A Preliminary Study on Soil–Gas Radon Geochemistry According to Different Bedrock Geology in Korea

Three study areas of Kwanak campus (Seoul National University), Boeun (Choongbuk) and Gapyung (Kyonggi) were selected and classified according to their bedrock types in order to investigate soil–gas radon concentrations. The mean values of radon concentrations decreased in the order of Gapyung (40BqL^–1) > Kwanak campus (30BqL^–1) > Boeun (22BqL^–1), and decreased in the order of granite gneiss > banded gneiss > granite > black slate–shale > mica schist > shale–limestone > phyllite schist according to bed rock types. Variation in radon emanation with water content in soils and with soil grain size was assessed by the modified Morse (1976) 3min method. Soil–gas radon concentrations increased with increasing water content in the range of less than about 6–16wt.%, but decreased above 6–16wt.%. Radon concentrations also increased with decreasing soil grain size. Radioactivity analysis of radionuclides of ²³⁸U series in some soil samples indicated their possible radioactive disequilibrium between ²²⁶Ra and ²³⁸U due to the differing geochemical behaviour of intermediate radionuclides. Thus, a radioactive isotope geochemical approach should be necessary for soil–gas radon study.     

Platinum pollution in road dusts, roadside soils, and tree barks in Seoul, Korea

This study presents the level of platinum in urban environment in and around Seoul, the capital city of Korea. Road dust, roadside soil, and tree bark samples were collected from the sites of various traffic volumes and from control sites in the suburbs. The above samples were analyzed for Pt by ICP-MS and other heavy metals by ICP-OES. Platinum levels in road dusts and roadside soils from Seoul were in the range of 3.8-444 ng/g (av. 115.0 ng/g) and 0.7-221 ng/g (av. 49.7 ng/g), respectively, whereas those in the suburbs were in the range of 2.3-5.2 ng/g (av. 3.9 ng/g) in road dusts and 0.4-5.1 ng/g (av. 2.4 ng/g) in roadside soils. The highest Pt levels in road dusts were found from major roads with high traffic volume. The remarkable difference in average Pt level between heavy traffic roads (av. 132.2 ng/g) and light traffic roads (av. 22.8 ng/g) reflects that an important source of Pt in roadside environment is automobile catalytic converter. High Pt level in road dust was found from the site of erratic stop-start driving condition, for example, 178 ng/g Pt in road dust around a vehicle crossing gate. Platinum level in tree barks ranged from 0.9 to 4.5 ng/g, which indicates the existence of Pt-containing particulate matter in the atmosphere. Road dusts with high Pt level were enriched in traffic-related heavy metals.     

Microbiological reduction of hexavalent chromium by indigenous chromium-resistant bacteria in sand column experiments

Indigenous bacteria that are resistant to high concentrations of Cr(VI) were isolated from a Cr-contaminated sediment. Sand column experiments were conducted using the isolated bacteria to investigate microbial effects on Cr(VI) reduction in open systems that simulated subsurface conditions. The indigenous Cr-resistant bacteria appeared to reduce Cr(VI) in the column experiments. When 12 mg/L of Cr(VI) was injected into the columns, the removal efficiencies of Cr(VI) by the isolated bacteria were 39.1%, 62.5%, and 63.6% at 24, 48, and 72 h retention times of Cr(VI) solution, respectively. These results imply that the linear velocity of groundwater or pore water should be less than 0.63 cm/h for effective removal of Cr(VI) in subsurface conditions. In comparison, the noninoculated control column did not show a significant variation in dissolved Cr(VI) concentration. The results indicated that reduction of Cr(VI) was occurring in the column due to the activity of the indigenous bacteria.     

Distributions of heavy metals in the sediments of South Korean harbors

Bottom sediments of harbors in the South Korea have been long suspected for metal contamination due to ship-based and urban-based activities for the past several decades. A number of areas have been suspected to impair ecosystem services to the local residents and drawn complaints from main stakeholders. Twelve contamination suspected harbors were subject to evaluate the level of contamination of Cr, Ni, Cu, Zn, As, Cd, Pb and Hg. The level of sediment contamination for each metal was evaluated comparing the relative enrichment of a given metal to pollution-insensitive aluminum. Regional background concentration of a given metal was also determined based on its down core measurement and sediment texture. Ecological risk posed by the presence of heavy metals was evaluated using the sediment quality guidelines (SQGs) developed by United States National Ocean and Atmosphere Administration (US NOAA) as benchmarks for evaluating sediment chemistry to aquatic organisms. Cu, Zn, Cd, Pb and Hg in the surface sediment were found to be higher than a factor of 1.5 than background sediments, and the overall metal contaminations of surface sediment can be regarded as medium-high- to high-priority sites in the sense of SQGs.     

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