

f PbB = PbA × 6.5

g PbB =1.5 × EXP(0.9361 × (PbA

- 0.1)/0.44), where 1.5 μg/dL is the background PbB, and 0.1 μg/m 3 is the median PbA for the study; model also adjusted for soil Pb concentration, which may reduce estimated slope

h ln(PbB) = Ln(PbA) × 0.213 +1.615 for the 1987 cohort, see t ext in Section 4.5.1 for more study details.

i PbB = PbA × 8.6

j PbB =Pb A × 3.6

k ln(PbB) = ln(PbA) × 0.05 +2.12

l PbB = PbA × 9.63

GM, geometric mean; GSD, geometric standard deviation; PbB, blood Pb concentration (μg/dL); PbA, air

- Pb concentration (μg/m 3 )



### 2.9.3 Ecological Effects and Corresponding Lead Concentrations

There is limited evidence to relate ambient air concentrations of Pb to levels of deposition 1



### onto terrestrial and aquatic ecosystems and to subsequent move ment of 2



### atmospherically

- deposited Pb through environmental compartments ( e.g., soil, sediment, 3



### water, biota). The proportion of observed effects of Pb attributable to Pb from 4



### atmospheric sources is difficult to assess due to a lack of information not only on 5



### bioavailability, as affected by the specific characteristics of the receiving ecosystem, but 6



### also on deposition, and on kinetics of Pb distribution in ecosystems in long

- term exposure 7



### scenarios. Therefore, the connection between air concentration and ec osystem exposure 8



### continues to be poorly characterized for Pb

, and the contribution of atmospheric Pb to 9



### specific sites is not clear. 10



### Furthermore, the level at which Pb elicits a specific effect is difficult to establish in 11



### terrestrial and aquatic systems, due to the influence of other environmental variables on 12



### both Pb bioavailability and toxicity, and also to substantial species differ ences in Pb 13



### susceptibility. Current evidence indicates that Pb is bioaccumulated in biota; however, 14February 2012 2

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– Do Not Cite or Quote 

### the sources of Pb in biota have only been identified in a few studies, and the relative 1



### contribution of Pb from all sources is usually not known. There are large differences in 2



### species sensitivity to Pb, and many environmental variables ( e.g., pH, organic matter) 3



### determine the bioavailability and toxicity of Pb. 4



### 2.9.4 Concentration

- Response Functions for Health Effects

With each successive assessment to

- date, the epidemiologic and toxicological study 5



### findings show that progressively lower blood Pb levels or Pb exposures are associated 6



### with cognitive deficits and behavioral impairments (Section 5.3.9 ). C

- R functions have 7



### been examined across different populations and the interpretation of these functions 8



### depends on several factors including lifestage and Pb biomarker used for the analysis. 9



### Compelling evidence for a steeper slope for the relationship between blood Pb level and 10



### children’s IQ at lower blood Pb levels was presented in the 2006 Pb AQCD based on the 11



### international pooled analysis of seven prospective cohort studies by Lanphear et al. 12



### ( 2005 )

, a subsequent reanalysis of these data focusing on the shape of the concentration 13



### response function ( Rothenberg and Rothenberg, 2005 )

, and several individual studies 14



### noted in Fi gure 2

- 2 . The majority of the epidemiologic evidence from stratified analyses 15



### comparing the lower and the higher ends of the blood Pb distributions in dicates larger 16



### negative slopes at lower blood Pb levels. 17February 2012 2

- 64 Draft

– Do Not Cite or Quote Note: Studies are presented in order of increasing mean blood Pb level.

a Strata refer to peak blood Pb level measured in child at any point during follow up.
FSIQ = full

- scale IQ, MDI = mental development index. Effect estimates are standardized to a 1 μ g/dL increase in blood Pb level. Black symbols represent effect estimates among all subjects or in highest blood Pb stratum. Blue symbols represent eff ect estimates in lower

blood Pb strata.



### Fi gure 2

- 2 Comparison of associations between blood Pb and cognitive function among various blood Pb strata.

Relatively few studies examined the shape of the concentration

- response relationship 1



### between Pb in bl ood or bone and effects in adults. There is uncertainty regarding the 2



### frequency, duration, timing and level of exposure contributing to the blood Pb or bone Pb 3



### levels in the adult population studied. Some of t he populations examined ( e.g., NHANES, 4



### NAS) are likely to have higher past than recent Pb exposure. Other populations 5



### ( e.g., worker populations) studied have ongoing exposure to Pb. As described elsewhere 6



### in the document (Section 4.3 , Section 5.3 , Section 5.4 , Section 5.5 ), the interpretation of 7



### the study findings depends on the exposure history and the choice of the biomarker in the 8



### context of what is known about that exposure history. 9



### In NHANES analyses describing the C

- R function for blood Pb level and neurocognitive 10



### effects in adults , only log

- linear models were used to fit the data ( Krieg et al., 2010 ; 11



### Krieg and Butler, 2009 ; Krieg et al., 2009 )

. With regard to C

- R relationships for 12



### cumulative exposure metrics, nonlinearity in the BMS and NAS cohorts of 13 Study

Lanphear et al. (2000)

Bellinger and Needleman (2003)

Canfield et al. (2003) Tellez

- Rojo et al. (2006)

Jusko (2011)

Kordas et al. (2006) Lanphear et al. (2005)

Schwartz (1994) Blood Pb Timing

Concurrent

Peak

Lifetime avg Concurrent

Peak

Concurrent Concurrent

Early childhood Outcome

Reading score

FSIQ

FSIQ Bayley MDI

FSIQ

Math score FSIQ

FSIQ Blood Pb stratum (μg/dL)

All

<10

<7.5

<5

<2.5

>10

<10

All

<10 a ≥10

<10

5

- 10

<5

All

< 10

all

<10 ≥10 a

<10 a

≥7.5 a

<7.5 a

>15

≤15 ◄

◄

◄ ► Sample size

4853

4681

4526

4043

2467

NR

NR

172

101 90

294

101

193

174

96

532

293 1089

244

1230

103

NR

NR

- 4

- 3

- 2

- 1 0 1

Change in Cognitive Function Score per 1 μg/dL increase in blood Pb level (95% CI)February 2012 2

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– Do Not Cite or Quote 

### community

- dwelling older adults was examined with the use of quadratic terms, 1



### penalized splines, or visual inspection of bivariate plots ( Bandeen

- Roche et al., 2009 ; 2



### Weisskopf et al., 2007a ; Shih et al., 2006 )

. There was some evidence for nonlinearity for 3



### some but not all cognitive tests or subjects in the NAS cohort (Section 5.3.10 ). In 4



### analyses of the BMS coho rt, observations of a statistically nonsignificant quadratic term 5



### ( Shih et al., 2006 ) or spline ( Bandeen

- Roche et al., 2009 ) for tibia Pb indicated that a 6



### linear model adequately fit the relationship between tibia Pb level and v arious tests of 7



### cognitive performance. 8



### Concentration

- response relationships were examined in several epidemiologic studies of 9



### blood pressure and mortality (Section 5.4.5 ). With regard to the concentration

- response 10



### relationship, meta

- analysis of human studies found that each doubling of blood Pb level 11


### (between 1 and >40 μg/dL measured concurrently in most stud ies) was associated with a 12



### 1 mmHg increase in systolic BP and a 0.6 mmHg increase in diastolic BP ( Nawrot et al., 13



### 2002 )

. However, there is uncertainty in the concentration

- response relationship to 14



### card iovascular endpoints at lower blood Pb levels since most studies model a linear 15



### relationship. Weaver et al. ( 2 010 ) provided the results of further analysis of this Korean 16



### worker cohort, with a focus on determining the functional form of the 17



### concentration

- response relationships. The coefficient indicated that every doubling of 18



### blood Pb level was associated with a systolic BP increase of 1.76 mmHg. The J test, a 19



### statistical test for determining which, if either, of two functional forms of the same 20



### variable, provides superior fit to data in non

- nested models. Davidson and MacKinnon 21



### ( 1981 ) returned a p

- value of 0.013 in fav or of the natural log blood Pb level, over the 22



### linear blood Pb level specification. This analysis indicates that systolic BP increase in this 23



### cohort is better described as a logarithmic function of blood Pb level within the blood Pb 24



### level range of the stud y than by a linear function. Animal toxicological studies provide 25



### support for this concentration response relationship. Few studies that focused on 26



### Pb

- induced hypertension in experimental animals have included more than two exposure 27



### concentrations; however these few studies appear to have a supralinear (concave 28



### downward) dose response. 29



### Studies investigating both all

- cause and cardiovascular mortality report both linear and 30



### non

- linear relationships (Section 5.4.5 ). Findings from NHANES analyses were mixed 31



