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BASELINE RISK ASSESSMENT OVERVIEW

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  1. BASELINE RISK ASSESSMENT OVERVIEW Dawn A. Ioven Senior Toxicologist U.S. EPA – Region III 4 April 2012

  2. WHAT IS RISK? • Definition: probability of harm or loss • Risk = Hazard x Exposure • Risk can be voluntary or involuntary • Interpretation of risk differs for each of us • Predictive risk assessment (U.S. EPA) vs. health study (ATSDR, Health Department)

  3. PURPOSE OF BASELINE RISK ASSESSMENT • Characterize current and potential future risks to human health and the environment • Determine the need for remedial action • Aid stakeholders in understanding potential site-related risks • Satisfy Federal regulations requiring the assessment of risk at Superfund sites

  4. BASELINE RISK ASSESSMENT PROCESS • Hazard Identification • Exposure Assessment • Toxicity Assessment • Risk Characterization • Uncertainty Analysis

  5. HAZARD IDENTIFICATION • Gather and analyze relevant site data • Identify Chemicals of Potential Concern (CoPCs) • CoPCs are chemicals that may contribute significantly to site-related risks • Determined by comparison to generic risk-based screening levels or regulatory criteria • Identification process also considers essentiality, frequency of detection, and background conditions

  6. EXPOSURE ASSESSMENT • Analyze contaminant releases • Identify potentially-exposed populations (current and future) • Identify potential exposure pathways • Estimate exposure point concentrations for CoPCs • Estimate contaminant intake (dose) for each CoPC

  7. EXPOSURE ASSESSMENT (cont.) Common Land-Use Scenarios • Residential • Occupational • Commercial / Industrial • Construction • Recreational • Other • Agricultural • Trespassing • Maintenance (Landscaping)

  8. EXPOSURE ASSESSMENT (cont.) Common Exposure Pathways • Surface soil • Subsurface soil • Ground water • Air • Surface water • Sediment

  9. EXPOSURE ASSESSMENT (cont.) Common Exposure Routes • Ingestion • Soil • Ground water • Surface water • Sediment • Dermal contact • Soil • Ground water (bathing) • Surface water • Sediment • Inhalation • Soil (outdoor vapors, airborne particulate, vapor intrusion) • Ground water (showering, vapor intrusion) • Air

  10. EXPOSURE ASSESSMENT (cont.) Generic Dose Equation - Ingestion Dose = (C x CR x EF x ED) / (BW x AT) where: C = contaminant concentration, media-dependent CR = contact rate, media-dependent EF (days/yr) = exposure frequency ED (yrs) = exposure duration BW (kg) = body weight AT (days) = averaging time Generic Dose Equation - Inhalation Exposure Concentration = (CA x ET x EF x ED x CF) / AT where: CA (ug/m3) = contaminant concentration in air ET (hrs/day) = exposure time EF (days/yr) = exposure frequency ED (yrs) = exposure duration CF (1 day/24 hrs) = conversion factor AT (days) = averaging time

  11. TOXICITY ASSESSMENT • Collect qualitative and quantitative toxicity information for CoPCs • Determine appropriate toxicity values for CoPCs to estimate risks • Reference Dose (RfD) • Inhalation Reference Concentration (RfC) • Carcinogenic Slope Factor (CSF) • Inhalation Unit Risk (IUR)

  12. RISK CHARACTERIZATION • Combine Exposure Assessment with Toxicity Assessment to describe potential for adverse health effects

  13. RISK CHARACTERIZATION (cont.) Cancer Risks Risk = CSF x Dose where: CSF (mg/kg/day)-1 = Carcinogenic Slope Factor Risk = IUR x EC where: IUR (ug/m3)-1 = Inhalation Unit Risk, chemical-specific EC (ug/m3) = exposure concentration Non-Cancer Risks HQ = Dose / RfD where: HQ (unitless) = Hazard Quotient RfD (mg/kg/day) = Reference Dose HQ = EC / (RfC x 1000 ug/mg) where: HQ (unitless) = Hazard Quotient EC (ug/m3) = exposure concentration RfC (mg/m3) = Reference Concentration, chemical-specific

  14. RISK CHARACTERIZATION (cont.) • Unacceptable Risk • Excess cancer risk greater than 1E-04 • probability of developing cancer from defined exposure is greater than 1 in 10,000 • For non-cancer impacts, sum of HQs for similar target organs is greater than 1 • “safe” dose is exceeded

  15. UNCERTAINTY ANALYSIS • Describe assumptions and significant unknowns associated with risk assessment process • Quantitative measure of variability and sensitivity of each input parameter can be performed via Monte Carlo Analysis

  16. NATIONAL RESEARCH COUNCIL RISK ASSESSMENT PARADIGM Risk Assessment Risk Management National Research Council, 1983 Dose-Response Assessment Statutory and Legal Considerations Public Health Considerations Risk Characterization Hazard Identification Regulatory Decisions Control Options Social Factors Exposure Assessment Economic Factors

  17. Asbestos • Two mineral groups • Serpentine • Single asbestosform variety (chrysotile) • Amphibole • Several asbestosform varieties (crocidolite, amosite, anthophyllite, tremolite, actinolite)

  18. Asbestos Investigations • No method has been found that reliably predicts asbestos concentrations in air given concentrations at the source. • Levels of asbestos in air from source disturbance are measured, not predicted. • Activity-Based Sampling (ABS)

  19. Asbestos ABS Sampling • Potential limitations • Representativeness of samples over an area of concern • Generalizing snapshot findings to future exposures • Engaging in dissimilar activities • Differing environmental conditions

  20. Asbestos ABS Sampling (cont.) • Remedy to limitations • Bias sampling towards most contaminated asbestos sources • Perform aggressive soil disturbance (raking), to generate maximum air concentrations • Sample when environmental conditions are favorable to maximum airborne release • Apply conservative exposure assumptions and tox criteria in Baseline Risk Assessment

  21. Asbestos Risks • Inhalation • Carcinogenic • Lung cancer • Mesothelioma • Laryngopharyngeal cancer • GI tumors (possibly) • Non-Cancer • Asbestosis • Pleural disease

  22. Asbestos Risk Equation Generic Risk Equation - Inhalation ELCR = EPC x TWF x IUR where: ELCR = Excess Lifetime Cancer Risk, the risk of developing cancer due to site-related exposure EPC = Exposure Point Concentration, the concentration of asbestos fibers in air (f/cc) IUR = Inhalation Unit Risk (f/cc)-1 TWF = Time Weighting Factor, to account for less-than-continuous exposure during a one-year exposure, where: TWF = [Exposure time (hours exposed/day ) / 24] x [Exposure frequency (days/year ) / 365]

  23. Example TWFs TWFs for Example Exposure Scenarios Exposure ScenarioHrs/DayDays/YearTWF Continuous 24 365 1 Baseline residential 24 350 0.96 Gardening 10 50 0.057 Recreational 1 156 0.018 Child playing in soil 2 350 0.080 TWF = [Exposure time (hours exposed/day ) / 24] x [Exposure frequency (days/year ) / 365]

  24. Asbestos IURs • Cancer risk estimates depend not only on EF and ED, but also on age at first exposure • Refer to handout (Table 2 and Table 3 from EPA Asbestos Framework) for IURs

  25. Estimation of Potential Cumulative Risk from Asbestos ELCRc = Σ EPCi • TWFi • IURLTLi where: ELCRc = the cumulative excess cancer risk to an individual from exposure to multiple environments or multiple scenarios

  26. Example Risk Calculation for Asbestos • Refer to handout (Example 3 from EPA Asbestos Framework)