Distribution and Fractionation of Heavy Metals in Long-Term and Short-Term Contaminated Sediments

Sequential extraction procedures were used in the present study to investigate the distribution and fractionation patterns of Cu, Zn, Pb, and Cd in sediments collected from Huludao City and the Songhua River, respectively. Results indicate that heavy metals added to the sediments for a short time were present as exchangeable, carbonatic, and Fe/Mn-oxide-bound phases. Heavy metals residing in the sediments for a long time were mainly present in carbonatic, Fe/Mn-oxide-bound, and organic fractions. After being spiked with hydroxylapatite, the metals present in the exchangeable phase in the short-term contaminated sediments were transformed to the carbonatic and Fe/Mn-oxide-bound phases and, to a lesser degree, the organic phase and residues. Cu in the long-term contaminated sediments was inclined to change from both exchangeable and carbonatic phases to an organic phase, and Pb was inclined to change from carbonatic and Fe/Mn-oxide-bound phases to organic and residual phases. Generally, the addition of hydroxylapatite led to the shift of the heavy metals from more labile to more stable phases and facilitated the stabilization of heavy metals in the sediments. However, a better effectiveness was reached in the long-term contaminated sediments, possibly due to the differences of organic carbon content and initial metal fractionation between the two sediments. A better hydroxylapatite effectiveness and a lower stability difference between the two sediments could be achieved if the reaction time between sediments and hydroxylapatite was extended.