### with Schober et al. ( 20 06 )

, reporting a linear association between the relative hazard for 32



### all cause mortality with blood Pb, and Menke et al. ( 2006 )

, reporting a non

- linear 33



### relationships between blood Pb level and the hazard ratio for all cause, MI, stroke, and 34



### cancer mortality. There is uncertainty regarding the frequency, duration, timing and 35



### magnitude of exposure contributing to the blood Pb levels among the NHANES 36



### population studied; individuals in this population are likely to have higher past than 37



### recent exposures. Weisskopf et al

. ( 2009 ) examined the concentration

- response 38February 2012 2

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– Do Not Cite or Quote 

### relationships of patella and tibia Pb with mortality. Concentration

- response rel ationships 1



### were approximately linear for patella Pb on the log HR scale for all CVD, but appear 2



### nonlinear for IHD (p <0.10). The peak HR is shown around 60 μ g/g, beyond which the 3



### HR tends to decrease. It is important to note the wide confidence limits, whi ch increase 4



### uncertainty at the lower and upper bounds of patella Pb levels. The strongest associations 5



### were observed between mortality and baseline patella Pb concentration. Baseline tibia Pb 6



### levels were more weakly associated with CVD mortality. Tibia bon e Pb level is thought 7



### to reflect a longer cumulative exposure period than is patella bone Pb level because the 8



### residence time of Pb in trabecular bone is shorter than that in cortical bone. 9



### Concentration response information was provided in a small number of studies of 10



### Pb

- related nephrotoxicity in the occupational setting ( Weaver et al., 2003b ; Ehrlich et al., 11



### 1998 )

. Data in 267 Korean Pb workers in the oldest age tertile (mean age = 52 year s) 12



### revealed no threshold for a Pb effect (beta = 0.0011, p = <0.05; regression and lowess 13



### lines shown), however the mean blood Pb level in this population was 32 μ g/dL ( Weaver 14



### et al., 2003b )

. 15



### Non

- linear concentration/exposure response relationships or attenuation of these 16



### relationships at higher expo sure levels is reported in the occupational literature for a 17



### variety of effects. Explanations for this phenomenon include greater exposure 18



### measurement error, competing risks, and saturation of biological mechanisms at higher 19



### exposure levels, and exposure

- d ependent variation in other risk factors ( Stayner et al., 20



### 2003 )

. With respect to Pb exposure, different biological mechanisms may operate at 21



### different exposure levels and/or there may be a lower incremental effect of Pb due to 22



### covarying ris k factors such as low SES, poorer caregiving environment, and other higher 23



### environmental exposures. The 2006 Pb AQCD also considered the explanation for the 24



### supralinear concentration response function postulated by Bowers and Beck ( 2006 )

, who 25



### stated that “a supralinear slope is a required outcome of correlations between a data 26



### distribution where one is lognormally distributed and the other is normally distributed.” 27



### The 2006 Pb AQCD determined that, while the conclusions drawn by Bowers and Beck 28



### may be true under certain conditions, their assumptions ( e.g., that IQ are sco res forced 29



### into a normal distribution) were not generally the case in the epidemiologic analyses 30



### showing a supralinear concentration response function. To support this conclusion, the 31



### 2006 Pb AQCD cited Hornung et al. ( 2006 )

, which provided evidence that the IQ data 32



### used in the pooled analysis of seven studies by Lanphear et al. ( 2005 ) were not 33



### normalized and a log

- linear model (a linear relationship between IQ and the log of blood 34



### Pb) provided the best fit. 35



### The factors contributing to the supralinear relationship between blood Pb levels and 36



### neurocognitive function in children has not been examined widely in epidemi ologic 37February 2012 2

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### studies to date. However, in several populations, higher blood Pb levels have been 1



### measured in susceptible groups such as those with higher poverty, greater exposure to 2



### tobacco smoke, lower parental education, and lower birth weight ( Lanphear et al., 2005 ; 3



### Lanphear et al., 2000 )

. It has been suggested that in populations of low SES, poorer 4



### caregiving environment, and greater social stress, the incremental effect of Pb exposure 5



### may be attenuated due to the overwhelmingly larger effects of these other risk factors 6



### ( Schwartz, 1994 )

. Several studies found significant associations of these 7



### sociodemographic risk factors with neurocognitive deficits, and Miranda et al. ( 2009 ) 8



### found that indicators of SES ( i.e

., parental education and enrollment in a free/reduced fee 9



### lunch program) accounted for larger decrements in EOG scores than did blood Pb level 10



### ( Figure 5

- 7 ). Few studies have compared Pb effect estimates among groups in different 11



### sociodemographic strata, and the limited data are mixed. Greater Pb

- associated 12



### neurocognitive deficits were reported in low

- SES groups by Bellinger et al. ( 1990 )

. In a 13



### meta

- analysis of eight studies, Schwartz ( 1994 ) found a smaller decrement in IQ per 14



### 1 μ g/dL increase in blood Pb level for studies in disadvantaged populations (

- 2.7 points 15



### [95% CI:

- 5.3,

- 0.07]) than for studies in advantaged populations (

- 4.5 points [95% CI: 16



### - 5.6,

- 2.8]). It is important to note that blood Pb level is associated with deficits in 17



### neurocognitive function in both higher and lower SES groups; howe ver, it is unclear what 18



### differences there are between groups in the decrement per unit increase in blood Pb and 19



### whether these differences can explain the nonlinear concentration

- response relationship. 20



### In support of epidemiologic findings, toxicological stu dies provided some evidence that 21



### compared with control or higher Pb exposures ( e.g., 150 ppm ), lower Pb exposures 22



### ( e.g., 50 ppm ) during gestation and lactation (possibly with offspring stress co

- exposure) 23



### impaired learning and memory as indicated by increa sed FI responses on schedule 24



### controlled behavior tests ( Rossi

- George et al., 2011 ; Cory

- Slechta, 1994 )

. The 2006 P b 25



### AQCD did not identify a biological mechanism for a steeper slope at lower than at higher 26



### blood Pb levels but such a mechanism was not ruled out. In fact, several lines of 27



### toxicological evidence support the possibility of lower and higher Pb exposures act ing 28



### through differentially activating mechanisms underlying cognition. 29



### As detailed in Section 5.3.10 , the shape of the C

- R relationship for dopami ne varied 30



### across studies. However, relative to higher Pb exposures, lower Pb exposures were found 31



### to reduce LTP ( Gilbert et al., 1999 ) and glutamate release in the hippocampus ( Lasley 32



### and Gilbert, 2002 )

. LTP is one indication of synaptic plasticity (Section 5.3.8.4 ) and is 33



### considered to mediate learning and memory. Glutaminergic neurotransmission via its 34



### NMDA receptor has been implicated in learning and memory (Section 5.3.8.8 ). Thus, 35



### these differential responses to lower versus higher Pb exposures may provide mechanistic 36



### understanding and addition al biological plausibility for the nonlinear associations of Pb 37February 2012 2

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### exposure or blood Pb levels with neurodevelopmental outcomes observed in animals and 1



### children. 2



### While epidemiologic studies have not examined widely the shape of the 3



### concentration

- response rel ationship for other nervous system effects, as detailed in 4



### Section 5.3.10 , toxicological studies have found nonlinear C

- R relationships for diverse 5



### outcomes such as rod and retinal effects in the visual system ( Giddabasappa et al., 2011 ; 6



### Fox et al., 2010 )

, motor function ( Leasure et al., 2008 )

, and hippocampal neurogenesis 7



### ( Fox et al., 2008 ; Gilbert et al., 2005 )

. 8



### The supralinear concentration

- response relationship widely documented for Pb is 9



### consistent with the lack of a threshold for Pb

- associated nervous system effects in 10



### children becaus e a smaller effect estimate would be expected at lower blood Pb levels if a 11



### threshold existed. However, an important limitation of previous studies in terms of 12



### identifying whether a threshold exists, is the limited examination of effects in populations 13



### or blood Pb strata with blood Pb levels more comparable to the current U.S. population 14



### mean. While Schwartz ( 1994 ) did not find evidence for a threshold in the Boston study 15



### data, the mean blood Pb in that population was 6.5 μ g/dL, and 56% of subjects had a 16



### blood Pb level >5 μ g/dL. Recent studies indicate a downward shift in the distribution of 17



### blood Pb le vels ( i.e., 50% of subjects in the 2001

- 2004 NHANES population had a blood 18



### Pb <1 μ g/dL ( Braun et al., 2008 )

. Additionally, more sensitive quantification methods 19



### have improved the detection limits, for example, from 0.6 μ g/dL in 1999

- 2002 NHANES 20



### to 0.025 μ g/dL in 2003

- 2004 NHANES allowing categorization of children in multiple 21



### blood Pb quantiles below 1 μ g/dL ( Braun et al., 2008 )

. Consequently, the examination of 22



### populations with large proportions of subjects at very low b lood Pb levels has improved 23



### the ability to discern a threshold for Pb

- associated nervous system effects. In the 24



### 2001

- 2004 NHANES population, Braun et al. ( 2008 ) found higher odds ratios for 25



### conduct disorder and ADHD among children with blood Pb levels 0.8

- 1.0 μ g/dL (2nd 26



### quartile) compared with children with blood Pb levels 0.2

- 0.7 μ g/dL (1st quartile). 27



### However. th e large proportions of adolescents in NHANES analyses who were born the 28



### 1970s may have had higher past Pb exposures that contributed to associations observed 29



### with concurrent blood Pb levels. Nonetheless, several recent studies reported associations 30



### between blood Pb levels and deficits in cognitive and behavioral endpoints in children 31



### ages 8

- 11 year s with mean or quantile blood Pb levels <2 μ g/dL ( Cho et al., 2010 ; Kim et 32



