Heavy metal content of plastic waste in agricultural ditches: Distinction and relation between exogenously adsorbed...

Plastic waste in agricultural environments can act as a sink and a source of heavy metal contaminants. However, the relationship between plastic waste and heavy metals under actual environment conditions remains poorly understood. In this study, sediments and plastic waste were collected from two agricultural ditches in the Dongting Lake basin, China. Pb, Cd, Cr, Cu, and Zn concentrations were determined in ditch sediments, and surface-associated and intrinsic metal concentrations in plastic waste were investigated. Zn exhibited the highest concentration in exogenous plastic waste (231.76 ± 75.94 mg/kg), endogenous plastic waste (119.31 ± 56.04 mg/kg), and sediments (96.71 ± 25.25 mg/kg). This finding reflects the combined influence of environmental accumulation and metal additives within plastics. Overall, endogenous Pb, Cr, and Cu concentrations were 5.0, 13.9, and 4.8 times higher, respectively, than exogenous concentrations, suggesting that the potential release of these additive-derived metals warrants future monitoring and assessment. PE showed relatively higher endogenous metal concentrations. Correlation analysis indicated that the relationships between exogenous and endogenous metals varied across environmental conditions and polymer type, indicating that these factors affected the exogenous adsorption and endogenous release of heavy metals in plastics. This study provides field-based evidence from actual agricultural ditches and highlights the need for greater attention to interactions between plastic waste and heavy metals. It thus offers empirical support for managing combined plastic-heavy metal pollution in agricultural environments.