Soil structures and immobilization of typical contaminants in soils in response to diverse microplastics

Microplastics (MPs) accumulation in soil ecosystems has become a worldwide issue. The influence of MPs on soil structures and contaminant transport has not been clearly unraveled. This study conducted soil column experiments covering four different treatments: soil without MPs (CK), soil with 0.5 wt% polyethylene (S+PE), soil with 0.5 wt% polyacrylonitrile (S+PAN), and soil with 0.5 wt% polyethylene terephthalate (S+PET). The interconnections between changes in soil structures and shifts in sorption efficiency for typical hydrophobic organic contaminants (e.g., phenanthrene (PHE)) and heavy metal (e.g., lead (Pb (II)) by soils induced by MPs were explored. MPs-added soils contained fewer macro-aggregates and lower aggregate stability compared to CK. Three MPs, particularly PE, promoted PHE sorption by soils but reduced Pb (II) sorption, which occurred in soils with or without dissolved organic carbon. The comparison between experimental and predicted sorption capacity, as well as the one-point sorption data of different aggregate sizes, showed that such variations in PHE and Pb (II) sorption were related to the shifts in soil aggregates besides from the physical mixture of soils with MPs. This finding is perspective to give an in-depth understanding of the effects of different MPs types on soil micro-environments and transport for contaminants.