Characterization of Lake Ladoga sediments. I. Toxicity to Chironomus riparius and Daphnia magna

Toxicity of surficial sediment of Lake Ladoga, Russia, was studied using bioassays with a midge, Chironomus riparius and Daphnia magna. Many Lake Ladoga sediments caused high mortality of midge larvae in 10-d growth and 40-d emergence tests. In most sediments the biomass production of chironomids was also lowered. However, no statistically significant effect on timing of emergence was observed. Sediment elutriate or pore water tests did not exhibit toxicity to Daphnia magna. The adverse effects observed in midge bioassays indicate the presence of toxic chemicals. It cannot be excluded, however, that the variable sediment physico-chemical characteristics could also have had some effect.