Distribution, Chemical Speciation, and Environmental Risk Assessment of Heavy Metals in Tailings Soils near Dexing Copper Mine, China

To complement information of heavy metals' distribution, chemical speciation, activity and environmental risks in agricultural soils surrounding tailings, a total of 16 samples obtained from the 4 # tailings site of Dexing copper mine of China were investigated. The total concentrations of heavy metals Zn, Fe, Cu, Pb, Cd, Cr, Hg, As, Mn, Ag, Co, and Ni were determined by inductively coupled plasma-atomic emission spectrometry. Chemical speciations of Cu, Cd, and Zn were investigated with the procedures recommended by Tessier(1979). Two different assessment approaches (GB 15618-1995 and risk assessment code, RAC) were employed to estimate heavy metals' environmental risks. Results indicated that heavy metals, especially Cu and Cd were in high levels of accumulation in these samples. Chemical speciation analysis results revealed that Cu was mainly in organic matter bound fraction (ORG) and residual fraction(RES), and Cd was predominantly in exchangeable fraction(EXC), while Zn appeared mainly with the RES fraction. Environmental risk analysis results showed that Cd was in "heavy" pollution level (classification Ⅲ) in almost all samples, which may exert "high" or "very high" environmental risks. Whereas, for Cu, one fourth samples showed "heavy" pollution level, but were located in "low" or "medium" environmental risk ranks. For Zn, many samples were grouped in "light" pollution level (classification Ⅱ), but were related to "medium" and "high" environmental risk ranks. These results indicated heavy pollution and high environmental risk of Cd in soils surrounding the 4# tailings site, which should be paid more attention to. Meanwhile, for Cu and Zn, the contrary results obtained by different environmental risk assessment approaches, may suggest that a more scientific, adequate environmental risk assessment criterion should consider both total content and chemical speciation activity of heavy metals.

To complement information of heavy metals＇ distribution, chemical speciation, activity and environmental risks in agricultural soils surrounding tailings, a total of 16 samples obtained from the 4 # railings site of Dexing copper mine of China were investigated. The total concentrations of heavy metals Zn, Fe, Cu, Pb, Cd, Cr, Hg, As, Mn, Ag, Co, and Ni were determined by inductively coupled plasma-atomic emission spectrometry. Chemical speciations of Cu, Cd, and Zn were investigated with the procedures recommended by Tessier（1979）. Two different assessment approaches （GB 15618- 1995 and risk assessment code, RAC ） were employed to estimate heavy metals＇ environmental risks. Results indicated that heavy metals, especially Cu and Cd were in high levels of accumulation in these samples. Chemical speciation analysis results revealed that Cu was mainly in organic matter bound fraction （ORG） and residual fraction （ RES）, and Cd was predominantly in exchangeable fraction （EXC）, while Zn appeared mainly with the RES fraction. Environmental risk analysis results showed that Cd was in ＂heavy＂ pollution level （ classification m ） in almost all samples, which may exert ＂high＂ or ＂very high＂ environmental risks. Whereas, for Cu, one fourth samples showed ＂heavy＂ pollution level, but were located in ＂low＂ or ＂medium＂ environmental risk ranks. For Zn, many samples were grouped in ＂light＂ pollution level （ classification II ）, but were related to ＂ medium＂ and ＂ high＂ environmental risk ranks. These results indicated heavy pollution and high environmental risk of Cd in soils surrounding the 4# tailings site, which should be paid more attention to. Meanwhile, for Cu and Zn, the contrary results obtained by different environmental risk assessment approaches, may suggest that a more scientific, adequate environmental risk assessment criterion should consider both total content and chemical speciation activity of heavy metals.