Influence of the environmental conditions on the fractionation of heavy metals in the Fenhe reservoir sediment

Abstract

The BCR sequential extraction and EDTA single extraction method were applied to study the fractionation, concentration and bioaccessibility of the heavy metals in the sediment of Fenhe reservoir in North China. The sequential extraction schemes identify the non-residual metal among three basic operationally-defined host fractionations, namely, the soluble, exchangeable and carbonate bounded fractionation (F1), Fe‐Mn oxides bounded fractionation (F2) and sulphide/organic matter bounded fractionation (F3). The metal extracted by the EDTA was defined as the bioaccessible fractionation (B) as well. The results showed the fractionation and concentration of heavy metals were influenced by the environmental condition. The bio-mineralization of natural organic matters in sediment as well as the microbial and chemical influence was the key factor controlling the distribution characteristics of different fractionations of heavy metals, including the dissolved iron content in the overlying water. The ratios of the sum of the three non-residual fractionations to the total concentration ((F1+F2+F3)/T) of Cd and Zn in the non-sterile sediment were higher than those in sterile sediment; the F2/ T value of Pb was the highest, which was 25.12, 3.47 and 12.40 times as those of Cd, Zn and Cr respectively. The variation characteristic of (F1+F2+F3)/T value of Cr was particular compared to the other three heavy metals. The EDTA single extraction experiment showed that the ratios of the bioaccessible fractionation to total concentration (B/T) of Cd and Pb in sediment were high enough to 24.96% and 39.56% respectively, while those of Zn and Cr were both below 5%, showing slim bioaccessibility. Taking the high bioaccessibility of F1 fractionation into consideration, the elevated B/T values of Cd and Pb were confirmed by the significant linear regression existed between the value of F1/T and the total concentration. As for Pb, the positive linear regression equations between the value of (F1+F2+F3)/T (y) and B/T (x) in sediment was as follow: y = 0.9519x + 0.1265 (R 2 = 0.9289), which was different from other three heavy metals. The experiment results also indicated in the water-sediment interface, the higher potential environmental effect of heavy metal, the higher degree of the metal diffusion from the sediment to the overlying water, thus it will be a threat to drink water quality in the reservoir.