Despite intensive use of plastics in agriculture, little is known about the occurrence of microplastics (MPs) in agro-environment. To identify the effect of internal sources and environmental fate on MP appearance in farmland, we examined four soil types with different agricultural practices representing either direct application of polyethylene (PE) film—the inside (GS-in) and outside (GS-out) soils of greenhouse and mulch-film use soils (MS)—or rare use of plastics (rice-paddy soils; RS). MP abundance was 10–7,630 items kg^-1, with the order of GS-in, GS-out, RS, and MS. Besides the highest MP abundance, rare PE-sheet (4% of MPs) and increased MP abundance with sizes decreasing were unique for GS-in, implying the presence of internal sources other than PE-film and continued MP accumulation. Contrarily, in other outside soils high PE-sheet appearance (10–31%) indicated substantial input via fragmentation of applied PE-film (for GS-out and MS) or via surface-runoff (for RS) while drastic decline of small-sized MPs in order of MS > RS > GS-out than expected from steady-state fragmentation implied significant removal of MPs by surface runoff and/or infiltration. Our results suggest the importance of internal sources and environmental fate as significant factors affecting the occurrence of MPs in agricultural soils.

尽管在农业中大量使用塑料，但对于农业环境中微塑料（MPs）的发生知之甚少。为了确定内部来源和环境命运对农田中MP外观的影响，我们检查了四种土壤类型，采用了不同的农业实践，分别代表直接施用聚乙烯（PE）膜-内部（GS-in）和外部（GS-out）温室和覆盖膜土壤使用土壤（MS）或很少使用塑料（稻田土壤； RS）。MP含量为10–7,630千克kg ^-1，其顺序为GS-in，GS-out，RS和MS。除了最高的MP含量外，稀有的PE片材（占MP的4％）和MP含量的增加（尺寸减小）对于GS-in而言是独特的，这意味着存在除PE膜以外的内部来源和MP的持续积累。相反，在其他外部土壤中，高PE片外观（10-31％）表示通过施加的PE膜碎裂（对于GS-out和MS）或表面径流（对于RS）有大量输入，而小PE的急剧下降。尺寸大小的MPs按MS> RS> GS-out的顺序比稳态碎裂所预期的要大，这意味着通过表面径流和/或渗透将MPs大量去除。我们的结果表明，内部来源和环境命运的重要性是影响农业土壤中MP发生的重要因素。