May 2011 i DRAFT

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# Chapter 2 Contents

Chapter 2. Integrative Health and Ecological Effects Overview

________________________________ ________________ 2

- 1

2.1. Ambient Lead: Source to Concentration

________________________________ _________________________ 2

- 2

2.1.1. Sources, Fate and Transport of Ambient Lead

________________________________ _____________ 2

- 2

2.1.2. Monitoring and Concentrations of Ambient Air Lead

________________________________ _______ 2

- 3

2.1.3. Ambient Lead Concentrations in Non

- Air Media and Biota

________________________________ __ 2

- 5

2.2. Exposure to Ambient Lead

________________________________ ________________________________ ____ 2

- 5

2.3. Toxicokinetics

________________________________ ________________________________ _____________ 2

- 7

2.4. Lead Biomarkers

________________________________ ________________________________ ___________ 2

- 8

2.5. Healt h Effects

________________________________ ________________________________ ______________ 2

- 9

Table 2

- 1. Summary of causal determinations between exposure to Pb and health

outcomes

________________________________ ___________________________ 2

- 10

2.5.1. Neurological Effects

________________________________ ________________________________ 2

- 10

Figure 2

- 1. Snapshot of evidence for the spectrum of effects to the nervous system associated with Pb exposure. Green=animal toxicological studies (left side); purple=epidemiological studies (right side).

________________________ 2

- 13

2.5.2. Cardiovascular Effects

________________________________ ______________________________ 2

- 13

2.5.3. Renal Effects

________________________________ ________________________________ _____ 2

- 15

2.5.4. Immune System Effects

________________________________ _____________________________ 2

- 17

2. 5.5. Heme Synthesis and RBC Function

________________________________ ____________________ 2

- 18

2.5.6. Reproductive Effects and Birth Outcomes

________________________________ _______________ 2

- 20

2.5.7. Effects on Other Organ Systems

________________________________ ______________________ 2

- 21

2.5.8. Cancer

________________________________ ________________________________ __________ 2

- 23

2.5.9. Human Health Effects and Corresponding Blood Pb Levels

________________________________ _ 2

- 24

Table 2

- 2. Summary of Pb

- induced health effects in children and the lowest mean blood Pb level in the population(s) studied

______________________________ 2

- 25

Table 2

- 3. Summary of Pb

- induced health effects in adults and the lowest mean blood Pb level in the population(s) studied

________________________________ ___ 2

- 26

2.6. Ecological Effects

________________________________ ________________________________ _________ 2

- 26

Table 2

- 4. Summary of causal determinations for Pb in plants, vertebrates and

invertebrates

________________________________ _____________________ 2

- 27

2.6.1. Summary of Terrestrial Ecosystem Effects

________________________________ ______________ 2

- 28

2.6.2. Summary of Aquatic Ecosystem Effects

________________________________ ________________ 2

- 30

2.6.3. Bioaccumulation of Lead in Terrestrial and Aquatic Biota as it Affects Ecosystem Services

________ 2

- 33

2.6.4. Mortality

________________________________ ________________________________ _________ 2

- 34

2.6.5. Growth Effects

________________________________ ________________________________ ____ 2

- 35

2.6.6. Physiological Stress

________________________________ ________________________________ 2

- 35

2.6.7. Hematological Effects

________________________________ ______________________________ 2

- 36

2. 6.8. Developmental and Reproductive Effects

________________________________ _______________ 2

- 37

2.6.9. Neurobehavioral Effects

________________________________ _____________________________ 2

- 38

2.6.10. Community and Ecosystem Level Effects

________________________________ _______________ 2

- 39

2.6.11. Ecological Effects and Corresponding Pb Concentrations

________________________________ ___ 2

- 40

2.7. Integration of Health and Ecological Effects Overview

________________________________ _____________ 2

- 41

Table 2

- 5. Summary of Causal Determinations for Health and Ecological Effects

________ 2

- 42

2.7.1. Modes of Action Relevant to Downstream Health and Ecological Effects

______________________ 2

- 42

Table 2

- 6. Related human health effects resulting from the MOAs of Pb and the lowest level eliciting the MOA

________________________________ _____________ 2

- 43

2.8. Policy Relevant Considerations and Human Health

________________________________ ________________ 2

- 46

2.8.1. Air

- to

- Blood Relationships

________________________________ __________________________ 2

- 46May 2011 ii DRAFT

– DO NOT CITE OR QUOTE Table 2

- 7. Summary of Estimated Slopes for Blood Pb to Air Pb Re lationships in

Children

________________________________ ________________________ 2

- 48

2.8.2. Concentration

- Response Functions

________________________________ ____________________ 2

- 48

Figure 2

- 2. Comparison of associations between blood Pb and cognitive function among

various blood Pb strata.

________________________________ ____________ 2

- 49

2.8.3. Timing and Duration of Exposure

________________________________ _____________________ 2

- 52

Figure 2

- 3. Associations of cognitive function in children with different degrees of changes in blood Pb levels over time.

________________________________ __ 2

- 53

2.8.3.1. Persistence of Effects

________________________________ _______________________ 2

- 54

2.8.4. Susceptible Populations and Lifestages

________________________________ _________________ 2

- 54

2.8.4.1. Children

________________________________ ________________________________ _ 2

- 55

2.8.4.2. Adu lts

________________________________ ________________________________ ___ 2

- 55

2.8.4.3. Sex

________________________________ ________________________________ _____ 2

- 55

2.8.4.4. Race and Ethnicity

________________________________ _________________________ 2

- 56

2.8.4.5. Socioeconomic Status

________________________________ _______________________ 2

- 56

2.8.4.6. Genes

________________________________ ________________________________ ___ 2

- 57

2.8.4.7. Pre

- exi sting Conditions

________________________________ _____________________ 2

- 57

2.8.4.8. Nutrition and Lifestyle Factors

________________________________ ________________ 2

- 57

2.8.4.9. Stress and Cognitive Reserve

________________________________ _________________ 2

- 58

2.8.4.10. Co

- exposure of Lead with Metals or Other Chemicals

______________________________ 2

- 58

2.9. Summary

________________________________ ________________________________ ________________ 2

- 59

Table 2

- 8. Summary of evidence from epidemiologic, animal toxicological and ecological studies on the effects associated with exposure to Pb

______________ 2

- 60 Chapter 2 References

________________________________ ________________________________ _____________ 2

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# Chapter 2. Integrative Health and Ecological Effects Overview

The subsequent chapters of this ISA will present the most policy relevant information related to this 

### 1

review of the science supporting the NAAQS for Pb. This chapter integrates the key findings from the 

### 2

d isciplines evaluated in this current assessment of the Pb scientific literature, which includes studies of Pb 

### 3

sources, fate and transport of Pb, ambient air concentrations, exposure assessments, toxicokinetics, 

### 4

biomarkers and models of Pb burden, health (e .g., both toxicology and epidemiology), and ecological 

### 5

effects of Pb. The EPA framework for causal determinations described in Chapter 1 has been applied to 

### 6

the body of scientific evidence in order to collectively examine the health and ecological effects attributed 

### 7

to Pb exposure in a two

- step process. The first step is to establish causal relationships followed by 

### 8

identification of concentration

- response relationships 

### 9

As described in Chapter 1, EPA assesses the results of recent relevant publications, bui lding upon 

### 10

evidence available during the previous NAAQS reviews, to draw conclusions on the causal relationships 

### 11

between relevant pollutant exposures and health or environmental effects. This ISA uses a five

- level 

### 12

hierarchy that classifies the weight of ev idence for causation: 

### 13

 Causal relationship 

### 14

 Likely to be a causal relationship 

### 15

 Suggestive of a causal relationship 

### 16

 Inadequate to infer a causal relationship 

### 17

 Not likely to be a causal relationship 

### 18

Beyond judgments regarding causality are questions relev ant to quantifying health or 

### 19

environmental risks based on the understanding of the quantitative relationships between pollutant 

### 20

exposures and health or ecological effects. Once a determination is made regarding the causal relationship 

### 21

between the pollutant and outcome category, important questions regarding quantitative relationships 

### 22

include: 

### 23

 What is the concentration

- response, exposure

- response, or dose

- response relationship in the 

### 24

human population? 

### 25

Note: Hyperlinks to the reference citations throughout this document will take you to the NCEA H ERO database (Health and Environmental Research Online) at http://epa.gov/hero . HERO is a database of scientific literature used by U.S. EPA in the process of developing science
assessments such as the Integrated Science Assessments (ISA) and the Integrated Ris k Information System (IRIS)

.May 20 11 2

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– DO NOT CITE OR QUOTE  What exposure conditions (dose or exposure, exposure pat hways, duration and pattern) are 

### 1

important? 

### 2

 What populations and lifestages appear to be differentially affected i.e., more susceptible to 

### 3

effects? 

### 4

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

### 5

functions, etc.) appear to be affected or are more sensitive to effects? 

### 6

To address these questions, in the second step of the EPA framework, the entirety of quantitative 

### 7

evidence is evaluated to identify and characterize potential concentration

- response relationships. This 

### 8

requ ires the evaluation of the levels of the pollutant and the exposure durations at which effects were 

### 9

observed for exposed populations including potentially susceptible populations. 

### 10

This chapter summarizes and integrates the newly available scientific evide nce that best informs 

### 11

consideration of the policy

- relevant questions that frame this assessment, presented in Chapter 1. 

### 12

Section 2.1 discusses the trends in ambient Pb sources and concentrations, including the fate and transport 

### 13

of Pb in the environment, a nd provides a brief summary of the topics covered. Section 2.2 presents the 

### 14

evidence regarding exposure to ambient Pb and describes air

- related Pb exposure pathways. Section 2.3 

### 15

provides a discussion of the toxicokinetics of Pb and Pb biomarkers are discus sed in Section 2.4. 

### 16

Section 2.5 summarizes effects of Pb on specific health endpoints and Section 2.6 summarizes the 

### 17

evidence relating to the ecological effects of Pb. Section 2.7 integrates the scientific evidence across 

### 18

various health and ecological endp oints highlighting common modes of action where applicable. Finally, 

### 19

Section 2.8 provides a discussion of policy relevant considerations including air

- to

- blood relationships, 

### 20

concentration

- response relationships, timing and duration of exposure and suscept ible populations. 

### 21

Section 2.9 is a summary of the health and ecological effects of Pb. 

### 22



# 2.1. Ambient Lead : Source to Concentration

2.1.1. Sources, Fate and Transport of Ambient Lead

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

### 23

2006 Pb AQCD ( U.S. EPA, 2006 ) , which documented the decline in ambient air Pb emissions following 

### 24

the ban on alkyl

- Pb additives for on

- road gasoline. Pb emissions declined by 98% from 1970 to 1990 and 

### 25

then by an additional 77% from 1990 to 2008, at which time emissions were 1,200 tons per year. Data 

### 26

from the 2008 National Emissions Inventory (NEI) ( U.S. EPA, 2011 ) illustrate that piston engine aircraft 

### 27

emissio ns now comprise the largest share (~49%) of total atmospheric Pb emissions; the 2008 NEI 

### 28

estimated that 590 tons of Pb were emitted from this source. Other sources of ambient air Pb, beginning 

### 29

with the largest, include metals processing, fossil fuel combus tion, other industrial sources, roadway 

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– DO NOT CITE OR QUOTE related sources, and historic Pb. Chemical speciation of Pb had also been fairly well characterized in the 

### 1

2006 Pb AQCD ( 2006 ) . Estimates from the 1986 Pb AQCD ( U.S. EPA, 1986

, 2006 ) for organic 

### 2

automotive Pb emissions provides an upper bound fo r organic vapor emissions of 20% of total Pb 

### 3

dibromide and Pb bromide emissions from piston engine aircraft. Recent speciation studies of smelting 

### 4

and battery

- recycling operations have shown that Pb sulfide and Pb sulfates are abundant within the 

### 5

emissions mixture for such industrial operations. 

### 6

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

### 7

atmospheric Pb is primarily associated with fine particulate matter (PM). Global atmospheric Pb 

### 8

deposition peaked in the 1970 s, followed by a more recent decline. On a local scale, Pb concentrations in 

### 9

soils (including urban areas where historic use was widespread) can be substantial, and coarse Pb

- bearing 

### 10

PM experiences cycles of deposition and resuspension that serve to distri bute it. Both wet and dry 

### 11

deposition are important removal mechanisms for atmospheric Pb. Because Pb in fine particles is 

### 12

typically fairly soluble, wet deposition is more important for fine Pb. In contrast, Pb associated with 

### 13

coarse particles is usually in soluble, and removed by dry deposition. However, local deposition fluxes are 

### 14

much higher near local industrial sources and a substantial amount of emitted Pb is deposited near 

### 15

sources, leading to high soil Pb concentrations. Resuspension by wind and traffi c can be an important 

### 16

source of airborne Pb near sources where Pb occurs in substantial amounts in surface dust. 

### 17

Environmental distribution of Pb occurs mainly through the atmosphere, from where it is deposited 

### 18

into surface waters and soil. Pb associated w ith coarse PM deposits to a great extent near sources, leading 

### 19

to high soil concentrations, while fine Pb

- bearing PM can be transported long distances, leading to 

### 20

contamination of remote areas. Surface waters act as an important reservoir, with Pb lifetime s largely 

### 21

controlled by deposition and resuspension of Pb in sediments. Substantial amounts of Pb from vehicle 

### 22

wear and building materials can also be transported by runoff waters without becoming airborne. Pb 

### 23

containing sediment particles can be remobiliz ed into the water column, and sediment concentrations tend 

### 24

to follow those in overlying waters. 

### 25



## 2.1.2. Monitoring and Concentrations of Ambient Air Lead

In recognition of the role of all PM sizes in ambient air Pb exposures, including the ingestion of 

### 26

particles deposited onto surfaces, the indicator for the Pb NAAQS is Pb in total suspended particulate 

### 27

(Pb

- TSP). Although there is a lower rate of error in estimating ambient Pb from Pb

- PM 10 monitoring than 

### 28

from Pb

- TSP monitoring, the Pb

- TSP indicator was retained i n 2008 because ingestion after deposition in 

### 29

the upper respiratory tract was considered an important component of Pb exposure. A new federal 

### 30

reference method (FRM) for Pb

- PM 10 has been implemented in which ambient air is drawn through an 

### 31

inertial particle size separator for collection on a polytetrafluor o ethylene (PTFE) filter. Several FEMs 

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– DO NOT CITE OR QUOTE have also been approved. The FRM is based on flame AAS. ICPMS is under consideration as a new FRM 

### 1

for Pb

- TSP. 

### 2

Monitoring for ambient Pb levels is required for all areas where Pb levels have been shown or are 

### 3

expected to contribute to maximum concentrations of 0.10 μg/m3 or greater over a 3

- year time period. Pb 

### 4

is monitored routinely at state and local air monitoring stations (SLAMS) that report data used for 

### 5

NAAQS complia nce to the air quality system (AQS) database

. Pb monitoring requirements have 

### 6

experienced several changes since publication of the 2006 Pb AQCD ( U.S. EPA, 2006 ) . In addition to 

### 7

FRM monitoring, Pb is also routinely measured in smaller particle fractions in th e chemical speciation 

### 8

network (CSN), interagency monitoring of protected visual environment (IMPROVE), and the national 

### 9

air toxics trends station (NATTS) networks, and is planned for the national core multipollutant monitoring 

### 10

network (NCore) network. Whil e monitoring in multiple networks provides extensive geographic 

### 11

coverage, measurements between networks are not directly comparable in all cases because different 

### 12

particle size ranges are sampled in different networks. Depending on monitoring network, Pb i s monitored 

### 13

in TSP, PM 10 , or PM 2.5 . Monitors reporting to the AQS were considered for the purpose of this ISA to be 

### 14

source oriented if they were designated in AQS as source oriented

, or they were located within 1 mile of a 

### 15

0.5 ton per year or greater sourc e, as noted in the 2005 NEI ( U.S. EPA, 2008 ) . Non

- source oriented 

### 16

monitors were those monitors not considered to be source oriented. 

### 17

Ambient air Pb concentrations have declined drastically ove r the period 1980

- 2009. The median 

### 18

annual concentrations have dropped by 97% from 0.87 μg/m 3 in 1980 to 0.025 μg/m 3 in 2009. While the 

### 19

sharpest drop in Pb concentration occurred during 1980

- 1990, a declining trend was observed between 

### 20

1990 and 2009. Compar ed to 1980

- 1990, a smaller reduction was observable among source oriented Pb 

### 21

concentration (56%) and non

- source oriented Pb data (51%) for 2000

- 2009. 

### 22

AQS data for source oriented and non

- source oriented monitoring were analyzed for 2007

- 2009. 

### 23

For source or iented monitoring, the three

- month rolling average was measured to be above the level of 

### 24

the NAAQS in fourteen counties across the U.S. Pb concentrations, seasonal variations, inter

- monitor 

### 25

correlations, and wind data were analyzed for six counties: Los Angeles County, CA; 

### 26

Hillsborough /Pinellas Count ies , FL; Cook County, IL; Jefferson County, MO; Cuyahoga County, OH; and 

### 27

Sullivan County , TN. Spatial and temporal variability of Pb concentrations in each county were 

### 28

commonly high. Meteorology, distance from sources, and positioning of sources with respect to the 

### 29

monitors all appeared to influence the level of concentration variability acro ss time and space. PM size 

### 30

distribution also influenced how far the particle will travel upon initial emission or resuspension before 

### 31

being deposited. Additionally, resuspension and urban background levels of Pb were uncertain influential 

### 32

factors of ambien t Pb concentrations. Given variability in these conditions, it was very difficult to predict 

### 33

how Pb concentration varies over time and space. This was consistent with field studies to characterize Pb 

### 34

concentrations that were described in the literature. 

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– DO NOT CITE OR QUOTE Si ze distribution of Pb

- bearing PM was demonstrated to vary substantially for several studies 

### 1

presented, depending on the nature of Pb sources and proximity of the monitors to the Pb sources. 

### 2

Variation in the correlation of size fractionated Pb samples among different land use types may be 

### 3

explained by differences in sources across land use types. Additionally, Pb concentrations exhibited 

### 4

varying degrees of association with other criteria pollutant concentrations. Overall, Pb was moderately 

### 5

associated with PM 2.5 , PM 10 and NO 2 . Pb was moderately associated with CO in fall and winter only. The 

### 6

poorest associations were observed between Pb and O 3 . Among trace metals, the strongest association was 

### 7

with Zn. Br, Cu, and K concentrations also exhibited moderate asso ciations with Pb concentrations. Such 

### 8

correlations may suggest some common sources affecting the concentrations of various pollutants. 

### 9



## 2.1.3. Ambient Lead Concentrations in Non

- Air Media and
Biota

Atmospheric deposition has led to measurable Pb concentrations obs erved in rain, snowpack, soil, 

### 10

surface waters, sediments, agricultural plants, livestock, and wildlife across the world, with highest 

### 11

concentrations near Pb sources, such as metal smelters. After the phase

- out of Pb from on

- road gasoline, 

### 12

Pb concentrations have decreased considerably in rain, snowpack, and surface waters. Declining Pb 

### 13

concentrations in tree foliage, trunk sections, and grasses have also been observed. In contrast, Pb is 

### 14

retained in soils and sediments, where it provides a historical record of deposition and associated 

### 15

concentrations. In remote lakes, sediment profiles indicate higher Pb concentrations in near surface 

### 16

sediment as compared to pre

- industrial era sediment from greater depth and indicate peak concentrations 

### 17

between 1960 and 1980 ( when leaded on

- road gasoline was at peak use ) . Concentrations of Pb in moss, 

### 18

lichens, peat, and aquatic bivalves have been used to understand spatial and temporal distribution patterns 

### 19

of air Pb concentrations. Ingestion and water intake are the major rou tes of Pb exposure for aquatic 

### 20

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

### 21

terrestrial wildlife. Overall, Pb concentrations have decreased substantially in media through which Pb is 

### 22

rapidly transported , such as air and water. Substantial Pb remains in soil and sediment sinks. Although in 

### 23

areas less affected by major local sources, the highest concentrations are below the surface layers and 

### 24

reflect the phase

- out of Pb from on

- road gasoline and emissions reductions from other sources. 

### 25



# 2.2. Exposure to Ambient Lead

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

### 26

( 2006 ) , which found air Pb concentrations in the U.S. and associated biomarkers of exposure to have 

### 27

decreased substantially follo wing the ban on Pb in gasoline as well as earlier bans on Pb in house

- hold 

### 28

paints and solder. Pb exposure is difficult to assess because Pb has multiple sources in the environment 

### 29May 20 11 2

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– DO NOT CITE OR QUOTE and passes through various media. The atmosphere is the main environmental t ransport pathway for Pb, 

### 1

and atmospheric Pb is primarily associated with fine particulate matter, which can deposit to soil and 

### 2

water. In addition to primary emission of particle

- bearing or gaseous Pb to the atmosphere, Pb can be 

### 3

suspended to the air from soil or dust, and a fraction of that suspended Pb may originate from waters used 

### 4

to irrigate the soil. Air

- related pathways of Pb exposure are the focus of this assessment. In general, air



### 5

related pathways include those pathways where Pb passes through amb ient air on its path from a source to 

### 6

human exposure. In addition to inhalation of Pb from ambient air, air

- related Pb exposure pathways 

### 7

include inhalation and ingestion of Pb from indoor dust and/or outdoor soil that originated from recent or 

### 8

historic amb ient air (e.g., air Pb that has penetrated into the residence either via the air or tracking of soil). 

### 9

Non

- air

- related exposures include occupational exposures, hand

- to

- mouth contact with consumer goods 

### 10

in which Pb has been used, or ingestion of Pb in drin king water conveyed through Pb pipes. Most Pb 

### 11

biomarker studies do not indicate speciation or isotopic signature, and so non

- air exposures are reviewed 

### 12

in this section because they can also contribute to Pb body burden. 

### 13

Section 4.1 presents data illustrat ing potential exposure mechanisms. Several studies suggested that 

### 14

soil can act as a reservoir for historically deposited and contemporaneous Pb emissions from industrial or 

### 15

other activities. Exposure to soil contaminated with deposited Pb can occur through resuspended PM as 

### 16

well as shoe tracking and hand

- to

- mouth contact. In general, soil Pb concentrations tended to be higher 

### 17

within inner

- city communities compared with suburban neighborhoods. Infiltration of Pb dust has been 

### 18

demonstrated, and Pb dust has be en shown to persist in indoor environments even after repeated 

### 19

cleanings. Measurements of particle

- bound Pb exposures reported in this assessment have shown that 

### 20

personal exposure to Pb is typically higher than indoor or outdoor ambient Pb concentrations. These 

### 21

findings regarding personal exposure may be related resuspension of Pb that occurs with body movement. 

### 22

Observational studies using biomarkers of Pb as exposure metrics are also included in Section 4.1. 

### 23

The median blood Pb level for the entire U.S. p opulation is 1.2 μg/dL and the 95th percentile blood Pb 

### 24

level is 3.7 μg/dL, based on the 2007

- 2008 NHANES data ( NCHS, 2010 ) . Among children aged 1

- 5 

### 25

years, the median and 95th percentiles were slightly higher at 1.4 μg/dL and 4.1 μg/dL, respectively. 

### 26

Overall, trends in blood Pb levels have been decreasin g among U.S. children and adults over the past 20 

### 27

years. Concurrent changes in isotopic ratios of blood Pb samples reflect changes in source composition 

### 28

over the past several decades. Several studies have regressed blood Pb as a function of environmental P b 

### 29

samples such as air Pb or Pb dust fall. Recent studies have observed a relationship between blood Pb and 

### 30

soil Pb concentration. Studies have suggested that blood Pb is associated with exposure to Pb paints in 

### 31

older homes, Pb released into drinking water, and occupational work with materials containing Pb. 

### 32

Studies that examine blood Pb as a function of ambient air Pb measurements are discussed in Section 

### 33

2.8.1 that follows. 

### 34

Sequential extraction has been used to estimate the gastric bioavailability of par ticle bound Pb after 

### 35

exposure occurs. Findings from these studies have been mixed, ranging from 13 to 86%, but such 

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– DO NOT CITE OR QUOTE variation is likely a function of the particle sizes from which the Pb was extracted as well as the acid 

### 1

mixture used to simulate gastric ju ices. Estimates of bioavailability of inhaled organic Pb to the lungs are 

### 2

available only from older studies in the literature and suggest a that it is possible for all inhaled organic 

### 3

Pb to enter the blood stream ( Chamberlain et al., 1975 )

. 

