Factors influencing natural occurrence of fluoride-rich groundwaters: a case study in the southeastern part of the Korean Peninsula

Factors regulating the occurrence of fluoride in groundwater were investigated using natural isotope tracers and geochemical data in the southeastern part of Korea where about 10% of the total public water-supply wells (n=422) inspected in this study had fluoride levels exceeding the drinking water limit of Korea (1.5 mg/l). The F-rich public wells are mostly distributed along the major faults, especially in the terrain of the F-rich granitic rocks. The stable isotope analysis results provide substantial information for the relative ages of groundwaters. It is revealed that the F-rich groundwaters are deeply circulating paleogroundwaters and occur along the faults due to upward flow along the fault plane. While reacting with granitic rocks for a prolonged period, the F concentrations of groundwater are continuously enriched even after the groundwater reaches an equilibrium state with respect to fluorite (CaF2) due to removal of Ca by precipitation of calcite (CaCO3). These observations reflect that rock chemistry, groundwater age, well depth, and geologic structure are the important factors controlling the occurrence of high F groundwaters. However, high F groundwaters are rarely observed in the fault zones where the associated fractures are widely developed. Isotopic signature provides an evidence for deep penetration of recently recharged groundwater into the wide fault zone, indicating that the hydrologic condition of the fault is also an important factor controlling the occurrence of high F groundwaters.     

Simultaneous Measurements of Atmospheric Pollutants and Visibility with a Long-Path DOAS System in Urban Areas

In this paper, the applicability of a Long-Path Differential Optical Absorption Spectroscopy (LP-DOAS) system was checked for the feasibility of the simultaneous measurement of trace gases (such as O₃, NO₂, SO₂, and HCHO) and atmospheric visibility (light extinction by aerosols) in Asian urban areas. Field studies show that an LP-DOAS system can simultaneously measure the key pollutants (such as O₃, NO₂, SO₂, and HCHO) at detection limits in the ppb/sub-ppb range as well as the Mie extinction coefficient with an uncertainty of 0.1 km^–1 at time resolution of a few minutes. It is thus concluded that the use of LP-DOAS system is feasible for simultaneous measurement of gaseous pollutants as well as an atmospheric extinction coefficient which is tightly bound to fine particulate concentration.     

Modeling of road traffic noise and estimated human exposure in Fulton County, Georgia, USA

Environmental noise is a major source of public complaints. Noise in the community causes physical and socio-economic effects and has been shown to be related to adverse health impacts. Noise, however, has not been actively researched in the United States compared with the European Union countries in recent years. In this research, we aimed at modeling road traffic noise and analyzing human exposure in Fulton County, Georgia, United States. We modeled road traffic noise levels using the United States Department of Transportation Federal Highway Administration Traffic Noise Model implemented in SoundPLAN?. After analyzing noise levels with raster, vector and fa?ade maps, we estimated human exposure to high noise levels. Accurate digital elevation models and building heights were derived from Light Detection And Ranging survey datasets and building footprint boundaries. Traffic datasets were collected from the Georgia Department of Transportation and the Atlanta Regional Commission. Noise level simulation was performed with 62 computers in a distributed computing environment. Finally, the noise-exposed population was calculated using geographic information system techniques. Results show that 48% of the total county population [N=870,166 residents] is potentially exposed to 55 dB(A) or higher noise levels during daytime. About 9% of the population is potentially exposed to 67 dB(A) or higher noises. At nighttime, 32% of the population is expected to be exposed to noise levels higher than 50 dB(A). This research shows that large-scale traffic noise estimation is possible with the help of various organizations. We believe that this research is a significant stepping stone for analyzing community health associated with noise exposures in the United States.     

Distribution of perfluorochemicals between sera and milk from the same mothers and implications for prenatal and postnatal exposures

The levels of six perfluorocarboxylates (PFCAs), four perfloroalkylsulfonates (PFASs), and one sulfonamide were measured in paired samples of maternal serum, umbilical cord serum, and breast milk. The maternal and cord sera were strongly correlated with each other for all measured compounds (r > 0.5 and p < 0.01). Nevertheless, there was a significant difference in compound composition profile between the two sera matrices, with a more depletion of the longer chain compounds in cord serum. The transfer efficiency values from maternal to cord serum (TF_CS/MS) decreased by 70% with each increasing unit of -CF₂ chain within a PFCA group, and for perfluorooctanesulfonate (PFOS), by a half compared to perfluorooctanoate (PFOA). In contrast to the strong correlation in concentrations between the two sera matrices, the pattern of compounds in breast milk differed considerably with those in sera. Accordingly, compound- and matrix-specific transfer must be considered when assessing prenatal and postnatal exposure.     

