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Patterns of Lesion Occurrence

Hepatic lesions were probably the most reliable histological markers of contaminant exposure in winter flounder, which is consistent with current literature on histopathological biomarkers in fish (Hinton et al. 1992, Varanasi et al. in press). Hydropic vacuolation and nonspecific necrotic lesions appeared to be particularly useful for field assessment of anthropogenic stress in this species. Hydropic vacuolation was found in up to 50% and necrotic lesions in up to 25% of winter flounder collected from heavily contaminated sites in Boston Harbor, Raritan Bay, and Long Island Sound, but it was found in less than 5% of fish from minimally contaminated areas. Hydropic vacuolation has also been detected in rock sole (Lepidopsetta bilineata), starry flounder (Platichthys stellatus), and white croaker (Stehr 1990; Stehr et al. 1991; Myers et al. 1992; in press) from contaminated sites on the West Coast, and it appears to be associated with the development of cholangiocytic neoplasms (Harshbarger and Clark 1990). Consequently, it is of considerable value as a histopathologic biomarker. Similarly, hepatocellular necrosis and related lesions are well established as biomarkers of contaminant exposure, and they have been observed in both field and laboratory studies in a variety of fish species (Meyers and Hendricks 1985; Hinton et al. 1992). A variety of other hepatic lesions, including neoplasms, foci of cellular alteration, nonneoplastic proliferative lesions, and spongiosis hepatis, were also observed in flounder from these sites. Prevalences of these lesions were substantially lower (e.g., 2 to 10%) than prevalences of hydropic vacuolation and hepatocellular necrosis, but their pattern of distribution was reflective of an association with contaminant exposure, confirming their utility as histopathologic biomarkers.

Megalocytic hepatosis and nuclear pleomorphism, two closely related toxicopathic and presumably degenerative hepatic conditions described in English sole and highly correlated with contaminant exposure in that species (Myers et al. 1987, 1990, 1991, 1992, in press), showed no relationship with contaminant exposure in winter flounder. Megalocytic hepatosis was not observed at all, while nuclear pleomorphism was found in less than 2% of winter flounder examined and did not occur at elevated prevalences in flounder from contaminated sites.

Consequently, changes in nuclear size observed in this study probably represent the normal range of variation in nuclear size for this species and do not represent a lesion. As nuclear pleomorphism and megalocytic hepatosis are characteristic bioindicators of contaminant exposure in English sole, as well as in several other bottomfish species (Myers et al. 1987, in press), the absence of these two lesions in winter flounder is a striking finding.

In general, the types of lesions observed in winter flounder in the present study and their distribution among the common sampling sites are similar to the findings of other investigators (Murchelano and Wolke 1985, 1991; Moore 1991; Carr et al. 1991). At heavily contaminated sites within Boston Harbor, for example, Murchelano and Wolke (1985, 1991) and Moore (1991) report preneoplastic and neoplastic lesions in 10 to 15% and hydropic vacuolation in 56 to 74% of winter flounder sampled. In contrast, in flounder from minimally contaminated sites in Cape Cod Bay, Massachusetts Bay, or Georges Bank, neoplasms were not observed, while vacuolated cell lesions were found in less than 10% of fish examined (Moore 1991, Murchelano and Wolke 1991).

In addition to hepatic lesions, fin erosion and a variety of idiopathic lesions in the kidney were monitored in this study so their utility as biomarkers could be evaluated. Renal lesions occurred at relatively low prevalences in winter flounder, and they did not appear to be closely related to contaminant exposure. Fin erosion, on the other hand, was found in a surprisingly high proportion of winter flounder collected from contaminated areas in Boston Harbor and Long Island Sound. Elevated prevalences of fin erosion have been reported previously in winter flounder collected from Boston Harbor (Williams 1981) and Raritan Bay (Ziskowski and Murchelano 1975). However, it is uncertain whether xenobiotics are a principal or merely a contributing etiologic factor in the development of these lesions.

