Responses of the freshwater snail, Lymnaea peregra, to pollutants as an indicator of ecological water quality

Abstract

Initially the L. peregra bioassay developed for use under laboratory conditions demonstrated reduced ingestion and egestion rates of L. peregra at sublethal exposure concentrations to aqueous solutions of cadmium and copper. The two organic compounds tested, the polyaromatic hydrocarbon pyrene and the pyrethroid insecticide lambda-cyhalothrin, did not inhibit ingestion or egestion at sublethal concentrations. Post-exposure median ingestion and egestion values (ECso) for copper were 15 and 13 J.lg/L and for cadmium were 0.05 and 5.6 J.lg/L respectively. The lethal effect values for L. peregra exposed to copper and cadmium were 115 J.lg/L (estimated laboratory derived LCso) and 2500 J.lg/L (LCso from literature) respectively were both higher than the estimated ECso values. This indicates the relevance of using these post-exposure sublethal endpoints for L. peregra exposed to these heavy metals. Investigation of the uptake of cadmium by L. peregra revealed that the major route was through aqueous solution with only minor contributions from contaminated food. The in situ bioassay was developed further under semi-natural (in microcosms) and field conditions. L. peregra showed reduced egestion following aqueous exposure to zinc in microcosm studies (at 0.5 J.lg/L), but again did not show a response to either of the organic contaminants lambda-cyhalothrin and the herbicide linuron. The L. peregra field bioassay was deployed at 9 historically contaminated sites throughout Scotland and Northern England. Post-exposure egestion rates were shown to be significantly reduced two metal contaminated sites. The inconsistency ofresults gained from the remaining sites may have been due to decreased sensitivity brought about by wide variation in egestion rates. The L. peregra bioassay is useful tool for the investigation of the effects of single stressors such as heavy metals. However, the lack of consistent results gained from the in situ deployments suggests that the L. peregra bioassay should be used, at this time, as one of a suite of tests to investigate the quality of freshwaters rather than as a discrete test.