Toxicity and mutagenicity of waste waters from Baikalsk Pulp and Paper Mill: Evaluation of pollutant contamination in Lake Baikal

Lake Baikal has no agricultural and only little municipal pollution. Instead a potential source of pollution is the Baikalsk Pulp and Paper Mill (BPPM). All waste waters of the mill are mechanically, biologically and chemically purified and there are sedimentation and aeration ponds at the final stage. In this study the efficiency of the waste water purification was detected by testing toxicity and mutagenicity. Waters and sediments were collected along the cellulose bleaching process and waste water treatment. Free and bound polychlorinated phenols, guaiacols, catechols, anisoles and veratroles were analysed. Cytotoxicity of diethylether-extracted waste waters was screened by measuring total protein content in a fish hepatoma cell line (PLHC-1). The mutagenicity of the water, sediment and tissue extracts of selected aquatic species was determined by a modified Ames test. Diethylether fractions of the effluents from BPPM were cytotoxicfor the PLHC-1 cells when concentrated. Biological purification of the waste waters did not affect the cytotoxicity (ED₅₀ ˜2.2 and ˜2.0 μml⁻¹ before and after). The cytotoxicity was decreased after chemical purification (ED₅₀ ˜3.7μml⁻¹) and even more after the aeration pond (ED₅₀ ˜4.2 μml⁻¹). Mutagens were found in nearly all water samples released after the pulp chlorination. However, the mutagenic activity was effectively decreased during both biological and chemical treatment of waste waters. Only the tissue extracts of seals and a few roach possessed mutagenic activity. In conclusion, even the modern waste water purification systems do not totally abolish potential toxicity and/or mutagenicity of the effluents.