Microplastics are plastic particles smaller than 5 millimeters. Sources of microplastics in agricultural soils include sludge from wastewater treatment plants, irrigation water, fertilizers and atmospheric deposits, as well as residues of plastic mulch and greenhouses that break down into microplastics. Microplastic particles are transported from the surface deeper into the soil by soil water, soil animals and agricultural activities. In the soil, microplastics undergo structural changes, which degrade their mechanical properties. The degradation of microplastics is slow and occurs under the influence of abiotic factors (UV radiation) and biotic factors (microorganisms). During biodegradation, microorganisms, with the help of enzymes, break down the polymer into monomers, which they use as a source of carbon and energy. Due to their considerable resistance to degradation, microplastic particles accumulate in the soil and consequently affect soil properties such as structure, porosity, water holding capacity, pH and C:N ratio. By influencing soil properties, microplastics also indirectly affect soil organisms. Microplastics in their surroundings can stimulate the growth of certain microorganisms, but they can also have a negative effect, inhibiting the growth of soil animals, such as earthworms. Microplastics can adsorb pollutants such as heavy metals and thereby increase their mobility in soil, posing environmental and health risks. Although research on the impact of microplastics on soil is mostly laboratory-based, it is clear that the increasing amount of microplastics in soil poses potential threats to soil, crops and human health.
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