Chairman's Introduction to Session on Bioassay, Risk Assessment and Epidemiology

In irtroducing this third session ofthe Conference, let us pause for a moment to see where we have been in the first two sessions. The descriptive epidemiology of feral fish populations strongly suggests that enzootics ofneoplasms are associated with contamination of their environment with carcinogens, procar-cinogens, and cancer promoters. Detailed biochemical studies on fish and shellfish from contaminated and clean localities further implicate xenobiotics in these enzootics. Furthermore, the edible portions of fish and shellfish have been shown to contain residues of some xenobictics and their metabolites. To what extent, then, do these enzootics represent a public health warning to human populations that might consume fish or shellfish from these contaminated habitats? In this third session we begin to examine this question. In assessing risks we need to know a number of things: a) What are the conditions ofexposure? Who is being exposed; to what; in what amounts and frequencies; in what way? We have already heard in previous sessions about sonme ofthe carcinogens found in habitats where fish suffer increased rates ofneoplasms, but there is still a great deal about these environments that we do not know as yet. Moreover, there is much to learn about the prevalence and nature ofcarcinctgens, procarcinogens, and promoters in the edible portions of fish and shellfish. Even if we were to fill in these gaps, we must still determine the extent to which human populations consume fish and shellfish in general, and from contaminated environments in particular. b) Identify adverse effects and relate these effects quantitatively to dose (i.e., establish a dose-response relationship). As already noted. a number of known and putative carcinogens have been found in polluted habitats where feral fish populations show evidence of increased rates ofneoplasms. However, the extent to which th.ese or other carcinogens are passed up the ibod chain to hurmans and the possibility that they undergo transformation along the way to forms that may be more or less hamfu tan the original remains to be determined in most instances. James Huff of NIEHS will discuss one standard method of identifying caricer risk in complex mixtures, the rodent chronic boassay; Huffdiscusses the considerations involved in conducting such a test and the feasibility of doing so. There is also controversy as to the nechanisms whereby some xenobiotics might contribute to cancer. This problem is exemplified by PCBs, which are common contaminants in fish. If PCBs are promoters rather than …