USE OF FISH BIOMARKERS TO ASSESS THE RECOVERY OF A LAKE ECOSYSTEM RECEIVING PULP AND PAPER-MILL EFFLUENTS

Between 1991 and 1993, a Finnish pulp and paper mill changed over to E CF bleaching and installed an activated sludge plant in place of of it s aerated lagoons. In order to assess the effects changes, one-year-ol d whitefish (Coregonus lavaretus, L. s.l.) were exposed in 1991 and 19 93 by caging to lake water receiving mill effluents of pulp and paper mill. Physiological and biochemical markers (liver ethoxyresorufin-O-d eethylase (EROD), uridine-diphosphate-glucuronosyltransferase (UDP-GT) , gluthatione-S-transferase (GST), plasma lactate dehydrogenase (LDH), aspartate-aminotransferase (ASAT), immunoglobulin-M (IgM)) and metabo lized chlorophenolic metabolites in the bile were determined. Chloroph enolic concentrations in bile decreased noteably between two years: in 1993 the level in the nearest exposure area (3 km from the mill) was 1/330 of that measured in 1991. In 1991, EROD induction showed clear d istance-related decrease. At the nearest exposure station, EROD induct ion was also five times higher in 1991 than in 1993, yet double that a t the reference stations upstream of discharge point in 1993. No stati stical differences were found in UDPGT, GST and ASAT levels between ex posed and controls. In 1991, plasma IgM levels were suppressed 6 km do wnstream of the mill's discharge point, but this was not observed in 1 993. According to this study, the biomarker responses in fish provided a good indication of new process measures and of subsequent recovery of polluted lake.