Two-dimensional reactive transport model as a new approach for identifying the origins and contribution of arsenic in a soil and water system.

Distribution of arsenic (As) in the environment can occur through various paths, depending on the interrelationship between soil and surface water, and groundwater. This study aimed to identify the origins and pathways of As among various potential origins in soil and water systems using two-dimensional reactive transport models (2D RTMs) and to evaluate the contribution of each origin to the geochemical distribution of As in the study area, which included a reservoir, two streams, and two abandoned mines. The 2D RTMs were prepared by combining hydraulic and geochemical reactive models. The MODFLOW-2005 package was used to simulate the water flow in the study area. The geochemical reaction and distribution of As were simulated using Geochemist's Workbench. The concentration of As in the reservoir was ∼50 µg/L, while that in the soils collected around the mine X and Y was 15.0-1853.2 mg/kg (median: 126.1 mg/kg) and 3.6-1629.2 mg/kg (median: 60.9 mg/kg), respectively. Hydraulic and geochemical input data were derived from field surveys and laboratory experiments. Based on the geochemical and hydrogeological input data, 2D RTMs determined that 32.0 kg of As accumulated into the reservoir over 18 years through surface water, which is from mines X (2.7 kg) and Y (29.3 kg). Hence, mine Y would be the primary origin of As to the reservoir. Based on 2D RTM, 2.4 kg of As entered the reservoir via groundwater (DO <0.1 mg/L). Also, precipitation of sulfide minerals (e.g., orpiment; As2S3) influences As dispersion and contribution under subsurface conditions. These modeling results suggest that 2D RTMs could be a new approach for identifying and assessing the contribution of potential As origins in soil and water system.

Potential of indigenous bacteria driven U(VI) reduction under relevant deep geological repository (DGR) conditions.

Understanding the biogeochemical U redox processes is crucial for controlling U mobility and toxicity under conditions relevant to deep geological repositories (DGRs). In this study, we examined the microbial reduction of aqueous hexavalent uranium U(VI) [U(VI)aq] by indigenous bacteria in U-contaminated groundwater. Three indigenous bacteria obtained from granitic groundwater at depths of 44-60 m (S1), 92-116 m (S2), and 234-244 m (S3) were used in U(VI)aq bioreduction experiments. The concentration of U(VI)aq was monitored to evaluate its removal efficiency for 24 weeks under anaerobic conditions with the addition of 20 mM sodium acetate. During the anaerobic reaction, U(VI)aq was precipitated in the form of U(IV)-silicate with a particle size >100 nm. The final U(VI)aq removal efficiencies were 37.7%, 43.1%, and 57.8% in S1, S2, and S3 sample, respectively. Incomplete U(VI)aq removal was attributed to the presence of a thermodynamically stable calcium uranyl carbonate complex in the U-contaminated groundwater. High-throughput 16S rRNA gene sequencing analysis revealed the differences in indigenous bacterial communities in response to the depth, which affected to the U(VI)aq removal efficiency. Pseudomonas peli was found to be a common bacterium related to U(VI)aq bioreduction in S1 and S2 samples, while two SRB species, Thermodesulfovibrio yellowstonii and Desulfatirhabdium butyrativorans, played key roles in the bioreduction of U(VI)aq in S3 sample. These results indicate that remediation of U(VI)aq is possible by stimulating the activity of indigenous bacteria in the DGR environment.

Discrimination methods for diesel origin by analyzing fatty acid methyl ester (FAME) composition in diesel-contaminated soil.

The biodiesel containing fatty acid methyl esters (FAMEs) are blended with refined diesel products. Here, we evaluate relative FAME composition ratio as a potential index to discriminate the pollution origin in diesel-contaminated soil. Artificially contaminated soil was prepared to mimic the release of petroleum products using four different refined diesels; in addition, the contaminated soil was put under natural weathering conditions. The variations in the relative FAME composition ratio was compared with those of the corresponding diesel origin using principal component analysis (PCA) for 60 days. All soil samples could be classified into four groups according to diesel origin using two principal components. The proposed method can be used to discriminate the specific diesel pollution origin in contaminated soils.

