Brown bullhead Ictalurus nebulosus from industrialized locales are often susceptible to environmentally-induced liver (hepatic and biliary) and skin neoplasms probably from exposure to PAHs (Baumann, 1998). Histopathological studies were conducted on brown bullhead that were collected in the mid 1980s from sites above and below the major sources of PCBs to the upper HR (Kim et al., 1989). As expected, mean concentrations of total PCBs in muscle were more than sixty-fold higher in bullhead collected from locales downstream of the PCB sources. However, there was no significant difference in the prevalence of gross abnormalities between the two exposure groups. Although tumors were absent in both groups, the prevalence of several histopathologic lesions suggestive of contaminant exposure was elevated in the PCB-contaminated group. The prevalences of histopathologies in liver, spleen, and kidney exceeded 75 percent in fish from the downriver site, compared to 2-13 percent in bullhead from the up-river reference site. While the absence of neoplasms in bullhead from the HR may be surprising given the vulnerability of bullhead to environmentally-induced carcinogenesis, PCBs usually do not induce DNA damage and perhaps the PAHs required to initiate DNA lesions may be in insufficient concentrations at these HR locales.
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