Pollution of agricultural soils by microplastics and their interaction with residual herbicides

Agricultural soils contaminated by microplastics (MPs) pose a significant con-cern regarding the efficacy of residual herbicides in controlling weeds. An im-portant part of this study was investigating how MPs interact with three residual herbicides: diuron, hexazinone, and S-metolachlor. The main focus was on identifying the most effective analytical methods for detecting MPs in soil matri-ces and assessing the sorption and desorption behavior of the herbicides. Near-infrared spectroscopy (NIR) and multispectral analysis were used, demonstrating high sensitivity in detecting MPs at various concentrations. High-performance liquid chromatography (HPLC) was used to assess the interaction between MPs and herbicides, enabling the determination of sorption and de-sorption isotherms. MPs were only detected at high concentrations (20%) using X-ray analysis. NIR at 2,300 nm and multispectral analysis at 395 nm showed greater accuracy and sensitivity in distinguishing between all levels of MPs. Scanning Electron Microscopy (SEM) revealed that MPs possess an amor-phous structure, distinct from crystalline soil, which may influence their interactions with other soil constituents. Regarding the interaction of MPs with herbicides, the presence of MPs influenced the sorption of S-metolachlor in the soil, resulting in up to a 10% increase in the amount of the herbicide sorbed, with a sorption coefficient (Kd) of 4.85 L kg-¹ with the addition of 5% MPs. However, there was no return of S-metolachlor to the soil solution, as demonstrated by a hysteresis (H) of 0.99 for the treatment with 5% MPs, compared to a control treatment with an H of 0.88. Diuron and hexazinone showed little interaction with MPs; the sorbed percentage of diuron was around 40% in all treatments (amended and unamended soils), with a Kd ranging from 1.84 to 2.12 L kg-¹. In the case of hexazinone, the behavior was similar, but the sorbed percentage was around 20% for all treatments (amended and unamended soils), with a Kd ranging from 1.63 to 2.03 L kg-¹. Only small amounts of both herbicides were taken up by plants. In all treatments (amended and unamended soils), approx-imately 15% of hexazinone and diuron was taken up. These interactions signifi-cantly impact herbicide efficacy in weed control and increase the risk of envi-ronmental contamination. Identifying these polymers and understanding the interaction of residual herbicides with MPs in agricultural soils is crucial for developing management strategies that consider the presence of MPs, thereby promoting more sustainable agricultural practices. Keywords: Residues plastic. Contamination. Analytical techniques. Sorption. Desorption