Although winter flounder exhibits a number of widely recognized toxicopathic liver lesions, in comparison with other teleost species which have been commonly used in carcinogenesis studies, its pathological response to environmental contaminants is quite distinctive. When exposed to carcinogenic compounds such as certain AHs, English sole and other widely studied species such as medaka, killifish, and rainbow trout characteristically respond in a manner that closely follows the mammalian pattern of histogenesis of neoplasia (Frith and Ward 1980, Couch and Harshbarger 1985, Myers et al. 1987, Myers et al. 1990). Early toxicopathic changes in this species typically include hepatocellular necrosis and megalocytosis in association with hepatocellular regeneration; preneoplastic focal lesions are common; and the majority of neoplasms observed in both field and laboratory studies are hepatocellular in origin (Myers et al. 1987, Myers et al 1990, Vogelbein et al. 1990, Metcalfe et al. 1988, Black et al. 1985, Hendricks et al. 1985, Schultz and Schultz 1984, Hawkins et al. 1990) . In contrast, the toxicopathic response exhibited by winter flounder is characterized by hydropic vacuolation of hepatocellular and biliary cells and biliary hyperplasia (this study, Moore 1991, Murchelano and Wolke 1985, 1991); a relatively low prevalence of altered foci ; and a predominance of cholangiocellular neoplasms over hepatocellular neoplasms. In recent field studies of winter flounder, for example, 42% to 90% of observed neoplasms were cholangiocellular (this study, Moore 1991, Murchelano and Wolke 1985, 1991). In contrast, cholangiocellular neoplasms account for only about 15% of liver neoplasms in English sole (Myers et al. 1987).

Several other teleost species, including starry flounder and white croaker sampled from contaminated sites on the West Coast as part of the NBSP (Stehr 1990, Stehr et al. 1991, Myers et al. 1992, in press), exhibit patterns of lesion occurrence similar to those observed in winter flounder. These findings suggest that toxicopathic response, and possibly histogenesis of neoplasia, may follow more than one pathway in teleost fish.

Age

For all classes of hepatic lesions described in this study, other than hepatocellular nuclear pleomorphism, the risk of disease occurrence increased significantly with increasing age. A similar relationship between lesion prevalence and age has been documented in other studies on winter flounder. For example, Wolke et al. (1985) report that neoplasms were found only in winter flounder greater than 25 cm in length, while Murchelano and Wolke (1991) report no tumors in fish less than 320 mm in length. Moore (1991) reports that prevalences of biliary proliferation, and hydropic vacuolation and neoplastic lesions in winter flounder increased with increasing length or age, and no neoplasms were observed in winter flounder below 300 mm or 5 years of age. Positive relationships between prevalences of liver nodules, neoplasms, and other toxicopathic lesions and fish age have been noted in several other species as well, including English sole from Puget Sound (Rhodes et al. 1987; Barrick et al. 1985; Myers et al. 1990, 1991, 1992), ruffe (Gymnocephalus cernuus) from the Elbe estuary (Kranz and Peters 1985), and bream (Abramis breama) from contaminated European rivers (Sloof and DeZwart 1982).

Age was also a significant risk factor for renal lesions and fin erosion. There is little information available on the relationship between fish age and the occurrence of fin erosion, but for renal lesions this result is consistent with previous observations in other flatfish species. For example, in previous studies in English sole (McCain et al. 1982, Rhodes et al. 1987), sclerotic, necrotic, and proliferative renal lesions all showed a significantly increased risk attributable to fish age. In West Coast NBSP studies (Myers et al. 1992), the risk of one or more categories of renal lesions increased with age in English sole, starry flounder, white croaker, black croaker (Cheilotrema saturnum), and flathead sole (Hippoglossoides elassodon). The significance of age as a factor in renal necrotic lesions in fish is not understood, although the susceptibility of the kidney to such injury has been shown to increase with age in mammals as well as fish (Finn 1983). As for sclerotic lesions, the increase in mesangial matrix density that characterizes mesangiosclerosis or glomerular hyalinization, two of the most common forms of these lesions, occurs as a cumulative nonspecific response to injury in a variety of chronic renal disease states (Schillings and Stekhoven 1980), as well as occurring as a normal part of the aging process in a number of vertebrates, including humans (Finn 1983).