### 4



# 2.3. Toxicokinetics

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

### 5

about 1% of Pb is found in the blood. Pb in blood is primarily (~99%) bound to red blood cells (RBCs). It 

### 6

has been suggested that the small fraction of Pb in plasma (<1%) may be the more biologically labile and 

### 7

toxicologically active fraction of the circulating Pb. Saturabl e binding to RBC proteins contributes to an 

### 8

increase in the plasma/blood Pb ratio with increasing blood Pb level concentration and curvature to the 

### 9

blood Pb

- plasma Pb relationship. As blood Pb level increases and the higher affinity binding sites for Pb 

### 10

in RBCs become saturated at approximately 40 μg/dL blood, a larger fraction of the blood Pb is available 

### 11

in plasma to distribute to brain and other Pb

- responsive tissues. 

### 12

The burden of Pb in the body may be viewed as divided between a dominant slow compartme nt 

### 13

(bone) and a smaller fast compartment (soft tissues) . Pb uptake and elimination in soft tissues is much 

### 14

faster than in bone. Pb accumulates in bone regions undergoing the most active calcification at the time of 

### 15

exposure. During infancy and childhood, b one calcification is most active in trabecular bone (e.g., 

### 16

patella); whereas, in adulthood, calcification occurs at sites of remodeling in cortical (e.g., tibia) and 

### 17

trabecular bone ( Aufderheide & Wittmers, 1992 )

. A high bone formation rate in early childhood results in 

### 18

the rapid uptake of circulating Pb into mineralizing bone; however, bone Pb i s also recycled to other 

### 19

tissue compartments or excreted in accordance with a high bone resorption rate ( O'Flaherty, 1995 ) . Thus, 

### 20

most of the Pb acquired early in life is n ot permanently fixed in the bone. 

### 21

The exchange of Pb from plasma to the bone surface is a relatively rapid process. Pb in bone 

### 22

becomes distributed in trabecular and the more dense cortical bone. The proportion of cortical to 

### 23

trabecular bone in the human bo dy varies by age, but on average is about 80 to 20. Of the bone types, 

### 24

trabecular bone is more reflective of recent exposures than is cortical bone due to the slow turnover rate 

### 25

and lower blood perfusion of cortical bone. Some Pb diffuses to deeper bone re gions where it is relatively 

### 26

inert, particularly in adults. These bone compartments are much more labile in infants and children than in 

### 27

adults as reflected by half

- times for movement to the plasma (e.g., cortical half

- time = 0.23 years at birth, 

### 28

3.7 years at 15 years of age, and 23 years in adults; trabecular half

- time = 0.23 years at birth, 2.0 years at 

### 29

15 years of age, and 3.8 years in adults) ( Leggett, 1993 ) . Due to the more rapid turnover of bone mineral 

### 30

in children, changes in blood Pb concentration are thought to more closely parallel changes in total body 

### 31

burden. However, some Pb accumulated in bone during childhood does persist into lat er life. Potential 

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– DO NOT CITE OR QUOTE mobilization of Pb from the skeleton could occur in adults at times of physiological stress associated with 

### 1

enhanced bone remodeling such as during pregnancy and lactation, menopause or in older adulthood

, 

### 2

extended bed rest, hyperparathy roidism, and weightlessness. Regardless of age, however, similar blood 

### 3

Pb concentrations in two individuals (or populations) do not necessarily translate to similar body burdens 

### 4

or similar exposure histories. 

### 5

The kinetics of elimination of Pb from the body reflects the existence of fast and slow pools of Pb 

### 6

in the body. The dominant phase of Pb kinetics in the blood, exhibited shortly after a change in exposure 

### 7

occurs, has an elimination half

- life of ~20

- 30 days. An abrupt change in Pb uptake gives rise to a 

### 8

relatively rapid change in blood Pb, to a new quasi

- steady state, achieved in ~75

- 100 days (i.e., 3

- 4 times 

### 9

the blood elimination half

- life). A slower phase may become evident with longer observation p eriods 

### 10

following a decrease in exposure due to the gradual redistribution of Pb among other compartments via 

### 11

the blood. Therefore, a single blood Pb concentration may reflect the near

- term or longer

- term history of 

### 12

the individual to varying degrees, depend ing on the relative contributions of internal (e.g., bone) and 

### 13

external sources of Pb to blood Pb, which in turn will depend on the exposure history and possibly age



### 14

related and individual

- specific (e.g., pregnancy, lactation) characteristics of bone turno ver. In general, 

### 15

higher blood Pb concentrations can be interpreted as indicating higher exposures (or Pb uptakes); 

### 16

however, they do not necessarily predict higher body burdens, especially in adults. 

### 17



# 2.4. Lead Biomarkers

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



### 18

term exposure history that determines body burden and Pb in bone. The contribution of bone Pb to blood 

### 19

Pb changes depending on the duration and intensity of the exposure, age, and various other physi ological 

### 20

variables that may affect bone remodeling (e.g., nutritional status, pregnancy, and menopause). Blood Pb 

### 21

in adults is typically more an index of recent exposures than body burden, whereas bone Pb is an index of 

### 22

cumulative exposure and body burden. In children, due to faster exchange of Pb to and from bone, blood 

### 23

Pb is both an index of recent exposure and potentially an index of body burden. In some physiological 

### 24

circumstances (e.g., osteoporosis), bone Pb may contribute to blood Pb in adults. The d isparity between 

### 25

blood Pb and body burden may have important implications for the interpretation of blood Pb 

### 26

measurements in some epidemiology studies. Conceptually, measurement of long

- term Pb body burden 

### 27

(i.e., based on tibia Pb) may be the appropriate m etric if the effects of Pb on a particular outcome are 

### 28

lasting and cumulative. However, if the effects of Pb on the outcome represent the acute effects of current 

### 29

exposure, then blood Pb may be the preferred metric. In the absence of clear evidence as to w hether a 

### 30

particular outcome is an acute effect of recent Pb dose or a chronic effect of cumulative Pb exposure, both 

### 31

blood and bone metrics should be considered. 

### 32May 20 11 2

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– DO NOT CITE OR QUOTE Cross

- sectional studies that sample blood Pb once generally provide an index of recent exposu res. 

### 1

In contrast, cross

- sectional studies of bone Pb and longitudinal samples of blood Pb concentrations over 

### 2

time provide an index of cumulative exposure and are more reflective of average Pb body burdens over 

### 3

time. The degree to which repeated sampling w ill reflect the actual long

- term time

- weighted average 

### 4

blood Pb concentration depends on the sampling frequency in relation to variability in exposure. High 

### 5

variability in Pb exposures can produce episodic (or periodic) oscillations in blood Pb concentrati on that 

### 6

may not be captured with low sampling frequencies. 

### 7

The concentration of Pb in urine is a function of the urinary Pb excretion and the urine flow rate. 

### 8

Urine flow rate requires collection of a timed urine sample, which is often problematic in epidem iologic 

### 9

studies. Collection of un

- timed ( “ spot ” ) urine samples, a common alternative to timed samples, requires 

### 10

adjustment of the Pb measurement in urine to account for variation in urine flow ( Diamond, 1988 )

. 

### 11

Urinary Pb concentration reflects, mainly, the e xposure history of the previous few months; thus, a single 

### 12

urinary Pb measurement cannot distinguish between a long

- term low level of exposure or a higher acute 

### 13

exposure. Thus, a single urine Pb measurement, or a series of measurements taken over short

- tim e span, is 

### 14

likely a relatively poor index of Pb body burden for the same reasons that blood Pb is not a good indicator 

### 15

of body burden. On the other hand, long

- term average measurements of urinary Pb can be expected to 

### 16

better reflect body burden. 

### 17



# 2.5. Health Eff ects

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

### 18

health effects associated with exposure to Pb. The results from the health studies evaluated in 

### 19

combination with the evidence from other disciplines (e. g., fate and transport, exposure sciences, 

### 20

toxicokinetics) contribute to the causal determinations (Section 1.6.4) made for the health outcomes 

### 21

discussed in this assessment. In the following sections a discussion of the causal determinations will be 

### 22

presen ted for the health effects for which sufficient evidence was available to conclude a causal or likely 

### 23

to be causal relationship (Table 2

- 1) . Although not presented in depth in this chapter, a detailed discussion 

### 24

of the underlying evidence used to formulate each causal determination can be found in Chapter 5 of this 

### 25

document. 

### 26May 20 11 2

- 10 DRAFT

– DO NOT CITE OR QUOTE Table 2

- 1. Summary of causal determinations between exposure to Pb and health

outcomes

Outcome Causality Determination

Neurological Effects Causal Relationship

Cardiovascular Effects Causal Relationship

Renal Effects Causal Relationship
Immune System Effects Causal Relationship
Effects on Heme Synthesis and Red Blood Cell Function Causal Relationship
Reproductive Effects and Birth Outcomes Causal Relationship

Cancer Likely Causal Relationship



## 2.5.1. Neurological Effects

The 2006 Pb AQCD concluded that the collective body of epidemiologic studies provides clear and 

### 1

consistent evidence for the effects of Pb exposure on neurocognitive function in children. This conclusion 

### 2

was substantiated by findings in diverse populations that blood Pb levels were associated with a broad 

### 3

spectrum of cognitive and behavioral endpoints, including IQ, higher

- order processes such as language 

### 4

and memory, academic achievement, behavior and conduct, sensory acuities, and changes in brain 

### 5

structure and activity as assessed by magnetic resonance imaging (MRI) or magnetic resonance 

### 6

spectroscopy (MRS). Toxicological studies not only provided coherence with similarly consistent findings 

### 7

for Pb

- induced impairments in learning, behavior, and sensory acuit ies, but also provided biological 

### 8

plausibility by characterizing mechanisms for Pb

- induced neurotoxicity. These mechanisms included Pb



### 9

induced inhibition of neurotransmitter release and decreases in synaptic plasticity, neuronal 

### 10

differentiation, and blood

- brain

- barrier integrity. Both epidemiologic studies ( in children ) and 

### 11

toxicological studies

, demonstrated neurocognitive deficits in association with blood Pb levels at and 

### 12

below 10 μg/dL, and evidence from both disciplines supported a nonlinear exposure

- r esponse 

### 13

relationship, with greater effects estimated for lower blood Pb levels. Among environmentally

- exposed 

### 14

adults, the most consistent findings were associations between cumulative Pb exposure, as assessed by 

### 15

serial blood Pb or bone Pb measurements, and cognitive deficits. 

### 16

Building on this strong body of extant evidence, recent studies continue to demonstrate 

### 17

associations between Pb exposure and neurological effects. While recent epidemiologic studies in 

### 18

children continue d to demonstrate associations wi th IQ, most evidence emphasize d associations of blood 

### 19

Pb levels (as low as 2 μg/dL) with specific indices of neurocognitive function such as reading and verbal 

### 20

skills, memory, visuospatial processing, and academic achievement. Nonetheless, these newer find ings 

### 21

are concordant with the previous body of evidence given that IQ is a global measure of cognitive function 

### 22

that reflects the integration of several neurocognitive domains. Additional coherence for findings in 

### 23May 20 11 2

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– DO NOT CITE OR QUOTE children is provided by evidence in animals that blood Pb levels of 1.8 μg/dL and higher are associated 

### 1

with decrements in learning and memory. New findings in animals emphasize d the role of stress in 

### 2

potentiating the low dose effects of Pb on behavior and memory. In animals, the developmental peri od is 

### 3

the most sensitive window for Pb

- dependent neurotoxicity, whereas in children, concurrent blood Pb was 

### 4

generally found to be the best predictor of cognitive decrements. 

### 5

Recent studies in children continue to support associations of Pb exposure (blood Pb levels 3

- 11 

### 6

μg/dL) with a range of behavioral problems from anxiety and distractibility to conduct disorder and 

### 7

delinquent behavior. Whereas previous evidence was not compelling, new evidence indicates associations 

### 8

comparing the lowest quartiles of blood Pb level (0.8

- 1 μg/dL versus <0.8 μg/dL) and ADHD. These 

### 9

findings for ADHD are well supported by observations in animals of Pb

- induced increased response rates 

### 10

and impulsivity. Both epidemiologic studies in children and toxicological studies demon strate 

### 11

associations of Pb exposure with deficits in visual acuity and hearing and auditory processing. New 

### 12

evidence from toxicological studies demonstrates these effects at lower exposure levels (blood Pb levels 

### 13

<15 μg/dL). Combined evidence for Pb

- associa ted neurocognitive deficits (e.g., inattention, conduct 

### 14

disorder, and effects on sensory function ) provides plausible mechanisms by which Pb exposure may 

### 15

contribute to academic underachievement and to more serious problems of delinquent behavior. 

### 16

Studies of adults without occupational Pb exposure have not provided consistent evidence for 

### 17

associations between blood Pb and the range of neurological effects. One explanation for the weaker 

### 18

evidence may be that cognitive reserve may compensate for the effects o f Pb exposure on learning new 

### 19

information. Compensatory mechanisms may become less effective with increasing age, explaining the 

### 20

consistent associations between measures of cumulative Pb exposure and neurocognitive deficits. Among 

### 21

recent studies of adults, blood Pb and bone Pb are associated with essential tremor and Parkinson ’ s 

### 22

disease, respectively. Consistent with these findings, toxicological studies demonstrate Pb

- induced 

### 23

decreased dopaminergic cell activity in the substantia nigra, which contributes t o the primary symptoms 

### 24

of Parkinson ’ s disease. Biological plausibility also is provided by observations of developmental Pb 

### 25

exposures of monkeys and rats inducing neurodegeneration in the aged brain. A recent epidemiological 

### 26

study indicated that early

- life ALAD activity, a biomarker of Pb exposure, may be associated with 

### 27

schizophrenia later in adulthood. Consistent with these findings, toxicological studies have observed Pb



### 28

induced emotional changes in males and depression in females. It is not surprising t hat Pb exposure may 

### 29

increase the risk of different neurological endpoints in children and adults given the predominance of age



### 30

dependent neurological processes, in particular, neurogenesis and brain development in children and 

### 31

neurodegeneration in adults. 

### 32

Extensive evidence from toxicological studies, as well as evidence in some aquatic and terrestrial 

### 33

animal taxa (Section 2. 6 .9) clearly substantiates the biological plausibility for epidemiologic findings by 

### 34

characterizing mechanisms underlying neurologica l effects. Pb induces complex neurochemical changes 

### 35

in the brain that differ by region of the brain, neurotransmitter type, age, and sex of the organism. These 

### 36May 20 11 2

- 12 DRAFT

– DO NOT CITE OR QUOTE changes remain aberrant over time but are dynamic in nature. Pb exposure of animals induces chan ges in 

### 1

the transmission of dopamine, which plays a key role in cognitive functions mediated by the prefrontal 

### 2

cortex and in motor functions mediated by the substantia nigra. Current toxicological research has been 

### 3

expanded to document that early

- life Pb ex posure can contribute to neurodegeneration and neurofibrillary 

### 4

tangle formation in the aged brain. Pb exposure can affect NMDA receptors, which can contribute to 

### 5

mood disorders. Synapse formation, adhesion molecules, and nitrosative stress continue to be a reas in 

### 6

which research is being conducted related to Pb

- associated neurotoxicity. Finally, the new area of 

### 7

epigenetics shows that Pb exposure affects methylation patterns in rodent brains. These toxicological data 

### 8

provide coherence with epidemiologic obser vations, in particular, associations of Pb exposure with 

### 9

cognitive deficits, Parkinson ’ s disease, and mood disorders. 

### 10

In summary, recent evidence substantiates and expands upon the established epidemiologic and 

### 11

toxicological literature demonstrating the ne urological effects of Pb exposure. Both the consistency of 

### 12

evidence across toxicological and epidemiologic studies and the coherence of findings across the full 

### 13

spectrum of neurological endpoints, from mechanistic changes to impairments in cognitive functi on and 

### 14

behavior and to poorer academic achievement and delinquency, are illustrated in Figure 2

- 1. In 

### 15

epidemiologic studies of children, consistently positive associations of blood Pb levels with deficits in 

### 16

neurocognitive function, attention, and sensory acuities support observed associations with academic 

### 17

underachievement, which in turn, may explain associations with delinquent and criminal behavior. In 

### 18

particular, observations of cognitive and behavioral deficits in association with blood Pb levels in th e 

### 19

range of 1

- 2 μg/dL indicate that a threshold may not exist for the neurological effects of Pb in children. 

### 20

Epidemiologic findings are strengthened by their biological plausibility in light of toxicological study 

### 21

findings and their coherence with toxicolo gical findings for similar or parallel endpoints and for the 

### 22

mechanisms underlying the neurological effects. The collective body of evidence integrated across 

### 23

epidemiologic and toxicological studies and across the spectrum of neurological endpoints is suff icient to 

### 24

conclude that there is a causal relationship between Pb exposures and neurological effects

. 

### 25May 20 11 2

- 13 DRAFT

– DO NOT CITE OR QUOTE Figure 2

- 1. Snapshot of evidence for the spectrum of effects to the nervous system associated with Pb exposure. Green=animal toxicological studies (left side); purple=epidemiological studies (right side).



## 2.5.2. Cardiovascular Effects

The 2006 Pb AQCD concluded that there was a relationship between increased Pb exposure and 

### 1

increased adverse cardiovascular outcomes, including increased blood pressure (BP) and in creased 

### 2

incidence of hypertension ( U.S. EPA, 2006 ) . Meta

- analysis of these studies found that each doubling of 

### 3

blood Pb level (between 1 and >40 μg/dL) was associated with a 1 mmHg increase in systolic BP and a 

### 4May 20 11 2

- 14 DRAFT

– DO NOT CITE OR QUOTE 0.6 mmHg increase in diastolic BP. In addition, most of the reviewed studies using cumulative Pb 

### 1

exposure measured by adult bone Pb levels showed increased BP. Toxicological studies provided 

### 2

evidence for exposure to low levels of Pb (e.g., 2 μg/dL) resulting in increased BP in experimental 

### 3

animals that persists long after the cessation of Pb exposure and also provided mechanistic evidence to 

### 4

support the biological plausibility of Pb

- induced hypertension, including oxidative stress, altered 

### 5

sympathetic activity, and vasomodulator imbalance. Finally, limi ted evidence suggested a connection 

### 6

between Pb exposure and the development of IHD, cerebrovascular disease, peripheral vascular disease 

### 7

( PVD ) and mortality. 

### 8

Building on the strong body of evidence presented in the 2006 Pb AQCD, recent studies continue 

### 9

to support associations between Pb exposure and exposure biomarkers and cardiovascular effects with 

### 10

recent epidemiologic studies informing past uncertainties (e.g., confounding, low Pb exposures). A recent 

### 11

study suggested that Pb has an acute effect on BP as a function of recent dose measured by blood Pb and a 

### 12

chronic effect on hypertension risk as a function of cumulative exposure measured by tibia Pb ( Martin et 

### 13

al., 2006 ) . This study also verified the magnitude of change in BP observed in the past meta

- analysis. 

### 14

Additionally, recent epidemiologic studies prov ided evidence for associations between blood Pb and 

### 15

hypertension in adults with relatively low blood Pb levels; a positive relationship was found in the 

### 16

NHANES (1999

- 2002) data set at a geometric mean blood Pb level of 1.64 μg/dL ( Muntner et al., 2005 )

. 

### 17

Animal toxicological studies also provide support for effects of low blood Pb level on increased BP with 

### 18

statistically significant increase s shown in animals with blood Pb levels as low as 2 μg/dL. New studies 

### 19

also demonstrate a partial reversibility of Pb

- induced increased BP following Pb exposure cessation or 

### 20

chelation. 

### 21

Epidemiologic studies continue to investigate the relationship between bone Pb and increased BP. 

### 22

Recent epidemiologic studies also emphasize the interaction between cumulative Pb exposure and factors 

### 23

that moderate or modify the Pb effect on BP and hypertension (e.g., chronic stress and metabolic 

### 24

syndrome). Further, recent epi demiologic studies found that the effects of Pb on cardiovascular endpoints 

### 25

( including BP, pulse pressure [ PP ] , and QT interval ) were modified by genotypes ( including ALAD and 

### 26

genes involved in hemochromatosis or Fe metabolism ) . Epidemiologic and toxicolog ical studies also 

### 27

provide d evidence for Pb exposure to contribute to increased development of atherosclerosis, thrombosis, 

### 28

ischemic heart disease, peripheral artery disease, arrhythmia, and cardiac contractility. Animal 

### 29

toxicological evidence continues to build on the evidence supp orting the biological plausibility leading to 

### 30

these cardiovascular alterations. New evidence extends the potential continuum of Pb

- related 

### 31

cardiovascular effects in adults by demonstrating associations of Pb concentrations in blood and bone 

### 32

with both cardi ovascular and all

- cause mortality. 

### 33

In summary, new studies evaluated in the current review support or expand upon the strong body of 

### 34

evidence presented in the 2006 Pb AQCD that Pb exposure is causally associated with cardiovascular 

### 35

health effects. Both ep idemiologic and toxicological studies continue to demonstrate a consistently 

### 36May 20 11 2

- 15 DRAFT

– DO NOT CITE OR QUOTE positive relationship between Pb exposure and increased BP or hypertension development in adults and 

### 1

this relationship is observed in more recent studies of adults with blood Pb l evels ( mean: 2 μg/dL) lower 

### 2

than those reported in the 2006 Pb AQCD. While some studies evaluate concentration

- response 

### 3

relationships of blood Pb with BP or mortality, the information is inconclusive (Section 2. 8

. 2 ). Recent 

### 4

studies investigating measures o f cumulative Pb exposure measures and suggest that bone Pb related 

### 5

strongly to hypertension risk. Evidence of Pb increasing the risk of development of other cardiovascular 

### 6

diseases also is shown. By demonstrating Pb

- induced oxidative stress including  ̇NO i nactivation, 

### 7

endothelial dysfunction leading to altered vascular reactivity, activation of the RAAS, and vasomodulator 

### 8

imbalance, toxicological studies have characterized the mode of action of Pb and provided biological 

### 9

plausibility for the consistently po sitive associations observed in epidemiologic studies between blood 

### 10

and bone Pb and cardiovascular effects. These observed associations between Pb exposure and 

### 11

cardiovascular morbidity are supported by recent reports of increased cardiovascular mortality. 

### 12

Collectively, the evidence integrated across epidemiologic and toxicological studies as well as across the 

### 13

spectrum of cardiovascular health endpoints is sufficient to conclude that there is a causal relationship 

### 14

between Pb exposures and cardiovascular hea lth effects

. 

### 15



## 2.5.3. Renal Effects

The 2006 Pb AQCD stated that “ in the general population, both circulating and cumulative Pb was 

### 16

found to be associated with a longitudinal decline in renal function ” , evidenced by increased serum 

### 17

creatinine and decreased creatini ne clearance ( U.S. EPA, 2006 ) . These findings were substantiated by the 

### 18

coherence of effects observed across epidemiologic and toxicological studies. Toxicological studies 

### 19

provided mechanistic evidence to support the biological plausibility of Pb

- induced ren al effects, including 

### 20

oxidative stress leading to  ̇NO inactivation. Uncertainty remained on the implications of effects in 

### 21

children, confounding, hyperfiltration, and reverse causality. 

### 22

Recent epidemiologic studies in general and patient populations of adu lts have, with few 

### 23

exceptions, been consistent in observing associations between bone or blood Pb levels and worse kidney 

### 24

function ; and provide important evidence that nephrotoxicity occurs at current population Pb biomarker 

### 25

levels. Further, current eviden ce does not allow for the identification of a threshold for Pb

- related 

### 26

nephrotoxicity. The odds of reduced eGFR increased by 36% (95% CI: 0.99, 1.85) at blood Pb levels as 

### 27

low as 1.6

- 2.4 μg/dL and by 56% (95% CI: 1.17, 2.08) at blood Pb >2.4 μg/dL. These s tudies benefit from 

### 28

a number of strengths that vary by study but include : comprehensive assessment of Pb dose (using bone 

### 29

Pb [ as a measure of cumulative body burden ], and chelatable Pb [ as a measure of bioavailable Pb ]) ; 

### 30

prospective study design; and stati stical approaches that utilize a range of exposure and outcome 

### 31

measures, while adjusting for numerous kidney and Pb risk factors. General population studies also 

### 32

benefit from large populations in both Europe and the U

. S. At blood Pb levels that are common in the 

### 33May 20 11 2

- 16 DRAFT

– DO NOT CITE OR QUOTE general U.S. population, Pb increases the risk for clinically relevant effects particularly in susceptible 

### 1

populations such as those with underlying chronic medical diseases that increase chronic kidney disease 

### 2

(CKD) risk such as diabetes mellitus a nd hypertension and co

- exposure to other environmental 

### 3

nephrotoxicants. The uncertainty around the role of reverse causality, which attributes increases in blood 

### 4

Pb levels to compromised kidney excretion rather than as a causative factor for CKD, was reduc ed by 

### 5

evidence that the association between blood Pb and serum creatinine occurred over the entire serum 

### 6

creatinine range, including the normal range where reverse causality would not be expected. Further, 

### 7

recent studies have extended the limited body of e vidence for effects of Pb on the kidney in children. 

