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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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Glossary

A

Absolute bioavailability
The fraction (or percentage) of an ingested (or dermally applied, as applicable) dose that is absorbed and reaches systemic circulation.

Anion
A negatively charged ion.

B

Bioaccessibility
Refers to the results from chemical extraction tests that have been developed to try to simulate or predict the RBA of chemicals from soil. In this context “bioaccessibility” is interchangeable with “in vitro extraction testing,” wherein experimental systems have been developed to assess the potential for human exposure to chemicals in soil by capturing a critical component that affects bioavailability.

Bioavailability
For assessing potential exposures from environmental media, bioavailability refers to the portion of the total quantity of a chemical present that is absorbed by a living organism (Klassen 2013), and reaches the central (blood) compartment, whether exposure occurs via the GI tract, skin, or lungs (NEPI 2000).

C

Cation
A positively charged ion.

cytochrome P450
A large group of intracellular enzymes involved in the oxidative metabolism of a broad spectrum of endogenous and exogenous chemicals, particularly abundant in the liver.

H

Human health risk assessment (HHRA)
The process of characterizing the nature and magnitude of health risks to humans from exposure to chemicals and other stressors that may be present in the environment (USEPA 2015a).

I

In vitro method
Experiment or procedure performed under controlled laboratory conditions and outside an organism, for example inside a test tube or culture dish. The bioaccessibility tests described in this guidance are in vitro methods.

In vivo method
Experiment or procedure performed using living organisms. The bioavailability tests described in this guidance are in vivo methods.

O

Oxyanion
An anion containing one or more oxygen atoms bonded to another element.

R

Relative oral bioavailability (RBA)
Refers to the ratio of the absorption of a chemical from soil, relative to the absorption in the exposure medium used in the critical toxicity study (the study that forms the basis for the cancer slope factor or reference dose).

S

Site-specific bioavailability assessment
The process of determining the relative oral bioavailability (RBA) of a specific chemical contaminating the soils at a site. The assessment includes identifying specific soil samples, selecting and conducting test methods, interpreting laboratory results, evaluating uncertainties in the measurements, and estimating RBA values for the site.

Soil
An unconsolidated mixture of mineral matter, organic matter, and pore space filled with air (soil gas) and water.

V

Validation
procedure to ensure that a method or a process is fit for its intended purpose. In the context of bioavailability considerations, validation ensures that a given in vitro bioaccessibility method can predict the RBA of a contaminant in a specific soil type accurately and reliably enough for use in human health risk assessment. Validation can be achieved by experimentally measuring a set of performance parameters including, but not limited to, accuracy, precision, selectivity, limit of detection, limit of quantitation. Different agencies may have different requirements to consider a method as validated.

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Glossary Lookup List

AJAX progress indicator
  • Absolute Bioavailability
  • anion
  • bioaccessibility
  • bioavailability
  • cation
  • cytochrome P450
  • human health risk assessment
  • human health risk assessment (HHRA)
  • human health risk assessments
  • in vitro method
  • In vitro methods
  • in vivo method
  • in vivo methods
  • oxyanion
  • relative oral bioavailability
  • relative oral bioavailability (RBA)
  • site-specific bioavailability assessment
  • soil
  • validation


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