Hyerim Ryu

Ecological Risk Characterization in a Military Heavy Metals– and Explosives-Contaminated Site

ABSTRACT Potential ecological risks of two heavy metals (Cu, Pb) and three explosives (TNT, RDX, HMX) were determined for a military gunnery range. Since a portion of the site will be submerged after the construction of a flood control reservoir, risk assessment of the site was conducted over two time points: at the current state and after the construction of the flood control reservoir. Terrestrial plants, terrestrial invertebrates, birds, mammals, and aquatic invertebrates were selected as affected ecological receptors at the study site. Potential noncarcinogenic risk was found only in one terrestrial site for Cu and RDX at both time points: For terrestrial plants, ecological hazard quotient (EHQ) by Cu was 1.22. For terrestrial invertebrates, EHQs for Cu and RDX were 1.38 and 6.47, respectively. EHQs in the aquatic environment increased to some extents after the reservoir construction, but the values were less than 1.0. A comparison between EHQs before and after the construction for the same site shows that the reservoir construction would not significantly increase the overall ecological risk, suggesting that the reservoir construction influenced the potential ecological risks at the study site, but the changes were acceptable. Uncertainties involved in the assessment process were identified and discussed.

Detoxification of phenol through bound residue formation by birnessite in soil: Transformation kinetics and toxicity

Oxidative coupling reaction of phenol mediated by birnessite was studied in aqueous phase and soil. Phenol was readily transformed by birnessite and almost all phenol disappeared in both samples after 24 hours of reaction. Phenol transformation kinetics was investigated by plotting reaction time against logarithm concentrations of residual phenol, revealing that exponential decrease of phenol was evident both in aqueous phase and soil, and maximum removal rates were 2.31–2.54 times higher in the presence of soil. Reaction products of phenol were identified by LC-MS and capillary electrophoresis. In aqueous phase, polyphenols were formed by self-coupling reaction of phenoxy radicals whereas phenol was found to be present as bound residues in soil, probably due to the cross-coupling reaction between the radicals and soil organic matter. Microtox System was employed to determine the toxicity after birnessite treatment, and the toxicity of phenol-spiked solution and soil samples decreased remarkably compared to that of phenol solution before treatment.

Field Applicability Study of Landfarming for Petroleum Hydrocarbons Contaminated Soils

ABSTRACT The landfarming treatment for the remediation of the petroleum contaminated soil at the returned U.S. Military bases wasinvestigated in this study. Specifically, the bioaugmentation performance using various commercially available petroleum-degrading bacteria was evaluated and the directions for enhancing the performance of the landfarming treatment weresuggested. The environmental factors of the soils at the returned U.S. Military bases chosen for remediation indicate thatthe landfarming treatment can be used as the remediation technique; however, the addition of nitrogen or phosphorus isrequired. The lab-scale landfarming treatment tests using the model soil and the site soil showed that the degradationefficiency was greater with the model soil than the site soil and that the treatment performance was not affected by thenumber of bacteria present in the soil in the range of 10 6 -10 12 CFU/g. These results suggest that the successful landfarmingtreatment depends on the petroleum degradability of bacteria used and the environmental conditions during the treatmentrather than the number of petroleum-degrading bacteria used. Key words: Landfarming, Petroleum-contaminated soil, Soil remediation, Petroleum-degrading bacteria, Contaminantaging

