Vertical Distribution Of Heavy Metals And Their Potential Ecological Risk Assessment In The Agricultural Soil Of The Peri-urban-Area

In order to deeply understanding of the contamination and vertical distribution characteristics of heavy metals in the farmland soil of the Peri-urban-Area in the Eastern Suburbs of Kaifeng, providing reference for blocking of heavy metals in the soil vertical migration behavior and protection of groundwater quality and safety by analyzing of the migration of heavy metal elements in the vertical direction.The eastern outskirts of the industrial agglomeration area in Kaifengas the study area, on the basis of field investigation,selecting P1?near to the Huafei River? and P2?Huafei River and chemical fertilizer plant interaction polluted area? and P3?control area? three sample areas, collected a total of 13 soil profiles,280 soil profile samples.ICP-MS was used for the determination of Cd, Cr, Pb, Ni, Cu and Zn six kinds of heavy metal content, Tessier extraction method were used to study the chemical forms of the heavy metal element based on, also also physicochemical properties of soil were analyzed. Based on characteristics of vertical distribution of the form and the total amount of heavy metal elements in the study area and its influencing factors, and vertical changing characteristics of the potential ecological risk of Kaifeng in the eastern outskirts of the farmland soil heavy metal pollution was analyzed based on improved Hakanson potential ecological risk index method in the evaluation.This paper is in divided into five parts:Part ?:Pollution status of agricultural soils at home and abroad and its research progress. This partis about the research background and significance, the status of heavy metal pollution, source, the research progress of the vertical migration of heavy metals in soil profile and the evaluation methods of soil pollution. At last, it points out the innovation and characteristics of this research compared with the previous research.Part ?:Study area survey and sample collection and analysis test. This part first briefly introduces the natural situation of the study area and water and soil pollution status, and then focuses on the sample collection program, and finally focuses on the research of the test analysis methods and process control.Part ?:Results and analysis. First on the pollution characteristics of heavy metals in the surface soil of the study area are analyzed, then focuses on the analysis of the total metal concentrations and speciation in soil profile in vertical distribution characteristics, then, combined with the soil physical andchemical properties and comparative analysis method to explore the influencing factors of the vertical distribution of heavy metals in the study area, finally, based on the improved Hakanson potential ecological risk index method of typical samples of soil pollution status to carry out assessment of potential ecological risk.Part ?:Come to conclusion. By the results of the third part analysis obtained in the study area is not the same area soil heavy metals and its forms of vertical distribution characteristics, clear vertical movement of heavy metals in the influence factors, revealing the kinds of vertical heavy metal potential ecological risk degree.Part ?:Conclusion. Points out the shortcomings of this paper and the need to continue to study the contents and thanks.The main conclusions of this study can be summed up as follows:?1?Through the study of staggered characteristics of heavy metal pollution in the agricultural surface soil ofthe Eastern suburb of Kaifeng city,Cu,Cd, Pb and Zn occurred accumulation phenomenon and the content exceeded the fluvo aquic soil background value int he agricultural surface soil, and Cr and Ni content in surface soil layer were lower than fluvo aquic soil background values.Among them, the heavy metal pollution index of Huafei River sewage irrigated soil in order from high to low: Cd?13.86? >Pb?2.76? > Zn?2.49? >Cu?1.67? >Cr?0.73? >Ni?0.61?, the pollution degree of Cd reached the severe pollution, the pollution degree of Pb, Zn elements to moderate pollution, Cu element pollution to light pollution; heavy metal pollution index of Huafei River and surface mining enterprises interaction contaminated soil from high to low is that: Cd?38.93? > Zn?10.83? >Pb?3.39? >Cu?2.17? >Cr?0.80? >Ni?0.69?,the pollution degree of Cd, Pb, Znreached the severe pollution, and Cu pollution degree to moderate pollution; heavy metal pollution area in surface soil from high to low is that:?2.48? Cd > Zn?1.40? >Pb?1.21? >Cu?1.19? >Cr?0.73? >Ni?0.67? and Cd pollution degree to moderate pollution,the pollution degree of Pb, Zn and Cu is to light pollution. Huafei River sewage irrigated area surrounding agricultural soil by four kinds of heavy metals?Cu, Pb, Zn, Cd? pollution, compared to the cross contamination zone and the Huafei River sewage irrigation area, except by sewage irrigation of heavy metals, but also by the industrial and mining enterprises emissions of the heavy metals pollution?Cd, Pb,Zn, Cu?.?2? through the study on vertical distribution of heavy metals in the agricultural soil profile ofthe Eastern suburb of Kaifeng city,when there existenough heavy metals?Zn, Cu, Cd and Pb?, there exist obvious surface aggregation phenomenon, the lower layers of the soil heavy metal content will decreased first and then tend to be stable, often in the surface soil?0¹0cm? heavy metal content in section maximum, in the soil?10⁴5cm? of dropped sharply soil changes of heavy metal contents in the stabilized and smaller than the background value. Cr, Ni were less affected by the impact of exogenous pollution or not affected by exogenous pollution, Cr, Ni two kinds of heavy metals in the soil distribution is not obvious regularity.The main pollution factor in the agricultural soil ofthe Eastern suburb of Kaifeng city is Cd, the content of Cd in the soil?0¹5cm? of sewage irrigation area reached 1.62mg·kg^-1,exceed the soil environmental quality standard, the content of Cd in the soil?16⁴0cm? depth increase substantially reduced, the content of Cd in the soil?40¹10cm?is near 0.13mg·kg^-1.The content of Cd in the soil?0²5cm? of the interactive pollution area exceeded the soil environmental quality standards, which in the soil? 0¹5cm? Cd is mean to 4.47mg·kg^-1, to achieve the Cd, the average content of soil 16³0cm average values of Cd content1.40mg·kg^-1,the soil?31⁴5cm? for the average content of Cd element 0.34mg·kg^-1,10⁴5cm soil with depth increase sharply, in 45¹10cm in soil Cd elements in uniform, in the average value of 0.17mg·kg^-1float near. Control the average content of the soil?0¹10cm? in all soil Cd were all lower than the secondary standard of soil environment quality, average concentration of Cd in the soil?0-10cm? reach0.33mg·kg^-1, average content of Cd in the soil?11²5cm?is 0.18mg·kg^-1, the content of Cd in the soil?31³5cm? appeared peak 0.23mg·kg^-1, which may due to soil Cd downward migration or soil tillage caused and the rest of the soil in the content of Cd in uniform, in the average 0.13mg·kg^-1 near the floating.?3? through the study of staggered farmland soil heavy metals in the distribution of the eastern suburbs of urban and rural analysis of the Cd element in the sewage irrigation mainly in residual form?11.10%⁶9.97%?, Fe Mn oxide?1.51%¹6.14%?, carbonate bound?8.88%⁴6.49%?, ion exchange state?5.79%⁵3.72%? existed mainly in residual Zn elements state?38.78%⁹4.84%?, organic bound?3.78%²0.01%?, Fe Mn oxide?0.03%²4.81%? is in the form of Cu, Pb and Ni elements mainly in residual and organic bound and Fe Mn oxide, carbonate bound form, Cr elements mainly in residual form?62.03%⁸8.63%?, organic bound?2.58%¹3.56%?, ion exchange state?3.34%²0.85%? exists in the form of.Cd of Huafei River Industrial and mining enterprises cross contamination zonemainly to carbonate and residual state?28.10%⁷1.44%? and iron manganese oxidation state 2.74%¹3.40% binding state?14.16%²7.71%?, ion exchange state?5.52%⁴2.70%? existence, Zn, Pb, Ni and other elements mainly in residual fraction, organic bound and Fe Mn oxide bound and carbonate combined forms exist Cu mainly in residual fraction?58.62%⁹1.18%? organic bound 1.25%²9.32%, iron and manganese oxidation state?3.19%¹2.97%? and Cr mainly to ion and residual state?50.22%⁸4.40%? exchange state?6.76%³0.81%? exist.Cd of control area mainly to carbonate and residual state?44.01%⁷4.19%? combined with state?12.51%²1.79%?, ion exchange state?5.04%¹8.67%? existence, Cu and Zn exists mainly in residual form, bound to organic matter in the form of, Pb, Ni and other elements mainly in residual state, combined with state machine, iron and manganese oxidation state, carbonate combined forms exist and Cr mainly to ion and residual state?76.12%⁸6.52%? exchange state?7.63%¹8.54%? exist.Except for residual state, the percentage content of the main form of four kinds of heavy metal elements?Zn, Pb, Cu, Cd? showed in the soil surface layer is the highest, then decreases with the increase of soil depth gradually decreased, and then tends to be stable, the variation trend of each heavy metal in the soil profile in the change