A Study On Migration And Enrichment Of Heavy Metals In Soil And Their Ecological Effects In Chongqing Metropolitan Area

The study of heavy element pollution in soil is one of focus and most important researches in environmental science,agricultural geology,eco-chemistry and applied chemistry.1772 surface soil samples and the deep soil samples were gathered,and four typical polluted areas to gather 7 different plants and their root soil samples were selected,and the contents of As,Cu,Zn,Pb,Cd,Hg,Cr,Ni in soil,plants, root soil and stones were analyzed and tested.According to data statistic and space analysis,the article study the heavy metals distributed characteristic in soil environment of Chongqing metropolitan area and to summarize their enrichment disciplines,using three different indexes and integrating national soil environmental quality standard to evaluate the soil quality of Chongqing metropolitan area.Based on the research result,giving suggestion to the structure of land using,industry adjusting and soil protesting and pollution control.The main conclusions of study show following:(1)According to mathematics statistics to 440 deep soil samples of Chongqing metropolitan area,proposing the background contents of heavy metals completely in this area in the first time.As is 5.819ug/g,Cd is 0.133 ug/g,Cr is 76.140 ug/g,Cu is 23.830 ug/g,Hg is 0.053 ug/g,Ni is 30.648 ug/g,Pb is 25.480 ug/g,Zn is 75.837 ug/g.(2)Discovering enrichment coefficients of the content of six heavy metals,As,Cu,Zn,Pb,Cd and Hg,in surface soil to deep soil are over 1,which demonstrates that these metals been effected from outside migration.The enrichment coefficients of Cd and Hg are over 2.2 and 1.5,showing that the effecting from outside environment is strong.The degree of Cr,Ni in surface soil is low.(3)According to the result of research,the distribution of some heavy metals in surface soil affects by stratum influence obviously.The content of As in Triassic stratum is higher than other stratums.(4)According the research to the correlation between the element contents and heavy metals in soil,the enrichment of heavy metals has related to some elements.It is significant positive correlation between U and As,Cd,Zn,Cr,Hg,Ni,Pb.The distribution of U is close to many heavy metals in soil.(5)The relationship between pH and heavy element contents in soil has some rules.There are two modes between pH and heavy element contents in soil while the pH is 4 to 9.The first one is Aerofoil Mode,that is the heavy element content appear the peak or the least value in the extent.The other is Growing Mode,that is the content of heavy metals grow while the pH value growing.As,Cd,Cu,Hg,Pb and Zn belong to Aerofoil Mode and Cr,Ni belong to Growing Mode.The heavy element content in soil is higher than other extents while the pH value from 7 to 8.The weak alkaline soil main locates city subdivision and the area near banks of Yangtze River in Chongqing metropolitan area.(6)The relationship between the heavy metals distribution and altitude is closely. The heavy element content is trend to increase while the altitude is rising.There are two different distribute modes:Wave Mode and Flat Mode.As,Pb,Hg belong to Wave Mode and Cd,Cr,Cu,Ni,Zn belong to Flat Mode.The elements distributions, which belong to Wave Mode,are sudden change to geological background.That is be turbulent by the input or output from outside in some height.The elements distributions,which belong to Flat Mode,are continuous change from geological background,and that is low effect from manpower or outside resources.(7)According to data analysis and space integrated for 1772 surface soil samples from Chongqing metropolitan area and comparing the national soil environmental quality standard,the evaluation result shows that the pollution of Cd and Hg is seriously.The two elements are the most pollution in eight heavy metals and the pollution is area shape.83.97%samples in all are polluted by Cd,and the pollution rates of Cr,Pb,Zn are 13.32%,13.77%,13.32%.The complex evaluation result by Nemerow Index,Geoaccumulation Index and Potential Ecological Risk Index,the clean soil main locate Jielong-Shentong-Daguan region,Lingfen and western Beibei. There are heavy or middle pollution by complex heavy metals in Jindaoxia and Baishiyi.(8)In the four typical polluted areas of Chongqing metropolitan area,the ability of enrich heavy metals is stronger than other plants.The pumpkin is security,which enrich heavy metals ability is low.The Complex Security Risk is high in swamp cabbage in Jinkou,rice in Baishiyi and potato in Wangjiachang.It is ought to warn and void in agriculture industry structure.(9)Because of the accumulated effect of heavy metals in human body,based on the formula of Nemerow Index,the article proposes Complex Security Risk Index of crops and the evaluation method to it in the first time.It makes the crop quality to different levels.According to the study of enrich different heavy metals from the soil. The different plants enrich different heavy metals are different.Based on this factor, the result shows that it is ought to avoid culture Sweet Potato and Swamp Cabbage in high content of Cr soil.Though the content of heavy metals in rice seed is lower than the national standard,based on the physiological enrichment function to heavy metals, it is ought to avoid culture rice in high content of Cd soil as much as possible.And the Complex Security Risk Index of potato being cultured in high content of As soil is low.(10)Using the research result of geochemistry,the article proposes the extend directions of city subdivision of Chongqing in the first time.The direction of North East is the priority extend direction,the South West is the second priority extend direction,the North West is requirement limited direction,and the South East is limited direction.The Jielong,Shentong,Daguan and Lingfen region can be priority to develop green food and to establish the bases of green industry for the Vegetable Basket Project.(11)Based on analyzing the pollution strength and space characteristics of the heavy metals in soil of Chongqing metropolitan area,the article divides three different prevention and cure areas in the metropolitan area.The different areas are the Clean Protecting Area,Pollution Resource Control Area and Pollution Eliminate Area.The prevention and cure measures are different to different areas.The complex measure is to control the pollution emission,and to reduce the migration of heavy metals from high content areas,and to start ecological govern in agriculture area,and to protect clean soil avoiding pollution from outside environment.