Soil productivity is crucial for agroecosystems that sustain our growing population. Plastic materials have been increasingly used to enhance soil productivity. However, their use and unintentional introduction through irrigation water and biosolids have led to the accumulation of plastic and microplastics (< 1mm, MPs) in soil, which is known to be a sink for plastic. Despite the adverse impacts of MPs on soil ecosystem functions, including nutrient cycling and water regulation, the quantification of MP concentrations in soil remains limited. Moreover, the concentrations and distribution of MPs in the subsoil remain largely unknown despite evidence of vertical migration of MPs in soil.
To address this knowledge gap, the current study aimed to quantify the vertical distribution of MPs in various soil types and agricultural uses to better understand the risk of MP contamination in groundwater systems.
Soil profile samples (1.2 m depth) were collected from three different soil types and land uses in Germany. After oven drying at 50°C, samples were fractionated (1000 µm, 250 µm, 25 µm) using stainless steel mesh sieves. Subsequently, 10 g of sample was weight out into precleaned accelerated solvent extraction (ASE) cells and spiked with 40 µg polystyrene (PS-d5) internal standard. The ASE sample extraction (DCM at 180 °C, 1500 psi) was followed by double-shot Pyr-GC/MS analysis quantifying PS, PC, PMMA, PP, PET, PE, and PVC. Field and processing blanks were processed alongside the samples.
Soil samples are currently being analyzed for MP concentrations. The results are expected to show the overall highest MP concentration in the plowing layer as well as the highest concentration of larger MPs. Along the soil profile the MP concentrations expected to decrease with smaller particle sizes increasing. Overall, this study is expected to reduce the uncertainty around of MP concentration measurements in soil.