Immobilization Of Toxic Metals In Soil And Its Ecological Risk On Farmland Surrounding Representative Tannery

More and more attention has been paid to soil pollution caused by tanning.In this study,The pollution characteristics and ecological risks of 8 heavy metals(Pb,Cd,Cr,Hg,Ni,Hg,Cu,Zn)in farmland surrounding a typical tanning enterprise were evaluated,by means of single factor index,Nemero index and potential ecological risk index were used.In addition,principal component analysis and geostatistical analysis are used to determine the distribution characteristics and sources of pollutants.The results showed that the soil in the study area was at a moderate ecological risk level,and the maximum value of the Nemero index was 10.97,which was considered as serious pollution.The order of the ecological risk of each metal element is: Hg > Cd > Cr > Cu > Pb > As > Ni > Zn;Analysis of surface soil samples in the study area revealed that only Cr(33.4-3830 mg/kg),Cd(0.11-0.42 mg/kg)and Hg(0.06-0.72mg/kg)exceeded the risk screening value specified in GB 15618-2018.The three heavy metals also accumulated in the profile soil(0-40cm).According to principal component analysis and geostatistical analysis,the sources of chromium in soil samples in the study area are different from other heavy metals.In this study,the content of heavy metals in brown rice was not significantly correlated with the concentration of total metals and the content of DTPA-extractable metals.After long-term aging and reduction under natural conditions,the chromium in soil in the study area could not be effectively extracted by DTPA and uptaked by plants.Clay minerals have been proposed as amendments for remediating metal-contaminated soils owing to their abundant reserves,high performance,simplicity of use and low cost.Two novel clay minerals,Maifan stone and illite/smectite clay,were examined in the in situ immobilisation of soil metals.The application of 0.5% Maifan stone or illite/smectite clay to field soils significantly decreased the fractions of diethylenetriaminepentaacetic acid(DTPA)-extractable Cd,Ni,Cr,Zn,Cu and Pb.Furthermore,the Maifan stone and illite/smectite clay treatments resulted in 35.4% and 7.0% reductions in the DTPAextractable fraction of Cd,respectively.Quantitatively,the Maifan stone treatment reduced the metal uptake in B.rapa ssp.Pekinensis,B.campestris and S.oleracea from 11.6% to 62.2%,4.6% to 41.8% and 11.3% to 58.2%,respectively;illite/smectite clay produced reductions of 8.5% to 62.8% and 4.2% to 37.6% in the metal uptake in B.rapa ssp.Pekinensis and B.campestris,respectively.In addition,the application of 0.5% Maifan stone and illite/smectite in soils did not significantly affect soil p H or the growth of the three vegetables,indicating that the two clay minerals had a negligible impact on the vegetable yield.Therefore,both Maifan stone and illite/smectite clay are promising amendments for contaminated soil remediation.