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?