Biomedical subjects

C M Kao

Publications and source records attributed to C M Kao.

At least 37 records · Page 2Linked to original sources

PubMed2001

Evaluation of natural attenuation rate at a gasoline spill site.

Contamination of groundwater by gasoline and other petroleum-derived hydrocarbons released from underground storage tanks (USTs) is a serious and widespread environmental problem. Natural attenuation is a passive remedial approach that depends upon natural processes to degrade and dissipate contaminants in soil and groundwater. Currently, in situ column technique, microcosm, and computer modeling have been applied for the natural attenuation rate calculation. However, the subsurface heterogeneity reduces the applicability of these techniques. In this study, a mass flux approach was used to calculate the contaminant mass reduction and field-scale decay rate at a gasoline spill site. The mass flux technique is a simplified mass balance procedure, which is accomplished using the differences in total contaminant mass flux across two cross-sections of the contaminant plume. The mass flux calculation shows that up to 87% of the dissolved total benzene, toluene, ethylbenzene, and xylene (BTEX) isomers removal was observed via natural attenuation at this site. The efficiency of natural biodegradation was evaluated by the in situ tracer method, and the first-order decay model was applied for the natural attenuation/biodegradation rate calculation. Results reveal that natural biodegradation was the major cause of the BTEX mass reduction among the natural attenuation processes, and approximately 88% of the BTEX removal was due to the natural biodegradation process. The calculated total BTEX first-order attenuation and biodegradation rates were 0.036 and 0.025% per day, respectively. Results suggest that the natural attenuation mechanisms can effectively contain the plume, and the mass flux method is useful in assessing the occurrence and efficiency of the natural attenuation process.

Biodegradation, Environmental↗

PubMed2001

Application of microbial enumeration technique to evaluate the occurrence of natural bioremediation.

Natural bioremediation is believed to be the major processes that account for both containment of the petroleum-hydrocarbon plume and reduction of the contaminant concentrations. In this study, the feasibility of applying the microbial enumeration technique was assessed for natural biodegradation evaluation at three selected gasoline spill sites. At each site, two monitor wells were installed along the groundwater flow, and one multilevel sampler (MLS) was installed to delineate the vertical distribution of the contaminant plume. Two continuous soil cores were collected at each site to evaluate the horizontal distribution of the microbial activity. Soil samples were used for microbial enumeration, grain-size distribution analysis, and sediment extraction. In situ tracer study was performed using 1,2,4-trimethylbenzene (1,2,4-TMB) as the tracer to study the efficiency of contaminant biodegradation. Investigation results demonstrate the agreement between microbial enumeration and other evaluation techniques for natural bioremediation (e.g., geochemical indicator analysis, tracer study). Results suggest that the microbial enumeration is useful in assessing the occurrence, efficiency, and status of the bioremediation. Because this technique provides insight into factors controlling contaminant biodegradation, it could be performed as the supplemental method for natural bioremediation evaluation at petroleum-hydrocarbon spill sites.

Benzene Derivatives↗

PubMed2001

Development of a biobarrier for the remediation of PCE-contaminated aquifer.

The industrial solvent tetrachloroethylene (PCE) is among the most ubiquitous chlorinated compounds found in groundwater contamination. The objective of this study was to develop a biobarrier system, which includes a peat layer to enhance the anaerobic reductive dechlorination of PCE in situ. Peat was used to supply primary substrate (electron donor) continuously. A laboratory-scale column experiment was conducted to evaluate the feasibility of this proposed system or PCE removal. This experiment was performed using a series of continuous-flow glass columns including a soil column, a peat column, followed by two consecutive soil columns. Anaerobic acclimated sludges were inoculated in all three soil columns to provide microbial consortia for PCE biodegradation. Simulated PCE-contaminated groundwater with a flow rate of 0.25 l/day was pumped into this system. Effluent samples from each column were analyzed for PCE and its degradation byproducts (trichloroethylene (TCE), cis-dichloroethylene (cis-DCE), vinyl chloride (VC), ethylene (ETH), and ethane). Results show that the decrease in PCE concentrations and production of PCE byproducts were observed over a 65-day operating period. Up to 98%, of PCE removal efficiency was obtained in this passive system. Results indicate that the continuously released organics from peat column enhanced PCE biotransformation. Thus, the developed biobarrier treatment scheme has the potential to be developed into a cost-effective in situ PCE-remediation technology, and can be utilized as an interim step to aid in system scale-up.