### al., 2009b ; Miranda et al., 2009 )

. In comparisons of various quantiles of blood Pb, 33



### Miranda et al. ( 2009 ) reported lower EOG scores in children in North Carolina with 34



### blood Pb levels of 2 μ g/dL compared with children with blood Pb levels of 1 μ g/dL. 35



### Collectively, t hese new findings in children, as summarized in this document, do not 36



### provide evidence for a threshold for the nervous system effects of Pb in the ranges of 37



### blood Pb levels examined to date. 38February 2012 2

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### 2.9.5 Pb Exposure and Nervous System Effects in Children

As discussed i n various sections across this document, there are uncertainties related to 1



### the frequency, timing, duration and level of Pb exposure contributing to the health effects 2



### observed in epidemiologic studies of adults and older children who are likely to have 3



### hi gher past than recent Pb exposure. Both blood Pb and bone Pb, which are the most 4



### common metrics of exposure/dose used in epidemiologic studies, are integrative 5



### measures and do not allow these aspects of exposure to be distinguished. Bone Pb is a 6



### measure of cumulative exposure in adults and is not typically used in studies of children. 7



### As discussed in Section 4.3.5 , blood Pb may reflect both recent exp osures and Pb 8



### released from the bone; the relative proportion of blood Pb from recent versus past 9



### exposure is uncertain in the absence of information on exposure timing and duration. 10



### Young children, however, do not have lengthy exposure histories and conse quently the 11



### interpretation of associations with blood Pb levels for this age group may be less 12



### complicated compared to older age groups. Several lines of evidence, which are 13



### discussed below, inform the interpretation of study findings as they relate to asp ects of 14



### exposure that can be attributed to the neurocognitive and behavioral effects of Pb 15



### observed in young children. 16



### A common limitation of epidemiologic studies is the potentially high correlation between 17



### Pb exposure metrics at different ages in childho od and with maternal Pb exposure 18



### metrics. In longitudinal studies of the effect of Pb in children, blood Pb levels remained 19



### relatively stable over time. Thus, it is difficult to distinguish effects of past and 20



### concurrent exposures. Further, concurrent b loo d Pb levels in children, although highly 21



### affected by recent exposure, are also influenced by their past exposure (including prenatal 22



### exposure) due to the rapid growth

- related bone turnover in children. Thus, concurrent 23



### blood Pb level in children also may r eflect cumulative dose (Section 4.3.5.1 ). There is 24



### some evidence that the influence of maternal Pb levels on postnatal blood Pb level is 25



### substantially reduced soon after birth. Simon et al. ( 2007 ) followed a cohort of 13 26



### children living near an Australian smelter from birth through 36 months. In general, 27



### immediately after birth, blood Pb levels fell for 1

- 2 months to approximately 47% of 28



### birth blood Pb level. After this initial fall, all infants' blood Pb levels rose with age until 29



### approximately 12 months old. There was a good correlation between child blood Pb level 30



### and child hand Pb loading (R 2 

### = 0.70) in this study, indicating the influence of concurrent 31



### Pb exposures on blood Pb during the early childhood year s. 32



### In epidemiologic studies, associations of cognitive function and behavior have been 33



### observed with prenatal, early

- childhood, lifetime average, and concurrent blood Pb levels 34



### as well as with childhood tooth Pb levels and it is difficult to ascertain which lifestage 35



### within childhood is associated with the greatest risk of Pb

- associated eff ects on cognition 36February 2012 2

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### (Section 5.3.9

, Table 5

- 13

, Table 5

- 14 ). Epidemiologic studies of Bayley MDI following 1



### children beginning in utero and through three year s of age indicate that short

- duration 2



### exposures in utero or during early childhood are associ ated with cognitive decrements in 3



### young children. Among studies with prenatal and concurrent blood Pb measurements, 4



### some found stronger associations for prenatal blood Pb levels ( Hu et al., 2006 ; Bellinger 5



### et al., 1984 )

, and other found stronger associations for concurrent blood Pb levels 6



### ( Wasserman et al., 1998 ; Wasserman et al., 1992 )

. Studies that found associations with 7



### concurrent blood Pb levels also tended to find associations with prenatal cord or maternal 8



### blood Pb levels. Thus, both postnatal child and maternal Pb exposures may contribute to 9



### lower cognitive function in young children. In addition, exposures that are reflected by 10



### concurrent blood Pb measured when children are older, by cumulative blood Pb levels or 11



### by tooth Pb levels have also been demonstrated to be associated with neurodevelopmental 12



### deficit s throughout school

- age and into adolescence. These findings are consistent with 13



### the understanding that the nervous system continues to develop throughout childhood. 14



### However, the weight of epidemiologic evidence supports associations of concurrent 15



### blood Pb level with neurodevelopmental effects ( i.e., cognition and behavior) in children 16



### (Section s 5.3.2.1 and 5.3.3.1 ). 17



### The persistence of neurodevelopmental effects from low

- level Pb exposure was also 18



### considered in the 2006 Pb AQCD, with some evidence suggesting that the effects of Pb 19



### on neurodevel opmental outcomes persisted into adolescence and young adulthood. The 20



### toxicological evidence continues to support a range of effects with prenatal and early 21



### postnatal Pb exposures which persist to adulthood ( Sections 5.3.2.1 and 5.3.2.4 ). A 22



### number of mechanisms, including changes in neurogenesis, synaptogenesis and synaptic 23



### pruning, long term potentiation, and neurotransmitter function have been identified that 24



### provide biolo gical plausibility for epidemiologic and toxicological findings of persistent 25



### cognitive and behavioral effects that result from short

- term Pb exposures during prenatal 26



### and early childhood periods. The persistence of effects appears to depend on the duratio n 27



### and window of exposure as well as other factors that may affect an individual’s ability to 28



### recover from an insult. 29



### Toxicological studies in the 2006 Pb AQCD highlighted the importance of Pb exposure 30



### during early life in promoting Alzheimer’s like pathol ogies in the adult rodent brain, with 31



### Pb

- induced neurodegeneration and formation of neurofibrillary tangles in aged animals in 32



### which blood Pb levels had returned to control levels after an earlier life Pb exposure 33



### ( U.S. EPA, 2006b )

. Recent toxicological studies continue to point to an early life window 34



### in which Pb exposure can contribute to pathological brain changes consistent with 35



### Alzheimer’s disease. The same Pb exposure ( i.e., dose and duration equivalent to the 36



### early life exp osure, to adult rodents) did not induce neurofibrillary tangles in the aged 37



### animals. However, blood Pb is not generally associated with Alzheimer’s disease in 38February 2012 2

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### epidemiologic studies of adults. In other studies, recent evidence indicates associations 1



### between early life ALAD activity, a biomarker of Pb exposure, and schizophrenia later in 2



### adulthood when schizophrenia typically manifests. Consistent with these findings, 3



### toxicological studies have shown NMDA pathway disruption with Pb exposure; 4



### manipulation of t his pathway is known to be associated with schizophrenia. There is also 5



### toxicological evidence for Pb

- induced emotional changes in males and the occurrence of 6



### depression changes in females. Sensitive windows of early life Pb exposure have been 7



### associated w ith persistent changes in adulthood as demonstrated with animal models of 8



### neurodegeneration, i.e., neurofibrillary tangle formation, and with epidemiologic findings 9



### for the psychotic disorder schizophrenia. These effects are not reflective of concurrent 10



### bl ood

- Pb levels at the age of manifestation of the pathology but instead are associated 11



### with an earlier life Pb exposure. 12



### 2.9.6 Populations Potentially At

- Risk for Health Effects

The NAAQS are intended to provide an adequate margin of safety for both the populati on 13



