Lead NAAQS Review:2nd Draft Risk Assessment

NTAA/EPA Tribal Air CallAugust 8, 2007

Deirdre Murphy and Zachary PekarOAQPS

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Overview

• Background– History of Lead NAAQS– Key Policy Aspects– Basis for Current Standard

• Current NAAQS Review– What’s changed since 1978?– Human Exposure & Risk Assessment

• Next Steps

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Background: Lead NAAQS History

• 1976 – Lead added to list of criteria pollutants – Court Order

• 1978 – Primary and Secondary NAAQS set– 1.5 µg/m3, quarterly average

• 1980s-90 – First lead NAAQS review– Criteria Document – 1986, with 1990 supplement– Staff Paper – Dec 1990

• 1991- Agency-wide Integrated Lead Strategy– Increased NAAQS enforcement, soil abatement, waste policy,

drinking water, products, recycling, research

• 2005 (Sept 14) -Court order– New lead NAAQS review

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Background:Key Policy Aspects

• Lead is a multimedia pollutant• Lead emitted into the air is distributed to other

media– Human exposures are dominated by ingestion route (e.g., indoor

dust)

• Lead emitted yesterday (or years ago) can remain available for human exposure– Resuspension of deposited lead contributes to this

• In addition to emissions to the air, there are various policy-relevant background exposures– Lead-based paint– Drinking water– Diet

• Lead introduced during food processing is background• Lead introduced to food chain via atmospheric deposition, however,

is policy-relevant exposure

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Background:Basis for Current Standard• Level

– Sensitive population• Young children, aged 1 to 5

– “maximum safe blood lead level” for individual children• 30 μg/dL blood (anemia symptoms at 40 ug/dL,1977 CD)

– Policy goal: keep 99.5% young children < maximum safe level• Translates to population mean of 15 ug/dL blood

– Non-air source contributions • 12 μg/dL blood

– Limit on air contribution • 3 μg/dL blood

– Estimated relationship of air lead to blood lead• 1 ug/m3 to 2 ug/dL blood

– Primary NAAQS - 1.5 μg/m3 air

• Averaging Time - calendar quarter• Form - not to be exceeded (maximum) value• Indicator - total suspended particulate (TSP) lead

Secondary Standard – set equal to primary

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Current NAAQS Review:What’s Changed Since 1978? (1)

• Emissions reduced dramatically, but still arise from many sources• Ambient air concentrations

– National mean reduced, but top 10% of sites still average almost 1 ug/m3

– Monitoring network provides incomplete coverage of today’s large emitters

• Ambient non-air concentrations – Surface concentrations reduced in quiet forest soils & lake sediments– Trends less clear in systems near sources and with more activity

• E.g., resuspension near roadways, primary smelter

• Human Exposure – Children’s Blood Lead– U.S. population levels substantially reduced (median: 15 ug/dL to <5 ug/dL)

• Health Effects - Adverse effects observed at dramatically lower exposures– More robust evidence for broad array of effects– Focus on children’s IQ (vs. blood effects)– No evidence of threshold

• Ecological Effects– Better understanding of Pb ecosystem mobility and transport– Screening levels developed to associate Pb levels with potential for effect

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Current NAAQS Review:What’s Changed Since 1978? (2)

• CDC advisory blood lead level for children – Initially set in 1960 (60 μg/dL)

• Revised in 1970 (30 μg/dL), and 1985 (25 μg/dL)– Current level set 1991 (10 μg/dL)

• Children with blood lead >advisory level should receive follow-up attention

– Reviewed by CDC in 2005• Recognized no “safe” threshold for blood lead levels in young

children• Did not change level as …

– Critical to focus resources on children where potential for effects remain greatest

– Setting a new level below 10 μg/dL would be an arbitrary decision– Feasibility & effectiveness of intervention activities below 10 μg/dL

not yet demonstrated• Emphasized importance of preventing childhood exposures

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Human Exposure and Risk:Assessment

• Case study approach– General urban case study

• Hypothetical (non-location specific) with simplifying assumptions, e.g., …– Uniform media concentrations and demographics across study area

– Point source-oriented case studies (large & medium)• Primary lead smelter• Secondary lead smelter

• Estimated blood lead levels for children– 7 years exposure (from birth)

• Predicted associated IQ points lost– Population distribution

• Assessed multiple air quality scenarios– current conditions, current NAAQS, alternate NAAQS

• Multiple sets of risk results for each combination of case study and air quality scenarios– Recognizes uncertainty in key modeling elements

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Human Exposure and Risk:Results

• Blood lead estimates – all case studies– Lower for all alternate standards compared to current NAAQS

• Risk - General urban case study– Average current conditions, <1 to 5 IQ point loss for average child

• < 1 IQ point from lead most recently in the air• <1 to 4 IQ point from recent plus past air Pb

– Current NAAQS • Average child, 1 to 4-5 IQ point loss from air-related lead exposures

– alternative NAAQS (0.5 – 0.05 ug/m3) • Average child, <1 to 2 IQ point loss from air-related lead exposures

– Most highly exposed sub-populations• Higher risks and greater risk reductions• Greater uncertainty associated with these estimates

• Risk - Primary lead smelter case study– Risk somewhat similar to general urban case study

• Risk - Secondary lead smelter case study– Lowest risk estimates

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Next Steps

• October, 2007 - Final Risk Assessment Report• November, 2007 - Policy Assessment

– Staff Paper/ANPR

• March, 2008 - Proposed Rule• Sept 1, 2008 - Final Rule