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Occurrence characteristics and environmental risk of microplastics in tropical China depend on land use patterns
Summary
Across four tropical agricultural land-use types in Hainan, China, microplastic abundance and polymer toxicity profiles differed significantly by land use, with rice fields exhibiting the highest hazard index due to high-hazard polymers, and fragmentation of larger plastic debris identified as the primary local source. The findings show that agricultural management practices — not climate alone — drive microplastic risk in food-producing soils, with direct implications for food safety in rice, a global dietary staple.
Microplastics (MPs, < 5 mm) are emerging soil pollutants; however, the regulation of their occurrence and ecological risks by land-use patterns in tropical agricultural regions remains insufficiently limited. This study investigated the occurrence and risks of MPs and mesoplastics (5–25 mm) across four intensively cultivated land-use types in Hainan: paddy fields, vegetable plots, orchards, and rubber plantations. Mesoplastics were present at all sites, primarily as fibrous polyethylene (PE) and polypropylene (PP) fragments (10–25 mm). MPs exhibited pronounced differences based on land use, with orchards and rice fields showing the highest abundances, while rubber plantations had the lowest. The primary types were fragments and fibers, with particle size distribution characteristics in vegetable plots and orchards being less than 100 μm, whereas in rice fields and rubber plantations, they ranged from 100 to 500 μm. Furthermore, the similar plastic composition (PE and PP) between mesoplastics and MPs indicates that the fragmentation of mesoplastics in agricultural production is a significant source of MPs. Risk assessment revealed that although all land uses were classified as Level I by the pollution load index (PLI) model, the hazard index indicated a markedly higher Level III risk in rice fields due to high-hazard polymers. Overall, agricultural practices—rather than climate alone—shaped both the abundance and polymer toxicity profiles of MPs. These findings provide scientific evidence to support land-use-specific management of plastic residues in tropical agricultural soils.