Particle Surface Hydrophobicity and the Dechlorination of Chloro-Compounds by Iron Sulfides

Halogenated aliphatic compounds (HACs) can be reduced by iron sulfides in aqueous systems. Generally, the thermodynamics and kinetics of dehalogenation reactions are controlled by the mineralogical and particle surface characteristics of the iron sulfide, the composition of the HAC and reaction conditions such as component concentrations, pH and Eh. In this theoretical and experimental investigation of CCl₄ and C₂Cl₆ reduction by FeS and FeS₂, the roles of hydrophobic and hydrophilic sites on the iron sulfides were analyzed. Experimental data obtained through zeta potential measurements, were used along with the Gouy-Chapman model and the simple two-layer surface complexation model to relate iron sulfide surface hydroxyl densities to the degree of HAC dehalogenation. The surface hydroxyl site densities of FeS and FeS₂ were found to be 0.11 sites/nm² and 0.21 sites/nm², respectively. During the dehalogenation reaction process, CCl₄ was found to decrease to its first intermediate product CHCl₃ within the first 20 hours followed by a slower process of conversion to CH₂Cl₂. The results also show that FeS is less hydrated (more hydrophobic) than FeS₂. For CCl₄ and C₂Cl₆, FeS is a better dehalogenator than FeS₂. These results imply that particle surface hydrophobicity is a critical factor in surface-mediated dehalogenation of chlorinated compounds.     

Improvement of nuclide leaching resistance of paraffin waste form with low density polyethylene

Low-level liquid borate wastes have been immobilized with paraffin wax using a concentrate waste drying system (CWDS) in Korean nuclear power plants. The possibility for improving chemical durability of paraffin waste form was suggested in this study. A small amount of low density polyethylene (LDPE) was added to increase the leaching resistance of the existing paraffin waste form. The influence of LDPE on the leaching behavior of waste form was investigated by performing leaching test according to ANSI/ANS-16.1 procedure during 325 days. It was observed that the leaching of nuclides immobilized within paraffin waste form made a marked reduction although little content of LDPE was added to waste form. The acceptance criteria of paraffin waste form associated with leachability index (LI) and compressive strength after the leaching test were fully satisfied with the help of LDPE.     

Distribution and hydrodynamic model of the Keumdong oil spill in Kwangyang Bay, Korea

Oil concentrations in the seawater, seabed sediments, and shoreline sediments were measured from the samples collected 165 days after the Keumdong oil spill accident, which had occurred in Kwangyang Bay of the South Sea, Korea in September 1993. Distribution patterns of the concentrations in the seabed and shoreline sediments have allowed us to hindcast the transport and fate of the spilled oil. Overall, the patterns agree better with the southward (seaward) surface water circulation than with the northward (landward) bottom water circulation over the region. Rapid, initial dispersal of the spilled oil to the south and its subsequent grounding onto the intertidal seabed sediments, as well as onto the shorelines, appear to have made ineffective the subsurface oil transport by the bottom current.     

Differences in Eye and Hand Movements of Novice and Experienced Press Operators

Presses are very widely used in industrial and commercial companies and are often the source of serious accidents occurring during operation. Most of the accidents are due to inadequate training of novice operators. Continuous recordings of eye and hand movements of five novice operators and five experienced operators in press operation were made. Significant difference between novice and experienced operators was observed in eye fixation time, eye movement patterns, hand dwell time, and eye-hand coordination. Also, differences were observed in spatial distribution of eye fixations during the die-closing portion of a stroke. There were no significant differences between novice and experienced operators in the eye and the hand movement time. The results could be used as basic data to establish a guide determining the method and training period to train novice operators.     