### as a whole and those groups with unique factors that make them potentially at increased 14



### risk for health effects in response to ambient air pollutants. Interindividual variation in 15



### human responses to air pollution exposure suggests that some populations are at 16



### increased risk for detrimental effects of ambient exposure to an air pollutant. 17



### Epidemiologic studies reporting results from stratified analyses designed to identify 18



### effect measure modifiers comprise the overall weight of evidence for conclusions re lated 19



### to the increased risk of specific populations to the Pb

- related health effects presented in 20



### Section 6.3. Supporting evidence from toxicological studies provide biological 21



### plausibility for conclusions and summarizes factors that potentially influence Pb levels 22



### within the body (Section 6.1 ) and factors related to differential Pb exposures 23



### (Section 6.2 ). The factors that were evaluated are listed in Table 2

- 8

. 24February 2012 2

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### Table 2

- 8 Factors e valuated that m ay d etermine p opulations p otentially at

i ncreased r isk from l ead

Physiological Factors that Influence the

Internal Distribution of Lead Population Characteristics Potentially Related to Differential Lead Exposure Factors Potentially Related to Increased

Risk of Lead Induced Health Effects

Age (Section 6.1 and Section 4.4 ) Age (Section 6.2.1 ) Age (Section 6.3.1 , and Section 5.3.8 )

Sex (Section 6.2.2 ) Sex (Section 6.3.2 )

Genetics ( Section 6.1

, Section 4.1 , Section 4.2 ) Genetics (Section 6.3.3 )

Pre

- existing Disease (Section 6.3.4 )

Race and Ethnicity (Section 6.2.3 ) Race and Ethnicity (Section 6.3.6 )

Socioeconomic Status (Section 6.2.4 ) Socioeco nomic Status (Section 6.3.7 )

Proximity to Pb Sources (Section 6.2.5

, Section 3.2 , Section 3.3 , Section 3.5 , and
Section 4.1 )

Residential Factors (Section 6.2.6 )

Lifestyle Factors

Smoking (Section 6.3.5 )

Body Mass Index (Section 6.3.8 )

Alcohol Consumption (Section 6.3.9 )

Nutrition (Section 6.1 and Secti on 4.2 ) Nutrition (Section 6.3.10 )

Stress (Section 6.3.11 )

Cognitive Reserve (Section 6.3.12 )

Co

- exposure (Section 6.1 and Section 4.2 ) Other metals (Section 6.3.13 )



### Studies are included in Section 6.3 only if analyses were conducted to identify the 1



### presence or absence of effect measure modification. By virtue of their design some cohort 2



### studies, including cohort studies of pregnant women o r other populations or lifestages 3



### with no comparison group, are discussed in the endpoint

- specific sections rather than in 4



### C hapter 6 . This integrati ve summary, however, draws on evidence relating to potentially 5



### at

- risk populations and lifestages appearing throughout this document. Also, 6



### physiological factors that influence the internal distribution of Pb, population 7



### characteristics potentially related to differential Pb exposure and factors potentially 8



### related to increased risk of Pb induced health effects are considered together in this 9



### integrative summary. 10February 2012 2

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### 2.9.6.1 Age and/or Lifestage

Infancy and Early Childhood

It is recognized that Pb can cross the placen ta to affect the developing nervous system of 1



### the fetus ( Section 4.2.2.4 ). Further, elevated blood Pb levels among mothers present a 2



### potential expos ure to their children through breast milk. This transfer of Pb from mother 3



### to fetus is observed to occur partly from the remobilization of the mother’s bone stores 4



### (Section 4.2.2.4 ). Other biokinetic factors that vary by age, including bone turnover and 5



### absorption, also affect blood Pb levels. Typically, children have increased exposure to Pb 6



### compared with adults because children’s behaviors and activ ities include increased hand

7



### to

- mouth contact, crawling, outdoor play, and poor hand

- washing that typically result in 8



### increased ingestion compared with adults. Blood Pb among different age groups are 9



### shown in Table 6

- 1 . Blood Pb levels are highest among the young children and decrease 10



### with increasing age of the child. 11



### There is evidence of increased susceptibility to the neurocognitive effects of Pb exp osure 12



### during several lifestages throughout childhood (Section 5.3.2.1 to Section 5.3.8 , and 13



### Section 6.3.1.1 ). Exposure to environmental toxicants during prenatal and/or early 14



### postnatal development may alter the normal course of morphogenesis and maturation that 15



### occurs in utero and early in life, resulting in changes that affect structure or function of 16



### the central nervous system via altered neuronal growth and/or synaptogenesis/pruning 17



### s tructure (Section 5.3.9 ). Synaptic pruning, which is active throughout early childhood 18



### (ages 1

- 4 year s), may underlie the elevated risk of young ch ildren to environmental 19



### exposures. Overall evidence indicates early childhood as a lifestage of increased risk for 20



### Pb

- related health effects with epidemiologic studies report associations with cognition 21



### (Section 5.3.9 ) among the youngest age groups (6 months to 3 year s). Toxicological 22



### studies provide support for the younger age groups being especially sensitive to Pb 23



### exposure. Toxicological studies have reported that younger animals, whose nervous 24



### systems are developing ( i.e., laying down and pruning neuronal circuits) and whose 25



### junctional barrier systems in the brain ( i.e., the blood brain barrier) and GI system 26



### ( i.e., gut closure) are immature, are more at risk from the effects Pb exposure ( Fullmer et 27



### al., 1985 )

. Further, blood Pb level is associated with effects to the immune system 28



### (Section 5.6 ) of children. Findings of a recent study indicate that very young children 29



### may be at increased risk for Pb

- associated activation of humoral immune responses and 30



### perturba tions in cell

- to

- cell interactions that underlie allergic, asthma, and inflammatory 31



### responses (Section 5.6.2.1 and Section 5.6.3 ). 32February 2012 2

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### Adolescents

The 2007

- 2008 NHANES data suggest that sex

- based differences in blood Pb levels are 1



### not substantial until adolescence at which time blood Pb levels of boys are higher than 2



### girls. Anatomical understanding of brain development in the typically or normally 3



### developing child also helps to inform findings with associated pathologies by providing 4



### grounds for comparison. Findings from MRI studies have been used to detail anatomical 5



### changes within separate brain segments in the normally developing child and adolescent, 6



### from age 3

- 30 (Section 5.3.9 ). Through out adolescence, normal brain development 7



### remains dynamic. Volumes of specific regions vary largely by sex and age, but also 8



### include inter

- individual variation. Studies have linked concurrent blood Pb level as well 9



### as other blood Pb metrics) in adolescents to decrements in cognitive function, delinquent 10



### or criminal behavior (Section 5.3.3.1 ). Delays in puberty onset (Section 5.8.1.3 ) and renal 11



### effects (Section 5.5.1.1 ) are also observed in association with concurrent blood Pb level 12



### in cross

- sectional studies of adolescents. However, the populations of older children 13



### studied generally had higher past exposures, which may have influenced the findings of 14



### these studies. 15



### Adulthood

There is uncertainty regarding the frequency, duration, timing and magnitude of exposure 16



### contributing to the blood Pb levels among the adult population studied. Associations of 17



### both blood Pb and/or bone Pb with blood pressure, hypertension and mortality, renal, 18



### imm une, hematological, and reproductive effects. Blood Pb and bone Pb levels tend to be 19



### higher in older adults (>65 year s) compared with the general population. Higher average 20



### and median bone and blood Pb levels among older adults could potentially be due to a 21



### shared experience of higher historical Pb exposures stored in bone in conjunction with 22



### remobilization of stored Pb during bone loss (Section 4.2 ). In recent studies, age was 23



### specifically examined as an effect modifier of the association of Pb with mortality 24



### (Section 5.4.5 ), cognition (Section 5.3.2.5 ) and blood pressure (Section 5.4.2 ) in adults. 25



### Results for age

- related modification of the association between Pb and mortality were 26



### mixed and no difference by age was observed for the associations between Pb and 27



### cognitive function or blood pressure. Toxicological studies have shown in creases in 28



### Pb

- related health effects by age that may be relevant to nervous system effects in humans 29



### (Section 5.3.1 ). 30February 2012 2

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### 2.9.6.2 Sex

Multiple associations b etween Pb and various health endpoints have been examined for 1



### effect measure modification by sex (Section 6.3.2 ). Some studies reported differences 2



### between the associations for males and females; overall, the findings were mixed. For 3



### example, studies on cognition from the Cincinnati Lead Study cohort and a study in 4



### Poland reported males to be an at

- risk population, whereas studies from Australia poin ted 5



### to females as an at

- risk population. Toxicological studies continue to demonstrate 6



### increased susceptibility of males to Pb for specific endpoints such as sensory function, 7



### balance, liver hyperplasia, obesity, memory and gross motor skills. Males and fe males 8



### show differential susceptibility in other toxicological studies across a wide array of 9



### endpoints including of behavior, stress hormone homeostasis, and depression with some 10



### endpoints having greater effects in one sex versus the other based on the exp osure 11



### paradigm. 12



### 2.9.6.3 Genes

The 2006 Pb AQCD observed that genetic polymorphisms s have been implicated as 13



