Sources of Microplastics in Soil and Their Adverse Effects on Soil: A Review

Although plastic products nowadays widely mass-produced bring convenience to people, they definitely cause plastic pollutants to accumulate in the environment. Microplastics are generally defined as plastic particles less than 5 mm in size. Large amounts of such wastes are annually released and dumped into the environment so that they are now widely detected in open oceans, freshwater, marine organisms, soil, and sewage sludge, among others. Pollution with microplastics and the associated environmental hazards are nowadays a major global concern, with soil pollution with microplastics being of special importance because soils provide a wide range of ecosystem services essential for life while they house most of the microplastic waste released into the environment. A wide array of sources has been identified for soil pollution with these materials including composts, sewage sludge, irrigation, plastic mulch, littering, and atmospheric deposits. The transport and persistence of microplastics in soil are governed by the interaction effects of microplastic properties (namely, the extent of their swarm into the environment, particle size, and type of their constituent compounds) and environmental factors. Moreover, plastic materials present in soil can change the interactions among soil particles, water, chemical compounds, and living organisms to alter the different characteristics of agro-ecosystems. To shed more light on these issues, the present article provides a review of the research projects performed, both at the national and international levels, on the sources of microplastics in soil and their detrimental impacts on soil and human beings.