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Query: UMLS:C1835664 (TOC)
 2,763 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Dissolved oxygen cycling patterns in a tropical lake (Weija Lake) were shown to be useful as a potential indicator of biodegradable organic pollution, by dosing with liquid malt to give an additional organic burden of 2.5 and 5.0 mg l-1 TOC, and monitoring the DO values continuously for 140 h. These loadings were added to water columns (in tubes) suspended from a raft in a lake in south-east Ghana. The addition of organic pollution burden to the lake water produced two main effects: the mean DO value was lowered, and the amplitude of the DO cycle decreased as organic loading increased from 2.5 to 5.0 mg l-1 TOC. There was also an indication of heterotrophic respiration associated with organic inputs for the 5.0 mg l-1 added TOC suggesting a P/R ratio of well below 1.0. Taking the results of a DO cycling computer model together with those from the lake raft experiments, it can be concluded that dissolved oxygen cycles can be a good indicator of biodegradable organic pollution load.
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PMID:Evaluation of cycling patterns of dissolved oxygen in a tropical lake as an indicator of biodegradable organic pollution. 1047 31

A 5-year study was carried out on the growth curve of two strains of P. aeruginosa inoculated at a density of 10(2) cfu/ml into samples of natural mineral water with different levels of dissolved solids (TDS at 180 degrees C: 72.5 and 382 mg/l) and low organic content (TOC: 0.17 and 0.35 mg/l). The resulting growth curves were similar for both strains, with only slight differences depending on the different amounts of dissolved solids in the water. After 4-5 days counts were increased by 3 log units. This level was maintained until 70-100 days from inoculation, after which a slow decrease began, culminating in the death of one of the strains after 5 years. No difference in recovery was observed between the method using direct inoculation on Cetrimide Agar and the resuscitation technique (preincubation in Tryptone Soya Agar followed by inoculation on Cetrimide Agar) in the exponential phase of the growth curve. During the stationary and death phases, however, the enrichment technique gave statistically slightly higher counts than the selective technique, indicating the presence of damaged P. aeruginosa cells. The use of a resuscitation step when using Cetrimide Agar to assess bottled water quality is recommended.
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PMID:Survival and growth of Pseudomonas aeruginosa in natural mineral water: a 5-year study. 1063 6

Trihalomethanes (THMs) are important disinfection byproducts (DBPs) in drinking water. To understand the magnitude of exposure to THMs for the people in southern Taiwan, models are used to estimate the inhalation exposure associated with drinking water based on raw water quality. Two parts of models are used in this study, one for estimating THM concentration from raw water quality, and one for estimating inhalation exposure to people. Important raw water quality and operational parameters, including TOC, UV254, pH, temperature, chlorine dosage, and water residence time of a major water treatment plant in south Taiwan were collected. An empirical THM formation model was then employed to predict the THM concentration at consumers' dwellings based on the parameters collected. Differences between the predicted results and experimental data were found to be small, indicating that the model is appropriate. The predicted THM concentration distribution was served as input parameters for the exposure models. Three major scenarios associated with probable inhalation exposure of THMs, including shower, pre- and post-cooking activities, and cooking processes, were considered in the exposure models. The model results show that the mean inhalation exposure of THMs for shower, pre- and post-cooking activities, and cooking processes are 26.4, 1.56, 3.29 micrograms/day, respectively. The total inhalation exposure (summation of the three scenarios) was found to be comparable with that for direct ingestion, indicating that inhalation is an important pathway for THM exposure from drinking water.
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PMID:Inhalation exposure to THMs from drinking water in south Taiwan. 1068 75

In column experiments of Mexican wastewater irrigated soils the effects of changing water quality (untreated = UT, primary = PT and tertiary treated = TT wastewater) on carbon, nitrogen and heavy metal dynamics were investigated. In the column effluents the nitrate concentrations varied between 141-683 mg l-1. The total amount of leached TOC decreased in the order UT > PT > TT. Outflow concentrations of Pb ranged from 31.6-166.5 micrograms l-1 and of Cu from 31.2-146.8 micrograms l-1. Irrigation water quality influenced the Pb but not the Cu efflux. Cu seemed to be co-transported with TOC by preferential flow whereas there was no correlation of Pb and TOC concentrations in the effluents. The possibility of Pb transport through preferential flow paths is discussed.
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PMID:Carbon, nitrogen and heavy metal dynamics in long-term wastewater irrigated Mexican soils. 1084 23