Biotransformation↗

PubMed2001

Evaluation of TCDD biodegradability under different redox conditions.

Polychlorinated dibenzo-p-dioxins have been generated as unwanted by-products in many industrial processes. Although their widespread distribution in different environmental compartments has been recognized, little is known about their fate in the ultimate environment sinks. The highly stable dioxin isomer 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been called the most toxic compound known to man. In this laboratory microcosm study, TCDD bioavailability was evaluated under five reduction/oxidation (redox) conditions including aerobic biodegradation, aerobic cometabolism, methanogenesis, iron reduction, and reductive dechlorination. Activated sludge and aquifer sediments from a TCDD and a pentachlorophenol (PCP) contaminated site were used as the inocula. Acetate, sludge cake, and cane molasses were used as the primary substrates (carbon sources) in cometabolism and reductive dechlorination microcosms. After a 90-day incubation period, microcosms constructed under reductive dechlorination conditions were the only treatment showing promising remediation results. The highest TCDD degradation rate [up to 86% of TCDD removal (with an initial concentration of 96 microg/kg of soil)] was observed in the microcosms with anaerobic activated sludge as the microbial inocula and sludge cakes as the primary substrates. Except for reductive dechlorination microcosms, no significant TCDD removal was observed in the microcosms prepared under other conditions. Thus, application of an effective primary substrate to enhance the reductive dechlorination process is a feasible method for TCDD bioremediation. Bioremediation expense can be significantly reduced by the supplement of some less expensive alternative substrates (e.g., sludge cakes, cane molasses). Results would be useful in designing a scale-up in situ or on-site bioremediation system such as bioslurry reactor for field application.

Bacteria, Aerobic↗

PubMed2001

Regulating colored textile wastewater by 3/31 wavelength ADMI methods in Taiwan.

The wastewater from textile dyeing facilities is difficult to treat satisfactorily because of high compositional variability and high color intensity. To reduce colored effluents discharged into watercourses, the government of Taiwan adopted the Effluent True Color Standard in 1998. The true color discharge limit is 400 American Dye Manufactures Institute (ADMI) units. The adopted analytical method is the ADMI Tristimulus Filter Method (3 wavelength (WL) method), and the 31 WL ADMI method might be also adopted as an alternative for color value measurement. The refractory nature of textile dyes and the introduction of this new regulation present an environmental challenge to the Taiwanese textile industry. The main objectives of this study were to (1) evaluate the efficacy of current wastewater treatment systems for controlling the colored textile wastewater discharges, and (2) evaluate the correlations between 3 and 31 WL ADMI methods. Ten representative textile wastewater treatment facilities employing biological and chemical coagulation treatment technologies were selected to perform a 10-consecutive-day effluent sampling and analysis. Results show that a significant difference between 3 and 31 ADMI methods was observed. These two ADMI methods cannot be substituted for each other, and the discharge standard should be determined based on the selected testing method. Investigation results also suggest that the commonly used wastewater treatment technology (biological + chemical coagulation) fails to effectively remove dye from the colored textile wastewater. Sodium hypochlorite (NaOCl) addition was applied by most facilities as the temporary post-polishment step to comply with the color discharge standard.

Chemistry Techniques, Analytical↗

PubMed2001

Laboratory column studies for evaluating a barrier system for providing oxygen and substrate for TCE biodegradation.

