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PubMed1982

Bioactivation of halogenated hydrocarbons.

Halogenated hydrocarbons are an economically and toxicologically important group of chemicals. These compounds may produce toxic effects after metabolism to stable, but toxic, products or to reactive, electrophilic intermediates. The biotransformation reaction may involve oxidative or reductive reactions or may proceed with no change in oxidation state. The bioactivation reactions are catalyzed most frequently by cytochrome P-450-dependent monooxygenases, but glutathione S-transferases may also catalyze bioactivation reactions. Detailed reaction mechanism studies are useful in understanding the biotransformation and bioactivation pathways of halogenated hydrocarbons.

Biotransformation↗
PubMed1984

Relationships between the electrostatic potential, epoxide hydrase inhibition and carcinogenicity for some hydrocarbon and halogenated hydrocarbon epoxides.

For a group of nine hydrocarbon and halogenated hydrocarbon epoxides, there is shown to be a good correlation between their abilities to inhibit epoxide hydrase and the quantity Vmin /Es, where Vmin is the most negative value of the molecule's electrostatic potential in the neighborhood of the epoxide oxygen and Es is a factor that takes account of steric effects. It is also demonstrated that carcinogenicity, for thirteen epoxides, appears to be associated with Vmin having a relatively large negative value. On this basis, several other epoxides are predicted to be carcinogenic. The electrostatic potentials used in developing these relationships have been computed by an ab initio self-consistent-field molecular orbital procedure, using optimized molecular geometries.

Animals↗
PubMed1993

Kinetic Studies of Ammonia Monooxygenase Inhibition in Nitrosomonas europaea by Hydrocarbons and Halogenated Hydrocarbons in an Optimized Whole-Cell Assay.

The inhibitory effects of 15 hydrocarbons and halogenated hydrocarbons on NH(3) oxidation by ammonia monooxygenase (AMO) in intact cells of the nitrifying bacterium Nitrosomonas europaea were determined. Determination of AMO activity, measured as NO(2) production, required coupling of hydroxylamine oxidoreductase (HAO) activity with NH(3)-dependent NH(2)OH production by AMO. Hydrazine, an alternate substrate for HAO, was added to the reaction mixtures as a source of reductant for AMO. Most inhibitors exhibited competitive or noncompetitive inhibition patterns. The competitive character generally decreased (K(i) (E)/K(i) (ES) increased) as the molecular size of the inhibitors increased. For example, CH(4) and C(2)H(4) were competitive inhibitors of NH(3) oxidation, whereas the remaining alkanes (up to C(4)) and monohalogenated (Cl, Br, I) alkanes were noncompetitive. Oxidation of C(2)H(5)Br (noncompetitive) increased as the NH(4) concentration increased up to 40 mM, whereas oxidations of inhibitors with competitive character (K(i) (E) << K(i) (ES)) were diminished at 40 mM NH(4). Multichlorinated compounds produced nonlinear Lineweaver-Burk plots. Iodinated alkanes (CH(3)I, C(2)H(5)I) and C(2)Cl(4) were potent inhibitors of NH(3) oxidation. Maximum rates of NH(3), C(2)H(4), and C(2)H(6) oxidations were approximately equivalent, suggesting a common rate-determining step. These data support an active-site model for AMO consisting of an NH(3)-binding site and a second site that binds noncompetitive inhibitors, with oxidation occurring at either site.

Journal Article↗
PubMed1984

Survey of reproductive hazards among oil, chemical, and atomic workers exposed to halogenated hydrocarbons.

Several halogenated hydrocarbons are suspected of causing adverse reproductive effects. Because of such concerns, the Oil, Chemical, and Atomic Workers International Union surveyed the reproductive histories of two groups of workers. One group worked at plants engaged in the production or use of halogenated hydrocarbons (exposed) whereas the others had no such opportunity for exposure (nonexposed). Although a low response rate precludes firm conclusions, the 1,280 completed questionnaires provide useful data for generating hypotheses in this developing field of interest. A history of diagnosed cancer was reported more frequently among exposed workers. The infant mortality rate was also significantly elevated among the offspring of exposed workers. No risk gradient was observed for episodes of infertility, fetal loss, congenital defects, or low-birthweight offspring. Concerns with nonresponse, exposure characterization, possible confounding factors, and limited statistical power are addressed. The results provide further suggestions which help to direct studies of occupational reproductive risks.

Abnormalities, Drug-Induced↗
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↗
PubMed1982

Residues in the fat of ewes grazing on soil contaminated with halogenated hydrocarbons.

Three halogenated hydrocarbon compounds were applied to the surface of each of two .57 ha bluegrass plots in October. Each plot was stocked with 10 mature ewes 6 mo after application. Supplemental feed was not offered. Five ewes remained on the plots for 180 d, whereas the other five were removed and replaced at 60-d intervals. Average soil residues for the period of grazing were 13.3, 3.8, 29.3 and 32.8 mg/m2 HCB (hexachlorobenzene), DDE [1,1-dichloro-2,2-bi(p-chlorophenyl)ethylene], DDT [1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane] and PBB (polybrominated biphenyls), respectively, for plot 1 and 16.5 and 48.0 mg/m2 DDE and PBB, respectively, for plot 2. Average concentrations of residue in body fat of the five ewes grazing for 180 d were .37, .30 and .30 micrograms/g HCB, DDE and PBB, respectively, for plot 1 and 2.41 and .79 micrograms/g DDE and PBB, respectively, for plot 2. Average residue concentrations in ewes that grazed 60-d subperiods were nearly as great, which indicated that steady state residue levels were reached in less than 180 d. A second trial and was conducted 3 yr later after plowing and reseeding the plots, but only PBB was measured. Polybrominated biphenyl was distributed throughout the top 16 cm of soil but the quantity present had not changed appreciably from the first trial. After seven ewes/plot grazed 136 d, residues were detected in only one of the seven on plot 1, but were detected in all seven on plot 2 with an average concentration of only .032 micrograms/g. It is concluded that concentration of residue in body fat of ewes depended on the concentration of chemical at the soil surface and the amount of soil ingested.

