| Dingjiashan lead-zinc mining area in Youxi of Fujian Province was selected in this study,in order to control the heavy metal pollution of siol and use the contaminated cropland safely,the stuy based on the problem of soil heavy metal pollution existed in the proceeding of mining,through sample surveys in large region and geostatistical analysis,assessed the spatial variation of heavy metals and pollution conditions of the cropland around the mining area.According to the assessment results,the crops which ware growing in the cropland of the mining area were collected on purpose,the concentration capacity of heavy metal in different crops and the security of agricultural products were assessd systematicly.Then,combinated the results of soil pollution assessment and the security of agricultural products,came up with a plan which divided the cropland of the mining area into different zones that can make people use the polluted soil safely.The study results showed:(1)Mining tailings,diffusion and deposition of smelting dust which produced by the mining of lead-zinc mine,and the waste water of mining which was used to irrigate the cropland had polluted the soil of the mining area seriously.The pollution of lead(Pb),zinc(Zn)and cadmium(Cd)was more serious among the heavy metals that had been investigated,the maximum content reached 2470 mg/kg,1460 mg/kg and 5.70 mg/kg respectively,they all exceeded the permissible limits of China standard seriously.In addition,the contents of copper(Cu)and chromium(Cr)was relatively lower,and the contents of mercury(Hg)and arsenic(As)were lower than the permissible limits of China standard.The spatial variation characteristics of the heavy metals in the cropland soil showed like this:the contents of Pb,Zn,Cd in the vicinity of the mining mouth were higher than that of the distant place,the contents of heavy metals of the soil samples which were collected in the downstream were higher than that in the upstream,and the regions which were on the sides of the small ditch through which the mining waste water flowed had higher contents of heavy metals.The suty resulted that the heavy metals such as Cu,Pb,Zn and Cd which were brought by the mining of lead-zinc mine was the main reason of the pollution in the cropland of the mining area.(2)The mean of single-factor pollution index of Cu,Pb,Zn,Cd,Cr was 2.48,4.29,3.45,7.69 and 0.66 respectively,the mean of Nemerow comprehensive pollution index was 6.3,and the pollution extent of different elements was in this order:Cd>Pb>Zn>Cu>Cr.Almost 1/3 of the cropland was polluted by Cu,and the area of the region that was polluted slightly was largest;Nearly 2/3 of the cropland was polluted by Pb,and the area of the region that was polluted severely was largest;More than 2/3 of the cropland was polluted by Zn,and the area of the region that was polluted moderately and severely was larger;Pollution of Cd in the cropland of the mining was the most serious,and the total area of the region that was polluted moderately and severely was account for 87%of the whole cropland;the pollution extent of Cr was the lightest,only 3.19%of the cropland was polluted slightly.Most of cropland was polluted by several heavy metal elements compound,the area of the region that was polluted severely took up 75.5%of the cropland,and the area of the region that was polluted moderately took up 16.18%of the cropland.The data indicated that the cropland in the mining area was polluted by heavy metals seriously.(3)The test of the crops which were collected form the cropland in the mining area showed that they had been polluted by heavy metals in different degree,among which the pollution of Pb was the most serious,then Cd and Cr,and Cu and Zn were unaffected basicly.The order of pollution extent of different types of crops was as follows:leaf vegetables>rhizomes>solanaceous vegetables>beans>cucurbits;between two types of grain,the pollution index of rice was higher than corn.The concentration factors of the edible parts of crops about Cd,Cu,Zn were higher than Cr and Pb.The risk of Cd was higher in leafe vegetables and root crops,the security of maize,cowpea,eggplant and other 6 kinds of crops was higher to Cd.The risk of Pb is higher in rice and leafe vegetables,and pepper was the only kind of crop that was safe to Pb.The contents and concentration factors of Pb and Cd were lower in squash,cucumber,towel gourd,pepper,cowpea and string beans,and these crops had a strong tolerance to the soil which was contaminated by Pb and Cd,and the edible part of them were more safe.(4)According to the pollution types of Pb and Cd in soil and the risks of different crops about Pb and Cd,the varieties of crops which were suitable to be planted in specific polluted area were listed.In order to use the contaminated soil safely,the cropland in the mining area was divided into 14 categories of planting area,in which the areas of 8th category(the area which was polluted by Pb slightly,and polluted by Cd severely),the 11th category(the area which was polluted by Pb moderately,and polluted by Cd severely)and the 14th category(the area which was polluted by Pb and Cd severely in both)were larger and accounted for 76.39%of the total area of the cropland,and in these zones the soil was polluted by Pb and Cd more seriously,the crops,such as cucurbits,beans and solanaceous vegetables,which have a lower risk can be planted in these area.(5)According to the pollution types and extent of heavy metals,the results of security evaluation of the crops and safe use zoning of the cropland in the lead-zink mining area,the following strategies were listed in order to use the cropland safely:First,to carry out environmental publicity and improve the environmental awareness of the public;Second,strengthen the monitoring and management of mining waste water,and forbid the waste water to be discharged directly;Third,To irrigate and fertilizer the cropland scientifically,and prevent the soil from being polluted any more;The last,zone the planting area reasonable,and use the polluted cropland of the mining area safely. |
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