Contamination of microplastics in greenhouse soil subjected to plastic mulching

Abstract

This research quantified microplastics in greenhouse soils subjected to varying durations of plastic mulching and investigated the relationship between soil properties and microplastic contamination levels. Topsoil and subsoil samples were collected from two sites featuring plots without plastic film, and plots with plastic film for short and medium mulching durations. The results indicated that at Site A, no significant differences were observed between the non-plastic film plot and the plots with plastic film. The highest average number of microplastics in the subsoil was found in the plot with medium-duration mulching. However, there were no statistically significant differences between plots with no plastic mulching and those with plastic film after short or medium mulching durations. At Site B, the lowest average number of microplastics was observed in the non-mulching plot in both the topsoil and subsoil. There was no significant difference compared to plots with short or medium-duration mulching. The majority of microplastics in both the topsoil and subsoil were smaller than 50 µm. Microplastics, primarily composed of PVDF, PP, and PE, were not solely derived from plastic mulching but originated from plastic ropes, and fertilizer bags. Notably, the medium mulching durations exhibited higher PE microplastics. The concentrations of microplastics were positively correlated with total nitrogen and exchangeable potassium levels. In conclusion, microplastic contamination in the study areas came from additional sources beyond film mulching. Additionally, farmers can significantly reduce microplastic contamination in their soil by collecting plastic mulch from their fields before tilling at the start of each growing season.