No abstract

Various soil remediation techniques are available to remove or stabilize the metal in contaminated soil, in order to retard the metal toxicity or bioavailability. However, according to the inherent characteristics of those remedial techniques, several methods deteriorate the soil properties and produce secondary contaminants. We aim to the soil layer reversal method to retard the metal availability to rice and at the same time to leave intact the soil properties in paddy soil that are polluted with metals. The experimental paddy soil showed a relatively uniform profile in physicochemical properties up to 100 cm in depth. Surface soil (0 -50 cm) was contaminated with Cd and Pb but their concentrations as the soil depth increased, which was lower than Korean pollution threshold levels (1.5 and 100 mg kg -1 , respectively). The contaminated surface soil layers and the uncontaminated deeper soil layers were reversed with each other, and then rice (Oryza sativa L.) was cultivated in paddy fields. Concentrations of 0.1 M HCl extractable Cd and Pb in the reversed surface soil were 84 -91% and 78 -86% lower than those of the initial surface soils, respectively. Translocations of Cd and Pb to the rice in the reversed surface soil were relatively low (Cd 0.22-0.24 mg kg -1 ; Pb 1.1-1.3 mg kg -1 ), as compared to those of the control (Cd 0.95 mg kg -1 ; Pb 2.9 mg kg -1 ). The results demonstrate that the soil reversal technique can be an option to reduce the metal bioavailability in the paddy field, whereas the implication of the current soil remediation technology is not feasible from the practical or economic viewpoint.

Soils adjacent to the industrial complexes are known to be vulnerable to pollution with the diverse pollutant sources. This research assessed pollution level in the arable soils located nearby industrial complexes using different pollution indices. Both surface (0 -15 cm) and subsurface (15 -30 cm) soil samples were taken from 150 agricultural fields located nearby 15 industrial complexes. Total concentrations of As, Cd, Cu, Ni, Pb, Zn, and Hg in soils were determined after extracting with aqua regia and mostly were lower than the pollution threshold criteria for the agricultural soil designated by the Korean Soil Environment Conservation Act. The calculated PI values for As indicated the unpolluted status but those for all other metals were in the ranges of low to moderately polluted. The Igeo values for Cd and Zn indicated soils were in the unpolluted to moderately polluted ranges, but those for other metals were unpolluted. The Igeo evaluated the pollution level lower than PI due to the geochemical correction factor. The average PINemerow values for surface soil and subsurface soils were 1.26 and 0.73, respectively, indicating a higher pollution in surface soil than subsurface soil. Ranges of PINemerow values showed a wide spectrum of pollution level from clean to heavy pollution, depending on soil sampling sites. All pollution indices indicate that levels of pollution for Cd were higher than other metals. Also four pollution indices exhibited different levels of pollution, even though they are equally based on the total concentrations of heavy metals in soil. This discrepancy might be derived from the fact whether a pollution index considers the geochemical background level, an individual metal or overall metals. The results suggest that a suitable pollution index for the pollution assessment cannot be specified based on the total concentrations of metal in the arable soil.

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In the process of biological desulfurization of gases from landfills, huge amounts of biologically produced Sulfur (BPS) were produced as by-products. A study was conducted to find out the possibility of using it as an adsorbent for Pb 2+ . BPS was subjected to an adsorption test in an aqueous solution in the presence of Pb 2+ and compared with the removal efficiency of granular activated carbon (GAC), which is mainly used as an adsorbent for heavy metal. As a result of the Pb 2+ removal experiment using BPS, it was a two-step process in which 54.5% of the initial Pb 2+ was removed within 5 minutes by fast initial adsorption followed by slow adsorption. As a result of the isotherm adsorption experiment, the Pb 2+ adsorption to BPS was fitted the Langmuir isotherm model, and the maximum adsorption capacity of BPS (175.4 mg g -1 ) was about 3 times higher than that of GAC (67.11 mg g -1 ). The data from XPS demonstrated that the main adsorption mechanism was the complexation of Pb 2+ with the sulfide in the BPS. Therefore, it was confirmed that BPS has sufficient value to be recycled as a new adsorbent for Pb 2+ removal in wastewater.