Bioavailability in Environmental Risk Assessment

Introduction
Fundamental Concept of Bioavailability
Definition of Bioavailability
Unaltered Form
Systemic Circulation
Relationship Between Extent and Rate of Bioavailability
Extent of Bioavailability
Bioavailability in Health Risk Assessment
Biologically Effective Dose
Internal Dose and Average Daily Internal Dose
External Dose and Average Daily External Dose
Summary
Mechanism of Absorption
Respiratory System
Structure and Function
Rate-Limiting Processes for Gaseous Phase Contaminants
Other Factors Influencing Respiratory Bioavailability for Gases and Vapors
Rate-Limiting Processes for Particulate Phase Contaminants
Other Factors Influencing Respiratory Bioavailability for Aerosols
Gastrointestinal System
Structure and Function
Rate-Limiting Processes
Other Factors Influencing Oral Bioavailability
Skin
Structure and Function
Rate-Limiting Processes
Other Factors Influencing Dermal Bioavailability
Summary
Experimental Methods for Evaluating Bioavailability
General in Vivo Methods
Measurement of Blood Levels
Measurement of the Cumulative Urinary Excretion
Mass-Balance Technique
Measurement of Toxic Response
Specific Methods for the Inhalation Exposure Route
Determination of Deposition Fraction
Mechanical Clearance Fraction
Dissolution Rate
In Vitro Methods: Isolated Perfused Lung
Specific Methods for the Ingestion Exposure Route
Measurement of Fecal Excretion
Measurement of Liver Ratio
Dissolution Testing
Methods Based on the pH Partition Theory
Specific Methods for Dermal Exposure Route
Surface Disappearance
In Vitro Methods: Biological Membrane Models; Artificial Membrane Models
Summary
Exposure Routes and Bioavailability Factors for Selected Contaminants*
Arsenic
Cadmium
Chromium and Chromium Compounds
Copper
Mercury
Lead
2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD)
Polynuclear Aromatic Hydrocarbons (PAHs)
Benzene
Toluene
Polychlorinated Phenols
Phenol
Aniline
Bioavailability of Xenobiotics from Contaminated Sites
Identification of Exposure Routes
Reliability and Validity of the Bioavailability Factors
Choice of Experimental Methods
Analytical Capabilities
Species Differences
Mixtures and Vehicles
Mechanism of Toxicity
Chemical Forms
Exposure Duration and Frequency
Priority Needs for Further Research
Considerations for Applying Bioavailability to Health Risk Assessment
Metals
Organic Xenobiotics
Other Application Considerations
Risk Management Considerations
References
Glossary of Terms
Index

*For each of the contaminants in this section, the following is provided:
Exposure Routes and Receptors
Toxicokinetics (Following Absorption)
Bioavailability (Inhalation, Ingestion, Dermal)
Uncertainties
Conclusions
Recommendations