Effects Of Typical Fertilizers On Mercury Release In Greenhouse Soil And Its Mechanism

Mercury（Hg）is one of the most toxic heavy metals in the environment.It can stay in the atmosphere as gaseous element for a long time and eventually settle to the ecological environment on the surface.Leaf vegetables can not only absorb atmospheric mercury through leaves,but also enrich mercury in soil through root transport,and eventually harm human health by the food chain.Therefore,this study simulated the construction of vegetable planting greenhouses to explore the effects of microbial fertilizer and humic acid fertilizer on soil mercury release flux,soil total mercury and soil physical and chemical properties,and analyzed the mechanism of soil mercury release through adsorption experiments and material characterization.The main conclusions are as follows:（1）In the use of BF and HAF,mercury release fluxes at soil-atmosphere interface gradually decreased in each treatment groups as time went on or dosage increased.And the average values of mercury release fluxes of treatment groups of 1%-BF,3%-BF and 5%-BF were respectively913.24,766.03 and 686.37[ng·（m~2·h）^-1],the order was 1%-BF>3%-BF>5%-BF in descending sequence,similarly,the average values were respectively 1188.66,890.32 and 776.16[ng·（m~2·h）^-1]for the treatment groups of 1%-HAF,3%-HAF and 5%-HAF,and the sort was 1%-HAF>3%-HAF>5%-HAF in descending sequence.（2）Total mercury concentration of Soil in each treatment groups decreased gradually with the increase of time.The variation range of total mercury concentration in CK,1%-BF,3%-BF and 5%-BF groups was respectively 31.52-38.52,33.03-38.83,33.41-39.91 and 33.40-39.48mg/kg and overall reduction values were successively 7.00,5.79,6.50 and6.07 mg/kg,which indicating that BF was superior to CK.What’s more,for 1%-HAF,3%-HAF and 5%-HAF treatment groups,the range was orderly 31.32-39.06,29.61-37.78,30.55-37.39 mg/kg,and the overall reduction value was 7.74,8.17,6.84 mg/kg,respectively.Therefore,CK,1%-HAF and 3%-HAF treatment groups had the largest reduction value,while 5%-HAF treatment group had the smallest reduction value,which showing that BF and HAF could effectively fix mercury in soil.（3）When increasing dosage of the BF and HAF,Soil p H value decreased,but SOM content and soil Eh value increased.Bsides,it was found that soil total mercury content,soil SOM content and soil temperature were the important factors affecting the soil-atmosphere interface mercury release flux in this experiment through the correlation analysis.（4）In the light of the adsorption experiment,it can be seen that BF and HAF adsorption of mercury was a rapid adsorption process,the adsorption process of BF and HAF conforms to the quasi-second-order kinetic model,and the theoretical adsorption capacity（q_e）obtained by fitting was 32.89 mg/kg,which was basically consistent with the experimental data 32.55 and 32.68 mg/kg.The results showed that the adsorption was a rapid adsorption process dominated by chemical adsorption.According to the parameters obtained by fitting isothermal adsorption model,it can be known that HAF adsorption of mercury conforms to Langmuir model.The adsorption of mercury by BF accord with Freundlich model.What’s more,the adsorption mechanism of BF and HAF for mercury may be precipitation,physical adsorption,ion exchange,functional group complexation and cation-πbond coordination.（5）The functional groups of SOM existing BF and HAF could complexity with mercury so that the release of mercury at the Soil-atmsphere interface was restrained.What’s more,mercury had a series of reactions with HAF and BF,including ion exchange,precipitation,cationicπbond coordination and physical absorption,and can inhibited the mercury release flux of the soil contaminated by mercury.