Oxidative stress in the galaxiid fish, Galaxias maculatus, exposed to binary waterborne mixtures of the pro-oxidant cadmium and the anti-oxidant diclofenac

Chemical mixtures represent environmentally-realistic exposures of contaminants to aquatic biota. However, there remains a limited understanding of how toxicant mixtures may impact biological function, relative to their individual components. In the current study, oxidative stress responses of the freshwater galaxiid fish inanga (Galaxias maculatus) were examined following exposure to the pro-oxidant trace metal cadmium (2 or 9 μg L⁻¹), and the anti-oxidant pharmaceutical drug diclofenac (770 μg L⁻¹), individually or in simple binary mixtures. Cadmium exposure in the absence of diclofenac significantly decreased renal catalase activity, increased hepatic catalase activity, decreased renal superoxide dismutase (SOD) and decreased glutathione-S-transferase activity, effects that are suggestive of anti-oxidant defense inhibition and/or generation of increased reactive oxygen species. Diclofenac exposure in the absence of cadmium resulted in a decreased renal lipid peroxidation, consistent with its known anti-oxidant properties. The presence of waterborne diclofenac altered the effects of cadmium on catalase activity in the liver, SOD activity in the gill, and lipid peroxidation in the liver. Co-exposure with cadmium modulated diclofenac effects on lipid peroxidation in the kidney. These data indicate the capacity of each of these toxicants to offset biological effects of the other when both co-occur in urban waters at specific concentrations. This study also demonstrates the complexity of outcomes in contaminant mixtures, even when these stressors are presented as simple binary combinations.