Occurrence Characteristics and Regional Differences of Microplastics in Different Types of Manure Composts

Microplastic pollution in the soil has become a growing public concern globally. The application of livestock and poultry manure compost is considered to be an important pathway for the accumulation of microplastics in soils. However, the understanding of microplastic pollution in fecal compost is still limited. In this study, the distribution characteristics of microplastics in composts of commercial chicken, cow, goat, and pig manure in four provinces of China were investigated. Microplastics in manure composts were extracted by sieving and digestion with Fenton′s reagent, and their color, size, shape, type, and abundance were further analyzed. The results show that transparent, black, red, and blue are the dominant colors of microplastics in manure composts. The shapes of microplastics in manure composts include fibers, fragments, films and granules, with fibers being the highest. The dominant size of microplastics in manure composts is < 1 mm, which accounted for 27.6% to 69.5%; and the dominant polymer types of microplastics in manure composts are polyester (PES), polypropylene (PP), and polyethylene (PE), which accounted for 87.8% to 97.0%. The abundance of microplastics in manure composts ranges from (2 054.8 ± 493.9) to (9 131.0 ± 600.7) items·kg^-1. The results of this study confirmed that manure compost is an important source of microplastics in agricultural soil, and the contribution of manure compost application to the abundance of microplastics in agricultural soil of China is estimated to be 1.1 × 10¹⁴ items per year. The above results provide basic data and scientific basis for revealing the pollution characteristics and regional differences of microplastics in manure composts, and the source identification of microplastics in agricultural soils.