### 8

Toxicological studies contribute support to effects of Pb in the early life window of exposure adding to 

### 9

the strength of the association between Pb and altered renal function in children. 

### 10

CKD results in substantial morbidity and mortality and is an important risk factor for cardiac 

### 11

disease. As kidney dysfunction can increase BP and increased BP can lead to further damage to the 

### 12

kidneys, Pb

- induced damage to either or both the renal and cardiovascular syst ems may result in a cycle 

### 13

of increased severity of disease. Pb exposure has been causally linked to both increased BP and other 

### 14

cardiovascular effects (Section 5.4) and renal dysfunction and, it is possible that the cardiovascular and 

### 15

renal effects of Pb o bserved are mechanistically linked and are contributing to the progression of the 

### 16

diseases. Recently available animal toxicological studies strengthen the evidence regarding the 

### 17

mechanisms leading to these renal alterations including oxidative stress, whic h is also related to CVD, 

### 18

infiltration of lymphocytes and macrophages associated with increased expression of NF

- κB in proximal 

### 19

tubules and infiltrating cells, mitochondrial dysfunction, renal cell apoptosis, and glomerular hypertrophy. 

### 20

In summary, new st udies evaluated in the current review support or expand upon the strong body of 

### 21

evidence presented in the 2006 Pb AQCD that Pb exposure is associated with renal health effects. 

### 22

Epidemiologic studies continue to demonstrate a consistently positive relations hip between blood Pb level 

### 23

and kidney dysfunction at blood Pb levels comparable to those occurring in the current U.S. population 

### 24

with no evidence for a threshold across the range of levels studied. Uncertainty regarding effects in 

### 25

children, confounding, h yperfiltration, and reverse causality have been reduced through consideration of 

### 26

the recent evidence. By demonstrating Pb

- induced oxidative stress and describing mechanisms of acute 

### 27

changes following Pb exposure, toxicological studies provide biological pl ausibility for the associations 

### 28

observed in epidemiologic studies between Pb and kidney dysfunction. Collectively, the evidence 

### 29

integrated across epidemiologic and toxicological studies as well as across the spectrum of kidney health 

### 30

endpoints is sufficien t to conclude that there is a causal relationship between Pb exposures and renal 

### 31

health effects

. 

### 32May 20 11 2

- 17 DRAFT

– DO NOT CITE OR QUOTE 

## 2.5.4. Immune System Effects

The collective body of evidence integrated across epidemiologic and toxicological study findings 

### 1

consistently demonstrates that Pb exposu re is associated with changes in a spectrum of immune mediators 

### 2

and functions. The majority of results from animal studies indicates that immune changes are observable 

### 3

at blood Pb levels in the range of 2 to 8 μg/dL. Likewise, in the newly expanded body of epidemiologic 

### 4

studies in environmentally

- exposed children and adults, changes in immune function are demonstrated in 

### 5

association with mean blood Pb levels in the range of 1 to 10 μg/dL. 

### 6

The strength of evidence for Pb

- associated immune effects is derived not only from the consistency 

### 7

of associations but also from the coherence of findings between toxicological and epidemiologic studies 

### 8

and coherence of findings across the spectrum of related immune changes. Toxicological and 

### 9

epidemiologic evidence links hi gher Pb exposures with decreases in various T cell subtypes. These 

### 10

changes can affect cell

- to

- cell interactions that mediate acquired immunity required in subsequent 

### 11

memory responses to antigen exposures; however, it is unclear what effect the observed mag nitudes of 

### 12

changes may have in attenuating acquired immunity. 

### 13

The key immunomodulatory effect of Pb exposure, in terms of coherence across immune endpoints 

### 14

and implications for developing immune

- based diseases, is the skewing of immune function away from a 

### 15

Th1 phenotype towards a Th2 phenotype. In toxicological studies and epidemiologic studies, this shift is 

### 16

well demonstrated by suppressed production of Th1 cytokines (e.g., IFN

- γ) and increased production of 

### 17

Th2 cytokines (e.g., IL

- 4). A recent in vitro s tudy indicates that Pb may promote Th2 responses by acting 

### 18

directly on dendritic cells, the major effector in antigen response. An increase in IL

- 4 from activated Th2 

### 19

cells induces differentiation of B cells into Ab producing cells, thereby promoting the s ecretion of IgE, 

### 20

IgA, and IgG. In support of this well

- established mechanism, toxicological studies describe Pb

- induced 

### 21

changes in IgA, IgG, and IgM. Additionally, epidemiologic studies in children consistently link higher Pb 

### 22

exposures with increases in B cell abundance and increases in IgE. Observations of Pb

- associated 

### 23

increases in Th2 responses and circulating IgE levels provide biological plausibility for epidemiologic 

### 24

observations in children of associations of blood Pb with asthma and allergic conditi ons. Such 

### 25

epidemiologic data are sparse, and additional studies with more rigorous methodology (e.g., longitudinal 

### 26

design and adjustment for potential confounders such as smoking, SES, and exposures to other metals) 

### 27

are needed to substantiate the findings. 

### 28

Further evidence of Pb

- associated suppressed Th1 activity is provided by toxicological and 

### 29

epidemiologic observations that Pb exposure is associated with impaired killing capacity of macrophages 

### 30

and neutrophils. There is toxicological and epidemiologic e vidence of suppressed Th1 activity and effects 

### 31

on macrophage and neutrophil functional activities. This evidence provides biological plausibility for 

### 32

observations in animals of the Pb

- induced suppression of the DTH response and the observations in both 

### 33

ani mals and humans that Pb exposure and increases the risk of infection. 

### 34May 20 11 2

- 1 8 DRAFT

– DO NOT CITE OR QUOTE Toxicological studies and a limited set of epidemiologic studies demonstrate that Pb induces 

### 1

macrophages into a hyperinflammatory state as characterized by suppressed production of NO an d 

### 2

enhanced production of ROS , TNF

- α, and the immunosuppressive PGE 2 . Specialized macrophages 

### 3

residing in airways, reproductive organs, and in the nervous system indicate that immunomodulation may 

### 4

underlie the documented associations of Pb exposure with eff ects in these organ systems. Although 

### 5

limited mostly to toxicological studies, Pb has been shown to induce the generation of auto

- antibodies, 

### 6

suggesting that Pb exposure may increase the risk of autoimmune conditions. 

### 7

In summary, recent toxicological and epidemiologic studies support the strong body of evidence 

### 8

presented in the 2006 Pb AQCD that Pb exposure is associated with a broad spectrum of changes in both 

### 9

cell

- mediated and humoral immunity to promote a Th2 phenotype and inflammation. The consistency and 

### 10

coherence of findings among these related immune effects, in turn, establish the biological plausibility for 

### 11

Pb exposure being associated with increased susceptibility to infection, autoimmunity, allergy, and effects 

### 12

in other organ systems. Animal stud ies and to a limited extent, epidemiologic studies, demonstrate 

### 13

increased susceptibility of prenatal exposures and enhanced responses with co

- exposures to other metals. 

### 14

The consistency of findings and the coherence between toxicological and epidemiologic f indings across 

### 15

the continuum of related immune responses are sufficient to conclude that there is a causal relationship 

### 16

between Pb exposures and immune effects. 

### 17



## 2.5.5. Heme Synthesis and RBC Function

Consistent with conclusions of the 2006 Pb AQCD as well as prev ious assessments, recent 

### 18

evidence in the toxicological and epidemiologic literature supports the longstanding relationship between 

### 19

Pb exposure and effects on hematological endpoints, including altered heme synthesis, decreased RBC 

### 20

survival and function, an d increased RBC oxidative stress. 

### 21

Multiple occupational epidemiologic studies have shown that Pb affects several hematological 

### 22

parameters such as Hb, PCV, MCV, MCH, and MCHC. Although the majority of occupationally

- exposed 

### 23

adults had blood Pb levels in excess of 20 μg/dL, decreases in Hb and PCV were also observed in an 

### 24

occupational cohort with a mean blood Pb level of 7 μg/dL. In addition, Pb exposure was shown to reduce 

### 25

Ca

- ATPase and Ca

- Mg

- ATPase activity in RBC membranes at cord blood Pb levels of 3.54 μg/dL. 

### 26

Decreases in Ca

- ATPase and Ca

- Mg

- ATPase activity leads to an increase in RBC [Ca 2+ ] i , increased 

### 27

membrane fragility, and abnormal morphological changes. Studies in children are less consisten t than 

### 28

those investigating occupationally

- exposed adults; this may due to the comparatively shorter duration of 

### 29

and magnitude of exposure experienced by children. Toxicological studies have also observed decreases 

### 30

in hematocrit and hemoglobin and increases in hemolysis and reticulocyte density in rats and mice with 

### 31

blood Pb levels as low as 6.6

- 7.1 μg/dL. Pb exposure has also been observed to increase PS expression on 

### 32

RBC membranes, leading to cell shrinkage, e r yptosis, and destruction of the RBCs by macrop hages. 

### 33May 20 11 2

- 19 DRAFT

– DO NOT CITE OR QUOTE Suggestive evidence of disrupted hematopoiesis evidenced by decreased serum erythropoietin was 

### 1

observed in occupationally exposed adults with blood Pb levels of 6.4 μg/dL; toxicological studies in rats 

### 2

also indicate that Pb is cytotoxic to RBC

- proge nitor cells after chronic exposure. Taken together, these 

### 3

studies provide consistent evidence that exposure to Pb adversely effects RBC function and survival, and 

### 4

leads to the reduction of RBCs in circulation. Although this decrease in RBCs may be explaine d by both 

### 5

decreased cell survival and/or disruption of hematopoiesis, the observation of increased reticulocytes 

### 6

seems to represent compensation for decreased RBC survival due to Pb exposure. 

### 7

Pb has been found to inhibit several enzymes involved in heme s ynthesis, namely ALAD 

### 8

(cytoplasmic enzyme catalyzing the second, rate

- limiting, step of the heme biosynthesis pathway), 

### 9

coporphyrinogen oxidase (catalyses the 6th step in heme biosynthesis converting coporphyrinogen III into 

### 10

protoporphyrinogen IX), and fer rochelatase (catalyses the terminal step in heme synthesis converting 

### 11

protoporphyrin IX into heme). Recently, numerous epidemiologic studies have confirmed that decreases 

### 12

in RBC ALAD levels and activity are strongly associated with blood Pb levels in as lo w as 7.1 μg/dL in 

### 13

children and blood Pb levels as low as 6.4 μg/dL in adults. Decreases in blood ALAD activity were also 

### 14

seen in rats with blood Pb levels of 6.5 μg/dL. There is also a considerable body of evidence for a 

### 15

negative correlation between ALAD a ctivity and Pb concentration in various invertebrate and vertebrate 

### 16

taxa (Section 2. 6 .7). In addition to ALAD, recent studies have shown that Pb exposure inhibits the 

### 17

activity of ferrochelatase, leading to increased RBC ZPP in humans and animals. Pb has al so been shown 

### 18

to inhibit the activities of other enzymes in RBCs, including those involved in nucleotide scavenging, 

### 19

energy metabolism, and acid

- base homeostasis. 

### 20

Lastly, Pb exposure induces lipid peroxidation and oxidative stress in RBCs. Epidemiologic st udies 

### 21

have observed increases in MDA in occupationally

- exposed adults with blood Pb levels as low as 7.9 

### 22

μg/dL. Other measures of oxidative stress observed included lowered activities of SOD, GR, and CAT, 

### 23

and increased CRP. Indices of RBC oxidative stress were also seen in adolescents and children exposed to 

### 24

Pb. In vitro and in vivo studies have also demonstrated that prior, con

- current, or subsequent treatment 

### 25

with various antioxidants has been shown to at least partially ameliorate Pb

- induced oxidative st ress in 

### 26

RBCs. 

### 27

In conclusion, the recent epidemiologic and toxicological literature provides strong evidence that 

### 28

exposure to Pb is associated with numerous deleterious effects on the hematological system, including 

### 29

altered heme synthesis mediated through d ecreased ALAD and ferrochelatase activities, decreased RBC 

### 30

survival and function, decreased hematopoiesis, and increased oxidative stress and lipid peroxidation. The 

### 31

consistency of findings in the epidemiologic and toxicological literature and coherence ac ross the 

### 32

disciplines is sufficient to conclude that there is a causal relationship between Pb exposure and heme 

### 33

synthesis and RBC function. 

### 34May 20 11 2

- 20 DRAFT

– DO NOT CITE OR QUOTE 

## 2.5.6. Reproductive Effects and Birth Outcomes

Epidemiologic and toxicological studies of the effects of Pb on reproductive outcomes have 

### 1

covered outcomes such as female and male reproductive function, birth defects, spontaneous abortions, 

### 2

infant mortality, preterm birth, low birth weight, and developmental effects. 

### 3

Many of the Pb

- induced effects in toxicological studies have been observed at maternal blood Pb 

### 4

levels that do not result in overt clinical toxicity in the dams. Recent toxicological studies have shown the 

### 5

effects of Pb exposure during early development to include disruption of endocrine function; delay in the 

### 6

onse t of puberty and alteration in reproductive function later in life; and changes in morphology or 

### 7

histology in sex organs and placenta. Additionally, epidemiologic studies of reproductive factors among 

### 8

males and females investigated whether Pb levels were a ssociated with hormone levels, fertility, and onset 

### 9

of puberty. Epidemiologic studies showed associations between blood Pb and hormone levels for females. 

### 10

Studies of Pb and fertility are limited and inconsistent for females and males. Strong and consistent 

### 11

associations were observed between Pb levels in adult males exposed to Pb in occupational settings with 

### 12

blood Pb as low as 20

- 45 μg/dL and sperm count and quality. Decreased sperm viability and altered 

### 13

morphology in sperm is also observed in invertebrate species (Sections 7.2.4 and 7.3.4) Multiple studies 

### 14

of Pb and puberty have shown inverse associations between blood Pb levels and delayed pubertal 

### 15

development for girls and boys. These associations are consistently observed in multiple epidemiologic 

### 16

studie s and demonstrate effects on pubertal development at blood Pb levels <10μg/dL. 

### 17

Pb

- mediated changes in levels or function of reproductive and growth hormones have been 

### 18

demonstrated in past and more recent toxicological studies; however the findings are inc onsistent. More 

### 19

data are needed to determine whether Pb exerts its toxic effects on the reproductive system by affecting 

### 20

the responsiveness of the hypothalamic

- pituitary

- gonad axis or by suppressing circulating hormone levels. 

### 21

More recent toxicological stu dies suggest ed that oxidative stress is a major contributor to the toxic effects 

### 22

of Pb on male and female reproductive systems. Several recent studies showed an association between 

### 23

increased generation of ROS and germ cell injury as evidenced by destructio n of germ cell structure and 

### 24

function. Co

- administration of Pb with various antioxidant compounds either eliminated Pb

- induced 

### 25

injury or greatly attenuated its effects. In addition, many studies that demonstrated increased oxidative 

### 26

stress also reported in creased apoptosis, which is likely a critical underlying mechanism in Pb

- induced 

### 27

germ cell DNA damage and dysfunction. 

### 28

Overall, results of pregnancy outcomes were similar to those of the 2006 Pb AQCD; inconsistent 

### 29

evidence of a relationship with Pb was av ailable for preterm birth and little evidence was available to 

### 30

study the associations with spontaneous abortions. The previous Pb AQCD included a few studies that 

### 31

reported possible associations between Pb and neural tube defects, but the recent epidemiolog ic studies 

### 32

found no association. Possible associations were observed between Pb and low birth weight when 

### 33

epidemiologic studies used measures of maternal bone Pb or air exposures, but the associations were less 

### 34May 20 11 2

- 21 DRAFT

– DO NOT CITE OR QUOTE consistent when using maternal blood Pb or um bilical cord and placenta Pb. Effects of Pb exposure 

### 1

during early development in toxicological studies included reduction in litter size, implantation, birth 

### 2

weight and postnatal growth. 

### 3

Additional evidence for Pb exposure negatively affecting development is provided by toxicological 

### 4

studies demonstrating developmental Pb exposures leading to impaired development of the retina, skin, 

### 5

teeth and altered development of the hematopoietic and hepatic systems. In summary, the recent 

### 6

toxicological and epidemiologi c literature provides strong evidence that Pb exposure is related to delayed 

### 7

onset of puberty in both males and females. Additionally, Pb exposure has been shown to have 

### 8

detrimental effects on sperm (at higher blood Pb levels in epidemiologic studies and l ower doses in the 

### 9

toxicological literature). Furthermore, evidence from invertebrate and vertebrate taxa in both terrestrial 

### 10

and aquatic ecosystems provide additional support for reproductive and developmental effects associated 

### 11

with Pb exposure (Sections 2.6.8, 7.2.4, and 7.3.4). The data on preterm birth, low birth weight, 

### 12

spontaneous abortions, birth defects, hormonal influences, and fecundity are less consistent between the 

### 13

toxicological and epidemiologic literature. Despite some inconsistencies for par ticular endpoints, the 

### 14

evidence for Pb

- related reproductive effects is strengthened by the coherence with similar findings in 

### 15

invertebrate species. The collective body of evidence integrated across epidemiologic and toxicological 

### 16

studies, with a focus on t he strong relationship observed with negative effects on sperm and delayed 

### 17

pubertal onset, is sufficient to conclude that there is a causal relationship between Pb exposures and 

### 18

reproductive effects and birth outcomes

. 

### 19



## 2.5.7. Effects on Other Organ Systems

In th e 2006 Pb AQCD, exposure to Pb was shown to exert effects in organ systems not yet 

### 20

explicitly covered in the preceding sections of this document. These organ systems included the liver, 

### 21

gastrointestinal tract, endocrine system, bone and teeth. In the curre nt document, effects on these organ 

### 22

systems, as well as effects on the respiratory system, have been organized in one section because the 

### 23

amount of new evidence appearing since the 2006 Pb AQCD is limited. The few recent studies, however, 

### 24

find that Pb may negatively affect the function of these systems at lower blood Pb levels than previously 

### 25

described. 

### 26

There is evidence from recent epidemiologic and toxicological studies that exposure to Pb results 

### 27

in altered liver function and hepatic toxicity, including the observation of altered serum protein levels, 

### 28

increased serum enzyme activities, and altered hepatic lipid metabolism. Multiple studies in humans and 

### 29

animals have obs erved hepatic oxidative stress ( generally indicated by an increase in lipid peroxidatio n , 

### 30

along with a decrease in GSH levels and CAT, SOD, and GPx activities ) following exposure to Pb. 

### 31

Effects observed in occupational cohorts of painters, battery

- and jewelry

- workers

, as well as animal 

### 32May 20 11 2

- 22 DRAFT

– DO NOT CITE OR QUOTE toxicological studies ( applying a wide range of exposur e regimens ) , occurred at blood Pb levels >20 

### 1

μg/dL. 

### 2

Relatively few human studies have been conducted on gastrointestinal toxicity of Pb since the 

### 3

completion of the 2006 Pb AQCD. GI symptoms were observed in battery workers and painters exposed 

### 4

to Pb in Ind ia (mean blood Pb level = 42.40 ± 25.53 and 8.04 ± 5.04 μg/dL, respectively). Toxicological 

### 5

evidence for Pb

- induced GI health effects in rats includes altered muscle relaxations and markers of 

### 6

oxidative stress in the gastric fundus and mucosa. The observat ion of oxidative stress was accompanied 

### 7

gastric mucosal damage following short

- term, sub

- chronic and chronic exposures. The anterior intestine 

### 8

of fish has also been identified as a target of Pb (Section 2.6.2). 

### 9

The endocrine processes most impacted by expo sure to Pb include changes in thyroid function, as 

### 10

well as alteration in sex and stress hormone profiles. TSH was negatively correlated with blood Pb in 

### 11

women that ate fish contaminated with Pb as well as other chemicals (median blood Pb level = 1.7 μg/dL, 

### 12

less than the detection limit for the study), and FT4, but not FT3, was decreased in adolescent male auto 

### 13

repair workers (blood Pb level = 7.3 ± 2.92 μg/dL). Significant differences in the levels of sex hormones, 

### 14

including total and free testosterone, est radiol, aromatase, and luteinizing hormone, were observed in 

### 15

Belgian adolescents residing in areas with different levels of industrial pollution including Pb (mean 

### 16

blood Pb levels of 2.2 μg/dL.) Toxicological evidence for similar effects was observed in ad ults cow 

### 17

reared in an environment containing Pb and other contaminants: positive correlations were reported 

### 18

between blood Pb and plasma T3, T4, and estradiol levels. In study of children (mean age 9.5 years) 

### 19

challenged with an acute stressor, increasing bl ood Pb was associated with significant increases in 

### 20

salivary cortisol responses comparing blood Pb levels of 1.1

- 1.4 μg/dL to blood Pb levels <1 μg/dL. 

### 21

Multiple epidemiologic studies investigated the association between Pb exposure and bone and 

### 22

tooth healt h in adults. High blood Pb has been observed to be associated with decreased BMD in non



### 23

Hispanic white males (blood Pb level = 4.9 μg/dL). In elderly women, blood Pb levels (≥ 8 μg/dL) were 

### 24

associated with an increased risk of falls and fractures, includin g osteoporosis

- related falls. Lin ear 

### 25

skeletal growth in children (7

- 17 years of age [ mean blood Pb level = 7.7 μg/dL) ]) , was negatively 

### 26

correlated with increasing blood Pb levels . Epidemiologic studies ( investigating Pb exposure and tooth 

### 27

loss ) report ed that long

- term, cumulative exposure to Pb is associated with increased odds of tooth loss, 

### 28

periodontitis in men and women, and that periodontitis is associated with oxidative stress/damage in 

### 29

individuals exposed in an occupational setting. 

### 30

New toxicology studies have reported ocular effects (i.e., retinal progenitor cell proliferation) at 

### 31

blood Pb levels as low as <10 μg/dL (Section 5.3.4.3), and one human study reported an association 

### 32

between heavy smoking, increased blood Pb, and cataracts. Investigation of the respiratory effects of Pb 

### 33

exposure has been limited; however, cross

- sectional studies have indicated an association of increasing 

### 34

blood Pb with increased prevalence of respiratory tract illnesses (Section 5.6.4.1) and asthma in children 

### 35May 20 11 2

- 23 DRAFT

– DO NOT CITE OR QUOTE (Section 5. 6.4.2). Additionally, Pb

- induced production of ROS is implicated in increased BR and 

### 1

decrements in lung function (Section 5.6.4.3). 

### 2



## 2.5.8. Cancer

Toxicological literature on the genotoxic, mutagenic, and carcinogenic potential of Pb includes 

### 3

strong evidence of e ffects in laboratory animals. Both the International Agency for Research on Cancer 

### 4

(IARC) and the National Toxicology Program (NTP) have examined the role of Pb in cancer. IARC 

### 5

classified inorganic Pb compounds as probable human carcinogens and organic Pb compounds as not 

### 6

classifiable ( IARC, 2006 ; Rousseau et al., 2005 ) . The NTP reported Pb and Pb compounds to be 

### 7

‘ reasonably anticipated to be human carcinogens ’ ( NTP, 2004 )

. 

### 8

In laboratory studies, high

- dose Pb has been demonstrated to b e an animal carcinogen. Pb is likely 

### 9

to be a human carcinogen based on strong evidence from animal toxicology data ( IARC, 2006 ; Waalkes et 

### 10

al., 1995 ) and less definitive e pidemiological data. Mechanistic understanding of the carcinogenicity of Pb 

### 11

is expanding with work on the antioxidant selenium and metallothionein, a protein that binds Pb and 

### 12

reduces its bioavailability. Pb is clastogenic and mutagenic in some but not all models. Clastogenicity and 

### 13

mutagenicity may be possible mechanisms contributing to cancer , but are not necessarily associated with 

### 14

the induction of cancer . Due to the disruption of metal cofactors binding to Zn

- finger proteins, Pb has the 

### 15

potential to ind uce indirect effects that can contribute to carcinogenicity via interactions at hormone 

### 16

receptors, at cell

- cycle regulatory proteins, with tumor suppressor genes like p53, with DNA repair 

### 17

enzymes, and with histones. These indirect effects may act at a post

- translational level to alter protei n 

### 18

structure and DNA repair. In addition , some evidence of epigenetic changes associated with Pb exposure 

### 19

is available in the recent literature. Epigenetic changes may further alter DNA repair or change the 

### 20

expression of a tumor suppressor gene or oncogene. Thus, the animal toxicology literature provides a 

### 21

strong base for understanding the potential contribution of Pb exposure to cancer in laboratory animals. 

