Bioavailability Strategies & Resources for Risk Assessment

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Clarence Stevens
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1 Bioavailability Strategies & Resources for Risk Assessment Jim Lavelle, PhD CDM Inc. Tucson, AZ Todd Bragdon, PE CDM Inc. Denver, CO

2 Objectives Improve Understanding of Bioavailability Strategies (2008 SERDP/ESTCP Workshop): Typical regulatory approaches for characterizing soils/sediments do not include measurements of bioavailability to receptors. Some contaminants (metals) are less available to cause harm to receptors than is suggested by extrapolating effects based on total soil/sediment concentrations. Assessing contaminant bioavailability can result in setting more technically defensible cleanup goals and establishing more realistic cleanup priorities, while still ensuring protection of human health and the environment.

3 Agenda Discuss Concept of Relative Bioavailability Assessment (RBA) Review Standard Risk Assessment Calculations Review RBA Use in Risk Assessment Identify RBA Analytical Tools and Resources Review a Project Example Regulatory Acceptance & Guidance

4 Concept of Bioavailability Discuss Concept of Relative Bioavailability Assessment (RBA) Some Metals - Lead Other Inorganic Consituents - Arsenic In 1990s, EPA Region 8 Began Evaluation RBA for Lead at Several Mine Superfund Sites (Butte, MT; Leadville, CO) CDM (Jim Lavelle, Roger Olsen) Provided Technical Assistance to EPA for RBA Assessment

5 Risk Assessment Refresher (Cont.) Non-carcinogenic risks via exposure to soil: where, RMC = Risk Management Criteria for Soil/Sediment (mg/kg) RfDo,i = Oral & Inhal. Chronic Reference Dose (mg/kg-day) -1 RBA used to adjust intake or reference dose accounts for difference in adsorption (water/soil):

6 Risk Assessment Refresher Carcinogenic risks from exposure to soil: where, RMC = Risk Management Criteria for Soil/Sediment (mg/kg) Sfo,i = Oral & Inhal. Carcinogenic Slope Factor (mg/kg-day) -1 RBA used to adjust intake or slope factor accounts for difference in adsorption (water/soil):

7 RBA Use in Risk Assessment RBA Used to Modify Reference Dose & Slope Factor: RBA Values are Less than 1.0 For Non-Carcinogenic Risks: given RBA<1, RfD Increases, RMC increases For Carcinogenic Risks: given RBA<1, SFadj. Decreases, RMC increases

Estimating RBA In Vitro Bioaccessibility Assay (IVBA) also

$IBVA measures fraction of metal solubilized from soil sample$ under simulated stomach conditions.

8 Estimating RBA In Vitro Bioaccessibility Assay (IVBA) also known as Relative Bioavailability Procedure (RBLP): Leach Test Developed by EPA Region 8 and University of Colorado - Boulder IBVA measures fraction of metal solubilized from soil sample under simulated stomach conditions. Mass of metal in filtered extract is compared to mass introduced in test RBA is ratio < 1.0

lead, large data base for in vivo bioavailability measurements Regression

9 Estimating RBA (Cont.) Relative bioaccessibility must be converted to relative bioavailability For lead, large data base for in vivo bioavailability measurements Regression equation to calculate bioavailability from bioaccessibility For arsenic, similar large in vivo data base Less certainty in calculating bioavailability

10 Weight of Evidence Tools For Some Metals (e.g. Arsenic), IVBA Test Conditions Not Optimized and/or Difficulties Exist with In Vivo Assays EPA Recommends Using Weight of Evidence Approach (EPA 1997): Electron Scanning Microprobe (CU-Boulder) EPA Region 8 RBA Database (CU-Boulder) Evaluates Geochemistry of Soil/Sediment and Uses Previous RBA Data

11 Electron Microprobe Photomicrograph 2 Iron sulfide grain containing 636 mg/kg arsenic.

Soil/Sediment Characterization Utilize Standard Characterization Techniques Assess Background Metals Total Concentrations Assess Site-Specific Metals Total Concentrations, Toxicity Characteristic,

