Bio-concentration of per- and polyfluoroalkyl substances and mercury in feathers of waterbirds from a key conservation reserve, Southwest China

From a One Health perspective, per- and polyfluoroalkyl substances (PFAS) and mercury (Hg) are global contaminants of concern due to their persistence, bioaccumulation, and toxic effects on wildlife. The waterbirds, as key indicators of wetland ecosystems, are particularly vulnerable to multiple pollutants, yet interspecific patterns of accumulation and co-exposure remain poorly understood. In our study, we collected 141 feather samples from three representative waterbird species (Black-necked Crane Grus nigricollis, Ruddy Shelduck Tadorna ferruginea, and Eurasian Moorhen Gallinula chloropus) in Huize Black-necked Crane National Nature Reserve, Southwest China. Results revealed species-specific contamination patterns: Black-necked Cranes exhibited the highest mean Hg concentrations (2.94 ± 1.05 μg/g), whereas Eurasian Moorhen showed the highest mean PFAS burdens (191.99 ± 191.88 ng/g). Although Eurasian Moorhens displayed intermediate concentrations, they were the only species showing a significant positive correlation between Hg and PFAS (r = 0.54, p < 0.05), suggesting overlapping exposure pathways. Trophic guild and body size emerged as key predictors: omnivorous species and larger individuals consistently exhibited lower PFAS loads, while Hg concentrations were more strongly shaped by foraging ecology and aquatic dietary pathways than by body size. Collectively, these findings demonstrated that even within protected wetlands, waterbirds face substantial risks from multi-pollutant exposure. This underscored the urgent need for integrated monitoring and targeted conservation strategies to mitigate the combined ecological risks posed by Hg and PFAS in critical migratory habitats.