Microplastic Incorporation into Soil in Agroecosystems

Background: We live in a plastic age (Thompson et al. , 2009), with (typically defined as plastic particles < 5 mm) becoming an appreciated aspect of environmental pollution. Research has been focused on aquatic systems, especially the oceans, but there is current shift to more strongly consider terrestrial ecosystems (Rillig, 2012; Horton et al. , 2017). In particular agroecosystems are coming into focus a major entry point for microplastics in continental systems (Nizzetto et. , 2016b), where contamination might occur via different sources as sludge or plastic mulching (Steinmetz et al. , 2016). Given the central role agroecosystems, including their soil biodiversity (Rillig et al. , 2016), in production, such numbers are potential cause for concern. Field data on microplastic presence in agricultural soils are still not widely, but nevertheless this material is certain to arrive at the soil. The fate of material deposited at the soil surface is not clear: may be removed by wind or water erosion, becoming airborne, or may lost by surface runoff (Nizzetto et al. , 2016a). Nevertheless, a part of the microplastic (or nanoplastic following further) is expected to enter the soil. The degree of hazard by microplastic to various soil biota is not clear. Direct comes from experimental work on earthworms, on which microbeads had effects (Huerta Lwanga et al. , 2016; also reviewed in Horton et al. , 2017). Data on impacts on other soil biota groups are not available. However, et al. (2012) have shown that polystyrene beads can be taken up by the Caenorhabditis elegans; this means the material could also accumulate the soil food web (Rillig, 2012). Movement into soil is an important aspect assessing risk: will soil biota be exposed to microplastics? Here, we what is known about movement of such particles in soil, which players factors could influence this, and we chart avenues for research aimed at movement and distribution of microplastic in agricultural soils.