Widespread presence of plastic mulch has led to macroplastic (MaP) pollution. While this issue is widely explored in aquatic ecosystems, MaP pollution on land has been neglected. In 2019, we conducted a large-scale survey of MaPs in Northwest China in 0-30 cm soil with long-term mulching. Samples of MaP debris were collected from 67 sites across Gansu, east Qinghai, and north Shannxi Provinces. All visible MaP pieces for each site were separated and weighed. The mass of each MaP piece was calibrated by size measured in digital images. The MaP mass averaged 47.2 kg ha-1, and the number of MaPs averaged 266.2 pieces ha-1. The mass and number of MaPs varied from site to site. The mean size of MaPs was 19.5 cm2 piece-1 or 28.0 mg piece-1. More importantly, the number of small MaP pieces (<5 and 5-20 cm2 piece-1) accounted for 76.7% of the total number of MaPs detected, and small-sized plastic debris (<10 and 10-25 mg piece-1) were detected in 70.1% of the sampling sites. The percentage of small fragments increased before 15-year of mulching and then declined. However, the amount of medium-large debris (20-50 and >50 cm2 piece-1) showed a trend opposite to that of small fragments. The percentage of MaPs was greater in the small size group than in the medium-large size group. The arid to semi-arid area exhibited higher MaP contamination compared with the semi-arid to the semi-humid area. These observations indicate that plastic debris residing in soil tend to be fragmented, making plastic film recovery more challenging and causing severe soil pollution. Further studies are required to regulate plastic mulch methods and explore the degradation process.
Keywords: Agriculture soil; Long-term film mulching; Macroplastic debris; Northwest China.
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