Neurodevelopmental toxicity of black carbon in zebrafish: behavioral and metabolomic insights

Black carbon (BC), a combustion-derived particulate pollutant, is increasingly detected in aquatic ecosystems. While its respiratory and cardiovascular effects are well documented, its neurotoxicity in aquatic organisms remains poorly understood. In this study, zebrafish (Danio rerio) embryos were exposed to environmentally relevant BC concentrations (0, 0.05, 0.5, and 5 mg/L) for 168 h. BC induced dose-dependent developmental toxicity, manifested as reduced body length and eye size, elevated heart rate, and morphological abnormalities. Behavioral assays revealed deficits in locomotion and phototaxis. Neurochemical analysis revealed concentration-dependent reductions in serotonin (5-HT) and gamma-aminobutyric acid (GABA). Transgenic imaging indicated impaired neuronal and glial development in the embryos. Untargeted metabolomics revealed disruptions in multiple pathways, particularly glycine, serine, threonine, taurine, and hypotaurine metabolism, which correlated with behavioral changes. These findings provide the first integrative evidence that BC neurotoxicity involves both structural damage to the developing nervous system and broad metabolic disturbances. Our results highlight BC as a previously underrecognized neurotoxicant of ecological concern.