A comparative study on the distribution behavior of microplastics through FT-IR analysis on different land uses in agricultural soils

Plastic materials have been variously exposed to arable land for decades through soil mulching, plastic housing, and sewage sludge composting. Their mechanical abrasion and biochemical degradation induce the proliferation of myriad microplastics that can further be broken into smaller nano-sized pieces that can be further accumulated in living organisms (including soil invertebrates, fruits, and vegetables); they can also be widely dispersed in neighboring environments. Despite the intensive use of plastics in agriculture, little is known about their origin of occurrence and environmental fate, especially with a size below 100 mu m. Therefore, in this study, microplastics with a size in the range of 20-2,000 mu m were investigated in soil samples obtained from three different con-ditions of land uses: tilled with plastic mulch, bare ground (i.e., uncultivated land), and in between the green-houses of the farmland D located in Namyangju-si, Gyeonggi-do, Republic of Korea. They were primarily identified using Fourier transform infrared (FT-IR) spectroscopy coupled with a microscope. Prior to performing the analysis, microplastic extraction from the soil samples was validated using standardized high-density poly-ethylene (HDPE) microplastics of various sizes ranging from 20 to 500 mu m. As a result, the number of micro -plastics was estimated to be (241 +/- 52), (195 +/- 37), and (306 +/- 56) particles per kg of dry soil in tillage, bare ground, and in between greenhouses, respectively. They consist of polyethylene (PE), polypropylene (PP), and poly(ethylene terephthalate) (PET), which are the basic constituents of commonly used agricultural products. The particle size distribution depends on the type of plastic, the time elapsed since their usage, and the degree and duration of environmental exposure; the plastic particle sizes were smaller in tillage and around the greenhouses since agricultural films have been weathered for a long time, whereas those with relatively large sizes were found in the uncultivated.

Automated summary

Plastic materials have been exposed to arable land for decades, leading to the proliferation of microplastics that can further accumulate in living organisms and disperse in neighboring environments. However, little is known about their origin and fate in agriculture, especially with a size below 100 μm.