CHRONIC ECOTOXICITY OF ZN AND PB TO THE ZEBRA MUSSEL DREISSENA-POLYMORPHA

Organisms in contaminated aquatic ecosystems are often exposed to toxicants for their entire lifetime. In order to evaluate the ecological consequences of long-term exposure to metals, we studied the relation between short-term and long-term effects of Zn and Pb on the filtration rate and survival of zebra mussels (Dreissena polymorpha) in laboratory experiments. The results indicated that the effects of Zn and Pb on the filtration rate of D. polymorpha increased when the exposure time was increased, but it remained unclear whether the decrease in filtration rate is caused by accumulation of metals by the mussels or by the metal concentration in the water, or both. The capacity of D. polymorpha to regulate the body concentration of the essential metal Zn decreased when the exposure time was increased, whereas the non-essential metal Pb could not be regulated by the zebra mussel. Not only the concentration of metal accumulated is of importance for survival, but also the rate of accumulation. It was concluded that the relation between short-term and long-term toxicity was different for each metal and could not be predicted from the results of the short-term experiments.