Monitoring the recovery of a polluted lake with biomarkers: Responses of whitefish (Coregonus lavaretus L. s.l.) experimentally exposed to pulp and paper mill effluents

A kriging interpolation of fish biomarker data was utilized as a novel tool to describe the ecotoxicological status of a lake polluted by pulp and paper mill effluents. Liver ethoxyresorufin O-deethylase (EROD) activity, hematological and immunological biomarkers were studied in juvenile whitefish (Coregonus lavaretus L. s.l.) experimentally exposed for one month to effluents from three pulp and paper mills at southern Lake Saimaa. In comparison with the reference areas, liver EROD activitiy was 40%–80% higher in whitefish 3–6 km downstream of one of the mills. Liver EROD was positively correlated with the effluent tracers, lake-water sodium and conductivity. No remarkable differences between whitefish from mill and reference sites in their plasma immunoglobulin M, blood hematocrit, hemoglobin, glucose and lactate levels were observed. In this study, liver EROD activity in whitefish 3–6 km downstream of one of the mills in 1996 was 14%–15% of that recorded in 1991, i.e. before introduction of ECF bleaching and the activated sludge treatment of effluents at the mill in 1992. Our results are comparable with, and confirm the findings of a related caging experiment in 1995, indicating a decreased but still continued exposure of the fish to pulp mill effluent compounds.