Assessment and source identification of As and Cd contamination in soil and plants in the vicinity of the Nui Phao Mine, Vietnam.

This study investigated the contamination levels and sources of As and Cd vicinity area from Nui Phao mine that is one of the largest tungsten (W) open pit mines in the world. Soil and plant samples were collected from the study area to identify the concentrations of As and Cd using aqua-regia or HNO3 digestion. According to the Vietnamese agricultural soil criteria, all soil samples were contaminated with As and Cd. The distribution of As concentration is related to the distance from the Nui Phao mine. The higher As concentrations were measured in the area close to the mine. However, the Cd distribution in the soil showed a different pattern from As. Enrichment factor and Geoaccumulation Index (Igeo) indicated that As in the soil is derived from the mining activities, while Cd could have other geogenic or anthropogenic sources. The ranges of As and Cd concentration in polished rice grains in the Nui Phao mine area exceeded the CODEX criteria (0.2 mg/kg), which indicated extreme contamination. The arsenic concentration between soil and plant samples was determined to be a positive correlation, while the Cd concentration showed a negative correlation, implying that As and Cd have different geochemical behavior based on their sources.

Comparison of five extraction methods for evaluating cadmium and zinc immobilization in soil.

The remediation of soil contaminated with heavy metals is an ongoing environmental concern. Paddy soils contaminated with Cd and Zn were collected from around abandoned metals mines in Korea. Limestone and steel slag were mixed with the collected soil, as amendments for Cd and Zn immobilization. Sequential extraction, lettuce cultivation and five single extraction methods were carried out to assess the effects on Cd and Zn immobilization using amendments. The exchangeable fraction of Cd and Zn was decreased and Fe-Mn oxides fraction increased by stabilization using amendments. In addition, the accumulation of Cd and Zn in lettuce decreased in treated soil and indicated the Cd and Zn immobilization effect in soil by the amendments. The extractable Cd and Zn by CaCl2 and Mehlich-3 in the untreated soils were higher than that of treated soils, whereas Cd and Zn extraction by ethylenediaminetetraacetic acid (EDTA), diethylene tetramine penta-acetic acid (DTPA) and toxicity characteristic leaching procedure (TCLP) has a small or no difference between the untreated and treated soils. The extraction results by CaCl2 and Mehlich-3 methods present reasonable results for Cd and Zn immobilization in soil than EDTA, DTPA and TCLP methods. Therefore, the choice of appropriate extraction method is very important when there is the assessment of Cd and Zn immobilization efficiency.

Human health risk assessment of cadmium exposure through rice consumption in cadmium-contaminated areas of the Mae Tao sub-district, Tak, Thailand.

The Mae Tao sub-district is located in the Mae Tao watershed, an important cadmium (Cd)-contaminated area in Thailand. This study was conducted to (i) determine Cd concentrations in rice collected from households in the area, (ii) assess the Cd exposure and potential health risk (HQ) from rice consumption in local adults and (iii) investigate how the factors of individual characteristics and consumption behavior affect the level of HQ. A total of 159 rice samples were collected from households in all 6 villages of the Mae Tao sub-district for analysis of Cd by inductively coupled plasma mass spectrometry. Biodata information and rice consumption behavior were surveyed from local residents at the same time as rice sample collection. Approximately 19.8% and 19.1% of white rice and sticky rice, respectively, contained total Cd higher than the Codex maximum standard of Cd in rice (0.4 mg kg-1). Locally grown rice contained an average of 1.5 times more Cd than retail rice. Cd exposure from consuming only sticky rice was the highest (2.26 × 10-3 mg kg-1 day-1), followed by the consumption of both types of rice (1.39 × 10-3 mg kg-1 day-1) and the consumption of only white jasmine rice (6.30 × 10-4 mg kg-1 day-1). The highest and lowest average HQ values were found in the only sticky rice consumption pattern (2.263) and the only white rice consumption pattern (0.630), respectively. The potential health risk from Cd in each rice consumption pattern was mainly influenced by the total Cd concentration in rice and the rice ingestion rate.