### influencing the absorption, retention, and toxicokinetics of Pb in humans, with the 14



### majority of discussion focused on the aminolevulinate dehydratase (ALAD ) and vitamin 15



### D receptor (VDR) polymorphisms ( U.S. EPA, 2006b )

. Studies published since then 16



### continue to indicate that variants of the VDR and the ALAD polymorphism have been 17



### associated with varied internal Pb concentrations. Overall, studies of ALAD observed 18



### increased Pb

- related health effects associated with certain gene variants. Other genes, 19



### such as VDR, MTHFR, APOE, HFE, DRD4, GSTM1, TNF

- α, and eNOS, may also 20



### affect the risk of Pb

- related health effects but conclusions are limited due to the small 21



### number of studies (Section 6.3.3 ). 22



### 2.9.6.4 Pre

- existing Conditions

Studies have also been performed to examine whether certain morbidities increase an 23



### individual’s risk of Pb

- related effects on health. Recent studies have explored 24



### relationships for autism, atopy, diabetes, and hypertension; however, there were generally 25



### few studies available that evaluated conditions such as autism and atopy. The 2006 Pb 26



### AQCD concluded that diabetes and hypertension may result in increased risk of 27



### Pb

- associated declines in renal function ( U.S. EPA, 2006b )

. However, a recent study 28



### indicates that diabetes was not related to increased risk of Pb

- related cardiovascular 29



### outcomes, and there were mixed results regarding the potential for hypertension to 30February 2012 2

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### increase the risk of Pb

- related effects on renal function and cardiovascular effects 1



### (Section 6.3.4 ). 2



### 2.9.6.5 Race and E thnicity

Higher blood Pb and bone Pb levels among African Americans has been well 3



### documented ( U.S. EPA, 2006b )

. Recent studies are consistent with those previous 4



### findings (Section 6.2.3 ). Greater tibia Pb, but not patella Pb or blood Pb levels, was 5



### reported in the Baltimore population studied by Theppeang et al. ( 2008b )

. This finding 6



### may indicate greater historical exposure among African Americans compared to 7



### Caucasians. In addition, a higher proportion of blacks compared with other race

- ethnicity 8



### groups has been rep orted in Census blocks where soil Pb concentration is higher, whereas 9



### the proportion of whites was higher in low soil Pb Census blocks for a study of New 10



### Orleans soil exposure ( Campanella and Mielke, 2008 )

. The results of recent 11



### epi demiologic studies suggest that there may be race/ethnicity

- related increased risk for 12



### cardiovascular effects and delayed puberty, although the overall understanding of 13



### potential effect measure modification by race/ethnicity is limited by the small number of 14



### studies. Additionally, these results may be cofounded by other factors, such as 15



### socioeconomic status (Section 6.3.6 ). 16



### 2.9.6.6 Socioeconomic Status

Socio economic factors have sometimes been associated with Pb biomarkers, although 17



### these relationships have not always been consistent ( U.S. EPA, 2006b )

. On a national 18



### level, the gap between income levels with respect to blood Pb has been decreasing. 19



### However, blood Pb level of children remains higher depending on income, enrollment in 20



### Medicaid and poverty income ratio (PIR), which is the ratio of family in come to the 21



### poverty threshold appropriate for a given family size (Section 6.2.4 ). Although there are a 22



### limited number of studies, there is some evi dence that Pb

- associated neurocognitive 23



### effects may be larger in magnitude among lower SES populations (Section 6.3.7 ). There 24



### is also evidence that some cognitive effects of prenatal Pb exposure may be transient and 25



### that recovery is greater among children reared in households with more optimal 26



### caregiving characteristics and in children whose concurrent blood Pb levels were low 27



### ( Bellinger et al., 1990 )

. In a meta

- analysis, Schwartz ( 1994 ) found that in studies in 28



### higher SES populations, blood Pb was associated with a greater decrement in IQ than in 29



### low SES populations 30February 2012 2

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### 2.9.6.7 Proximity to Pb Sources and Residenti al Factors

Proximity to an industrial Pb source or Superfund site likely contributes to higher Pb 1



### exposures ( U.S. EPA, 2006b )

. Recent studies show that soil Pb concentrations may be 2



### higher in some urban areas as a result of contemporaneous and/or historical Pb sources 3



### (Section 6.2.5 ). Consistent with findings of the 2006 Pb AQCD ( U.S. EPA, 2006b )

, child 4



### blood Pb level was significantly associated with renovation activities in older homes as 5



### well as housing factors ( e.g., year of construction, floor and windowsill condition). It has 6



### also been observed that windowsill dust Pb was significantly a ssociated with the presence 7



### of deteriorated indoor paint. Other studies of renovation activities involving removal of 8



### Pb paint have included measurements of highly elevated blood Pb among children and 9



### adult workers. Living in a home built prior to 1950, wh ere old home age is a surrogate for 10



### presence of Pb paint, has also been shown to be a significant predictor of blood Pb. 11



### (Section s 4.1.3.2 and 6.2.6 ). 12



### 2.9.6.8 Lifestyle Factors

Body mass index (BMI), obesity and alcohol consumption have been examined in 13



### epidemiologic and toxicological studies. Modifica tion of associations between Pb with 14



### mortality and HRV was not observed by BMI or obesity (Section 6.3.8 ). There is limited 15



### evidence on the potential for alcohol consumption as a modifier of Pb

- related effects 16



### (Section 6.3.9 ) and mixed findings on whether smoking modifies the relationshi p 17



### between Pb and health effects (Section 6.3.5 ). 18



### 2.9.6.9 Nutritional Factors

It is well established that diets sufficient in minerals such as calcium, iron , and zinc offer 19



### some protection from Pb exposure by preventing or competing with Pb for absorption in 20



### the GI tract (Section 6.1 ). The 2006 Pb AQCD included studies that indicated individuals 21



### with iron

- deficiency and malnourishment had greater inverse associations between Pb 22



### and cognition/intellect ( U.S. EPA, 2006b )

, and recent epidemiologic and toxicological 23



### studies continu e to observe greater Pb

- related health effects among individuals with low 24



### levels of iron (Section 6.3.10 ). Calcium intake from diet and vitamin D supplement can 25



### modify blood Pb levels in women of various ages. Calcium supplementation during 26



### pregnancy and lactation may decrease the amount of Pb to which the developing fetus of 27



### infant is exposed. The evidence for this seems especially strong for prote ction during 28



### pregnancy and more mixed for protective effects of calcium during lactation. There is 29



### little recent evidence available on the potential for zinc or other as modifiers of Pb

- related 30February 2012 2

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### health effects associations. A recent study in China reported that children who regularly 1



### consumed breakfast had lower blood Pb levels than those children that did not eat 2



### breakfast ( Liu et al., 2011b )

. Recent toxicological studies r indicate that diets designed to 3



### limit or reduce caloric intake and induce weight loss have been associated with increas ed 4



### blood Pb levels and an epidemiologic analysis reported that regular consumption of 5



### breakfast reduced blood Pb levels in children, compared with children who did not eat 6



### breakfast (Section 6.1 ). 7



### 2.9.6.10 Stress and Cognitive Reserve

Animal toxicology findings described in the 2006 Pb AQCD demonstrated interactions 8



### between Pb exposure and stress. Pb

- exposed animals reared in cages with enriched 9



### environments ( toys) perform better in the Morris water maze than their Pb

- exposed 10



### littermates who were reared in isolation. New findings indicate a potentiating effect of 11



### stress on behavior and memory at low

- dose Pb exposures. Although examined in a 12



### limited number of st udies, recent epidemiologic studies observed modification of the 13



### association between Pb and various nervous system and cardiovascular effects by 14



### stress

- level and also indicated that maternal self

- esteem may attenuate the negative 15



### effects observed of Pb on MDI and PDI scores. Toxicological studies have demonstrated 16



### that early life exposure to Pb and maternal stress can result in altered responses in 17



### multiple systems, including altered corticosterone and neurotransmitter levels. 18



### Additionally, toxicological st udies have demonstrated that immune stress also affects 19



### associations with Pb (Section 6.3.11 ). 20



### 2.9.6.11 Co

- exposure of Lead with Metals and Chemicals

Other exposures have also been studied to assess how they affected the uptake and 21



