A comparative study on the developmental toxicity of three dihydroxynaphthalene positional isomers in zebrafish...

Dihydroxynaphthalenes (DHNs) are widely detected in combustion-derived pollution. However, their isomer-specific developmental toxicity remains poorly understood. In this study, we systematically compared the developmental toxicity of three DHN isomers-1,5-dihydroxynaphthalene (1,5-DHN), 2,3-dihydroxynaphthalene (2,3-DHN), and 2,7-dihydroxynaphthalene (2,7-DHN)-using zebrafish embryos as a vertebrate model. Exposure to DHNs induced distinct, isomer-dependent developmental abnormalities, with 2,3-DHN exerting the most severe effects. Prominent phenotypes included cranial hemorrhage, disrupted cerebrovascular architecture, abnormal erythrocyte distribution, impaired hematopoietic stem cell development, and selective suppression of immune cell populations. In addition, DHN exposure resulted in pronounced neurodevelopmental and craniofacial defects, particularly in the 2,3-DHN treated group. Biochemical analyses revealed significant accumulation of reactive oxygen species (ROS), elevated lipid peroxidation, and disruption of antioxidant enzyme activities, indicating oxidative stress as an important toxicological response. Consistent with these findings, transcriptional analysis demonstrated isomer-specific alterations in genes associated with vascular development, apoptosis, and neurodevelopment, whereas proliferation-related gene expression remained largely unaffected. These results demonstrate that DHN exposure induces multisystem developmental toxicity in zebrafish in a strongly isomer-dependent manner, following the toxicity ranking of 2,3-DHN > 1,5-DHN > 2,7-DHN. Subtle differences in hydroxyl substitution position translate into pronounced differences in redox reactivity and biological outcomes, highlighting oxidative stress as a key contributing mechanism associated with DHN-induced developmental toxicity. These findings demonstrate that environmental transformation of polycyclic aromatic hydrocarbons does not necessarily attenuate toxicity, but may generate derivatives with distinct and potentially enhanced toxicological profiles. Collectively, this study underscores the necessity of incorporating oxygenated PAHs and isomer-specific effects into environmental toxicology and ecological risk assessment.