The vertical migration of a pesticide mixture in sandy soil is strongly driven by their sorption behavior and can be altered by Polyethylene Microplastics

With the revelation of microplastics in soil, their interaction with organic chemicals has received increasing attention due to their hydrophobic surfaces, substantial sorption capacity, and large specific surface area. However, existing studies focus mainly on individual pollutants rather than their coexistence in environmental mixtures. Our study aimed to extend focus from single compounds to complex contamination by 20 pesticides which we applied to reference sandy soil. Stainless steel columns were filled with soil with or without the addition of 1 % w/w polyethylene (PE) microplastics cryo-milled to irregular shape and sieved to a size of 200-600 µm. The columns were continuously rinsed with ten pore volumes (PVs) of the pesticide-contaminated solution. The leachates were collected and measured every 0.2 PV using LC-MSMS to derive breakthrough curves (BTCs). The results showed that migration rates decreased with increasing hydrophobicity (as D_OW and K_OC), while the leaching order of pesticides was unaffected by the microplastics. However, PE microplastics promoted the vertical migration of five slowly leaching pesticides despite their high sorption affinity to the soil. Overall, our results indicate that the sorption capacity of soils contaminated with microplastics for such chemicals can be decreased, promoting faster leaching and enhancing the potential of groundwater contamination. This study extends previous research from a single pesticide to various co-presences, while connecting the physicochemical properties of pesticides, microplastic contamination, and vertical migration patterns.