### absorption of Pb. Recent toxicological studies that have examined the addition of arsenic 22



### (As) to Pb and Cd mixtures report increases in bioavailability of Pb (Section 6.1 ). The 23



### 2006 Pb AQCD reported that the majority of studies examined other metals as potential 24



### confounders rather than effect measure modifiers ( U.S. EPA, 2006b )

. Recent 25



### epidemiologic studies have, however, begun to explore the possible interaction between 26



### Pb and other metals. These studies report some stronger associations between Pb and 27



### various health endpoints with co

- exposure to Cd, As and Mn (Section 6.3.13 ); some 28



### studies indicate that coexposures may increase bioavailability of Pb (Section 6.1 ). Since 29



### Pb is acid soluble, fluoridation may increase Pb concentration in water through leaching 30



### from pipes and Pb solder (Section 4.1.3.3 ) 31February 2012 2

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### 2.9.6.12 Summary of At

- Risk Populations

As shown in Table 2

- 9 ( Table 6

- 4 ) the most well

- substantiated at risk population for the 1



### effects of Pb expos ure is children. Evidence for all other factors was limited. Among 2



### children, the youngest age groups were observed to be most at risk of elevated blood Pb 3



### levels, with levels decreasing with increasing age of the children. Recent epidemiologic 4



### studies of i nfants/children detected increased risk of Pb

- related health effects, and this 5



### was supported by toxicological studies. Synaptic pruning, which is active throughout 6



### early childhood (ages 1

- 4 year s), may underlie the elevated risk of neurodevelopmental 7



### effec ts in young children to environmental exposures. Other factors that have been 8



### studied with regard to the influence on Pb

- related risk are listed in Table 2

- 9 below. 9



### Table 2

- 9 Summary of evidence for factors that potentially increase the risk of

lead

- related health effects

Factor Evaluated Potentially Related to Increased Risk

Age (Section 6.3.1 ) Children

Sex (Section 6.3.2 ) Males, a Females a

Genetics (Section 6.3.3 ) ALAD a , VDR a *, DRD4 a *, GSTM1 a , TNF

- α a , eNOS a , APOE a , HFE a

Pre

- existing Disease (Section 6.3.4 ) Autism a , Atopy ab , Hypertension b

Smoking (Section 6.3.5 ) Smokers a

Race/Ethnicity (Section 6.3.6 ) Non

- Hispanic Blacks a , Hispanics a

Socioeconomic Status (SES) (Section 6. 3.7 ) Low SES a

Nutrition (Section 6.3.10 ) Iron deficiency a

Stress (Section 6.3.11 ) High stress a

Cognitive Reserve (Section 6.3.12 ) Low cognitive reserve ab

Other Metals (Section 6.3.13 ) High/co

- exposure to Cd a , As a , Mn a

a Evidence for this factor was limited.

b Possible mediatorFebruary 2012 2

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## 2.10 Summary

Table 2

- 10 summarizes the main conclusions from the 2006 Pb AQCD and from this 1



### assessment, including causality determinations, regarding the health and ecological 2



### effects of Pb. 3



### Table 2

- 10 Summary of evidence from epidemiologic, animal toxicological and ecological studies on the effects associated with exposure to Pb

Outcome/Effect Conclusions from the 2006 Pb AQCD Conclusions from the (2012

- 2nd Draft) Pb ISA

Health Outcomes:

Nervous System Effects The 2006 Pb AQCD did not integrate the evidence across specific endpoints within the nervous system to make conclusions regarding role of Pb in causing effects for the organ system as a whole. Based most heavi ly on cognitive function decrements and behavioral problems in children, the collective body of evidence is sufficient to conclude that there is a causal relationship between Pb exposures and nervous system effects.

Neurocognitive Function and Learning Children:

The overall weight of the available evidence provides clear substantiation of neurocognitive decrements being associated in young children with blood

- Pb concentrations in the range of 5

- 10 μg/dL, and possibly lower. Prenatal, early childhood, lifetime average, and

concurrent blood Pb levels were associated with decrements in IQ and specific indices of learning and memory; however, concurrent blood Pb level was the strongest predictor. Recent epidemiologic studies in children continue to

demonst rate associations of concurrent blood Pb level with IQ decrements; most new evidence emphasizes associations of concurrent blood Pb levels with specific indices of neurocognitive function ( e.g., verbal skills, memory, learning visuospatial processing). The weight of evidence supports associations in populations with mean

blood Pb levels 2

- 7 μg/dL.

Adults :

Among environmentally

- exposed adults, bone Pb levels but not blood Pb levels were associated with poorer cognitive performance. These findings point to an effect of long

- term cumulative Pb exposure. Consistent with previous studies, the weight of evidence in

new studies indicates associations of cumulative Pb exposure metrics with cognitive performance in environmentally

- exposed adults. However, as the se outcomes are observed in adults with likely higher past Pb exposures, uncertainty exists as to the Pb exposure level, frequency, duration, and timing contributing to the observed

associations

Neurobehavioral Effects Children:

Several epidemiologic studies reported associations between Pb exposure and effects that ranged from inattention and aggression in children to delinquent

behaviors and criminal activities in adolescents and young adults. Most studies examined blood Pb leve ls measured earlier in childhood (means ~ 10 μg/dL), tooth Pb, or bone Pb. There was little examination of concurrent blood Pb levels. Uncertainty remained regarding whether Pb exposure was an independent predictor of neurobehavioral effects. Results from studies
of ADHD were inconclusive. Suggestive relationship for

both blood and bone Pb with withdrawn behavior and anxiety symptoms in children. Recent studies in children continue to support associations of Pb exposure with a range of effects, largely inat tention and hyperactivity, and also misconduct delinquent behavior. In new studies, the weight of evidence supports associations with concurrent blood Pb in populations with lower mean blood Pb levels (2

– 5 μg/dL) than those in previous studies. New evidenc e indicates associations of concurrent blood Pb levels with ADHD diagnosis and contributing diagnostic indices in populations with mean

blood Pb levels 2

- 4 μg/dL.February 2012 2

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– Do Not Cite or Quote Outcome/Effect Conclusions from the 2006 Pb AQCD Conclusions from the (2012

- 2nd Draft) Pb ISA

Neurobehavioral, Mood and Psychiatric Effects Adults:

Associations of Pb exposure with behavioral outcomes were not widely examined in environmentally

- exposed

adults. In the few available new studies of environmentally

exposed adults, blood and bone Pb levels are associated with symptoms of depression and anxiety.

Sensory Organ Function The selective action of Pb on retinal rod cells and bipolar
cells is well documented in earlier AQCDs. There was

coherence between the extensive animal and the limited available human literature reporting associations between concurrent blood Pb levels (po pulation means

7

- 12 μg/dL) and decreased auditory function in children. The limited available new epidemiologic studies on sensory organ function in children examined children with high blood Pb levels ((means > 30 μg/dL. A recent toxicological study foun d retinal effects in male rodents who had been exposed at gestation through 10 day s of age at exposures resulting in lower blood Pb levels (~12 μg/dL) than those at which effects had been previously reported.

Neurodegenerative Diseases In the limited body of epidemiologic studies, blood and

bone Pb levels were not associated with Alzheimer’s disease or Amyotrophic Lateral Sclerosis among environmentally

- exposed adults. Each study had
sufficient limitations. A few case

- control studies report associations be tween bone Pb levels and PD in environmentally

- exposed adults. Recent toxicological evidence suggests that early life Pb exposure may be associated with neurodegeneration in

adult animals.

Cardiovascular Effects The 2006 Pb AQCD did not integrate the evi dence across specific endpoints within the cardiovascular system to make conclusions regarding role of Pb in causing effects for the organ system as a whole. The weight of the evidence continues to support and expand upon the strong body of evidence that P b exposure is associated with increased blood pressure and hypertension in adults. The evidence is sufficient to conclude that there is a causal relationship between Pb exposures and cardiovascular effects; however, as these

outcomes are observed in adults with likely higher past Pb exposures, uncertainty exists as to the Pb exposure level, frequency, duration, and timing contributing to the observed

associations.

Blood Pressure A meta

- analysis of numerous epidemiologic studies estimated that a doubling o f blood Pb level ( e.g., from 5 to 10 μg/dL) was associated with a 1 mmHg increase in systolic BP and a 0.6 mmHg increase in diastolic BP.” Recent epidemiologic and toxicological studies continue to support associations between long

- term Pb exposure and

in creased BP. Associations of increased BP with blood and bone Pb concentrations are observed in populations with

lower mean blood Pb levels.

Hypertension Epidemiologic studies consistently demonstrated associations between Pb and incidence of hypertension with suggestive evidence that bone Pb may be associated with hypertension. Animal studies demonstrated that long

- term exposure to Pb resulted in hypertension that persisted after cessation of exposure. Recent studies, including those using bone Pb as a me tric of cumulative exposure, continue to demonstrate associations of hypertension with Pb levels in adults at lower population Pb concentrations. Recent studies have emphasized the interaction of cumulative exposure to Pb with other factors including stres s.

Cardiovascular Mortality The evidence for an association of Pb with cardiovascular mortality is limited but supportive. Recent studies address limitations of previous studies and provide additional evidence for an association of Pb with

cardiovascular mortality in adults. Specific causes of mortality that were associated with Pb could be related to increased BP and hypertension.