Reductive dissolution and sequestration of arsenic by microbial iron and thiosulfate reduction.

Iron oxide and oxy-hydroxide are commonly used for remediation and rehabilitation of arsenic (As)-contaminated soil and water. However, the stability of As sequestered by iron oxide and oxy-hydroxide under anaerobic conditions is still uncertain. Geochemical properties influence the behavior of As; in addition, microbial activities affect the mobility of sequestered As in soil and water. Microbial-mediated iron reduction can increase the mobility of As by reductive dissolution of Fe oxide; however, microbial-mediated sulfate reduction can decrease the mobility of As by sulfide mineral precipitation. This study investigated the geomicrobial impact on the behavior of As and stability of sequestered As in iron-rich sediment under anaerobic conditions. Increase in Fe(II) concentrations in water was evidence of microbial-mediated iron reduction. Arsenic concentrations increased with Fe(II) concentration; however, the thiosulfate reduction process also induced immobilization of As through the precipitation of AsFeS. Therefore, microbial-mediated iron reduction and thiosulfate reduction have opposite influences on the mobility of As under anaerobic condition.

Identification of the microbes mediating Fe reduction in a deep saline aquifer and their influence during managed aquifer recharge.

In this study, indigenous microbes enabling Fe reduction under saline groundwater conditions were identified, and their potential contribution to Fe release from aquifer sediments during managed aquifer recharge (MAR) was evaluated. Sediment and groundwater samples were collected from a MAR feasibility test site in Korea, where adjacent river water will be injected into the confined aquifer. The residual groundwater had a high salinity over 26.0 psu, as well as strong reducing conditions (dissolved oxygen, DO<2.0mg/L; oxidation-reduction potential, ORP<-100 mV) with high Fe(2+) concentrations. The indigenous microbes that mediate the reduction of Fe-minerals in this deep saline aquifer were found to be Citrobacter sp. However, column experiments to simulate field operation scenarios indicated that additional Fe release would be limited during MAR, as the dominant microbial community in the sediment would shift from Citrobacter sp. to Pseudomonas sp. and Limnohabitans sp. as river water injection alters the pore water chemistry.

Identification of refined petroleum products in contaminated soils using an identification index for GC chromatograms.

Hydrocarbons found in the environment are typically characterized by gas chromatography (GC). The shape of the GC chromatogram has been used to identify the source of petroleum contamination. However, the conventional practice of simply comparing the peak patterns of source products to those of environmental samples is dependent on the subjective decisions of individual analysts. We have developed and verified a quantitative analytical method for interpreting GC chromatograms to distinguish refined petroleum products in contaminated soils. We found that chromatograms for gasoline, kerosene, and diesel could be divided into three ranges with boundaries at C6, C8, C16, and C26. In addition, the relative peak area (RPA(GC)) of each range, a dimensionless ratio of the peak area within each range to that of the total range (C6-C26), had a unique value for each petroleum product. An identification index for GC chromatograms (ID(GC)), defined as the ratio of RPA(GC) of C8-C16 to that of C16-C26, was able to identify diesel and kerosene sources in samples extracted from artificially contaminated soils even after weathering. Thus, the ID(GC) can be used to effectively distinguish between refined petroleum products in contaminated soils.

Targeted removal of trichlorophenol in water by oleic acid-coated nanoscale palladium/zero-valent iron alginate beads.

