Research On Safe Utilization And Regulation Technology Of Mercury-polluted Farmland

More than 1.6%of the soil inorganic mercury pollutants in China exceed the standard.At present,there are still vacant methods for reasonable restoration of mercury-contaminated farmland.In this paper,we conducted a study on a Hg-contaminated farmland in Wuxi Ehu Lake,selected vegetables and oil crops with low Hg accumulation in edible parts,studied the feasibility of alternative planting of horticultural plants,and compared a variety of soil Hg deactivators and the use of deep turning.The effect of regulation on the reduction of Hg content in vegetable edible parts,etc.The research results can provide theoretical and practical guidance for the safe and efficient use of Hg-contaminated farmland.The specific research results are as follows:1.The 20-point mercury-contaminated farmland in this area was analyzed at 20 points,the physical and chemical properties of the soil in different tillage layers,the total amount of Hg and the effective state content:the results show that the soil in this area is weakly acidic(pH 5.88);The organic matter content is low(24.8%);the average total Hg content in the surface soil of 0-20cm is 2.204 mg/kg(the soil over-limit standard is 0.5 mg/kg),and the effective mercury content is 0.0339 mg/kg,which belongs to heavily polluted soil with Hg;The effective state content of total Hg and Hg is negatively correlated with soil depth.As the soil depth increases,the effective state of Hg and the total Hg content gradually decrease.2.In the Hg-contaminated farmland,there are 10 kinds of vegetables such as leafy vegetables(convolvulus,cabbage,spinach,amaranth,garland chrysanthemum),eggplants(cucumber,cowpea,broad bean),rhizomes(sweet potato,radish),etc.,Analysis and determination of Hg content in edible parts of vegetables and total accumulation of Hg in non-edible parts.The results show that different vegetable types have different accumulation levels of Hg.In general,the accumulation degree of Hg:leafy vegetables>rhizome>solar fruit;the edible parts of water spinach,cabbage,spinach Hg content exceeds national standards,not suitable for consumption.The Hg contents of edible parts of eggplant cucumber,broad bean grains,and rhizome sweet potatoes were 0.0081,0.0071,and 0.0086 mg/kg dry weight,which were lower than the food Hg limit standard(0.01 mg/kg dry weight).In addition,the non-edible parts of sweet potatoes,cucumbers,and fava beans were enriched with Hg of 117.66,64.60,and 66.96 mg/hm2,respectively,indicating that planting these three vegetables can not only be eaten safely,but also effectively remove Hg,Is the ideal planting vegetable for mercury contaminated farmland.3.From June 2018 to April 2020,6 oil crops including soybean,peanut,sesame,rape,evening primrose and oil sunflower were planted in Hg-contaminated farmland,and the edible parts Hg of each oil crop were analyzed and determined Content and total Hg accumulation in non-edible parts.The results showed that the Hg contents of rapeseed,peanut,soybean,oil sunflower,evening primrose seed were 0.0072,0.0068,0.0072,0.0058,0.0086 mg/kg dry weight,which were lower than the national food Hg limit standard(0.01 mg/kg dry weight),the grain is safe and edible.The mercury removal amounts of rape,peanut,soybean,evening primrose,and sunflower are 129.2、25.09、23.31、46.50and 53.30 mg/hm2·season respectively.Comprehensive crop growing season and economic benefit analysis,soybean and peanut are grown in summer One of the oil sunflowers,planting yellow primrose or rape in winter,is a safe and efficient farming method that uses mercury to contaminate farmland,and at the same time has a certain restoration effect.4.From March 2018 to the present,3 garden plants such as Photinia frasery,Phalaenopsis euphratica,and Euonymus japonicus have been planted on 6 acres of Hg contaminated farmland.During the experiment period,it was found that these three garden plants all grow normally and show no symptoms of toxicity,and can be used as an alternative plant for Hg-contaminated farmland.5.In addition,the effects of soil deep turning(turning 40-60cm soil layer to the surface)and various soil Hg deactivators(mineral elements,etc.)on the Hg content of several vegetable edible parts were compared.At the same time,the effects of three common biochars:sludge biochar,rice husk biochar,and straw biochar on the physical and chemical properties and available Hg content of Hg-contaminated soil were compared.The results show that the addition of 3%straw biochar can significantly reduce the effective Hg content in the soil(the highest reduction is 66.50%),significantly increase the soil pH(up to 1.32 units),and significantly increase the soil organic matter content(The maximum increase is 27.04%).Soil deep turning and applying mineral elements could significantly reduce the mercury content of crops.When applying mineral materials after deep turning,the total Hg content of cabbage and radish was reduced by 23.9%and 59%respectively,compared with the blank control group.The content of Hg in plant was also reduced by mineral materials,and the content of Hg in spinach and Garland chrysanthemum was reduced by 43.2%and 32.9%respectively.The application of three kinds of biochar can reduce the Hg content of cabbage and water spinach.Among them,the application of 3%straw and rice husk biochar has the best effect.The Hg content reduction ratio of cabbage and water spinach is the highest by 70.6%(3%rice husk),87.6%(3%Straw biochar).The results of the study indicate that Hg-contaminated sites can sample oil crops and garden plants for safe alternative planting.Compared with leafy vegetables,eggplants and root vegetables have better safety in the farmland polluted by this concentration of Hg.The research results provide an important reference for the safe and rational use and restoration of Hg contaminated farmland.