Occurrence, sources, and risks of microplastics in agricultural soils of Weishan Irrigation District in the lower reaches of the Yellow River, China.

Microplastics (MPs) have been widely detected in the soil environment. The Weishan Irrigation District is the largest irrigation area in the lower reaches of the Yellow River. However, little is known about MP pollution levels in the soils of this area. Forty-two soil samples, two water samples, and two organic fertilizer samples were collected to study the occurrence and sources of MP in the soils of four land use types. Different characteristics of MP were integrated to trace the sources of MP in soils and ecological risks associated with specific MP characteristics were evaluated. The average abundances of MPs in the soils of vegetable fields, crop fields, orchard fields, and woodlands were 900, 512, 615, and 633 items/kg, respectively. MPs were predominantly 0.2-1 mm in size (> 78 %), primarily blue/purple and transparent in color (> 60 %), mainly film, fiber, and fragment in shape (> 78 %), and mostly polyethylene in polymer type (> 36 %). Irrigation water, organic fertilizers, and plastic inputs are the major sources. Ecological risks based on MPs with specific characteristics were higher than those based on total MP. The source-based strategies developed are helpful to the prevention and control of MP pollution in irrigation districts.