PubMed Health⌕ Search

Biomedical subjects

H F Schöler

Publications and source records attributed to H F Schöler.

At least 19 recordsLinked to original sources
PubMed2004

Assessment of interfacial mass transfer in water-unsaturated soils during vapor extraction.

This paper presents results of a numerical investigation of soil vapor extraction (SVE) systems at the laboratory scale. The SVE technique is used to remove volatile chlorinated hydrocarbons (VCHC) from the water-unsaturated soil zone. The developed numerical model solves equations of flow, transport and interfacial mass transfer regarding an isothermal n-component and three-phase system. The mathematical model is based on a simple pore network and phase distribution model and designed to be scaled by a characteristic length. All mathematical expressions are structured into VCHC specific and VCHC non-specific parameters. Furthermore, indicators are introduced that help to separate thermodynamic equilibrium from thermodynamic non-equilibrium domains and to determine the controlling physical parameters. For numerical solution, the system of partial differential equations is discretized by a finite volume method and an implicit Euler time stepping scheme. Computational effort is reduced notably through techniques that enable spatial and temporal adaptivity, through a standard multigrid method as well as through a problem-oriented sparse-matrix storage concept. Computations are carried out in two dimensions regarding the laboratory experiment of Fischer et al. [Water Resour. Res. 32 (12) 1996 3413]. By varying the characteristic length scale of the pore network and phase distribution model, it is shown that the experimental gas phase concentrations cannot be explained only by the volatility and diffusivity of the VCHC. The computational results suggest a sorption process whose significance grows with the aqueous activity of the less or non-polar organic compounds.

Absorption↗
PubMed2003

Formation of chloroacetic acids from soil, humic acid and phenolic moieties.

The mechanism of formation of chloroacetates, which are important toxic environmental substances, has been controversial. Whereas the anthropogenic production has been well established, a natural formation has also been suggested. In this study the natural formation of chloroacetic acids from soil, as well as from humic material which is present in soil and from phenolic model substances has been investigated. It is shown that chloroacetates are formed from humic material with a linear relationship between the amount of humic acid used and chloroacetates found. More dichloroacetate (DCA) than trichloroacetate (TCA) is produced. The addition of Fe(2+), Fe(3+) and H(2)O(2) leads to an increased yield. NaCl was added as a source of chloride. We further examined the relationship between the structure and reactivity of phenolic substances, which can be considered as monomeric units of humic acids. Ethoxyphenol with built-in ethyl groups forms large amounts of DCA and TCA. The experiments with phenoxyacetic acid yielded large amounts of monochloroacetate (MCA). With other phenolic substances a ring cleavage was observed. Our investigations indicate that chloroacetates are formed abiotically from humic material and soils in addition to their known biotic mode of formation.

Acetates↗
PubMed2003

Fluxes of trichloroacetic acid between atmosphere, biota, soil, and groundwater.

Trichloroacetic acid (TCA), in former times used as a herbicide in agriculture, is now ubiquitous and almost evenly distributed in precipitations of the Northern and Southern Hemisphere, despite larger emissions of the possible precursors tetrachloroethene and 1,1,1-trichloroethane in the Northern Hemisphere. The permanent input of a herbicidal compound into most vulnerable ecosystems might lead to adverse effects to biota (plants, microorganisms, etc.). TCA soil levels of coniferous forests in mountainous regions of Central Europe are significantly elevated. Mass balance calculations show that precipitation as sole source of TCA in soil seems to be of minor importance and provide evidence for a natural formation of TCA within soil itself. In addition, the isolation of a chlorinating enzyme in soil and laboratory experiments with humic acid, iron and halide point to an omnipresent chlorinating capability of nature producing polyhalogenated organic compounds such as TCA. In this paper we present an overview of TCA levels in the environment and provide a new estimate about the extent of a natural TCA formation, especially in soil.

Atmosphere↗
PubMed2002

Estimating distribution and retention of mercury in three different soils contaminated by emissions from chlor-alkali plants: part I.