The available data indicate that sediment-water partitioning, bioaccumulation, and the toxicity responses for tributyltin (TBT) are predictable when using some of the assumptions and tenets of the equilibrium partitioning method, toxicokinetic modeling (1CFOK), and critical body residue (CBR) approach. Because TBT is ionizable, its speciation is strongly affected by pH, which appears to cause large variations in the octanol-water partition coefficient. In marine systems, and in freshwater systems with high pH, TBT occurs predominantly in the hydroxide form, which may explain the hydrophobic properties and its EqP behavior. Organic carbon in sediment (> 0.2%) appears to be the major controlling factor for sediment-water partitioning. The equilibrium organic carbon-normalized sediment-water partition coefficient (Koc) in marine environments is approximately 32,000 (log10 Koc approximately 4.5), which was determined from direct measurement and confirmed by the relationship between the lipid-normalized bioconcentration factor (BCF) in porewater and the biota-sediment accumulation factor (BSAF). The conclusion that sediment-water partitioning of TBT in marine systems follows EqP is supported by the similarity between its Kow and Koc and the correlation between the sediment-water partition coefficient (Kp) and sediment TOC, which results from the influence of organic carbon on pore-water concentrations. Even though the rates of uptake and elimination control tissue residues and lipid content appears to have no bearing on the amount of TBT that is accumulated, the species specific BSAF is useful for examining bioaccumulation, sediment-water partitioning, and the toxicity response. Although TBT is hydrophobic and appears to have a propensity to accumulate in lipid, the rates of uptake and elimination, not thermodynamics, appear to control whole-body tissue concentrations. Support for a toxicokinetic approach for predicting tissue residues is found in BCF and BSAF values for several species that are far in excess of that predicted by simple thermodynamic partitioning and in the comparisons of observed and predicted bioaccumulation values based on toxicokinetic coefficients. This observation is counter to the assumption of EqP that the route of uptake is of no consequence under equilibrium conditions. For TBT, it appears that kinetics determine tissue residues and that body lipid is important only for regulating the toxic response, not the amount bioaccumulated. Unlike those for neutral hydrophobic organic compounds, the toxicokinetics for this one toxicant are highly variable in diverse species but relatively accurate in predicting the amount bioaccumulated and the resulting toxicity response. For the CBR approach to be useful, a relatively constant tissue residue for a given biological response is necessary. Several studies support the CBR approach because certain biological effects, such as mortality and growth inhibition, occur at a relatively constant TBT tissue concentration. For TBT, the lethal whole-body tissue concentration affecting 50% of individuals (LR50) exhibits little variation, occurring at approximately 48 micrograms/g (166 nmol/g) dry weight in a range of species. Direct evidence and correlation of the LC50 and the bioconcentration factor (BCF) support this observation. Impaired growth, a sublethal response, also appears to be associated with a relatively constant tissue concentration, which has also been demonstrated by direct measurement and indirectly by regression of the BCF and LOEC. The lowest-observed-effect tissue residue (LOER) associated with impaired growth for several species was approximately 3 micrograms/g (10.4 nmol/g) dry wt. Because of the small number of studies linking growth impairment and tissue concentrations, additional studies are needed to confirm these values. (ABSTRACT TRUNCATED)
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PMID:Predicting the fate and effects of tributyltin in marine systems. 1086 75

Methods for non-invasive, in situ, measurements of biofilm optical density and biofilm optical thickness were evaluated based on Pseudomonas aeruginosa experiments. Biofilm optical density, measured as intensity reduction of a light beam transmitted through the biofilm, correlates with biofilm mass, measured as total carbon and as cell mass. The method is more sensitive and less labor intensive than other commonly used methods for determining extent of biofilm mass accumulation. Biofilm optical thickness, measured by light microscopy, is translated into physical thickness based on biofilm refraction measurements. Biofilm refractive index was found to be close to the refractive index of water. The P. aeruginosa biofilms studied reached a pseudo steady state in less than a week, with stable liquid phase substrate, cell and TOC concentrations and average biofilm thickness. True steady state was, however, not reached as both biofilm density and roughness were still increasing after 3 weeks.
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PMID:Quantification of biofilm accumulation by an optical approach. 1116 96

