Are zebra mussels restricted by toxicant levels in the River Meuse? a review

Abstract

This paper questions if chemical barriers prevent the occurrence of benthic invertebrates in the river Meuse. To this purpose an ecotoxicological analysis is presented, using published observations on the zebra musselDreissena polymorpha, a tolerant species that maintains populations in the river. Zebra mussels collected or exposed at the Belgian-Dutch border contained high levels of several groups of toxicants, and mixture toxicity is likely to occur. A recently developed bio-assay, using the filtration rate of the zebra mussel, demonstrated strong inhibitory effects of water from the river Meuse. To determine which (combination of) toxicants cause such effects, laboratory experiments with toxicant mixtures were carried out. It was demonstrated that in a mixture of five metals (Cu, Zn, Ni, Cd, Pb) the metals contributed to the toxicity of the mixture below the No Observed Effect Concentrations (NOEC) for these metals when tested individually. The average concentration of Cu, Zn and possibly Pb in Meuse water exceed the NOEC values for filtration rate. Thus, it seems likely that joint effects of different (groups of) toxicants in the river Meuse cause the overall toxicity of the water for the zebra mussel, explaining the marginal populations at the test site, while other river species are absent there. It is suggested that toxicants in the river Meuse restrict the recolonisation of the river by invertebrate species more sensitive than the zebra mussel. This will be studied using invertebrates of different sensitivities (molluscs, arthropods), enabling the assessment of toxicity at different stages of water quality improvement of the river Meuse.