The Uncertain Risks We Run: Hazardous Materials

Abstract

The problems of risk assessment are discussed from the dual point of view of:

• 1. Who is exposed — and to how much and

• 2. Given the estimated levels of exposures, what estimates of risk can be developed.

The major issue of concern is that in general there is inadequate data on who is exposed, and almost no data on how much exposure there is. Individual exposure monitoring is rarely done (except for such things as radiation, through radiation badges) making it impossible to associate individual exposure with subsequent disease — if any. It is often difficult to know how many employees are exposed to a given agent. Before monitoring is undertaken an agent usually has to come under suspicion, thereby making inevitable unmonitored exposures to materials later found to be hazardous.

The mathematical models for extrapolation from species to species vary enormously in the predictions they yield, even when one accepts all the assumptions about species-to-species jumping. Recent work derived from Whittemore and Keller would seem to imply that in a multi-stage cancer process, the initiator stage dose-effect may pile up early in the life history of exposure, implying that several short term exposures to different carcinogens may create more risk than one long-term exposure. Promoting agents, according to this model, on the other hand, seem to have a different mode of action — with far more rapidly diminishing residual effects — so that the promoter may “have to be there” for its effect to be manifest. These different modes of action have implications for research and applications for prevention.