Accumulation of microplastics in greenhouse soil after long-term plastic film mulching in Beijing, China

Intensive use of plastic film and organic fertilizer in the greenhouse has resulted in microplastic contamination of soil. However, microplastic pollution in different types of greenhouses has not been reported so far. The contamination of microplastics in three different types of greenhouses (abandoned greenhouse, normal greenhouse, and simple greenhouse) were investigated. The abundance of microplastics in abandoned greenhouse reached as high as 2215.56 ± 1549.86 items kg-1, followed by normal greenhouse (891.11 ± 316.71 items kg-1), and simple greenhouse (632.50 ± 566.93 items kg-1). The mean abundance of microplastic organic fertilizer, and irrigation water were 1486.67 ± 140.48 items kg-1, and 4.2 items L-1, respectively. The abundance of microplastics in the shallow soils of abandoned greenhouse (826.67 ± 261.02) and normal greenhouse (560.00 ± 52.92 items kg-1) were lower than those in the deep soils (1073.33 ± 306.16 and 720.00 ± 111.36 items kg-1), while the simple greenhouse showed the opposite result. Microplastic was found to be primarily fragment-shaped, white in color, and 0-1 mm in size, and the polymers of microplastics were polypropylene (PP) and polyethylene (PE). White was the most frequently observed color in the abandoned greenhouse (46.1%) and normal greenhouse (32.2%), while the dominant color in the simple greenhouse was yellow (23.1%). This study provides first-hand data for the pollution characteristics of microplastics in different greenhouse soils and explores the primary sources of microplastics in the greenhouse soil.