Study On The Control Mechanism Of Iron-Based Montmorillonite-Bacterial Fertilizer-Organic Fertilizer On The Soil Mercury Release In Greenhouse

As an important mineral resource in China,mercury has made great contributions to China's economic construction and development.Due to long-term mining and extensive tailings treatment,the environment around the mining area has been heavily polluted by heavy metals.Take the Wanshan Mercury Mine in Tongren city,Guizhou Province as an example,long-term mining and unreasonable mining methods have caused the excessive mercury content in the surrounding soil(5.10-790mg.kg^-1).Studies have shown that,the intake of mercury in the leaf vegetables in the greenhouse of mining area was not only enriched in the root,but also absorbed the gaseous mercury in the air through the leaf stomata,which causes the mercury content of leaf vegetables to exceed the standard,and affects human health.Based on this conclusion,this study took the development of agricultural products in the mercury mining area in Wanshan District,Tongren City,Guizhou Province as a reference,simulated the construction of vegetable greenhouses outdoors,and took mercury-contaminated soil as the research object,the effects of Fe-MMT-bacterial fertilizer-organic fertilizer system on soil mercury release flux,total mercury,form of mercury,soil physical and chemical properties were studied.At the same time,the mechanism of soil mercury release control was analyzed based on the methods of adsorption-desorption experiments and material characterization.The main conclusions are as follows:(1)Compared with the natural soil treatment group,all the experimental groups could increase the biomass of Chinese cabbage's;and compared with the artificial mercury contaminated soil treatment group,the organic fertilizer treatment group and the bacterial fertilizer+organic fertilizer treatment group could increase the biomass of the cabbage in the soil and the amount is 8.5 g and 5.5 g,respectively.The biomass of cabbage was decreased in both the bacterial fertilizer treatment group and the Fe-MMT treatment group.In the Fe-MMT treatment group,the mercury content in roots(0.037 mg.kg^-1)was lower than that in the artificial mercury contaminated soil treatment group(0.19mg.kg^-1),and the mercury content in roots was higher in other treatment groups,which could promote the absorption of mercury in roots.The mercury content of leaves was less than that of roots.The mercury content of leaves in the bacterial fertilizer+organic fertilizer+8%Fe-MMT treatment group,organic fertilizer+Fe-MMT treatment group,Fe-MMT treatment group and bacterial fertilizer treatment group was lower compared with the treatment group of artificial mercury contaminated soil,which inhibited the absorption of gaseous mercury,while the remaining treatment groups promoted the absorption of gaseous mercury.(2)Except for the bacterial fertilizer treatment group,the mercury release flux at the rustic interface on the 60th day of the other experimental treatment groups was lower than that of the artificial mercury contaminated soil treatment group,while the other treatment groups showed inhibition;in addition,the mercury release fluxes of soil mercury from day 5 to day 60 were less than those on day 0.The total mercury content in the experimental groups decreases with time compared with the artificial mercury contaminated soil treatment group.In each treatment group,the proportion of unavailable state in the soil gradually increased with the time,and available state gradually decreased with the time;but in the bacterial fertilizer treatment group and the bacterial fertilizer+organic fertilizer treatment group,the proportion of unavailable state in the soil was lower than that of the artificial mercury contaminated soil treatment group,and the available state was higher than that of the artificial mercury contaminated soil treatment group,which increased the potential ecological hazards of mercury in the soil.At the same time,the risk assessment code(RAC),biological transport factor(TF)and accumulation factor(BCF)were used to evaluate the hazard risk of mercury.The results showed that the RAC value of mercury in the multiple treatment groups was between 1-10%which showed a low risk level.The TF_root-leaf value of mercury in the bacterial fertilizer+organic fertilizer+8%Fe-MMT treatment group,organic fertilizer+Fe-MMT treatment group,bacterial fertilizer+Fe-MMT treatment group and bacterial fertilizer treatment group were lowe.In addition,except for the bacterial fertilizer+organic fertilizer+1%Fe-MMT treatment group,the bacterial fertilizer+organic fertilizer treatment group and the bacterial fertilize+Fe-MMT treatment group,the BCF_leaves<BCF_roots in the other experimental groups,indicating that the bioaccumulation capacity in the leaves of Chinese cabbage was less than that of the roots.(3)The results of adsorption and desorption showed that the effects of pH,adsorbent quality,initial mercury concentration and adsorption time on the adsorption of mercury by Fe-MMT in the water-soil mixed system were different.Among them,the increase of pH,adsorbent quality and initial mercury concentration will increase the adsorption amount of mercury,but the adsorption time has little effect on the amount of mercury adsorption and the adsorption process is fast adsorption.The adsorption kinetics of mercury on Fe-MMT belongs to the pseudo-second-order model.The Langmuir and Freundlich models were more suitable for describing the isotherm adsorption process.It showed that in addition to physical adsorption according to the characterization analysis,the-SH,-OH,-S^2-,-COOH and-NH₂ groups contained in the Fe-MMT and soil can be adsorbed by complexing or precipitation with mercury.Compared with the artificial mercury contaminated soil treatment group,the soil pH in most experimental treatment groups decreased slightly,while the soil organic matter(SOM),cation exchange capacity(CEC)and oxidation-reduction potential(Eh)increased slightly.According to the correlation analysis of SPSS,it is concluded that the physical adsorption and chemical action of Fe-MMT-bacterial fertilizer-organic fertilizer on mercury lead to the decrease or increase of mercury release flux,and it is also affected by soil physical and chemical indexes and natural factors.For example,therewas a significant positive correlation between soil mercury release flux and soil temperature(P<0.05).In addition,redox potential and light intensity were also indirectly positively correlated with soil mercury release flux.