Microplastics On Soil Properties And Heavy Metal Patterns Of Alternating Wetting And Drying Heavy Metal Morphology

Most studies have only investigated the effects of MPs on soil sediment properties in relatively stable arid,semi-arid or fully wet systems,but frequent alternate wetting and drying(AWD)is also a common environmental system in soil sediments and wetland ecosystems containing HMs contamination in many regions,and it is necessary to investigate the differences in the effects of MPs on soil properties in AWD.In this study,a riparian zone soil in southwest China was incubated with HMs and MPs contamination and indoor AWD simulation experiments were completed to investigate the effect of MPs on soil properties with different irrigation patterns;at the same time,the complexation mechanism of SDOM and HMs under MPs stress was also investigated by using SDOM and HMs after AWD.The main results of this study are as follows:(1)The addition of MPs reduced soil N and P nutrients;the magnitude of changes in each physicochemical property in soil under AWD was greater compared to Dry.For soil Cu,Cr and Cd forms,the addition of MPs reduced the proportion of oxidizable state to some extent.The activities of catalase and dehydrogenase,which are involved in redox reactions in soil,were significantly reduced under MPs stress,while the trends of sucrase,urease and acid phosphatase,which are related to carbon,nitrogen and phosphorus,were closely related to carbon,nitrogen and phosphorus,and the enzyme activities were more susceptible to MPs in AWD.(2)The results of α and β diversity showed that the diversity of the remaining MPs,except for PE,was significantly reduced under Dry and the microbial structure was significantly altered.The results of correlation analysis showed that the activity of many microbial purposes was enhanced in AWD flooding mode,and they were more sensitive to the changes and feedbacks of environmental parameters.According to the symbiotic network analysis,it is clear that the structure of soil microorganisms exposed to MPs is significantly disrupted;according to the structural equation model,physicochemical properties are the main factors affecting the changes of microbial metabolic activities under Dry,while enzyme activity may be the key factor in AWD(3)The addition of different types of MPs changed the carbon,nitrogen and phosphorus content of soil dissolved organic matter(SDOM);total organic carbon(TOC),total organic nitrogen(TON)and total organic phosphorus(TOP)were significantly changed in SDOM under MPs stress;in addition,changes in SUVA254,SUVA260 and SUVA280 indicated that MPs reduced soil aromaticity,hydrophobicity and humification;the results of fluorescence spectroscopy analysis indicated the presence of one aromatic protein fraction(C1),one fulvic acid-like fraction(C2)and two humic acid-like fractions(C3)in SDOM of each treatment group.(4)SDOM indirectly alters soil Cu and Cd morphology through the effects of MPs on physicochemical properties and microbial communities.In addition,the complexation stability constants of different fractions of SDOM with Cu(II)were significantly lower under MPs stress,and overall MPs stress promoted the release of Cu(II)from different fractions of SDOM,which was one of the main reasons for the decrease in the proportion of oxidizable state of soil HMs,while unlike Cu(II),the complexation of various fractions of SDOM with Cd(II)was not significant under MPs stress.The binding order of SDOM with Cu(II)and Cd(II)did not change much in different treatment groups overall,in the order of humic-like → fulvic-like →aromatic protein,while the number of peaks associated with the complexation of SDOM with these two metal ions decreased.The results suggest that the stress of MPs mainly reduces the complexation ability of each component by affecting the complexation sites and affinity of each component with HMs,etc.rather than the complexation order of different components.This paper provides theoretical support for the impact of MPs on soil and remediation measures by studying the effects of each MPs on soil properties and the state of HMs under different environmental conditions,and analyzing the effects of MPs on different types of soil ecology as a whole.