• Heavy metals;
  • Toxicity identification evaluation;
  • Daphnia magna;
  • Chemical speciation


The ecotoxicological and chemical response of five metals (Cd, Cr, Cu, Ni, and Zn) to selective fractionation techniques was assessed using the organism Daphnia magna. The metals Cu and Zn revealed similar toxicity patterns, showing an increased toxicity when lowering the pH, a marked reduction in toxicity after addition of ethylenediaminetetraacetic acid (EDTA). Similar toxicity reductions were obtained by passing the metal solutions over ion exchangers, activated charcoal, and filtration/solid-phase extraction units at neutral and basic pHs. The discrimination between Cu- and Zn-toxicity occurred in the oxidant reduction test, i.e., Zn toxicity was not affected by the addition of Na2S2O3, while Cu toxicity was strongly reduced. A second cluster was formed by Cd and Ni. The toxicity of both metals markedly decreased in the EDTA, ion exchangers, activated charcoal, filtration, and solid-phase extraction tests at high pHs. Discrimination between the toxicity of both metals was accomplished with the graduated pH test, in which a pH-independent toxicity response was found for Ni while the toxicity of Cd increased at lower pHs. Compared with the other metals, a very distinct toxicity pattern for Cr was observed. From the applied fractionation techniques, only the graduated pH and the anion resin tests resulted in a marked change in Cr toxicity. The produced toxicity patterns for each individual metal could therefore be used as fingerprints (i.e., toxicity identification fingerprints) in order to identify the toxicity caused by individual metals for D. magna.