Interactions between water flow and microplastics in silt loam and loamy sand

The threat of microplastics (MPs) intervention in cropland always results in water flow alteration, which is the leading cause behind MP transport and distribution. This study investigated water infiltration and MP transport and distribution on MP-contaminated silt loam and loamy sand to explore how water flow and MP affect each other and reveal their mechanisms. The results indicated that water infiltration increased as the content of MPs present in the soils increased from 1 to 7% (w/w), which increased the MPs in deeper soil layers. For the silt loam sample, the MP concentration first increased to higher levels at 15-20 cm and then decreased. The MPs with sizes of 0-150 and 150-500 mu m were found in excess at 25-to-30-cm and 5-to-20-cm depths, respectively. In the case of the loamy sand sample, the MP concentration gradually increased up to 30-cm depth, and the MPs with sizes of 0-150 and 150-500 mu m were found in excess at 5-to-10-cm and 15-to-30-cm depths, respectively. The increased infiltration was due to the increased hydraulic conductivity resulting from inhibition of soil particle aggregation, increased soil porosity, and strong hydrophobicity of MP particles. The difference in proportions of various MP particle sizes in soil layers was due to the differences in migration ability in pores for various soil samples and MP particle aggregation features.