The industrial solvent trichloroethylene (TCE) is among the most ubiquitous chlorinated compounds found in groundwater contamination. The objective of this study was to develop a biobarrier system containing oxygen-organic releasing material to enhance the aerobic cometabolism of TCE in situ. The oxygen-organic material, which contains calcium peroxide and peat, is able to release oxygen and primary substrates continuously upon contact with water. Batch experiments were conducted to design and identify the components of the oxygen-organic releasing material, and evaluate the oxygen and organic substrate (presented as COD equivalent) release from the designed oxygen-organic material. The observed oxygen and chemical oxygen demand (COD) release rates were approximately 0.0246 and 0.052 mg/d/g of material, respectively. A laboratory-scale column experiment was then conducted to evaluate the feasibility of this proposed system for the bioremediation of TCE-contaminated groundwater. This system was performed using a series of continuous-flow glass columns including a soil column, an oxygen-organic material column, followed by two consecutive soil columns. Aerobic acclimated sludges were inoculated in all three soil columns to provide microbial consortia for TCE biodegradation. Simulated TCE-contaminated groundwater with a flow rate of 0.25 l/day was pumped into this system. Effluent samples from each column were analyzed for TCE and other indicating parameters (e.g., pH, dissolved oxygen). Results show that the decreases in TCE concentrations were observed over a 4-month operating period. Up to 99% of TCE removal efficiency was obtained in this passive system. Results indicate that the continuously released oxygen and organic substrates from the oxygen-organic materials enhanced TCE biotransformation. Thus, the biobarrier treatment scheme has the potential to be developed into an environmentally and economically acceptable remediation technology.

Biodegradation, Environmental↗

PubMed2001

Control of non-point source pollution by a natural wetland.

Wetland creation and restoration is a reliable and efficient technology for the remediation of contaminated water. Knowledge from the natural wetland systems would be necessary to enhance the operational efficiency of constructed wetlands. In this study, a mountainous wetland located in McDowell County, North Carolina, USA was selected to demonstrate the effects of the natural filtration and restoration system on the maintenance of surface water quality. The hydraulic retention time (HRT) for the wetland was 10.5 days based on the results from a dye release study. Water quality monitoring of the wetland was conducted from May to August 1997. One major storm event and baseline water quality samples were collected and analyzed. Analytical results indicate that this wetland removed a significant amount of non-point source (NPS) pollutants [more than 80% N removal, 91% of total suspended solid removal, 59% of total phosphorus removal, and 66% of chemical oxygen demand (COD) removal] caused by the studied storm event. Sediment accretion monitoring results indicate that the accretion rate in the wetland was only 4 mm/year. Therefore, the wetland would require 100 years to fill at the measured sediment accretion rate. The high organic content of sediments (16%) indicates that the wetland is building the characteristic organic layer on the bottom of the wetland. Results from this study would be very useful in the maintenance of natural wetlands and design of constructed wetlands for water treatment.

Conservation of Natural Resources↗

PubMed2001

Effects of subsurface heterogeneity on natural bioremediation at a gasoline spill site.

A test cell of 3-m by 6-m located at the mid-point of a gasoline spill site was selected to test the hypothesis that the rate of hydrocarbon biodegradation is influenced by the spatial distribution of the electron acceptors, aqueous geochemistry, and microbial population. Multilevel samplers (MLSs) were installed at four corners of the test cell for groundwater sampling. Sampling ports were placed at 0.3-m intervals from 1.5 to 4.8 m below land surface (bls). A 0.91-m by 12.7-cm sediment core (from 3.3 to 4.2 m bls) in the center of the MLSs was collected. The core was cut into 7 sections, and each was used for sediment extractions, microbial enumeration, grain size distribution, and microcosm studies. Groundwater analytical results indicate that iron reduction was the dominant biodegradation process within this test cell. Iron-reducing process caused the preferential removal of certain compounds. Microbial enumeration results show that the distribution of microbial population varied with depth and sediment materials. Lower microbial population was observed in those sections with higher portion of clayey materials. The less permeable materials would limit the bacterial transport, decrease the bioavailability of Fe(III) to iron-reducing bacteria, and thus cause the low biodegradation activity. Results suggest that using blended sediments for biodegradation rate measurements may provide misleading results.

Biodegradation, Environmental↗

PubMed2001

Evaluation of atrazine removal processes in a wetland.

