Polypropylene Macroplastics and Microplastics Impact the Immobilization Behaviors of Cd by Biochar

Plastics and heavy metals are likely to coexist in agricultural soils. Previous studies reported that biochar can effectively immobilize heavy metals and improve soil quality of microplastic-contaminated soil. However, the potential effects of plastics (include macroplastics and microplastics) on the interaction between biochar and heavy metals in agricultural soils is still largely unknown. In this study, the effects of plastics and biochar on soil properties and cadmium (Cd) immobilization were investigated through a 120-day incubation experiment. Rice husk biochar and different doses (0.1%, 1%, and 7%) of polypropylene macroplastics and microplastics were added to Cd-contaminated agricultural soil. Results showed that biochar could partially alleviate the impact of macroplastics on soil properties, and both macroplastics and microplastics inhibited Cd immobilization by biochar. Compared to the biochar addition alone (CK2), the immobilization efficiency of Cd decreased respectively by 22.29%−34.28% and 64.81%−89.20% when macroplastics and microplastics coexisted with biochar. This study further revealed that plastics inhibited Cd immobilization by biochar mainly through physical hamper, dilution, occupying adsorption sites of soil fractions and biochar, and decreasing soil pH. Collectively, these findings provide theoretical references and new insights regarding the application of biochar in Cd-contaminated soil in the presence of plastics.