Multiple genotoxicity biomarkers in fish exposed in situ to polluted river water

Specimens of rainbow trout (Oncorhynchus mykiss) were either kept in an aquarium under laboratory conditions or caged in the River Po (Northern Italy), upstream or downstream the confluence with the River Lambro, a small yet heavily polluted tributary. Genotoxicity biomarkers, evaluating the internal dose or early biological effects, were monitored after 7, 15 and 30 days of in situ exposure. With the exception of a slight increase of aminopyrine-N-demethylase and uridine-5'-diphospho-glucuronosyl-transferase, no significant effect was produced in fish kept upstream the River Lambro, as compared to control fish kept in the aquarium. In contrast, the responsibility of this tributary in carrying sublethal doses of both genotoxic agents and enzyme inducers into the main river was proved by the significant occurrence of early biological alterations in fish caged downstream. In fact, (a) bile extracts contained frameshift mutagens requiring metabolic activation, with a prevalence of liposoluble components after a short exposure, followed by a time-related increase of conjugated components, in minor part with glucuronic acid; (b) the monooxygenases aminopyrine-N-demethylase, uridine-5'-diphospho-glucuronosyl-transferase and, with sharp differences, arylhydrocarbon hydroxylase and 7-ethoxyresorufin-O-deethylase were enhanced in liver microsomal fractions; (c) the liver cytosolic fractions had an enhanced ability to convert 3-amino-1-methyl-5H-pyrido(4,3)indole into mutagenic metabolites in S. typhimurium; (d) cytogenetic damage was demonstrated by an increased frequency of micronuclei in peripheral blood erythrocytes.