Relative Bioavailability Adjustment Factor for the San ... · PDF filefor the San Jacinto...

Relative Bioavailability Adjustment Factor for the San Jacinto River Waste Pits Considerations Relevant to Site-Specific Evaluation

Integral Consulting Inc. December 16, 2014

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Discussion Overview

• Summary of Respondents’ position on the relative bioavailability adjustment (RBA) factor

• Site overview and conceptual exposure models for hypothetical future scenarios

• Derivation of PCLs and rationale supporting the selected RBA for the San Jacinto River Waste Pits (SJRWP) Site

• Additional technical support for the use of RBA = 0.5 at the SJRWP Site

• Additional site context and logistical considerations

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Position Summary

• An RBA factor of 0.5 is appropriate for the SJRWP because of the characteristics of sediments and the dioxins and furans (D/F) mixture in the waste

• The preponderance of scientific evidence clearly indicates that absorption by people of D/F from soil is “…likely to be substantially less than 100%...” (USEPA 2010)

• Conceptual exposure models addressed by the risk assessment and the PCLs reflect hypothetical future scenarios and very conservative assumptions

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SJRWP Site Overview

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Reasonably Anticipated Future Receptors, North of I-10

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Reasonably Anticipated Future Receptors, Soil Investigation Area 4

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History of RBA at SJRWP

• January 2012: Draft Exposure Assessment Memorandum (EAM) to EPA

• April 24, 2012: Received EPA comments on EAM

• May 22, 2012: Final EAM to EPA

• December 2012: Draft BHHRA, Draft RI Report to EPA

• March 25, 2013: Respondents receive EPA’s conditional approval

— EPA commented on RBA in Comment #10

— Additional detail was added as requested

• May 2013: Final BHHRA, Final RI Report submitted to EPA

• February 2014: Letter regarding RBA to EPA in response to questions

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Supporting Technical Experts

• Ann Bradley

— Human health risk assessment lead

• Mike Ruby

— Bioavailability expert

» Lead and arsenic: 1990–2004 (including SERDP grant)

» Dioxins/furans: 2000–2005 (for Dow at Midland)

» PAHs: 2008–present (SERDP grant)

» National Research Council Committee on the Bioavailability of Contaminants from Soils and Sediments (2000–2002)

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Derivation of PCLs and the RBA Factor

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Terminology

• Bioavailability: fraction of dioxin in soil that is absorbed into the body

• Relative bioavailability (RBA): ratio of absorption from soil to absorption from the matrix used in the critical toxicity study. For dioxins this would be absorption from corn oil (noncancer endpoint) or diet (cancer endpoint).

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RBA for noncancer = Absorption of dioxin from soil Absorption of dioxin from test matrix

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PCL Calculation

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TH = Target hazard index (unitless) AT = Averaging time (days)1 BW = Body weight (kg) ED = Exposure duration (years) EF = Exposure frequency (days/year) FI = Fraction of total intake that is related to the study area (unitless) IRs = Ingestion rate for soil (mg/day) RBAs = Relative bioavailability adjustment factor (unitless) RfD = Reference dose (pg/kg-day) TDI = Tolerable daily intake (pg/kg-day) CF1 = Conversion factor 1 (0.000001 kg/mg) CF2 = Conversion factor 2 (1000 pg/ng) 1 For noncarcinogenic and threshold carcinogenic endpoints, AT equals the exposure duration in years multiplied by 365 days/year.

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PCL Calculation

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TH = Target hazard index (unitless) AT = Averaging time (days)1 BW = Body weight (kg) ED = Exposure duration (years) EF = Exposure frequency (days/year) FI = Fraction of total intake that is related to the study area (unitless) IRs = Ingestion rate for soil (mg/day) RBAs = Relative bioavailability adjustment factor (unitless) RfD = Reference dose (pg/kg-day) TDI = Tolerable daily intake (pg/kg-day) CF1 = Conversion factor 1 (0.000001 kg/mg) CF2 = Conversion factor 2 (1000 pg/ng) 1 For noncarcinogenic and threshold carcinogenic endpoints, AT equals the exposure duration in years multiplied by 365 days/year.

