Polyvinyl chloride microplastics reduce Cd(II) adsorption and enhance desorption with soil-dependent mechanisms

Abstract

Soil co-contamination by cadmium (Cd) and microplastics has raised increasing concern. The presence of microplastics can impact the Cd(II) adsorption and desorption in soil, but this impact differs for diverse soil properties. Here, batch experiments in upland soil in Wuhan (WHS) and paddy soil in Liuyang (LYS) were carried on to reveal the effect of polyvinyl chloride (PVC) microplastics on the adsorption behaviors and mechanisms. PVC promoted the desorption of Cd(II) from the soil and increased its potential bioaccessibility. The adsorption of Cd(II) in LYS was more susceptible to the influence of PVC compared to that in WHS, while the desorption of Cd(II) from WHS was more prone to be affected. Cd(II) is inclined to aggregate in solution and be docked by the adsorption site as the type of aggregate. The aggregation of Cd(II) increased and the amount of adsorption sites deduced when contaminated by PVC. Isotherms revealed that the co-contamination of PVC inhibited the Cd(II) adsorption by increasing the boundary layer effect and blocking the active sites. Characterizations confirmed that Cd(II) would be complexed with oxygen-containing functional groups and react with phosphorus to generate Cd3P2 or CdP2. C-O was the primary oxygen-containing functional group complexed with Cd(II) in LYS, while CO for WHS. The better adsorption property and stronger interactions of Cd(II) in LYS was associated with its higher concentration of organic matter and available phosphorus. This study provides new insights into the fates of Cd(II) in the different PVC co-contaminated representative soils.