12 Soil/Sediment Characterization Utilize Standard Characterization Techniques Assess Background Metals Total Concentrations Assess Site-Specific Metals Total Concentrations, Toxicity Characteristic, Leaching Potential (TCLP, SPLP, MWMP) Use EPA Method 1311/6010B/7000 Series or other standard analytical methods and/or x-ray fluorescence (XRF) techniques Collect Additional Samples for RBA Evaluation IBVA Testing; Microprobe Testing

13 Example Project Uranium Mine

Uranium Mine Project Colorado Designated Mine Operations (DMO) Permitting Process Requires Assessment of Toxicity of Waste Rock Piles Collected background samples, site-specific

14 Uranium Mine Project Colorado Designated Mine Operations (DMO) Permitting Process Requires Assessment of Toxicity of Waste Rock Piles Collected background samples, site-specific samples and screened total concentrations against RMC Developed by U.S. Bureau of Land Management (BLM 2004) Arsenic (As) Identified as Potential Contaminant of Concern in Waste Rock

15 Uranium Mine Project (Cont.) Submitted Additional Samples for IVBA and Microprobe Analyses to Evaluate Arsenic Calculated RBA Values Ranged from 0.64 to 2.32; RBA Cannot Be > 1.0 Difficulties with RBA Determination Resulted From: Relatively Low Total Concentrations of Arsenic (<45 mg/kg) Sample Heterogeneity - Ability to Split Samples for Analyses (e.g. Total Metals & IBVA)

16 Uranium Mine Project (Cont.) Samples Processed Using Magnetic Separation Artificially Enrich Arsenic Concentration Rerun IBVA; RBA Values of 0.29 to 0.63 (2 Results Out of Range) Weight of Evidence Approach Microprobe Analyses Indicated Arsenic Present with Crystalline Iron Sulfide and Uranium Arsenic w/ Crystalline Iron Sulfides (Pyrite) Likely Stable in Stomach Fluid (IVBA Leachate)

Uranium Mine Project (Cont.) Weight of Evidence Approach (Cont.) EPA Database Indicated RBA Values of 0.38 to 0.51 (Different Geochemistry Iron OxyHydroxides More Soluble) RBA Value of 0.

17 Uranium Mine Project (Cont.) Weight of Evidence Approach (Cont.) EPA Database Indicated RBA Values of 0.38 to 0.51 (Different Geochemistry Iron OxyHydroxides More Soluble) RBA Value of 0.63 Selected Revised Risk Management Criteria: RMC (Soil, As) = 37 mg/kg (w/o RBA) RMC (Soil, As) = 59 mg/kg (w RBA) Highest Site-Specific Concentration (Soil, As) = 45 mg/kg < RMC No Further Action

18 Bioavailability Resources University of Colorado Laboratory for Environmental & Geochemical Studies (LEGS) Dr. John Drexler (303) EPA Region 8 Bioavailability Website

19 Bioavailability Resources (Cont.) SERDP/ESTCP SERDP & ESTCP Expert Panel Workshop on Research & Development Needs for Understanding and Assessing the Bioavailability of Contaminants in Soil & Sediment (Nov. 2008) Bioavailability of Lead at Small Arms Range Soils, ESTCP Project ER-0222 (Oct. 2009) BLM Guidance Risk Management Criteria for Metals at BLM Mining Sites (October 2004)

FINAL REPORT. Validation of an In Vitro Bioaccessibility Test Method for Estimation of Bioavailability of Arsenic from Soil and Sediment

FINAL REPORT. Validation of an In Vitro Bioaccessibility Test Method for Estimation of Bioavailability of Arsenic from Soil and Sediment FINAL REPORT Validation of an In Vitro Bioaccessibility Test Method for Estimation of Bioavailability of Arsenic from Soil and Sediment ESTCP Project ER-200916 Susan Griffin U.S. EPA Region 8 Yvette Lowney