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1. Overall, hepatic lesions proved to be extremely reliable histological markers of contaminant exposure in winter flounder. Hydropic vacuolation and nonspecific necrotic lesions showed particular utility as indicators of anthropogenic stress. Both lesions occurred at high prevalences in winter flounder from heavily contaminated sites and showed a clear gradient in prevalence from heavily to minimally contaminated sites. In addition, they were closely correlated with levels of several classes of organic contaminants in fish tissue and fluids, sediments, and stomach contents.

2. Hepatic neoplasms, foci of cellular alteration, and nonneoplastic proliferative lesions such as biliary hyperplasia were also found in winter flounder from several heavily contaminated sites, but these lesions were not as highly correlated with chemical contaminant levels as might be expected in view of laboratory and field studies in other teleost fish linking environmental carcinogens to the development of neoplasms. Such relationships may have been difficult to identify in winter flounder for several reasons, including: 1) the relatively low prevalence of neoplasms and FCA (e.g., 2-10%) in this species; 2) the long latency period for the development of these lesions; 3) the fact that winter flounder is a relatively mobile species; and 4) the lack of a reliable measure of chronic exposure to certain classes of environmental carcinogens, such as AHs.

3. Nuclear pleomorphism and megalocytic hepatosis, two closely related toxicopathic and presumably degenerative hepatic conditions described in English sole and highly correlated with contaminant exposure in that species, either did not occur or were found only at low prevalences in winter flounder and did not show any relationship with indicators of contaminant exposure.

4. Those compounds clearly identified as risk factors for pathological conditions in winter flounder were AHs, DDTs, and chlordanes. However, because these three classes of contaminants generally occurred together in sediments, and animals were exposed to a mixture of agents simultaneously, it was difficult to evaluate the relative importance of these three classes of contaminants in the development of pollution-associated disease in winter flounder.

5. In addition to chemical contaminants, certain biological factors, particularly age and sampling season, had a significant influence on disease prevalence and should be accounted for in analyses examining relationships between contaminant exposure and disease.

6. PCBs did not emerge as significant risk factors for any pathological condition observed in winter flounder. Not only did PCB levels in sediment, stomach contents, and liver fail to correlate with lesion prevalences, but perhaps more importantly, fish sampled from one site (New Bedford Harbor) that had high levels of PCBs in sediments but relatively low levels of other contaminants had low prevalences of all pathological conditions monitored in this study. While this does not eliminate the possibility that PCBs may play a promotional role in the development of neoplastic lesions, or function as toxicants in concert with other compounds such as AHs, it does suggest that they are not the primary etiologic agents for either neoplastic lesions or regenerative and degenerative conditions in winter flounder.

7. Renal lesions were not highly correlated with levels of organic contaminants in sediments, stomach contents, bile or liver of winter flounder. Of the three classes of lesions monitored in this study (proliferative, necrotic, and sclerotic), only necrotic lesions showed any evidence of a relationship to contaminant exposure.

8. Fin erosion prevalences were relatively high at certain heavily contaminated sites especially within Boston Harbor, and were significantly correlated with contaminant concentrations in sediments and stomach contents, and with biliary FAC concentrations. Because biotic factors such as fungal or bacterial pathogens as well as xenobiotic contaminants may be associated with the development of fin erosion, it is not as specific a biomarker as other toxicopathic lesions, but data from this study indicate that it may be a useful indicator of contaminant exposure in winter flounder.

9. The toxicopathic response typically exhibited by winter flounder exposed to organic contaminants (e.g., hydropic vacuolation of hepatocellular and biliary cells and biliary hyperplasia, and a predominance of cholangiocellular neoplasms over hepatocellular neoplasms) is quite different from patterns of lesion occurrence associated with the histogenesis of neoplasia in mammals and fish species such as medaka (Oryzias latipes), rainbow trout, and English sole. The types of lesions found in winter flounder in contaminated areas have also been noted in other bottomfish (e.g., starry flounder and white croaker) at contaminated sites on the West Coast sampled in the NBSP. These species differences suggest that toxicopathic response, and possibly histogenesis of neoplasia, may follow more than one pathway in teleost fish.

10. Although the present analysis identified several chemical risk factors for disease in winter flounder, the relative importance of different types of contaminants in the development of specific lesion types in winter flounder is not clear. The associations between organic contaminants and disease conditions observed in winter flounder examined in the NBSP may provide the foundation for future cause-and-effect studies which can examine in a more systematic fashion the roles that specific organic contaminants, alone or in combination, may play in the etiology of pollution-associated disease in winter flounder.

We thank Tracy Collier and John Stein of the Environmental Conservation Division and Doug Wolfe, Donna Turgeon, Carol-Ann Manen, Harris White, and Jawed Hameedi of NOAA National Ocean Services for reviewing the manuscript, and Ms. Sharon Giese for editorial assistance. These studies were partially supported by the Office of Ocean Resources Conservation and Assessment (NOAA National Ocean Services) as part of the National Status and Trends Program, and by the NOAA Coastal Ocean Program.

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