Occurrence and Characteristics of Microplastics in Soils of Greenhouse and Open-Field Cultivation Using Plastic Mulch Film

There is a major knowledge gap concerning the extent of microplastic pollution in agronomic regions of China, which represent a plastic use hotspot. This study investigated the characteristics of microplastics distributed in agricultural soils of three typical regions (Beijing (BJ), Shandong (SD), and Xinjiang (XJ)) with two plastic film mulching modes (greenhouse (G) and conventional field-based film mulching (M)) in China. The average abundance of microplastic under G and M mode was 3.60×104 particles kg-1 and 3.01×104 particles kg-1, respectively; and the estimated weight of microplastics per kg of dry soils in BJ, SD, and XJ was 3.12 mg kg-1, 5.63 mg kg-1, and 7.99 mg kg-1, respectively. Microplastics in farmland were mainly of a small particle size (50 to 250 μm), with their abundance decreasing with increasing particle size. Among the microplastics detected, polyethylene and polypropylene were the two dominant types present, accounting for 50.0% and 19.7%, respectively. In addition, plastic film mulching mode (G vs. M) had a stronger effect on microplastic distribution than agronomic region. This research provides key data to support the development of guidelines for the sustainable use of agricultural plastic film and an assessment of the environmental risk of microplastics.