Occurrence and emission characteristics of microplastics in agricultural surface runoff under different natural rainfall and short-term fertilizer application

Abstract

Land-based microplastics (MPs) are considered the primary source of MPs in aquatic environments, with runoff being a major pathway for their transfer from soil to surface water. However, the transportation characteristics of MPs via agricultural surface runoff remain unclear. In this study, we investigated the occurrence and emission characteristics of MPs in agricultural surface runoff under various short-term fertilizer applications and natural rainfall events using laser direct infrared imaging analysis (LDIR). MPs from fertilizers and soils co-migrated with the agricultural runoff. The abundance and concentration of MPs in runoff were 145.90±22.48~2,043.38±89.51 items·L-1 and 39.17±21.94~523.04±47.85µg·L-1, respectively. Small and low-density MPs, such as polyethylene (PE), chlorinated polyethylene (CPE), and polyurethane (PU) in film/fragment form with 20~50µm exhibited a higher mobility. No statistical differences were observed in the distribution of runoff MPs with the application of different fertilizers. There was a significant positive relationship between runoff MP abundance and rainfall intensity. The annual emission load in this study area was 116.73g·hm-2, indicating that the transportation of MPs via agricultural surface runoff cannot be ignored. This study is conducive to understanding the migration behavior of MPs in soil-water environments in a better manner. Environmental significanceLand-based microplastics (MPs) serve as the primary source of contamination in aquatic ecosystems, with surface runoff being the predominantly transport pathway. However, the emission load and characteristics associated of MPs in agricultural runoff remain unclear. This study investigated the occurrence and emission of MPs in agricultural surface runoff under various short-term fertilization and natural rainfall. Co-migration of soil and fertilizer-derived MPs was observed. The maximum abundance and concentration of MPs in runoff were 2,043.38±89.51 items·L-1 and 523.04±47.85µg·L-1, respectively. Small and low-density MPs were easily mobilized. This study emphasizes the transportation of MPs via agricultural surface runoff cannot be ignored.