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PubMed2004

Curing efficiency and heat generation of various resin composites cured with high-intensity halogen lights.

The objective of this study was to assess the curing efficiency and heat generation of two high-intensity halogen lamps, the Astralis 10 HIP (1100 mW cm(-2)), and Optilux 501 Boost (1000 mW cm(-2)) in curing three resin composites (InTen-S, Tetric Ceram, and Filtek Z250). It was expected that the two lamps, having similar irradiance would give rise to the same curing efficiency and heat generation. The curing efficiency was evaluated by Vickers hardness and depth of cure measurements. Heat generation in the resin composites was studied in standardized restorations using a thermocouple. No significant differences were observed in curing efficiency between the two lamps for the three resin composites. The temperature rise in the composites during curing was between 11.2 degrees C and 16.2 degrees C. At subsequent irradiation, after the composites had been cured, the temperature rise was between 8.2 degrees C and 12.1 degrees C. The Optilux 501 generated, in all cases, less heat than the Astralis 10. This was not expected based on the irradiance, but could be accounted for by the differing spectra.

Analysis of Variance↗
PubMed1973

Correlation of the cardiac sensitizing potential of halogenated hydrocarbons with their physicochemical properties.

The cardiac sensitizing potencies of a range of 14 halogenated hydrocarbons were assessed in conscious dogs by comparing the partial pressures (Pcs) needed to sensitize the heart to adrenaline. These were found to be directly related to their saturated vapour pressures (Ps) and the ratio Pcs/Ps was approximately constant although the values of partial pressures differed nearly 700-fold. It is suggested that cardiac sensitization is probably a structurally non-specific action and may be regarded as another example of physical toxicity.

Anesthetics↗
PubMed1989

Microbiological methods for the cleanup of soil and ground water contaminated with halogenated organic compounds.

There is growing interest in the enhancement of microbial degradative activities as a means of bringing about the in situ cleanup of contaminated soils and ground water. The halogenated organic compounds are likely to be prime targets for such biotechnological processes because of their widespread utilisation and the biodegradability of many of the most commonly used compounds. The aim of this review is to consider the potential for microbiological cleanup of haloorganic-contaminated sites. The technologies available involve the provision of suitable environmental conditions to facilitate maximum biodegradation rates either in the subsurface or in on-site bioreactors. Methodologies include the supply of inorganic nutrients, the supply of oxygen gas, the addition of degradative microbial inocula and the introduction of co-metabolic substrates. The potential efficiencies and limitations of the methods are critically discussed from a microbiological viewpoint with respect to substrate degradability and population responses to supplementation.

Bacteria↗
PubMed1983

Allergic contact dermatitis due to highly reactive halogenated compounds.

10 cases of dermatitis in a fine organic chemicals plant are reported. These cases were all due to exposure to chemical compounds with reactive bromine or chlorine atoms. This type of chemical is always extremely irritant, but evidence is put forward to suggest that these cases were the result of allergic sensitization. Chemicals with reactive halogen atoms should always be handled with extreme care and patch testing should be approached with caution.

Adult↗
PubMed1985

Effect of a homologous series of halogenated methanes on pulmonary uptake of 5-hydroxytryptamine in isolated perfused rat lung.

The potency of halogenated methanes to inhibit uptake of 5-hydroxytryptamine (5-HT) from the pulmonary circulation was studied using an isolated, perfused and ventilated rat lung preparation. The agents were vaporized and mixed with the inlet air. The results indicate that the degree of chlorination is the most important factor for potency of the methanes to inhibit lung uptake of 5-HT. When hydrogen was substituted with fluorine the potency was decreased dramatically. Bromine seemed to have the opposite effect. The data also suggested that the degree of chlorination was more important rather than hydrophobic/hydrophilic balance of the solvent molecule. These effects seem to be correlated with the narcotic effects of the substances studied.

Animals↗
PubMed1979

Pharmacokinetics of halogenated hydrocarbons.

Pharmacokinetic modeling is being applied to chemicals posing health hazards because of their presence as contaminants in our environment. This paper presents a rationale for constructing mathematical models based on anatomic and physiological principles. Pharmacokinetic investigations incorporating such models are illustrated for two halogenated hydrocarbons that exhibit different patterns of disposition in the rat: 2,2',4,4',5,5'-hexachlorobiphenyl and Kepone. The models permit interspecies comparison and prediction of normal pharmacokinetic behavior and alterations induced by intervention measures. As an example a theoretical limit is predicted in the case of a treatment for Kepone poisoning involving oral administration of adsorbents.

Animals↗
PubMed1989

Spectroscopic studies of cutaneous photosensitizing agents--XIV. The spin trapping of free radicals formed during the photolysis of halogenated salicylanilide antibacterial agents.

