Sensitivity of health endpoints: effect on conclusions of studies

The types of biological response to an environmental agent can depend on dose, thus in this case a family of widely different dose-response relationships would be expected. For those situations where the magnitude of the effect may be determined on probabilistic grounds as a function of dose ("stochastic" model), no particular dose-response relationship-may necessarily be inferred; the appropriate model still depends on the biological processes under consideration. Some examples of different conclusions concerning dose-response are given for studies of effects of lead and carbon monoxide at low doses. With increasingly sensitive measures of physiologic responses, these can be detected at exposures close to background, but for many cases the question remains whether an observed response really represents a true toxic effect. The application of epidemiologic data for regulatory purposes may depend on identification of the response to an agent appropriate for preventive measures. The conclusions one reaches about studies of health effects of environmental agents can be markedly influenced by the types of health endpoints under consideration.