Environmental Risk Analysis

Environmental risk is generally defined as the risk to human or ecological health due to a technological or natural event leading to exposure. Such an “event” may be sudden or catastrophic and the resulting exposure may be severe and acute; or the event may be spread over time (chronic), the exposure may be cumulative, sometimes low levels of exposure building up to produce the effect. A flood, chemical accident, or nuclear bomb detonation are catastrophic events leading to acute, often high-level exposure. Ordinary levels of air or water pollution, smoking, alcohol, and dietary factors are examples of chronic, low-level exposure. Depending on the rates of such exposure, the body may be able to metabolize the agents of chronic exposure and even get rid of them with little or no health consequence. When the exposure is chronic and low-level, it is hard to establish the cause-effect relationship.

An analysis of risk begins with the identification of a hazard, assessment of exposure, determination of the relationship between the dose or level of exposure and the degree of effect from the biological response to the dose. This dose-response relationship is usually obtained from data on cellular, animal, and sometimes (rarely) human experiments. The “human experiment” is most often accidental or at least unintended exposure from an accident or event. The exposure to radioactive iodine fallout to a large population from nuclear bomb testing in the 1950’s in the U.S., resulting in large levels of thyroid cancer in people in certain locations, or exposure from chemical spills are examples.

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