Sampling Season

In addition to age, the risk of occurrence of certain lesion types appeared to be related to the season of sampling. Female winter flounder which were sampled at heavily contaminated sites in Boston Harbor and Raritan Bay during the winter spawning season were less likely to exhibit hydropic vacuolation and nonspecific necrotic lesions than females sampled in late spring after spawning was completed. This suggests that spawning populations may be partially composed of fish migrating from other less contaminated areas, that are not normally resident at the sampling sites at other times of the year. This theory is supported by studies on winter flounder migration patterns during the spawning season, which suggest that, for the most part, winter flounder are organized into distinct spawning groups that return to their respective spawning grounds year after year (Black et al. 1988, Saila 1961). Outside of the spawning season, however, many of these fish disperse to offshore waters and the stocks mix (Danila 1989). In Narragansett Bay, for example, certain subpopulations of fish congregate in highly contaminated estuaries of the upper bay to spawn, but at other periods these same animals may mingle with other populations in less polluted lower Narragansett Bay or offshore (Black et al. 1988). Consequently, fish captured at an area during the spawning season are not necessarily representative of the population that resides there during the rest of the year.

Gender

The data from the present study suggest that female winter flounder are slightly less likely than male winter flounder to develop certain lesions, including neoplasms, spongiosis hepatis, and necrotic lesions in the kidney. The finding that female winter flounder were less susceptible than males to hepatic neoplasms was somewhat surprising, as other studies have found little or no effect of gender on neoplasm prevalence in winter flounder (Murchelano and Wolke 1991, Moore 1991). Nor did gender appear to have any effect on neoplasm prevalence in English sole (Rhodes et al. 1987; Myers et al. 1990, 1991, 1992). The differences in lesion prevalences observed in the present study between male and female flounder collected at the same time (i.e., during spring NBSP sampling, outside the spawning season) were relatively small, so it is possible that they represent a sampling anomaly rather than a true biological difference. However, true gender-associated differences in susceptibility to lesion development could arise as a result of the differences in the migratory behavior of male and female winter flounder. Studies of winter flounder migration patterns indicate that adult females are generally more mobile than males, often spending extended periods offshore to feed during summer months (Black et al. 1988, Valdez 1989, Danila 1989), in areas where contaminant exposure would be greatly reduced. Also, there is evidence that activities of xenobiotic metabolizing enzymes are affected differently by the reproductive cycle in males and females (Snowberger and Stegeman 1987, Snowberger-Gray et al. 1991) so there is the potential for gender-associated differences in the metabolism of toxic compounds and in the concentrations of toxic or carcinogenic intermediates produced. Consequently, it would be premature to draw any conclusions about the effect of gender on hepatic lesion susceptibility in winter flounder without additional research.

Gender had no apparent influence on proliferative or sclerotic renal lesions in winter flounder, but males appeared to have a higher risk of developing necrotic renal lesions. Increased risk of various types of kidney lesions in males were also reported for English sole (necrotic lesions), flathead sole (proliferative lesions), and hornyhead turbot (Pleuronichthys verticalis , proliferative lesions) (Myers et al. 1992). These results are in contrast to the studies of Rhodes et al (1987) which showed no influence of gender on renal lesions in English sole. It is not clear why such a relationship should exist, but its consistency across a variety of species suggests that it may have some biological foundation and consequently may merit further research.

