BIOMONITORING OF SOUTH ESTONIAN WATERS BY MEANS OF XENOBIOTIC METABOLISM OF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) LIVER

The aquatic pollution in waters of Tartu County (South Estonia) was mo nitored by measuring biotransformation enzyme activities in rainbow tr out (Oncorhynchus mykiss) liver. Juvenile fish were caged for 3 weeks in winter and in spring at selected study areas: Lake Vortsjarv, the s econd largest lake in Estonia, representing an agricultural and recrea tional area as well as an important fishing site, and River Suur Emajo gi, whose main source of pollution is in the form of improperly treate d urban sewage from the town of Tartu. To obtain an overview of the de gree of contamination, the contents of polycyclic aromatic hydrocarbon s were determined in selected samples of fish muscle. During both seas ons, cytochrome P-450-dependent monooxygenase (MO) activities in rainb ow trout liver showed the highest values in the fishing harbor area in L. Vortsjarv. During winter, elevated MO activities were measured in fish in R. Suur Emajogi up to 3 km downstream from the town of Tartu, compared with the values from the upstream reference area. In the spri ng, MO activities at the same site did not reach such high levels as e arlier. At that time, the contaminants in R. Suur Emajogi were much mo re diluted than in winter. This was due to the much higher runoffs and possibly causes the lack of induction. Conjugation enzyme activities did not show any significant changes in any of the studies conducted.