Assessment of mixture toxicity of copper, cadmium, and phenanthrenequinone to the marine bacterium Vibrio fischeri.

Transition metals and polycyclic aromatic hydrocarbons (PAHs) are cocontaminants at many sites. Contaminants in mixtures are known to interact with biological systems in ways that can greatly alter the toxicity of individual compounds. The toxicities (individually and as mixtures) of copper (Cu), a redox-active metal; cadmium (Cd), a nonredox active metal; and phenanthrenequinone (PHQ), a redox-active oxygenated PAH, were examined using the bioluminescent bacterium Vibrio fischeri. We found that the cotoxicity of Cu/PHQ was dependent on the ratio of concentrations of each chemical in the mixture. Different interaction types (synergism, antagonism, and additivity) were observed with different combinations of these toxicants. The interaction types changed from antagonism at a low Cu to PHQ ratio (1:4), to additive at an intermediate Cu to PHQ ratio (2:3), to synergistic at higher Cu to PHQ ratios (3:2 and 4:1). In contrast to Cu/PHQ mixtures, the cotoxicity of Cd/PHQ did not change at different mixture ratios and was found for the most part to be additive. For the individual chemicals and their mixtures, reactive oxygen species (ROS) production was observed in V. fischeri, suggesting that individual and mixture toxicity of Cu, Cd, and PHQ to V. fischeri involves ROS-related mechanisms. This study shows that mixture ratios can alter individual chemical toxicity, and should be taken into account in risk assessment.