Microplastic contamination in waterbirds and their habitats: evidence from little egrets (Egretta garzetta) in tropical rice fields

Microplastic (MP) pollution in rice fields has become a major environmental threat. Birds often serve as indicators of environmental pollution, and feathers are the most commonly used indicator because they can be sampled non-invasively. However, studies examining the ingestion of plastic by waterbirds in tropical rice fields are lacking. Therefore, to explore the potential threat of MP pollution on waterbirds inhabiting rice fields and evaluate the potential role of bird feathers in assessing MP pollution, we investigated MP accumulation in sediment, water, feather, and feces samples collected from different nesting sites (Wuji Village and Chongwei Village) of little egrets (Egretta garzetta) on Hainan Island, China, and evaluated possible correlations among feathers, feces, and environment. MPs were significantly more abundant in sediment, feather, and feces samples from Wuji Village than in those from Chongwei Village, suggesting the importance of habitat contamination as an exposure source for MP ingestion. MPs were more abundant on feathers than in feces based on the number of MP pieces per gram of sample. The identified MPs were predominantly small and fragment-shaped. Polyethylene and polypropylene were the most abundant polymer types, indicating that anthropogenic activities were the likely source of MPs. Correlation analysis revealed highly significant correlations between feathers and habitats in terms of MP characteristics. The results indicate that waterbirds in rice fields are seriously exposed to MP contamination and highlight the potential role of feathers as biomonitors and vectors of MPs in natural environments.