EPA Presentation to Moffett RAB on TCE July 17, 2008

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EPA presentation to the Moffett Field Restoration Advisory Board on July 17, 2008, regarding TCE.

EPA presentation to the Moffett Field Restoration Advisory Board on July 17, 2008, regarding TCE.

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  • 1. TCE Update Former NAS Moffett Field Restoration Advisory Board Meeting July 17, 2008 Stan Smucker - Toxicologist U.S. EPA Region 9
  • 2. Tonight’s Topics
    • TCE Toxicity and EPA’s Health Risk Assessment
    • Update to the Region 9 PRG Screening Table and New Inhalation Guidance
    • Breakdown Products of TCE in the Environment
  • 3. What is TCE?
    • Trichloroethylene (TCE) is a solvent that has been widely used by industry as a cleaning and degreasing agent. TCE is a volatile organic chemical (VOC) which means it evaporates readily in air.
  • 4. TCE - Current EPA Practices
    • Maximum Contaminant Level (MCL) of 5 parts per billion (ppb) TCE is the drinking water standard
    • No similar EPA standard for vapor intrusion pathway and indoor air
    • EPA is currently reassessing TCE toxicity
  • 5.
    • Purpose: Identify potential health effects of TCE and how much exposure to TCE causes harmful effects
    • Where we are at: - 1 st EPA Toxicity Assessment in the 1980’s - 1 st EPA draft Assessment Update 2001 - 2 nd EPA draft Assessment Update 2008/2009 - Final Update expected sometime in 2010 or beyond
    • Where to go for more information: Go to http://www.epa.gov/ncea/
    • and click on the "TCE" link under "Risk Assessments“
    TCE Toxicity Assessment Update
  • 6. What Type of Adverse Health Effects are Associated with TCE?
      • Kidney, liver, lymphoma Other?
      • Mechanism of Action - initiator? - promoter?
      • Acute effects (CNS depression)
      • Various other systemic effects (e.g., liver, kidney)
      • Reproductive, developmental, neurological disorders
      • Immunologic effects
    Non-Cancer Cancer
      •  Multiple Adverse Endpoints
      •  Uncontrolled Growth of Cells
    NASA Graphic Interaction with HAP
  • 7. TCE Exposure Guidelines
    • Set at protective levels to provide a sufficient margin of safety for everyone, including “sensitive” individuals (diabetics, people taking drugs that affect the liver, infants and pregnant women)
    • Because guidelines are developed with a margin of safety, the possibility of health effects occurring is low even if slightly above the guideline
  • 8.  
  • 9. Preliminary Remediation Goal TCE in Indoor Air (Residential)
    • Health-Based Criteria
    • - Protective of Cancer Effects
    • - Protective of Non-Cancer Effects
    • - Protective of both Short-Term and Long-Term Exposures
    • Margin of Safety
    • - Accounts for Sensitive Groups
    • - Data Gaps in the Science
    • Other Considerations
    • - Can be Reliably Measured using Current Laboratory Methods (Detection Limit = 0.14 ug/m 3 )
    • - Typically Above “Background” TCE Levels Measured in Mountain View Air
    Interim Guideline = 1 ug/m 3 TCE
  • 10. 2008 Update to EPA Region 9 Preliminary Remediation Goals (PRG) Table
    • The Region 9 PRGs have been harmonized with similar risk-based screening levels used by Regions 3 and 6 into a single table
    • Incorporates the latest Risk Assessment Guidance and Agency Toxicity Values
    • The updated PRG screening table is available at: http://epa-prgs.ornl.gov/chemicals/index.shtml
  • 11. What’s New in the 2008 PRG Table
    • Per EPA’s updated Cancer Guidelines an additional safety factor for children (0 – 16 years) is included for cancer-causing substances that are determined to damage DNA through a mutagenic mechanism of action
    • Incorporates new inhalation exposure equations from Risk Assessment Guidance for Superfund (RAGS Part F) in anticipation of the release of this new EPA guidance later this year
    • A new column has been added to the PRG Table that presents indoor air screening values for workers in addition to residents
  • 12. Impact of new EPA Inhalation Guidance on Decision-making at MEW and Moffett
    • Residential TCE numbers for the MEW site do not change since indoor air criteria using both the “old” and “new” equations round to 1 ug/m 3 TCE that EPA Region 9 is currently using
    • The updated PRG screening table presents a generic PRG of 6.1 ug/m 3 TCE for workers based on an 8 hour exposure time
    • The draft RI report for vapor intrusion for MEW/Moffett describes a worker exposure time of 9.5 hours per day. This site-specific exposure time results in a PRG of about 5 ug/m 3 TCE (up from 2.7 ug/m 3 TCE that Region 9 calculated using the “old” exposure equation)
  • 13. “ Old” Equation (RAGS 1989) Target Risk x Body Weight x Averaging Time x 1000 ug/mg Inhalation SF x Inhalation Rate x Exposure Frequency x Exposure Duration = 2.7 micrograms per cubic meter TCE New vs. Old PRG Equation for Indoor Workers “ New” Equation (RAGS 2008) Target Risk x Averaging Time Inhalation UR x Exposure Time x Exposure Frequency x Exposure Duration = 5.2 micrograms per cubic meter TCE
  • 14. Questions / Comments?
  • 15. TCE Breakdown Products in Subsurface (Anaerobic Conditions) TCE cis-1,2-DCE trans-1,2-DCE Vinyl Chloride Ethene
  • 16. TCE is transformed in the atmosphere by the action of sunlight and the main degradation products are represented by dichloroacetyl chloride, formyl chloride and phosgene. Other, but less important reactions, are direct photolysis and reaction with ozone. ATSDR Tox Profile for TCE 1997 TCE Breakdown Products in Air
  • 17. More Questions / Comments?