Chemical characteristics of long-range transport aerosol at background sites in Korea

In this study, background concentration sites of Deokjeok and Gosan, which were deemed suitable for monitoring the impact of long-range transported air pollutants, were selected. An investigation of the source types of pollutants, their locations, and relative quantitative contributions to the particulate concentrations at both sites using appropriate methodologies to make initial estimations was conducted. Episodic measurements of PM_2.5, PM₁₀, and size distribution, along with its ion and carbon components were performed from 2005 to 2007, and a comprehensive analysis of the results was conducted utilizing back trajectory analysis. As for frequency of wind direction, it was quite apparent that the two sites are heavily influenced by air masses originating from the eastern and northern regions of China. For PM_2.5 and PM₁₀, the mass concentrations from north and east China were higher than other cases, originating from the ocean. In the northerly-wind case, meteorological properties for Deokjeok and Gosan and the influence of carbon emissions from northwest Korea resulted in a changing of air mass properties during transport. As was the case with mass concentration, the highest contribution for ionic and carbon components of PM_2.5 and PM₁₀ for both sites appeared for the westerly wind case. A specially high relative contribution, greater than 1.4 times, was apparent in the secondary aerosol case because of a large influence of long-range transported pollutants from east China. Carbon components exhibited different behaviors for the northerly and westerly wind cases compared with secondary aerosol. The major reason for this discrepancy appears to be the carbon emissions from northwest Korea.     

Evaluation of Dynamically Dimensioned Search Algorithm for Optimizing SWAT by Altering Sampling Distributions and Searching Range

The primary advantage of Dynamically Dimensioned Search (DDS) algorithm is that it outperforms other optimization techniques in both convergence speed and searching ability for parameter sets that satisfy statistical guidelines while requiring only one algorithm parameter (perturbation factor) in the optimization process. Conventionally, a default value of 0.2 is used as the perturbation factor, where a normal distribution is applied with mean sampling distribution of zero and variance of one. However, the perturbation factor sensitivity to the performance of DDS for watershed modeling is still unknown. The fixed‐form sampling distribution may result in finding parameters at the local scale rather than global in the sampling space. In this study, the efficiency of DDS was evaluated by altering the perturbation factor (from 0.05 to 1.00) and the selection of sampling distribution (normal and uniform) on hydrologic and water quality predictions in a lowland agricultural watershed in Texas, United States. Results show that the use of altered perturbation factor may cause variations in convergence speed or the ability to find better solutions. In addition, DDS results were found to be very sensitive to sampling distribution selections, where DDS‐N (normal distribution) outperformed DDS‐U (uniform distribution) in all case scenarios. The choice of sampling distributions could be the potential major factor to be attributed for the performance of auto‐calibration techniques for watershed simulation models.     

Effect of biochar amendment on tylosin adsorption-desorption and transport in two different soils

The role of biochar as a soil amendment on the adsorption-desorption and transport of tylosin, a macrolide class of veterinary antibiotic, is little known. In this study, batch and column experiments were conducted to investigate the adsorption kinetics and transport of tylosin in forest and agricultural corn field soils amended with hardwood and softwood biochars. Tylosin adsorption was rapid at initial stages, followed by slow and continued adsorption. Amounts of adsorption increased as the biochar amendment rate increased from 1 to 10%. For soils with the hardwood biochar, tylosin adsorption was 10 to 18% higher than that when using the softwood biochar. Adsorption kinetics was well described by Elovich equation ( ≥ 0.921). As the percent of biochar was increased, the rates of initial reactions were generally increased, as indicated by increasing α value at low initial tylosin concentration, whereas the rates during extended reaction times were generally increased, as indicated by decreasing β value at high initial tylosin concentration. A considerably higher amount of tylosin remained after desorption in the corn field soil than in the forest soil regardless of the rate of biochar amendment, which was attributed to the high pH and silt content of the former. The breakthrough curves of tylosin showed that the two soils with biochar amendment had much greater retardation than those of soils without biochar. The CXTFIT model for the miscible displacement column study described well the peak arrival time as well as the maximum concentration of tylosin breakthrough curves but showed some underestimation at advanced stages of tylosin leaching, especially in the corn field soil. Overall, the results indicate that biochar amendments enhance the retention and reduce the transport of tylosin in soils.     

