Seok-Hwi Kim

Co-contamination of arsenic and fluoride in the groundwater of unconsolidated aquifers under reducing environments.

The co-contamination of arsenic (As) and fluoride (F(-)) in shallow aquifers is frequently observed worldwide, and the correlations between those contaminants are different according to the redox conditions. This study geochemically explores the reasons for the co-contamination and for the redox-dependent correlations by investigating the groundwater of an alluvial aquifer in Korea. Geochemical signatures of the groundwater in the study area show that the As concentrations are enriched by the reductive dissolution of Fe-(hydr)oxides, and the correlations between As and F(-) concentrations are poor comparatively to those observed in the oxidizing aquifers. However, F(-) concentrations are strongly dependent on pH. Desorption/adsorption experiments using raw soils and citrate-bicarbonate-dithionite treated soils indicated that Fe-(hydr)oxides are the important As and F(-) hosts causing the co-contamination phenomenon. The weaker correlation between F(-) and As in reducing aquifers is likely to be associated with sulfate reduction, which removes As from groundwater without changing the F(-) concentration.

Importance of surface geologic condition in regulating As concentration of groundwater in the alluvial plain

The arsenic (As) concentrations in the groundwater of alluvial plains generally show high spatial variability. We geochemically explore the factors causing the spatial variability in an alluvial plain that is mainly used for rice cultivation, the commonest land-use pattern in alluvial plains of Asia. We investigate the chemical processes, sources of chemicals that affect the behavior of As, and their relationships with the geologic conditions at seven multilevel sampler sites. All sites showed As concentrations that increased with depth at shallow levels and decreased at greater depths, which is the typical vertical pattern in alluvial aquifers where Fe-(hydr)oxide reduction is the major As release mechanism. Data show that NO(3) and SO(4) originating from the land surface play important roles in suppressing the increase in As concentration by buffering the redox potential at shallow depths and by precipitating As with sulfide minerals at deep depths, respectively. The As concentration in the intermediate depth range was also low in the presence of SO(4), because its reduction can occur together with Fe-(hydr)oxide reduction in a wide range of redox potentials. As a result, the maximum As concentrations at the sites where the land was covered with a thick silt layer (approximately 5m) were 3- to 5-times higher than those at other sites due to the supply of NO(3) and SO(4) from land surface being largely limited by the silt layer. This indicates that the surface geology could be an important indicator for the As concentration in alluvial groundwater.

Arsenic concentration in porewater of an alkaline coal ash disposal site: Roles of siderite precipitation/dissolution and soil cover

The geochemical behavior of As in porewaters of an alkaline coal ash disposal site was investigated using multilevel samplers. The disposal site was in operation from 1983 until 1994 and was covered with 0.3-0.5m thick soils in 2001 when this study was initiated. Sequential extraction analyses and batch leaching experiments were also performed using the coal ash samples collected from the disposal site. The results suggest the important roles of siderite (FeCO(3)) precipitation/dissolution and soil cover, which have been ignored previously. Arsenic levels in the porewater were very low (average of 10microgL(-1)) when the site was covered with soil due to coprecipitation with siderite. The soil cover enabled the creation of anoxic conditions, which raised the Fe concentration by the reductive dissolution of Fe-(hydr)oxides. Because of the high alkalinity generated from the alkaline coal ash, even a small increase in the Fe concentration (0.66mgL(-1) on average) could cause siderite precipitation. When the soil cover was removed, however, an oxidizing condition was created and triggered the precipitation of dissolved Fe as (hydr)oxides. As a result, the dissolution of previously precipitated As-rich siderite caused higher As concentration in the porewater (average of 345microgL(-1)).

Relations of As concentrations among groundwater, soil, and bedrock in Chungnam, Korea: Implications for As mobilization in groundwater according to the As-hosting mineral change

Arsenic (As) concentrations and As-bearing minerals in bedrock and soil, and their relations with groundwater concentrations were investigated in a small agricultural area of Korea. The As concentration of the bedrock shows a wide variation (<0.5-3990 mg/kg) and is well correlated with that in the contacting groundwaters (23-178 μg/L). Soils, the weathering product of bedrock, show the lower and more dispersed As concentrations (8.8-387 mg/kg) than the bedrock. But the soil As concentrations are very high relative to those reported from other areas. The As concentrations in the shallow groundwaters are comparatively low (<20 μg/L) and are independent of the soil concentration. Arsenopyrite is the major As-bearing mineral in the bedrock and its oxidation controls the As levels in deep groundwater. In contrast, As mostly resides in soil as Fe-(hydr)oxide-bound forms. Due to low pH and oxidizing redox condition, the release of As from Fe-(hydr)oxides is largely suppressed, and the shallow groundwater shows low As concentrations generally satisfying the drinking water limit. However, it is suggested that the disturbance of soil geochemical conditions by land use changes would cause a serious As contamination of the shallow groundwaters.

