The individual transport, cotransport and immobilization with solar pyrolysis biochar of microplastics and plasticizer in sandy soil

The transport behaviors and immobilization of microplastics and plasticizer in soil have attracted increasing concern. In this study, the individual transport and cotransport mechanisms of polyvinyl chloride MPs (PVC MPs) and dimethyl phthalate (DMP), as well as their immobilization by solar pyrolysis biochar (SPBC) were investigated. Compared to SPBC (>1.52 mg g) and sandy soil (>0.045 mg g), PVC MPs exhibited higher DMP adsorption capacity (>39.2 mg g) via halogen bonds and so on. The DMP exhibited high mobility in sandy soil, which lightly influenced by soil metal oxides and organic matter. The PVC MPs showed low mobility in sandy soil, which was significantly controlled by metal oxides (increasing TMR by 24.37 %) but lightly influenced by soil organic matter (increasing TMR by 3.69 %). The PVC MPs and DMP mutually inhibited the mobility with each other's, and PVC MPs showed weak carrier effect on DMP mobility during cotransport process. The addition of SPBC in sandy soil effectively immobilized DMP (reducing TMR by 27.13-45.23 %), whereas slightly increased PVC MPs mobility by 4.26-7.43 %. This work firstly revealed the antagonistic cotransport mechanisms and SPBC immobilization effect of PVC MPs and DMP in sandy soil, contributing to the advanced risk assessment and remediation strategies for co-contaminated soils.