Characteringzing Non-point Source Heavy Metals' Pollution Andthe Effects Of Acid Rainin Urban Village Of Shenzhen

This research investigated 6 heavy metals(ie.Pb,Cr,Mn,Cu,Znand Ni)in urban village of Shenzhen,and heavy metals' pollution of non-fixed sources(Road-deposited Sediments)and fixed sources(external wall surface of buildings)affected by typical acid rain.Additionally,characteristics of heavy metals' distribution in runoff and river were analysied and an evaluation for primary sources of dissolved and particulate heavy metals influenced by acid rain was carried out in this study.In the labortary-scale desorption of heavy metals non-fixed source(influenced by runoff)influenced by acid rain,Mn and Zn presented sensitivity to extreme pH(pH=3.0).However,there was no great difference when pH was higher than 4.0.Particle size had played an important role in heavy metal desorption,which was found that the larger particle size,the higher dissolved ratio.The dissolved ratio of heavy metals decreased in the order of Industrial > Residential > Commercial,which was possiblely influenced by organic matter.The highest dissolved loading for all metals combined was found in the <75 ?m fraction in industrial and residential areaunder general acid rain(pH 4.0-5.6),while the highest dissolved loading for all metals combined was found in the 150-300 ?m in commercial area.The research outcomes also indicated that >150 ?m RDS contributed 50% of the total soluble heavy metals at pH 4.0-5.6.Fixed source(external wall surface of buildings)also produced heavy metals' desorption under acid rain in the labortary-scale.It was found that A paint with potential heavy metal pollution was worst,followed by black cement,white cement and B paint.Heavy metals' desorption from the four kinds of material went through two stages: the early desorption stage and steady desorption stage.The main heavy metal dissolved from fixed source materials were Mn and Zn,and desorption of Zn was higher than Mn.In addition,total dissolved loading of Zn and Mn from fixed materials was pH-dependent.It is also found that average annual total dissolution loading decreased between 30% and 85% from pH 3.0 to 7.0.This research also monitored urban river water quality in urban village and found that the end of river was polluted with heavy metals.Mn was the most polluted element,and its concentration was worse than the quality specified in the III class of surface water quality standard(GB3838-2002),in 70% events.In terms of solubility,Mn was most sensitive to pH in river,because the dissolved proportion of Mn in spring and summer was no more than 30% compare to the proportion of over 65% in acid rain season(fall and winter).Zn represents the most abundant anthropogenic pollution in the river.The highest concentrations of Zn was in the summer,suggesting that fixed source area could continue to produce zinc non-point source pollution.So,dissolved part of Zn in same position of river was relatively stable.In the evaluation of dissolved amounts of heavy metals from a typiacal rainfall,it is observed that fixed materials were the primary source for dissolved part of heavy metals,especially for Mn and Zn,while suspened solids were particulate part of heavy metals.So,to control the desorption of heavy metals from fixed source is able to reduce the amounts of dissolved heavy metals affected by acid rain in urban village area.