Biomarker responses and resin acids in fish chronically exposed to effluents from a total chlorine-free pulp mill during regular production.

This study used rainbow trout (Oncorhynchus mykiss) to investigate the biological effects of long-term exposure to a total chlorine-free (TCF) pulp mill effluent. Fish tanks were set up on the premises of the pulp mill, and fresh effluent water was led through a pipe directly from the pulp mill to the tanks. The fish were exposed to effluent for up to 50 days and kept for up to 70 days afterward to study the recovery process. Two independent experiments were carried out. Ethoxyresorufin-O-deethylase (EROD), glutathione-S-transferase (GST), and glutathione reductase (GR) activity were elevated in fish exposed to a 2% concentration of pulp mill effluent, as were levels of DNA adducts. These effects could be detected during exposure and also after a period of recovery. The results demonstrate that the pulp mill effluent contains substances that affect the detoxification process and also have genotoxic potential. The continued occurrence of effects after a 70-day recovery period was demonstrated in both experiments, and may indicate that the effluent contained compounds with persistent properties. The content of free and conjugated resin acids in the bile of the fish was found to be a useful indicator of exposure to pulp mill effluent.