The positive effects of polypropylene and polyvinyl chloride microplastics on agricultural soil quality

Microplastics are widespread contaminants in agricultural soils. Owing to the different properties of microplastics and soil components, microplastics may affect the function and stability of soil ecosystems. However, the effects of microplastics on agricultural soil quality remain largely unknown. The 3-month pot experiments were performed to investigate the responses of soil physical (i.e., soil bulk density, saturation moisture capacity, and porosity), chemical (i.e., pH, CEC, TOC, TN, TP, and AK content), and biological indicators (i.e., catalase, urease, and dehydrogenase activity) to polypropylene (PP) and polyvinyl chloride (PVC) microplastics with different concentrations (i.e., 0.1%, 0.3%, and 1.0%, w/w). Soil bulk density was significantly (p < 0.05) decreased after exposure to PP, which was attributed to the low density of PP. But apart from that, PP and PVC had negligible effects on other soil physical properties. Although PP and PVC decreased soil pH, it remained within the neutral range. Owing to the higher content of carbon, PP had a stronger promoting effect on TOC content than PVC. Soil CEC increased with PP concentration, and 1% (w/w) PP significantly increased soil CEC. The activities of soil catalase, urease, and dehydrogenase increased after exposure to PP and PVC at certain concentrations. Generally, PP had a stronger promoting effect on soil enzyme activity than PVC. Microplastic effects on soil quality depended on microplastic types and concentrations. Overall, PP and PVC microplastics induced several positive effects, such as increasing soil enzyme activity, soil CEC, and TOC content, and decreasing soil bulk density, on soil quality. Our research findings highlight the positive effects of microplastics on agricultural soil fertility.