Screening and prioritizing the precursors of improvised explosive devices from commodity chemicals being controlled under Korean regulations

Improvised explosive devices (IEDs) have become an alternative method for terrorists or criminals who face difficulties in obtaining traditional explosives as threatening tools. The ease of obtaining precursor materials from commodity chemicals in the free market and the ease of generating bombs through the hands of novices have created problems. Controlling the potential precursors to defeat illegal acquisition is not trivial due to their widespread use as common merchandise among chemical industries and consumers. However, efforts to identify the potential precursors may be the first step for devising appropriate control measures. In this study, we proposed a systematic screening method for identifying potential IED precursors (IEDPs) from commodity chemicals, which are regulated by Korean controls. We identified 25 potential IEDPs from 3980 candidate chemicals that can be diverted into IEDs or homemade bombs but are not likely to be solely used as an IED. We also developed a methodology of prioritizing the potential precursor chemicals to assess the urgency of controls using a scoring system with four criteria: previous listing as an official precursor; past record of being encountered in criminal use; volume of commercial circulation, which denotes the probability of exposure to individuals; and the degree of regulatory counter-measures against illegal acquisitions that are currently effective in Korea.     

Anatomical localization and stereoisomeric composition of <Emphasis Type="Italic">Tribolium castaneum</Emphasis> aggregation pheromones

We report that the abdominal epidermis and associated tissues are the predominant sources of male-produced pheromones in the red flour beetle, Tribolium castaneum and, for the first time, describe the stereoisomeric composition of the natural blend of isomers of the aggregation pheromone 4,8-dimethyldecanal (DMD) in this important pest species. Quantitative analyses via gas chromatography–mass spectrometry showed that the average amount of DMD released daily by single feeding males of T. castaneum was 878 ± 72 ng (SE). Analysis of different body parts identified the abdominal epidermis as the major source of aggregation pheromone; the thorax was a minor source, while no DMD was detectable in the head. No internal organs or obvious male-specific glands were associated with pheromone deposition. Complete separation of all four stereoisomers of DMD was achieved following oxidation to the corresponding acid, derivatization with (1R, 2R)- and (1S, 2S)-2-(anthracene-2,3-dicarboximido)cyclohexanol to diastereomeric esters, and their separation on reversed-phase high-performance liquid chromatography at −54°C. Analysis of the hexane eluate from Porapak-Q-collected volatiles from feeding males revealed the presence of all four isomers (4R,8R)/(4R,8S)/(4S,8R)/(4S,8S) at a ratio of approximately 4:4:1:1. A walking orientation bioassay in a wind tunnel with various blends of the four synthetic isomers further indicated that the attractive potency of the reconstituted natural blend of 4:4:1:1 was equivalent to that of the natural pheromone and greater than that of the 1:1 blend of (4R,8R)/(4R,8S) used in commercial lures.     

Characteristics of roadside air pollution in Korean metropolitan city (Daegu) over last 5 to 6 years: temporal variations, standard exceedances, and dependence on meteorological conditions

The present study performed a roadside data analysis to provide baseline data for exploring associations between environmental exposure to four gaseous pollutants and health effects on residents living near roadways. The yearly roadside concentrations of CO and SO₂ showed a well-defined decreasing trend, whereas those of NO₂ and O₃ exhibited the reverse trend. In most cases, the diurnal trends of the roadside concentrations were well-defined for all seasons, plus the daytime concentrations were higher than the nighttime concentrations. In contrast to the other target pollutants, the daytime O₃ concentrations observed at the roadside sites were lower than those observed at the residential site, likely due to high-levels of fresh NO from traffic emissions that rapidly react with O₃, thereby reducing the O₃ roadside level. The Sunday roadside concentrations of CO, NO₂, and SO₂ were similar to or somewhat lower than the weekday concentrations. Conversely, for O_3, the Sunday roadside concentrations were similar to or somewhat higher than the weekday concentrations. The higher O₃ concentrations on Sunday may be due to the reduced titration from a decrease in NO_x emissions under VOC-limited conditions (low VOC/NO_x conditions). The monthly averages of O₃ concentrations exhibited the reverse seasonal variation to the other target compounds, with peak O₃ concentrations between April and June, and the second peak between August and October. It is also suggested that for O₃, the 8-h standard is more stringent than the 1-h standard, while for NO₂ and SO₂, the 1-h standard is more stringent than the 24-h standard. The multiple regression equations obtained from the relationship between the concentrations and five meteorological parameters indicated that the number and type of meteorological variables in the equations varied according to the pollutant, monitoring station, or season.     

