Pollutant Exposure for Chinese Wetland Birds: Ecotoxicological Endpoints and Biovectors

Levels of heavy metals and organic contaminants in main waters from China were reviewed from literature data to assess the ecological risks of pollutants for wetland birds and the biotransport of pollutants mediated by migratory wetland birds. Cr, Cu, and Pb and polycyclic aromatic hydrocarbons (PAHs) dominated in sediments, with higher concentrations in rivers and estuaries than in lakes and seas. Plants are the main dietary sources of less hydrophobic organic pollutants, while sediment is the primary source of more hydrophobic PAHs in birds. The hazard index (HI) for birds was mainly contributed by mercury (Hg) and polybrominated diphenyl ethers (PBDEs) and ranked as piscivore > omnivore > herbivore. Pollutant exposure risks to birds depend on the biomagnification potential of pollutants, food items of birds, and pollution levels in habitats. Migratory birds are important biovectors of persistent and bioaccumulative pollutants that may serve as a vital geochemical cycling process in addition to atmospheric deposition. This study provided a comprehensive overview of water environment pollution in China and the potential risks for high trophic level wetland birds in aquatic ecosystems. The results also identified the pollution hotspots of wetland birds and habitats, which provide new insights into bird conservation and biodiversity protection.