Mercury emissions from chlor-alkali plants have been past and present sources of soil contamination with Hg. Here we calculate net mercury (Hg) deposition to soils in the vicinity (100-1000-m downwind) of three-chlor alkali plants. Calculations were based on spatial distribution patterns of Hg concentrations in soils, which were extrapolated by kriging. Moreover, we investigated to what extent Hg deposition depends on the elevation of receptors and canopy throughfall. Mercury concentrations in soil exceed background values up to a factor of 56 and show enrichment factors between 2 and 5.8 calculated from the median Hg concentration. Net deposition rates range between 2356 and 8952 microg m(-2) year(-1), which is up to 224-fold the background values. Net deposition of Hg to soils at the three sites varies between 1.2 and 2.4% of total emitted Hg. Highest deposition rates were found at sites with extended elevated or forested areas. Here, Hg concentrations in soils increased by a factor of up to 7.3 in elevated (+180 m) forest areas compared to non-elevated grassland soils.

Air Pollutants↗
PubMed2002

Binding and mobility of mercury in soils contaminated by emissions from chlor-alkali plants.

Chlor-alkali plants are known to be an important source of Hg emissions to the atmosphere and related contamination of soils in their vicinity. In the present study, the results of Hg speciation and mobility of Hg in soils affected by Hg emissions from three chlor-alkali plants are compared. Solid phase mercury speciation analyses was carried out using a mercury-thermo-desorption technique with the aim of distinguishing elemental Hg [Hg(0)] from Hg(II)-binding forms. Mercury species in soil leachates were distinguished using an operationally defined method, which is based on the reactivity of soluble Hg compounds. Results show that the Hg(0) emitted from the plants could not be detected in any of the investigated soils. This indicates quantitative re-emission or oxidation of this Hg species in the atmosphere or soils. In most soils Hg was predominately bound to organic matter. Only in sandy soils deficient in organic matter was Hg, to a larger extent, sorbed onto mineral soil components. Leachable Hg in most soils occurred as non-reactive, soluble organic Hg complexes such as fulvic acid-bound Hg, and reach their highest values (90 microg kg(-1)) in soils rich in organic matter. Concentrations of reactive, soluble Hg compounds were highest in sandy soils where the content of organic matter was low. Leachability of Hg was found to be inhibited in soils with a high content of clayey soil components. The distribution of Hg in soil profiles suggests that migration of Hg to deeper soil layers (approx. 20 cm) is most effective if Hg is bound to soluble organic complexes, whereas reactive Hg or weak Hg complexes are effectively retained in the uppermost soil layer (5 cm) through sorption on mineral surfaces.

Air Pollutants↗
PubMed2001

Abiotic Fe(III) induced mineralization of phenolic substances.

The redox process between iron(III) (in dissolved form and as the mineral phase ferrihydrite) and phenolic substances has been examined. We investigated the relationship between the structure and reactivity for the dihydrobenzene reductants catechol, hydroquinone and resorcine, and for the 2-methoxyphenol guaiacol with iron(III), by determining the rate of the Fe(III) reduction as well as the production of CO2. This work demonstrates that catechol and guaiacol will be effectively oxidized to CO2 by reducing iron(III). Hydroquinone shows a reduction of iron(III), but no accompanying mineralization could be determined. In contrast, resorcine showed no reaction with Fe(II). The deciding factor on whether or not mineralization occurs were controlled by the position of the hydroxy groups. It is shown that phenolic substances with two hydroxy groups in the orthoposition or at least one hydroxy group and a methoxy group can be oxidized to CO2 while iron(III) is reduced.

Carbon Dioxide↗
PubMed2000

Halocarbons produced by natural oxidation processes during degradation of organic matter.

