What Do We Know About the Effects of Microplastics on Soil?

In this century, climate change is unparalleled and the most sensitive environmental problem humanity faces, with potentially very serious consequences in the coming decades. Other important challenges include the urgent need to reduce the volume of pollutants discharged into various environmental compartments and mitigate the effects of their release on the functioning of natural ecosystems. In this context, plastic pollution is a primary environmental concern. This issue is drawing increased attention from governments and the global scientific community since the ubiquitous presence of plastic in all environmental compartments (water, soil, air, and biota) is causing deleterious effects that have not yet been fully studied or understood. Microplastics (MPs) (particle size <5 mm) have been widely detected in aquatic and terrestrial ecosystems, prompting a need for studies that assess their impact on these ecosystems. Anthropogenic activities such as the use of plastics for agricultural mulching, irrigation with wastewater, application of soil amendments (e.g. sewage sludge and compost), and atmospheric deposition turn soil into one of the largest storage reservoirs for MPs. Furthermore, pollutants (organic contaminants, toxic metals, pathogens) that adhere to and are transported with MPs can pose an additional major environmental risk. The persistence of MPs in soils, due to their low biodegradability, can change the soils' physicochemical properties and affect their microbial communities and enzymatic activities, potentially causing negative impacts in terrestrial ecosystems. Recent research has also identified a high risk of MP transfer from terrestrial ecosystems into the human food chain, anticipating MP pollution as a future threat to food security and sustainable agriculture. This chapter condenses the current understanding of the occurrence, sources, and potential ecological risks of MPs in terrestrial soil ecosystems.