Kaolinite reduced Cd accumulation in peanut and remediate soil contaminated with both microplastics and cadmium

Abstract

Microplastics (MPs) increase the effective state of heavy metals (HMs) in soil and seriously threaten the yield and quality of peanuts (Arachis Hypogea L.). Kaolinite (KL) has the potential to ameliorate MP- and HM- contaminated soils, but the mechanism of action between them is not well understood. Therefore, 60-day experiments were conducted, where KL (1 %, 2 %) and MPs (0.1 %, 1 %) were individually or jointly mixed into soils with different cadmium (Cd) concentrations (0.5, 2.5, and 5.0 mg·kg⁻¹) to cultivate peanuts in a greenhouse. Finally, soil-bioavailable Cd, peanut dry weight, peanut Cd concentrations, the pH, cation exchange capacity (CEC), dissolved organic carbon (DOC), microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) were determined. It was shown that MPs negatively affected the peanut dry weight and increased the content of soil-bioavailable Cd and Cd concentration in peanut. In the MP- and Cd-contaminated soils, KL mitigated the negative influence of MPs by increasing the dry weight of peanuts by 8.40 %−40.59 %, decreasing the soil-bioavailable Cd by 23.70–35.74 %, and significantly decreasing peanut Cd concentrations by 9.65–30.86 %. The presence of MPs decreased soil pH (7.69–7.87) and the CEC (20.96–23.95 cmol·L⁻¹) and increased the soil DOC (1.84–2.26 mg·kg⁻¹). KL significantly increased soil pH (7.79–8.03) and the CEC (24.96–28.28 cmol·L⁻¹) and mitigated the adverse influence of MPs on the pH and CEC of Cd-contaminated soils. A regression path analysis (RPA) evidenced that KL decreased Cd accumulation in plants by changing the properties of soil contaminated with MPs and Cd. The research results revealed the mechanism of KL on peanut growth and Cd absorption in MP- and Cd-contaminated soil. The results of this study provide a foundation to improve the quality of MP- and HM-contaminated soils and realize safe peanut production.