The abundance, characteristics and distribution of microplastics (MPs) in farmland soil—Based on research in China

Microplastics (MPs) in farmland soil deteriorate soil environment and increase food toxicity, thereby threatening the agricultural production environment and human safety. However, a systematic understanding of MPs pollution in farmland soil is lacking in China. Therefore, the relevant literature was comprehensively discussed to discuss the abundance, characteristics, distribution and influencing factors of MPs in farmland soil. The conclusions are as follows: (1) The highest and lowest MPs abundance were in marginal tropical humid and plateau temperate semi-arid regions, accounting for 7579 n/kg and 48 n/kg, respectively. (2) The main shapes of MPs in farmland soil are fragment/flake and fiber, accounting for 44.0 % and 34.4 %, respectively. The MPs are mostly transparent (21.8 %) and black (21.5 %). Among the MPs types, polyethylene (PE) and polypropylene (PP) are dominant, accounting for 26.2 % and 19.0 %, respectively. The main size of MPs in farmland soil is 0.1-0.5 mm, with average proportions was 51.4 %. (3) Compared with non-fertilizing and non-mulching, the MPs abundance in the fertilizing and mulching farmland soils increased by 170 % and 232 %, respectively. (4) In the farmland soil, the MPs abundance was significantly positive with temperature, sunshine hour, and altitude. (5) In farmland soil of China, the most commonly used MPs dispersion treatment was H2O2 solution digestion, the extracting solution commonly used for density flotation was NaCl solution, and microscopic and spectroscopic measurements were typically used measurements. The results could provide a basis for monitoring the MP abundances in farmland soil and preventing the transfer of MPs pollution in soil.