Biomarker responses along a pollution gradient: Effects of pulp and paper mill effluents on caged whitefish

Abstract

Lake Saimaa (SE Finland) is a large oligotrophic lake receiving biologically treated effluent from a bleached kraft pulp and paper mill. Hatchery-reared juvenile whitefish ( Coregonus lavaretus L. s.l.), a species known to feed on plankton and other particulates, were caged using a technique developed and optimized for this species and were exposed for one month in five downstream stations (3.3–16 km). Two reference stations (4.5–8.5 km) upstream from the effluent outlet were used. An exposure gradient of chlorinated organics was assessed by determining concentrations of conjugated chlorophenolics (CPs) in bile and CPs as well as extractable organic halogens (EOX) in gut lipids. Activities of liver cytochrome P4501A (CYP1A) monooxygenase and two conjugation enzymes, uridinediphospho glucuronosyltransferase (UDP-GT) and glutathione S-transferase (GST), were measured as indicators of exposure. Humoral antibody (IgM) level in plasma was used to estimate immune capacity. Other blood parameters were also analyzed. Fish caged nearest the mill (3.3 km) had concentrations of CPs in bile 50-fold that of upstream reference fish. A gradual, distance-related, decrease of CPs in bile was seen. A similar trend was seen in EOX and concentrations of CPs in gut lipid. Induction of CYP1A, measured as activity of 7-ethoxyresorufin O-deethylase (EROD), was seen in fish at all downstream sites. At the site nearest the mill, EROD activity was 13-fold higher compared to the reference area. No significant changes were seen in liver UDP-GT or GST. Levels of plasma IgM were 58–97% of reference values in fish caged at downstream from the outfall. We conclude that biomarkers in this study implicated the effluent as a causal factor and that relative severity of exposure was inversely related to distance from the effluent source.