Characteristics And Evaluation Of Heavy Metal Pollution In Farmland Soil Around A Tungsten Tailings Pond

The heavy metal pollution of soil caused by long-term storage of tailings has recently attracted more and more attention from NPC deputies.In this paper,40 soil samples and 8 rice samples were collected from farmland soil and rice around a tungsten mine tailings pond in Jiangxi Province,in which area we made analysis of pollution characteristics of Cu,Zn,Pb,Cd and As in soil-rice system.The chemical forms of five heavy metal elements in farmland soil were analyzed by BCR continuous extraction method,and the bioavailability of heavy metals was analyzed by bioavailability coefficient.Single factor pollution index,comprehensive pollution index and potential ecological hazard were used to evaluate the heavy metal pollution degree in the surrounding farmland soil of tailings.Many pathways such as single factor index,comprehensive pollution index and plant enrichment coefficient were used to evaluate the heavy metal pollution degree of rice in farmland,and Pearson correlation analysis method was used to analyze the correlation between heavy metals and explore the source of heavy metals in the soil-rice system.In this paper,it provided a certain theoretical basis for the subsequent treatment and restoration work of mine and tailings.The main research conclusions were as follows:(1)The concentration of heavy metals Cu,Zn,Pb,Cd and As in the farmland soil around the tailings pond was 64.79-193.54 mg/kg,73.93-228.64 mg/kg,97.43-198.14mg/kg,0.87-2.85 mg/kg and 35.82-54.95 mg/kg,respectively,The average content exceeds the soil background value of Jiangxi Province by 5.22 times,1.89 times,4.28 times,15.8 times,and 4.42 times respectively.According to the standard of soil environmental quality agricultural land risk control(test),the concentration of Cu,Pb,Cd,and As exceeded 2.13 times,1.96 times,5.27 times,and 1.15 times,respectively,The average concentration of Zn did not exceed the standard,and the heavy metal in all the farmland sampling sites exceeded the standard in the order of Cd > Cu > Pb > As.(2)The results of single-factor pollution index showed that the soil was seriously polluted by Cd and Cu.The farmland soil was also polluted by Pb,while slightly polluted by Zn and As.The comprehensive pollution assessment indicated that the soil heavy metal pollution around the tailings pond was serious,especially in thefarmland near the tailings.The potential ecological hazard evaluation indicated that the most important ecological hazard of the farmland around the tailings pond was CdThe potential ecological hazard evaluation indicates that the most important ecological hazard of the farmland around the tailings pond is the Cd in the five heavy metals investigated.(3)The results of continuous extraction of BCR showed that the morphology of Cd in farmland soil was mainly reducible and weak-acid,while other elements were mainly residual-state.The average bioavailability coefficient of each heavy metal were Cd(69.33%)> Zn(43.54%)> Pb(35.17%)> Cu(20.3%)> As(5.84%).Bioavailability coefficient of Cd was biologically effective and could cause potential harm to the soil-rice system and environment,so Cd should be paid sufficient attention.(4)The contents of Cu,Zn,Pb,Cd and As in farmland of rice ranged from 16.67-29.43 mg/kg,15.73-21.27 mg/kg,3.16-4.51 mg/kg,0.31-0.82 mg/kg,0.12-0.18mg/kg,respectively.The average values of Pb and Cd exceeded the national food standards by 18.9 times and 2.55 times respectively.The single factor pollution evaluation indicated that the rice were severely polluted by Pb and Cd.The comprehensive pollution assessment indicated that the rice in the farmland around the tailings pond were seriously polluted by heavy metals.The enrichment factor analysis showed that the enrichment ability of different heavy metals in rice was different.The enrichment ability of five heavy metals was Cd(32.07%)>Cu(22.1%)>Zn(15.06%)>Pb(2.85%))>As(0.324%).(5)According to the correlation coefficient analysis results showed that the original source of Cu,Zn,Pb,Cd and As in the soil were same from the tailings pond in the northeast direction of the farmland.There was a significant positive correlation between most heavy metals in soil and in rice.This indicated that heavy metals in soil may have similar sources or reason of forming.This homologous relationship would cause complex pollution of heavy metals.