Toxicity of sediments polluted by the pulp and paper industry to a midge ( Chironomus riparius Meigen)

Abstract

The toxicity of pulp mill effluent contaminated sediments to benthic animals was studied using Chironomus riparius as the test organism. The mortality, growth, occurrence of deformities, and emergence of the larvae grown in such sediments were compared to larvae grown in an unpolluted sediment. Many Chironomus species are quite tolerant to environmental conditions and live in contaminated sediments with very low oxygen concentration. Chironomids larvae were found at all sites at Lake Saimaa where the sediment samples were taken. These midges were, therefore, considered as relevant for sediment toxicity studies in the study area. The sediments were characterized for lipophilic organic halogen compounds (EOX), sediment total organic halogen (SOX) and certain heavy metals. The concentrations of both EOX and SOX were 20–40-times higher in the polluted area than in the control area, whereas the concentration of heavy metals was at the same level as in the control area. The toxicity tests showed that the mortality and number of deformities in polluted sediments of Lake Saimaa, Finland, were comparable with unpolluted sediments from the same area. The larvae grew as much or more in the most polluted sediments of Lake Saimaa and in the Lake Ladoga sediments than in the reference sediment from Lake Saimaa. This is possibly due to eutrophication caused by the nutrients in the wastewaters. The highest mortality (40%) was noticed for sediments that were collected at Lake Ladoga close to the city of Sortavala, Russia, which has no wastewater treatment system.