Concentrations of organic pollutants in seabirds from the tropical southwestern Atlantic Ocean are explained by differences in foraging ecology

Persistent organic pollutants are a potential threat for marine vertebrates in both coastal and offshore areas. In this study, organic pollutants were evaluated in the blood and feathers of four seabird species that forage in the tropical southwestern Atlantic Ocean. Red-billed tropicbirds (Phaethon aethereus) and brown boobies (Sula leucogaster) were sampled in the Abrolhos Archipelago, 70 km from the coast, and used as proxies of nearshore contamination. The Trindade petrel (Pterodroma arminjoniana) was sampled on Trindade Island, 1200 km offshore, and the Atlantic yellow-nosed albatross (Thalassarche chlororhynchos) was sampled at sea, both used as proxies of pelagic contamination. Concentrations of organohalogen pesticides (∑OHP) and polychlorinated biphenyls (∑PCB) were generally higher in the booby, the most nearshore forager, followed by the tropicbird, petrel and the albatross. Carbon isotope values (δ¹³C) were positively associated with ∑OHP and ∑PCB in the blood of seabirds and explained 28.6% of the variation in pollutant data, suggesting higher concentrations of pollutants in the nearshore marine habitats, where δ¹³C is generally higher. Nitrogen isotope values (δ¹⁵N) also had a positive influence over pollutant concentrations and explained 13% of pollutant data, suggesting an influence of trophic level. Variations in polycyclic aromatic hydrocarbon (∑PAH) concentrations among species, and relationships with isotopic values were less clear. Furthermore, the concentrations of organic pollutants were substantially higher in 2019 than 2022, which suggests greater environmental pollution in 2019 that could be related to urban and agricultural sources. Results demonstrate relationships between seabird ecology and organic pollutants in the tropical marine environment and highlight the importance of assessing multiple species in monitoring pollutant concentrations in wildlife.