Heavy metal concentrations and pollution assessment of limestone forests in Huaxi district,Guiyang City

The concentrations of heavy metals(Cu,Zn,Mn,Cd,Ni,Pb and Co)were measured in limestone forests in Huaxi district,Guiyang,and assessment of heavy metal pollution was conducted by comparisons of our results with the background values of heavy metals of limestone soils in both Guizhou Province and in China.The results showed that the abundance of heave metals in the limestone rocks was in the order Pb(40.21mg·kg-1)NiMnCoCuCdZn(5.78mg·kg-1).In the limestone soils,Mn( 451.16 mg·kg-1)had the highest concentration and Cd( 2.87mg·kg-1)had the lowest one of all test metals,with variation coefficients ranged from 8.57% to 63.10% for the seven heavy metals.On average,the concentration of Zn( 55.16 mg·kg-1)was significantly lower than the background values of heavy metals of limestone soils in Guizhou Province(82.40 mg·kg-1)and in China(110.20 mg·kg-1),respectively;while the contents of Cu、Mn、Cd、Pb、Ni、Co were higher than or similar with these background values.Correlation analyses showed that the five heavy metals(Cu,Zn,Mn,Ni and Co)came from the same recourses,and so did of Ni and Pb,Cd and Pb,and Cd and Co.Because of limestone soils with high contents of Ca and Mg elements,Cd and Pb were accumulated in the study sites.Comprehensive pollution index indicated the forest-lands were seriously polluted by heavy metals,with the highest index value of Cd( 4.94),next to Pb( 1.82),and the lowest values of Zn and Mn.Ecological risk index showed that Cd had the highest potential to cause ecological damage in study area,followed by the order Pb Ni Co Cu Mn Zn.Our results indicated that both comprehensive pollution index and ecological risk index were considerably higher in bare-lands than forest-lands.