Effects of Microplastics from Face Masks on Physicochemical and Biological Properties of Agricultural Soil: Development of Soil Quality Index “SQI”

Microplastics (MPs) are of great interest for study because they accumulate in environmental systems, such as terrestrial ones, which include agricultural soils. Unfortunately, in recent years, due to the COVID-19 pandemic, many face masks have been discarded in the environment, causing an increase in this type of MP. This accumulation can influence the physicochemical and biological properties of soil derived from its microbial activity. In the present study, different concentrations of MPs from commercial polypropylene (PP) face masks were mixed with agricultural soil. Four different treatments with the following MP concentrations were studied: T1: 0%, T2: 0.5%, T3: 1%, and T4: 5% w w−1. C and N mineralization experiments were carried out over time at the microcosm level, where physicochemical, enzymatic and ecophysiological indicators were analyzed. Based on the analyzed indicators, a soil quality index called the Unified Weighted Additive Index (SQIu) was developed. The resulting SQIu showed Nmin as the indicator with the closest relationship to the quality of the soils with MPs. Once the SQIu was determined, the T4 treatment showed significant differences (p≤0.05) with respect to the control, presenting a higher quality value. The importance of conducting more research on the dynamics of C and N in different soils with different types, sizes, and concentrations of MPs can help to establish strategies to measure the effects of MPs on soils at the local, national, and international levels.