Polycyclic aromatic hydrocarbon exposure drives measurable health declines in threatened sea turtles along the South Atlantic coast: a ten-year multi-regional assessment.

Sea turtles are sentinels capable of integrating chronic exposure and complex contaminant mixtures across marine systems, serving as models for chemical stress assessments in free-ranging wildlife. Polycyclic aromatic hydrocarbons (PAHs), including alkylated homologues, constitute a persistent source of chemical pressure to this group along the Brazilian coast, where offshore oil production and coastal urbanization have intensified in the last decades. In the present study, the Petrobras Marine Biota Monitoring System (SIMBA) environmental monitoring database was integrated with laboratory-based stranding surveillance data to produce the most extensive multi-species PAH bioaccumulation assessment for South Atlantic sea turtles to date. The dataset comprises the compositional profiles of 37 parent and alkylated PAHs quantified in 1651 liver and 800 adipose tissue samples obtained from 1670 individuals sampled between 2015 and 2024 across 19 coastal Brazilian regions (∼2280 km). Chelonia mydas was the most frequently sampled species (89.3%), presenting high hepatic Σ37 PAH concentrations (mean 50.7 ± 225 ng g-1 wet weight). Chemical profiles were dominated by low-molecular-weight and alkylated PAHs, consistent with sustained petrogenic and coastal anthropogenic inputs. A mixture modeling employing a weighted quantile sum regression identified significant associations between specific PAHs, particularly benzo[a]anthracene, anthracene, and acenaphthene, and reduced Health Index (HI) scores, with the strongest negative associations observed in juveniles. Spatiotemporal analyses revealed marked interannual variability in PAH body burdens, including pronounced regional peaks in 2015 and 2024. These findings indicate that chronic exposure to multiple PAHs is associated with reduced health status in free-ranging marine megafauna, highlighting the value of incorporating alkylated compounds and mixture-based approaches into coastal chemical monitoring frameworks.