Toxic effects of combined exposure to cadmium and diclofenac on freshwater crayfish (Procambarus clarkii): Insights from antioxidant enzyme activity, histopathology, and gut microbiome

In recent years, excessive discharge of pollutants has led to increasing concentrations of cadmium (Cd) and diclofenac (DCF) in water; however, the toxicity mechanism of combined exposure of the two pollutants to aquatic animals has not been fully studied. Procambarus clarkii is an economically important aquatic species that is easily affected by Cd and DCF. This study examined the effects of combined exposure to Cd and DCF on the tissue accumulation, physiology, biochemistry, and gut microflora of P. clarkii. The results showed that Cd and DCF accumulated in tissues in the order of hepatopancreas > gill > intestine > muscle. The hepatopancreas and intestines were subjected to severe oxidative stress, with significantly increased antioxidant enzyme activity. Pathological examination revealed lumen expansion and epithelial vacuolisation in the hepatopancreas and damage to the villous capillaries and wall in the intestine. The co-exposure to Cadmium (Cd) and Diclofenac (DCF) disrupts the Firmicutes/Bacteroidetes (F/B) ratio, impairing the regular functioning of intestinal microbiota in carbon (C) and nitrogen (N) cycling. This disturbance consequently hinders the absorption and utilization of energy and nutrients in Procambarus clarkii. This study offers critical insights into the toxicological mechanisms underlying the combined effects of Cd and DCF, and suggests potential approaches to alleviate their adverse impacts on aquatic ecosystems.