### 22

Multiple epidemiologic studies have been performed examining th e association with cancer 

### 23

incidence and mortality with Pb exposure assessed using biological measures and exposure databases. 

### 24

Mixed results have been reported for cancer mortality studies; one strong epidemiologic study of US 

### 25

adults ( Schober et al., 2006 ) demonstrated a positive association between blood Pb and cancer mortality, 

### 26

but the other studies reported null results ( Menke et al., 2006 ) . Although the previous P b AQCD reported 

### 27

that some studies were suggestive of an association between Pb exposure and lung cancer, current studies, 

### 28

which mostly examined occupational exposure observed no associations. Most studies of Pb and brain 

### 29

cancer were null among the overall study population, but positive associations were observed among 

### 30

individuals with certain genotypes. A limited amount of research on other types of cancer has been 

### 31

performed. The previous Pb AQCD reported evidence that suggested an association between Pb ex posure 

### 32May 20 11 2

- 24 DRAFT

– DO NOT CITE OR QUOTE and stomach cancer, but recent studies of this association are lacking, with only one study published since 

### 1

the last Pb AQCD ( U.S. EPA, 2006 ) , which reported mixed results. 

### 2

Among epidemiologic studies on genotoxicity, positive associations were obser ved between high 

### 3

Pb blood levels and sister chromatid exchange (SCE) among adults but not children. Other epidemiologic 

### 4

studies of DNA damage reported inconsistent results. Consistent with previous toxicological findings, Pb 

### 5

does appear to have genotoxic a ctivity inducing SCE, MN and DNA strand breaks. Only PbCrO 4 

### 6

produces chromosomal aberrations but this effect is likely due to chromate. Pb does not appear to be very 

### 7

mutagenic unless a cell signaling pathway was disturbed. 

### 8

Epigenetic effects, particularly with respect to methylation and effects on DNA repair were 

### 9

observed consistently. In humans, epigenetic studies examining Pb and LINE

- 1 and Alu consistently 

### 10

demonstrated an inverse association between patella Pb and global DNA LINE

- 1 methylation ( Pilsner et 

### 11

al., 2009 ; R. O. Wright et al., 2010 ) . Toxicological stu dies show that Pb can activate or interfere with a 

### 12

number of signaling and repair pathways, though it is unclear whether these are in response to epigenetics 

### 13

or genotoxicity. Thus, an underlying mechanism is still unknown, but likely involves either genomi c 

### 14

instability or epigenetic modifications or both. 

### 15

Overall, there is some epidemiologic evidence supporting associations between Pb and cancer. 

### 16

Strong evidence from toxicological studies demonstrates an association between Pb and cancer, 

### 17

genotoxicity/clast ogenicity or epigenetic modification. The collective body of evidence integrated across 

### 18

epidemiologic and toxicological studies is sufficient to conclude that there is a likely causal relationship 

### 19

between Pb exposures and cancer. 

### 20



## 2.5.9. Human Health Effects and C orresponding Blood Pb
Levels

Tables 2

- 2 and 2

- 3 summarize the health effects in children (and adults and the lowest blood Pb 

### 21

level at which the weight of the evidence substantiates a causal relationship. The 2006 Pb AQCD did not 

### 22

identify a safe level of ex posure for Pb and concluded that any threshold for Pb neurotoxicity would have 

### 23

to exist at levels distinctly lower than the lowest exposures examined in the epidemiologic studies 

### 24

included in the assessment. Recent studies continue to find associations betw een a wide range of health 

### 25

endpoints and increasingly lower levels of blood Pb. The lack of a reference population with blood Pb 

### 26

levels reflecting pre

- industrial Pb exposures continues to limit the ability to identify a threshold. 

### 27

Estimates of “ background ” blood Pb levels have been measured in ancient bones from pre

- industrialized 

### 28

societies. These studies suggest that the level of lead in blood in pre

- industrial humans was approximately 

### 29

0.016 μg/dL ( Flegal & Smith, 1992 ) , approximately 65

- fold lower than that currently measured in U.S. 

### 30

population s. In this context, a blood Pb level of 1 μg/dL is not relatively low. Further, if a threshold did 

### 31May 20 11 2

- 25 DRAFT

– DO NOT CITE OR QUOTE ex ist , in order to demonstrate i t, the scale at which blood Pb level is measured will likely have to be 

### 1

adjusted to parts per million (μg/L) instead of parts per hundred thousand (μg/dL). 

### 2

Table 2

- 2. Summary of Pb

- induced health effects in children and the lowest mean blood
P b level in the population(s) studied

Blood
Pb
Level Neurological Effects Renal Effects Immune Effects Effects on Heme Synthesis and RBC
Function

20 μg/dL • Macrophage hyper

inflammation i

15 μg/dL • Lymphocyte activation j • Increased Zn protoporphyrin p

• Lipid peroxidation q

10 μg/dL • Delinquent behavior a

• Increased hearing threshold b • Altered antioxidant enzyme activities r

• Decreased ALAD activit ies s

• Altered hematological

parameters (i.e., decreased hemoglobin) t

5 μg/dL

1 μg/dL • Inattention c

• Decrements in full scale IQ d

• Decrements in specific

neurocognitive domains e

• Poorer school performance f

• ADHD g Decreased eGFR h • Increased B cell abundance k

• Increased IgE l

• Increased risk of infection m

• Decreased T cell abundance n

• Allergic sensitization o • Decreased Ca

- Mg ATPase activity u

Note: Endpoints where the weight of the evidence, overall, substantiates the causal association with blood Pb levels in the range noted on the figure

. Since no evident threshold has yet been clearly established for most effects, the existence of such effects at still lower bl ood Pb levels cannot be ruled out based on available information.

Supporting references: Wright et al

. ( 2008 ) a ; Hwang et al. ( 2009 ) and Schwartz and Otto ( 1991 ) b ; Nicolescu et al. ( 2010 ) c ; Kim et al. ( 2009 ) d ; Krieg et al. ( 2010 ) e ; Miranda et al. ( 2009 ) f ; Braun et al. ( 2006 ) and Braun et al. ( 2008 ) g ; Fadrowski et al. ( 2010 ) h ; Pineda

- Zavaleta et al. ( 2004 ) I ; Lutz et al. ( 1999 ) j ; Sarasua et al. ( 2000 ) k ; Karmaus et al. ( 2005 ) l ; Karmaus et al. ( 2005 ) m ; Karmaus et al. ( 2005 ) n ; Jedrychowski et al. ( 2011 ) o ; Wang et al. ( 2010 ) p ; Ahamed et al. ( 2006 ) q ; Ahamed et al. ( 2005 ) r ; Wang et al. ( 2010 ) s ; Riddell et al. ( 2007 ) t ; Huel et al. ( 2008 ) uMay 20 11 2

- 26 DRAFT

– DO NOT CITE OR QUOTE Table 2

- 3. Summary of Pb

- induced health effects in adults and the lowest mean blood
P b level in the population(s) studied

Blood
Pb Level Neurological Effects Cardiovascular
Effects Renal Effects Immune Effects Reproductive Effects and
Birth
Outcomes Effects on Heme Synthesis and RBC Function

30 μg/dL • Arrhythmia g • Decreased neutrophil function p • Sperm abnormalities u • Decreased hematocrit w

• Decreased Ca

- Mg

ATPase activity x

20 μg/dL • Impaired renal tubular function n • Increased auto

antibodies q

15 μg/dL • Brain MRI changes a

• Increased hearing

threshold b

10 μg/dL

• Criminal arrest c • Lipid peroxidation y

• Decreased

antioxidant enzyme activities y

• Altered

hematological parameters (e.g., decreased hemoglobin, packed cell volume) z

• Decreased serum

erythropoietin aa

• Increased Zn

pro toporphyrin bb

• Altered ALAD

activity bb

5 μg/dL

1 μg/dL • Decrements in cognitive function d

• Essential tremor e

• Mood disorders f • Mortality h

• Decreased HRV i

• Ischemic heart

disease j

• Peripheral Artery

Disease k

• Hypertension l

• Increased BP m • Elevated serum creatinine o ( ↓ creatinine clearance, GFR) • Shift to Th2 cytokines r

• Increased

bronchial reactivity s

• Increased

inflammation t • Delayed p uberty v

Note: Endpoints where the weight of the evidence, overall, substantiates the causal association with blood Pb levels in the range noted on the figure

. Since no evident threshold has yet been clearly established for most effects, the existence of such effects at still lower blood Pb levels cannot be ruled out based on available information

. Supporting references: Brubaker et al. ( 2010 ; 2009 ) a ; Hwang et al. ( 2009 ) and Chuang et al. ( 2007 ) b ; Wright et al. ( 2008 ) c ; Krieg et al. ( 2009 ) d ; Dogu et al. ( 2007 ) e ; Bouchard et al. ( 2009 ) f ; Reza et al. ( 2008 ) g ; Menke et al. ( 2006 ) h ; Park et al. ( 2009 ) i ; Jain et al. ( 2007 ) j ; Muntner et al. ( 2005 ) k ; Scinicariello et al. ( 2010 ) and Park et al. ( 2009 ) l ; Scinicariello et al. ( 2010 ) and Martin et al. ( 2006 ) m ; Sun et al. ( 2008 )

, Lin and Tai

- yi ( 2007 ) and Wang et al. ( 2010 ) n ; Tsaih et al. ( 2004 )

, Akesson et al. ( 2005 ) and Yu et al. ( 2004 ) o ; Valentino et al. ( 1991 ) p ; El

- Fawal et al. ( 1999 ) q ; Kim et al. ( 2007 ) r ; Min et al. ( 2008 ) s ; Songdej et al. ( 2010 ) t ; Telisman et al. ( 2007 ) and Hsu et al. ( 2009 ) u ; Hauser et al. ( 2008 )

, Williams et al. ( 2010 )

, Denham et al. ( 2005 )

, Selevan et al. ( 2003 ) and Wu et al. ( 2003 ) v ; Karita et al. ( 2005 ) w ; Abam et al. ( 2008 ) x ; Ergurhan

- Ilhan et al. ( 2008 ) y ; Ukaejiofo et al. ( 2009 ) z ; Sakata et al. ( 2007 ) aa ; Wang ( 2010 ) bb



# 2.6. Ecological Effects

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

### 1

Pb. The results from the studies evaluated in combination with the evidence from other disciplines (e.g., 

### 2

fate and transport) contribute to the causal determ inations for the ecological outcomes discussed in this 

### 3

assessment. In the following sub

- sections

, a discussion of the causal determinations is presented for the 

### 4May 20 11 2

- 27 DRAFT

– DO NOT CITE OR QUOTE ecological effects. Effects determined to be causal at the species level contribute to the body of evidence 

### 1

for causal effects at the community and ecosystem scale. Where the causal determination varies 

### 2

substantially between types of organisms (typically between plants and other organisms), the divergence 

### 3

is noted. 

### 4

The evidence used to formulate ea ch causal determination is summarized here, and the 

### 5

corresponding detailed discussion can be found in Chapter 7 of this document. In Chapter 7, the effects on 

### 6

terrestrial (Section 7.2) and aquatic (Section 7.3) ecosystems are presented separately, and each of the 

### 7

sections first discusses effects at the species level, followed by community and ecosystem levels. In each 

### 8

of the two main sections, biogeochemistry and chemical effects of Pb that influence bioavailability are 

### 9

considered first, as Pb must first mo ve from the environmental media (soil, water, sediment etc.) into 

### 10

biota. Next, uptake of Pb from soil and water are discussed, then new information on biological effects of 

### 11

Pb on plants, invertebrates and vertebrates, followed by data on exposure

- response relationships. 

### 12

Ecosystem

- scale responses to Pb exposure are considered along with critical loads, characterization of 

### 13

sensitivity and vulnerability, and the effect of Pb on ecosystem services. Finally, in Section 7.4, a 

### 14

synthesis of the effects of Pb obser ved across terrestrial and aquatic habitats is presented along with 

### 15

causal determinations for those effects , which are also summarized in Table 2

- 4 below . In this chapter, Pb 

### 16

effects on terrestrial and aquatic systems from Chapter 7 are summarized (Section s 2.6.1 and 2.6.2); 

### 17

followed by a summary of the evidence for the causal determinations (Sections 2.6.3 to 2.6.10) and 

### 18

consideration of atmospheric deposition of Pb as related to ecological effects (Section 2.6.11). 

### 19

Table 2

- 4. Summary of causal determinat ions for Pb in plants, vertebrates and
invertebrates

Effect Causality Determination

Bioaccumulation

– All Organisms Causal Relationship
Mortality

- Plants Inadequate to Infer Causal Relationship
Mortality

- Vertebrates and Invertebrates Causal Relationship

Growth

- Plants Causal Relationship

Growth

- Invertebrates Causal Relationship

Growth

- Vertebrates Suggestive of a Causal Relationship
Physiological Stress

– All Organisms Causal Relationship
Hematological Effects

– Invertebrates and Vertebrates Causal Relationship
Development and Reproduction

- Invertebrates and Vertebrates Causal Relationship
Development and Reproduction

- Plants Inadequate to Infer Causal Relationship

Neurobehavior

– Invertebrates and Vertebrates Causal Relationship
Community and Ecosystem Level Effects Causal RelationshipMay 20 11 2

- 28 DRAFT

– DO NOT CITE OR QUOTE 

## 2.6.1. Summary of Terrestrial Ecosystem Effects

Section 7.2 focuses on the effects of Pb in terrestrial systems. Pb in terrestrial ecosystems is either 

### 1

deposited directly onto plant surfaces, or incorporated into soil where it can bind with organic matter or 

### 2

dissolve in pore water. The amount of Pb diss olved in soil pore water determines the impact of soil Pb on 

### 3

terrestrial ecosystems to a much greater extent than the total amount present. It has long been established 

### 4

that the amount of Pb dissolved in soil solution is controlled by at least six variable s: (1) solubility 

### 5

equilibria; (2) adsorption

- desorption relationship of total Pb with inorganic compounds; (3) adsorption



### 6

desorption reactions of dissolved Pb phases on soil organic matter; (4) pH; (5) CEC; and (6) aging. Since 

### 7

2006, further details have b een contributed to the understanding of the role of pH, cation exchange 

### 8

capacity (CEC), organic matter, and aging. Smolders et al. ( 2009 ) demonstrated that the two most 

### 9

important determinants of both Pb solubility and toxicity in soils are pH and CEC. However, they had 

### 10

previously shown that aging, primarily in the form of initial leaching following deposition, decreases 

### 11

soluble metal fraction by approximately one order of magnitude ( Smolders et al., 2007 ) . Since 2006, 

### 12

organic matter has been confirmed as an important influence on Pb sequestration, leading to longer

- term 

### 13

retention in soils with higher organic matter content, and also creating the potential for later release of 

### 14

deposited Pb. Aging, b oth under natural conditions and simulated through leaching, was shown to 

### 15

substantially decrease bioavailability to plants, microbes, and vertebrates. 

### 16

There is evidence over several decades of research previously reviewed in Pb AQCDs and in recent 

### 17

studies reviewed in this ISA that Pb bioaccumulates in plants, invertebrates and vertebrates in terrestrial 

### 18

systems. Studies wit h herbaceous species growing at various distances from smelters added to the 

### 19

existing strong evidence that atmospherically transported P b is taken up by plants. These studies did not 

### 20

establish the relative proportion that originated from atmospheric Pb deposited in the soil, as opposed to 

### 21

that taken up directly from the atmosphere through the leaves. Multiple new studies showed that in tre es, 

### 22

the latter is likely to be very substantial. One study attempted to quantify it, and suggested that 50% of the 

### 23

Pb contained in Scots Pine in Sweden is taken up directly from the atmosphere. Studies with herbaceous 

### 24

plants found that in most species test ed, soil Pb taken up by the roots is not translocated into the stem and 

### 25

leaves. Studies with trees found that soil Pb is generally translocated from the roots. 

### 26

Since the 2006 Pb AQCD, various species of terrestrial snails have been found to accumulate Pb 

### 27

from both diet and soil. New studies with earthworms have found that both internal concentration of Pb 

### 28

and mortality increase with decreasing soil pH and CEC. In addition, tissue concentration differences 

### 29

have been found in species of earthworms that burro w in different soil layers. The rate of accumulation in 

### 30

each of these species may result from layer differences in interacting factors such as pH and CEC. 

### 31

Because earthworms often sequester Pb in granules, some authors have suggested that earthworm Pb is 

### 32

n ot bioavailable to their predators. There is some evidence that earthworm activity increases Pb 

### 33

availability in soil, but it is inconsistent. In various arthropods collected at contaminated sites, recent 

### 34May 20 11 2

- 29 DRAFT

– DO NOT CITE OR QUOTE studies found gradients in accumulated Pb that corre sponded to gradients in soil with increasing distance 

### 1

from point sources. 

### 2

There were a few new studies of Pb bioavailability and uptake in birds since the 2006 Pb AQCD. 

### 3

Several found tissue levels in birds that indicated exposure to Pb, but none of the loc ations for these 

### 4

studies was in proximity to point sources, and the origin of the Pb could not be identified. A study at the 

### 5

Anaconda Smelter Superfund site found increasing Pb accumulation in gophers with increasing soil Pb 

### 6

around the location of capture. A study of swine fed various Pb

- contaminated soils showed that the form 

### 7

of Pb determined accumulation. New studies were able to measure Pb in the components of various food 

### 8

chains that included soil, plants, invertebrates, arthropods and vertebrates. They confirmed that trophic 

### 9

transfer of Pb is pervasive, but no consistent evidence of trophic magnification was found. 

### 10

Evidence in this review further supports the findings of the previous Pb AQCDs that biological 

### 11

effects of Pb on terrestrial organisms vary w ith species and lifestage, duration of exposure, form of Pb, 

### 12

and soil characteristic s. In photosynthetic organisms, experimental studies have added to the existing 

### 13

evidence of photosynthesis impairment in plants exposed to Pb, and have found damage to phot osystem II 

### 14

due to alteration of chlorophyll structure, as well as decreases in chlorophyll content in diverse taxa, 

### 15

including lichens and mosses. A substantial amount of evidence of oxidative stress in response to Pb 

### 16

exposure has also been produced. Reacti ve oxygen species were found to increase in broad bean and 

### 17

tomato plants exposed to increasing concentrations of soil Pb, and a concomitant increase in superoxide 

### 18

dismutase, glutathione, peroxidases, and lipid peroxidation, as well as decreases in catalase were observed 

### 19

in the same plants. Monocot, dicot, and bryophytic taxa grown in Pb

- contaminated soil or in 

### 20

experimentally spiked soil all responded to increasing exposure with increased antioxidant activity. In 

### 21

addition, reduced growth was observed in some experiments, as well as genotoxicity, decreased 

### 22

germination, and pollen sterility. 

### 23

In terrestrial invertebrates, evidence for Pb effects have included neurological and reproductive 

### 24

endpoints. Recently published studies have shown neuronal damage in nemato des exposed to low 

### 25

concentrations of Pb (2.5 μM), accompanied by behavioral abnormalities. Reproductive adverse effects 

### 26

were found at lower exposure in younger nematodes, and effects on longevity and fecundity were shown 

### 27

to persist for several generations. Increased mortality was found in earthworms, but was strongly 

### 28

dependent on soil characteristics including pH, CEC, and aging. Snails exposed to Pb through either 

### 29

topical application or through consumption of Pb

- exposed plants had increased antioxidant act ivity, and 

### 30

decreased food consumption, growth, and shell thickness. Effects on arthropods exposed through soil or 

### 31

diet varied with species and exposure conditions, and included diminished growth and fecundity, 

### 32

endocrine and reproductive anomalies, and body deformities. Increasing concentration of Pb in the 

### 33

exposure medium generally resulted in increased effects within each study, but the relationship between 

### 34

concentration and effects varied between studies, even when the same medium, e.g., soil, was used. 

### 35

E vidence suggested that aging and pH are important modifiers. 

### 36May 20 11 2

- 30 DRAFT

– DO NOT CITE OR QUOTE Effects on amphibian and reptiles included decreased white blood cell counts, decreased testis 

### 1

weight, and behavioral anomalies. However

, large differences in effects were observed at the same 

### 2

co ncentration of Pb in soil, depending on whether the soil was freshly amended or field

- collected from 

### 3

contaminated areas. As in most studies where the comparison was made, effects were smaller when field



### 4

collected soils were used. In some birds, maternal el evated blood Pb level was associated in recent studies 

### 5

with decreased hatching success, smaller clutch size, high corticosteroid level, and abnormal behavior. 

### 6

Some species evidenced little or no effect of elevated blood Pb level. Effects of dietary exposur e were 

### 7

studied in several mammalian species, and cognitive, endocrine, immunological, and growth effects were 

### 8

observed. 

### 9

Evidence reviewed in Sections 7.2.3 and 7.2.4 demonstrates clearly that increased exposure to Pb is 

### 10

generally associated with negative effects in terrestrial ecosystems. It also demonstrates that many factors, 

### 11

including species and various soil physiochemical properties, interact strongly with Pb concentration to 

### 12

modify those effects. In these ecosystems, where soil is generally the main component of the exposure 

### 13

route, Pb aging is a particularly important factor, and one that may be difficult to reproduce 

### 14

experimentally. Without quantitative characterization of those interactions, characterizations of exposure



### 15

response relationships would likely not be transferable outside of experimental settings. Since the 2006 

### 16

Pb AQCD, a few studies of exposure

- response have been conducted with earthworms, and results have 

### 17

been inconsistent. 

### 18

New evidence of effects of Pb at the community and ecosystem s cale include several studies of the 

### 19

ameliorative effects of mycorrhizal fungi on plant growth, attributed to decreased uptake of Pb by plants, 

### 20

although both mycorrhizal fungus and plant were negatively affected. Most recently published research 

### 21

on communit y and ecosystem scale effects of Pb has focused on soil microbial communities, which have 

### 22

been shown to be impacted in both composition and activity. Many recent studies have been conducted 

### 23

using mixtures of metals, but have tried to separate the effects o f individual metals when possible. Soil 

### 24

microbial activity was generally diminished, but in some cases recovered ov er time. Species and genotype 

### 25

composition were consistently altered, and those changes were long

- lasting or permanent. Recent studies 

### 26

have ad dressed differences in sensitivity between species explicitly, and have clearly demonstrated high 

### 27

variability between related species, as well as within larger taxonomic groupings. Mammalian no 

### 28

observed effect concentration (NOEC) values expressed as blood Pb levels were shown to vary by a 

### 29

factor of 8, while avian blood NOECs varied by a factor of 50 ( Bu ekers et al., 2009 ) . Protective effects of 

### 30

dietary Ca have been found in plants, birds, and invertebrates. 

### 31



## 2.6.2. Summary of Aquatic Ecosystem Effects

Section 7.3 focuses on the effects of Pb in aquatic systems. Once atmospherically

- derived Pb enters 

### 32

surface waters, its fate and bioavailability are influenced by Ca 2+ concentration, pH, alkalinity, total 

### 33May 20 11 2

- 31 DRAFT

– DO NOT CITE OR QUOTE suspended solids, and dissolved organic carbon (DOC, including humic acids ) . In sediments, Pb 

### 1

bioavailability may be influenced by the presence of other metals , sulfides, Fe and Mn oxides and 

### 2

physical disturbance. In many, but not all aquatic organisms, Pb dissolved in the water can be the primary 

### 3

exposure route to gills or other biotic ligands. As recognized in the 2006 Pb AQCD and further supported 

### 4

in this rev iew, chronic exposures to Pb may also include dietary uptake, and there is an increasing body of 

### 5

evidence showing that differences in uptake and elimination of Pb vary with species. Currently available 

### 6

models for predicting bioavailability focus on acute t oxicity and do not consider all possible routes of 

### 7

uptake. They are therefore of limited applicability, especially when considering species

- dependent 

### 8

differences in uptake and bioaccumulation of Pb. 

### 9

According to the 2006 Pb AQCD, and further supported in this review, Pb adsorption, 

### 10

complexation, chelation, etc., are processes that alter bioavailability to aquatic biota. Given the low 

### 11

solubility of Pb in water, bioaccumulation by aquatic organisms may preferentially occur via exposure 

### 12

routes other than dire ct absorption from the water column, including ingestion of contaminated food and 

### 13

water, uptake from sediment pore waters, or incidental ingestion of sediment. 

