ECOTOXICOLOGICAL ASSESSMENT OF A RECIPIENT LAKE SEDIMENT OF BLEACHED-KRAFT PULPING DISCHARGES

Abstract

We assessed the biological status of age—dated sediments in Lake Saimaa, a recipient lake for wastewaters from pulp and paper industry for more than 100 years that has also received kraft pulp bleaching wastewater since 1954. Adenosine triphosphate content dropped in the recipient sediment from the top 1 cm (deposited in the 1990s) to 4 to 6 cm below the sediment surface (deposited in 1980s) by a factor of 1,000 but increased again in deeper, older layers (23 cm). The dominant species in the diatom community, Aulacoseira alpigena and Cyclotella kützingiana, disappeared and were replaced by Asterionella formosa in the 4- to 6-cm layer. This layer was three- to fivefold more toxic to Vibrio fischeri (as measured by the median effective concentration) and slightly genotoxic (as measured by the SOS—chromotest induction ratio, IC/I0 for Esherichia coli PQ37) compared with the layers above and below it. The 4- to 6-cm layer also contained up to 4,900 mg of solvent—soluble organic halogen (per kilogram of sediment dry weight). Enzyme activity (chitinase, phosphatase, α-glucosidase, and β-glucosidase) was detected at depths of 0 to 1 cm and 4 to 6 cm, and more than 90% of the enzymes were bound to the particulate matter. Ninety—seven percent of the organic halogen in the sediment was particle bound. Apparently, full ecological recovery occurred in the layer from 0 to 1 cm, which had accumulated in 1990s, after the discharging pulp mill discontinued use of Cl2 in the bleaching process and installed full—scale biological treatment for the wastewaters.