A systematic review of the effects of microplastics and nanoplastics on the soil-plant system

Global pollution resulting from the presence of microplastics (MPs) and nanoplastics (NPs) in the environment has significantly intensified due to the production of plastic and its improper disposal. This scenario endangers all forms of life and services in aquatic and terrestrial ecosystems at an unprecedented rate. Although the number of studies evaluating this issue has increased over the last decade, the impacts of plastics have not been sufficiently defined and delimited, mainly in terrestrial environments. This systematic review presents the research progress on the interaction of MPs and NPs with soil-plant systems, providing key questions for future research. The selected publications (n = 85) evaluated various types of polymers, especially polyethylene and polystyrene, placed in the soil in different shapes (e.g., film, fragment, sphere, and fiber) and sizes (ranging from 0.02 to 7000 μm). In general, they revealed that distinct characteristics of MPs/NPs can influence the germination and development of plants, with wheat, rice, maize, and lettuce being the most studied. The main assessed endpoints were length and biomass, often segmented between root and shoot, and a comparative analysis between treatments containing MPs and NPs and the control (without contamination) provided different results, namely positive, negative, and no significant differences. These findings indicated that MPs/NPs may have more aboveground than belowground effects on plant growth. The combined presence of plastic waste with other contaminants or substances can change the physical, chemical, and biological properties of the soil, directly and indirectly affecting plant growth and soil health. However, most of those studies were developed with artificial contamination and on a laboratory scale. Since soils are dynamic and complex systems, there is still a gap of knowledge to be investigated to improve representativeness and address current limitations.