### 14

There are considerable differences between species in the amount of Pb taken up from the 

### 15

environment and in the levels of Pb retained in the organism and closely related species can vary greatly 

### 16

in bioaccumulation of Pb and other non

- essential metals. Recent studies on uptake of Pb by aquatic plants 

### 17

and algae support the findings of previous P b AQCDs that all plants tend to sequester larger amounts of 

### 18

Pb in their roots than in their shoots, and provide additional evidence for species differences in 

### 19

compartmentalization of sequestered Pb and in responses to Pb in water and sediments. In inverteb rates, 

### 20

Pb can be bioaccumulated from multiple sources, including the water column, sediment, and dietary 

### 21

exposure. Since the last review, new studies using stable isotopes have enabled simultaneous 

### 22

measurement of uptake and elimination in several aquatic o rganisms to assess the relative importance of 

### 23

water versus dietary uptake. In uptake studies of various invertebrates, Pb was mainly found in the gills 

### 24

and digestive gland/hepatopancreas. There is more information now on the cellular and subcellular 

### 25

distri bution of Pb in invertebrates than there was at the time of writing the 2006 Pb AQCD. Specifically, 

### 26

localization of Pb at the ultrastructural level has been assessed in several species. 

### 27

The conclusions of the 2006 Pb AQCD that the gill is a major site of P b uptake in fish and that 

### 28

there are species differences in the rate of Pb accumulation and distribution of Pb within the organism are 

### 29

supported in this review. The anterior intestine has been newly identified as a site of uptake of Pb through 

### 30

dietary expos ure studies. There are few new studies on Pb uptake by amphibians and mammals. At the 

### 31

time of the publication of the 2006 Pb AQCD, trophic transfer of Pb through aquatic food chains was 

### 32

considered to be negligible. Measured concentrations of Pb in the tiss ues of aquatic organisms were 

### 33

generally higher in algae and benthic organisms than in higher trophic

- level consumers, indicating that Pb 

### 34

was bioconcentrated but not biomagnified. Some studies published since the 2006 Pb AQCD support the 

### 35May 20 11 2

- 32 DRAFT

– DO NOT CITE OR QUOTE potential for trans fer of Pb in aquatic food webs, while other studies indicate that Pb concentration 

### 1

decreases with increasing trophic level (biodilution). 

### 2

Evidence in this ISA further supports the findings of the previous Pb AQCDs that waterborne Pb is 

### 3

highly toxic to aqu atic organisms, with toxicity varying with species and lifestage, duration of exposure, 

### 4

form of Pb, and water quality characteristics. Effects of Pb on algae reported in the 2006 Pb AQCD are 

### 5

further supported by evidence from additional species in this rev iew. They include decreased growth, 

### 6

deformation and disintegration of cells, and blocking of the pathways that lead to pigment synthesis, thus 

### 7

affecting photosynthesis. Effects on plants supported by additional evidence in this review include 

### 8

oxidative dam age, decreased photosynthesis and reduced growth. The mechanism of Pb toxicity in plants 

### 9

is likely mediated by damage to photosystem II through alteration of chlorophyll structure. Elevated 

### 10

levels of antioxidant enzymes are commonly observed in aquatic pla nt, algae, and moss species exposed 

### 11

to Pb. 

### 12

Since the 2006 Pb AQCD, there is additional evidence for Pb effects on antioxidant enzymes, lipid 

### 13

peroxidation, stress response and osmoregulation in aquatic invertebrates. Studies of reproductive and 

### 14

development al effects of Pb in this review provide further support for findings in the 2006 Pb AQCD. 

### 15

These new studies include reproductive endpoints for rotifers and freshwater snails as well as 

### 16

multigenerational effects of Pb in mosquito larvae. Growth effects are observed at lower concentrations in 

### 17

some aquatic invertebrates since in the 2006 Pb AQCD, including juveniles of the freshwater snail 

### 18

Lymnaea stagnalis where growth is affected at <4 μg Pb/L ( Grosell et al., 2006 ) . Behavioral effects of Pb 

### 19

in aquatic invertebrates reviewed in this ISA include decreased valve closing speed in scallops and slower 

### 20

feeding rate in blackworms. 

### 21

Evidence in this ISA supports the findings of reproductive, behavioral, and growth effects in 

### 22

previous Pb AQCDs, as well as effects on blood parameters in vertebrates. Additional mechanisms of Pb 

### 23

toxicity have been elucidated in the gi ll and the renal system of fish since the 2006 Pb AQCD. 

### 24

Furthermore, the mitogen

- activated protein kinases, ERK1/2 and p38 MAPK were identified for the first 

### 25

time as possible molecular targets for Pb neurotoxicity in a teleost ( Leal et al., 2006 ) . In the 2006 Pb 

### 26

AQCD, amphibians were considered to be relatively tolerant to Pb. Observed responses to Pb exposure 

### 27

included decreased enzyme activity (e.g., ALAD reduction) and changes in behavior. Since the 2006 Pb 

### 28

AQCD, studies conducted at concentrations approaching environmental levels of Pb have indicated 

### 29

sublethal effects on tad pole endpoints including growth, deformity, and swimming ability. 

### 30

Concentration

- response data from plants, invertebrates and vertebrates is consistent with findings 

### 31

in previous AQCDs of species differences in sensitivity to Pb in aquatic systems. In this I SA ( and 

### 32

previous AQCDs )

, aquatic plant growth was shown to be adversely affected by Pb exposure. The lowest 

### 33

EC 50 for growth observed in marine microalgae and freshwater microalgae was in the range of 100 μg 

### 34

Pb/L. In the 2006 Pb AQCD, concentrations at whic h effects were observed in aquatic invertebrates 

### 35

ranged from 5 to 8,000 μg/L. Several studies in this review have provided evidence of effects at lower 

### 36May 20 11 2

- 33 DRAFT

– DO NOT CITE OR QUOTE concentrations. Among the most sensitive species , growth of juvenile freshwater snail s ( L. stagnalis ) wa s 

### 1

inhibited at an EC 20 of <4 μg Pb/L. ( Grosell & Brix, 2009 ; Grosell et al., 2006 )

. A chronic value of 10 μg 

### 2

Pb/L obtained in 28

- day exposures of 2

- month

- old Lampsilis siliquoidea juveniles was the lowest genus 

### 3

mean chronic value ever reported for Pb ( N. Wang et al., 2010 ) . In the 2006 Pb AQCD, adverse effects 

### 4

were found in freshwater fish at concentrations ranging from 10 to >5,400 μg Pb /L, generally depending 

### 5

on water quality variables (e.g., pH, hardness, salinity). Additional t esting of Pb toxicity under conditions 

### 6

of varied alkalinity, DOC, and pH has been conducted since the last review. However, adverse effects in 

### 7

fish observed in recent studies fall within the range of concentrations observed in the previous Pb AQCD. 

### 8

Since t he 2006 Pb AQCD, additional evidence for community and ecosystem level effects of Pb 

### 9

have been observed primarily in microcosm studies or field studies with other metals present. Ecological 

### 10

effects associ ated with Pb, reported in previous Pb AQCDs

, include alteration of predator

- prey dynamics, 

### 11

species richness, species composition, and biodiversity. New studies in this ISA provide evidence in 

### 12

additional habitats for these community and ecological

- scale effects, specifically in aquatic macrophyte 

### 13

communities and sediment

- associated communities. Different species may exhibit different responses to 

### 14

Pb

- impacted ecosystems dependent not only upon other environmental factors (e.g., temperature, pH), but 

### 15

also on the species sensitivity, lifestage, or seasonally

- aff ected physiological state. 

### 16



## 2.6.3. Bioaccumulation of Lead in Terrestrial and Aquatic Biota as it Affects Ecosystem Services

Pb deposited on the surface of, or taken up by organisms has the potential to alter the services 

### 17

provided by terrestrial and aquatic biota to humans. Ecosystem services are the benefits people obtain 

### 18

from ecosystems. They include supporting, provisioning, regulating and cultural services that are vital for 

### 19

the functioning of the biosphere and provide the basis for the delivery of tangible ben efits to human 

### 20

society. There is compelling evidence over several decades of research and in recent studies reviewed in 

### 21

this ISA (Sections 7.2.3 and 7.3.3.) that Pb bioaccumulates in plants, invertebrates and vertebrates in 

### 22

terrestrial and aquatic systems. Generally, there are considerable differences between species in the 

### 23

amount of Pb taken up from the environment

, and in the amounts of Pb retained in the organism. In order 

### 24

for Pb to reach a biological receptor, the metal must first cross the membranes of organisms to reach the 

### 25

target organ or site of storage. This process varies between plants, invertebrates and vertebrates, and 

### 26

furthermore, uptake and sequestration are at times similar in unrelated species, while substantially 

### 27

different between related o nes. Uptake of Pb from environmental media is dependent upon the 

### 28

bioaccessibility of Pb (reviewed in Chapter 3) which is influenced by many factors including, but not 

### 29

limited to, temperature, pH, presence of humic acid and dissolved organic matter, presenc e of other 

### 30

metals, and speciation of Pb. 

### 31May 20 11 2

- 34 DRAFT

– DO NOT CITE OR QUOTE Pb is bioaccumulated in plants, invertebrates and vertebrates inhabiting terrestrial and aquatic 

### 1

systems that receive Pb from atmospheric deposition. This represents a potential route for Pb mobilization 

### 2

into the f ood web or into food products. For example, Pb bioaccumulation in leaves and roots of an edible 

### 3

plant may represent an adverse impact to the provisioning of food, an essential ecosystem service. Recent 

### 4

research has suggested that dietary Pb (i.e., Pb adsor bed to sediment, particulate matter, and food) may 

### 5

contribute to exposure and toxicity in primary and secondary order consumers (including humans). 

### 6

Although there is no consistent evidence of trophic magnification

, there is substantial evidence of trophic 

### 7

transfer. It is through consumption of Pb

- exposed prey or Pb

- contaminated food that atmospherically 

### 8

deposited Pb reaches species that may have very little direct exposure to it. Overall, based on the 

### 9

consistency of findings across taxa, the evidence is suf ficient to conclude that there is a causal 

### 10

relationship between Pb exposures and bioaccumulation of Pb that affects ecosystem services 

### 11

associated with terrestrial and aquatic biota. 

### 12



## 2.6.4. Mortality

The relationship between Pb exposure and mortality has been well demonstrated in terrestrial and 

### 13

aquatic species as presented in Sections 7.2.5 and 7.3.5 of this ISA and in the previous Pb AQCDs. 

### 14

Toxicological studies have established LC 50 values for some species of plants, invertebrates and 

### 15

vertebrates. From the LC 50 data on Pb in this review and previous Pb AQCDs a wide range of sensitivity 

### 16

to Pb is evident across taxa. However, the LC 50 is usually much higher than current environmental levels 

### 17

of Pb, even though physiological dysfunction that adversely impacts the fitness of an organism often 

### 18

occurs well below concentrations that result in mortality. 

### 19

Pb is generally not phytotoxic to pla nts at concentrations found in the environment away from 

### 20

point

- sources, probably due to the fact that plants often sequester large amounts of Pb in roots, and that 

### 21

translocation to other parts of the plant is limited. Invertebrates are generally more sensi tive to Pb 

### 22

exposure than other taxa, with survival adversely impacted in a few species at concentrations occurring 

### 23

near point

- sources, or at concentrations near ambient levels. These impacted species may include 

### 24

candidate or endangered species. The freshwa ter mussel Lampsilis rafinesqueana (Neosho mucket), is a 

### 25

candidate for the endangered species list. The EC 50 for foot movement (a measure of viability) for newly 

### 26

transformed juveniles of this species was 188 μg Pb/L. Other invertebrates such as odonates ma y be 

### 27

tolerant of Pb concentrations that greatly exceed environmental levels. 

### 28

Thirty day LC 50 values for larval fathead minnows ranged from 39 to 1

, 903 μg/L in varying 

### 29

concentrations of DOC, CaSO 4 and pH. ( Grosell et al., 2006 ) . In a recent study of rainbow trout fry at 2

- 4 

### 30

weeks post

- swim up, the 96

- hour LC 50 was 120 μg Pb /L at a hardness of 29 mg/L a s CaCO 3 , a value 

### 31

much lower than in testing with older fish ( Mebane et al., 2008 )

. 

### 32May 20 11 2

- 35 DRAFT

– DO NOT CITE OR QUOTE The evidence is inadequate to conclude that there is a causal relationship between Pb and 

### 1

mortality in plants. 

### 2

The evidence is sufficient to conclude that there is a causal relationship between Pb exposures 

### 3

and mortality in sensitive terrestrial and aquatic animal taxa. 

### 4



## 2.6.5. Growth Eff ects

Evidence for Pb effects on growth is strongest in plants, with limited information in invertebrates 

### 5

and vertebrates. There is evidence over several decades of research that Pb inhibits photosynthesis and 

### 6

respiration in plants, both of which reduce gro wth ( U.S. EPA, 1977

, 2006 ) . Many laboratory and 

### 7

greenhouse toxicity studies have reported effects on plants, and t here are few field toxicity studies. Pb has 

### 8

been shown to affect photosystem II with the hypothesized mechanism being that Pb may replace either 

### 9

Mg or Ca in chlorophyll, altering the pigment structure and decreasing the efficiency of visible light 

### 10

absorpti on by affected p lants. Decreases in chlorophyll a and b content have been observed in various 

### 11

algal and plant species. The lowest 72

- hour EC 50 for growth inhibition reported for algae was 105 μg Pb/L 

### 12

in Chaetoceros sp. Most primary producers experience EC 50 values for growth in the range of 1,000 to 

### 13

100,000 μg Pb/L ( U.S. EPA, 2006 )

. 

### 14

In previous Pb AQCDs, growth effects of Pb have been reported in fish (growth inhibition), birds 

### 15

(changes in juvenile weight gain), and frogs (delayed metamorphosis, smaller lar vae). Growth effects 

### 16

observed in invertebrates and vertebrates underscore the importance of lifestage to overall Pb 

### 17

susceptibility. In general, juvenile organisms are more sensitive than adults. Several studies since the last 

### 18

review have demonstrated effec ts of Pb on growth at lower concentrations than in previous literature. 

### 19

Among the animal taxa tested, aquatic invertebrates were the most sensitive to the effect of Pb, with 

### 20

adverse effects being reported as low as 4 μg Pb/L. Growth of juvenile freshwater snails L. stagnalis was 

### 21

inhibited at EC 20 <4 μg Pb/L ( Grosell & Brix, 2009 ; Grosell et al., 2006 ) . In the freshwater mussel, 

### 22

fatmucket ( L. siliquoidea ) juveniles were the most sensitive lifestage ( N. Wang et al., 2010 ) . A chronic 

### 23

value of 10 μg Pb/L in a 28

- day exposure of 2

- month

- old fatmucket juveniles was the lowest genus mean 

### 24

chronic value ever reported for Pb. 

### 25

Evidence is sufficient to conclude that th ere is a causal relationship between Pb exposures and 

### 26

growth effects in plants and invertebrates. Evidence is suggestive of a causal relationship between 

### 27

Pb exposures and growth effects in vertebrates. 

### 28



## 2.6.6. Physiological Stress

In this ISA and previous Pb AQCDs, there is consistent and coherent evidence of upregulation of 

### 29

antioxidant enzymes and increased lipid peroxidation associated with Pb exposure in many species of 

### 30

plants, invertebrates and vertebrates. In plants, increases of antioxidant enzymes with Pb exposure occur 

### 31May 20 11 2

- 36 DRAFT

– DO NOT CITE OR QUOTE in algae, aquatic mosses, floating and rooted aquatic macrophytes, and terrestrial species. There is 

### 1

considerable evidence for antioxidant activity in invertebrates, including gastropods, mussels, and 

### 2

crustaceans, in response to Pb expos ure. Upregulation of antioxidant enzymes are also observed in fish. 

### 3

Across all biota, there are differences in the induction of antioxidant enzymes that appear to be species



### 4

dependent. 

### 5

Additional stress responses observed in terrestrial and aquatic inverte brates include elevated heat 

### 6

shock proteins, osmotic stress and decreased glycogen levels. Heat shock protein induction by Pb 

### 7

exposure has been observed in zebra mussels and mites. Tissue volume regulation is adversely affected in 

### 8

freshwater crabs. Glycoge n levels in the freshwater snail Biomphalaria glabrata were significantly 

### 9

decreased at near environmentally

- relevant concentrations (50 μg Pb/L and higher) ( Ansaldo et al., 2006 )

. 

### 10

Upregulation of antioxidant enzymes and increased lipid peroxidation are considered to be reliable 

### 11

biomarkers of stress, and suggest that Pb exposure induces a stress response in th ose organisms, which 

### 12

may increase susceptibility to other stressors and reduce individual fitness. 

### 13

Evidence is sufficient to conclude that there is a causal relationship between Pb exposures and 

### 14

physiological stress in plants, invertebrates and vertebrate s. 

### 15



## 2.6.7. Hematological Effects

Hematological responses are commonly reported effects of Pb exposure in invertebrates and 

### 16

vertebrates in both aquatic and terrestrial systems. In environmental assessments of metal

- impacted 

### 17

habitats, ALAD is a recognized biomarker of Pb exposure ( U.S. EPA, 2006 ) . ALAD activity is negatively 

### 18

correlated with total Pb concentration in bivalves. Lower ALAD activity has been significantly correlated 

### 19

with elevated blood Pb levels in fish and mammals as well. In the 1986 Pb AQCD, decreases in RBC 

### 20

ALAD activity follo wing Pb exposure were well documented in birds and mammals. Further evidence 

### 21

from the 2006 Pb AQCD and this review for Pb effects on ALAD enzymatic activity including effects in 

### 22

bacteria, amphibians and additional field and laboratory studies on fish sugge st this enzyme is an 

### 23

indicator for Pb exposure across a wide range of taxa. Limited evidence of Pb effects on other blood 

### 24

parameters including altered serum profiles and changes in white blood cell counts in fish and amphibians 

### 25

support the finding of the h ematological system as a target for Pb in natural systems. This evidence is 

### 26

strongly coherent with observations from human epidemiologic and animal toxicology studies where a 

### 27

causal relationship was identified between exposure to Pb and hematological effec ts in humans and 

### 28

laboratory animals (Sections 2.5. 5 and 5.7). Based on observations in both terrestrial and aquatic 

### 29

organisms and additionally supported by toxicological and epidemiological findings in laboratory animals 

### 30

and humans

, evidence is sufficient to conclude that there is a causal relationship between Pb exposures 

### 31

and hematological effects in invertebrates and vertebrates. 

### 32May 20 11 2

- 37 DRAFT

– DO NOT CITE OR QUOTE 

## 2.6.8. Developmental and Reproductive Effects

Evaluation of the literature on Pb effects in aquatic and terrestrial species indicates that exposure to 

### 1

Pb is associated with adverse effects on development and reproduction. Evidence in this review and the 

### 2

previous Pb AQCDs from invertebrate and vertebrate studies indicate that Pb is adversely affecting 

### 3

reproductive performance in multiple species. In plants, few studies are available that specifically address 

### 4

reproductive effects of Pb exposure. 

### 5

Several new studies of snails, clams and rotifers support previous findings of adverse impacts to 

### 6

embryonic development. In addition to affecting the embryo, Pb can alter developmental timing, sperm 

### 7

morphology and hormone homeostasis. In fruit flies , Pb exposure increased time to pupation and 

### 8

decreased pre

- adult development. Sperm morphology was altered in earthworms exposed to Pb



### 9

contaminated soil s. Pb may also disrupt hormonal homeostasis in invertebrates as studies with moths have 

### 10

suggested. 

### 11

Reproductive effects have also been observed in multi

- generational studies. Larval settlement rate 

### 12

and rate of population increase was adversely impacted in rotifers. Rotifers have decreased fertilization 

### 13

rate associated with Pb exposure that appeared to be due to decreased viability of sperm and eggs. 

### 14

Evidence of multi

- generational toxicity of Pb is also present in terrestrial invertebrates, specifically 

### 15

spr ingtails, mosquitoes, carabid beetles and nematodes where decreased fecundity in progeny of Pb



### 16

exposed individuals was observed. 

### 17

In aquatic vertebrates there is evidence for reproductive and developmental effects of Pb. Pb



### 18

exposure in frogs has been demon strated to delay metamorphosis, decrease larval size and produce subtle 

### 19

skeletal malformations. Previous Pb AQCDs have reported developmental effects in fish, specifically 

### 20

spinal deformities in larvae. In the 2006 Pb AQCD, decreased spermatocyte developmen t in rainbow trout 

### 21

was observed at 10 μg Pb /L and in fathead minnow testicular damage occurred at 500 μg Pb/L. In fish, 

### 22

there is new evidence in this ISA of Pb effects on steroid profiles. Reproduction in fathead minnows was 

### 23

affected in breeding exposures following 300

- day chronic toxicity testing. However, reproductive 

### 24

performance was unaffected in zebrafish ( Danio rerio ) exposed to Pb

- contaminated prey. Additional 

### 25

reproductive parameters in fish observed to be impacted by Pb include decreased oocyte diame ter and 

### 26

density in toadfish associated with elevated Pb levels in gonad. 

### 27

In terrestrial vertebrates, evidence from Chapter 7 and in previous Pb AQCDs indicates an 

### 28

association between observed adverse reproductive effects and Pb exposure. Decreased testis w eight was 

### 29

observed in lizards. In mammals, few studies in the field have addressed Pb specifically, due to most 

### 30

available data in wild or grazing animals being from near smelters, where animals are co

- exposed to other 

### 31

metals. Other reproductive endpoints i ncluding spontaneous abortions, pre

- term birth, embryo 

### 32

development, placental development, low birth weight, subfecundity, hormonal changes, and teratology 

### 33

were also affected, but less consistently. New toxicological data support trans

- generational effects , a 

### 34May 20 11 2

- 38 DRAFT

– DO NOT CITE OR QUOTE finding that is also an area of emerging interest in the ecology. The e vidence presented in Section 5.8 is 

### 1

sufficient to conclude that there is a causal relationship between Pb exposure and reproductive effects in 

### 2

humans and laboratory animals. The str ongest and most consistent evidence, which was coherent across 

### 3

epidemiologic and toxicological studies, was for effects of Pb on sperm and the onset of puberty in males 

### 4

and females. 

### 5

Adverse effects of Pb on reproduction in invertebrates and vertebrates ind icate that Pb is likely 

### 6

affecting fecundity of Pb

- exposed organisms in both aquatic and terrestrial habitats, and the evidence is 

### 7

sufficient to conclude that ther e is a causal relationship between Pb exposures and reproductive 

### 8

effects in terrestrial and aquatic invertebrates and vertebrates. In plants, the evidenc e is inadequate 

### 9

to conclude a causal relationship between Pb exposures and plant reproductive effects. 

### 10



## 2.6.9. Neurobe havioral Effects

Evidence from laboratory studies and limited data from field studies reviewed in Chapter 7 have 

### 11

shown adverse effects of Pb on neurological endpoints in both aquatic and terrestrial animal taxa. These 

### 12

include changes in behaviors that may decrease the overall fitness of the organism. There is also evidence 

### 13

from both invertebrate and vertebrate studies that Pb adversely affects behaviors that may decrease the 

### 14

ability of an organism to escape predators or capture prey. 

### 15

Central nervous system effects in fish recognized in previous Pb AQCDs include effects on spinal 

### 16

neurons and brain receptors. New evidence from this review identifies the MAPKs ERK1/2 and p38 MAPK 

### 17

as possible molecular targets for Pb neurotoxicity in catfish ( Leal et al., 2006 ) . Additionally, there is new 

### 18

evidence for neurotoxic action of Pb in inve rtebrates with exposure to Pb observed to cause changes in 

### 19

the morphology of GABA motor neurons in nematodes ( C. elegans ) ( Du & Wang, 2009 )

. 

### 20

Decreased food consumption of Pb

- contaminated diet has been demonstrated in some invertebrates 

### 21

(snails) and vertebrates (lizards, pigs). Pb may also decrease the ability of an organism to capture prey or 

### 22

escape predation. For exa mple, Pb exposure has been demonstrated to adversely affect prey capture 

### 23

ability of certain fungal and fish species, and the motility of nematodes was adversely affected in Pb



### 24

contaminated soils ( Wang & Xing, 2008 ) . In a laboratory study, Pb

- exposed gull chicks exhibited 

### 25

abnormal behaviors such as decreased walking, erratic behavioral thermoregulation and food begging that 

### 26

could make them more vulnerable in the wild ( Burger & Gochfeld, 2005 ) . Lizards exposed to Pb through 

### 27

diet in the laboratory exhibited abnormal coloration and posturing behaviors. Other behavioral effects 

### 28

affected by Pb exposure include increased hype ractivity in fish and hypoxia

- like behavior in frogs. 

