Coexistence of microplastics and Foramsulfuron in soil: effects on herbicide persistence and soil functionality

Microplastics (MPs) in agricultural soils pose a major environmental issue since they persist and alter the soil chemical and physical properties, affecting its overall health. Applying digestate to soil may introduce MPs, which can adsorb agrochemicals, and alter their behaviour. This study examined Foramsulfuron (FRS) degradation and adsorption in two soils (S1 and S2), with and without MPs and digestate (D) amendment. The results showed that MPs prolonged FRS half-life (+ 17% in S1 and + 21% in S2 relative to the control), whereas D reduced it by 10% in both soils. The experimental FRS adsorption isotherm data fitted with the Freundlich equation. The low K _fa values (between 1.07 and 2.05 µmol ^(1−1/n) kg ^− 1 L ^1/n ) suggested limited herbicide adsorption in soils, which increased with MPs and D in the order (S) < (S + MPs) < (S + D + MPs). In S1, MPs and D enhanced adsorption hysteresis, while in S2, MPs reduced the soil's FRS retention capacity. The effects of the copresence of FRS and MPs on soil functionality were evaluated by quantifying dehydrogenase, β-glucosidase, and urease activities at 3-, 10- and 24-days post-herbicide application. In the short term (3 days after FRS treatment), these enzymatic activities were stimulated by FRS, MPs, and D, likely due to added carbon and energy sources for soil microbes. The effects varied by soil type, exposure time, and interactions between treatments. This study demonstrated that MPs and digestate amendment significantly influenced herbicide fate, persistence, and soil microbial activity.