A new material was developed and evaluated for the targeted removal of trichlorophenol (TCP) from among potential interferents which are known to degrade removal activity. To achieve TCP-targeted activity, an alginate bead containing nanoscale palladium/zero-valent iron (Pd/nZVI) was coated with a highly hydrophobic oleic acid layer. The new material (Pd/nZVI-A-O) preferentially sorbed TCP from a mixture of chlorinated phenols into the oleic acid cover layer and subsequently dechlorinated it to phenol. The removal efficacy of TCP by Pd/nZVI-A-O was not affected by co-existing organic substances such as Suwannee River humic acid (SRHA), whereas the material without the oleic acid layer (Pd/nZVI-A) became less effective with increasing SRHA concentration. The inorganic substances nitrate and phosphate significantly reduced the reactivity of Pd/nZVI-A, however, Pd/nZVI-A-O showed similar TCP removal efficacies regardless of the initial inorganic ion concentrations. The influence of bicarbonate on the TCP removal efficacies of both Pd/nZVI-A and Pd/nZVI-A-O was not significant. The findings from this study suggest that Pd/nZVI-A-O, with its targeted, constant reactivity for TCP, would be effective for treating this contaminant in surface water or groundwater containing various competitive substrates.

The role of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans in arsenic bioleaching from soil.

Bioleaching of As from the soil in an abandoned Ag-Au mine was carried out using Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. A. ferrooxidans is an iron oxidizer and A. thiooxidans is a sulfur oxidizer. These two microbes are acidophilic and chemoautotrophic microbes. Soil samples were collected from the Myoungbong and Songcheon mines. The main contaminant of the soil was As, with an average concentration of 4,624 mg/kg at Myoungbong and 5,590 mg/kg at Songcheon. A. ferrooxidans and A. thiooxidans generated lower pH conditions during their metabolism process. The bioleaching of As from soil has a higher removal efficiency than chemical leaching. A. ferrooxidans could remove 70 % of the As from the Myoungbong and Songcheon soils; however, A. thiooxidans extracted only 40 % of the As from the Myoungbong soil. This study shows that bioleaching is an effective process for As removal from soil.

Competitive inhibition of cytosolic Ca2+-dependent phospholipase A2 by acteoside in RBL-2H3 cells.

The aim of this study was to investigate whether acteoside isolated from Clerodendron trichotomum Thunberg may act as a selective inhibitor of phospholipase A(2) in RBL-2H3 cells. Acteoside dose-dependently inhibited 0.5 µM melittin-induced release of [(3)H]arachidonic acid, which was due to the inhibition of cytosolic Ca(2+)-dependent phospholipase A(2) (cPLA(2)) rather than secretory PLA(2) (sPLA(2)). In Dixon plots, the apparent K ( i ) value of acteoside on cPLA(2) was 5.9 µM and the inhibitory pattern appeared to be a competitive inhibitor. The above data, suggests that acteoside acts as a competitive inhibitor of cPLA(2) in RBL-2H3 cells.

Stabilization of the As-contaminated soil from the metal mining areas in Korea.

The stabilization efficiencies of arsenic (As) in contaminated soil were evaluated using various additives such as limestone, steel mill slag, granular ferric hydroxide (GFH), and mine sludge collected from an acid mine drainage treatment system. The soil samples were collected from the Chungyang area, where abandoned Au-Ag mines are located. Toxicity characteristic leaching procedure, synthetic precipitation leaching procedure, sequential extraction analysis, aqua regia digestion, cation exchange capacity, loss on ignition, and particle size distribution were conducted to assess the physical and chemical characteristics of highly arsenic-contaminated soils. The total concentrations of arsenic in the Chungyang area soil ranged up to 145 mg/kg. After the stabilization tests, the removal percentages of dissolved As(III) and As(V) were found to differ from the additives employed. Approximately 80 and 40% of the As(V) and As(III), respectively, were removed with the use of steel mill slag. The addition of limestone had a lesser effect on the removal of arsenic from solution. However, more than 99% of arsenic was removed from solution within 24 h when using GFH and mine sludge, with similar results observed when the contaminated soils were stabilized using GFH and mine sludge. These results suggested that GFH and mine sludge may play a significant role on the arsenic stabilization. Moreover, this result showed that mine sludge can be used as a suitable additive for the stabilization of arsenic.