trend of the total similarity, percentage content of all forms of Cr and Ni in the soil profile has no obvious trends.?4?Research and analysis of factors affecting by means of Kaifeng in the eastern outskirts of the peri urban area of farmland soil heavy metal content of the vertical distribution of soil p H and Cd, Pb, Cu, Zn, Cr five kinds of heavy metals was significantly negatively related to organic matter and Cu, Zn, Cd, Pb, Cr 5 kinds of heavy metals showed a certain degree of positive correlation, Ca CO3 and Cu, Zn, Cd, Pb four kinds of heavy metals was significantly negatively correlated with soil sand and Ni showed a significant negative correlation, Fe, Mn and Cr was significantly positively correlated with Ni showed significant positive correlation.Soil physical and chemical properties on heavy metals content distribution influence factors include: Cd ion exchange state and Ca CO3 was negatively correlated, and organic matter was positively related; Cd carbonate bound state and soil silt was positively related, and soil sand was negatively correlated; Cd of iron and manganese oxidation state and p H and Ca CO3 was negatively correlated with organic matter was positively related. The ion exchange state of Zn was negatively correlated with p H, and the was positively correlated with Fe, and the carbonate bound state of Zn was negatively correlated with Mn and p H elements. All the forms of Zn were negatively correlated with Ca CO3 and positively correlated with organic matter. The organic binding state of Cu was negatively correlated with p H and Ca CO3, and positively correlated with the organic matter and Fe element. The carbonate bound state of Ni was negatively correlated with p H, organic matter and Fe elements, and Ca CO3 was positively correlated with Ni; the organic binding state of was positively correlated with organic matter and soil sand grains, and negatively correlated with Ca CO3 and soil clay. Pb bound to organic matter and p H is negative correlation,and organic matter, Fe and Mn were positively related; carbonate Pb binding state was positively correlated with the organic matter, and Ca CO3, soil sticky grains were negative correlation; Pb of iron and manganese oxidation state and Ca CO3 was negatively correlated with organic matter was positively related. The organic binding state of Cr, Fe Mn oxidation state were negatively correlated with p H and Ca CO3, and positively correlated with organic matter. The carbonate bound state of Cr was negatively correlated with sand and Mn elements. The carbonate bound state of Ni was negatively correlated with p H, organic matter and Fe elements, and Ca CO3 was positively correlated with Ni; the organic binding state of was positively correlated with organic matter and soil sand grains, and negatively correlated with Ca CO3 and soil clay.?5? through the transitional of Kaifeng in the eastern outskirts of the urban and rural farmland soil; heavy metal; potential ecological risk assessment, in the study area, Zn, Cr, Pb, Cu, Ni five kinds of heavy metals in the soil profile risk index are lower than the 17.091, belonging to a slight degree of risk. The main potential ecological risk factorurban and rural eastern suburbs of Kaifeng staggered farmland soil is Cd, the in surface soil of ecological risk index in the strong degree of risk, ecological risk index of Cd in the eastern outskirts of Kaifeng urban and rural staggered farmland topsoil between 409.819¹021.74, the Huafei River sewage irrigated soil surface in between 208.745⁵58.418, in the cross contamination of soil surface in between 650.90¹613.03, belong to strong degree of risk; and in the control soil surface area in48.369¹05.386 between, belongs to the medium risk level and the strong degree of risk. Six kinds of heavy metals of integrated ecological risk index in the eastern outskirts of Kaifeng urban and rural staggered farmland topsoil in 434.438¹063.973 between, in the Huafei River sewage irrigated soil surface in between 228.654⁵90.739, in the cross contamination of soil surface in between 681.110¹668.971,belong to strong degree of risk; and in the control soil surface area in 65.131¹25.545 between, belongs to the medium risk level and the strong degree of risk.The study area and plots in soil ecological risk index?E? of Cd and the integrated ecological risk index?RI? of Zn, Cr, Pb, Cu, Ni, Cd in the vertical upward showed in the soil?0⁴5cm? with soil depth increasing reduction, keeping stable values in the soil?46¹10cm?, and the changes of the content of Cd in the soil profile variation trend of similar.