Relationships Between Chemical Contaminants and Idiopathic Lesions

In addition to determining prevalences of suspected toxicopathic lesions at the sampling sites, we attempted to examine the relationships between prevalences of these lesions and specific contaminants using logistic regression. As mentioned earlier, the analysis had certain limitations. For example, because of the time and cost involved in doing detailed chemical analyses, most classes of contaminants were measured in composite samples rather than in individual fish. The number of samples available for inclusion in analyses was relatively small, and it was not possible to examine relationships between contaminant levels and disease in individual fish. In addition, the high degree of intercorrelation among different classes of contaminants measured in tissue, stomach contents, and sediment made it difficult to determine the effects of specific compounds or groups of compounds on disease prevalence. However, this analysis was not intended to determine the precise chemical etiology of idiopathic disease in winter flounder. Rather, its objective was to provide preliminary information about the possible roles that selected organic contaminants might play in the development of disease conditions, thus providing direction for future research. With these considerations in mind, the discussion below attempts to interpret the significance of the associations identified between lesion types and parameters of contaminant exposure, especially in terms of their toxicologic significance.

Hydropic Vacuolation

Of the lesions tested, hydropic vacuolation showed the strongest and most consistent relationships with levels of organic contaminants measured in sediment, stomach contents, and liver and bile. Concentrations of DDTs, chlordanes, and AHs (or metabolites) measured in all compartments were significant risk factors for this lesion. The observed relationships between tissue contaminant levels and the occurrence of hydropic vacuolation provide evidence of a chemical etiology for this lesion, and help to establish its validity as a biomarker of contaminant-induced stress. However, because concentrations of all three of these classes of organic contaminants in sediments were highly correlated and winter flounder are exposed to them simultaneously, it was difficult to determine the relative importance of DDTs, chlordanes, and AHs in the development of hydropic vacuolation. The problem is further compounded by the fact that in a recent laboratory study (Moore 1991), this lesion was not induced in winter flounder by intraperitoneal injection or dietary exposure of winter flounder to high levels of either chlordane or the AH, benzo[a]pyrene (BaP). It is not clear why this was so, but is may be that exposure to the complex mixture of chemicals present in urban sediments is necessary for the generation of hydropic vacuolation. Alternatively, hydropic vacuolation may be caused by an unknown and unmeasured etiologic agent that covaries with the measured contaminants. Whatever the case, it would be premature to dismiss AHs, chlordanes, or DDTs as potential risk factors for this lesion without further investigation. This is particularly true as hydropic vacuolation has also been associated with exposure to organic contaminants in starry flounder and white croaker from contaminated sites sampled on the West Coast in the NBSP. In starry flounder, AHs, PCBs, and DDTs were all found to be significant risk factors for the development of this lesion, while in white croaker hydropic vacuolation was most closely associated with exposure to PCBs (Myers et al. 1992). Laboratory exposure studies with multiple species using intact sediments, organic extracts of urban sediments, and model compounds may be needed to determine how various classes of AHs and CHs, alone or in concert, may contribute to the development of this lesion.

Nonspecific Hepatocellular Necrosis

Nonspecific necrotic lesions were positively associated with AH concentrations in sediment and stomach contents, and with levels of FACs in bile. These consistent associations between AHs and necrotic lesion over several compartments strongly support AHs as a significant risk factor for hepatic necrosis. Moreover, laboratory data support the role of AHs as necrogenic agents in winter flounder (Moore 1991) and other fish species (Wyllie et al. 1980, Meyers and Hendricks 1985, Pitot 1988). Necrotic lesions were also positively associated with DDT and chlordane concentrations in sediments and stomach contents, but they showed little relationship with concentrations of these contaminants in liver tissue. As concentrations of chlordanes and DDTs in liver are a more reliable measure of chronic exposure to these compounds than concentrations in either sediment or stomach contents, the lack of relationship between concentrations of DDTs and chlordanes in liver and prevalences of necrotic lesions may be an indication that these contaminants are not major risk factors for the development of these lesions. However, laboratory exposure to chlordanes has induced necrotic lesions in winter flounder (Moore 1991), and both chlordanes and DDTs have been shown to have necrogenic effects on the liver in mammals (Hodge et al. 1967; Murphy 1986). Consequently, they may be significant risk factors for the development of necrotic lesions if animals are exposed to sufficiently high doses of these compounds. Prevalences of necrotic lesions were not correlated with levels of PCBs in sediments or in stomach contents or liver tissue of winter flounder. In fact, in winter flounder from New Bedford Harbor, which had the highest concentrations of PCBs in sediment of all the Northeast sites, the prevalence of necrotic lesions was less than 4%. The lack of relationship between PCBs and idiopathic disease in winter flounder was a striking finding of this study and will be discussed in detail later in this report.

