Effects of Microplastics on the Transport of Soil Dissolved Organic Matter in the Loess Plateau of China

Microplastics (MPs) pollution and dissolved organic matter (DOM) affect soil quality and functions. However, the effect of MPs on DOM and underlying mechanisms have not been clarified, which poses a challenge to maintaining soil health. Under environmentally relevant conditions, we evaluated the major role of polypropylene particles at four micron-level sizes (20, 200, and 500 μm and mixed) in regulating changes in soil DOM content. We found that an increase in soil aeration by medium and high-intensity (>0.5%) MPs may reduce NH4+ leaching by accelerating soil nitrification. However, MPs have a positive effect on soil nutrient retention through the adsorption of PO43– (13.30–34.46%) and NH4+ (9.03–19.65%) and their leached dissolved organic carbon (MP-leached dissolved organic carbon, MP-DOC), thereby maintaining the dynamic balance of soil nutrients. The regulating ion (Ca2+) is also an important competitor in the MP-DOM adsorption system, and changes in its intensity are dynamically involved in the adsorption process. These findings can help predict the response of soil processes, especially nutrient cycling, to persistent anthropogenic stressors, improve risk management policies on MPs, and facilitate the protection of soil health and function, especially in future agricultural contexts.