Non-Additive Toxicity of Bi-Metal Mixtures to Fathead Minnows

Much research has been conducted to assess the toxicity of metals to aquatic organisms. Most of the research has focused on the toxicity of individual metals. Recently, attention has been paid to metal mixture toxicity because metals are usually present as mixtures in contaminated environments. The literature review indicates that metal mixtures may be additive, synergistic, or antagonistic to freshwater species. However, the data is not consistent and is dependent on the metal and organisms. The goal of this research is to use a systematic experimental design to characterize the toxicity of Cu, Zn, Cd and Ni mixtures to Pimephales promelas. Standard 96h toxicity tests were conducted with larval P. promelas based on the US EPA methods to determine metal mixture effects. All experiments were conducted in synthetic moderately hard water. Results of this study indicate that the toxicity of Cu-Zn, Cu-Ni, and Zn-Ni bi-mixtures was synergistic. These results suggest a joint mechanism of toxicity of these metal bi-mixtures in larval P. promelas. However, a biphasic dose response was found for Cd and Zn mixtures and P. promelas. The effect was antagonistic over all Zn concentrations. Results of this study are important for developing a Biotic Ligand Model for metal mixtures and useful for setting mixture water quality guidelines for metals