Microplastic contamination in tropical estuaries: contrasting accumulation patterns in oysters driven by local features and condition index

Microplastic (MP) contamination in estuarine environments has raised increasing concern due to its persistence and potential impacts on marine organisms. This study investigated the spatial distribution and drivers of MP contamination in oysters ( Crassostrea sp.) collected from two urbanized tropical estuaries in northeastern Brazil: the Potengi River Estuary (PRE) and the Buranhém River Estuary (BRE). MP concentrations ranged from 0.76 to 9.08 particles g -1 across both estuaries, with a predominance of small (<1000 µm), fibrous (68%), and colorless (34%) particles. Polymer composition was dominated by artificial cellulosic particles and polyethylene terephthalate. Generalized linear models revealed that MP concentrations were significantly influenced by condition index, population density, human modification levels, and spatial differences among estuaries. Thus, MP distribution within each estuary exhibited distinct spatial patterns associated with anthropogenic influence. Notably, even areas with low population density present moderate to high MP contamination, suggesting that multiple factors simultaneously influence MP inputs, distribution, and retention in estuarine systems, including mangrove zones and near sandy beaches. Such findings highlight the importance of integrating biological and landscape-scale predictors to better understand microplastic exposure in coastal ecosystems.