Halogenated chemicals have numerous industrial and agricultural uses. In addition, chlorine used for treatment of drinking water and wastewater combines with organic chemicals to form chlorinated compounds such as chloroform. Some processes used to manufacture paper also use chlorine and can form chlorinated compounds. Several halogenated compounds are known or suspected mammalian carcinogens.
Oral papillomas (Fig. 3.8) occurred on 73% of black bullheads (Ameiurus [=Ictalurus] melas) living in a pond filled with chlorinated wastewater of domestic origin (Grizzle et al., 1981). After neoplasms were discovered, less chlorine was used for effluent disinfection, and the total residual chlorine concentration entering the pond decreased from 1.0-3.1 mg l-1 to 0.25-1.2 mg l-1 (monthly averages). Three years after the chlorination rate was reduced, prevalence of neoplasms had decreased to 23% (Grizzle et al., 1984). This population of fish has since been extirpated, presumably because reproduction was not successful in the contaminated water.
There was no evidence that viruses were present in the oral papillomas on black bullheads living in chlorinated wastewater (Grizzle et al., 1984). Except for low concentrations of chloroform (9.0-13.5 mg l-1) and bromodichloro-
methane (0.7 mg l-1) present in the water, chemicals suspected to be carcinogens were not detected in water or sediment of the pond. Some organic extracts of the wastewater tested positive for mutagenicity in Ames tests; extracts were most mutagenic during the summer (Grizzle etal., 1984). Tan etal. (1981) presented evidence for induction of mixed function oxidase systems and for hepatic dysfunction in black bullheads exposed to chlorinated wastewater.
Black bullheads confined to cages in the pond receiving chlorinated wastewater developed oral papillomas after 2-18 months (Grizzle et al., 1984). Papillomas did not develop in control fish, nor in exposed brown bullheads, yellow bullheads (Ameiurus [=Ictalurus] natalis) and channel catfish. Compared with exposed black bullheads and control channel catfish, exposed channel catfish had increased levels of hepatic glucuronosyltransferase which could conjugate active metabolites and thereby reduce the effects of carcinogens.
Neuroblastomas in coho salmon were attributed to halogenated compounds in chlorinated-dechlorinated water (Meyers and Hendricks, 1984). However, similar neoplasms, diagnosed as malignant schwannomas and ependymo-blastomas, also occurred in coho salmon reared in well water that had not been chlorinated (Masahito et al., 1985).
Croaker (Nibea mitsukurii) collected from several locations along the Pacific coast of Japan had chromatophoromas, but prevalence was especially high at a location polluted by effluent from a pulp mill (Kinae et al., 1990). An ether extract of effluent from the pulp mill was mutagenic, and several chlorinated compounds were identified by gas chromatography/mass spectrometry. During surveys from 1973 to 1981, frequency of chromato-phoromas on croaker collected near the pulp mill averaged 47.3%, compared with 0-8.5% at other locations. Between 1977 and 1979, treatment of the wastewater was improved and contaminated sediment was removed; prevalence of chromatophoromas decreased to 20% for 1984-1987. Neoplasms were noted on other fish species collected from the area polluted by the pulp mill, but the number of fish sampled was insufficient for analysis. Sea catfish (Plotosus anguillaris) from this location had a 13.5% prevalence of cutaneous melanosis. A chromatophoroma developed on one croaker of 100 exposed for 13 months to sea water containing 10% effluent. Melanosis developed on 70% of the experimentally exposed sea catfish, compared with 10% of control fish.
Carcinogenicity of brominated compounds to fish has seldom been studied. Rainbow trout fed 1,2-dibromoethane (2 g kg-1 dry weight in diet) developed gastric papillomas and a low incidence of hepatocellular carcinomas (Hendricks et al., 1995). After 18 months, frequency of these gastric papillomas was higher in males (41%) than in females (21%).
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