Renal Effects The 2006 Pb AQCD did not integrate the evidence across specific endpoints within the renal system to

make conc lusions regarding role of Pb in causing effects for the organ system as a whole. Circulating and cumulative Pb was associated with longitudinal decline in renal function in adults. Toxicological studies

demonstrated that initial accumulation of absorbed Pb occurred primarily in the kidneys and noted a hyperfiltration phenomenon during the first 3 months of exposure, followed by decrements in kidney function. Recent epidemiologic and toxicological studies evaluated in the current review support or expand up on the strong body of evidence indicating that Pb exposure is associated with kidney dysfunction ( e.g., lower creatinine clearance, higher serum creatinine, and lower GFR) in nonoccupationally

- exposed adults. The evidence is
sufficient to conclude that the re is a causal relationship between Pb exposures and renal health effects; however,

as these outcomes are most often observed in adults with likely higher past Pb exposures, uncertainty exists as to the Pb exposure level, frequency, duration, and timing

co ntributing to the observed associations.February 2012 2

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- 2nd Draft) Pb ISA

I mmune System Effects The 2006 Pb AQCD did not integrate the evidence across specific endpoints within the immune system to make conclusions regarding role of Pb in causing effects for the organ system as a whole. The consistency and coherence of findings across the continuum of related immune parameters that demonstrate a stimulation of Th2 responses in toxicological studies combined with the supporting epidemiologic evidence in
children are sufficient to conclude that there is a causal relationship between Pb exposures and immune system
effects.

Children:

Several epidemiologic studies suggested that Pb exposure may be associated with effects on cellular and humoral immunity in children. The principal effects

demonstrated were decreases in T cell abundance and increases in serum immunoglobulin E levels with concurrent blood Pb levels > 10 μg/dL. Toxicological evidence supported these findings with extensive evidence for prenatal and early postnatal Pb exposures skewing toward Th2 cytokine production and affecting

downstream events such as inflammation and decreased responses to antigens ( e.g., delayed type hypersensitivity, bacterial resistance). A small body of new studies supports the previous

evidence that Pb exposure is associated with immune
effects in children. New studies in children added to the evidence for associations of blood Pb levels with asthma, allergy, and IgE. The consistency and coherence of findings among related immune effects that support a shift from a Th1 to a Th2 phenotype establishes the biological plausibility for epidemiologic observations of associations with asthma, allergy and inflammation

- related effects in other organ systems.

Adults:

In the large body of studies in occupationally

- exposed adults, the most consistent findings were reduced neutrophil functionality in workers with blood Pb levels > 30 μg/dL. Pb exposure

- associated immune effects were not widely examined in environmentally

- exposed adults.

Several toxicolo gical studies found a Pb

- induced shift to Th2 cytokine production and a hyperinflammatory phenotype of macrophages in adult animals with long

term (> weeks) exposure. A small body of available studies provides new evidence

for immune effects in environment ally

- exposed adults. Specific endpoints varied among studies but were

consistent with increased inflammation. Associations were observed in populations with a wide range of mean concurrent blood Pb levels (3

- 22 μg/dL). However, as these

outcomes are observ ed in adults with likely higher past Pb exposures, uncertainty exists as to the Pb exposure level, frequency, duration, and timing contributing to the observed

associations

. A few available toxicological studies find Pb

associated immune effects in adult mice.

Heme Synthesis and RBC Function Children:

Pb exposure was associated with disruption in heme synthesis with increases in blood Pb levels of approximately 20 μg/dL sufficient to halve ALAD activity

and inhibit ferrochelatase. Risk of clinical anemia in children becomes apparent at high blood Pb levels: 10% probability of anemia was estimated to be associated with ~ 20 μg/dL Pb at 1 year of age, 50 μg/dL at 3 years of age, and 75 μg/dL at 5 years of age. Recent epidemiologic studies provide stro ng evidence that exposure to Pb is associated with numerous deleterious effects on the hematological system in children, including altered hematological parameters (Hb, MCV, MCH, RBC count), perturbed heme synthesis mediated through

decreased ALAD and ferr ochelatase activities, and oxidative stress. Associations were observed in populations with mean (or median) blood Pb concentrations as low as approximately 5 μg/dL.

Adults:

Pb exposure was associated with disruption in heme synthesis with increases in blood Pb levels of approximately 20 μg/dL sufficient to halve ALAD activity and inhibit ferrochelatase. Exposures to Pb resulting in blood concentrations < 40 μg/dL appear to be tolerated without decreases in blood hemoglobin or hematocrit,

however chan ges in erythropoiesis do occur at these

blood levels. Recent epidemiologic studies provide strong evidence exposure to Pb is associated with numerous deleterious effects on the hematological system, including altered hematological parameters (Hb, MCV, MCH, RBC count), perturbed heme synthesis mediated through decreased ALAD and ferrochelatase activities, decreased erythropoiesis, and oxidative stress.

Reproductive Effects and Birth Outcomes The 2006 Pb AQCD did not integrate the evidence across specific endpoints within the reproductive system to make conclusions regarding role of Pb in causing effects for the organ system as a whole. The collective body of evidence integrated across epidemiologic and toxicological studies with a focus on the strong relat ionship observed with negative effects on sperm and delayed pubertal onset is sufficient to conclude that there is a causal relationship between Pb exposures and reproductive and developmental effects.

Children:February 2012 2

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- 2nd Draft) Pb ISA

No epidemiologic studies of delayed onset of puberty

were reviewed. Recent toxicological and epidemiologic studies provide strong evidence for delayed onset of puberty in males and females. The weight of evidence for delayed onset of puberty was among children ages 6

- 18 years with
mean/media n blood Pb levels less than 5 μg/dL.

Adults:

Epidemiologic evidence suggested small associations between Pb exposure and male reproductive outcomes including perturbed semen quality and increased time to pregnancy. Associations between Pb exposure and male reproductive endocrine status were not observed in the occupational populations studied. Toxicological studies provided evidence that Pb produced effects on male and female reproductive junction and development and disrupts endocrine function. Recent toxicological and epidemiologic studies provide strong evidence for effects on sperm. Evidence on pregnancy outcomes was inconsistent and less coherent across disciplines for preterm birth, spontaneous abortion, low birth weight, birth defects, hormonal i nfluence and fecundity.

Cancer Epidemiologic studies of highly exposed occupational populations suggest a relationship between Pb and cancers of the lung and the stomach; however the evidence is limited by the presence of various potential confounders, i ncluding metal coexposures ( e.g., to arsenic, cadmium), smoking, and dietary habits. The
2003 NTP and 2004 IARC reviews concluded that Pb and Pb compounds were probable carcinogens, based
on limited evidence in humans and sufficient evidence in

animals. Ba sed on animal data and inadequate human data Pb and Pb compounds would be classified as likely carcinogens according to the EPA Cancer Assessment Guidelines for Carcinogen Risk Assessment. The toxicological literature continues to provide the strongest evi dence for Pb exposure and cancer with supporting evidence provided by the epidemiologic literature. Epidemiologic studies of cancer incidence and mortality reported inconsistent results.The evidence i is sufficient to conclude that there is a likely causal relationship between Pb exposure and cancer.

Ecological/Welfare Effects:

Physiological Stress Terrestrial Organisms:

Pb exposure may cause lipid peroxidation and changes in glutathione concentrations. There are species
differences in resistance to oxidative stress. Recent studies continue to support previous associations of Pb exposure with physiological stress. New evidence includes upregulation of antioxidant enzymes, production of reactive oxygen species and increased lipid peroxidation

associate d with Pb exposure in additional species of terrestrial plants, invertebrates and vertebrates. Experimental exposures increasing from background concentrations to concentrations higher than near point sources result in increasing effects. The evidence is

s ufficient to conclude a causal relationship between Pb exposure and physiological stress in terrestrial plants,

invertebrates and vertebrates.

Aquatic Organisms:

Pb exposure associated with alterations in enzymes involved in physiological stress responses. Recent studies continue to support previous associations of Pb exposure with physiological stress. New evidence includes upregulation of antioxidant enzymes, production of reactive oxygen species and increased lipid peroxidation

associated with Pb exposure in additional species of aquatic plants, invertebrates and vertebrates and decreased glycogen levels in freshwater snails. Observed effects generally occurred at concentrations that typically
exceed Pb levels in U.S. waters with limited evidenc e for effects associated with Pb at polluted sites. The evidence is sufficient to conclude a causal relationship between Pb exposure and physiological stress in aquatic plants.February 2012 2

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- 2nd Draft) Pb ISA

Hematological Effects Terrestrial Organism p s:

Pb effects on heme synthesis were documented in the
1986 Pb AQCD and continue to be studied in terrestrial biota. Changes in ALAD are not always related to adverse effects but may simply indicate exposure. The linkage between effects of Pb on blood paramet ers is well documented, however, the linkage between hematological indicators and ecologically relevant effects

is less well understood. Consistent with previous studies, the weight of the evidence in new studies continues to support findings of Pb

effect s on heme synthesis and ALAD enzyme activity. New studies in birds near historical mining areas and altered serum profiles and blood cell counts in vertebrates provide evidence for additional species and hematological endpoints potentially effected by Pb. The evidence is sufficient to conclude a causal relationship between Pb exposure and hematological effects in invertebrates and vertebrates in terrestrial ecosystems.