Several antibacterial halogenated salicylanilides, including 3,3',4',5-tetrachlorosalicylanilide (TCSA) and 3,4',5-tribromosalicylanilide (TBSA) are known to cause photoallergy. We have carried out photochemical and spin trapping studies to determine whether free radicals may be involved in the photoallergic response. Irradiation (lambda greater than 300 nm) of TCSA in buffered (pH 7.4) 50% ethanol resulted in the rapid loss of the 3-chloro atom, followed by the much slower release of 5- and then the 4'-chloro atoms to give 3'-chlorosalicylanilide as a stable photoproduct. Under the same conditions TBSA successively lost the 3-, 5- and 4'-bromine atoms to give salicylanilide. When TCSA or TBSA were irradiated (lambda = 356 nm) in buffered (pH 7.4) 50% ethanol containing 2-methyl-2-nitrosopropane (MNP) only solvent-derived free radicals were detected. However, irradiation (lambda = 356 nm) of TCSA and MNP in 0.1 N NaOH generated an ESR spectrum consisting of a broad triplet (aN = 15.6 G). This spectrum was attributed to the adduct formed by the reaction of MNP with the aryl radical generated by the loss of a chlorine atom from the sterically hindered 3-(or 4'-)-position. Under the same conditions TBSA initially generated a broad triplet (aN = 15.5 G) similar to that observed for TCSA. However, upon further irradiation a 21-line spectrum (aN = 14.4 G, a2H = 2.0 G and a2H = 0.9 G) appeared.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-Bacterial Agents↗
PubMed1995

Theoretical investigation of excimer and exciplex states of uracil and halogen derivatives: effect of nonparallelism of bases.

Theoretical modeling of initial steps of the photodimerization mechanism of uracil, 5-methyl-and 5-halogen derivatives was performed. The interaction energy of bases in stacked dimers in the ground and lowest excited states was calculated as a function of the distance between the base planes and of the rotation angles within the perturbation theory for the extended Hückel treatment. The existence of excimer and exciplex region on the potential surface of the excited state was revealed. The excimer (exciplex) geometry has the planes nonparallel with more close contact of the C5-C6 bonds as compared to the ground state of dimers. The results provide new information useful for understanding the photodimerization mechanism of bases and testifies that the singlet excimer state can be a precursor of the photodimerization reaction.

Halogens↗
PubMed1990

Degradation of halogenated aliphatic compounds by the ammonia- oxidizing bacterium Nitrosomonas europaea.

Suspensions of Nitrosomonas europaea catalyzed the ammonia-stimulated aerobic transformation of the halogenated aliphatic compounds dichloromethane, dibromomethane, trichloromethane (chloroform), bromoethane, 1,2-dibromoethane (ethylene dibromide), 1,1,2-trichloroethane, 1,1,1-trichloroethane, monochloroethylene (vinyl chloride), gem-dichloroethylene, cis- and trans-dichloroethylene, cis-dibromoethylene, trichloroethylene, and 1,2,3-trichloropropane, Tetrachloromethane (carbon tetrachloride), tetrachloroethylene (perchloroethylene), and trans-dibromoethylene were not degraded.

Ammonia↗
PubMed1991

Biodegradation of halogenated organic compounds.

In this review we discuss the degradation of chlorinated hydrocarbons by microorganisms, emphasizing the physiological, biochemical, and genetic basis of the biodegradation of aliphatic, aromatic, and polycyclic compounds. Many environmentally important xenobiotics are halogenated, especially chlorinated. These compounds are manufactured and used as pesticides, plasticizers, paint and printing-ink components, adhesives, flame retardants, hydraulic and heat transfer fluids, refrigerants, solvents, additives for cutting oils, and textile auxiliaries. The hazardous chemicals enter the environment through production, commercial application, and waste. As a result of bioaccumulation in the food chain and groundwater contamination, they pose public health problems because many of them are toxic, mutagenic, or carcinogenic. Although synthetic chemicals are usually recalcitrant to biodegradation, microorganisms have evolved an extensive range of enzymes, pathways, and control mechanisms that are responsible for catabolism of a wide variety of such compounds. Thus, such biological degradation can be exploited to alleviate environmental pollution problems. The pathways by which a given compound is degraded are determined by the physical, chemical, and microbiological aspects of a particular environment. By understanding the genetic basis of catabolism of xenobiotics, it is possible to improve the efficacy of naturally occurring microorganisms or construct new microorganisms capable of degrading pollutants in soil and aquatic environments more efficiently. Recently a number of genes whose enzyme products have a broader substrate specificity for the degradation of aromatic compounds have been cloned and attempts have been made to construct gene cassettes or synthetic operons comprising these degradative genes. Such gene cassettes or operons can be transferred into suitable microbial hosts for extending and custom designing the pathways for rapid degradation of recalcitrant compounds. Recent developments in designing recombinant microorganisms and hybrid metabolic pathways are discussed.

