JM

Chapter 24 Part 1: RISK ASSESSMENT AND THE PERCEPTION OF RISK

Risk Assessment and the Perception of Risk

Risk Assessment Terminology

  • Defined by the National Academy of Sciences (NAS) in 1983.
    • Hazard: The inherent ability of a chemical to cause an adverse effect.
    • Risk: The probability of a hazard occurring under specific exposure conditions.
    • Risk Assessment: A quantitative process to determine hazard, exposure, and risk.
    • Risk Management: Selection of appropriate actions based on social, economic, and other considerations.

Risk

  • Probability of harm under specific conditions.
  • Combination of:
    • Probability/likelihood of an adverse event.
    • Consequences/level of harm resulting from the event.

Risk Assessment

  • Methodology for evaluating human health effects and environmental consequences of chemical exposure.
  • Recognized value and limitations in public health and rational management decisions.
  • Always partially based on financial considerations.

Human vs. Ecological Risk Assessment

  • Human Risk Assessment: Focuses on exposed human populations and methodologies for assessing human health risks.
  • Ecological Risk Assessment: Addresses non-human species (wildlife, plants).
    • More complex due to diverse ecosystems and species.

Overview of Risk

  • Regulatory bodies face challenges in setting exposure limits:
    • Underestimating risk: potential overexposure of the population.
    • Overcalculating risk: unnecessary public costs for management.

Concerns About Costly Cleanups

  • Serious concerns about the public benefits of extremely costly cleanups of areas deemed hazardous.

Challenges for Regulatory Agencies

  • Limited human data: inferences often based on animal toxicity studies using high exposure levels.

Exposure Levels

  • The question is not about risks at high exposure levels (e.g., 10 ppm ozone).
  • But rather, what are the risks at more realistic environmental exposure levels?

Real-Life Exposures

  • Humans are exposed to multiple chemicals simultaneously.
  • These chemicals can interact in complex and unpredictable ways in the body and environment.

The “Process” of Risk Assessment

  • Hazard Recognition: Identify a chemical hazard.
  • Dose-Response Assessment: Assess the potential for injury at different exposure levels; determine a quantitative dose-response for a toxic endpoint.
  • Exposure Assessment: Collect analytical data on environmental concentrations or amounts of chemical(s).

Safety Factors

  • Toxicity testing in laboratory animals is often the primary basis for evaluating chemical hazards.
  • "Safety factors" are used to compensate for uncertainties in extrapolating from animals to humans.
    • Safety factors involve setting exposure levels significantly lower than thresholds observed in the lab.
  • Intake assumptions are made for humans, considering all exposure routes.
  • All information is assessed to characterize the existence and magnitude of risk to public health.

Risk Assessment Components

  • Hazard Identification: What toxicities are associated with exposures to the chemical(s)?
  • Dose-Response Assessment: What are the health problems associated with the chemical at different levels of exposure?
  • Exposure Assessment: Who is exposed, and to how much?
  • Risk Characterization: What are the excess risks in the exposed population?