Integrated transcriptomic and metabolomic analyses reveal toxic effects of medium-chain chlorinated paraffins on Paralichthys olivaceus fry

An increase in medium-chain chlorinated paraffins (MCCPs) in marine ecosystems caused by large-scale production is a serious threat to aquatic organisms. However, its toxicity to marine organisms, especially the molecular mechanisms, is unclear. In this study, Paralichthys olivaceus fry were exposed to 1, 10, or 100 μg/L of MCCPs for 14 days. A comprehensive approach combining biochemical parameter detection, transcriptomic, and metabolomic methods was used to investigate the toxicity mechanisms. The enzymatic activities of catalase and superoxide dismutase increased with longer exposure time, while glutathione levels increased slightly, suggesting that the redox balance was disrupted. The level of malondialdehyde was highest on day 4, indicating oxidative damage. Transcriptomic analysis revealed that there were 23 differentially expressed genes at 1 µg/L, 3628 at 10 µg/L, and 2019 at 100 µg/L. It inhibited growth and development by influencing protein synthesis, glucose metabolism and other pathways. Metabolomic analysis showed that there were 152 differentially expressed metabolites at 1 µg/L, 186 at 10 µg/L, and 540 at 100 µg/L, primarily affecting lipid metabolism. Moreover, disruptions in nucleotide metabolism and signal transduction have been revealed using transcriptomics and metabolomics. In addition, several key protein (e.g., JNK, LPC, IGF1R) and metabolites (e.g., betaine, xanthosine) could initially be used as potential markers of MCCPs exposure, but further verification is still required. This study provides new insights into the potential effects of MCCPs on marine life.