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Tetrachlorinated Dioxins and Furans Predominant at SJRWP

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Application of RBAs from EPA 2010

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Table 1. Summary of RBA Studies of Dioxins in Soil

Reference Species Dioxin and Furan

Congener Reported RBAs (percent) Average RBA from Study (percent)

Bonaccorsi 1984 Rabbit TCDD 32 32 Lucier 1986 Rat TCDD 22, 45 33.5 McConnell 1984 Guinea pig TCDD 8,11 9.5 Shu 1988 Rat TCDD 44, 49, 38, 43, 45, 37 42.7 Umbriet 1986 Guinea pig TCDD <1, 24 12.5 Wendling 1989 Guinea pig TCDD 7, 30, 2, 1.6 10.2 Average of TCDD Studies 23

Budinsky 2008a Swine PCDD/F 23, 27 25 Budinsky 2008b Rat PCDD/F 37, 66 51.5 Finley et al 2009 Rat PCDD/F 16.7, 48.4, 37.7, 46.5, 33.3 36.5 Wittsiepe 2007 Swine PCDD/F 28.4 28.4

Source:

USEPA (2010), Table 1

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RBA for SJRWP BHHRA

• January 2012: Submit EPA review drafts of EAM and Toxicological and Epidemiological Studies Memorandum

— Propose use of tolerable daily intake (TDI) to evaluate cancer and noncancer effects

— Propose RBA of 0.5

• February 2012: EPA issues noncancer RfD for TCDD

• RBA of 0.5 is conservative for use with the noncancer RfD (basis of Site PCLs)

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Toxicity Criteria

RBA from EPA 2010

Adjustment for Basis of Critical Study

Final RBA

TDI 0.23 0.5 0.46

RfD 0.23 None (a) 0.23

(a) Reference material used in existing RBA studies are appropriate for use with the RfD.

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RBA: Additional Supporting Technical Information

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Outline

• Context for an RBA adjustment

• EPA’s evaluation of dioxin RBA studies and their assay evaluation framework

• State of the science

• Application of an RBA to the San Jacinto site

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Context for RBA Adjustment

• RBA adjustments address oral exposures only (not dermal)

• Complete exposure pathway involving direct contact with soil or sediment

• At SJRWP site:

— Future recreational visitor

— Future outdoor commercial worker

— Future construction worker

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EPA Evaluation of Dioxin RBA Studies and Assay Evaluation Framework

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• RBA of dioxin in soils can be expected to be less than 100%

• Available studies are not adequate and sufficient to estimate an RBA less than 100%

• A preferred animal model or bioassay protocol has not been established for predicting soil RBA in humans

February 2014

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Dioxin RBA Studies

• Nine studies between 1984 and 2009 (six between 1984 and 1989)

• EPA considers six of them to be valid for soil RBA assessment

• Three of these studies provide TEQ-based RBA estimates

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Existing Soil Dioxin RBA Studies

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Study

Number of soils

Animal Model

TOC (%)

Dioxin/Furan Source

RBA (%)

Finley et al. 2009 5 Rat <1

Operating industrial facility

17-48 (mean of 36) TEQ-weighted

Budinsky et al. 2008

Residential - 1 Swine 1.5 Incinerator Swine: 23, 27 TEQ-weighted

Floodplain - 1 Rat 2.7 Chlor-alkali

plant Rat: 37, 66

TEQ-weighted

Wittsiepe et al. 2007 1 Swine 6.8 Sludge-treated

soil

28 TEQ-weighted

Shu et al. 1988 6 Rat NA Times Beach

Contaminated oil/soil

37 – 49 (mean of 43)

Lucier et al. 1986 2 Rat NA

Minker site TCDD-

contaminated soil

22, 45

Bonaccorsi et al. 1984 1 Rabbit NA Soil

Seveso, Italy 32

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Existing Soil Dioxin RBA Studies

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Study

Number of soils

Animal Model

TOC (%)

Dioxin/Furan Source

RBA (%)

Finley et al. 2009 5 Rat <1

Operating industrial facility

17-48 (mean of 36) TEQ-weighted

Budinsky et al. 2008

Residential 1 soil Swine 1.5 Incinerator Swine: 23, 27

TEQ-weighted

Floodplain 1 soil

Rat 2.7 Chlor-alkali

plant Rat: 37, 66

TEQ-weighted

Wittsiepe et al. 2007 1 Swine 6.8 Sludge-treated

soil

28 TEQ-weighted

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RBA Values From Existing Studies

