Microplastics in Agricultural Systems: Analytical Methodologies and Effects on Soil Quality and Crop Yield

Around one million metric ton of plastics is produced worldwide daily. Plastic contamination is aggravated when the particles reach sizes between 5 mm and 1 μm, giving rise to microplastics, which are omnipresent in the environment, especially in agroecosystems. To appreciate the magnitude of this problem, this review analyzes 177 scientific works to focus on the occurrence and effects of microplastics in agricultural soils. Firstly, the sources, behavior and fate of microplastics in agroecosystems are evaluated. Then, in the absence of a standard methodology for the study of microplastics in farmland soils, the procedures which have been employed for microplastic separation (density and floatation in 73% of the discussed works), identification and quantification (stereomicroscopy, 77%; infrared analysis, 62%) are addressed to provide a practical work guideline. Finally, we highlight the interaction between microplastics and soil microbiota, fauna and vegetation (negative effects reported in 83% of cases), including crop production (decrease in growth parameters in 63% of the reports). From this review, it can be inferred that microplastics may disrupt the biophysical environment of farmland soil, potentially leading to economic losses and to their entrance into the trophic food chain, affecting human feeding and health.