Neoplasms and FCA

In the present study, prevalences of neoplastic and preneoplastic lesions in winter flounder were not strongly associated with concentrations of organic contaminants in sediments, stomach contents, or biliary FACs. Those associations which were observed (i.e., with chlordanes and AHs) were relatively weak and, for no clear reason, occurred only with contaminant concentrations in stomach contents. However, AHs are well established as genotoxic carcinogens in mammals (Williams and Weisburger 1986), and there is substantial evidence that they act in the same way in fish (Varanasi et al. 1989d). AHs have been demonstrated to bind to hepatic DNA (Smolarek et al. 1987, Varanasi et al. 1986a,b, 1989b,c; Shugart et al. 1987), and administration of AHs in laboratory studies has led to the development of neoplastic or preneoplastic lesions in several fish species (Schiewe et al. 1991, Metcalfe et al. 1988, Black et al. 1985, Hendricks et al. 1985, Schultz and Schultz 1984, Hawkins et al. 1990). Moreover, several epidemiological studies, including histopathological field surveys of English sole in Puget Sound, show strong correlations between AH levels in sediments and metabolites of AHs in bile (Krahn et al. 1986) and prevalences of neoplasms and preneoplastic focal lesions (Malins et al. 1984; Landahl et al. 1990; Myers et al. 1990, 1991, 1992).

It is not entirely clear why correlations between AH exposure and FCA and neoplasms in winter flounder were not as strong as correlations observed in other flatfish species (e.g., English sole) (Malins et al. 1984, 1985; Landahl et al. 1990; Myers et al. 1990). One explanation could be that the relatively low prevalences of neoplasms and FCA detected in this study made it difficult to establish a relationship between AH exposure and these lesions in winter flounder. Moreover, because AHs are largely metabolized and do not accumulate in fish tissue (Varanasi et al. 1989d, Stein et al. 1987), we currently have no reliable measure of chronic AH exposure. Levels of metabolites in bile are generally reliable measures of short-term exposure in other flatfish species (Krahn et al. 1986). However, biliary concentrations of FACs decline substantially within a few weeks after a single exposure to AHs (Collier and Varanasi 1991), so FAC levels are likely to be elevated only when animals are in or have recently left contaminated areas. For territorial species such as English sole, this does not present a problem, but in a more mobile species such as winter flounder, it may cause complications. The difficulty of obtaining an accurate assessment of chronic AH exposure in winter flounder may partially account for the relatively weak relationships observed in this study between neoplastic and preneoplastic lesions and AH exposure. It should also be kept in mind that there is a long latency period for the development of neoplasms and related lesions. Consequently, although environmental contaminants is likely to be critical factor in the etiology of these lesions, their occurrence may not be highly correlated with concentrations of contaminants in sediment or in fish tissues at the time the animals are collected, especially in a relatively mobile species such as winter flounder.

