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At least 199 records · Page 11Linked to original sources
PubMed1999

A comparison of the ability of forest and agricultural soils to mineralize chlorinated aromatic compounds.

Soils were sampled from two agricultural fields, two relatively pristine forests, and one suburban forest in Ontario, Canada. The ability of these soils to mineralize 2,4-dichlorophenoxyacetate, 3-chlorobenzoate, 4-chlorophenol, 2,4-dichlorophenol, pentachlorophenol, and atrazine was determined using 14C-labeled substrates. Direct pre-exposure was necessary before atrazine mineralization could be detected; however, it was not necessary for degradation of any of the other chemicals. 2,4-dichlorophenoxyacetate and pentachlorophenol mineralization was much higher in the agricultural soils relative to the pristine forest soils, but 3-chlorobenzoate and 2,4-dichlorophenol mineralization rates showed the opposite trend. Mineralization of 4-chlorophenol was about equivalent in all soils. Suburban forests soils were indistinguishable from agricultural soils with respect to their degradation of 2,4-dichlorophenoxyacetate and chlorobenzoate. Additionally, they were better able than any of the soils to withstand the toxic effects of pentachlorophenol. Pentachlorophenol mineralization was highly variable in the pristine forest soils, ranging from about 6 to 50%. Abiotic factors such as pH, soil type, and organic and moisture content did not account for these significant site differences. The selective forces responsible for these differences, and the possible differences in microbial populations are discussed.

Agriculture↗
PubMed1996

Factors that influence the level of contamination of human milk with poly-chlorinated organic compounds.

Polychlorinated organic compounds (POCs) accumulate in tissues with a high fat content. Nursed babies are exposed to POCs through the fat in human milk. Exposure levels are estimated to exceed those considered acceptable as a lifelong daily dose. Nevertheless, mothers are still positively advised as to breast-feeding. In 1988, a survey on contamination of human milk with POCs was carried out in The Netherlands. Levels of ten different organochlorine pesticides (OCPs), eight polychlorinated biphenyl (PCB) congeners, and seventeen polychlorinated dibenzodioxin (PCDD) and -dibenzofuran (PCDF) congeners were determined by use of gaschromatographic techniques with either electron-capture or mass-spectrometric detection. Information on some factors potentially influencing the level of contamination of human milk was obtained by questionnaires. The estimated response amounted to 71 percent. Regression analysis was used to investigate associations between determining factors and specific contaminants. It appeared that maternal age was positively associated with POC concentrations. Traditional omnivorous diet was associated with lower concentrations of POCs when compared to all other types of diet. The post-pregnancy Quetelet Index [by definition calculated as weight/(length)2] and the cumulated period of previous breast-feeding were negatively associated with POC concentrations. In conclusion, chemical behavior and environmental distribution patterns of the POCs measured in this study, if translated to factors of human exposure, are in accordance with the study results. Exposure levels will decrease if emissions can be further reduced. Still, in the near future, maternal age will probably rise (Vermunt 1992; Netherlands Central Bureau of Statistics 1992), whereas the duration of lactation in expected to decline. Consequently, there might be an increase in average POC-concentrations in human milk in the forthcoming years.

Analysis of Variance↗
PubMed2000

Energetics of anaerobic degradation pathways of chlorinated aliphatic compounds.

This minireview explores the energetics of the (anaerobic) oxidative and fermentative degradation of halogenated ethenes and ethanes. It is shown that these pathways are viable alternatives to the traditional routes that start with one or more reductive dechlorination steps. In contrast to reductive dehalogenation, oxidative and fermentative degradation pathways do not require an external source of reducing equivalents. This suggests that organisms that use these pathways are most likely to be found at high redox potentials, i.e, under conditions where competition for reducing equivalents is great.

Journal Article↗
PubMed1985

Mutagenicity of chlorinated products from soil humic substances.

Soil humic substances were chlorinated in solution, extracted with ether and subjected to mutagenicity assay. Mutagenicity was detected using Salmonella typhimurium TA 100, with or without S9 mix; mutagenic activity was found to be less with added S9 mix. Ether extracts were analyzed by gas chromatography-mass spectrometry (GC-MS) and various chlorinated and non-chlorinated compounds were detected, e.g. chlorinated esters, acetones and carboxylic acids, as well as non-chlorinated aromatics. The mutagenicity of the major chlorination products was examined. Chloral and 1,1,1,3,3-pentachloro-2-propanone (pentachloroacetone) were found to be mutagenic, and 1,1-dichloro-2-propanone (1,1-dichloroacetone) was a possible mutagen. The yields of these mutagens increased with an increase in chlorine concentration.

Animals↗
PubMed1991

Descriptors for isomer resolution of (bio-) distribution of chlorinated aromatic compounds.

Both Solubility Parameter (SOLPAR) and Linear Solvation Energy Relationship (LSER) theory utilize molar volume and energies as descriptors for distribution phenomena. They provide powerful methods for the prediction of the GLC retention indices of chlorobenzenes (CBzs) and tetrachlorodibenzo[p]dioxins (TCDDs). Almost complete isomer resolution is obtained with correlation coefficients (r) of greater than or equal to 0.9984 (CBzs) and greater than or equal to 0.9839 (TCDDs). The n-octanol/water partition coefficient (log Kow) of CBzs can be calculated with a standard error of regression of 0.04, which compares favourably with standard deviations of 0.03-0.26 in mean values based on four different experimental methods. The HPLC capacity factor of TCDDs on C18 columns can be predicted by SOLPAR with moderate accuracy (r = 0.9470), allowing for a preliminary calculation of log Kow. A simplified LSER method fails.

Chlorobenzenes↗
PubMed2002

Removal characteristics of trace compounds of landfill gas by activated carbon adsorption.

