Background Value And Enrichment Of Eight Heavy Metals In Soil Of Chongqing Metropolitian Area

Chongqing is China's youngest municipality,and also an important part of the upper reaches of the Yangtze River economic belt.As one of the old industrial bases in China,Chongqing has the obvious advantage of advanced manufacturing.However, the latest environmental quality monitoring shows that the environmental quality is not good enough in Chongqing economic zone.This paper investigates the distribution and geochemistry features of eight heavy metals(As,Cd,Cr,Cu,Hg,Ni,Pb,Zn) in the soil (shallow and deep) of Chongqing urban economic zone,and the main results are as follows:(1) The content of As in all of the formation in the study area is above the average level of the geosphere.The content of Cd in Upper Jurassic,Middle Jurassic and Triassic and that of Pb in Upper and middle Jurassic in original rocks of the study area are both higher than the average content of the geosphere.The content of other heavy metals is lower or equivalent.As a whole,compared with the average content of heavy metals in geosphere,that of the heavy metals in the study area has such a feature as there are more As,Cd and Pb,but less Cr,Cu,Hg,Ni and Zn.(2) The content of the eight heavy metals except As and Cu(except in triassic area) in deep soil is almost above the national average level.The content of all the eight heavy metals in top soil is much higher than that in the deep one.(3) The heavy metals content in original rocks,deep soil and shallow soil changes as follows:As,Hg,Zn and Pb,top soil＞deep soil＞original rocks;Cd and Cu,top soil＞original rocks＞deep soil;however,there is no evident rule for Cr and Ni.(4) Except Hg,all of the heavy metals content in top soil has significant positive correlation with the soil pH value,especially that of Cu,Ni and Zn.The content of Zn in top soil is most closely related to the increase of soil pH value,with Cr,Cu and Ni followed;and the content of As,Cd and Pb least increases with the soil pH value.(5) The content of Cu,Ni,Pb and Zn in the study area is the highest in yellow brown soil,and the same is true with the content of As,Cr and Hg in lime soil and that of Cd in brown soil.The content of As,Hg,Zn and Cu is the lowest in paddy soil,so is that of Cr and Ni in yellow brown soil,that of Cd in yellow soil,and that of Pb in lime soil.(6) The heavy metal congtent in top soil is related to the land types.The content of As and Hg changes significantly in different land types,following is the content of Cd, Cuand Zn;The content of Cr,Ni and Pb in top soil is even- distributed.(7) The heavy metal congtent in top soil is related to the landform.The content of As, Cd,Cr,Cu,Ni,Pb and Zn is higher in fold lifting low mountain than in other landforms.In valley plain,the content of Hg is the highest;Cr is the highest in erosion and denudation hilly region.(8) The single-factor pollution index evaluation of top soil shows the heavy metals pollution area Sequence is:Cd＞Pb＞Hg＞Zn＞Cr＞As＞Ni＞Cu..The Nemerow Synthetical Pollution Index evaluation shows that most parts of the study areas are slightly polluted.The heavily polluted areas lie in the northwest.We should take stonger measures to control pollution in study area.