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The hypothesis that phenanthrene, an aromatic compound without a hydroxyl group, can form nonextractable residues in soil with the aid of phenanthrene-biodegrading bacteria and birnessite was tested. The mutant strain Sphingobium yanoikuyae B8/36 successfully accumulated cis-phenanthrene dihydrodiol, and the intermediate was readily radicalized and coupled into soil organic matter in the presence of birnessite. Phenanthrene and the intermediate disappeared from the soil in 96 h in the presence of birnessite, but the intermediate accumulation occurred without birnessite. By determining the total organic carbon contents before and after birnessite treatment, it could be seen that birnessite did not mineralize cis-phenanthrene dihydrodiol. Fourier transform infrared and ultraviolet analyses suggest instead that the intermediate was incorporated into the soil organic matter, forming nonextractable, bound residues. Increases in the aromaticity and pH in birnessite-treated soil also present more evidence for bound residue formation. The soil in which bound residue formed did not exhibit an acute toxicity of phenanthrene, but evidence indicated that such toxicity existed in the freshly spiked soil. In addition, a long-term column test revealed that the bound residues could not be eluted by the combination of water, 80% methanol, and U.S. Environmental Protection Agency Toxicity Characteristic Leaching Procedure solution (pH 2.88) for four months, implying stability of the nonextractable residues in the soil. ; This research received substantial support from the Seoul Research and Business Development Program (10676). Additional financial support was provided by the Korea Science and Engineering Foundation through the Advanced Environment Biotechnology Research Center at POSTECH and by an Ecoriver 21 Project of the Ministry of Land, Transport, and Maritime Affairs of Korean Government.

This study investigated the ability of a saponin-based microbubble suspension to enhance aerobic biodegradation of phenanthrene by subsurface delivery. As the microbubble suspension flowed through a sand column pressure buildup and release was repeatedly observed, which delivered oxygen to the less permeable regions. Burkholderia cepacia RPH1, a phenanthrene-degrading bacterium, was mainly transported in a suspended form in the microbubble suspension. When three pore volumes of the microbubble suspension containing B. cepacia RPH1 was introduced into a column contaminated with phenanthrene (100 mg/kg), the oxygen content declined to 5% from an initial value of 20% within 5 days and correspondingly, 34.4% of initial phenanthrene was removed in 8 days. The addition of two further three pore volumes enhanced the biodegradation efficiency by a factor of 2.2. Our data suggest that a saponin-based microbubble suspension could be a potential carrier for enhancing the aerobic biodegradation under an oxygen-limiting environment. ; This work was sponsored by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government (MEST) (2009-0079618). An additional financial support was also provided by the Ecoriver 21 project of Ministry of Land, Transport and Maritime Affairs. The authors would like to thank the Engineering Research Institute at Seoul National University for its technical assistance.

In this research, a risk assessment was undertaken in order to develop the remediation and management strategy of a contaminated gunnery site, where a nearby flood controlling reservoir is under construction. Six chemicals, including explosives and heavy metals, posing potential risk to environmental and human health, were targeted in this study. A sitespecific conceptual site model was constructed, based on effective, reasonable exposure pathways, to avoid any overestimation of the risk. Also, conservative default values were adapted to prevent underestimation of the risk when site-specific values were not available. The risks posed by the six contaminants were calculated using the API's Decision Support System for Exposure and Risk Assessment, with several assumptions. In the crater-formed-area (Ac), the non-carcinogenic risks (i.e., HI values) of trinitro-toluene (TNT) and Cd were slightly larger than 1, but for RDX (Royal Demolition Explosives) was over 50. The total non-carcinogenic risk of the whole gunnery range was calculated to be 62.5, which was a significantly high value. The carcinogenicity of Cd was estimated to be about 10-3, while that for Pb was about 5×10-4, which greatly exceeded the generally acceptable carcinogenic risk level of 10-4–10-6. It was concluded from the risk assessment that there is an immediate need for remediation of both carcinogens and non-carcinogens before construction of the reservoir. However, for a more accurate risk assessment, further specific estimations of the changes in environmental conditions due to the construction of the reservoir will be required; and more over, the effects of the pollutants to the ecosystem will also need to be evaluated. ; This research was sponsored by the KOSEF through the Advanced Environmental and Biotechnology Research Center (AEBRC) at POSTECH. An additional financial support was also made by the Basic Research Program of the Korea Science & Engineering Foundation (Grant No. R01-2006-000-10136-0). The authors would also like to thank the Research Institute of Engineering Science, Seoul National University, for their technical assistance.