Introductory remarks: Session on genetic factors affecting pollutant toxicity.

Occupational and environmental toxicologists are faced with the responsibility of providing sound scientific data that can be used to ensure individuals that they can conduct their daily activities without undergoing any undue risk which might potentiate the development of disease. With the majority of chemicals in the environment, it has been generally assumed that there is some safe level of exposure that is of no threat to human health. To be able to predict the absolute safe level is the sought after goal; however, the possibility of achieving this level of precision is remote, and in fact no chemical is absolutely safe. Thus, it becomes vitally important to carefully define the population at risk, the mode of exposure, and the lowest concentration that will cause an adverse health effect. Great strides have been made from the days when the toxicologists were extrapolating low-level health effects from studies performed at high concentrations (LD50), with single pollutant exposures (03, NO2, SO2), inadequate analytical and monitoring techniques, and "unnatural" routes of exposure. It is now recognized that in many instances the action of one toxic agent can be modified by exposure to other agents. The possibility of various environmental pollutants interacting to cause effects that may be additive, synergistic, or antagonistic is always present. The inability to perceive ill effects from a single agent is now no longer a guarantee that, when combined with another test substance, an adverse health effect on the individual might not be noted. In addition to those studies that use complex