Research progress on the impact of freeze-thaw action driven by microplastics on the transformation of cadmium forms in soil

Microplastics, as a new type of environmental pollutant, due to their unique surface properties, can adsorb heavy metals or significantly affect the morphological transformation process of cadmium by altering the physicochemical properties of soil and the activity of microorganisms. This compound pollution poses a threat to soil ecological security and human health. In cold regions, freeze-thaw cycle is a common natural phenomenon, which can significantly affect the aging process of soil microplastics and the occurrence form of cadmium through seasonal temperature changes. Although existing studies have explored the individual effects of freeze-thaw action and microplastics on the form of cadmium, however, there is still a lack of understanding about the relevant mechanisms of how microplastics affect the transformation of cadmium forms in soil under freeze-thaw conditions. This article mainly reviews the interaction mechanism of freeze-thaw and microplastics on cadmium in soil. Firstly, it elaborates on the occurrence forms of cadmium in soil and its influencing factors. The process by which freeze-thaw action affects the morphological transformation of cadmium by altering the physicochemical properties of the soil is analyzed. Secondly, the mechanism of action of microplastics on the occurrence form of cadmium and the important influencing factors are discussed, including the physicochemical properties of microplastics (type, particle size, abundance and aging, etc.) and environmental conditions (pH, organic matter, etc.), Furthermore, the influence mechanism of the synergistic effect of freeze-thaw and microplastics on the morphological changes of cadmium is explored. Finally, three aspects are highlighted for the future research, which will enhance the understanding and recognition of the environmental behavior of heavy metals in soil in freeze-thaw areas under the background of climate change, and provide a theoretical basis for the development of environmental risk control technologies and policy-making for pollutants.