Runoff and accumulation of microplastics derived from polymer-coated fertilizer in Japanese paddy fields.

The article focuses on the runoff and accumulation of microplastics derived from polymer-coated fertilizers used in Japanese paddy fields. Through field surveys at 38 sites and literature review, the study quantified microcapsule (microplastic) runoff, finding that 61%–100% of runoff occurs between puddling and rice transplanting, with loads ranging from 2 to 482 mg/m². Water management practices and wind conditions significantly influence runoff amounts. The total annual microcapsule discharge from Japanese paddy fields was estimated at a median of 1,157 tons, contributing approximately 88% of Japan’s riverine microplastic outflow, while accumulated microcapsules in agricultural soils were estimated at about 75,623 tons. These findings indicate that paddy fields are a substantial and ongoing source of marine microplastics in Japan, highlighting the need for strategies to manage microplastic pollution alongside the agronomic benefits of polymer-coated fertilizers.