Changes in the spectroscopic response of soil organic matters by PBAT microplastics regulated the Cd adsorption behaviors in different soils

Contamination of microplastics (MPs) and heavy metals occurs frequently in terrestrial ecosystems, but their interactions remain unclear. A 60-day incubation experiment was conducted to study the behaviors of cadmium (Cd) in polybutylene adipate terephthalate (PBAT) MPs-contaminated soils, with different doses (1, 10%) and sizes (150-300 and 75-150 μm). Soil chemical properties, including the three-dimensional fluorescence of dissolved organic matter (DOM) and microbial diversity in both farmland and woodland soils were analyzed. Results showed that soil properties, especially the components and fluorescence characteristics of DOM varied with soil types and PBAT properties. Higher soil chemical properties and microbial diversity were found in woodland soils. The soluble microbial by-product substances and humic acid-like substance were dominated in soil DOM, while the proportions of fulvic/humic-acid like substances and soil humification decreased with the addition of 10% PBAT. Soil microbial diversity increased with doses of PBAT, but not sensitive to the sizes of PBAT. The adsorption capacity of Cd decreased with the addition of PBAT, especially in the 10% and 75-150 μm PBAT treatments. Both Langmuir and Freundlich models fitted well with the adsorption isotherms of Cd. Multiple correlation analyses showed that low molecular weight fractions, humus index of DOM and soil microbial diversity such as Shannon, Simpson, and Pielou all positively correlated with the adsorption behaviors of Cd in PBAT-contaminated soils. Biodegradable MPs can change soil quality and promote the release of soil Cd, which deserves further research attention.