Application Of Pennisetum Americanum And Soil Conditioning Technology In The Safe Use And Remediation Of Mercury Contaminated Farmland

Mercury（Hg）is a highly toxic global pollutant.Years of Hg mining and indigenous Hg smelting activities have caused serious Hg pollution in the mining area and surrounding ecosystems.Hg mining areas are located in mountainous areas,the economy is backward,and the land is poor.Even the heavily polluted land is responsible for agricultural production.The Hg pollution of cultivated land severely restricts the local economic development.Soil Hg pollution causes the Hg content of crops to exceed the standard,and eating these crops with the Hg content above the standard causes serious harm to the health of local residents.Therefore,the application of research on the safe utilization and restoration of Hg-contaminated soil in Hg mining areas is of great significance to maintaining agricultural safety in Hg mining areas.Pennisetum americanum has huge biomass and is a perennial herb.It can be used as forage feed and board material,and has great economic value.In this paper,the soil contaminated by different levels of Hg in Wanshan,Guizhou Province was used as the test object to compare the conditions of Pennisetum americanum and the Hg-accumulating plant Pteris vittata with soil conditioners such as bacterial fertilizer,organic acids,earthworms,and modified activated white soil.Under the situation of Hg enrichment,the safety,economic value and potential of soil Hg remediation of Pennisetum americanum in the soil of Wanshan Hg mining area were evaluated,and the Hg enrichment of plants by analyzing soil form Hg and microbial distribution The mechanism has been preliminarily discussed.The main conclusions are as follows:（1）The analysis of soil form mercury in each treatment showed that,compared with the control group,the modified activated clay treatment group increased the dissolved and exchangeable mercury content,but greatly reduced the oxidized mercury content(3.18±0.47 ng·g^-1,p<0.01),the reduction rate reached 76.02%.In the microbial fertilizer treatment group,the three forms of mercury all increased slightly,but none of them achieved significant effects.The distribution of microorganisms in the soil was analyzed by Qualcomm sequencing technology,and it was found that after the microbial fertilizer containing multiple microorganisms was added to the soil,the Bacillus in the microbial fertilizer became the dominant population in the single-application microbial fertilizer treatment group,and the microbial fertilizer+lemon none of the acid combination treatment groups became the dominant population.（2）Regardless of the low and high concentration of Hg contaminated soils,the Hg content in aboveground part of Pennisetum americanum(6.86±2.40-47.82±0.97ng·g^-1)did not exceed the national feed standard(100 ng·g^-1).Both the microbial fertilizer treatment group and the modified activated clay treatment group effectively reduced the total Hg content in each part of Pennisetum americanum.For low-concentration of Hg contaminated soils,there is little difference between the microbial fertilizer treatment group and the modified activated clay treatment group in reducing the Hg content of various parts of the plant.The reduction rates of total Hg in the upper leaves,lower leaves,stems and roots are 74.14%-76.36%,48.08%-55.08%,93.37%-94.66%and 50.91%-52.39%.For high concentrations of Hg contaminated soil,modified activated white clay also significantly reduced the Hg concentration in the upper leaves,bottom leaves,stems and roots of Pennisetum americanum by 69.34%,47.79%,44.18%and 34.51%,respectively.（3）In the low Hg pollution soil,citric acid treatment group,microbial fertilizer treatment group,earthworm treatment group,microbial fertilizer+earthworm treatment group,citric acid+earthworm treatment group,citric acid+microbial fertilizer+earthworm treatment group and modified activated white clay have obvious effect on reducing Methylmercury（Me Hg）in the stem and root of Pennisetum americanum,and the reduction range is 25..58%-60.47%,24.06%-77.68%respectively;while for leaf Me Hg,only The microbial fertilizer treatment group had a significant reduction effect on the upper and lower leaves of Me Hg,the reduction rates were 42.55%and 38.10%,respectively.In the high Hg pollution soil,the modified activated clay significantly reduced the Me Hg content（67.52%）in the upper leaves of Pennisetum americanum.（4）The safe utilization of plants and the evaluation of Hg enrichment efficiency show that Pennisetum americanum has a huge biomass,and its Hg extraction is much higher than that of Pennisetum americanum on the premise that the mixed Hg content of above-ground stems and leaves does not exceed the national feed standard the amount of Hg extracted from soil by other plants.Under the condition of soil Hg concentration of 4.74 mg·kg^-1,the amount of Hg extracted from the stems and leaves of Pennisetum americanum is 0.393 g·（mu·year）^-1,which is significantly higher than that of Pteris vittata stems and leaves.The extraction amount(0.04 g·（mu·year）^-1),the Hg extraction amount of the whole Pennisetum americanum is 4.158 g·（mu·year）^-1),which is significantly higher than that of the whole Pteris vittata quantity(0.115g·（mu·year）^-1).