Acute exposure to an environmentally relevant concentration of diclofenac elicits oxidative stress in the culturally important galaxiid fish Galaxias maculatus.

Diclofenac is a nonsteroidal anti-inflammatory drug (NSAID) of growing concern in aquatic environments worldwide; nevertheless, knowledge of its effects on aquatic biota is restricted to a few model species with limited information regarding its mechanisms of impact. In the present study, diclofenac accumulation, its effects on metabolic rate, ionoregulation, and oxidative stress were examined at environmentally relevant (0.17 µg L-1 ) and elevated (763 µg L-1 ) concentrations in a culturally and economically important galaxiid fish, inanga (Galaxias maculatus), from the Southern Hemisphere. This species is among the most widespread freshwater fish in the world but its sensitivity to emerging contaminants is unknown. Following an acute 96-h exposure, bioconcentration of diclofenac was measured in the inanga whole-body, resulting in an estimated bioconcentration factor of 87 for the 0.17-µg L-1 exposure concentration, approaching values where transfer through the food chain should be considered. Lipid peroxidation in the liver was significantly elevated at both 0.17- and 763-µg L-1 exposure concentrations but lipid peroxidation in the kidney and gill decreased after diclofenac exposure. Catalase activity was also elevated in the liver of inanga but activity decreased in the gill. There were no effects of diclofenac on metabolic rate or ion (sodium and calcium) influx rates. These data indicate that toxicologically relevant adverse outcomes and bioconcentration of diclofenac at environmentally relevant levels warrant additional study in this important fish. Environ Toxicol Chem 2018;37:224-235.