The extracellular polymer produced by a bacterium isolated from soil was employed in laboratory studies of desorption of a model polynuelear aromatic hydrocarbon (PAH), phenanthrene. The experimental results show that the selected extracellular polymer enhances the extent of release of soil-bound phenanthrene. A kinetic model was developed as an aid in interpreting the alterations in phenanthrene desorption resulting from polymer addition. The model employs a statistical gamma (gamma) distribution to describe spectrum of rate constants for transfer of phenanthrene from soil to water, and assumes instantaneous binding of phenanthrene to polymer and of polymer to the test soil. The relevant distribution coefficients and statistical parameters of the gamma distribution needed for the model were evaluated in independent experiments. Using these measured parameters, the model provides a satisfactory independent prediction of phenanthrene release from soil to aqueous phase at two test polymer concentrations, 50 mg TOC/L and 100 mg TOC/L. The success of the independent model predictions suggests a mechanism for the influence of extracellular polymer on phenanthrene desorption. The intrinsic, soil-specific, rate constants for solid to solution transfer of phenanthrene do not appear to be changed by bacterial polymer. Instead, polymer binding of phenanthrene in solution results in an increase in driving force for desorption by decreasing the solution concentration of the free, unbound, PAH molecule.
Water Res 2001 Mar
PMID:Phenanthrene desorption from soil in the presence of bacterial extracellular polymer: observations and model predictions of dynamic behavior. 1122 83

A lab-scale hybrid upflow sludge bed-filter (USBF) reactor was employed to carry out methanogenesis and denitrification of the effluent from an anaerobic industrial reactor (EAIR) in a fish canning industry. The reactor was initially inoculated with methanogenic sludge and there were two different operational steps. During the first step (Step I: days 1-61), the methanogenic process was carried out at organic loading rates (OLR) of 1.0-1.25 g COD l-1 d-1 reaching COD removal percentages of 80%. During the second step (Step II: days 62-109) nitrate was added as KNO3 to the industrial effluent and the OLR was varied between 1.0 and 1.25 g COD l-1 d-1. Two different nitrogen loads of 0.10 and 0.22 g NO3(-)-N l-1 d-1 were applied and these led to nitrogen removal percentages of around 100% in both cases and COD removal percentages of around 80%. Carbon to nitrogen ratio (C:N) in the influent was maintained at 2.0 and eventually it was increased to 3.0, by means of glucose addition, to control the denitrification process. From these results it is possible to establish that wastewater produced in a fish canning industry can be used as a carbon source for denitrification and that denitrifying microorganisms were present in the initially methanogenic sludge. Biomass productions of 0.23 and 0.61 g VSS:g TOC fed for Steps I and II, respectively, were calculated from carbon global balances, showing an increase in biomass growth due to denitrification.
Water Res 2001 Feb
PMID:Simultaneous methanogenesis and denitrification of pretreated effluents from a fish canning industry. 1122 93

Domestic and wine-distillery wastewaters were treated by semi-batch and continuous pH sequential ozonations. The process involves a succession of acidic and alkaline wastewater pH conditions. The alkaline periods allow oxidation of organic matter by hydroxyl radical and produce carbonates that eventually would inhibit the oxidation. On the other hand, the acidic periods favour the development of direct ozone reactions and strip off carbonates as carbon dioxide from the wastewater. Experimental results of pH sequential ozonation showed degradation and removal rates of wastewater pollutants higher than those achieved at constant either acidic or basic pH. The most significant improvement of ozone efficiency and pollutants removal were obtained by controlling the number of cycles, pH and time of acidic and alkaline phases. Also, ozonated wastewaters showed high biodegradability as deduced from their BOD/COD ratios. The feasibility of treating domestic and wine-distillery wastewater by an integrated activated sludge (ASP)-pH sequential ozonation system was evaluated. Integrated ASP-ozonation at constant pH processes were also carried out for comparative purposes. In these combined experiments, pH sequential ozonation showed advantages compared to ozonation at constant pH in reducing global parameters such as COD, TOC and TKN, but ozonation at constant pH led to higher removal of polyphenols and UV254 absorbing compounds.
Water Res 2001 Mar
PMID:pH sequential ozonation of domestic and wine-distillery wastewaters. 1123 88

A novel water quality index, the mutagen formation potential (MFP) is proposed for use in evaluation of the quality of drinking water which may contain pollutants capable of forming mutagens when chlorinated under the conditions used in water purification processes. A method for measuring MFP was established as follows. The water sample to be tested is diluted until the TOC reaches 3-4 mg l-1, the pH is adjusted to 7.0 +/- 0.2, sodium hypochlorite is added to obtain conditions where Cl/TOC = 3-4 mg Cl (mg C)-1, and the water sample is left standing for 24 +/- 2 h at room temperature. Thereafter, 21 of the chlorinated water sample at pH 2.0 +/- 0.1 is passed through a Sep-Pak Plus CSP-800 cartridge to adsorb any mutagens formed, and DMSO is applied to the cartridge to desorb the mutagens. Then, a 2 ml sample of the eluate is collected after the DMSO had begun to flow out of the cartridge and evaluated by the Ames Salmonella mutagenicity assay (preincubation method).
Water Res 2001 May
PMID:Method for measuring mutagen formation potential (MFP) on chlorination as a new water quality index. 1132 63


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