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  • Introduction and Historical Context

  • Definitions

  • Decision Making

  • Hazard Identification

    • Assessing Toxicity of Chemicals—Introduction

    • Assessing Toxicity of Chemicals—Approaches

      • Structure–Activity Relationships

      • In Vitro and Short-Term Tests

      • Animal Bioassays

      • Use of Epidemiologic Data in Risk Assessment

    • Integrating Qualitative Aspects of Risk Assessment

      • Mode of Action

  • Dose–Response Assessment

    • Integrating Quantitative Aspects of Risk Assessment

      • Threshold Approaches

      • Nonthreshold Approaches

      • Statistical or Probability Distribution Models

      • Models Derived from Mechanistic Assumptions

      • Toxicological Enhancements of the Models

  • Exposure Assessment

  • Risk Characterization

    • Variation in Susceptibility

  • Information Resources

  • Risk Perception and Comparative Analyses of Risk

  • Emerging Concepts

  • Public Health Risk Management

  • Summary


Introduction and Historical Context


In the 1970s Congress established a basic plan for environmental laws that authorized regulatory actions to protect public health and the environment. These science-based actions provided the foundation for environmental and human health risk assessment. Toxicological research and toxicity testing constitute the scientific core of risk assessment, which is used for evaluating potential adverse health impacts from chemical exposures. However, such considerations for risk evaluation were not new, since for decades the American Conference of Governmental Industrial Hygienists (ACGIH) set threshold limit values for occupational exposures and the US Food and Drug Administration (FDA) established acceptable daily intakes (ADIs) for pesticide residues and food additives. In 1958, the US Congress instructed the FDA in the Delaney Clause to prohibit the addition of all substances found to cause cancer in animals or humans to the food supply. Pragmatically, this policy allowed food sources that had nondetectable levels of these additives to be declared “safe.” As advances in analytical chemistry revealed that “nondetects” were not equivalent to “not present,” regulatory agencies were forced to develop “tolerance levels” and “acceptable risk levels.” Risk assessment methodologies blossomed in the 1970s with the rising need to address these issues and statues and to provide a common framework for considering human and ecological health effects (Albert, 1994).


Risk assessment was defined as a specific activity in 1983 in the National Research Council (NRC) publication Risk Assessment in the Federal Government: Managing the Process (Red Book). This book detailed steps for hazard identification, dose–response assessment, exposure analysis, and characterization of risks (NRC, 1983). These 4 basic framework steps now form the foundation framework for risk assessment and risk management approaches for many contexts such as children’s health and ecological health and they provide a consistent context for risk assessment frameworks across agencies nationally and worldwide. Risk assessment frameworks have been used by the Health and Safety Executive Risk Assessment Policy Unit of the United Kingdom (Great Britain and Health and Safety Executive, 1999) and by the World Health Organization (NRC, 2009; WHO, 2010) and all of these build from these common components. Fig. 4-1 illustrates a framework with bidirectional arrows demonstrating an ideal situation where mechanistic research feeds directly into risk assessments and critical data uncertainty drives research. The common elements of the basic risk assessment framework are shown in red highlight. Initially, attention in risk ...

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