### 29

These findings are coherent with findings from studies in laboratory animals described in Sections 

### 30

2.5.1 and 5.3 of the ISA that show that Pb induces changes in attention, increased response rates and 

### 31

motor function. The evidence presented in those sections is sufficient to conclude that there is a causal 

### 32

relationship between Pb exposure and neurobehavioral effects (Section 5.3). These data from laboratory 

### 33May 20 11 2

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– DO NOT CITE OR QUOTE toxicology studies, especially neurobehavioral findings and structural changes are highly coherent with 

### 1

data from ecological studies. Overall, the evidence from aquatic and terrestrial systems is sufficient to 

### 2

conclude that the re is a causal relationship between Pb exposures and neurobehavioral effects in 

### 3

invertebrates and vertebrates. 

### 4



## 2.6.10. Community and Ecosystem Level Effects

Uptake of Pb into aquatic and terrestrial organisms and subsequent effects on survival, 

### 5

reproduction, growth, behavior and other physiological variables at the species scale are likel y to result in 

### 6

effects at the population, community and ecosystem scale. The effects may include alteration of predator



### 7

prey dynamics, species richness, species composition, and biodiversity. There are few field studies that 

### 8

directly consider effects of Pb on these measures of ecosystem health. Ecosystem

- level studies are 

### 9

complicated by the confounding of Pb exposure with other factors such as trace metals and acidic 

### 10

deposition. In natural systems, Pb is often found co

- existing with other stressors, and obs erved effects 

### 11

may be due to cumulative toxicity. 

### 12

Most direct evidence of community and ecosystem level effects is from near point sources. For 

### 13

terrestrial systems evidence of impacts on natural ecosystems near smelters, mines, and other industrial 

### 14

sources of Pb has been assembled in previous decades. Those impacts include decreases in species 

### 15

diversity and changes in floral and faunal community composition. For aquatic systems, the literature 

### 16

focuses on evaluating ecological stress from Pb originating from urban and mining effluents rather than 

### 17

atmospheric deposition. In laboratory studies and simulated ecosystems, where it is possible to isolate the 

### 18

effect of Pb, this metal has been shown to alter competitive behavior of species, predator

- prey interactions 

### 19

and contaminant avoidance. These dynamics may change species abundance and community structure at 

### 20

higher levels of ecological organization. Effects of Pb on mortality, growth, physiological stress, blood, 

### 21

neurobehavioral and developmental and reproductive endpoints at the individual level are expected to 

### 22

have ecosystem level consequences, and thus provide consistency and plausibility for causality in 

### 23

ecosystem level effects. 

### 24

Avoidance response to Pb exposure varies widely in different species and this could affect 

### 25

community composition. For example, frogs and toads lack avoidance response while snails and fish 

### 26

avoid higher concentrations of Pb. New evidence , published since the 2006 Pb AQCD indicates that some 

### 27

species of worms will avoid Pb

- contaminated soil s ( Langdon et al., 2005 )

. 

### 28

In terrestrial ecosystems, most studies show decreases in microorganism abundance, diversity, and 

### 29

function with increasing soil Pb concentration. Specifically, shifts in nematode communities, bacterial 

### 30

species, and fungal diversity have been observed. Furt hermore, presence of arbuscular mycorrhizal fungi 

### 31

may protect plants growing in Pb

- contaminated soils. Increased plant diversity ameliorated effects of Pb 

### 32

contamination on a microbial community. 

### 33May 20 11 2

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– DO NOT CITE OR QUOTE Since the 2006 Pb AQCD, there is further evidence for effect s of Pb in sediment

- associated 

### 1

communities. Exposure to three levels of sediment Pb contamination (322, 1,225, and 1,465 μg Pb /g dry 

### 2

weight) in a microcosm experiment significantly reduced nematode diversity and resulted in profound 

### 3

restructuring of the co mmunity structure ( Mahmoudi et al., 2007 ) . Sediment

- bound Pb contamination 

### 4

appears to differentially affect members of the benthic invertebrate community, potentially altering 

### 5

ecosystems dynamics in s mall urban streams ( Kominkova & Nabelkova, 2005 ) . Although surface water 

### 6

Pb concentrations in monitored streams were determined to be very low, concentrations of the metal in 

### 7

sediment were high enough to pose a risk to the benthic community (e.g., 34

- 101 mg Pb/kg ). These risks 

### 8

were observed to be linked to benthic invertebrate functional feeding group, with collector

- gatherer 

### 9

species exhibiting larger body burdens of heavy metals than benthic predators and collector

- filtere rs. 

### 10

In a new study conducted since the 2006 Pb AQCD, changes to aquatic plant community 

### 11

composition have been observed in the presence of elevated surface water Pb concentrations at three lake 

### 12

sites impacted by mining effluents. The site with highest Pb co ncentration (103

- 118 μg Pb /L) had the 

### 13

lowest number of resident aquatic plant species when compared to sites with lower Pb concentrations (78

- 

### 14

92 μg Pb /L) ( Mishra et al., 2008 ) . This shift toward more Pb

- tolerant species is also observed in terrestrial 

### 15

plant communities near smelter sit es ( U .S. EPA, 2006 ) . Certain types of plants such as rooted and 

### 16

submerged aquatic plants may be more susceptible to aerially

- deposited Pb resulting in shifts in Pb 

### 17

community composition. High Pb sediment concentrations are linked to shifts in amphipod commun ities 

### 18

inhabiting plant structures. 

### 19

In many cases

, it is difficult to characterize the nature and magnitude of effects and to quantify 

### 20

relationships between ambient concentrations of Pb and ecosystem response due to existence of multiple 

### 21

stressors in natur al systems. However, the evidence for Pb effects at higher levels of ecological 

### 22

organization is sufficient to conclude that ther e is a causal relationship between Pb exposures and the 

### 23

alteration of species richness, species composition and biodiversity in terrestrial and aquatic 

### 24

ecosystems. 

### 25



## 2.6.11. Ecological Effects and Corresponding Pb
Concentrations

There is limited evidence to relate ambient air concentrations of Pb to levels of deposition onto 

### 26

terrestrial and aquatic ecosystems and subsequent movement of atmo spherically

- deposited Pb though 

### 27

environmental compartments (e.g., soil, sediment, water, biota). Current evidence indicates that Pb is 

### 28

bioaccumulated in biota; however, the sources of Pb in biota have only been identified in a few studies, 

### 29

and the relative contribution of Pb from all sources is usually not known. There are large differences in 

### 30

species sensitivity to Pb, and many environmental variables (e.g., pH, organic matter) determine the 

### 31

bioavailability and toxicity of Pb. However, the proportion of ob served effects of Pb attributable to Pb 

### 32May 20 11 2

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– DO NOT CITE OR QUOTE from atmospheric sources is difficult to assess due to a lack of information not only on bioavailability, as 

### 1

affected by the specific characteristics of the receiving ecosystem, but also on deposition, and on kinetic s 

### 2

of Pb distribution in ecosystems in long

- term exposure scenarios. 

### 3

Threshold levels for Pb in terrestrial and aquatic systems may serve as a tool for interpreting the 

### 4

effects of atmospherically deposited Pb as a component of total Pb loading. For soils, ecological soil 

### 5

screening levels (Eco

- SSLs) have been developed by the EPA for Pb. Eco

- SSLs are maximum 

### 6

contaminant concentrations in soils that are predicted to result in little or no quantifiable effect on 

### 7

terrestrial receptors. The Pb Eco

- SSL values for terrestrial birds, mammals, plants and invertebrates are 

### 8

11, 56, 120 and 1,700 mg Pb/kg soil (dry weight), respectively. In aquatic systems, national recommended 

### 9

ambient water quality criteria have been developed by the EPA Office of Water to protect aqua tic life and 

### 10

human health in surface waters. The ambient water quality criteria for Pb are expressed as a criteria 

### 11

maximum concentration (CMC) for acute toxicity and criteria continuous concentration (CCC) for 

### 12

chronic toxicity. In freshwater, the CMC is 65 μg Pb/L and the CCC is 2.5 μg Pb/L at a hardness of 100 

### 13

mg/L. In saltwater, these values are 210 μg Pb/L CMC and 8.1 μ g Pb/L CCC, respectively. These U.S. 

### 14

EPA Office of Water criteria we re published pursuant to Section 304(a) of the Clean Water Act

, and 

### 15

p rovide guidance to states and tribes to use in adopting water quality standards. 

### 16



# 2.7. Integration of Health and Ecological Effects Overview

The health and ecological effects considered for causal determination are summarized in the Table 

### 17

2

- 5. The health endpoints include neurological, cardiovascular, renal, immune, hematological and 

### 18

reproductive effects as well as cancer. The ecological endpoi nts considered for causal determination are 

### 19

bioaccumulation, mortality, growth, physiological stress, hematological effects, developmental and 

### 20

reproductive effects, neurobehavioral effects, and community and ecosystem level effects. The substantial 

### 21

overlap between the ecological and health endpoints considered in the causal determinations allowed for 

### 22

the integration of the evidence across these disciplines. 

### 23May 20 11 2

- 42 DRAFT

– DO NOT CITE OR QUOTE Table 2

- 5. Summary of Causal Determinations for Health and Ecological Effects

Outcome Human Health Causal Determination Ecological Receptors Causal Determination

Neurological Effects a Causal Relationship Causal Relationship: Invertebrates and Vertebrates

Cardiovascular Effects Causal Relationship N/A

Renal Effects Causal Relationship N/A

Immune System Effects Causal Relationship N/A
Heme Synthesis and RBC Function b Causal Relationship Causal Relationship: Invertebrates and Vertebrates

Reproductive Effects and Birth Out c ome c Causal Relationship Causal Relationship: Invertebrates and Vertebrates Inadequate to Infer Causal Relationship: Plants

Cancer Likely to be a causal relationship N/A

Bioaccumulation The causal determination for bioaccumulation was developed respective to the impact of bioaccumulation on ecosystem services. Thus, although Pb bioaccumulates in all organisms including humans, causality was not applicable
to bioaccumulation in humans. Causal Relationship

Mortality The strongest evidence of Pb

- induced mortality in humans was observed for cardiovascular
disease related mortality. Causal Relationship: Invertebrates and Vertebrates Inadequate to Infer Causal Relationship: Plants

Growth N/A Causal Relationship: Plants and Invertebrates Suggestive of a Causal Relationship: Vertebrates
Physiological Stress 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 Causal Relationship

a In ecological receptors

, the causal determination was developed considering neurobehavioral effects that can be observed in toxicological studies of animal mod els and studies of ecological effects in vertebrates and invertebrates

. The human epidemiologic evidence evaluated included a wider range of health endpoints such as cognition.

b The health hematological effects considered in the determination of causalit y 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.

c Reproductive health effects, including effects on sperm, as well as birth outcomes such as spontaneous abortion, were considered in the causal determination. In the ecological literature, a wide range of endpoints, including embryonic development, multigenerational st udies, d elayed metamorphosis, and altered steroid profiles, were considered

.



## 2.7.1. Modes of Action Relevant to Downstream Health and Ecological Effects

The diverse health and ecological effects of Pb are mediated through multiple, interconnected 

### 1

modes of action. This section summarizes the principle modes of action of human health endpoints 

### 2

associated with Pb exposure and the concentrations at which those effects are observed. Then, effects of 

### 3

Pb observed in organisms in aquatic and ter restrial ecosystems (Section 2.6 ) are evaluated along with 

### 4

evidence from human and laboratory animals to determine the extent to which common modes of action 

### 5May 20 11 2

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– DO NOT CITE OR QUOTE can be inferred from the observed effects. The rationale for this approach is that the mechanism of Pb 

### 1

toxicity is likely conserved from invertebrates to vertebrates to humans in some organ systems. 

### 2

Each of the modes of action discussed in Section 5.2 has the potential to contribute to the 

### 3

development of a number of Pb

- induced health effects (Table 2

- 6). Evidence for the majority of these 

### 4

modes of action is observed at low blood Pb levels in humans and laboratory animals, between 2 and 5 

### 5

μg/dL, and at doses as low as the picomolar range in animals and cells. Dose captures Pb exposure 

### 6

concentrations in in vitro systems or in animal mod els when no blood Pb level was reported. The 

### 7

observable effect levels in humans reported in Table 2

- 6 are limited by the data and methods available and 

### 8

do not imply that these modes of action are not acting at lower exposure levels or that these doses 

### 9

repr esent the threshold of the effect. 

### 10

Table 2

- 6. Related human health effects resulting from the MOAs of Pb and the lowest level eliciting the MOA

Mode of Action Related Health Effects ( ISA Section) Lowest Level at which MOA
Observed References

Blood Pb a Dose a

Altered Ion Status All Heath Effects of Pb 3.5 μg/dL 50 pM, acute Huel et al. ( 2008 ) ; Kern et al. ( 2000 )

Protein Binding Renal (5.5), Heme Synthesis and RBC Function (5.7) 6.4 μg/dL 50 μM, acute Chen et al. ( 201 0 ) ; Klann and Shelton ( 1989 )

Oxidative Stress All Heath Effects of Pb 5

- 10 μg/dL 10 μM, acute Quinlan et al. ( 1988 ) ; Ahamed et al. ( 2006 ) ; Yiin and Lin ( 1995 )

Inflammation Neurological ( 5.3), Cardiovascular (5.4), Renal (5.5), Immune (5.6), Respiratory (5.6.4), Hepatic (5.9.1) 3 μg/dL 0.01 μM, acute Kim et al. ( 2007 ) ; Chetty et al. ( 2005 )

Endocrine Disruption Reproductive Effects and Birth Outcomes (5.9), Bone and Teeth (5.9.4), Endocrine System (5.9.3) 2 μg/dL 20 ppm, acute Krieg ( 2007 ) ; Wiebe and Barr ( 1988 )

Cell Death/Genotoxicity Cancer (5.10), Reproductive Effects and Birth Outcomes (5.8), Bone and Teeth (5.9.4) 3.1 μg/dL 50 nM, acute Van et al. ( 2004 ) ; Bonacker et al. ( 2005 )

a Reported as blood Pb level and dose delivered (human, laboratory animal, and in vitro data).

Ecological studies have presented evidence for the occurrence of many of these modes of action in 

### 11

animals, and to some degree in plants, however the connection to ecological outcomes must usually be 

### 12

inferred because ecological studies are typically not des igned to address mode of action directly. The level 

### 13

at which Pb elicits a specific effect is more difficult to establish in terrestrial and aquatic systems due to 

### 14

the influence of environmental variables on Pb bioavailability and toxicity and substantial s pecies 

### 15

differences in Pb susceptibility. 

### 16

The alteration of cellular ion status (including disruption of Ca 2+ homeostasis, altered ion transport 

### 17

mechanisms, and perturbed protein function through displacement of metal cofactors) appears to be the 

### 18

major uni fying mode of action underlying all subsequent modes of action in plants, animals, and humans 

### 19

(Figure 5

- 1). Pb will interfere with endogenous cation homeostasis, necessary as a cell signal carrier 

### 20May 20 11 2

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– DO NOT CITE OR QUOTE mediating normal cellular functions. Pb is able to displace metal ions, such as Zn, Mg, and Ca 2+ , from 

### 1

proteins due to the flexible coordination numbers and multiple ligand binding ability of Pb, leading to 

### 2

abnormal conformational changes to proteins and altered protein function. Disruption of ion transport 

### 3

leadin g to increased intracellular Ca 2+ levels is due in part to the alteration of the activity of transport 

### 4

channels and proteins, such as Na +

- K + ATPase and voltage

- sensitive Ca 2+ channels. Pb can interfere with 

### 5

these proteins through direct competition between Pb and the native metals present in the protein metal 

### 6

binding domain or through disruption of proteins important in calcium

- dependent cell signaling, such as 

### 7

PKC or calmodulin. 

### 8

This competition between metals has been reported not only in human systems, but also in fish, 

### 9

snails, and plants. Altered Ca 2+ channel activity and binding of Pb with Na +

- K + ATPase in the gills of fish 

### 10

disrupts the Na + and Cl
- homeostasis, which may lead to ionoregulatory failure and death. Ca 2+ influx and 

### 11

ionoregulation has also been shown to be inhibited by Pb exposure in a sensitive species of snail, leading 

### 12

to a reduction in snail growth. In plants, substitution of the central atom of chlorophyll, Mg, by Pb 

### 13

prevents light

- harvesting, resulting in a breakdown of photosynthesis. Pb

- exposed animals also have 

### 14

decreased cellular energy production due to perturbation of mitochondrial function. 

### 15

Disruption of ion transport not only leads to altered Ca 2+ homeostasis, but can also result in 

### 16

perturbed neurotransmitter function. Pb

- exposure decreases evoked release of neurotransmitters, while 

### 17

simultaneously increasing spontaneous release of neurotransmitters through Ca 2+ mimicry. Evidence for 

### 18

these effects in Pb

- exposed experimental animals and cell cultures have been linked to altered 

### 19

neuro behavioral endpoints and other neurotoxicity. Neurobehavioral changes that may decrease the 

### 20

overall fitness of the organism have also been observed in aquatic and terrestrial invertebrate and 

### 21

vertebrate studies. There is evidence in tadpoles and fish to su ggest Pb may alter neurotransmitter 

### 22

concentrations, possibly resulting in some of these neurobehavioral changes. 

### 23

Altered cellular ion status following Pb exposure is also responsible for the inhibition of heme 

### 24

synthesis. Pb exposure is commonly associated with altered hematological responses in aquatic and 

### 25

terrestrial invertebrates, experimental animals, and human subjects. The proteins affected by Pb are highly 

### 26

conserved across species accounting for the common response seen in human health and ecological 

### 27

studies. This evolutionarily conserved response to Pb is likely the result of the competition of Pb with the 

### 28

necessary metal cofactors in the proteins involved in heme synthesis. 

### 29

Although Pb will bind to proteins within cells through interactions with sid e group moieties, thus 

### 30

potentially disrupting cellular function, protein binding of Pb may represent a mechanism by which cells 

### 31

protect themselves against the toxic effects of Pb. Intranuclear and intracytosolic inclusion body 

### 32

formation has been observed i n the kidney, liver, lung, and brain following Pb exposure to experimental 

### 33

animals. A number of unique Pb binding proteins have been detected, constituting the observed inclusion 

### 34

bodies. The major Pb binding protein in blood is ALAD with carriers of the AL AD

- 2 allele potentially 

### 35

exhibiting higher Pb binding affinity. Additionally, metallothionein is an important protein in the 

### 36May 20 11 2

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– DO NOT CITE OR QUOTE formation of inclusion bodies and mitigation of the toxic effects of Pb. Protein binding of Pb is a 

### 1

recognized mechanism of Pb detox ification in some terrestrial and aquatic biota. For example, plants can 

### 2

sequester Pb through binding with phytochelatin and some fish have the ability to store accumulated Pb in 

### 3

heat

- stable proteins. 

### 4

A second major mode of action of Pb is the development of oxidative stress, due in many instances 

### 5

to the antagonism of normal metal ion functions. Disturbances of the normal redox state of tissues can 

### 6

cause toxic effects and is involved in the majority of health and ecological outcomes observed after Pb 

### 7

expos ure. The origin of oxidative stress produced after Pb exposure is likely a multi

- pathway process. 

### 8

Studies in humans and experimental animals provide evidence to conclude that oxidative stress results 

### 9

from oxidation of δ

- ALA, NAD(P)H oxidase activation, mem brane and lipid peroxidation, and 

### 10

antioxidant enzyme depletion. Evidence of increased lipid peroxidation associated with Pb exposure 

### 11

exists for many species of plants, invertebrates, and vertebrates. Enhanced lipid peroxidation can also 

### 12

result from Pb pote ntiation of Fe 2+ initiated lipid peroxidation and alteration of membrane composition 

### 13

after Pb exposure. Increased Pb

- induced ROS will also sequester and inactivate biologically active • NO, 

### 14

leading to the increased production of the toxic product nitrotyros ine, increased compensatory NOS, and 

### 15

decreased sGC protein. Pb

- induced oxidative stress not only results from increased ROS production but 

### 16

also through the alteration and reduction in activity of the antioxidant defense enzymes. The biological 

### 17

actions of a number of these enzymes are antagonized due to the displacement of the protein functional 

### 18

metal ions by Pb. Increased ROS are often followed by a compensatory and protective upregulation in 

### 19

antioxidant enzymes, such that this observation is indicative of oxidative stress conditions. A number of 

### 20

studies in plants, invertebrates, and vertebrates present evidence of increased antioxidant enzymes with 

### 21

Pb exposure. Additionally, continuous ROS production may overwhelm this defensive process leading to 

### 22

decreased antioxidant activity and further oxidative stress and injury. 

### 23

In a number of organ systems Pb

- induced oxidative stress is accompanied by misregulated 

### 24

inflammation. Pb exposure will modulate inflammatory cell function, production of proinflammatory 

### 25

cytokin es and metabolites, inflammatory chemical messengers, and proinflammatory signaling cascades. 

### 26

Cytokine production is skewed toward the production of proinflammatory cytokines like TNF

- α and IL

- 6 

### 27

as well as leading to the promotion of Th2 response and suppr ession of Th1cytokines and Th1

- related 

### 28

responses. 

### 29

Pb is a potent endocrine disrupting chemical. Steroid receptors and some endocrine signaling 

### 30

pathways are known to be highly conserved over a broad expanse of animal phylogeny. Pb will disrupt 

### 31

the HPG axis evidenced in humans, other mammals, and fish, by a decrease in serum hormone levels, 

### 32

such as FSH, LH, testosterone, and estradiol. Pb interacts with the hypothalamic

- pituitary level hormone 

### 33

control causing a decrease in pituitary hormones, altered growth d ynamics, inhibition of LH secretion, 

### 34

and reduction in StAR protein. Pb has also been shown to alter hormone receptor binding likely due to 

### 35

interference of metal cations in secondary messenger systems and receptor ligand binding and through 

### 36May 20 11 2

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– DO NOT CITE OR QUOTE generation of RO S. Pb disrupts hormonal homeostasis in invertebrates necessary for reproduction and 

### 1

development. Pb also may disrupt the HPT axis by alteration of a number of thyroid hormones, possibly 

### 2

due to oxidative stress. These studies have been conducted in humans a nd animals, including cattle. 

### 3

However the results of these studies are mixed and require further investigation. 

### 4

Genotoxicity and cell death has been investigated after Pb exposure in humans, animals, plants, and 

### 5

cell models. High level Pb exposure to human s leads to increased DNA damage, however lower blood Pb 

### 6

levels have caused these effects in experimental animals and cells. Reports vary on the effect of Pb on 

### 7

DNA repair activity, however a number of studies report decreased repair processes following Pb 

### 8

exposure. There is some evidence in plants, earthworms, freshwater mussels and fish for DNA damage 

### 9

associated with Pb exposure. There is evidence of mutagenesis and clastogenicity in highly exposed 

### 10

humans, however weak evidence has been shown in animals an d cells based systems. Human 

### 11

occupational studies provide limited evidence for micronucleus formation (>10 μg/dL), supported by Pb



### 12

induced effects in both animal and cell studies. Micronucleus formation has also been reported in 

### 13

amphibians. Animal and plan t studies have also provided evidence for Pb

- induced chromosomal 

### 14

aberrations. The observed increases in clatogenicity may be the result of increased oxidative damage to 

### 15

DNA due to Pb exposure, as co

- exposures with antioxidants ameliorate the observed toxic ities. Limited 

### 16

evidence of epigenetic effects is available, including DNA methylation, mitogenesis, and gene expression. 

### 17

Altered gene expression may come about through Pb displacing Zn from multiple transcriptional factors, 

### 18

and thus perturbing their normal cellular activities. Consistently positive results have provided evidence 

### 19

of increased apoptosis following Pb exposure. 

### 20

Overall, Pb

- induced health and ecological effects can occur through a number of interconnected 

### 21

and evolutionarily well conserved modes of action that generally originate with the alteration of ion 

### 22

status. 

