| Heavy metals not only pollute soil,but also groundwater and plants.Therefore,it is of great significance to carry out pollution status analysis,pollution degree evaluation,pollution source analysis,simulated rainfall leaching study on the areas contaminated by heavy metals to understand the rules of migration and accumulation of heavy metals,prevent the aggravation of heavy metals on soil,water and plants,and protect human health and land resources.In this paper,51 surface soil samples were collected from the farmland near Longtang lead-zinc mine in Yongxing Town,Panxi.The contents of Cr,Ni,Cu,Zn,Cd and Pb in the soil samples were determined by icp-ms.The routine physical and chemical properties of the soil samples were determined,and the data of the measured heavy metal content were analyzed and processed.The pollution degree of heavy metals in farmland was evaluated by single factor pollution evaluation and nemero comprehensive pollution index method.Secondly,the main sources of 6 heavy metals were analyzed by multivariate statistics.At last,the field leaching experiment was carried out on two typical soil profiles,Tk-01(perennial unsaturated soil)and Tk-02(seasonal saturated soil),by configuring the leaching solution under six different conditions to simulate rainfall,so as to study the vertical distribution of heavy metals in the two soil profiles under different leaching conditions.The following results were obtained:(1)The p H value of shallow groundwater ranges from 7.05 to 7.87,with an average value of 7.32.The total dissolved solid concentration(TDS)ranged from107.11 to 254.91mg/L,with an average value of 165.83mg/L.The EC values range from 267.20 to 572.10μS/L,and the average value is 407.56μS/L.(2)Except for Pb,the average content of the other five heavy metals all exceeded the national soil environmental quality level ii standard,and the average content of the six metals all exceeded the background value of heavy metals in sichuan soil.The order of variation coefficient of the six metals is as follows: Zn >,Cd,>,Cr,>,Ni,>,Pb,> Cu.The variation range of the six metals is 17% ～ 51%.The maximum variation coefficient of Zn is 51%.(3)According to the average value of single-factor pollution index of heavy metals in 6,the soil in the study area was contaminated with heavy metals to the extent of Ni >,Cd,>,Cr,>,Zn,>,Cu,> Pb.The maximum value of nemero pollution composite index was 5.87,the minimum value was 1.01,and the average value was3.03.On the whole,the soil environmental quality in the study area was seriously polluted.(4)Using principal component analysis,the six metal sources can be divided into two types: the first factor is closely related to Zn,Cd,Cu and Pb,with strong homology;The second factor is closely related to Cu,Ni and Cr.The Cu that appears in both factors may have a complex source,and both sources have the carrying of Cu.In the correlation analysis of 6 heavy metals,the correlation between Cr and Ni is extremely significant,with the determination coefficient only 0.371 < 0.4,indicating that the content of Cr is not only influenced by Ni,but also by other metals.The correlation between Pb and Ni and Cr and between Cr and Zn and Cd was not significant,showing a certain heterogenicity.(5)The leaching test showed that the release of heavy metals in the leaching process was divided into two stages.The first stage was rapid release.Before the cumulative leaching liquid reached 1500 ml,the heavy metal content in the leaching liquid was high,but the release rate was slow.(6)Tk-01(perennial unsaturated zone),the influence of the p H value of the leaching solution on the migration and accumulation of metal Cr was greater than that of the concentration of phosphorus application.The effect of simulated precipitation solution p H=7.0 on Ni migration and enrichment was more obvious up to 80 cm,while the effect of different phosphorus application concentrations on Ni migration and accumulation was not obvious.The migration and accumulation of Cu in six leaching solutions were not obvious.The influence of p H value on Zn was stronger than that of phosphorus concentration.The p H value of the leaching solution has a greater influence on the migration and enrichment of metal Cd.The influence of different p H values on Pb was similar to that of different phosphorus concentrations,and the migration and accumulation of the three p H values were greater.Tk-02(seasonal saturation zone),the influence depth of migration accumulation of metal Cr was similar under different p H values of leaching solution and phosphorus concentration.The influence of different phosphorus concentration on Ni migration accumulation was stronger than that of different p H values.The influence depth of six leaching solutions on Cu migration and accumulation was up to 100 cm.The influence of different phosphorus concentration on the migration and accumulation of Zn was deeper than that of the leaching solution with different p H values.The influence depth of six leaching solutions on Cd migration and accumulation was up to 100 cm.The influence depth of six leaching solutions on Pb migration and accumulation was up to50 cm.(7)The cumulative release amount of heavy metals in the perennial unsaturated zone was more significantly affected by the leaching solution with different p H values,and the cumulative amount of Cr,Ni and Cu was higher than that of the seasonal saturated zone,while that of Zn,Cd and Pb was lower than that of the seasonal saturated zone.Under the leaching conditions with different phosphorus concentrations,the accumulations of the six metals in the perennial unsaturated zone were all lower than those in the seasonal saturated zone,and the accumulations of the six heavy metals in the perennial unsaturated zone increased with the increase of the concentration of phosphorus application.Under this condition,the six heavy metals in the seasonal saturated zone were more likely to lose by leaching than those in the perennial unsaturated zone. |
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