Risk Assessment And Medicago Sativa Remediation Of Agricultural Soil Contaminated With Heavy Metal In Mercury Mine Area In Tongren,Guizhou Province

In this study,39 topsoil samples and 82 agricultural products(including rice,vegetables,egg,pork and fish)samples were collected from Siqian,and concentrations of heavy metals in topsoil and agricultural products were determined by atomic fluorescence spectrometry(AFS)and inductively coupled plasma-mass spectrometry(ICP-MS),respectively.The degree of topsoil polluted by heavy metals was evaluated with the single pollution index method,Nemerow comprehensive pollution index method and potential ecological risk index method,whereas the level of agricultural products pollution by heavy metals was assessed with the single pollution index method.The target hazard quotient(THQ)and hazard index(HI)were calculated to assess the potential health risk for residents in Siqian through consuming the local agricultural products.Moreover,a pot experiment was conducted to study remediation effect of agricultural soil contaminated by Mercury(Hg)and Cadmium(Cd)through different kind of Medicago sativa inoculated with rhizobium.Results from this study are summarized as follows:(1)The average concentrations of As,Cd,Cr,Cu,Hg,Ni,Pb and Zn in topsoil of Siqian are 6.64,0.34,39.35,15.60,5.40,26.00,27.89 and 70.03 mg/kg.According the single pollution index,Siqian soil is heavily contaminated by Hg and slightly polluted by Cd.The comprehensive pollution index varys from 1.02 to 73.68,and79.5% of soil sampling sites are heavily contaminated.Moreover,the mean of the comprehensive potential ecological risk index is 1439,and there exists strong ecological risk with heavy metals in soil of Siqian.Hg is the most important source of the ecological risk.(2)The main Hg form in soil from Siqian is residual Hg,accounting for 82.64%,Whereas the water soluble and exchangeable Hg is just accounting for 0.12%,thus,the Hg in soil form has low mobility and bioavailability.On the contrary,the main Cd form in soil from Siqian is the water soluble and exchangeable Cd with high mobility and bioavailability,accounting for 45.69%.(3)The average concentrations of Hg in rice,vegetables,pork,fish and egg are9.53,5.38,146.2,155.5 and 61.74 ?g/kg,whereas the average levels of Cd in rice,vegetables,pork,fish are 34.19,24.76,8.32,25.00 ?g/kg and the content of Cd in egg is below detectable limit.According to the single pollution index,some kinds of them are polluted to various levels by Hg and Cd.For Hg,Chinese cabbage and egg with a pollution index of 1.07 and 1.23 are slightly contaminated,pork with a pollution index of 2.92 is moderately contaminated and garlic spout with a pollution index of 3.27 is heavily polluted.For Cd,only pepper with a pollution index of 1.29 is slightly polluted.The HI for dietary Hg and Cd intake is 1.52,which indicated that consumption of these agricultural products from Siqian posed a potential health risk to local residents.The total diet THQ of Hg is 1.03,accounting for 67.8% to the HI.Hence Hg is the main component contributing to potential human exposure.(4)The results of the pot experiment indicate that rhizobium inoculation can increase remediation effect of agricultural soil polluted with Hg and Cd by Medicago sativa,through promoting Medicago sativa growth and uptake with Hg and Cd.Juneng 995 has the highest remediation effect for Hg and Cd.