Lead NAAQS Review: 2nd Draft Risk Assessment

1
Lead NAAQS Review2nd Draft Risk Assessment

• NTAA/EPA Tribal Air Call
• August 8, 2007
• Deirdre Murphy and Zachary Pekar
• OAQPS

2
Overview

• Background
• History of Lead NAAQS
• Key Policy Aspects
• Basis for Current Standard
• Current NAAQS Review
• Whats changed since 1978?
• Human Exposure Risk Assessment
• Next Steps

3
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

4
BackgroundKey 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

5
BackgroundBasis 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 lt 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

6
Current NAAQS ReviewWhats 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 todays 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 Childrens Blood Lead
• U.S. population levels substantially reduced
  (median 15 ug/dL to lt5 ug/dL)
• Health Effects - Adverse effects observed at
  dramatically lower exposures
• More robust evidence for broad array of effects
• Focus on childrens 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

7
Current NAAQS ReviewWhats 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 gtadvisory 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

8
Human Exposure and RiskAssessment

• 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

9
Human Exposure and RiskResults

• Blood lead estimates all case studies
• Lower for all alternate standards compared to
  current NAAQS
• Risk - General urban case study
• Average current conditions, lt1 to 5 IQ point
  loss for average child
• lt 1 IQ point from lead most recently in the air
• lt1 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, lt1 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

10
Next Steps

• October, 2007 - Final Risk Assessment Report
• November, 2007 - Policy Assessment
• Staff Paper/ANPR
• March, 2008 - Proposed Rule
• Sept 1, 2008 - Final Rule