Contamination and leaching behavior of heavy metals in sediments from urban gully pot alongside some main roads in Seoul City, Korea

Pyeong‑Koo Lee* (Environmental Geochemistry Division, Korea Institute of geology, Mining & Materials, Taejon 305‑350, Korea, pklee@kigam.re.kr, fax : 042‑862‑5056, Tel

042‑868‑3371), Seong‑Taek Yun(Department of Earth & Env. Sci., Korea University, Seoul 136‑701, Korea), Sang‑Hoon Choi(Department of Earth & Env. Sci., Chungbuk Univ., Cheongju 361‑260, Korea)

Gully pots are a part of urban drainage system to buffer the runoff water fluxes from roads to rivers. The possibility of heavy metal pollution by contaminated bottom sediments from gully pots was studied under controlled conditions. The sediment samples from gully pots were characterized by the XRD analyses and the sequential extraction experiments.

The sediments from gully pots are characterized by very high concentrations of heavy metals (mean concentrations : Zn 2595.7 ,ig / g; Cd 9.8 ug / g; Cu 602. 5 ,rig / g; Pb 265.0 ug/g), because of a long‑term accumulation of vehicle‑ and industrial‑related pollutants. Mean Zn concentrations in both business (3873 ug/g) and commercial (3262 ,gg/g) areas are 2‑3 times higher than those in industrial area, suggesting that Zn may be derived from automobile traffic (including the rubber of automobile tires). The relatively low Pb levels throughout the whole study areas can be explained by the use of unleaded gasoline since 1987. Sequential extraction experiments illustrate that carbonate fraction acts as predominant carrier and oxides fraction is next in importance, representing about 88% of the total Zn concentration. Fraction IV, related to organic matter, is mostly significant for Cu. The main carriers of Pb are the fractions III, II and N, and in that order.

In order to assess the relative mobility of heavy metals in slightly acidic condition TCLP and leaching tests under different pH and time conditions were carried out. The Cd and Pb concentrations in all solutions were well below the regulatory level. However, Zn, Mn and Cd were found much more labile than Pb. The buffering effects of carbonates were found to greatly delay the onset of the leaching reactions and the extent of dissolution in most metals except for Ca and Mn. The study of leaching kinetics at pH's of 6 and 5 showed that Cd and Zn reached the maximum possible concentration within 3 days, while Pb did not show any sign of dissolution at both pH's. The absolute amounts of dissolved Cd and Zn increased several times by decreasing the pH from 6 to 5, indicating slightly acidified rain may result in significant metal dissolution and potential pollution of surface water.