Differences in mercury (THg) levels in Brown booby (Sula leucogaster) feathers from two environmentally distinct Brazilian archipelagos.

Mercury pollution is a matter of global concern due to its detrimental effects on ecosystems and human well-being. Seabirds generally occupy high levels within trophic chains and are often used as valuable indicators of marine pollution, including mercury contamination. We examined the concentrations of total mercury (THg) in the ventral feathers of Brown boobies (Sula leucogaster) from two distinct Brazilian archipelagos: one coastal and subtropical (Moleques do Sul) and one tropical and oceanic (São Pedro and São Paulo). We hypothesized that there would be differentiation in mercury levels between these archipelagos due to differences in geographical location and environmental conditions, where higher Hg levels would be found in Brown boobies from the coastal one since they are more exposed to anthropogenic sources from the continent. Additionally, we also investigated whether there were any differences in mercury levels based on sex and age. We found significantly higher THg levels in Brown boobies from São Pedro and São Paulo compared to those from Moleques do Sul, indicating differential levels of exposure to mercury sources. No significant differences between sexes or age classes, although juvenile individuals showed the lowest values. We suggest that the THg higher levels found in individuals from São Pedro e São Paulo can be due to the geological peculiarities of this archipelago, formed by mantle peridotites considered mercury hotspots. Our findings emphasize the importance of considering spatial and environmental factors in mercury biomonitoring and highlight the potential use of seabird feathers as a proxy for mercury contamination in marine environments.