Relations of arsenic concentrations among groundwater, soil and paddy from an alluvial plain of Korea

Serious groundwater arsenic (As) contaminations are frequently associated with alluvial plains, and which are mostly used for rice cultivation in Asian countries. Because rice cultivation requires large quantities of irrigation, the long-term use of Ascontaminated groundwater for irrigation may cause As contamination in the soil with a consequent impact on rice grains. In this study, we investigated As concentrations in groundwater, soil and rice and the soil properties from an alluvial plain of the Mankyeong River, Korea, to understand their relations from the viewpoint of As contamination in rice. Arsenic in the rice varied from 0.03 mg/kg to 0.22 mg/kg, with a mean of 0.13 mg/kg, which is much lower than the World Health Organization’s maximum permissible limit of As in rice (1.0 mg/kg). Some groundwater samples showed As concentrations much higher than the drinking water standard (10 ug/L). Despite the rice As is independent of groundwater As it showed a good relation with soil As and Fe-oxide fractions. Because As is mainly occurred in Fe-oxide fractions and the soil is mostly silty, it is speculated that under flooding conditions arsenic can easily mobilize to the soil solution and potentially be available for plants. However, this availability can be controlled by As uptake mechanisms and/or incomplete reduction of Fe-oxides. It is observed that rice As is significantly correlated with soil exchangeable-PO4 (r = −0.41, p < 0.05), indicating that PO4 competition in the soil-rhizosphere may be one of the factors controlling rice As.

Processes controlling the variations of pH, alkalinity, and CO2 partial pressure in the porewater of coal ash disposal site

Alkalinity, pH, and pCO2 are generally regarded as the most important parameters affecting trace element leaching from coal ashes. However, little is known about how those parameters are actually regulated in the field condition. This study investigated the processes controlling those parameters by observing undisturbed porewater chemistry in a closed ash disposal site. The site is now covered with 30-50 cm thick soils according to the management scheme suggested by the Waste Management Law of Korea and our results show the important role of soil cover regulating those parameters in the shallow porewater. Without the soil cover, the shallow porewater shows low pCO2 and alkalinity, and highly alkaline pH. In contrast, the porewater shows much higher alkalinity and near neutral pH range when the site was covered with the low permeability soils. This difference was caused by the CO2 supply condition changes associated with the changes in infiltration rate. The geochemical modeling shows that the calcite precipitations induced by porewater aging, dolomitization, and weathering of solid phases are the main processes controlling alkalinity, pH, and pCO2 in the deep saline porewaters. The weathering of coal ash plays the most important role decreasing the alkalinity in the deep porewater.

L-asparaginase and L-glutaminase activities in submerged rice soil amended with municipal solid waste compost and decomposed cow manure.

The field study was conducted to evaluate the effect of municipal solid waste compost (MSWC) as a soil amendment on L-asparaginase (LA) and L-glutaminase (LG) activities. Experiments were conducted during the wet seasons of 1997, 1998 and 1999 on rice grown under a submerged condition, at the Agriculture Experimental Farm, Calcutta University at Baruipur, West Bengal, India. The treatments consisted of control, no input; MSWC, at 60 Kg N ha− 1; well-decomposed cow manure (DCM), at 60 Kg N ha− 1; MSWC (30 Kg N ha− 1) + Urea (U) (30 Kg N ha− 1); DCM (30 Kg N ha− 1) + U (30 Kg N ha− 1) and Fertilizer, (at 60:30:30 NPK kg ha− 1) through urea, single superphosphate and muriate of potash respectively). LA and LG activities alone and their ratio with organic-C (ratio index value, RIV), straw and grain yield were higher in DCM than MSWC-treated soils, due to higher amount of biogenic organic materials like water-soluble organic carbon, carbohydrate and mineralizable nitrogen in the former. The studied parameters were higher when urea was integrated with DCM or MSWC, compared to their single applications. The heavy metals in MSWC did not detrimentally influence the above-measured activities of soil. In the event of long term MSWC application, changes in soil quality parameters should be monitored regularly, since heavy metals once entering into soil persist over a long period.

