Characterization of microplastics and the association of heavy metals with microplastics in suburban soil of central China

Microplastics (MPs) are ubiquitous in the aquatic and terrestrial environment and can absorb other kinds of pollutants on surfaces due to strong hydrophobicity and higher specific surface area. This study investigated the occurrence and distribution of MPs and the interaction of MPs and heavy metals in three different land types of central China. Results showed that the abundance of MPs ranged from 2.2 × 104 to 6.9 × 105 particle·kg-1, and 81.7% of particles measured ranged from 10 to 100 μm. The smaller sized particles made up the greater proportion of MPs in the study area. In woodland, the abundance of MPs (4.1 × 105 particle·kg-1) was significantly higher than that in vegetable plots (1.6 × 105 particle·kg-1) and vacant land (1.2 × 105 particle·kg-1). The most prevalent form of MP particles was fragments (53%), followed by fiber (15.2%). Polyethylene, polypropylene, polystyrene, polyamide, and polyvinyl chloride were commonly found at each sampling site, with polyethylene as the dominant form (36.1%). It was inferred that industrial production activities, litter, and sewage sludge might be the main sources of the MPs pollution. Moreover, MP particles in the soil environment contained different levels of heavy metals, including Cd, Cr, Pb, Ag, Cu, Sb, Hg, Fe, and Mn. The concentration of heavy metals in MPs, particularly Cd, Pb, Mn, and Hg, was closely related to the extent of heavy metal contamination in the soil environment, inferring that MPs in the soil can be vectors for transporting heavy metals. The synergistic effect of MPs and heavy metals might pose greater risks to soil organisms and soil safety.