Bacteria↗
PubMed1984

The destruction of halogenated organic chemicals by plasma pyrolysis.

Very high destruction efficiencies for halogenated chemicals have been achieved by plasma pyrolysis. Destruction efficiencies exceeded 99.9999999% for tests with polychlorinated biphenyls (PCBs). Preliminary tests with tetrachloromethane have obtained destruction efficiencies exceeding 99.99%. The plasma pyrolysis process involved the creation of a 250-kW plasma with a temperature in excess of 25 000 degrees C. The toxic material was injected into the plasma zone at a rate between 1 and 2 L/min. Thermochemical and photochemical dissociation of the toxic materials produced atoms and ions which recombined to form primarily H2, CO, HCl, and particulate carbon. The HCl was neutralized by NaOH. The flaring of the H2 and CO should destroy to a high degree any trace residuals. The application of plasma pyrolysis for the ultimate disposal of toxicological waste was also investigated. Rat carcasses containing mean lethal dosage of PCB were pyrolyzed.

Animals↗
PubMed1982

2,3,7,8-tetrachlorodibenzo-p-dioxin and related halogenated aromatic hydrocarbons: examination of the mechanism of toxicity.

In this review, we have examined the biochemical and toxic responses produced by halogenated aromatic hydrocarbons and have tried to develop a model for their mechanism of action. These compounds bind to a cellular receptor and evoke a sustained pleiotropic response. In many tissues this response consists of the expression of a battery of enzymes which are, for the most part, involved in drug metabolism, but in other tissues, those which develop toxicity, an additional set of genes is expressed which effects cellular involution, division, and/or differentiation. The toxicity of these compounds appears to be due to the sustained expression of a normal cellular regulatory system, of which we were previously unaware. In future investigations it is hoped that we will learn the nature and physiologic role of this regulatory system. Only then can we hope to understand the mechanism of toxicity of these compounds.

Animals↗
PubMed1977

Association of halogenated isoxazolylpenicillins with penicillinase-sensitive beta-lactam antibiotics. Microbiological evaluation on beta-lactamase-producing Enterobacteriaceae.

The validity of nonsimultaneous association of penicillinase-sensitive beta-lactam antibiotics with halogenated isoxazolylpenicillins was tested in various Enterobacteriaceae strains. With several bacterial strains, expecially if producers of beta-lactamase type IV, exposure of either the bacterial suspensions of the brothsupernatant to the isoxazolylpenicillins appears both in vivo and in vitro to reduce the extent of subsequent hydrolysis of penicillinase-sensitive beta-lactam antibiotics.

Animals↗
PubMed1984

Free radical intermediates under hypoxic conditions in the metabolism of halogenated carcinogens.

Many halogenated hydrocarbons are known to have carcinogenic potency, nevertheless, humans may be exposed to such xenobiotics for prolonged periods during industrial occupations. In this study, eight aliphatic haloalkanes, all suspected carcinogens, have been studied with respect to their metabolic activation to free radical intermediates, that may exert toxic effects when produced in vivo. The eight haloalkanes studied here are: carbon tetrachloride, chloroform, 1,2-dibromoethane, 1,1-dichloroethane, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2-trichloroethane and 1,1,2,2-tetrachloroethane. Using isolated rat hepatocytes as a model system, and electron spin resonance spectroscopy coupled to the spin trapping technique as a detection technique, it has been possible to demonstrate the formation of free radical derivatives, both under normoxic as well as under hypoxic conditions from carbon tetrachloride, chloroform, 1,1,1-tetrachloroethane and 1,1,2,2-tetrachloroethane. In contrast, free radical production was only detectable under hypoxic conditions when 1,2-dibromoethane, 1,1-dichloroethane, 1,2-dichloroethane and 1,1,2-trichloroethane were added to the hepatocyte suspensions. It is known that some xenobiotics that usually undergo oxidative pathways of metabolism can be metabolized differently when the oxygen concentration is substantially diminished. Evidence have been obtained suggesting that such different types of metabolism may be of relevance in vivo. Possible relationships between free radical production, metabolic activation, covalent binding and carcinogenic potency are discussed.

Animals↗
PubMedDate not supplied

Hormonal interactions in the effects of halogenated aromatic hydrocarbons on the developing brain.