Agricultural non-point source (NPS) pollution is considered to be the largest single category resulting in water quality deterioration. Pesticide is one of the main detrimental agricultural NPS constituents causing the impairment of water bodies. In this study, a mountainous wetland located in McDowell County, North Carolina, was selected to demonstrate the effects of the natural wetland system on the removal of NPS pesticide (atrazine) pollution to maintain the surface water quality. The selected wetland receives water from two unnamed creeks, which drain primarily agricultural lands. The hydraulic retention time (HRT) for the wetland was approximately 10.5 days based on the results from a dye release study. Water quality monitoring of the wetland was conducted from March to October 1998. One major storm and baseline water quality samples were analyzed. Analytical results indicate that the wetland completely removed NPS atrazine flushed from the upgradient agricultural lands. Laboratory microcosm experiments were conducted to evaluate the feasibility of using the wetland sediments as the microbial sources to enhance the atrazine biodegradation. Microcosm results suggest that atrazine can be degraded under anaerobic or reductive dechlorinating conditions when sucrose was provided as the primary substrate. Atrazine can also serve as the nitrogen source for the growth of microorganisms under anaerobic conditions. Results from this study can provide us with further knowledge on evaluating the role of wetlands in controlling pesticide pollutants from stormwater runoff.

Agriculture↗

PubMed2001

Application of a constructed wetland for non-point source pollution control.

In Taiwan, non-point source (NPS) pollution is one of the major causes of impairment of surface waters. The main objective of this study was to evaluate the efficacy of using constructed wetlands on NPS pollutant removal and water quality improvements. A field-scale constructed wetland system was built inside the campus of National Sun Yat-Sen University (located in southern Taiwan) to remove (1) NPS pollutants due to the stormwater runoff, and (2) part of the untreated wastewater from school drains. The constructed wetland was 40 m (L) x 30 m (W) x 1 m (D), which received approximately 85 m3 per day of untreated wastewater from school drainage pipes. The plants grown on the wetland included floating (Pistia stratiotes L.) and emergent (Phragmites communis L.) species. One major storm event and baseline water quality samples were analyzed during the monitoring period. Analytical results indicate that the constructed wetland removed a significant amount of NPS pollutants and wastewater constituents. More than 88% of nitrogen, 81% of chemical oxygen demand (COD), 85% of heavy metals, and 60% of the total suspended solids (TSS) caused by the storm runoff were removed by the wetland system before discharging. Results from this study may be applied to the design of constructed wetlands for NPS pollution control and water quality improvement.

Ecosystem↗

PubMed2000

Enhanced TCDD degradation by Fenton's reagent preoxidation.

The dioxin isomer 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been called the most toxic compound known to man. Because of its poor bioavailability and low biodegradibility, bioremediation technology cannot effectively degrade TCDD when used alone. In this study, chemical pretreatment (partial oxidation) in combination with biodegradation technique was developed to efficiently remediate TCDD-contaminated soils. An oxidizing reagent [Fenton's Reagent (FR)] was applied in a slurry reactor to transform TCDD with a concentration of 96 microg per kg of soil to compounds more amenable to biodegradation. Up to 99% TCDD was transformed after the chemical pretreatment process. The slurry reactor was then converted to a bioreactor for the following biodegradation experiment. The detected TCDD oxidation byproducts including chlorophenols (CPs) and chlorobenzenes (CBs) were transformed in this bioreactor under aerobic conditions. Two other biodegradation experiments were performed in parallel to investigate the biodegradabiliy of TCDD under aerobic and anaerobic conditions without chemical pretreatment. Approximately 53% TCDD was transformed under anaerobic conditions possibly due to the reductive dechlorination process using organic materials contained in the activated sludge as the primary substrates. No TCDD degradation was observed under aerobic conditions. Results show that FR can oxidize TCDD to less-chlorinated and less-toxic byproducts, promoting their bioavailability to microbial communities. The bench-scale results indicate that the two-stage (partial oxidation followed by biodegradation) system has the potential to be developed to remediate TCDD-contaminated soils on-site.

Biodegradation, Environmental↗

PubMed2000

Antimutagenicity of ethanol extracts of bee glue against environmental mutagens.

