Spatial distribution of microplastics in Mollisols of the farmland in Northeast China: the role of field management and plastic sources

Abstract

Although microplastics (MPs) have been widely found in farmland soil, the influence of pollutant sources and farmland management on MPs migration and distribution is poorly understood. In this study, we investigated the distribution of MPs in the 0–30 cm soil layers of vegetable fields with long-term mulching and surrounded by complex pollution sources under three management methods (MMs) (MM1, high fertilization dose and moderate tillage frequency; MM2, moderate fertilization dose and high tillage frequency; MM3, low fertilization dose and low tillage frequency) in Mollisols of Northeast China. Geostatistics combined with classical statistics were used to clarify the distribution of MPs and their driving factors. The results indicated that the polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyethylene terephthalate (PET), polyether urethane (PEUR) and a mixture of “PE and PP” (PE:PP) were found in the 0–30 cm soil layer. The dominant sizes of PE-MPs and non-PE-MPs (NPE-MPs) were 1–5 mm and <1.0 mm in the 0–30 cm soil layer. The abundance of MPs was higher in the 20–30 cm soil layer near the irrigation wells than in the 0–20 cm soil layer, and the spatial distribution of MPs was random in both layers. The distances from sampling points to the polluted sources (e.g., residential area, landfill and single farmhouse) were not significantly correlated (p > 0.05) with the abundance of MPs in the 0–30 cm soil layer, but were significantly correlated (p < 0.05) with the abundance of MaPs. The effect of fertilization dose (0.201–0.248) on the abundance of MPs was greater than that of tillage frequency (0.170–0.188). Generally, the distribution of MPs was directly affected by the distribution of MaPs in the farmland soil, while the polluted sources surrounding the farmland indirectly affected the distribution of MPs by influencing the MaPs sources. MPs formation was more affected by fertilization than by tillage. This study clarified the effects of pollution sources and MMs on the distribution of MPs in farmland soils, and provided guidance for better management of MPs contamination in farmlands.