Intracellular Ca Mobilization and Beta-hexosaminidase Release Are Not Influenced by 60 Hz-electromagnetic Fields (EMF) in RBL 2H3 Cells.

The effects of extremely low frequency electromagnetic fields (EMF) on intracellular Ca(2+) mobilization and cellular function in RBL 2H3 cells were investigated. Exposure to EMF (60 Hz, 0.1 or 1 mT) for 4 or 16 h did not produce any cytotoxic effects in RBL 2H3 cells. Melittin, ionomycin and thapsigargin each dose-dependently increased the intracellular Ca(2+) concentration. The increase of intracellular Ca(2+) induced by these three agents was not affected by exposure to EMF (60 Hz, 1 mT) for 4 or 16 h in RBL 2H3 cells. To investigate the effect of EMF on exocytosis, we measured beta-hexosaminidase release in RBL 2H3 cells. Basal release of beta-hexosaminidase was 12.3±2.3% in RBL 2H3 cells. Exposure to EMF (60 Hz, 0.1 or 1 mT) for 4 or 16 h did not affect the basal or 1 µM melittin-induced beta-hexosaminidase release in RBL 2H3 cells. This study suggests that exposure to EMF (60 Hz, 0.1 or 1 mT), which is the limit of occupational exposure, has no influence on intracellular Ca(2+) mobilization and cellular function in RBL 2H3 cells.

Morinda citrifolia Inhibits Both Cytosolic Ca-dependent Phospholipase A(2) and Secretory Ca-dependent Phospholipase A(2).

This study investigated the effects of the methanol extracts of Morinda citrifolia containing numerous anthraquinone and iridoid on phospholipase A(2) (PLA(2)) isozyme. PLA(2) activity was measured using various PLA(2) substrates, including 10-pyrene phosphatidylcholine, 1-palmitoyl-2-[(14)C]arachidonyl phosphatidylcholine ([(14)C]AA-PC), and [(3)H]arachidonic acid (AA). The methanol extracts suppressed melittin-induced [(3)H]AA release in a concentration-dependent manner in RAW 264.7 cells, and inhibited cPLA(2)/sPLA(2)-induced hydrolysis of [(14)C]AA-PC in a concentration- and time-dependent manner. A Dixon plot showed that the inhibition by methanol extracts on cPLA(2) and sPLA(2) appeared to be competitive with inhibition constants (K(i)) of 3.7microg/ml and 12.6microg/ml, respectively. These data suggest that methanol extracts of Morinda citrifolia inhibits both Ca(2+)-dependent PLA(2) such as, cPLA(2) and sPLA(2). Therefore, Morinda citrifolia may possess anti-inflammatory activity secondary to Ca(2+)-dependent PLA(2) inhibition.

Effect of Extremely Low Frequency Electromagnetic Fields (EMF) on Phospholipase Activity in the Cultured Cells.

This study was conducted to investigate the effects of extremely low frequency electromagnetic fields (EMF) on signal pathway in plasma membrane of cultured cells (RAW 264.7 cells and RBL 2H3 cells), by measuring the activity of phospholipase A(2) (PLA(2)), phospholipase C (PLC) and phospholipase D (PLD). The cells were exposed to the EMF (60 Hz, 0.1 or 1 mT) for 4 or 16 h. The basal and 0.5 µM melittin-induced arachidonic acid release was not affected by EMF in both cells. In cell-free PLA(2) assay, we failed to observe the change of cPLA(2) and sPLA(2) activity. Also both PLC and PLD activities did not show any change in the two cell lines exposed to EMF. This study suggests that the exposure condition of EMF (60 Hz, 0.1 or 1 mT) which is 2.4 fold higher than the limit of occupational exposure does not induce phospholipases-associated signal pathway in RAW 264.7 cells and RBL 2H3 cells.