The antimutagenicity of ethanol extracts of bee glue (propolis) (EEBG) was evaluated, using Salmonella typhimurium strain TA98 as a test model, against two direct mutagens, 4-nitro-O-phenylenediamine (4-NO) and 1-nitropyrene (1-NP), and two indirect mutagens, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and benzo[a]pyrene (B[a]P) with S9 mix. EEBG was shown to suppress the mutagenicity of these compounds in a dose-dependent fashion. To delineate the mechanism of action of the antimutagenic effects of EEBG on the two indirect mutagens IQ and B[a]P, two possible points of blocking were considered: (1) cytochrome P-450 activity (route 1) and (2) interaction with microsome-generated proximate mutagens to generate an inactive complex (route 2). Our results clearly demonstrated, at a very low dose, remarkable suppression of the mutagenicity of both compounds by inhibiting either route 1 or route 2 pathway. Further studies indicated that EEBG was capable of inhibiting both the activities of hepatic cytochrome P-450 IA1-linked 7-ethoxyresorufin-O-deethylase (EROD) and IA 2-linked 7-ethoxycoumarin-O-deethylase (ECD) in a similar dose-dependent manner. Taken together, we demonstrated that EEBG was a good inhibitor for mutagenicity of direct mutagens, 1-NP and 4-NO, as well as for the indirect mutagens IQ and B[a]P in the presence of S9 mix via inactivation of microsomal enzyme activities (e.g. EROD and ECD) or antagonizing metabolic generation of the proximate mutagens of IQ and B[a]P.

7-Alkoxycoumarin O-Dealkylase↗

PubMed2000

Non-iterative methods incorporating a priori source distribution and data information for suppression of image noise and artefacts in 3D SPECT.

Non-iterative methods have been developed for image reconstruction in 3D SPECT with uniform attenuation and distance-dependent spatial resolution. It was observed that these methods can, in general, be susceptible to data noise and other errors, yielding conspicuous image artefacts. In this work, we developed and evaluated a regularized inverse-filtering approach for effective suppression of noise and artefacts in 3D SPECT images without significantly compromising image resolution. The proposed approach allows the incorporation of a priori random image field and data information and can thus robustly control the degree of suppression of noise and artefacts in 3D SPECT images. Using computer simulations, we evaluated and compared quantitatively images reconstructed from data sets of various noise levels by the use of the proposed methods and the existing non-iterative methods. These numerical results clearly demonstrated that the proposed regularized inverse-filtering approach can effectively suppress image noise and artefacts that plague the existing non-iterative methods, thus yielding quantitatively more accurate 3D SPECT images. The proposed regularized inverse-filtering approach can also be generalized to other imaging modalities.

Algorithms↗

PubMed2000

Genomic expression programs in the response of yeast cells to environmental changes.

We explored genomic expression patterns in the yeast Saccharomyces cerevisiae responding to diverse environmental transitions. DNA microarrays were used to measure changes in transcript levels over time for almost every yeast gene, as cells responded to temperature shocks, hydrogen peroxide, the superoxide-generating drug menadione, the sulfhydryl-oxidizing agent diamide, the disulfide-reducing agent dithiothreitol, hyper- and hypo-osmotic shock, amino acid starvation, nitrogen source depletion, and progression into stationary phase. A large set of genes (approximately 900) showed a similar drastic response to almost all of these environmental changes. Additional features of the genomic responses were specialized for specific conditions. Promoter analysis and subsequent characterization of the responses of mutant strains implicated the transcription factors Yap1p, as well as Msn2p and Msn4p, in mediating specific features of the transcriptional response, while the identification of novel sequence elements provided clues to novel regulators. Physiological themes in the genomic responses to specific environmental stresses provided insights into the effects of those stresses on the cell.

Carbon↗

PubMed1999

Intrinsic bioremediation of trichloroethylene and chlorobenzene: field and laboratory studies.

