Phosphogypsum leachate exacerbates histological damage, oxidative stress, apoptosis in the liver, and genotoxicity of heat-stressed zebrafish (Danio rerio)

Elevated global temperature amplifies environmental stressors, such as phosphogypsum leachate, which is released from open-air stockpiled or landfilled phosphogypsum under rainwater leaching. In this study, we investigated the impact of phosphogypsum leachate exposure on heat-stressed zebrafish (Danio rerio). Thermal stress significantly increased the body length and weight of zebrafish, while the hepatosomatic index remained unchanged. Histopathological damage, such as ballooning degeneration, fatty degeneration, and stasis dilatation, was observed in heat-stressed zebrafish liver by exposure to phosphogypsum leachate. Phosphogypsum leachate also increased the level of malondialdehyde (MDA) and altered the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and peroxidase (POD) in the liver of heat-stressed zebrafish, indicating the occurrence of oxidative stress and oxidative damage. Phosphogypsum leachate promoted heat stress-induced apoptosis via the p53-mitochondrial pathway, with upregulation of p53, PUMA, Bax, Apaf-1, Caspase3 gene expression, and downregulation of Bcl-2 gene expression in zebrafish liver. Additionally, DNA damage in heat-stressed zebrafish exposed to phosphogypsum leachate is more severe than that observed under high-temperature condition alone. These data indicated that phosphogypsum leachate exacerbates histopathological damage, oxidative stress, apoptosis in the liver, and genotoxicity in heat-stressed zebrafish. This study provided novel insights for evaluating the toxic impacts of phosphogypsum leachate on aquatic organisms in the context of global warming.