Ecotoxicological assessment of a recipient lake sediment of bleached-kraftpulping discharges

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 1 00 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, old er layers (23 cm). The dominant species in the diatom community, Aulacoseir a alpigena and Cyclotella kutzingiana, disappeared and were replaced by Ast erionella formosa in the 4- to 6-cm layer. This layer was three- to fivefol d more toxic to Vibrio fischeri (as measured by the median effective concen tration) and slightly genotoxic (as measured by the SOS-chromotest inductio n ratio, I-C/I-0 for Esherichia coli PQ37) compared with the layers above a nd 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 activ ity (chitinase, phosphatase, alpha-glucosidase, and beta-glucosidase) was d etected at depths of 0 to 1 cm and 4 to 6 cm, and more than 90% of the enzy mes were bound to the particulate matter. Ninety-seven percent of the organ ic halogen in the sediment was particle bound. Apparently, full ecological recovery occurred in the layer from 0 to I cm, which had accumulated in 199 0s, after the discharging pulp mill discontinued use of Cl-2 in the bleachi ng process and installed full-scale biological treatment for the wastewater s.