Activities at a former fire training area at Robins Air Force Base in Georgia, USA resulted in contamination of groundwater with a mixture of trichloroethylene (TCE) and chlorobenzene (CB). Results from the field investigation suggest that intrinsic bioremediation process is occurring, which caused the decrease in TCE and CB concentrations, and increase in TCE degradation byproducts [e.g., dichloroethylene isomers (DCEs), vinyl chloride (VC)] concentrations. Contaminated groundwater samples collected from this site were used to conduct microbial enumeration tests, and used as the inocula for microcosm establishment. Results from the microbial enumeration study indicate that methanogenesis was the dominant biodegradation pattern within the source and mid-plume areas, and the aerobic biodegradation process dominated the downgradient area. Laboratory microcosm experiments were conducted to evaluate the feasibility of using CB as the primary substrate to enhance the intrinsic biodegradation of TCE. Microcosm results suggest that CB can serve as the primary substrate (electron donor), and enhance TCE biodegradation to less-chlorinated compounds under both aerobic cometabolism and reductive dechlorination conditions.

Chlorobenzenes↗

PubMed1998

Image restoration and reconstruction with a Bayesian approach.

We have extended Johnson's Bayesian method for image restoration and reconstruction by introducing diagonal line sites, using symmetric neighborhood configurations, and employing an additional hyperparameter for estimation of line sites. A general formulation for arbitrary neighborhood configurations was derived. The major part of this paper deals with the conduct of computer simulations intended to examine the effect of the hyperparameters, the diagonal line sites, and the size of the neighborhood configuration on the performance of the proposed Bayesian method. We show that, for optimal performance, distinct hyperparameters should be used for the intensity sites and line sites. The results also suggest that a large neighborhood configuration should be used. By comparing the near-optimal restored images, we demonstrated that the use of diagonal line sites, along with the symmetric configurations thus made possible, can effectively remove the blocky edge artifacts and produce images of better quality. When the method was applied to positron emission tomography (PET) image reconstruction, our results showed that the quality of the reconstructed images was improved for both computer-simulated and real patient PET data.

Algorithms↗

PubMed1997

Engineered intermodular and intramodular polyketide synthase fusions.

BACKGROUND: Modular polyketide synthases (PKSs) are very large multifunctional enzyme complexes that synthesize a number of medicinally important natural products. The modular arrangement of active sites has made these enzyme systems amenable to combinatorial manipulation for the biosynthesis of novel polyketides. Here, we investigate the involvement of subunit interactions in hybrid and artificially linked PKSs with several series of intermodular and intramodular fusions using the erythromycin (6-deoxyerythronolide B synthase; DEBS) and rapamycin (RAPS) PKSs. RESULTS: Several two-module and three-module derivatives of DEBS were constructed by fusing module 6 to either module 2 or module 3 at varying junctions. Polyketide production by these intramodular fusions indicated that the core set of active sites remained functional in these hybrid modules, although the ketoreductase domain of module 6 was unable to recognize unnatural triketide and tetraketide substrates. Artificial trimodular PKS subunits were also engineered by covalently linking modules 2 and 3 of DEBS, thereby demonstrating the feasibility of constructing single-chain PKSs. Finally, a series of fusions containing DEBS and RAPS domains in module 2 of an engineered trimodular PKS revealed the structural and functional tolerance for hybrid modules created from distinct PKS gene clusters. CONCLUSIONS: The general success of the intermodular and intramodular fusions described here demonstrates significant structural tolerance among PKS modules and subunits and suggests that substrate specificity, rather than protein-protein interactions, is the primary determinant of molecular recognition features of PKSs. Furthermore, the ability to artificially link modules may considerably simplify the heterologous expression of modular PKSs in higher eukaryotic systems.

Amino Acid Sequence↗

PubMed1997

Image reconstruction for dynamic PET based on low-order approximation and restoration of the sinogram.

Many image-reconstruction methods have been proposed to improve the spatial resolution of positron emission tomography (PET) images and, thus, to produce better quantification. However, these techniques, which are designed for static images, may be inadequate for good reconstruction from dynamic data. We present a simple, but effective, reconstruction approach intended specifically for dynamic studies. First, the level of noise in dynamic PET data is reduced by smoothing along the time axis using a low-order approximation. Next, the denoised sinograms are restored spatially by the method of projections onto convex sets. Finally, images are reconstructed from the restored sinograms by ordinary filtered backprojection. We present experimental results that demonstrate substantial improvements in region-of-interest quantification in actual and simulated dopamine D-2 neuroreceptor-imaging studies of a monkey brain.

Animals↗