Study On The Interaction Mechanism Between Microplastics And Cadmium During The Aging Process And Its Phytotoxic Effects

The large quantity of microplastics（MPs）entered into the environments as an emerging persistent pollutant and they brought up the widely concerns on the ecological health risks.In this presentation,three microplastics（PE,PVC and PS）were selected as research objects.Under an air photo-aging system,the physicochemical characteristics of microplastics were investigated after the different aging times（8 d and 16 d）.The aging behaviors of different PS at 0.1μm,50μm and 100μm were also studied.On this basis,the interaction between aging MPs and Cd was further explored and their synergetic stress on the maize growth was carried out.The specific works were written as follows.（1）Different particle sizes of PE/PVC/PS were exposed to UV light（at a wavelength365 nm）.Under an aging process,the changes of their physicochemical characteristics were investigated.It was found that the type and particle size of MPs were important factors in the aging process of MPs.Among them,PE shows the most difficult to be aged and PS_0.1with the smallest size is the easiest one.The aging process causes the change of color,cracks and folds on the surface.The specific surface area of MPs may be reduced by fragmentation and agglomeration as the aging time increases.Different types and numbers of oxygen-containing functional groups are generated on the surface of MPs.The O/C element content ratio and CI index are proportional to the aging time.The number of negative charges on the surface of MPs shows an increasing trend.（2）The adsorption kinetics and isotherms of Cd²⁺by MPs and aging MPs were investigated,indicating the interaction between aging PS-DOM and Cd²⁺.The results showed that aging process could increase the adsorption capacity of Cd²⁺by MPs.The adsorption of Cd²⁺on MPs was as followed as PS₁₀₀>PVC₁₀₀>PE₁₀₀,also increased with a particle size PS_0.1>PS₅₀>PS₁₀₀.The adsorption kinetics of Cd²⁺on MPs was more consistent with the proposed secondary kinetic model.The adsorption of Cd²⁺on MPs was a combination of physical and chemical adsorption and the later one revealed a crucial one in adsorption.After aging process,PS-DOM has a good fluorescence response and is able to bind to Cd²⁺and thus undergo static burst.（3）The phytotoxicity of aged PS-DOM and Cd²⁺on the growth of maize seedlings was investigated.The results showed that the PS₅₀ exposure after aging process had no effect on seed germination and the combining exposure could alleviate the inhibition of Cd²⁺on seed germination.However,the aging PS_0.1 could significantly inhibit seed germination rate and the combining exposure had no significant effect on Cd²⁺-stressed seed germination.The single Cd²⁺exposure significantly inhibited the growth of root length and plant height of maize seedlings,while PS₅₀ and PS_0.1 at co-exposure significantly reduced the metallic stress on seedling roots and partially restored the dry weight of underground parts.Aging PS-DOM significantly reduced the inhibition of seed germination,maize root length and plant height when co-exposed with Cd²⁺,but did not alleviate the reduction of plant biomass caused by Cd²⁺.