Iron and organo-bentonite for the reduction and sorption of trichloroethylene

Hybrid barriers using dechlorination and immobilization were studied to remove trichloroethylene (TCE) in this study. Hybrid barriers of iron filings and organo (hexadecyltrimethylammonium, HDTMA)-bentonite were simulated in columns to assess the performance of the hybrid barriers. TCE reduction rate for the mixture of zero valent iron (ZVI) and HDTMA-bentonite was approximately seven times higher than that for ZVI, suggesting the reduction of TCE was accelerated when HDTMA-bentonite was mixed with ZVI. For the column of two separate layers of iron and HDTMA-bentonite, TCE reduction rate was nearly similar to that for ZVI alone, but the partition coefficient (Kd) was 4.5 times higher than that for ZVI only. TCE was immobilized in the first layer with HDTMA-bentonite due to sorption, and then dechlorinated in the second layer with iron filings due to reduction. The HDTMA-bentonite and minimally-desorbed HDTMA from the organo-bentonite are believed to contribute the increase in TCE concentration on iron surface so that more TCE could be available for reduction. Therefore, the incorporation of HDTMA-bentonite into ZVI not only can effectively retard the transport of chlorinated organic contaminants from landfill leachate or oil shock in subsurface environment, also can expedite the reduction rate of TCE.     

Estimating Maximum Concentrations for Open Path Monitoring Along a Fixed Beam Path

ABSTRACT

Researchers have applied open path optical sensing techniques to a variety of workplace and environmental monitoring problems. Usually these data are reported in terms of a path-average (or path-integrated) concentration. When assessing potential human exposures along a beam path, this path-average value is not always informative, since concentrations along the path can vary substantially from the beam average. The focus of this research is to arrive at a method for estimating the upper-bound in contaminant concentrations over a fixed open beam path. The approach taken here uses a statistical model to estimate an upper-bound concentration based on a combination of the path-average and a measure of the spatial variability computed from point samples along the beam path. Results of computer simulations and experimental testing in a controlled ventilation chamber indicate that the model produced conservative estimates for the maximum concentration along the beam path. This approach may have many applications for open path monitoring in workplaces or wherever maximum concentrations are a concern.     

Chemical characteristics of fine particulate matters measured during severe winter haze events in Ulaanbaatar,Mongolia

In order to investigate the chemical characteristics of atmospheric aerosol measured during a severe winter haze event, 12-hr PM_2.5 (particulate matter with an aerodynamic diameter ≤2.5 μm) samples were collected at an urban site in Ulaanbaatar, Mongolia, from January 9 to February 17, 2008. On average, 12-hr PM_2.5 mass concentration was 105.1 ± 34.9 μg/m³. Low PM_2.5 mass concentrations were measured when low pressure developed over central Mongolia. The 12-hr average organic mass by carbon (OMC) varied from 6.4 to 132.3 μg/m³, with a mean of 54.9 ± 25.4 μg/m³, whereas elemental carbon (EC) concentration ranged from 0.1 to 3.6 μgC/m³, with a mean of 1.5 ± 0.8 μgC/m³. Ammonium sulfate was found to be the most abundant water-soluble ionic component in Ulaanbaatar during the sampling period, with an average concentration of 11.3 ± 5.0 μg/m³. In order to characterize the effect of air mass pathway on fine particulate matter characteristics, 5-day back-trajectory analysis was conducted, using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The haze level was classified into three categories, based on the 5-day air mass back trajectories, as Stagnant (ST), Continental (CT), and Low Pressure (LP) cases. PM_2.5 mass concentration during the Stagnant condition was approximately 2.5 times higher than that during the Low Pressure condition, mainly due to increased pollutant concentration of OMC and secondary ammonium sulfate.

Implications: Mongolia is experiencing rapid rates of urbanization similar to other Asian countries, resulting in air pollution problems by the growing number of automobiles and industrialization. Ulaanbaatar, capital of Mongolia, is inherently vulnerable to air pollution because of its emission sources, topography, and meteorological characteristics. Very limited measurements on chemical characteristics of particulate matter have been carried out in Ulaanbaatar, Mongolia.