A study assessing the comparative molecular toxicities of heavy metals to multiple strains of Daphnia magna

The freshwater crustacean Daphnia magna is used extensively in ecotoxicological testing throughout the world. In addition, acute toxicity tests using Daphnia are required during chemical risk assessment including under EU Registration, Evaluation, Authorisation and restriction of Chemicals (REACH). Multiple studies have reported variation in the response of different strains of Daphnia to toxicant exposure including heavy metals. \n \nIn this thesis, 10 strains of Daphnia magna were obtained from international research institutions and the comparative molecular toxicities of the heavy metals cadmium and copper to these strains was investigated A standard measure of acute toxicity, the acute immobilisation test was performed, in addition to the use of mass spectrometry-based metabolomics in order to assess sensitivity and metabolic differences between these strains. Up to 12-fold differences in sensitivity between strains of Daphnia were observed. Considerable differences in the basal metabolism of these strains was also discovered and correlated with relative sensitivity of the strains to cadmium and copper. \nTogether these findings show for the first time that strains of Daphnia magna are metabolically different in addition to identifying a significant limitation in the use of Daphnia in regulatory decision making: results from independent laboratories using different strains of Daphnia may not agree.