Volatile halogenated organic compounds (VHOC) play an important role in atmospheric chemical processes-contributing, for example, to stratospheric ozone depletion. For anthropogenic VHOC whose sources are well known, the global atmospheric input can be estimated from industrial production data. Halogenated compounds of natural origin can also contribute significantly to the levels of VHOC in the atmosphere. The oceans have been implicated as one of the main natural sources, where organisms such as macroalgae and microalgae can release large quantities of VHOC to the atmosphere. Some terrestrial sources have also been identified, such as wood-rotting fungi, biomass burning and volcanic emissions. Here we report the identification of a different terrestrial source of naturally occurring VHOC. We find that, in soils and sediments, halide ions can be alkylated during the oxidation of organic matter by an electron acceptor such as Fe(III): sunlight or microbial mediation are not required for these reactions. When the available halide ion is chloride, the reaction products are CH3Cl, C2H5Cl, C3H7Cl and C4H9Cl. (The corresponding alkyl bromides or alkyl iodides are produced when bromide or iodide are present.) Such abiotic processes could make a significant contribution to the budget of the important atmospheric compounds CH3Cl, CH3Br and CH3I.

Atmosphere↗
PubMed2000

The behaviour of N-(phenylsulfonyl)-glycine and phenacetin in a municipal sewage treatment plant--a case study.

The behaviour of N-(phenylsulfonyl)-glycine (PSG) and phenacetin (PHE) in a municipal sewage treatment plant near Heidelberg, Germany, was investigated in the summer of 1997. For that purpose, 10 g of each substance was dissolved and poured simultaneously into the influent. In addition to the spiked compounds, the samples of the influent, the biological stage and the effluent were analyzed for N-(phenylsulfonyl)-sarcosine (PSS), N-methyl-N-(phenylsulfonyl)-amide (MPS), N-methyl-phenacetin, N-methyl-N-(phenylsulfonyl)-epsilon-aminocaproic (PSC) acid and its degradation product N-methyl-N-(phenylsulfonyl)-gamma-aminobutyric (PSB) acid. Within 24 h PHE could be detected almost quantitatively in the effluent. Since N-methyl-phenacetin could not be found in any of the samples, apparently no methylation of the amino-group of PHE took place. The amount of PSG in the effluent was within 24 h 26.0 g, which is more than two fold higher than added. The decrease of PSG between biological stage and effluent and the increase of PSS within the same time correlate well. Therefore, the formation of PSS by microbial methylation of PSG in the sewage treatment plant must be assumed.

Acetaminophen↗
PubMed1998

N-(phenylsulfonyl)-glycine--a new contaminant in sewage- and surface water.

River samples (e.g. river Rhine, river Neckar, Germany) and samples from five communal sewage treatment plants were investigated for N-(phenylsulfonyl)-glycine, -alanine and -sarcosine, as well as for the corresponding p-toluene analogues. As result of this screening we identified N-(phenylsulfonyl)-glycine as a hitherto unknown polar contaminant. In surface waters the concentrations of N-(phenylsulfonyl)-glycine ranged between 50 and 850 ng/l. In communal sewage treatment plants the concentrations varied: The substance was only found in one influent with a concentration of 1200 ng/l; in the biological step and in the effluent its concentrations ranged from 80 to 300 ng/l. N-(phenylsulfonyl)-alanine, N-(p-toluenesulfonyl)-glycine, -sarcosine and -alanine were found neither in surface nor in sewage waters.

Alanine↗
PubMed1996

A new pyrrolidinedithiocarbamate screening method for the determination of methylmercury and inorganic mercury relation in hair samples by HPLC-UV-PCO-CVAAS.

A new analytical screening technique for the determination of methylmercury and inorganic mercury in hair samples by HPLC-PCO-CVAAS has been developed. It is based on the extraction of mercury compounds by a buffered sodium pyrrolidinedithiocarbamate solution, separation by reversed-phase HPLC, post column oxidation by UV-irradiation, reduction with alkaline sodium borohydride, and determination by cold vapour atomic absorption detection. The standard deviation was 7% and recoveries were 90% for both compounds. The limit of detection (S/N = 3) for both compounds was calculated to be about 4 ppb.

