Exposure to short-chain chlorinated paraffins induces mortality in marine medaka larvae through neurotoxicity and oxidative stress.

Despite the strict regulation of short-chain chlorinated paraffins (SCCPs), they continue to be detected in marine environments and organisms worldwide. However, their toxicity to marine fish has been scarcely studied. In this study, the effect of different concentrations of SCCPs (0-1000 μg L⁻) on the early life stages of the marine medaka Oryzias melastigma was evaluated. The impacts of SCCPs on the embryonic stage of O. melastigma were considered negligible, while significant growth retardation was observed during the larval stages after 13 days of exposure, with the median lethal concentration (LC) determined as 227 μg L⁻. Exposure to SCCPs for 4 days resulted in melanosome dispersion, immobilization, disruption of feeding activity, and an increase in acetylcholinesterase activity, suggesting that SCCPs induce neurotoxicity in the cholinergic system, leading to mortality through starvation. Dose-dependent DNA damage, fluctuations in mitochondrial respiration, and increases in intracellular reactive oxygen species content and apoptosis were observed after 4 days of exposure, indicating strong induction of oxidative stress. In addition, potential endocrine disruption was observed, as SCCPs significantly decreased cortisol content and modulated the mRNA expressions of genes involved in the hypothalamic-pituitary-interrenal axis. Taken together, exposure to SCCPs resulted in mortality and growth retardation, primarily through neurotoxicity and oxidative stress in marine medaka larvae.