Development of Korean Risk-Based Corrective Action (K-RBCA) Software

위해성에 근거한 복원 전략(Risk-Based Remediation Strategy, RBRS)은 위해성평가(Risk Assessment)를 통하 여 오염지역의 위해성 또는 오염원을 효율적으로 관리하 기 위한 의사결정과정이다. 이는 토양에 잔류하는 오염물 질의 농도에 의존하여 오염지역 복구 및 수준을 결정하던 기존의 방법과는 다르게, 오염물질의 수용체에 대한 노출 가능성과 위해성에 근거하여 오염지역의 복구 여무 결정 및 정화 수준을 결정하는 방법으로, 미국, 네덜란드, 영국 등 선진국에서 이미 널리 시행되고 있다. 선진국에서는 위 해성평가를 보다 수월하게 수행할 수 있도록 전문적인 소 프트웨어를 개발하여 사용하고 있다. 미국의 RBCA Tool Kit for Chemical Releases(ASTM, 2007), APIs DSS (American Petroleum Institute, 1999)와 CalTOX (California EPA, 2002), 영국의 CLEA(DEFRA and EA, 2002), 네덜란드의 CSOIL(RIVM Netherlands, 2001)등과 같은 소프트웨어가 대표적이며, 이러한 소프트 웨어들은 위해성평가를 하기 위해 필요한 기본적인 데이 터베이스와 노출 시나리오, 위해도 및 목표정화수준 산정 기능 등을 제공하여 평가자가 쉽게 이해하고 수행할 수 있도록 한다. 위해성평가 소프트웨어의 기본이 되는 위해 성평가 매뉴얼은 대부분 미국의 Soil Screening Guidance (US EPA, 1996)와 Risk-Based Corrective Action(ASTM, 1995)을 따르고 있으며, 영국(DEFRA and EA, 2002)과 네덜란드(RIVM, 2001)는 이를 바탕으로 자국의 현황에 맞게 수정하여 사용하고 있다. 우리나라도 2005년 ‘토양환경보전법’을 개정하여 위해 성평가에 대한 근거 조항을 도입함으로써 제도적 기반을 마련하였으나 그 이후 본격적으로 시행되지 못하고 있다. 여러 가지 사회적, 제도적 이유가 있으나 위해성평가의 수 행 주체가 불분명하고 본격적인 평가를 위한 기술적 기반 이 충분히 조성되지 못한 데 기인하는 측면이 크다. 위해 성평가를 위한 기술적 지원을 위하여 본 연구진에서는 한 국형 위해성평가 소프트웨어를 개발하였고, 이를 Korean Risk-Based Corrective Action(K-RBCA)라고 명명하였다. 본 기술자료에서는 미국에서 개발되어 사용 중인 RBCA Tool Kit for Chemical Releases, APIs DSS, CaLTOX 를 중심으로 위해성평가 소프트웨어를 분석하여 위해성평 가 소프트웨어의 주요 기능과 기본적인 설정이 어떠한지 살펴보고, 기존 상용 소프트웨어를 기반으로 한국의 위해 성평가 시행 수준에 적합한 기능과 설정을 가진 소프트웨 어 개발에 대한 연구 결과를 기술하였다.

Phenanthrene metabolites bound to soil organic matter by birnessite following partial biodegradation

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.

Enhanced reactivity of hydroxylated polycyclic aromatic hydrocarbons to birnessite in soil: Reaction kinetics and nonextractable residue formation

Phenanthrene and pyrene were not transformed by birnessite (delta-MnO2) in the presence of phenol. The phenoxy radicals generated from phenol by birnessite did not act as a mediator for polycyclic aromatic hydrocarbon radical reaction under the studied conditions. In contrast, 9-hydroxyphenanthrene and 1-hydroxypyrene were remarkably sensitive to birnessite. The disappearance patterns of the test compounds both in the aqueous phase and soil followed first-order kinetics, with a linear relationship found between the rate constants and the surface area of birnessite. Moreover, the data indicated that the reaction was faster in the presence of soil than in the aqueous phase probably because of the presence of hydroxyl groups in soil organic matter. Sequential solvent extraction was not successful in the recovery of 9-hydroxyphenanthrene from the birnessite-treated soil samples, and capillary electrophoresis data suggest the formation of nonextractable residues of the compound in soil. In addition, the acute toxicity determined by Microtox declined approximately 8.3 times in the soil samples treated with birnessite compared to untreated samples, demonstrating that the toxic compound was no longer present as its parent form.

Analysis on the Risk-Based Screening Levels Determined by Various Risk Assessment Tools (II): Derivation of Particulate Emission Factor at Former Janghang Smelter Site

This paper presents the short-term and long-term measures to determine the fugitive dust concentration in a contaminated site, which is a crucial step for the determination of particulate emission factor (PEF) for risk assessment. As a long-term measure, USEPA method employing Q/C value (inverse of the ratio of the geometric mean air concentration to the emission flux at center of a 0.5-acre square source) seems to be suitable as it reflects regional-specific meteorological conditions. However, it requires nation-wide database collection and interpretation. Use of ASTM method is an alternative as a short-term measure. The method is readily field-applicable as PEF calculation equation is simple and input parameters can be easily derived at the site of interest as well without the nation-wide efforts. Using ASTM method, PEF at the Former Janghang Smelter Site was determined. According to various mode of aggregate size distribution and fractions of vegetative cover, which are the most important factors in PEF calculation, PEF values at the Former Janghang Smelter Site varied greatly. When the mode of aggregate size distribution was set at 0.25 mm, PEF values at the Former Janghang Smelter Site was 5~20 times higher than the default PEF value (i.e., 35 ) shown in the current Korean Soil Contamination Risk Assessment Guidance. On contrast, when the mode was set at 2 mm, PEF values at the Former Janghang Smelter Site was 160~640 times lower than the default PEF value in the Korean Guidance.

