Polycyclic aromatic hydrocarbons in loggerhead sea turtles (Caretta caretta) embryos: Occurrence, tissue distribution and associated biological responses

Maternal transfer of environmental contaminants represents a critical pathway that occurs during the early life stages of marine vertebrates, however, the occurrence and the fate of polycyclic aromatic hydrocarbons (PAHs) in sea turtle embryos remain poorly characterized. This study investigated environmental PAH burdens and tissue distribution in loggerhead turtle (Caretta caretta) embryos collected from nesting sites along the anthropogenically impacted Ionian coast (Mediterranean Sea). Chemical analyses of yolk and liver tissues were integrated with histological, molecular, and protein endpoints to evaluate contaminant uptake and physiological responses during development. PAHs were detected in yolk across developmental stages (total concentrations up to ~14.8 ng/g) and in 70% of liver samples, suggesting a maternal transfer process. Hepatic PAH levels showed significant positive correlations with Cytochrome P450 (CYP1A) expression, indicating activation of detoxification pathways during organogenesis. In contrast, hepatic lipid content and melanomacrophages abundance were not associated with contaminant levels, suggesting that their presence primarily triggered biotransformation responses without detectable histopathological alteration. Variability in yolk protein profiles and their correlations with PAHs concentrations highlighted intra-clutch heterogeneity influencing contaminant partitioning and embryonic exposure dynamics. These findings demonstrate active uptake and metabolic processing of PAHs during embryonic development and identify hepatic molecular responses as sensitive indicators of early life exposure. The study advances understanding of contaminant dynamics in protected marine vertebrates and highlights the importance of maternal transfer pathways in ecological risk assessment of PAHs in Mediterranean ecosystems.