Hepatic biotransformation enzymes of fish exposed to non-point source pollution in small streams

The response of hepatic phase I and phase IIbiotransformation enzymes in brown trout(Salmo trutta f. fario) and stone loach(Barbatula barbatula) to differentpollution exposure scenarios was investigatedduring a 5-year-study. Phase I enzymes wereassessed by means of7-ethoxyresorufin-O-deethylase (EROD) activityand cytochrome P4501A (CYP1A) protein level,and phase II enzymes were measured by thecatalytic activity of glutathione-S-transferase(GST). Fish were exposed in the laboratory totap water (controls) or under semi-fieldconditions in so-called bypass systems to waterfrom two streams, with one of the streams(Krähenbach) receiving contaminants mainlyfrom non-point sources (for instance, surfacerun-off), and the second stream (Körsch)receiving contaminants from both non-pointsources and point sources (sewage plants). Inaddition to the fish in the bypass systems,feral fish from the streams were sampled. Thequestions addressed by the study were: (1) isit possible to discriminate the study sites onthe basis of hepatic biotransformation indices?(2) are the metabolic enzyme responses of thetwo species, brown trout and stone loach,comparable? (3) are the metabolic enzymeresponses of fish from the bypass systemscomparable to those of feral fishes? HepaticEROD activities were elevated in both browntrout and stone loach exposed in the bypasssystems compared to the laboratory control. Adiscrimination of the two field sites relativeto pollution intensity was possible by hepaticEROD activities of brown trout only, whereasbiotransformation enzymes of stone loach showedno consistent differences between the stream.Hepatic GST levels of both speciesdid not discriminate between the streams orbetween streams and laboratory. The enzymeresponses measured in fishes from the bypasssystems were comparable to those of feralfishes living in the streams. The findings ofthis study point to critical factors for thebiological monitoring of low-level pollutionwith complex chemical mixtures, including theselection of appropriate test species,monitoring endpoints, and sampling strategies.