In summary, the long latency period for the development of neoplasms and related lesions, the lack of reliable measures of chronic exposure to potential environmental carcinogens, and the low prevalence of these lesions, may all have contributed to weak correlations between neoplasms and related lesions and potential etiologic agents such as AHs. However, because AHs are well established as carcinogens in several species of fish, they should not be dismissed as toxicologically significant risk factors for hepatic neoplasms and focal lesions in winter flounder. The association between chlordane levels in stomach contents and neoplasms is too weak to be considered as evidence for involvement of chlordanes or other pesticides in the development of neoplasia in winter flounder, particularly as is it not consistent across all compartments (i.e., sediment, liver, and stomach contents). However, an association between chlordane and neoplasms is not inconsistent with current theories on carcinogenesis. While pesticides such as chlordanes and other chlorinated hydrocarbons show little evidence of genotoxicity and are generally not considered to be primary carcinogens (Pereira 1983, Rossi et al. 1983), they are classified as possible promoters that facilitate tumor development by cells which have been genetically altered by genotoxic compounds, such as certain AHs (O'Brien 1967). Moreover, hepatocarcinogenic or promotional effects of chlorinated pesticides have been found in fish (Halver 1967). In West Coast NBSP studies, one class of chlorinated pesticides, the DDTs, were identified as a strong risk factor for hepatic neoplasms in English sole (Myers et al. 1992). Consequently, chlordanes may play a role in the etiology and development of neoplasms in winter flounder, although it seems unlikely that they are the primary agents of initiation.

Proliferative Lesions

Proliferative lesions such as biliary and hepatocellular regeneration were significantly correlated with levels of chlordanes in both stomach contents and liver tissue. This is quite interesting, as laboratory exposure to chlordane induced both hepatocellular necrosis and lesions resembling biliary proliferation in winter flounder (Moore 1991). Aside from chlordanes, no other organic contaminants emerged as significant risk factors for proliferative lesions in the present study. However, in laboratory studies, these lesions have been induced in winter flounder by exposure to BaP (Moore 1991), as well as in other fish by exposure to hepatotoxic or hepatocarcinogenic compounds, including AHs (Schiewe et al. 1991, Hendricks et al. 1984, Nunez et al. 1991). As with neoplasms, the relatively low prevalence of proliferative lesions, coupled with the lack of a reliable chronic measurement of AH exposure, may have obscured the potential toxicological relationship between AHs and these lesions.

Spongiosis Hepatis

Aside from a relatively weak correlation with chlordane levels in stomach contents, prevalences of spongiosis hepatis showed no relationship with levels of measured organic contaminants in sediments, stomach contents, or tissues. Although this lesion has been observed in laboratory exposures of medaka and sheepshead minnow to carcinogens (Hinton et al. 1984, 1988; Couch and Courtney 1987), and in winter flounder exposed to BaP in the laboratory (Moore 1991), it does not show strong evidence of a chemical etiology in winter flounder on the basis of the present study. Moreover, because of its low prevalence (< 5%) even in urban sites, it is unlikely to be useful as a biomarker of contaminant exposure in field studies.

Megalocytic Hepatosis/Nuclear Pleomorphism

Prevalences of nuclear pleomorphism in winter flounder were unrelated to contaminant concentrations in sediment, stomach contents, or liver, and, as noted previously, megalocytic hepatosis was not observed in flounder sampled as part of this study. Nuclear pleomorphism and megalocytic hepatosis are characteristic toxicopathic responses to AH exposure in English sole, as well as in several other bottomfish species (Myers et al. 1987, 1992, in press), and their rarity in winter flounder is an indication that this species may differ somewhat from other widely studied teleost fish in its pathological response to environmental contaminants.