### 23



# 2.8. Policy Relevant Considerations and Human Health

2.8.1. Air

- to

- Blood Relationships

The 1986 Pb AQCD described epidemiological studies of relationships between air Pb and blood 

### 24

Pb. Much of the pertinent earlier literature described in the 1986 Pb AQCD was drawn from a meta



### 25

analysis by Brunekreef ( 1984 ) . In addition to the meta

- analysis of Brunekreef ( 1984 ) , seven more recent 

### 26

studies have provided data from which estimates of the blood Pb

- air Pb slope can be derived for children 

### 27

(Table 2

- 7 ). The range of estimates from these seven studies is 1

- 9 μg/dL per μg/m 3 , which encompasses 

### 28

the estimate from t he Brunekreef ( 1984 ) meta

- analysis of (3

- 6 μg/dL per μg/m 3 ). The Schnaas ( 2004 ) had 

### 29May 20 11 2

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– DO NOT CITE OR QUOTE a particularly strong experimental design in that is the only longitudinal study in which blood Pb 

### 1

concentration was monitored repe atedly in individual children from age 6 months to 10 years. For 

### 2

children who experienced the largest declines in air Pb (i.e., from 2.8 to <0.1 μg/m 3 ), the predicted blood 

### 3

Pb

- air Pb slope (adjusted for age, year of birth, SES, and use of glazed pottery) w as 0.213 ln[μg/dL 

### 4

blood] per ln[μg/m 3 air]. The cross

- sectional study done by Ranft ( 2008 ) attempted to account for 

### 5

potential covariates that influence blood Pb (e.g., soil Pb co ncentration, gender, environmental tobacco 

### 6

smoke, fossil heating system and parental education). It is the only study that reported a logarithmic blood 

### 7

Pb

- linear air Pb relationship, which results in an upward curvature of the blood Pb

- air Pb relationship 

### 8

(i.e., the blood Pb

- air Pb slope increases with increasing air Pb concentration). In other studies (or based 

### 9

on other studies), the blood Pb

- air Pb relationship was either log

- log ( Brunekreef, 1984 ; Hayes et al., 

### 10

1994 ; Schnaas et al., 200 4 ) , wh ich predicts an increase in the blood Pb

- air Pb slope with decreasing air Pb 

### 11

concentration or linear ( Hilts, 2003 ; Schwartz & Pitcher, 1989 ; Tripathi et al., 2001 ) , w hich predicts a 

### 12

constant blood Pb

- air Pb slope across all air Pb concentrations. These differences may simply reflect 

### 13

model selection by the investigators; alternative models are not reported in these studies. Because air Pb 

### 14

contributes to Pb in soil and i ndoor dusts, adjustment for the correlated covariates such as soil Pb would 

### 15

introduce a downward bias in the slope estimate. 

### 16May 20 11 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 Children

Reference Study Methods Model Description B lood Pb

– Air Pb Slope (μg/dL per μg/m 3 )

Brunekreef et al. ( 1984 ) Location: Various countries Years: 1974

- 1983 Subjects: C hildren (varying age ranges) Analysis : Meta analysis of 18 studies Model: Log

- Log Blood Pb: 5

- 41 μg/dL (mean range for studies) Air Pb: 0.2

- 10 μg/m 3 (mean range for studies) All children: 18 a , 6.1 b
Children < 20 μg/dL : 13 a , 3.0 b

Hayes et al. ( 1994 ) Location: Chicago, IL Years: 1974

- 1988 Subjects: 0.5

- 6 yr (9,604 blood Pb measurements) A nalysis: Regression of blood Pb screening and quarterly average air Pb Model: Log

- Log Blood Pb: 12

- 30 μg/dL (annual GM range) Air Pb: 0.5

- 1.2 μg/m 3 (annual GM range) 24 a , 5.7 b

Hilts et al. ( 2003 ) Location: Trail, BC Years: 1989

- 2001 Subjects: 0.5

- 6 yr (292

- 536 blood Pb measurements/yr) A nalysis: Regression of blood Pb screening and community air Pb following upgrading of a local smelter Model: Linear Blood P b: 4.7

- 11.5 μg/dL (annual median range) Air Pb: 0.03

- 1.1 μg/m 3 (annual median range) 6.5

Ranft et al. ( 2008 ) Location: Germany Years: 1983

- 2000 Subjects: 6

- 11 yr (n = 843) A nalysis: Pooled regression 5 cross

- sectional studies Model: Log

- Linear Bloo d Pb: 2.2

- 13.6 μg/dL (5th

- 95th percentile) Air Pb: 0.03

- 0.47 μg/m 3 (5th

- 95th percentile) 3.2 c

Schnaa s et al. ( 2004 ) Location: Mexico City Years: 1987

- 2002 Subjects: 0.5

- 10 yr (n = 321) A nalysis: Regression of longitudinal blood Pb measurements and annual average air Pb data Model: Log

- Log Blood Pb: 5

- 12 μg/dL (annual GM range) Air Pb: 0.7

- 2.8 μg/m 3 (annual mean range) 4.8 a , 1.1 b

Schwartz and Pitcher ( 1989 ) , U.S. EPA (1986) Location: U

. S

. Years: 1976

- 1980 Subjects: 0.5

- 7 yr (n = 7,000) A nalysis: 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

Schwartz and Pitcher ( 1989 ) , U.S. EPA ( 1986 ) Location: Chicago, IL Years: 1976

- 1980 Subjects: 0

- 5 yr (n = 7,000) A nalysis: 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) 7.7

Tripathi et al. ( 2001 ) Location: Mumbai, India Years: 1984

- 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

a At an air concentration of 0.15 μg/m 3

b At an air concentration of 1 μg/m 3

c For a change in air Pb concentration from 0.025 to 0.465 μg/m 3

GM, geometric mean



## 2.8.2. Concentration

- Response Functions

With each successive assessment to

- date, the epidemiologic and toxicological study findings show 

### 1

that progressively lower blood Pb levels are associated with cognitive deficits and behavioral impairments 

### 2May 20 11 2

- 49 DRAFT

– DO NOT CITE OR QUOTE as well as other outcomes ( U.S. EPA, 2006 ) (Tables 2

- 2 and 2

- 3). Furthermore, in the 2006 Pb AQCD, 

### 1

compelling evidence for a steeper slope for the relations hip between blood Pb level and children ’ s IQ at 

### 2

lower blood Pb levels was presented based on the international pooled analysis of seven prospective 

### 3

cohort studies by Lanphear et al. ( 2005 ) , a subsequent reanalysis of these data focusing on the shape of 

### 4

the concentration response function ( Rothenberg & Rothenberg, 2005 ) , and several individual studies. 

### 5

This body of with the addition of more recent studies is presented Figure 2

- 2. The majority of the 

### 6

epidemiologic evi dence from stratified analyses comparing the lower and the higher ends of the blood Pb 

### 7

distributions indicates larger slopes at lower blood Pb levels. Relatively few studies examined the 

### 8

concentration

- response relationship between Pb in blood or bone and n eurocognitive effects in adults. Of 

### 9

the studies that did examine this relationship, findings were mixed with some studies reporting a linear 

### 10

relationship with cognition and others reporting non

- linear relationships. 

### 11

Reference Exposure Period Outcome Blood Pb strata

Lanphear et al. ( 2000 ) Concurrent Reading score All

<10
<7.5
<5
<2.5

Bellinger and Needleman ( 2003 ) Early childhood FSIQ >10

<10

Canfield et al. ( 2003 ) Lifetime avg FSIQ All

<10

Tellez

- Rojo et al. ( 2006 ) Concurrent Bayley MDI ≥10
<10

5

- 10

<5

Hu et al. ( 2006 ) Prenatal Bayley MDI/10 >1.226 a

<1.226 a

Kordas et al. ( 2006 ) Concurrent Math score All

<10

Lanphear et al. ( 2005 ) Concurrent FSIQ ≥10

<10 ≥7.5

<7.5

Schwartz ( 1994 ) Early childhood FSIQ >15

≤15

Change in Cognitive Score (95% CI)

Note: a = Pb levels measured in plasma of maternal blood during 1 st trimester of pregnancy. FSIQ = full

- scale IQ, MDI = mental development index. Effect estimates are
standardized to a 1 μg/dL increase in blood Pb level . Black symbols represent effect estimates among all subjects or i n highest blood Pb stratum. Red symbols represent effect estimates in lower blood Pb strata. Effect estimates without error bars are from studies that did not provide sufficient info rm ation in order to calculate 95% CIs.

Figure 2

- 2. Comparison of associations between blood Pb and cognitive function among various blood Pb strata.

Concentration

- response relationships were examined in several epidemiologic studies of blood 

### 12

pressure and mo rtality. In a study of Korean workers, the Pb

- induced increase in systolic blood pressure 

### 13

was better described by a log linear function of blood Pb level than by a linear function ( Weaver, 2010 )

. 

### 14May 20 11 2

- 50 DRAFT

– DO NOT CITE OR QUOTE Animal toxicological studies provide support for this concentrat ion response relationship. Few studies 

### 1

that focused on Pb

- induced hypertension in experimental animals have included more than two exposure 

### 2

concentrations; however these few studies appear to have a supralinear (concave downward) dose 

### 3

response and do not c onflict with the epidemiologic findings. 

### 4

Studies investigating both all

- cause and cardiovascular mortality report both linear and non

- linear 

### 5

relationships. Findings from NHANES analyses were mixed with Schober et al. ( 2006 )

, reporting a linear 

### 6

association between the relative hazard for all cause mortality with blood Pb, and Menke et al. ( 2006 )

, 

### 7

reporting a non

- linear relationships between blood Pb level and the hazard ratio for all cause, MI, stroke, 

### 8

and cancer mortality. This latter analysis provided evidence for an association between blood Pb and 

### 9

cardiovascular mortality in the NHANES population, where the mean blood Pb level was 2.58 μg/dL, and 

### 10

the hazard ratio of Pb with cardiovascular mortality reached its maximum at blood Pb levels between of 6 

### 11

and 7 μg/dL. Non

- linear relationships between patella bone Pb and log HR for all

- cause, cardiovascular, 

### 12

and IHD mortality were reported by Weisskopf et al. ( 2009 )

. 

### 13

Concentration response information was provided in a small number of studies of Pb

- related 

### 14

nephrotoxicity in the occupational setting ( Ehrlich et al., 1998 ; Weaver et al., 2003 ) . Data in 267 Korean 

### 15

Pb workers in t he oldest age tertile (mean age = 52 years) revealed no threshold for a Pb effect (beta = 

### 16

0.0011, p = <0.05; regression and lowess lines shown), however the mean blood Pb level in this 

### 17

population was 32 μg/dL ( Weaver et al., 2003 )

. 

### 18

Non

- linear concentration/exposure response relationships or attenuation of these relationships at 

### 19

higher exposure levels is reported in the occupational literature for a variety of exposures. Explanations 

### 20

for this phenomenon include greater exposure mea surement error, competing risks, and saturation of 

### 21

biological mechanisms at higher exposure levels, and exposure

- dependent variation in other risk factors 

### 22

( Stayner et al., 2003 ) . Non

- linear concentration response functions are reported in the air pollution 

### 23

literature ( Smith & Peel, 2010 ) . With respect to Pb exposure, different bio logical mechanisms may 

### 24

operate at different exposure levels and/or there may be a lower incremental effect of Pb due to covarying 

### 25

risk factors such as low SES, poorer caregiving environment, and other higher environmental exposures. 

### 26

In addition, the 2006 P b AQCD considered the explanation for the supralinear concentration response 

### 27

function postulated by Bowers and Beck ( 2006 ) , who stated that “ a supralinear slope is a required 

### 28

outcome of correlations between a data distribution where one is log

- normally distributed and the other is 

### 29

normally distributed. ” The 2006 Pb AQCD determined that, while the conclusions drawn by Bowers and 

### 30

Beck may be true under certain conditions, their assumptions (e.g., that IQ are scores forced into a normal 

### 31

distribution) were not generall y the case in the epidemiologic analyses showing a supralinear 

### 32

concentration response function. To support this conclusion, the 2006 Pb AQCD cited Hornung et al. 

### 33

( 2006 ) , which provided evidence that the IQ data used in the pooled analysis of seven studies by 

### 34

Lanphear et al. ( 2005 ) were not normalized and a log

- linear model (a linear relationship between IQ and 

### 35

the log of blood Pb) provided the best fit. 

### 36May 20 11 2

- 51 DRAFT

– DO NOT CITE OR QUOTE The current body of evidence on the effects of Pb allows cr itical evaluation of several of the 

### 1

aforementioned explanations for the supralinear curve concentration response function in epidemiological 

### 2

studies. For example, in several populations, higher blood Pb levels have been measured in susceptible 

### 3

groups such as those with higher poverty, greater exposure to tobacco smoke, lower parental education, 

### 4

and lower birth weight ( Lanphear et al., 2000 ; Lanphear et al., 2005 ) . It has been suggested that in 

### 5

populations of low SES, poorer caregiving environment, and gre ater social stress, the incremental effect 

### 6

of Pb exposure may be attenuated due to the overwhelming effects of these other risk factors ( Schwartz, 

### 7

1994 ) . Several studies have found significant associations of these sociodemographic risk factors with 

### 8

neurocognitive d eficits, and Miranda et al. ( 2009 ) found that indicators of SES (i.e., parental education 

### 9

and enrollment in a free/reduced fee lunch program) accounted for larger decrements in EOG scores than 

### 10

did blood Pb level (Fig ure 5

- 10). Few studies have compared Pb effect estimates among groups in 

### 11

different sociodemographic strata, and the limited data are mixed. Some have found greater Pb

- associated 

### 12

neurocognitive deficits in low

- SES groups ( Bellinger et al., 199 0 ; Schwartz, 1994 )

. In a meta

- analysis of 

### 13

eight studies, Schwartz ( 1994 ) found a smaller decrement in IQ per 1 μg/dL increase in blood Pb level for 

### 14

studies in disadvantaged populations (

- 2.7 points [95% CI:

- 5.3,

- 0.07]) than for studies in 

### 15

nondisadvantaged populations (

- 4.5 points [95% CI:

- 5.6,

- 2.8]). It is important to note that blood Pb is 

### 16

associated with deficits in neurocognitive function in both higher and lower SES groups; however, it is 

### 17

unclear what differences there are between groups in the decrement per unit increase in blood Pb and 

### 18

whether t hese differences can explain the nonlinear dose

- response relationship. 

### 19

Although, the 2006 Pb AQCD did not identify a biological mechanism for a steeper slope at lower 

### 20

than at higher blood Pb levels such a mechanism was not ruled out. In fact, several lines of evidence 

### 21

support the possibility of low

- dose and high dose

- Pb acting through different mechanisms. For example, 

### 22

in mice, lower

- dose Pb is associated with differential responses of the neurotransmitters dopamine and 

### 23

norepinephrine compared with control treatment and higher doses ( Leasure et al., 2008 ; Virgolini et al., 

### 24

2005 ) . These differential responses of neurotransmitter systems to low

- dose Pb versus a higher

- dose Pb 

### 25

may provide mechanistic understanding of the nonlinearity of Pb

- induced behavioral changes in animals 

### 26

and may also explain the nonlinear blood Pb

- neurocognitive and neurobehavioral associations reported 

### 27

widely among children. Additional evidence points to diff erences in hormonal homeostasis by Pb 

### 28

exposure level. In male mice with chronic Pb exposure (PND21 to 9 months of age), basal corticosterone 

### 29

levels are significantly lower in the 50 ppm exposure group versus control or 150 ppm Pb. 

### 30

Additional mechanistic un derstanding comes from differences in histological changes found in Pb



### 31

exposed animals. Compared with high

- dose Pb, low

- dose Pb stimulates greater induction of c

- fos, a 

### 32

marker of neuronal activation and action potential firing ( Lewis & Pitts, 2004 ) . These findings may 

### 33

underlie the nonlinear association between Pb exposure and learning and the U

- shaped behavioral dose



### 34

responsiveness seen with amphetamine

- induced motor activity in males after GLE ( Leasure et al., 2008 )

. 

### 35May 20 11 2

- 52 DRAFT

– DO NOT CITE OR QUOTE Sensory organ findings also show v astly different outcomes with low versus higher doses of Pb. 

### 1

High

- dose Pb produces subnormal retinal ERGs and low

- dose Pb produces supernormal ERGs in both 

### 2

children ( Rothenberg et al., 2002 ) and rodents ( Fox & Chu, 1988 ; Fox & Farber, 1988 ; Fox et al., 1991 )

. 

### 3

Inv erted U

- shaped dose

- response curves have been seen for rod photoreceptor numbers or neurogenesis 

### 4

( Giddabasappa et al., 2011 ) , retinal thickness ( Fox et al., 2010 ) , and rod cell proliferation ( Giddabasappa 

### 5

et al., 2011 ) . Thus, these dichotomous histological findings are coherent with the functional retinal test or 

### 6

the ER G where high

- dose Pb produces subnormal ERGs and low

- dose Pb produces supernormal ERGs. 

### 7

Hierarchical enzyme activity also may explain nonlinear Pb dose

- response relationships. The 

### 8

phosphatase enzyme calcineurin has been shown to be inhibited by high dose P b exposure and stimulated 

### 9

by low dose Pb exposure ( Kern & Audesirk, 2000 ) . At low doses of Pb, Pb displaces calcium at its 

### 10

binding sites on calmodulin and by acting as a calmodulin agonist at calcineurin ’ s catalytic A subunit, 

### 11

stimulates calcineurin activity. At high Pb doses, Pb can bind directl y to a separate calcium

- binding B 

### 12

subunit, overriding the calmodulin

- dependent effect and turning off the activity of calcineurin. 

### 13

Interestingly, mice with modulated calcineurin expression exhibit aberrant behavior related to 

### 14

schizophrenia ( Miyakawa et al., 2003 ) or impaired synaptic plasticity and memory ( Zeng et al., 2001 )

. 

### 15

This example of the stimulatory effects of Pb at low doses and inhibitory effects of Pb a t high doses gives 

### 16

another example of biological plausibility for the non

- monotonic dose response of Pb reported in multiple 

### 17

studies. 

### 18



## 2.8.3. Timing and Duration of Exposure

Epidemiologic studies reviewed in the 2006 Pb AQCD observed neurocognitive deficits in 

### 19

association with prenatal, peak childhood, cumulative childhood, and concurrent blood Pb levels. Among 

### 20

longitudinal studies that examined blood Pb level at multiple time points, several found that concurrent 

### 21

blood Pb was associated with the largest decrement in IQ. A common limitation of epidemiologic studies 

### 22

was the high correlation among Pb exposure metrics at different ages, making it difficult to distinguish 

### 23

among eff ects of Pb exposure at different ages and to ascertain which developmental time periods of Pb 

### 24

exposure were associated with the greatest risk of neurodevelopmental morbidity. Although prospective 

### 25

cohort studies have provided valuable information on the eff ects of Pb exposure at different periods of 

### 26

development, including the prenatal period and early childhood, the limitations noted in the previous 2006 

### 27

Pb AQCD remain. Collectively, the epidemiologic evidence has not identified one unique time window of 

### 28

exp osure that poses the greatest risk to cognitive function in children (Figure 2

- 3). However, toxicological 

### 29

studies included in the 2006 Pb AQCD demonstrated that developmental exposure to Pb was the most 

### 30

sensitive window for Pb

- dependent neurotoxicity and r ecent toxicological studies continue to support this 

### 31

finding. 

### 32May 20 11 2

- 53 DRAFT

– DO NOT CITE OR QUOTE Reference Outcome Blood Pb Variable Examined

Tong et al. ( 1998 ) FSIQ, 11

- 13 yr. < 10.2 decline age 2 to 11

- 13

10.2

- 16.2 decline age 2 to 11

- 13

> 16.2 decline, age 2 to 11

- 13

Bellinger et al. ( 1990 ) GCI, 24 and 57 mo Concurrent, Prenatal < 3 a

Concurrent, Prenatal 3

- 10 a

Concurrent, Prenatal ≥ 10 a

Chen et al. ( 2005 ) FSIQ, 7 yr. Low 2 yr, (<24.9), Low 7 yr, (<7.2)

Low 2 yr, (<24.9), High 7 yr, (≥ 7.2)

High 2 yr, (≥ 24.9), Low 7 yr, (<7.2)

High 2 yr, (≥ 24.9), High 7 yr, (≥ 7.2)

Hornung et al. ( 2009 ) FSIQ, 6 yr. 0.5 ratio age 6 to 2 yr b

2.0 ratio age 6 to 2 yr b

Change in Cognitive Score (95% CI)

Note: a Effect estimates represent associations between concurrent blood Pb level and cognitive function (standardized to standard deviation) in children categorized by prenatal blood Pb level.

b Values represent the ratio of blood Pb level at age 6 years to that at age 2 years. FSIQ = Full

scale IQ, GCI = General Cognitive Index. Cognitive function scores were standardized to their standard deviation. Effect estimates in red represent blood Pb level var iables associated with the greater decrease in cognitive function.
Figure 2

- 3. Associations of cognitive function in children with different degrees of changes in blood Pb levels over time.

The 2006 Pb AQCD noted the importance of the duration of exposure in animal studies of a wide 

### 1

array of effects including neurological, cardiovascular, renal, immune and reproductive effects of Pb. 

### 2

Generally, epidemiologic studies of the effect of Pb exposure on human health have not been designed to 

### 3

assess duration of exposure needed to induce those effects. Some exceptions are cohort studies with 

### 4

repeated blood Pb measurements and cognitive assessments within short intervals of time during 

### 5

pregnancy and in the first y ear of life (every 3 months). Studies have reported associations between 

### 6

prenatal blood Pb levels and decrements in mental development (Bayley MDI) in children assessed 

### 7

between 3 and 6 months ( Bellinger et al., 1984 ; Dietrich et al., 1986 ; Dietrich et al., 1987 ; Shen et al., 

### 8

1998 ) . In particular, Rothenber g et al. ( 1989 ) observed that maternal blood Pb levels from week 36 of 

### 9

pregnancy to delivery was associated with less ability of infants to self

- quiet in the first 30 days of life. 

### 10

Additionally, in the Cincin nati cohort, blood Pb levels measured at neonatal day 10 also were associated 

### 11May 20 11 2

- 54 DRAFT

– DO NOT CITE OR QUOTE with MDI decrements at age 3 and 6 months ( Dietrich et al., 1986 ; Dietrich et al., 1987 ) . Consistent with 

### 1

the neurotoxicology literature, findings from these studies indicate that short

- duration Pb exposure during 

### 2

critical periods of in utero or neonatal development are associated with cognitive impairments in young 

### 3

infants. 

### 4

2.8.3.1. Persistence of Effects

The issue of persistence of the neurodevelopmental effects of low

- level Pb exposure was also 

### 5

considered in the 2006 Pb AQCD, with some evidence suggesting that t he effects of Pb on 

### 6

neurodevelopmental outcomes persisted into adolescence and young adulthood. However, in these 

### 7

studies, blood Pb levels remained relatively stable over time. Thus, the effect of concurrent exposures was 

### 8

not ruled out. In addition, the pe rsistence of effect appears to depend on the duration of exposure as well 

### 9

as other factors that may affect an individual ’ s ability to recover from an insult. Toxicological studies 

### 10

from the 2006 Pb AQCD highlighted the importance of Pb exposure in early lif e in promoting 

### 11

Alzheimer ’ s like pathologies in the adult brain

, demonstrating Pb

- induced neurodegeneration and 

### 12

formation of neurofibrillary tangles. Recent toxicological studies continue to point to an early life window 

### 13

in which Pb exposure can contribute to pathological brain changes consistent with Alzheimer ’ s disease. 

### 14

Blood Pb generally is not associated with Alzheimer ’ s disease in epidemiological studies of adults. 

### 15

However, recent evidence indicates associations between early life ALAD activity, a bioma rker of Pb 

### 16

exposure, and schizophrenia later in adulthood. Consistent with these findings, toxicological studies have 

### 17

observed Pb

- induced emotional changes in males and depression changes in females. 

### 18



## 2.8.4. Susceptible Populations and Lifestages

Potential susceptibility factors examined in Chapter 6 of this document include lifestage, sex, 

### 19

genes, pre

- existing diseases/conditions, race and ethnicity, SES, BMI, nutrition, stress, cognitive reserve 

### 20

(e.g., the resilience of the mind), and co

- exposure to other metals/toxicants. Studies are included in 

### 21

Chapter 6 if the findings for the susceptible population or lifestage were compared across strata with and 

### 22

without the potential susceptibility factor. By virtue of their design some cohort studies, includ ing cohort 

### 23

studies of pregnant women or other populations or lifestages with no comparison group, are discussed in 

### 24

the endpoint

- specific sections rather than in Chapter 6. This integrative summary, however, draws on 

### 25

evidence relating to potentially suscept ible populations and lifestages appearing throughout this 

### 26

document. Also in Chapter 6

, separate discussions of studies that evaluate factors that influence Pb 

### 27

exposure and uptake , and studies that examine the modification of the association of Pb with heal th 

### 28

endpoints by a possible susceptibility factor are presented . In this integrative summary both types of 

### 29

studies are considered together. 

### 30May 20 11 2

- 55 DRAFT

– DO NOT CITE OR QUOTE 

### 2.8.4.1. Children

Children may be more highly exposed to Pb compared to adults without occupational exposure to 

### 1

Pb, through t heir behaviors (e.g., hand

- to

- mouth contact). Blood Pb levels are highest among the 

### 2

youngest children and decrease with incr easing age of the child (Table 6

- 1). Biokinetic factors that vary 

### 3

by age, including bone turnover and absorption, also affect blood Pb levels . Childhood, as a susceptibility 

### 4

factor related to Pb exposure and dose, is discussed in more detail in sectin 6.1.1.1. The kinetics of Pb, 

### 5

and how absorption, distribution, and elimination may vary depending on lifestage, is discussed in 

### 6

Section 4.2

. 

