Sediment toxicity bioassays for assessment of contaminated sites in the Nervion River (Northern Spain).: 1.: Three-brood sediment chronic bioassay of Daphnia magna Straus

The ecotoxicity of sediments from ten contaminated sites of the Nervion river catchment were assessed with the three-brood chronic sediment bioassay of Daphnia magna. Three additional locations were used as reference sites and one site as control for every bioassay. Survival, number and biomass of neonates and final adult biomass were measured as chronic ecotoxicity endpoints. High mortality of daphnids was observed at one site where sediment was heavily contaminated by metals. At the remaining sites only sublethal reproductive responses were observed, including inhibition of maturity and hence of reproduction, brood delay, reduction in number of neonates and lower adult final biomass. Hormetic responses in adult final biomass and number of neonates per brood were observed where toxicant concentrations were low or were not bioavailable. Female fecundity increased with size in the controls but the reproductive effort is lower in daphnids exposed to contaminated sediments. This was interpreted as an auto-conservative strategy of the species.