Aquatic Organisms:

In metal impacted habitats, ALAD is a recognized
biomarker of Pb exposure. Changes in ALAD are not always related to adverse effects but may simply indicate exposure. In fish, Pb effects on blood chemistry have been documented with Pb concentrations ranging from 100 to 10,000 μg Pb/L. Consistent with previous studies, t he weight of the evidence in new studies continues to support findings of Pb effects on ALAD and expands this evidence to additional species of bacteria, invertebrates, and vertebrates as well

as new studies on altered blood cell counts in vertebrates.

The evidence is sufficient to conclude a causal relationship between Pb exposure and hematological effects in invertebrates and vertebrates in aquatic ecosystems.

Neurobehavioral

Effects Terrestrial Organisms:

Exposure to Pb in laboratory studies and simulated ecosystems may alter species competitive behaviors, predator

- prey interactions and contaminant avoidance

behaviors. Recent studies continue to support previous evidence that Pb exposure is associated with behavioral alterations. New

studies ident ify possible molecular targets for Pb neurotoxicity in invertebrates and there is new evidence in a few invertebrate and vertebrate species for behavioral effects associated with Pb exposure ( i.e., feeding and escape behaviors). The evidence is sufficient to conclude that there is a likely causal relationship between Pb exposure and neurobehavioral effects in terrestrial

invertebrates and vertebrates.

Aquatic Organisms:

Exposure to Pb has been shown to affect brain receptors in fish and may alter avoidance behaviors and predator

prey interactions. Recent studies continue to support previous evidence that Pb exposure is associated with behavioral alterations. New studies identify possible molecular targets for Pb neurotoxicity in fish and provide ad ditional evidence for Pb effects on behaviors in aquatic organisms that may impact predator avoidance (swimming). The evidence is sufficient to conclude that there is a likely causal relationship between neurobehavioral effects in aquatic invertebrates

and vertebrates.February 2012 2

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- 2nd Draft) Pb ISA

Developmental and Reproductive Effects Terrestrial Organisms:

No information on reproduction in plants. There are an insufficient number of studies that consider Pb effects on plant reproduction. Thus the evidence is inadequate to infer a causal relationship for terrestrial plants

Limited evidence in invertebrates and vertebrates. Recent studies in a few taxa expand the evidence for Pb effects on developmental and reproductive endpoints for

invertebrates and vertebrates at concentrations that generally exceed Pb levels in U.S. soils. In some organisms, exposure

- dependent responses in development and reproductive outcomes are observed in experiments where exposure increases from background level to levels greater than near point sources. D at a on terrestrial species is supported by toxicological data from mammals in the

context of human health research. The evidence is

sufficient to conclude a causal relationship in terrestrial

invertebrates and vertebrates.

Aquatic Organisms:

No reviewed studies on reproductive effects in aquatic plants.

Reproductive and developmental effects reported in a few species of invertebrates at <50 μg Pb/L and in fish at <150 μg Pb/L Recent evidence supports previous findings of reproductive

and deve lopmental effects of Pb in aquatic biota and differential lifestage response at near ambient concentrations of Pb in some organisms. The evidence is inadequate to conclude a causal relationship for plants, and sufficient to conclude a causal relationship i n invertebrates and vertebrates.

Growth Terrestrial Organisms:

Pb inhibits photosynthesis and respiration in plants.

Limited evidence for growth effects in soil invertebrates,

avian and mammalian consumers. Recent studies support previous findings of Pb effects on plant growth with some evidence for exposure

- dependent decreases in some plant species’ biomass in soil amended with 30 mg Pb/kg soil. The evidence is adequate to conclude a causal relationship in p lants.

Limited studies considered effects on growth in invertebrates and vertebrates. The evidence is inadequate to conclude a causal relationship for terrestrial

invertebrates and vertebrates.

Aquatic Organisms:

Evidence for growth effects in algae, aquatic plants and aquatic invertebrates

Most primary producers experience EC 50 s for growth in the range of 1,000 to 100,000 μg Pb/L The weight of the evidence continues to support growth effects of Pb in aquatic plants and invertebrates.Recent

studies on growth in invertebrates find effects of Pb at lower concentrations than previously reported. The evidence is sufficient to conclude a causal relationship between Pb exposure and growth in aquatic plants and invertebrates. Growth inhibition in one species o f freshwater snail was observed at <4 μg Pb/L in juveniles.

Lowest genus mean chronic value for Pb reported at 10 μg
Pb/L in a freshwater mussel.

The evidence is inadequate to conclude a causal relationship between Pb exposure growth effects in aquatic

ver tebrates.February 2012 2

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- 2nd Draft) Pb ISA

Survival Terrestrial Organisms:

No information on mortality in plants. Effects of Pb on

invertebrates and vertebrates include decreased survival.

In terrestrial and avian species toxicity was observed in laboratory studies over a wide range of doses (<1 to >1,000 mg Pb/kg body weight • day) ( U.S. EPA,

2005b )

. Recent studies i n invertebrates and vertebrates support previous associations between Pb exposure and mortality. The evidence is inadequate to conclude a causal relationship between Pb exposure and survival for terrestrial plants. The evidence is sufficient to conclude a causal relationship in terrestrial vertebrates and

invertebrates.

Aquatic Organisms:

No studies reviewed on mortality in plants at current
concentrations of Pb in the environment.

Pb impacted survival of some aquatic invertebrates at

< 20 μg Pb/L dependent upon water quality variables ( i.e., DOC, hardness, pH).

Range of 96

- hour LC 50 values in fathead minnow: 810

- >5,400 μg Pb/L The weight of evidence continues to support Pb effects on survival of aquatic invertebrates and vertebrates and indicates that there are effects in a few species at lower concentrations than previously reported.

New evidence for effects in a few invertebrates: at

<20 μg Pb/L

New evidence in fish for impacts to survival at <100 μg Pb/L dependent upon water quality pa rameters and lifestage

96

- hour LC 50 values as low as 41 μg Pb/L in fathead
minnows tested in natural waters from across the U.S.

The evidence is inadequate to conclude a causal relationship between Pb exposure and survival for aquatic plants. The evidenc e is sufficient to conclude a causal relationship between Pb exposure and survival for aquatic

invertebrates and vertebrates.

Community and Ecosystem Level Effects Terrestrial Ecosystems:

Effects of Pb difficult to interpret because of the presence of other stressors including metals. The 1986 Pb AQCD reported shifts toward Pb

- tolerant communities at 500 to 1,000 mg Pb/kg soil.

In the 2006 Pb AQCD, decreased species diversity and changes i n community composition were observed in ecosystems surrounding former smelters. New evidence for effects of Pb in soil microbial communities add to the body of evidence for effects at higher levels of biological organization. However, most

evidence for Pb toxicity to terrestrial biota is from single

species assays. Uncertainties exist in generalizing effects

observed under small

- scale, predicted conditions up to effects at the ecosystem level however, uptake of Pb into terrestrial organisms and subsequent effects on reproduction, growth and survival at the species level is likely to lead to effects at the population, community and ecosystem level. The evidence is sufficient to conclude that there is a likely causal relationship between Pb exposure

and the a lteration of species richness, species composition and biodiversity in terrestrial ecosystems.

Aquatic Ecosystems:

Most evidence of community and ecosystem level effects is from near point sources, usually mining effluents.

Effects of Pb difficult to interpret because of the presence of other stressors including metals.

Generally, there is insufficient information available for single materials in controlled studies to permit evaluation of specific impacts on higher levels of organization (beyond the individual organism). New evidence for Pb effects on sediment

- associated and aquatic plant communities add to the body of evidence of effects at higher levels of biological organization. However, most evidence for Pb toxicity to aquatic biota is from singl e

species assays. Uncertainties exist in generalizing effects

observed under small

- scale, predicted conditions up to effects at the ecosystem

- level however, uptake of Pb into aquatic organisms and subsequent effects on reproduction, growth and survival at the species level is likely to lead to effects at the population, community and ecosystem level. The evidence is sufficient to conclude that there is likely to be a causal relationship between Pb exposure and the alteration of species richness, species com position and biodiversity in aquatic ecosystems.

1February 2012 2

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