The Effects Of Resistance Control And Remediation Of Arsenic And Cadmium Contaminated Soil

Rice is one of the major cereal crops in China.In recent years,the incidences of"cadmium rice"and"arsenic rice"produced by heavy metal-contaminated soil in China have aroused widespread concern in society,threatening the quality of agricultural products and human health.At present,there have been a lot of studies on the single remediation of Cd or As contaminated-soil,but the opposite geochemical behaviors of Cd and As in paddy soil have led to a greater difficulty in simultaneous remediation of Cd and As contaminated-soil.In this study,the effects of water management and the combination of mercapto-palygorskite（MPAL）and hematite on the reduction of Cd and As in rice grain were investigated.Additionally,we investigated the effects of different treatments on soil physical and chemical properties,the availability and speciation distribution of Cd and As in the soil,and the soil microbial community diversity,in order to provide theoretical basis and technical support for the remediation of Cd-As combined pollution of farmland soil.The main results are as follows:（1）The application of MPAL under wetting and flooding conditions significantly reduced the concentration of Cd in rice grain,and such a reduction increased with the increase of the applied doses;As for As in rice grain,the addition of MPAL significantly reduced the concentration of As in rice grain only under flooding conditions,and the lowest As concentration in rice grain were observed at a 0.05%application dose of MPAL.MPAL treatment had no significant influence on soil p H,but might change soil Cd fractions by decreasing the soluble+exchangeable fraction and increasing the crystalline iron oxide bound fractions,and eventually significantly reducing the available Cd in the soil.The content of soil DTPA-Cd decreased by 22.6%～52.8%as compared to the control,and MPAL treatment had a smaller effect on soil DTPA-Cd content under flooding conditions than under wetting conditions.Under flooding conditions,As in organic matter bound fractions significantly increased,and MPAL treatment significantly decreased soil DTPA-As by11.8%～17.9%as compared to the control.Besides,MPAL treatment had no significant effect on soil DTPA-As under wetting conditions.（2）The application of MPAL promoted the formation of iron plaque on the surfaces of rice roots.Under both water conditions,MPAL application could reduce the total Cd concentration in the iron plaque,but the As concentration in the iron plaque increased under flooding conditions.The concentration of Cd in rice node I from MPAL-treated soil was the highest,which was significantly higher than the Cd concentration in rice roots,was about 1.78～8.65 times higher than that of other nodes.In the MPAL treatments,TF_cob-grain and TF _root-node3 showed a decreasing trend with the increase of MPAL application dose,and the transport coefficient of Cd under flooding conditions was lower than that under wetting conditions.（3）The application of MPAL in combination with hematite can significantly increase the biomass of rice grains while also reducing Cd and As concentration in rice plants,with Cd concentration in rice grain significantly decreasing from 0.05 mg·kg^-1 in the control treatment to0.02 mg·kg^-1,and As concentration in rice grain decreasing from 1.50 mg·kg^-1 to 1.35 mg·kg^-1,but the reduction effect on grain As was not significant.MPAL in combination with hematite had a significantly reduction effect on DTPA-Cd and DTPA-As content in the soil,but the reduction effect on DTPA-As was not significant.Meanwhile,sequential extraction results showed that the application of MPAL in combination with hematite increased the portions of Cd and As in the amorphous iron oxides bound fractions,while significantly decreased Cd in the crystalline iron oxides bound fractions.（4）Water management and MPAL treatments had significant effects on soil bacterial richness,diversity,and composition,and the soil bacterial Alpha diversity under flooding conditions was higher than that under wetting conditions.In the MAPL treatments,the abundance of soil bacterial community structure at phylum level and genus level was different between flooding conditions and wetting conditions.Under wetting conditions,the relative abundance of Actinobacteria was the highest,and the application of MPAL decreased the abundance of Bryobacter but promoted the abundance of Anaeromyxobacter;while under the flooding conditions,MPAL application decreased the abundance of Anaeromyxobacter but promoted the abundance of Bryobacter,but the difference was not significant.Redundancy analysis（RDA）analysis showed that Cd in Mn-oxides bound fractions in soil had the most significant effect on bacterial community structure under wet management,and DTPA-As had the most significant effect on bacterial community structure in soil under flooding conditions.