Risk is the potential for harm. Although the concept of risk—and some of the same analytic tools—are also used in finance and actuarial science, as well as to describe threats from natural events, this discussion focuses on risks to human health and the environment from toxic pollution.

Risk=f(Hazard, Exposure)

The magnitude and severity of risk are a function of the types of harm (i.e., the hazards, or what can go wrong) and the extent and likelihood of exposure. If the elements of hazard and exposure are not both in play, there is no biophysical risk to health or the environment. However, the perception of risk can be as damaging, with potential for destroying trust and sapping resources and emotional energy. Maintaining an appropriate balance between the level of social concern about a threat on the one hand and the extent of its social...