### 7

It is recognized that Pb can cross the placenta to affect the developing nervous system of the fetus 

### 8

(Sections 4.2.2.4, 5.3.2.1) and there is evidence of increased susceptibility to the neurocognitive effects of 

### 9

Pb exposure during several lifestages throughout childhood and into adolescence (for more detail, see 

### 10

Section 5.3.2.1). Further, Pb exposure is associated with effects on the renal (Section 5.5.2.3), immune 

### 11

(Section 5.6) and heme synthesis and RBC function (Section 5.7) of children. A limited number of studies 

### 12

of immune parameters, transferring saturation, and iron

- deficiency anemia that stratified children by age 

### 13

report stronger associations among the youngest children. Childhood, as a susceptibility factor related to 

### 14

Pb

- induced health effects , is discussed in more detail in Section 6.2.1.1. 

### 15

2.8.4.2. Adults

There is evidence that both recent and/or cumulative exposure to Pb may result in health outcomes 

### 16

during adulthood, as indicated by consistent associations of blood Pb or bone Pb with cardiovascular 

### 17

diseases and mortality, renal, immune, hematological, and reproductive effects. Blood Pb and bone Pb 

### 18

levels tend to be higher in older adults (>65 years) compared with the general population. Mobilization 

### 19

(Section 4.2.2.2) of Pb from the bone stores may oc cur during periods of physiological stress, including 

### 20

older adulthood (Section 6.1.1.2). In recent studies, age was specifically examined as an effect modifier of 

### 21

the association of Pb with mortality, cognition and blood pressure in adults; findings for mo rtality were 

### 22

mixed while little evidence of modification by age was reported for the other specific outcomes. 

### 23

Toxicological studies support the plausibility of differences in susceptibility to health effects depending 

### 24

on lifestage. 

### 25

2.8.4.3. Sex

In a recent NHANES analysis and several other studies, gender

- based differences in blood Pb level 

### 26

were observed among the adolescent and adult age groups, with higher blood Pb levels among males. The 

### 27

gender

- based differences were not substantial among the youngest age groups (1

- 5 years old and 6

- 11 

### 28

years old). Studies of effect measure modification of the association of Pb and various health endpoints 

### 29

including neurological effects such as cognition, kidney function blood pressure immune effects and 

### 30May 20 11 2

- 56 DRAFT

– DO NOT CITE OR QUOTE cancer by sex were conduct ed. Overall, findings were mixed with the most consistent evidence reported 

### 1

for neurological endpoints. Recent epidemiologic evidence increased the consistency of collective 

### 2

evidence base and pointed to males having increased susceptibility for Pb

- associat ed neurotoxicity. 

### 3

Toxicological studies continue to demonstrate increased susceptibility of males for endpoints such as 

### 4

sensory function, balance, stress hormone homeostasis, and brain membrane composition. Sex differences 

### 5

were also observed in toxicologic al studies across a wide array of endpoints including of behavior, 

### 6

memory, gross motor skills, obesity, and retinal decrements. See Section 6.1.2 and 6.2.2 for more details. 

### 7

Hormone levels may affect susceptibility to Pb

- related health effects and associat ions among 

### 8

females may vary based on hormonal status, such as menopause or ovary removal. Toxicological and 

### 9

epidemiologic evidence supports the potential susceptibility to Pb effects based on hormonal status with 

### 10

findings on delayed onset of puberty and ch anges to the female reproductive tract. 

### 11

2.8.4.4. Race and Ethnicity

Higher blood Pb and bone Pb levels among African Americans have been documented and recent 

### 12

studies continue support previous findings. Further, larger proportions of both non

- Hispanic blacks and 

### 13

M exican American children have blood Pb levels exceeding 5 μg/dL of blood. The 2006 Pb AQCD noted 

### 14

that a clear downward temporal trend was apparent in NHANES data during the previous two decades but 

### 15

that blood Pb level was declining at different rates for g roups within the population, which were defined 

### 16

by race, as well as income and demographic factors include age of housing. Recent data suggest that the 

### 17

gap in Pb exposure between African American and White subjects is decreasing, but African Americans 

### 18

stil l tend to have higher blood Pb levels. Evidence of increased association of Pb with cardiovascular 

### 19

outcomes among non Hispanic blacks and Mexican Americans was reported for the NHANES population. 

### 20

Results of other recent epidemiological studies suggest that there may be race related susceptibility for 

### 21

additional outcomes but the evidence is limited and confounding or modification by other factors, such as 

### 22

SES, may be present. See Sections 6.1.3 and 6.2.7 for additional details. 

### 23

2.8.4.5. Socioeconomic Status

The 2006 Pb AQCD noted that the geometric mean blood Pb concentration varied with SES and 

### 24

other demographic characteristics that have been linked to Pb exposure. The gap between SES groups 

### 25

with respect to Pb level appears to be diminishing, with Pb level being high er but not significantly higher 

### 26

among lower income subjects. Lower SES individuals appear to represent a susceptible population. For 

### 27

example, a study of Pb and IQ reported greater inverse associations among those in the lowest SES 

### 28

groups. There is also evi dence that some cognitive effects of prenatal Pb exposure may be transient and 

### 29

that recovery is greater among children reared in households with more optimal caregiving characteristics 

### 30

and in children whose concurrent blood Pb levels were low ( Bellinger et al., 1990 ) . In contrast, t here is 

### 31May 20 11 2

- 57 DRAFT

– DO NOT CITE OR QUOTE some evidence that Pb

- associated neurocognitive effects may be larger in magnitude among higher SES 

### 1

populations. In a meta

- analysis, Schwartz ( 1994 ) found that in studies in higher SES populations, blood 

### 2

Pb was associated with a greater decrement in IQ than in low SES populati ons. See Sections 6.1.4 and 

### 3

6.2.8 for additional details. 

### 4

2.8.4.6. Genes

Several genes were examined as potential modifiers the associations between Pb and health effects. 

### 5

Epidemiologic and toxicological studies reported ALAD and VDR variants may be health

- related 

### 6

susceptibility factors. Although limited, evidence suggests that risk of Pb

- associated neurocognitive 

### 7

deficits in children also may be modified by variants in genes for APOE, MTHFR, and dopamine 

### 8

receptors. Other genes examined that may also affect suscepti bility to Pb

- related health effects were 

### 9

DRD4, GSTM1, TNF

- alpha, eNOS, and HFE. See Section 6.2.4 for additional details. 

### 10

2.8.4.7. Pre

- existing Conditions

Pre

- existing diseases/conditions also have the potential to affect the association of Pb exposure 

### 11

with health endpoints have been studied in relation to autism, diabetes, and hypertension. Recent 

### 12

epidemiologic studies did not support modification of Pb and health endpoints by diabetes; however, past 

### 13

studies have found diabetics to be a more susceptible population with regard to effects on renal function. 

### 14

Recent epidemiological studies support finding from the 2006 Pb AQCD that hypertension is observed to 

### 15

be a susceptibility factor i with both renal effects and heart rate variability demonstrating stronger 

### 16

associati ons among hypertensive individuals compared to those that are normotensive. Although the 

### 17

evidence is limited, current research has shown that in autistic children, blood Pb level is differentially 

### 18

correlated with expression of immune

- related genes. See Sec tion 6.2.5 for additional details. 

### 19

2.8.4.8. Nutrition and Lifestyle Factors

Body mass index (BMI), alcohol consumption, and nutritional factors were examined in recent 

### 20

epidemiologic and toxicological studies. Modification of associations between Pb and various heal th 

### 21

effects (mortality and heart rate variability) was not observed by BMI or obesity. Also, no modification 

### 22

was observed in an epidemiologic study of renal function examining alcohol consumption as a modifier, 

### 23

but a toxicological study supported the possib ility of alcohol as a susceptibility factor. Among nutritional 

### 24

factors, those with iron deficiencies were observed to be a susceptible population for Pb

- related health 

### 25

effects in both epidemiologic and toxicological studies. Other nutritional factors, such as calcium, zinc, 

### 26

and protein, demonstrated the potential to modify associations between Pb and health effects in 

### 27

toxicological studies. Recent epidemiologic studies of these factors were either not performed or observed 

### 28

no modification. Folate was also e xamined in a recent epidemiologic study of birth size but no interaction 

### 29May 20 11 2

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– DO NOT CITE OR QUOTE was reported between Pb and folate. Further study of these and other nutritional factors will be useful in 

### 1

determining susceptibility among individuals with various nutritional levels /deficiencies. See Sections 

### 2

4.2, 6.2.9, 6.2.10, and 6.2.11 for additional details. 

### 3

2.8.4.9. Stress and Cognitive Reserve

Animal toxicology findings described in the 2006 Pb AQCD demonstrated interactions between Pb 

### 4

exposure and stress. Namely, Pb

- exposed animals reared in cages with enriched environments (toys) 

### 5

perform better in the Morris water maze than their Pb

- exposed li ttermates who were reared in isolation. 

### 6

New findings indicate a potentiating effect of stress on behavior and memory at low

- dose Pb exposures. 

### 7

In comparison, epidemiologic evidence for such interactions has been sparse. However, consistent with 

### 8

historical animal studies, a recent epidemiological study indicated that positive social environment of 

### 9

children as characterized by maternal self

- esteem, may lessen the impact of Pb exposure on 

### 10

neurodevelopment. S elf

- perceived stress was shown to modify the association of bone Pb with 

### 11

hypertension. In addition, a greater association of Pb with cognitive function was found in workers with 

### 12

lower co gnitive reserve (Sect ions 6.2.1 2 and 6.2.1 3). 

### 13

2.8.4.10. Co

- exposure of Lead with Metals or Other Chemicals

The 2006 Pb AQC D reported that the majority of studies e xamined other chemicals as confounders 

### 14

and not effect measure modifiers ( U.S. EPA, 2006 ) . Although the body of evidence remains limited, 

### 15

recent epidemiologic studies have begun to explore the possible interaction betw een Pb and other metals 

### 16

or chem ical agents . These studies report some stronger associations between Pb and various health 

### 17

endpoints with co

- exposure to Cd, As, Mn, fluoride, tobacco smoke and urban pollutants. 

### 18

Epidemiologic and toxicological studies have r eported increased susceptibility to Pb

- related health 

### 19

effects among those with high Cd levels. Modification of associations of Pb with levels of reproductive 

### 20

hormones and renal dysfunction were reported in epidemiologic studies. Toxicological evidence of a 

### 21

synergism between Pb and Cd with regard to renal toxicity supported the epidemiological evidence. In 

### 22

addition, exposure to Pb and As was associated with effects on immune function in children living near a 

### 23

smelter and a statistical interaction between the metals was observed. Studies suggest that co

- exposure to 

### 24

As may increase the bioavailability of Pb establishing the plausibility of increased susceptibility of Pb



### 25

related health effects when co

- exposed to As. An interaction was also reported between Pb an d Mn ( Y. 

### 26

Kim et al., 2009 ) in a study of IQ. Fl has been identified as a potential sus ceptibility factor in a 

### 27

toxicological study but has not yet been explored in epidemiologic studies. The toxicological reported that 

### 28

co

- exposure of Pb and Fl increased Pb deposition in calcified tissues. Since Pb is acid soluble, 

### 29

fluoridati on may increase Pb concentration in water through leaching from pipes and Pb solder. 

### 30

Additional details of the studies summarized, are found in Sections 6.2.14 and 6.2.15. 

### 31May 20 11 2

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– DO NOT CITE OR QUOTE Recent studies suggested that Pb

- associated neurotoxicity in children are exacerbate d with 

### 1

co

- exposures to environmental tobacco smoke but findings from recent epidemiologic studies examining 

### 2

modification by smoking for other outcomes are mixed. Exposure to urban areas with larger industrial 

### 3

sources and higher traffic has been suggested t o increase Pb body burden and risk of Pb exposure. An 

### 4

ecological study reports an association of accumulated metals in the soil (e.g., Pb, Zn, Cd, Ni, Mn, Cu, 

### 5

Co, Cr and V) with reduced learning achievement among the students at the school ( Mielke et al., 2005 )

. 

### 6



# 2.9. Summary

This section summarizes the main conclusions of this assessment regarding the he alth and 

### 7

ecological effects of Pb and, for health outcomes, the concentrations at which those effects are observed. 

### 8

The conclusion s from the 2006 Pb AQCD and the causality determinations for the health and ecological 

### 9

effects of Pb exposure from this review are summarized in Table 2

- 8

. 

### 10

The 2006 Pb AQCD reviewed a strong body of evidence clearly substantiating the health effects of 

### 11

Pb at contemporary exposure levels. Neurological effects in children and cardiovascular effects in adults 

### 12

were the effects that were best substantiated as occurring at blood Pb concentrations as low as 5 to 10 

### 13

μg/dL. Other newly demonstrated immune and renal system effects among general population groups 

### 14

were also emerging as low

- level Pb

- exposure effects of potential public health concern. New 

### 15

epidemiologic and toxicological studies support the findings of the previous assessement and provide 

### 16

additional evidence for these effects at increasingly lower levels. 

### 17

The major conclusions reached in the 2006 Pb AQCD for terrestrial ecosyst ems focused on 

### 18

evidence from smelter sites or other industrial point sources with elevated levels of Pb where death of 

### 19

vegetation was found to cause a near

- complete collapse of the detrital food web, creating a terrestrial 

### 20

ecosystem in which energy and nut rient flows were minimal. In aquatic ecosystems, the best documented 

### 21

links between Pb and effects on the environment were with effects on individual organisms. 

### 22

Bioaccumulation of Pb in aquatic organisms was shown to alter the aquatic environment. Further, it was 

### 23

noted that alteration of ecological interactions (e.g., species competitive behaviors, predator

- prey 

### 24

interactions, and contaminant avoidance behaviors) may have negative effects on species abundance and 

### 25

community structure. However, the fact that bo th terrestrial and aquatic systems frequently contain 

### 26

multiple metals and other stressors made it difficult to attribute observed adverse effects to Pb. 

### 27

The current document presents detailed reviews of the scientific literature on the effects of Pb in 

### 28

aq uatic and terrestrial ecosystems, but, also integrates the evidence of effects across aquatic and terrestrial 

### 29

habitats. The ecological endpoints considered for causal determination are bioaccumulation, mortality, 

### 30

growth, physiological stress, hematological effects, developmental and reproductive effects, and 

### 31

neurobehavioral effects. The substantial overlap between the ecological and health endpoints considered 

### 32May 20 11 2

- 60 DRAFT

– DO NOT CITE OR QUOTE in the causal determinations allowed the integration of the evidence across these disciplines. Thi s 

### 1

organizational scheme represents an evolution from the structure of the 2006 Pb AQCD and lends 

### 2

additional weight to the ecological evidence by reducing the uncertainty associated with attributing 

### 3

ecosystem effects to Pb rather than other metals or toxica nts that co

- occur with Pb since much of the 

### 4

evidence documenting the effects and modes of action of Pb comes from controlled animal experiments. 

### 5

Table 2

- 8

. Summary of evidence from epidemiologic, animal toxicological and ecological
studies on the effects a ssociated with exposure to Pb

Health Outcome Conclusions from the 2006 Pb AQCD Conclusions from the 2011 Ist Draft Pb ISA

Neurological Effects Causal relationship

Neurocognitive
Function and Learning The collective body of epidemiologic studies provided clear and consistent evidence for the effects of Pb exposure on decreasing neurocognitive function in
children. Recent epidemiologic studies in children continue to demonstrate associations with IQ; most evidence emphasizes associations of blood Pb
levels as low as 2 μg/dL with specific indices of neurocognitive function (e.g., verbal skills, memory, learning visuospatial processing). Among environmentally exposed adults, the most consistent findings were associations of cumulative Pb exposure metrics with cognitive deficits.

Neurobehavioral Effects Several epidemiologic studies reported associations between Pb exposure and that ranged from inattentiveness to self

reported delinquent behaviors to criminal activities. Uncertainty remained regarding the critical time period of Pb exposure. In addition, uncertainties 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 depression and anxiety symptoms. Recent st udies in children continue to support associations of Pb exposure (blood Pb levels 3

- 11 μg/dL) with a range of effects from anxiety and distractibility to conduct disorder and delinquent
behavior. New evidence indicates associations
between blood Pb levels as low as 1 μg/dL and ADHD diagnosis and contributing diagnostic
indices.

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 animal and the human literature on the effects of chronic Pb exposure on auditory function. No new epidemiologic studies on sensory organ function. Recent toxicological studies find retinal
effects in male rodents at lower blood Pb levels (~12 μg/dL)May 20 11 2

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– DO NOT CITE OR QUOTE Neurodegenerative
Diseases Several epidemiologic studies of Pb exposure and Alzheimer’s disease, or dementia did not report associations association, but each study had sufficient
limitations. Recent epidemiological studies report associations with PD and essential tremor. Emerging toxicological evidence suggests that early life exposure may be associated with neurodegeneration in adult animals.

Cardiovascular
Effects Epidemiologic studies consistently
demonstrated associations between Pb exposure and increased risk of CVD outcomes. Experimental toxicology confirmed Pb effects on the cardiovascular system observed in epidemiol ogic studies. Causal relationship

Blood Pressure A doubling of blood Pb level was associated with a 1 mmHg increase in systolic blood pressure and a 0.6 mmHg increase in diastolic blood pressure. Recent studies confirm these findings. Associations of increased BP with Pb exposure observed at blood Pb levels < 2 μg/dL.

Hypertension Suggestive evidence that cumulative Pb exposure 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 metric of cumulative exposure, confirm and add weight to previous findings. Associations of hypertension with Pb exposure observed at blood Pb levels < 2 μg/dL. Recent studies have emphasized the interaction of cumulative exposure to Pb with other factors including stress.

Cardiovascular Mortality Limited evidence in support of cardiovascular mortality. Recent st udies including an NHANES analysis of
the association of blood Pb with cause

- specific mortality and study of older adults, which used bone Pb as an exposure metric, addressed limitations of previous studies and provide
additional evidence for an associatio n of Pb with cardiovascular mortality.

Renal Effects Circulating and cumulative Pb exposure was associated with longitudinal decline in renal function. Experimental studies
demonstrated that initial accumulation of absorbed Pb occurred primarily in the kidneys and hyperfiltration phenomenon during the first 3 months of exposure
was noted. Causal relationship Recent studies expand upon the strong body of evidence that Pb exposure is associated with kidney dysfunction including increased serum
creatinine and decreased creatinine clearance at
blood Pb levels < 5 μg/dL.

Immune System
Effects Epidemiologic studies suggested that Pb exposure may be associated with effects on cellular and humoral immunity including changes in serum immunoglobulin E levels in children. Toxicological evidence supported these findin gs and provided evidence for effects on downstream events such as
inflammation and decreased host
resistance. Causal relationship Recent studies support the strong body of evidence that Pb exposure is associated with both
cell

- mediated and humoral immunity . The consistency and coherence of findings among related immune effects establishes the biological plausibility for epidemiologic observations of associations with infection, allergy and effects in other organ systems.May 20 11 2

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– DO NOT CITE OR QUOTE Heme Synthesis and RBC Function Pb exposure was associated with disruption in heme synthesis in both children and adults. Toxicological studies demonstrated that Pb interferes with red blood cell survival and mobility. Causal relationship
Recent epidemiologic and toxicological studies

pro vide strong evidence that exposure to Pb is associated with numerous deleterious effects on the hematological system including altered heme synthesis mediated through decreased ALD and ferrochelatase activities, decreased RBC survival and function, decreas ed hematopoiesis and increased oxidative stress and lipid peroxidation.

Reproductive
Effects and Birth
Outcomes 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 obser ved 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. Causal relationship
Recent toxicological and epidemiolo gic studies provide strong evidence for delayed onset of puberty in males and females as well as effects on sperm. Evidence on pregnancy outcomes was inconsistent and less coherent across disciplines for preterm birth, spontaneous abortion, low birth weigh t, birth defects, hormonal influence and fecundity.

Cancer Epidemiologic studies of highly exposed workers suggested a relationship between Pb and cancers of the lung and the stomach; the evidence was limited by confounding by metal co

- exposures (e.g., t o As,Cd), 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. Based on animal data and inadequate
human data P b and Pb compounds would be classified as likely carcinogens according to the EPA Cancer Assessment Guidelines for Carcinogen
Risk Assessment. Likely causal relationship Some epidemiologic evidence supporting
associations between Pb and cancer with the

str ongest evidence from animal toxicology between Pb and cancer, genotoxicity/clastogenicity, or epigenetic
modification.May 20 11 2

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– DO NOT CITE OR QUOTE Ecological/ Welfare
Effect Findings from 2006 Pb AQCD Conclusions in the 2011 1st Draft ISA

Bioaccumulation

as it affects Ecosystem Services Atmospheric Pb pollution has resulted in accumulation of Pb in terrestrial and aquatic systems throughout the world. In field studies in aquatic systems, Pb has been shown to significantly alter the aquatic environment through
bioaccumulation and alterations of community structure and function. Due to low solubility of Pb in water, dietary Pb (i.e., Pb absorbed to sediment, particulate matter and food) may contribute substantially to exposure and toxicity. Causal relationship
There is compelling e vidence from several
decades of research and in recent studies that Pb bioaccumulates in plants, invertebrates and vertebrates in terrestrial and aquatic ecosystems. Pb deposited on the surface of, or taken up by organisms has the potential to contribute t o exposure and toxicity in primary and secondary order consumers and alter the services provided by ecosystems (i.e., provisioning services).

Mortality No information on mortality in plants.
Effects of Pb on invertebrates and
vertebrates include decreased survival. Inadequate to infer a causal relationship for plants Insufficient evidence for mortality in plants.

Causal relationship in vertebrates and
i nvertebrates Recent studies provide additional evidence for Pb effects on mortality in invertebrates and
vertebrates.

Growth Evidence of growth effects in algae, aquatic plants, soil invertebrates and aquatic invertebrates. Limited evidence
in avian and mammalian consumers. Causal relationship in plants and invertebrates
Recent studies on growth in algae and invertebrates find effects of Pb at lower concentrations than previously, and additional evidence for growth effects in plants.

Suggestive causal r elationship in vertebrates Limited studies considered effects on growth in
vertebrates.

Physiological Stress Pb exposure may cause lipid peroxidation and changes in glutathione concentrations. There are species differences in resistance to oxidative

stress. Causal relationship Recent studies support the strong body of evidence for upregulation of antioxidant enzymes and increased lipid peroxidation ass ociated with Pb exposure in many species of plants,
invertebrates and vertebrates.

Hematological
Effects Pb effects on heme synthesis were documented in the 1986 AQCD and continue to be studied in aquatic and terrestrial biota. Changes in ALAD are
not alw ays related to adverse effects but may simply indicate exposure. Numerous studies have reported the effects of Pb exposure on blood chemistry in aquatic and terrestrial biota. Causal relationship
Recent studies expand the evidence for Pb effects
on ALAD en zyme activity in bacteria, invertebrates, and vertebrates and altered serum profiles and blood cell counts in vertebrates.May 20 11 2

- 64 DRAFT

– DO NOT CITE OR QUOTE Development and Reproduction No information on reproduction in plants.
Limited new evidence in invertebrates
and vertebrates. Inadeq uate to infer a causal relationship for plants

There are an insufficient number of studies that consider Pb effects on plant reproduction. Causal relationship in invertebrates and
vertebrates Recent studies expand the evidence for Pb effects on embryonic development as well as for multi

generational effects in invertebrates. In vertebrates, there is new evidence for delayed metamorphosis and altered steroid profiles in the few species studied.

Neurobehavior Exposure to Pb has been shown to affect
brain receptors in fish. Exposure to Pb in laboratory studies and simulated ecosystems may alter species competitive behaviors, predator

- prey interactions and contaminant avoidance
behaviors. Causal relationship Recent studies identify possible molecular targets for Pb neurotoxicity in invertebrates and fish.
There is new evidence in a few invertebrate and vertebrate species for behavioral effects associated with Pb exposure.

Community and Ecosystem Level Effects of Pb difficult to interpret because of the prese nce of other stressors including metals. Causal Relationship Uptake of Pb into aquatic and terrestrial organisms and subsequent effects on survival, reproduction, growth, behavior and other physiological variables at the species scale is likely to lead to effects at the population, community and ecosystem scale. There is additional evidence for effects of Pb in soil microbial communities, and in sediment

associated and aquatic plant communities.May 20 11 2

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– DO NOT CITE OR QUOTE 

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