Mineralogical and Chemical Characteristics of the Oyster Shells from Korea

SO2 가스 반응제로 사용되는 석회석의 대체 가능 물질로서 굴 패각의 광물학적 화학적 특성을 알아보았다. 생장환경에 따른 굴 패각의 특성을 파악하기 위하여 태안지역 및 통영지역의 굴 패각을 석회석과 비교하였고 추가로 보령 및 여수 지역의 굴 패각을 연구하였다. XRD 분석 결과 굴 패각은 아라고나이트로 구성되어 있는 폐각근 접합 부분 및 인대(ligament) 접합부분을 제외하고 방해석으로 구성되어 있으며 불순물로서 나타나는 해양 퇴적물이 패각 내 표면에 존재하거나 일부 패각 내 포유물 형태로 나타나기도 했다. 불순물 중 하나인 패각 표면의 따개비의 경우도 방해석으로 이루어져 있어 소성에 영향을 주지는 않을 것으로 판단된다. 현미경 관찰을 통하여 굴 패각의 미세구조를 파악할 수 있었다. 패각은 크게 각주층, 진주층, 초크층으로 구성되어 있는데 패각이 가장 큰 통영 굴 패각은 콘키올린(conchiolin)이라 불리는 단백질을 일부 함유하는 각주층과 진주층의 두께가 가장 작았으며 작은 크기의 태안 굴 패각의 경우 각주층과 진주층 두께가 가장 두꺼운 것으로 나타났다. 중간 크기의 패각 크기를 갖는 보령과 여수 굴 패각은 그 층들이 두 패각의 중간정도의 두께를 보여주었다. 이는 계속 바닷물 속에서 양식하는 통영과 조간대에서 공기와 바닷물 속에서 양식하는 태안의 생장 환경 차이로 판단된다. 굴 패각들은 석회석과 달리 상대적으로 높은 인과 황 함량을 보여주는데 이는 패각 내의 단백질에 의한 것이며 패각을 구성하고 있는 세 개의 층은 Mg 함량을 포함하여 일부 상이한 화학성분을 갖고 있기도 했다. 미량성분의 경우 패각의 경우 석회석 보다 Li의 함량이 상대적으로 많았으며 이는 바닷물 성분의 영향을 받았을 것으로 생각된다. 각 산지별 패각에서는 Zn의 함량 변화가 가장 커서 Zn의 함량은 생성환경에 가장 영향을 많이 받는 미량원소로 판단된다.

Critical Evaluation of the Recent Development and Trends in Submarine Groundwater Discharge Research in Asia

In majority of the arid and dry regions of the world and in monsoon-dependent countries in Asia, groundwater is a major freshwater resource for drinking and other uses. The coastal regions, which support maximum density of population, mainly depend on the ground water. Due to the population growth and the fact that about 50% of the world population now already live in coastal regions, the groundwater issues in the coastal areas are increasingly becoming crucial (UNWWDR, 2009). Over-exploitation of groundwater in these areas can potentially lead to saltwater intrusion, land subsidence, permanent damage to the ability of an aquifer to store and transmit water, and reduced discharges to rivers, streams, and critical aquatic habitat areas (Fig. 1). Further, coastal groundwater plays an important role in nutrient flux to the ocean. The influence of submarine groundwater discharge (SGD) on the coastal water quality, their biogeochemical process and their ecology are very significant in most of the coastal regions. Investigations of interactions between groundwater and coastal seawater have been restricted mainly to the case of water movement from sea to the land, i.e. saltwater intrusion (Segol and Pinder, 1976; Reilly and Goodman, 1987) while submarine groundwater discharge (SGD) considers the water output from a basin-scale hydrological cycle, representing an input into the ocean (Fig. 2). Open image in new window Figure 1: A compilation of processes affecting coastal groundwater. Open image in new window Figure 2: Schematic depiction of processes associated with SGD (modified after Taniguchi et al., 2002). Arrows indicate fluid movement.