Study On The Effect And Mechanism On Bioavailability Of Cadmium In Microplastics

The compounding effect of pollution formed by the adsorption of heavy metals in the environment by microplastics poses a potential threat to the soil environment.The study of microplastics in soil aqueous solution is more based on the distribution and occurrence of microplastics in soil environment,while the interaction between plastics and soil media is less studied.In this experiment,two kinds of microplastics and three typical soils were used as the research object.Using indoor static simulations and longterm incubation experiments,the effects of microplastics on soil Cd bioavailability and microbial diversity were studied and clarified,which is of great significance to describe its potential risks.(1)The adsorption and desorption of PP MPs and PBAT MPs on different soil aqueous solutions were analyzed by indoor simulation experiments.The results showed that soil types were an important factor influencing adsorption and desorption.The adsorption of heavy metals by soil aqueous solution-microplastics is mainly characterized by "dilution",and the adsorption process is dominated by chemical adsorption.The adsorption content of PBAT MPs was higher than that of PP MPs.The desorption content is proportional to the adsorption content,and the amount of microplastic additive has little effect on the desorption process.The results of adsorption and desorption of microplastics by three different soil aqueous solutions showed that laterite had the lowest adsorption and desorption capacity,black soil had the largest adsorption capacity and cinnamon soil had the largest desorption capacity.(2)The long-term incubation experiment of 1% PBAT MPs-60% soil maximum water holding capacity was conducted to study the physical and chemical properties and Cd bioavailability of different types of soil.Long-term incubation resulted in rough surface morphology PBAT MPs,easy degradation and oxidation of functional groups,and a gradual decrease in strength.The difference in adsorption content may be related to the O,Si,and Fe in soil.The addition of MPs slowed down the acidification of red and black soil,increased soil TOC and DOC content,and the type of soil colloid type and textural minerals,which could affect the electrostatic adsorption cation ability and nutrient composition.The microplastic soil aqueous solution systems reduce the bioavailability Cd.Environmental factors such as p H,TOC,DOC,TP and clay powder particle content in soil types are important indicators for controlling the bioavailability of Cd in soil.(3)Indoor 1% PBAT MPs-60% soil maximum water holding capacity long-term incubation experiments on the abundance of different types of soil bacteria indicated that microplastics caused changes in microbial diversity in different types of soil due to changes in the number of soil bacterial operational taxonomic units(OUT).The species diversity of cinnamon soil was higher than that of red and black soil,but its richness was low.Soil types screened for sensitive bacteria suitable for survival.The addition of PBAT MPs promoted the growth of Proteobacteria,Actinobaciota,Noviherbaspirillum,and inhibited the growth of Acidobacteria,Gemmatimonadota,Bacteroidota and Flavisolibacter,Gemmatimonas,Sphingomonas,unclassified-Vicinamibacterales,which led to the dynamic changes of relative abundance of bacterial community.Environmental factors such as p H,TP and TOC affect the tolerance of sensitive bacteria.The type of soil environment gives bacterial communities similar genetic functions.The addition of microplastics mainly affects the process of cell metabolism and soil types influences microbial metabolism through metabolism,human disease and environmental information technology.Through the above research,the effect and mechanism of microplastics on Cd bioavailability under different soil types were analyzed.This study can provide theoretical support for the development of microplastics.