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Bioavailability of Contaminants in Soil: Considerations for Human Health Risk Assessment

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1 Introduction
1 Introduction Overview
1.1 Using Bioavailability Information
1.2 Background
1.3 Definition of Terms
2 Regulatory Background
2 Regulatory Background Overview
2.1 Current Practices: Survey of State Regulators
3 Technical Background
3 Technical Background Overview
3.1 Soil Mineral Phases
3.2 Soil pH, Organic Matter, and Reactive Clay Minerals
3.3 Soil Particle Size
4 Decision Process
4 Decision Process Overview
4.1 Decision Process Flowchart
4.2 Is there a Method Available?
4.3 Could Bioavailability Assessment Affect the Remedial Decisions?
4.4 Do the Benefits of Bioavailability Assessment Justify the Costs?
4.5 Further Considerations
5 Methodology
5 Methodology for Evaluating Contaminant Oral Bioavailability Overview
5.1 In Vivo Approach
5.2 In Vitro Approach
6 Lead
6 Lead Overview
6.1 Fate and Transport
6.2 Toxicology and Exposure
6.3 Methodology for Quantifying RBA of Lead in Soil
6.4 When Does a Bioavailability Study Make Sense?
6.5 Case Studies
6.6 Using Bioavailability Methods to Evaluate Remedies (Bioavailability-Based Remediation)
7 Arsenic
7 Arsenic Overview
7.1 Fate and Transport
7.2 Toxicology and Exposure
7.3 Methodology for Evaluating Arsenic Bioavailability
7.4 When Does It Make Sense to Use Bioavailability?
7.5 Case Studies
7.6 Using Bioavailability Methods to Evaluate Remedies (Bioavailability Based Remediation)
8 PAHs
8 Polycyclic Aromatic Hydrocarbons (PAHs) Overview
8.1 PAH Sources and Exposure
8.2 General Toxicity of PAHs
8.3 Influences of Soil on Bioavailability of PAH
8.4 Methodology for Evaluating PAH Bioavailability
8.5 Dermal Absorption
8.6 Amendment Strategies and Permanence of Bioavailability
8.7 Case Study
9 Risk Assessment
9 Using Bioavailability Information in Risk Assessment Overview
9.1 Risk Calculations
9.2 Other Considerations and Limitations
10 Stakeholder Perspectives
10 Stakeholder Perspectives Overview
10.1 Stakeholder Concerns
10.2 Specific Tribal Stakeholder Concerns
10.3 Stakeholder Engagement
11 Case Studies
11 Case Studies Overview
11.1 Arsenic, Mining, CA
11.2 Arsenic, Pesticide, AR
11.3 Arsenic, Naturally occurring, UT
11.4 Arsenic, Smelter, AZ
11.5 Arsenic-contaminated tailings, OR
11.6 Lead, Industrial, Midwest US
11.7 PAH, Skeet targets, TX
11.8 Arsenic, Copper precipitation, UT
11.9 Arsenic, CCA wood preservative, CA
11.10 Arsenic, MGP coal ash, MI
11.11 Lead, Mining MT
11.12 Lead, Mining, MT
11.13 Lead, Smelter, UT
Additional Information
Review Checklist
Appendix A: Detailed Survey Responses
Appendix B: Chemical Reactions of Metals
Acronyms
Glossary
Acknowledgments
Team Contacts
Document Feedback

 

Bioavailability of Contaminants in Soil
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6.6 Using Bioavailability Methods to Evaluate Remedies (Bioavailability-Based Remediation)

Bioavailability-based remediation does not remove the soil contaminant, but rather reduces its bioavailability and, thus, the health hazard that may be associated with exposure. For example, excavation and replacement of contaminated soil is expensive and may be ecologically destructive. Applying in situ soil amendments that reduce contaminant bioavailability, however, is a cost-effective alternative that could limit or eliminate the need for excavation. Extensive research has shown a variety of soil amendments can successfully reduce lead bioavailability, most notably phosphate (P) fertilizers. Applying phosphate fertilizers, however, may inadvertently increase the bioavailability of other contaminants, such as arsenic (Scheckel et al. 2013). Phosphate amendment has been comprehensively reviewed, see (Chaney and Mahoney 2014;  Scheckel et al. 2013; Hettiarachchi and Pierzynski 2004).

Confirmation of reduced bioavailability after treatment with soil amendments may be problematic. Several studies have shown that USEPA Method 1340 potentially over predicts lead RBA in soils amended with P treatments (Obrycki 2017; Obrycki et al. 2016; Ryan et al. 2004; Zia et al. 2011; Scheckel et al. 2013). Consequently, Method 1340 has not been validated as an accurate predictor of the reduction of lead RBA achieved by soil amendments. Additional research is needed to determine the accuracy and precision of these and other IVBA methods to predict lead RBA, specifically in P-treated soils. Possible approaches being investigated for using IVBA of treated soils is to modify Method 1340 raising the extraction solution pH to 2.5 instead of 1.5, or simply use an alternative method (for example, IVG).

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