The removal characteristics of trace compounds and moisture in raw landfill gas (LFG) were studied. The LFG from the extraction well was saturated with water and moisture was eliminated by physical methods including cyclone-type dehydrator and compressor. The moisture removal efficiency of dehydrator and compressor was above 80%. As the moisture contents of LFG decreased, the toxic compounds like aromatics and chlorinated compounds were effectively removed by using the granular activated carbon. The breakthrough time and adsorption capacity of benzene, toluene, and ethyl benzene decreased rapidly when the relative humidity is over 60%. The effect of moisture was more pronounced at lower adsorbate concentrations tested than at higher concentrations. The breakthrough curves for multi-component mixtures show displacement effects. In the course of competing adsorption, adsorbates with strong interaction force to displace weakly bounded substances. Adsorption by activated carbon is in descending order of xylene, ethylbenzene, toluene, tri or tetrachloroethylene, benzene, carbon tetrachloride and chloroform in LFG, respectively.

Adsorption↗
PubMed2001

Effects of flue gas composition on the catalytic destruction of chlorinated aromatic compounds with a V-oxide catalyst.

When using catalytic flue gas cleaning, several flue gas compounds may influence oxidation reactions of hazardous volatile organic compounds, possibly leading to lower reaction rates and, thus, to an incomplete destruction. Experimental investigations were performed with regard to the influence of selected flue gas compounds, like hydrogen chloride, sulfur dioxide, oxygen, and water vapour, on the catalytic destruction behavior of chlorobenzenes under flue gas cleaning conditions of an incineration plant. For this purpose, a metal oxide catalyst was operated at different temperatures at a space velocity of 3600 h-1 in a laboratory-scale fixed bed reactor with model flue gases, and with real flue gases generated from the TAMARA waste incineration plant. The results obtained from the studies with model flue gas were analyzed with respect to reaction kinetics. These kinetics were applied for comparison with the experimental data gained in the real flue gas.

Catalysis↗
PubMed2006

Aqueous block copolymer-surfactant mixtures and their ability in solubilizing chlorinated organic compounds. A thermodynamic and SANS study.

Within the topic of surfactant enhanced solubilization of additives sparingly soluble in water, volumetric, solubility, conductivity, and small-angle neutron scattering (SANS) experiments on mixtures composed of alpha,omega-dichloroalkane, surfactant, copolymer, and water were carried out at 298 K. The triblock copolymers (ethylene oxide)132(propylene oxide)50(ethylene oxide)132 (F108) and (ethylene oxide)76(propylene oxide)29(ethylene oxide)76 (F68) were chosen to investigate the role of the molecular weight keeping constant the hydrophilic/hydrophobic ratio. The selected surfactants are sodium decanoate (NaDec) and decyltrimethylammonium bromide (DeTAB) with comparable hydrophobicity and different charged heads. The alpha,omega-dichloroalkanes were chosen as contaminant prototypes. For the water + surfactant + copolymer mixtures, both the volume and the SANS results straightforwardly evidenced that (1) monomers of NaDec and copolymer unimers generate small mixed aggregates, (2) monomers of DeTAB combined with copolymer unimers do not form aggregates, and (3) unimeric copolymer is solubilized into NaDec and DeTAB micelles. The alpha,omeaga-dichloroalkanes presence induces the F108 aggregation even at very low copolymer composition. The addition of surfactant disintegrates the F108 aggregates and, consequently, the additive is expelled into the aqueous phase. Once F108 is in the unimeric state, it forms copolymer-micelle aggregates which incorporate the oil. In the case of F68 both the volumetric and the SANS data reveal that the additive does not alter the copolymer unimeric state. Moreover, they show that for the aqueous DeTAB-F68 system the additive trapping in both the copolymer-micelle aggregate and the pure micelles takes place being enhanced in the former aggregate in agreement with solubility experiments. For the NaDec-F68 mixtures, an additional solubilization process in the premicellar copolymer-surfactant microstructures occurs. SANS and conductivity data show that the additive incorporation into the mixed and the pure micelles does not essentially influence the structural properties of the aggregates.

Journal Article↗
PubMed1999

A re-appraisal of the post-testicular action and toxicity of chlorinated antifertility compounds.

Some 30 years ago, alpha-chlorohydrin and some analogues were considered as close to the ideal contraceptive which acted rapidly and reversibly on the post-testicular maturation of spermatozoa. Despite their early promise, research funding was withdrawn only 5 years later because of what were considered to be unacceptable side-effects in primates. The literature on the toxic effects of these contraceptive agents was reviewed and was found to be wanting in respect to the rigour of scientific methods applied (impure compounds were used, inappropriate target populations were studied, excessive doses were employed, abstracts were cited from which no full publications subsequently arose). These compounds remain the closest approach yet to non-hormonal contraceptives for males and have led to the synthesis of related compounds which have a similar antifertility action but with much diminished toxicity. If toxicity remains a problem, a range of other compounds now known to have a similar antifertility action, should be investigated.

Animals↗
PubMed1988

Enzymatic dehalogenation of chlorinated nitroaromatic compounds.

4-Chlorobenzoate dehalogenase from Pseudomonas sp. strain CBS3 converted 4-chloro-3,5-dinitrobenzoate to 3,5-dinitro-4-hydroxybenzoate and 1-chloro-2,4-dinitrobenzene to 2,4-dinitrophenol. The activities were 0.13 mU/mg of protein for 4-chloro-3,5-dinitrobenzoate and 0.16 mU/mg of protein for 1-chloro-2,4-dinitrobenzene compared with 0.5 mU/mg of protein for 4-chlorobenzoate.

Biodegradation, Environmental↗