Pollution Characteristic And Accumulation Of Heavy Metal In Lead-zinc Mining Area In South China

A large number of heavy metal-rich gas,waste water and waste were easily being produced in the process of Lead-zinc mining exploitation and smelting.In natural condition,the heavy metal was difficult to be degraded and transformed.It can only be migrated and enriched when accumulated to a certain extent,which is toxic to organisms,and even threaten to human health.To date,the study on heavy metal pollution of mine was mainly focused on certain pollution source or single system of soil,plants,river water,atmospheric deposition;however,the regularity of heavy metal pollution in different functional areas was rarely reported,especially the migration regularity of heavy metal in various systems such as soil,plants,atmospheric depositon and river water.Therefore,indentifying the space-pollution characteristics and the regularity of migrationand accumulation of heavy metal in different functional areas of mine ore area are critical for establishing pollution warning system and strengthening the supervision of the government.In this paper,we selected the Southern typical lead-zinc mine,Youxi Lead-zinc mine ore,as research subject.The soil,atmospheric deposition,plants and river water from four major functional areas including tailing area,mining area,abandoned area and smelting area were surveyed,and the content of heavy metal(Cd,Pb,Zn,Cu,Cr)and chemical form of samplings were detected.The spatial analysis software,Surfer8.0 and Statistical software,SPSS were used to analyze the pollution characteristics,distribution,transformation,migration and accumulation ofheavy metal in different functional areas.The main results were as follows:(1)The heavy metal in soil showed various accumulation characteristics in Youxi Lead-zinc ore,the average content of Cd,Pb,Zn in soil all exceeded National Soil Environment Quality Standards Grade ?,reached the standard value 9.23,1.85,1.34 times.The distribution of Cd,Pb,Zn,Cu from different functional are all as follows:Abandoned smelting area>Mining area>smelting area>tailing area,The distribution of Cr as follow:Abandoned smelting area>Mining area>smelting area>tailing area.Coefficient of variation range was 19%-214%.Most area had reached a high degree of variation,an the correlation between different heavy metal had reached extremely significant level(P<0.001)showing high homology of pollution.Morphological analysis showed that Cd had the highest weak acid extractive form and Cu has the largest proportion of exchangeable form,while Pb,Zn,Cr mainly in residual form.(2)The average content of heavy metals in wet atmospheric deposition was as follows:Zn(309.91?g/L)>Pb(128.65?g/L)>Cu(96.45?g/L)>Cr(91.64?g/L)>Cd(1.61?g/L).The Pb and Zn has exceeded up to 2.56,1.82 times of surface water environmental quality standard(GB 3838-2002)Grade ?,while Cd,Zn,Cu did not exceed the reference standards.In addition,the result showed that there are significant correlationship among five heavy metals.Besides,the distribution of heavy metal in in wet atmospheric deposition was also presenting an obvious seasonal differences:Fall>Spring>summer,and another feature of the distribution of heavy metal in Lead-zinc ore is "high" in the northwest and "low" in the southeast.(3)In this study,18 families and 26 species plants in total were collected to analyze the difference of content of heavy metal in these plants.The result showed that Pteris multifida Poir has accumulated the most Cd,Zn,Cu and Cr.The maximum content of Pb was found in the Phragmites australis,reaching 1182.93 mg/kg,which has strong ability on Pb transportation from the root to the shoot.In addition,the maximum transportation capacity of Cd,Pb,Zn,Cu,Cr,were Pteris multifida Poir(1.87),Phragm ites australis(6.16),Pteris multifida(2.82),Rosa laevigata(2.65),Stenoloma chusanum(2.81),respectively.Transfer coefficient TF were all greater than 1,so they can transport more heavy metal to the aerial parts of plants.(4)The average content of Pb in river water had exceeded 2.3 times of the surface water environmental quality standard(GB 3838-2002)Grade ?,and exceed-rate reached 93.75%;however,the other elements did not exceed the reference standards.The distribution of Cd showed that Huakou river>Qili river>middle region>Xiekeng river>downstream region>upstream region.The distribution of Pb showed Huakou river>Xiekeng river>middle region>Qili river>downstream region>upstream region,while the distribution of Zn,Cu,Cr was not significantly changed(P>0.05).(5)The migration flux of heavy metals in lead-zinc ore from soil ecosystem to river ecosystem were as follows:Cd 0.12 mg/m2?Pb7.808mg/m2?Zn13.096 mg/m2?Cu3.424 mg/m2?Cr3.336mg/m2.The deposition flux of Cd,Pb,Zn,Cu,Cr from atmospheric ecosystem to soil ecosystem were 2.544 mg/m2,201.281 mg/m2,490.968 mg/m2,149.375 mg/m2 and Cr 141.173 mg/m2,respectively.The existing cumulative flux of soil heavy metals in the mining area were Pb2.16× 105 mg/m2?Zn1.26× 105 mg/m2?Cr2.19× 104 mg/m2?Cu2.78× 103 mg/m2?Cdl.97× 103 mg/m2.The annual increment cumulative flux of Cd,Pb,Zn,Cu,Cr in soil ecosystem wereCd 2.424 mg/m2,Pb193.473 mg/m2,Zn476.872 mg/m2,Cu45.951 mg/m2,Cr137.847 mg/m2,respectively.Thus input-speed of heavy metals through atmospheric wet deposition was more quickly than output-speed by river.As a result,heavy metal will be accumulated in the soil.