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Finley et al. 2009 Budinsky et al. 2008

Wittsiepe et al. 2007

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

Rela

tive

Bio

avai

labi

lity

(RBA

)

rats

swineFloodplain soil in rats

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Factors that Control Dioxin RBA From Soil

• Aging or weathering of dioxins in soils appears to reduce the RBA—SJRWP wastes are more than 45 years old

• Dioxin/furan binding to organic carbon (OC)

• Animal model (swine vs. rat). EPA has expressed a strong preference for swine as an oral bioavailability model

• Dioxin/furan congener composition in source material

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Organic Carbon in Site Sediments

• OC is the primary geosorbent for dioxins and furans in soil

• San Jacinto TOC:

— Upland sand area: 0.7

— Northern Pits: 1.5−2.1

— South Impoundment: 0.2−2.0

• Budinsky study TOC: 2.7 and 3.1

• Wittsiepe study TOC: 6.8

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Dioxin/Furan Congener Comparison

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SJRWP congener profile dominated by tetrachlorinated dioxins and furans

• Budinsky et al. 2008: — Urban soil: TCDD (50%)

and PeCDD (25%), all others <5%

— Floodplain soil: TCDF (33%), PeCDF (41%), HxCDF (11%), and all others <5%

• Wittsiepe et al. 2007: Dominated by PCDF congeners

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Technical Rationale for RBA = 0.5

• Selected RBA Factor is consistent with the published literature

— RBA of 0.5 is conservative relative to published RBAs for similar sites

• Weathering of sediments reduces absorption of dioxins and furans: wastes are more than 45 years old

• Organic carbon, including black carbon, in site sediments sorbs dioxins and furans

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Decision Context: Impoundments North of I-10

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Protective Concentration Levels Used in the FS

• North of I-10:

— Reasonably anticipated future uses:

» Recreational visitor

» Outdoor commercial worker

— Recreational visitor PCL: 220 ng TEQ/kg

— Commercial worker PCL: 1,300 ng TEQ/kg

• Values apply to soil or sediment

• Derivation based on both ingestion and dermal exposure routes

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If the RBA Factor Changes from 0.5 to 1

• Recreational visitor PCL: 220 ng TEQ/kg

— This value becomes 200 ng TEQ/kg (due to dermal exposure dominating risk estimates)

• Commercial worker PCL: 1,300 ng TEQ/kg

— This value becomes 750 ng TEQ/kg

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Baseline Sediments in Post-TCRA Environment: Recreational Visitor

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No change to FS with new RBA

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Baseline Sediments in Post-TCRA Environment: Commercial Worker

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Baseline Sediments in Post-TCRA Environment: Commercial Worker

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Decision Context: Soil Investigation Area 4

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Protective Concentration Levels Used in the FS

• Soil Investigation Area 4 (South of I-10)

— No risk to outdoor Commercial Worker, no PCL

— Reasonably anticipated future uses:

» Construction Worker

— Construction worker PCL: 450 ng TEQ/kg

• Value applies to depth-weighted average in top 10 feet of soil

• PCL incorporates both ingestion and dermal exposures

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If the RBA Factor Changes from 0.5 to 1

• Future Construction Worker PCL: 450 ng TEQ/kg

— This value becomes 240 ng TEQ/kg

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Result if RBA = 1

• Future Construction Worker PCL: 450 ng TEQ/kg — This value becomes 240 ng

TEQ/kg

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Considerations for Site-Specific RBA Study

1. Draft Sampling and Analysis Plan Addendum

2. Perform sampling that penetrates the TCRA cap

3. RBA study Work Plan, reviews, and discussion

4. Performance of the laboratory RBA study

5. Data analysis

6. Reporting

7. Revisions to HHRA, RI Report, Feasibility Study

Estimated timeframe: 1.5 to 2 years

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Summary

• An RBA factor of 0.5 is appropriate for the SJRWP because of the characteristics of sediments and the D/F mixture in the waste

• The preponderance of scientific evidence clearly indicates that absorption by people of D/F from soil is “…likely to be substantially less than 100%...” (USEPA 2010)

• Conceptual exposure models addressed by the risk assessment and the PCLs reflect hypothetical future scenarios and very conservative assumptions

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