| Mercury was a kind of heavy metal with highly toxic,strong migration,and can bioaccumulate and biomagnify in food chains.It had become a global pollutant widely concerned by people.With the development of industrial and mining,the content of soil mercury in many areas has increased multiple to hundreds of times.Due to the fact that the flooding of paddy field is conducive to the methylation of soil mercury,the inorganic mercury becomes a more toxic and bioaccumulative form of methylmercury,which makes the concentrations of THg and Me Hg in rice 10-100times higher than other crops.Rice consumption had become the main route of methylmercury exposure in some mercury mining areas,which seriously threatens the health of local residents.Therefore,it has important theoretical basis and practical significance to explore a stabilization/solidification material that can effectively reduce the concentrations of THg and Me Hg in rice.In this study,montmorillonite,selenium,chitosan and sodium sulfide were used as raw materials to prepare different kinds of selenium stabilization/solidification agents.Firstly,through the soil culture experiment,the selenium modified materials with better stabilization effect on soil mercury and its optimal use conditions were preliminarily selected,and the modified agents were characterized by FTIR,XRD,etc.then,through the rice pot experiment,the effect and mechanism of reducing mercury and methylmercury in rice were further explored.The main results are as follows:?1?The results of soil culture experiment showed that:among the eight kinds of selenium stabilization/solidification agents,montmorillonite modified by selenium chitosan,activated clay modified by selenium chitosan,montmorillonite modified by sodium selenite and activated clay modified by sodium selenite could significantly reduce the exchangeable mercury content of paddy soil,and the best reduction rate was montmorillonite modified by selenium chitosan?50.77%?,activated clay modified by selenium chitosan?55.97%?,followed by sodium selenite modified montmorillonite?47.58%?and activated clay modified by sodium selenite?45.55%?.The inhibition effect of selenized clay and selenite shell clay on exchangeable mercury in alkaline and neutral environment werebetter than that in acid environment.The stabilization effect of remediation agent on mercury in clayey soil and sandy soil is similar.?2?The results of FTIR and XRD showed that after the montmorillonite was modified by selenium,selenium was successfully loaded on the montmorillonite,and the basic structure of the montmorillonite was not changed.?3?The results of rice pot experiment showed that the remediation effect of selenide on rice mercury was significantly stronger than that of single montmorillonite and single selenium group.The montmorillonite was modified by selenide significantly improved the adsorption and fixation ability of total mercury?THg?and methylmercury?Me Hg?in paddy soil.Compared with the control group(rice THg 327.64±1.18 ng·g-1,Me Hg 269.11±2.38 ng·g-1),the addition of different selenium stabilization/solidification agents significantly reduced THg and Me Hg content in rice,with the reduction rate reaching 63.25%or more,among which selenide and selenium shell had the best effect,with the reduction rate of mercury and methylmercurywas more than 90%,while the reduction effect of these stabilization/solidification agents on mercury and methylmercury of rice in sandy soil was significantly lower than that in cohesive paddy soil.The reduction rates were68.89%and 73.64%,respectively.The addition of selenide stabilization/solidification agent significantly reduced exchangeable mercury and methylmercury in the soil,increased the partition coefficient of mercury and methylmercury in the solid-liquid phase of the soil,increased the adsorption and fixation capacity of the soil for mercury and methylmercury,and thus reduced the accumulation of THg and Me Hg in rice.?4?The results of the study on the stability of the restorer showed that the content of THg and Me Hg in rice decreased significantly in the second year,with the reduction rate ranging from 46.13% to 57.26% and 59.72% to 85.68%,respectively. |
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