Mixture toxicity of zinc, cadmium, copper, and lead to the potworm Enchytraeus albidus.

Central composite designs were used to develop surface response relationships for predicting the chronic toxicity of mixtures of zinc, cadmium, copper, and lead to the potworm Enchytraeus albidus. Surface response relationships were obtained for all binary mixtures of zinc, cadmium, copper, and lead as well as for mixtures with all four metals. For the binary mixture of zinc and cadmium, this approach and the toxit unit approach gave similar results. However, with the toxit unit approach no such surface response models can be developed. The experimental results indicated that effect predictions based on the concentration addition model were always higher than those obtained with the independent action model. The observed effect was lower than the effect predicted by the concentration addition model for all metal mixtures. Therefore it can be concluded that the concentration addition model represents a reasonable worst-case scenario for the risk assessment of metal mixtures in terrestrial ecosystems.