Analysis on the Risk-Based Screening Levels Determined by Various Risk Assessment Tools (I): Variability from Different Analyses of Cross-Media Transfer Rates

Risk-based screening levels (RBSLs) of some pollutants for residential adults were derived with risk assessment tools developed by United States Environmental Protection Agency (USEPA), American Society for Testing and Materials (ASTM), and Korea Ministry of Environment (KMOE) and compared each other. To make the comparison simple, ingestion of soil, dermal contact with soil, outdoor inhalation of vapors, indoor inhalation of vapors, and inhalation of soil particulates were chosen as exposure pathways. The results showed that the derived RBSLs varied for every exposure pathway. For direct exposure pathways (i.e., ingestion of soil and dermal contact with soil), the derived RBSLs varied mainly due to the different default values for exposure factors and toxicity data. When identical default values for the parameters were used, the same RBSLs could be derived regardless of the assessment tools used. For inhalation of vapors and inhalation of soil particulates, however, different analysis methods for cross-media transfer rates were used and different assumptions were established for each tool, identical RBSLs could not be obtained even if the same default values for exposure factors were used. Especially for inhalation of soil particulates pathway, screening level derived using KMOE approach (most conservative) was approximately 5000~10000 times lower than the screening level derived using ASTM approach (least conservative). Our results suggest that, when deriving RBSL using a specific tool, it is a prerequisite to technically review the analysis methods for cross-media transfer rates as well as to understand how the assessment tool derives the default values for exposure factors.

Human Risk Assessment of a Contaminated Site Using Korean Risk-Based Corrective Action (K-RBCA) Software

By using a newly developed Korean risk-based corrective action (K-RBCA) software (K-RBCA) and the RBCA Tool Kit, risk assessment was performed on a site that was contaminated with aromatic hydrocarbons and heavy metals. Eight chemicals including benzene, ethylbenzene, xylenes, naphthalene, benz(a) anthracene, benzo(b) fluoranthene, benzo(a) pyrene, and arsenic that exceeded the US EPA Soil Screening Level were chosen as the target pollutants. A conceptual site model was constructed based on the site-specific effective exposure pathways. According to the RBCA Tool Kit the carcinogenic risk of arsenic was larger than , which is the generally acceptable carcinogenic risk level. The K-RBCA estimated the same level of carcinogenic risk for arsenic. With the RBCA Tool Kit, the carcinogenic risk of benzo(a) pyrene was estimated to be about . However, with the K-RBCA benzo(a) pyrene did not exhibit any risk. The inconsistency between the softwares was attributed to the different fundamental settings (i.e., medium division) between the two softwares. While the K-RBCA divides medium into surface soil, subsurface soil, and groundwater, the RBCA Tool Kit divides medium into only soil and groundwater. These differences lead to the different exposure pathways used by the two softwares. The K-RBCA considers the exposure pathways in surface soil and subsurface soil separately to estimate risk, however, the RBCA Tool Kit considers the surface soil and subsurface soil as one and uses the integrated exposure pathways to estimate risk. Thus the resulting risk is higher when the RBCA Tool Kit is used than when the K-RBCA is used. The results from this study show that there is no significant difference in the risks estimated by the two softwares, thus, it is reasonable to use the K-RBCA we developed in risk assessment of soil and groundwater. In addition, the present study demonstrates that the assessor should be familiar with the characteristics of a contaminated site and the assumptions used by a risk assessment software when carrying out risk assessment.

ALTERED MOBILITY OF BENZ[a]ANTHRACENE IN THE PRESENCE OF p-XYLENE AND ITS IMPACT ON RISK IN THE SUBSURFACE

Concerns over soil and groundwater contamination by PAHs have been raised as they are often introduced into the subsurface as nonaqueous-phase liquid (NAPL) mixtures. However, characterizing the risk posed by a mixture of chemicals is a challenging task due to its uncertainty in quantifying the effects of the interaction between substances. This study focuses on the effects of phase-transforming interaction on the fate, transport, and risk assessment of a PAH in a PAH - NAPL mixture. The cell test was carried out using benz[a]anthracene (BaA) and p-xylene to verify the increased mobility of highly sorbed pollutants in the presence of less sorbed, mobile liquid pollutants. The experimental results showed that BaA had greater mobility in the presence of p-xylene than in its absence. The main transport mechanisms in the vadose zone were by dissolution into p-xylene or water. The developed model showed that transport of BaA was significantly faster in the presence of NAPL, but needs improvement. As well, risk assessment indicated that the oral carcinogenic risk of BaA calculated with the concentration in groundwater was 15∼ 87 times larger when mixed with NAPL than when present as a single contaminant. This study demonstrated that consideration of phase-transforming interaction is necessary to analyze the risk of a PAH - NAPL mixture. The improvement of the transport model will be the topic of our continuing research.