[Effects of Microplastics Coexisting in Vegetable Soil on the Change of Cadmium Bioavailability]

The multiple contamination of heavy metal-microplastics occurs frequently in soil； however, ecological risk research on this subject is still lacking. In a 60-day pot experiment, lettuce in soils was contaminated with different biodegradable microplastics （MPs） and heavy metal cadmium （Cd）. The basic physicochemical properties of the soil, Cd availability, and the accumulation and transfer effects of Cd in lettuce were analyzed. Additionally, three-dimensional fluorescence spectroscopy was used to analyze the composition characteristics of soil dissolved organic matter （DOM）. The results indicated that MPs reduced the soil cation exchange capacity （CEC） and the content of ammonium nitrogen （NH₄⁺-N） while increasing the content of soil dissolved organic carbon. The multiple contamination of MPs and Cd significantly enhanced the microbial source characteristics of soil DOM, reduced the humification degree of DOM, and significantly weakened its autochthonous characteristics. There was a significant positive correlation between the Cd-CaCl₂ content and the total Cd content in the soil, while the correlation with soil chemical properties was not significant. MPs increased the accumulation of Cd in lettuce roots, with no significant effect on the accumulation of Cd in the leaves （P>0.05）. The accumulation of Cd in lettuce roots and leaves was mainly influenced by the total Cd content in the soil and the Cd-CaCl₂ content （R>0.85, P<0.05） and decreased with the increase in the humification degree of soil DOM and the content of humic-like substances. This study can provide data support for the ecological risk assessment of composite pollution of soil microplastics and heavy metals.