Halogenated arylhydrocarbons (HAHs) exert a wide range of effects on the developing brain. These effects result in altered patterns of neuroendocrine function and behavior in adulthood, as well as changes in cognitive function. The underlying mechanisms have not yet been clearly defined. This paper briefly reviews the effects of HAHs on brain development, and proposes the hypothesis that interactions between different hormone-sensitive systems may contribute to the broad spectrum of responses observed after fetal or early postnatal HAH exposure. Physiological interactions between the effects of sex steroids, corticosteroids, and thyroid hormone are known to influence the development of the central nervous system (CNS). Since the biosynthesis and/or action of each of these hormones is sensitive to developmental HAH exposure, it is suggested that convergent effects of HAHs on different endocrine pathways may underlie some of the disruptive effects of these chemicals on CNS differentiation. Data are presented indicating that the disruptive effects of low dose dioxin exposure on sexual differentiation of the rat brain are probably not mediated through blockade of estrogen responses, but may instead involve subtle developmental changes in other endocrine systems, perhaps also affecting the feedback control of adrenocortical function. The potential for interactive endocrine effects illustrates the need for a fuller understanding of the range of biological activities of HAHs in the brain, so that the potential risks of low dose developmental exposure to these environmental toxicants can be predicted with greater certainty.

Adrenal Cortex Hormones↗
PubMed1989

Effects of halogenated hydrocarbons on rumen microorganisms.

Halogenated hydrocarbons such as polychlorinated biphenyls (PCB's), heptachlor (HEP), 1,1,1-trichloro-2,2-bis(p-chlorophenyl)-ethane (DDT), and pentachlorophenol (PCP) are environmental contaminants and, at times, can bioaccumulate in the food chain. Cattle have been contaminated in a variety of ways, but generally it is believed that they are only affected by high concentrations of the chemicals. Rumen microorganisms, however, may be affected at lower doses, thus possibly affecting the cow's growth and milk production. Polychlorinated biphenyls, HEP, DDT, and PCP were tested by a 1-stage in vitro fermentation procedure. Substrate utilization was determined by measuring percent dry matter disappearance. Four concentrations (0, 10, 50, and 100 ppm) were studied, and in vitro incubations were conducted for 24 and 48 hr. Samples were removed from 48-hr incubations to determine if the chlorinated hydrocarbons were metabolized during fermentation. Dry matter disappearance proved to be a reliable method to determine microbial activity in the presence of chemicals. Substrate dry matter disappearance for controls and all concentrations of PCB's, HEP, and DDT was approximately 50 and 80% at 24 and 48 hr, respectively. The PCP significantly (P less than 0.05) depressed the percent dry matter disappearance in 50- and 100-ppm cultures to 45 and 30% at 24 hr and 70 and 50% at 48 hr, respectively. Metabolic changes in the test chemicals were not detected by gas chromatographic analysis.

Animals↗
PubMed1977

Carcinogenicity studies on halogenated hydrocarbons.

A series of halogenated compounds was tested by oral intubation in 200 Osborne-Mendel rats and 200 B6C3F1 mice of both sexes. Carbon tetrachloride, used as a positive control, induced liver and adrenal tumors in mice and neoplastic nodules in the livers of rats. 1,2-Dibromoethane and 1,2-dibromo-3-chloropropane caused stomach tumors with many metastases in both rats and mice. Chloroform, known to cause hepatocellular carcinomas in mice, led in addition to kidney tumors in male rats. 1,2-Dichloroethane was much weaker than the analog, 1,2-dibromoethane, and induced only a few stomach tumors in rats. It increased liver and lung tumors in mice. Most of the compounds, namely, trichloroethylene, 1,1-dichloroethane, 1,1,2-trichloroethane, hexachloroethane, and tetrachloroethylene, increased hepatocellular carcinomas in mice but had little or no action in rats. Iodoform tended to increase thyroid tumors in male rats and hepatocellular carcinomas in male mice. The action of 3-chloropropene was questionable. No tumors could be attributed to 1,1,1-trichloroethane (methyl-chloroform).

Animals↗
PubMed1985

Utilization of adipose tissue biopsy in characterizing human halogenated hydrocarbon exposure.

Halogenated hydrocarbons have been successfully utilized for pest control in agriculture and public health. In industry, the polychlorinated biphenyls (PCBs) have been particularly useful. Unfortunately, residues have proven persistent and have been found widely dispersed in the environment. Because they have chemical properties that favor bioaccumulation, it is not surprising that many have been identified in animals and man. Such findings prompted public health concern and initiated review of potential adverse health impacts. In many instances this process has led to total prohibition of use or strict limitations. Highly lipophilic, the primary accumulation site in humans is adipose tissue. Analysis of adipose samples remains the preferred biologic index for estimating exposure. Improved instrumentation has lowered the limit of detection and improved the accuracy of quantification. Accumulated population experience has helped develop understanding of the dynamics of tissue partitioning in humans. Once such relationships have been adequately described, other less invasive procedures may be more confidently used for general surveillance purposes. Whenever adipose tissue is obtained, the blood compartment should also be sampled and the relationship reported. We have only begun to investigate the resulting partition ratio as an investigative tool.

Adipose Tissue↗