Effects Of Low-density Polyethylene Microplastics And Cadmium On Physical And Chemical Properties Of Loess And Growth Of Maize And Its Mechanism

At present,microplastics（MPs）and heavy metal pollution in the soil environment have become one of the major environmental pollution issues of concern to scholars at home and abroad.Numerous studies have shown that MPs entering the soil environment can affect soil structure and physicochemical properties,plant growth,etc;the heavy metal Cd is the most common contaminant in agricultural soils in China.MPs in soil can affect the morphological composition of heavy metals in soil and the phytoeffectiveness of heavy metals by influencing soil physicochemical properties and plant growth.However,the effects of combined MPs and Cd contamination on soil-plant systems are currently unknown.Due to the extensive use of agricultural mulching film,the most commonly used low-density polyethylene（LDPE）microplastic in mulching film has accumulated in the soil environment.The research on the impact of combined pollution of LDPE and Cd in soil on soil-plant system is still blank.This study set up a pot experiment to explore the effects of combined pollution of LDPE MPs with different particle size and dosage and Cd on soil properties,maize growth and Cd absorption and accumulation by maize,this paper attempts to reveal the law and mechanism of the combined pollution of MPs and Cd on the effectiveness of Cd plants,it is expected to provide a valuable reference for exploring the ecological risk and mechanism of combined pollution of MPs and Cd in soil to soil-plant system.The main results are as follows:（1）BET characterization results showed that there was no significant change in the specific surface area of LDPE extracted after pot experiment and LDPE and Cd Combined Pollution group;compared with LDPE group,when LDPE and Cd are combined polluted,the total pore volume and average pore diameter of 100μm LDPE did not change significantly,the total pore volume and average pore diameter of 1 mm LDPE are reduced.It can be seen from the SEM characterization results,there was no significant difference in the surface morphology of LDPE when it was polluted by LDPE and Cd.The FTIR characterization results showed that there was no new absorption peak in the FTIR spectrum of LDPE extracted after pot experiment,and the strength of functional groups was different.According to the XPS characterization results,LDPE is mainly composed of carbon element.After the pot experiment,the peak intensity of oxygen element on the surface of LDPE is enhanced and the peak intensity of carbon element is weakened;there was no significant difference in the surface chemical properties of LDPE when LDPE and Cd were combined polluted.（2）Compared with CK group,when LDPE was added alone,the dosage was 1%and the particle size was 100μm LDPE reduced soil EC by 47.1%;Compared with LDPE group,when LDPE and Cd were combined polluted,EC was increased in MP-L_0.1%+Cd,MP-L_1%+Cd and MP-S_1%+Cd groups,the EC of the MP-S_0.1%+Cd group was reduced by 44.5%.Compared with CK group,adding LDPE alone decreased soil CEC;Compared with LDPE group,the CEC was increased when LDPE and Cd were combined polluted,but the difference was not significant.Compared with LDPE group,soil SOC did not change significantly when LDPE and Cd were combined polluted.The single factor of LDPE particle size and dosage and their interaction significantly affected soil SOC.Compared with CK group,MP-L_0.1%、MP-S_0.1%、MP-L_1%and MP-S_1%groups reduced catalase activity by 28.1%,12.2%,55.9%and 32.1%respectively;Compared with LDPE group,the combined pollution of LDPE and Cd had no significant effect on catalase activity,and LDPE particle size significantly affected soil catalase activity.Compared with LDPE group,the soil invertase activity was decreased when LDPE and Cd were combined polluted,but the difference was not significant.When LDPE and Cd are combined polluted,compared with Cd group,MP-L_0.1%+Cd treatment group increased the content of available Cd in soil by 16.4%,compared with LDPE group,the content of available Cd in soil increased significantly when LDPE and Cd were combined polluted.（3）Compared with LDPE group,the maize plant height was significantly reduced when LDPE and Cd were combined polluted,the maize plant height was significantly correlated with LDPE dosage,and the interaction of LDPE dosage and Cd significantly affected the plant height.Compared with LDPE group,the combined pollution of LDPE and Cd had no significant effect on maize stem diameter,and the addition of Cd significantly inhibited the growth of maize stem diameter.Compared with CK group,LDPE group significantly reduced root length;Compared with LDPE group,the root length was increased when LDPE and Cd were combined polluted.Compared with CK group,when LDPE was added alone,MP-S_0.1%、MP-L_1%and MP-S_1%groups increased the content of MDA by 27.6%,29.9%and 20.1%,respectively;Compared with LDPE group,MP-L_0.1%+Cd、MP-S_0.1%+Cd and MP-L_1%+Cd groups increased the content of MDA.Compared with CK group,adding LDPE alone decreased POD activity;Compared with LDPE group,the combined pollution of LDPE and Cd increased the activity of POD.Compared with CK group,adding LDPE alone increased SOD activity;Compared with LDPE group,the combined pollution of LDPE and Cd increased the activity of SOD.Compared with CK group,adding LDPE alone decreased CAT activity;Compared with LDPE group,the combined pollution of LDPE and Cd reduced CAT activity.The single factor of LDPE particle size and dosage was significantly correlated with CAT activity in maize stems and leaves.Compared with CK group,when LDPE was added alone,the contents of chlorophyll a,chlorophyll b and carotenoids in MP-L_0.1%group were significantly reduced;Compared with LDPE group,when LDPE and Cd were combined polluted,MP-L_0.1%+Cd、MP-S_0.1%+Cd、MP-L_1%+Cd and MP-S_1%+Cd groups increased the contents of chlorophyll a,chlorophyll b and carotenoids.Compared with Cd group,the combined pollution of LDPE and Cd increased the content of Cd in stems,leaves and roots,but the effect was not significant.Cd addition significantly affected the Cd content in maize stems,leaves and roots.The single factor of LDPE particle size,the interaction of Cd and particle size significantly affected the Cd content in stems and leaves,and the single factor of LDPE particle size and dosage had a significant effect on the Cd content in roots.