Toxicity Determination of Zinc and Cadmium (Single and in Combination) with a Battery of Toxkit Microbiotests
Abstract : Toxicity tests were performed with 4 Toxkit microbiotests, based on aquatic species of different phylogenetic groups and representing different trophic levels, on 2 heavy metals (zinc and cadmium) which are common contaminants of the aquatic environment. The metals were tested out single on micro-algae (Algaltoxkit F™ with Selenastrum capricornutum), a ciliate protozoan (Protoxkit F™ with Tetrahymena thermophila), and 2 crustaceans (Daphtoxkit F™ with Daphnia pulexand Thamnotoxkit F™ with Thamnocephalus platyurus); combination experiments were performed on the micro-algae and one of the 2 crustaceans (D. pulex).
The study showed that cadmium is substantially more toxic than zinc for all the test biota used, but also revealed that the ratios between the L(E)C50s for the 2 metals was nearly the same for each species, namely a factor 4. The factorial experiments with binary mixtures showed that for the micro-algae, both metals showed “additivity” in accordance with the concentration-addition model of Anderson and Weber (1975). This was, however, not the case for the metal combinations applied to D. pulex, the outcome of which seemed to be dependent on the relative contributions of the individual metals.
Besides bringing additional information on the toxicity of 2 important metal contaminants to aquatic biota, the study also showed the difficulty of general application of models for predicting toxic impacts, and the need for toxicity testing of mixtures to determine their real hazard.
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