Impact of pH buffer capacity of sediment on dechlorination of atrazine using zero valent iron

This research investigated the role of the pH buffer capacity of sediment on the dechlorination of atrazine using zero valent iron (ZVI). The buffer capacity of the sediment was quantified by batch experiments and estimated to be 5.0 cmol OH^? · pH^?1. The sediments were spiked with atrazine at 7.25-36.23 mg kg^?1 (6.21 × 10^?7–3.09 × 10^?6 mol atrazine · g^?1 sediment) for the batch experiments. The buffer capacity of the sediment maintained the sediment suspension at neutral pH, thereby enabling continuous dechlorination until the buffer capacity of the sediment was depleted. The pseudo-first order dechlorination constants were estimated to be in the range of 1.19 × 10^?2?7.04 × 10^?2 d^?1 for the atrazine-spiked sediments.     

Impact of pH buffer capacity of sediment on dechlorination of atrazine using zero valent iron

This research investigated the role of the pH buffer capacity of sediment on the dechlorination of atrazine using zero valent iron (ZVI). The buffer capacity of the sediment was quantified by batch experiments and estimated to be 5.0 cmol OH(-) . pH(-1). The sediments were spiked with atrazine at 7.25-36.23 mg kg(-1) (6.21 x 10(-7)-3.09 x 10(-6) mol atrazine . g(-1) sediment) for the batch experiments. The buffer capacity of the sediment maintained the sediment suspension at neutral pH, thereby enabling continuous dechlorination until the buffer capacity of the sediment was depleted. The pseudo-first order dechlorination constants were estimated to be in the range of 1.19 x 10(-2)-7.04 x 10(-2) d(-1) for the atrazine-spiked sediments.     

Volatile pollutants emitted from selected liquid household products

BACKGROUND, AIM, AND SCOPE: To identify household products that may be potential sources of indoor air pollution, the chemical composition emitted from the products should be surveyed. Although this kind of survey has been conducted by certain research groups in Western Europe and the USA, there is still limited information in scientific literature. Moreover, chemical components and their proportions of household products are suspected to be different with different manufacturers. Consequently, the current study evaluated the emission composition for 42 liquid household products sold in Korea, focusing on five product classes (deodorizers, household cleaners, color removers, pesticides, and polishes). MATERIALS AND METHODS: The present study included two phase experiments. First, the chemical components and their proportions in household products were determined using a gas chromatograph and mass spectrometer system. For the 19 target compounds screened by the first phase of the experiment and other selection criteria, the second phase was done to identify their proportions in the purged-gas phase. RESULTS: The number of chemicals in the household products surveyed ranged from 9 to 113. Eight (product class of pesticides) to 17 (product class of cleaning products) compounds were detected in the purged-gas phase of each product class. Several compounds were identified in more than one product class. Six chemicals (acetone, ethanol, limonene, perchloroethylene (PCE), phenol, and 1-propanol) were identified in all five product classes. There were 13 analytes occurring with a frequency of more than 10% in the household products: limonene (76.2%), ethanol (71.4%), PCE (66.7%), phenol (40.5%), 1-propanol (35.7%), decane (33%), acetone (28.6%), toluene (19.0%), 2-butoxy ethanol (16.7%), o-xylene (16.7%), chlorobenzene (14.3%), ethylbenzene (11.9%), and hexane (11.9%). All of the 42 household products analyzed were found to contain one or more of the 19 compounds. DISCUSSION: The chemical composition varied broadly along with the product classes or product categories, and it was different from that reported in other studies abroad, although certain target chemicals were identified in both studies. This finding supports an assertion that chemical components emitted from household products may be different in different products and with different manufacturers. The chlorinated pollutants identified in the present study have not been reported to be components of cleaning products in papers published since the early 1990s. Limonene was identified as having the highest occurrence in the household products in the present study, although it was not detected in any of 67 household products sold in the U.S. CONCLUSIONS: The emission composition of selected household products was successfully examined by purge-and-trap analysis. Along with other exposure information such as use pattern of household products and the indoor climate, this composition data can be used to estimate personal exposure levels of building occupants. This exposure data can be employed to link environmental exposure to health risk. It is noteworthy that many liquid household products sold in Korea emitted several toxic aromatic and chlorinated organic compounds. Moreover, the current finding suggests that product types and manufacturers should be considered, when evaluating building occupants' exposure to chemical components emitted from household products. RECOMMENDATIONS AND PERSPECTIVES: The current findings can provide valuable information for the semiquantitative estimation of the population inhalation exposure to these compounds in indoor environments and for the selection of safer household products. However, although the chemical composition is known, the emissions of household products might include compounds formed during the use of the product or compounds not identified as ingredients by this study. Accordingly, further studies are required, and testing must be done to determine the actual composition being emitted. Similar to eco-labeling of shampoos, shower gels, and foam baths proposed by a previous study, eco-labeling of other household products is suggested.