Valve movement response of the mussel Dreissena polymorpha -- the influence of pH and turbidity on the acute toxicity of pentachlorophenol under laboratory and field conditions

The Dreissena-Monitor is a biological early warning system for the continuous monitoring of water quality, based on the computer assessment of valve movements in two groups of 42 zebra mussels (Dreissena polymorpha). In the laboratory, two series of toxicity tests were conducted with PCP. (1) At neutral pH conditions only the concentration of PCP was altered. The dose--response relationship revealed 15 g l–1 PCP for the number of valve movements and 20 g l–1 PCP for the percentage of open mussels. (2) At 50 g l–1 PCP the pH value was altered from 6.5 to 8.4, demonstrating an inverse relationship between the toxicity of PCP and the pH. The detection limits evaluated from a series of toxicity tests under the field conditions of the River Rhine at Koblenz were nearly ten times higher than those from the laboratory. During a second series of toxicity tests under the field conditions of the River Rhine at Bad Honnef, the toxicity of PCP seemed to be reduced in relation to the increasing turbidity. The differences between the results obtained under laboratory and field conditions are discussed with respect to the influence of the pH and turbidity at the toxicity of PCP on D. polymorpha