Journal Article↗
PubMed1994

Determination of methyl-, ethyl-, phenyl and total mercury in Neckar River fish.

Methyl-, ethyl- and phenyl mercury, total mercury and fat content were determined in fish fillet of the five different fish species: eel, perch, roach, chub and barbel. The organo mercury compounds were extracted according to a modified Westöö method and determined by using HPLC-cold vapour atomic absorption spectrometrie. Total mercury was determined according to EPA/AOAC. Total mercury in fish tissue varied between 16 and 812 micrograms/kg, methyl mercury between 10 and 770 micrograms/kg. It was found that at least 83% of total mercury is present as methyl mercury. Only a barbel exceeded the German maximum acceptable residue limit (500 micrograms/kg) with 812 micrograms/kg total mercury.

Animals↗
PubMed1992

[Halogenated organic compounds in swimming pool water].

18 different swimming pool waters in the Bonn-Rhein-Sieg area were analysed for trihalogenmethanes, halogenated acetic acids, 2,2-dichloropropionic acid, dihalogenacetonitriles and chloral hydrate. Most substances mentioned above were determined in almost every sample reaching total concentrations up to 538 micrograms/l. Considering the results one can see that some of the main pollutants are polar organic compounds like di- and trichloroacetic acid as well as chloral hydrate.

Acetonitriles↗
PubMed1990

[Solvents in drinking water from a thermostatic mixing battery].

In a hospital an odour of organic solvent could be smelled when a special thermostatic water mixer has been used. At no other water tap in the house a similar smell could be recognized. After stagnation overnight or after weekends the disgusting smell has been rather strong. The odour of organic solvent disappeared when the water had been running for some time. The organic compound in the drinking water has been identified and the thermostatic water mixer could be revealed as the source of the contamination. Further investigations of other thermostats showed a variety of alcoholic compounds which were used as thermostatic fluids.

Odorants↗
PubMed1988

[Sewer sediments--for the detection of the heavy metal containing waste water flow into sewer systems].

Increased heavy metal content often prevents agricultural application of sewage sludge. The identification of a singular pollutant requires time-consuming and cost intensive investigations. A gridlike investigation of sewer sediments offers an effective tool for the identification of heavy metal pollutants--even if the discharge of sewage occurs by batch processes. For the sewer sediments enrich the heavy metals during longer periods. By means of this methodology we succeeded in lowering the cadmium concentration of the sewage sludge within 3 months from 40 to 5 mg/kg DS and to enable its agricultural application.

Cadmium↗
PubMed1987

[Increase in the colony count in drinking water tanks caused by solvents from the coating material].

As a freshly coated storage tank was put into operation a permanent colony increase in the drinking water (up to 7400 cfu/ml) could be detected. By chlorine dosage (30 mg/l) colony counts were reduced. From a second storage tank which had been coated at the same time bituminous coating material and air samples could be taken. After the exposure of the bituminous coating material in aqua bidest. 48 organic compounds were found by GC/MS-analysis. The main compounds were xylene, ethylbenzene and 1,2,4-trimethylbenzene. These compounds were also found by GC-investigations of the air-samples. The dependence between the used organic solvents and the colony increase could be demonstrated by biodegradation tests of solvent compounds. It was found that about 50 per cent of the identified compounds could be degraded by microorganisms and therefore caused a colony increase in drinking water.

Bacteriological Techniques↗
PubMed1987

An improved extraction method for the quantitative analysis of pesticides in water.

An improved method for enrichment and analysis of chloropesticides (5), triazines (1, 4, 6), phosphoric acid esters and other compounds by a rotation perforator according to Ludwig (2, 3) is presented. Water fortified with pesticides was analysed according to this procedure. The organic extract was quantified by gas chromatography. The recovery rates ranged from 80% to more than 110%, whereas those compounds sensitive to hydrolysis and oxidation were insufficient. The above described method was applied to surface water and groundwater analysis.

Chromatography, Gas↗