Toxicity of sediments from the Stang Alar watershed (Brest) assessed by a battery of bioassays

Abstract

The toxicity of sediment samples taken along two streams of the Stang Alar watershed (under miscellaneous contaminations) was evaluated by several acute and chronic bioassays with freshwater and seawater organisms. Freshwater assays concerned the photosynthetic activity of an algal monoculture Selenastrum capricornutum and a natural phytoplankton community of lake Geneva, the survival of the cladoceran Daphnia magna and the embryolarval development of a fish Brachydanio rerio. Seawater assays were the Microtox test with the bacteria Photobacterium phosphoreum and an oyster Crassostrea gigas embryo stage test. The sediments of the main stream showed a high contamination by lead and zinc aswell as a greater toxicity compared to its tributary (under a low non-point source pollution). The toxicity was greater when the organisms were exposed to whole sediments compared to water extracts. The Microtox test lead to the better sensitivity and discriminatory ability among the different bioassays.