A comparative distribution fate of microplastics in between tillage and non-tillage at D farmland, Namyangju-si, Korea

초록

Microplastics have spread over to arable land for decades through various routes such as soil mulching, plastic houses, composting sewage sludge, and others. From these, they have been weathered to small pieces due to physical and biochemical reactions, further releasing micro or nano plastics, which can have been remained migrating through the phloem, consequently impeding the plant growth. It is urgent to investigate the distribution of microplastics in the soils collected from the D farmland, Namyangju-si, Korea (Fig. 1). They were taken from three different places in terms of the tillage cultivated perilla mulched with polyethylene film, near the plastic houses, and non-tillage covered by weeds. Microplastics in the samples were extracted by wet oxidation (34.5% H2O2, at 70℃), density separation using saturated NaCl solution and ZnCl2 solution, followed by filtration using a 100 μm-mesh sieve and 20 μm-mesh filters, made of stainless steel. Entailing removal of residual non-plastic organic matter and soil particles on a 20 μm-mesh filter, it was then dried overnight in an oven (50℃). The separated microplastics were characterized by FTIR spectroscopy (NicoletTM iNTM 10 Infrared Imaging Microscope, Thermo Scientific, USA), from which their abundancy was observed at 240.7, 195.2, and 306.5 particles per kg of dry soil around tilled, plastic houses, and non-tilled, respectively, with a predominance of polyethylene and polypropylene, where microplastics particles larger than 100 μm were more than 60% (Fig. 2). Furthermore, microplastics smaller than 20 μm was successfully sized by our developed process for extracting microplastics from soil samples.