Renal Lesions

In contrast to hepatic lesions, renal lesions in winter flounder were not highly correlated with concentrations of measured organic contaminants in fish or sediments. Of the three classes of lesions (proliferative, necrotic, and sclerotic) monitored in this study, only necrotic lesions showed any evidence of a relationship to contaminant exposure. Necrotic lesions were significantly elevated at Deer Island in Boston Harbor and showed significant positive correlations with concentrations of LAHs in sediment and stomach contents. Because of the relative lack of information on the effects of aromatic hydrocarbon exposure on the teleost kidney, the toxicological significance of this relationship is not clear. Although AHs are not widely regarded as nephrotoxicants in mammals (Hook and Hewitt 1986) or fish (Hinton and Lauren 1990), associations between AH exposure and renal lesions have been observed in other studies of bottomfish species. For example, in laboratory studies where English sole were exposed to BaP or an AH-enriched sediment extract, exposed fish showed a statistically higher incidence of tubular necrotic and proliferative lesions than controls (Schiewe et al. 1991). Moreover, in field-collected English sole and starry flounder, there was some evidence of increased risk of renal disease associated with elevated biliary FAC levels or sediment AHs (Myers et al. 1992). In comparison to hepatic lesions, associations between contaminants and renal disease were relatively weak, but because of the consistency of these associations among several species, the kidney lesions, especially necrotic or degenerative conditions should not be dismissed as potential indicators of the effects of environmental contaminants.

In this study there was little evidence of a relationship between chlorinated hydrocarbons and kidney disease in winter flounder. This was not unexpected, as pesticides and other chlorinated aromatic compounds are not generally considered to be potent renal toxins in either mammals (Hook and Hewitt 1986) or fish (Pritchard and Renfro 1984). However, exposure to DDTs or PCBs was linked to an increased risk of renal disease in flathead sole, white croaker, and English sole collected from urban areas along the West Coast in NBSP samplings (Myers et al. 1992), and degenerative lesions have been induced in teleost kidney by exposure to Arochlor 1254 (Nestel and Budd 1975) and DDTs (King 1962). In view of this evidence, it would be premature to dismiss chlorinated hydrocarbons (CHs) as potential risk factors for renal disease in winter flounder, although it is possible that the lack of relationship between CHs and renal disease in winter flounder represents a true species difference in sensitivity to these compounds as renal toxicants.

Although renal lesions were not strongly associated with concentrations of organic contaminants in sediments and winter flounder, they did appear at elevated prevalences at certain industrialized sites. Several metals present in sediments, including copper and chromium, have been shown to produce degenerative changes in the kidneys of winter flounder and rainbow trout (Onchorhynchus mykiss) in laboratory exposure studies (Baker 1969, Van der Putte et al. 1981), and metals have been identified as potential risk factors for necrotic and sclerotic kidney lesions in white croaker, English sole, and flathead sole sampled from the West Coast during the NBSP (Myers et al. 1992). The possible significance of metals as renal toxicants in winter flounder will be investigated in future studies.

Fin Erosion

Fin erosion prevalences were relatively high at certain heavily contaminated sites such as Mystic River, Deer Island, and Quincy Bay in Boston Harbor. Moreover, prevalences of this condition appeared to be strongly correlated with contaminant concentrations in sediments and stomach contents, and there was also some evidence of an increased risk of fin erosion in winter flounder with elevated biliary FAC concentrations. Although fin erosion has been reported at elevated prevalences in winter flounder from Boston Harbor and Raritan Bay (Williams 1981, Ziskowski and Murchelano 1975), to our knowledge this is the first study showing a significant association between exposure to specific contaminants and the risk of fin erosion in winter flounder. There is some evidence for a chemical etiology for fin erosion in various fish species (Sindermann 1990). However, in a study examining the relationships between contaminants and fin erosion in English sole (L.D. Rhodes, unpubl. data. Department of Biological Structure, University of Washington, Seattle, WA 98195), no significant associations were found between the presence of fin erosion and any specific xenobiotic compounds in sediment. In English sole, where prevalences of fin erosion were generally less than 1%, this lesion appeared to have an inflammatory etiology, with a number of biotic or abiotic factors, including parasites or wounds as well as exposure to irritants in sediment potentially serving as initial causes of the inflammation. Exposure to contaminants is only one of the many factors that may be associated with the development of fin erosion, so further verification is needed to confirm its chemical etiology and to determine whether xenobiotic compounds are principal or merely contributing etiologic factors in its development. However, the results of this study, as well as similar findings of increased prevalences of fin erosion in other NBSP species (Cross 1985, McCain et al. 1992), suggest it may have some utility as an indicator of environmental quality.

