How does soil contamination by microplastics interferes the sorption and desorption processes of three herbicides?

The increasing presence of microplastics (MPs) in agricultural systems may influence the environmental behavior of herbicides by affecting processes such as sorption and desorption, depending on the specific compound involved. This study aimed to evaluate the influence of different MP proportions on the sorption and desorption of three herbicides in soil. Hexazinone, diuron, and S-metolachlor were introduced into soil at concentrations of 0 % (control - unmodified soil), 1, 5, 10, 15, 20, and 100 % (w w) MPs, with the addition of 2 g of material (soil or MPs). Sorption and desorption isotherms were determined using the batch equilibrium method, followed by herbicide analysis via high-performance liquid chromatography (HPLC). The results indicated that the presence of MPs altered S-metolachlor sorption by approximately 10 % in soil amended with 5 % MPs, with K values ranging from 3.20 L kg to 4.85 L kg in unamended soil, suggesting increased herbicide retention in the presence of MPs. For hexazinone and diuron, sorption in the MPs treatments was comparable to the control, with similar behavior observed in desorption. These findings suggest that the presence of MPs in soil can modify the environmental fate of herbicides, potentially affecting their efficacy in weed control and increasing the risk of environmental contamination, particularly in agricultural soils polluted with these polymers.