Amount and Characteristics of Microcapsule Discharge Derived from Coated Fertilizer Applied to Paddy Fields

Abstract

The inflow amounts and transport processes of microplastics from every source should be further understood to determine the risk management of microplastics in terrestrial water bodies. Fertilizers containing coated microcapsules (diameter of 2–5 mm) applied to paddy fields can be a source of microplastics. In this study, the amount and characteristics of microcapsules discharged from the water drain of paddy fields were investigated in six paddy fields for two years. Year-round monitoring in two fields showed that more than 90% of the annual amount was discharged between starting irrigation and transplanting. The amounts of microcapsule discharges before transplanting from four fields were 70–520 × 10³ particles ha^-1 (ave. 243 × 10³ particles ha^-1) , 0.17–1.29 kg ha^-1 by weight (ave. 0.61 kg ha^-1) , and the discharge rate relative to the amount applied in the previous year was 0.9–6.7%. The microcapsule discharge was considered to be caused by standing water drainage, as well as overflow due to rainfall events. From one field out of six, the amount of discharge after transplanting may be equivalent to that before transplanting owing to insufficient water management.