PCBs and Idiopathic Disease in Winter Flounder

In this study PCBs did not emerge as significant risk factors for the development of any pathological condition in winter flounder. The lack of a relationship between concentrations of PCBs in tissue and sediments and prevalences of idiopathic disease in winter flounder was somewhat unexpected. In a similar study in which PCB concentrations in tissues of individual female winter flounder were measured and correlated with lesion occurrence (Johnson et al. 1992), PCB concentrations were positively correlated with prevalences of both hydropic vacuolation and biliary proliferation. Moreover, in starry flounder and white croaker examined as part of the West Coast NBSP, PCBs were found to be significant risk factors for hydropic vacuolation and other degenerative lesions (Myers et al. 1992), as well as contributory risk factors for the development of neoplasms. In the above-mentioned studies, however, fish were captured from sites where PCBs were present in combination with other contaminants such as AHs, DDTs, or pesticides. In the present study, fish were also collected from Clark's Point in New Bedford Harbor, a site where concentrations of PCBs in sediments and in winter flounder liver (approximately 3000 ng/g dry weight and 39,000 ng/g, respectively) were much higher than at any of the other Northeast Coast sampling sites, but levels of other contaminants in sediments and fish were moderate to low (Brown et al. in prep.). At the New Bedford site, then, PCBs were the major etiologic agent to which winter flounder were exposed, and under these conditions fish did not exhibit significantly elevated prevalences of any category of hepatic lesion, compared to flounder from the Rocky Point, Long Island Sound reference site. The prevalence of hydropic vacuolation, for example, was less than 6% in flounder from the PCB-contaminated New Bedford site, while prevalences of this lesion in flounder from several contaminated sites in Boston Harbor and Raritan Bay, where AHs and CHs co-occur in sediments, were over 40%. These findings suggest that while PCBs may contribute to the development of hydropic vacuolation, neoplasms, and other hepatic lesions in winter flounder by acting in concert with other contaminants such as AHs, they are not likely to be the primary etiologic agents.

It is not surprising that winter flounder from the New Bedford site which were exposed to PCBs alone did not exhibit high prevalences of neoplasms or preneoplastic lesions, because chlorinated hydrocarbons such as PCBs are not generally considered to be primary carcinogens in either fish or mammals (Silberhorn et al. 1990), although they may promote neoplasm development if animals are also exposed to genotoxic compounds such as certain AHs (Shelton et al. 1984, Safe 1989, Hendricks et al. 1990, Silberhorn et al. 1990). On the other hand, the finding that winter flounder from the New Bedford site did not develop degenerative or regenerative lesions, such as biliary hyperplasia and hydropic vacuolation, was unexpected, as exposure to PCBs has been associated with biliary proliferative lesions in mammals (Kimbrough et al. 1972, Kimbrough and Linder 1974), and with hydropic vacuolation in winter flounder in previous field studies (Johnson et al. 1992). However, the results of the present study suggest that if PCBs do contribute to the development of hydropic vacuolation, they do so in concert with other contaminants such as AHs.

In summary, using data gathered during the Northeast Coast NBSP, several potential chemical risk factors (e.g., AHs, DDTs, and chlordanes) were identified for idiopathic disease in winter flounder. Moreover, these data suggested that exposure to PCBs alone did not play a major role in lesion initiation, although it is possible that selected toxic PCB congeners (Safe 1984) or PCBs in combination with other contaminants could have an influence on lesion development. Because different classes of contaminants generally occurred together in sediments, and animals were exposed to a mixture of agents simultaneously, it was difficult to evaluate the roles that specific toxicants might play in the etiology of pollution-related disease in winter flounder on the basis of epizootiological data alone. However, the correlational evidence generated by the Northeast Coast NBSP provides valuable insights into involvement of chemical contaminants in lesion development in winter flounder, and it may be used to formulate definitive cause-and-effect studies of disease initiation and progression with potential etiologic agents present in urban environments.

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