Variability in the Response of Daphnia Clones to Toxic Substances: Are Safety Margins Being Compromised?

Abstract

Daphnia magna continues to be the most widely used organism in aquatic hazard assessment, for reasons relating to its ease of culture in the laboratory and the ability to maintain clonal lines of female individuals. However, despite its widespread use for estimation of the acute and chronic toxicity of new and existing substances, doubts still remain concerning its use as a representative of aquatic fauna, with interlaboratory variation in response being recognised as a serious problem. Experimental studies which have attempted to identify and quantify the components of interlaboratory variation in response (Baird et al., 1989, 1991; Soares et al., 1992) have indicated that both the genotype of the clone used in tests and the environmental conditions prior to and during the tests play significant roles in determining this variability. Moreover, it is clear that the relative response of clones does not remain consistent across the substances tested, not even for similar classes of substance, indicating that genotype-environment interactions also play an important role in governing response.