Identifying hot-spots for microplastic contamination in agricultural soils—a spatial modelling approach for Germany

Microplastic (MP) contamination in agricultural soils has recently gained significant attention in science and society. The continuous plastic waste generation and its low degradation rates indicate a cumulative effect of MP in the environment that calls for more research on the amounts and impacts of this contaminant. The most discussed agricultural sources for MP contamination of cropland are sewage sludge, compost, and plasticulture residues. However, knowledge about how much MP has been emitted into agricultural soils is scarce. Since MP distribution in soils is expected to be highly heterogeneous, its analysis in field samples provides mainly point information. To quantify the various MP sources and pathways within and across ecosystems, data-driven models represent crucial tools to scale these analytic results to a landscape level and to simulate effects of mitigation measures. Some recent modelling studies have estimated MP emissions based on production and consumption statistics at national level, but as of yet, spatially explicit regional quantification of MP emissions into agricultural soils are virtually missing in the scientific literature. Using data on MP analysis results from the literature in combination with national and regional statistics on sewage sludge, compost and organic waste production, as well as speciality cropping areas, we estimated the spatial distributions of cumulative MP mass inputs into agricultural soils in Germany. Although these estimates are based on limited data availability, our results provide first indications about locations where detailed soil analysis could be useful to investigate in situ processes and impacts. The methodology can be applied to other regions and continuously adapted when more knowledge on relevant sources, transport, accumulation, and degradation rates of MP in soils is gained in the future.