Adipose Tissue↗
PubMedDate not supplied

Taste aversions to several halogenated hydrocarbons.

Five halogenated hydrocarbons (chloral; trichloroethylene; 1,2-dichloroethylene; 1,2-dichloroethane and 1,1,2-trichloroethane) were evaluated in the taste aversion paradigm to determine thresholds for producing aversion effects. Comparisons were made between threshold determination for acute and repetitive conditioning trials. All of the compounds produced saccharin aversions following one pairing of the chemical exposure with saccharin ingestion. Repetitive conditioning trials did not alter the thresholds for producing aversions with any of the five compounds evaluated. Potencies of the compounds in producing conditioned taste aversions were chloral greater than 1,1,2-trichloroethane greater than 1,2-dichloroethane greater than 1,2-dichloroethylene greater than trichloroethylene.

Animals↗
PubMed1993

Bioactivation of halogenated hydrocarbons by cytochrome P4502E1.

Numerous halogenated hydrocarbons of the alkane, alkene, and alkyne classes are metabolized by P450 enzymes to products that elicit cytotoxic and/or carcinogenic effects. Such halogenated hydrocarbons include anesthetics (e.g., halothane and enflurane) and industrial solvents (e.g., carbon tetrachloride, chloroform, and vinylidine chloride). Formation of reaction intermediates from these compounds occurs via P450-promoted dehalogenation, reduction, or reductive oxygenation, with certain hydrocarbons undergoing all three reaction types. Of the multiple forms of P450 present in liver microsomes, P4502E1 has been identified as the primary catalyst of hydrocarbon bioactivation in animals and, most likely, in humans as well. As hepatic concentrations of this P450 enzyme are highly inducible by ethanol and similar agents, prior exposure to 2E1-inducing compounds can play a pivotal role in halogenated hydrocarbon toxicity. Considering that metabolism governs the cytotoxicity and carcinogenicity of halogenated hydrocarbons, an understanding of the mechanism(s) underlying 2E1 induction in man becomes all the more important.

Anesthetics↗
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↗
PubMed1993

Predicting rodent carcinogenicity of halogenated hydrocarbons by in vivo biochemical parameters.

Forty halogenated hydrocarbons of known rodent carcinogenicity (24 carcinogens, 16 noncarcinogens), including many promoters of carcinogenesis, nongenotoxic carcinogens, and hepatocarcinogens, were selected for study. The chemicals were administered by gavage in two dose levels to female Sprague-Dawley rats. The effects of these 40 chemicals on four biochemical assays [hepatic DNA damage by alkaline elution (DD), hepatic ornithine decarboxylase activity (ODC), serum alanine aminotransferase activity (ALT), and hepatic cytochrome P-450 content (P450)] were determined. Composite predictive parameters are defined as follows: CP = [ODC and P450], CT = [ALT and ODC], and TS = [DD or CP or CT]. The operational characteristics of TS for predicting rodent cancer were sensitivity 58%, specificity 81%, positive predictivity 82%, negative predictivity 57%, and concordance 68%. The concordance for the Ames test (45%) and structural alerts (SA; 46%) was much lower. TS also outperformed the Ames test and SA in producing fewer false positives (the specificity of TS was 81% vs. only 63% for the Ames test and 57% for SA). For predicting the carcinogenicity of the most difficult halogenated hydrocarbons (Ames and SA negative chemicals), TS was capable of successfully predicting the carcinogenicity of 8 (carbon tetrachloride, chloroform, alpha-hexachlorocyclohexane, kepone, mirex, monuron, p,p'-DDE, and 2,4,6-trichlorophenol) out of 16 of these non-DNA-reactive halogenated hydrocarbon carcinogens. All 8 of these halogenated hydrocarbons were positive in either CP or CT. This evidence shows that nongenotoxic carcinogenesis is best predicted by nongenotoxic parameters such as CP or CT (components of the predictor TS).

Animals↗
PubMed1994

Depression of calcium dynamics in cardiac myocytes--a common mechanism of halogenated hydrocarbon anesthetics and solvents.

Individual halogenated hydrocarbons (HC) have recently been demonstrated to depress Ca2+ dynamics in cardiomyocytes during excitation-contraction coupling. In the present study, eight widely used HC were systematically compared for their effects on Ca2+ dynamics in neonatal rat cardiomyocytes by means of spectrofluorometric analysis of fura-2-Ca(2+)-binding. Cells were exposed to dichloromethane (DCM), dichloroethane (DCE), 1,1,2-trichloroethane (112-TCE), trichloroethylene (TRI), halothane (HAL), 1,1,1-trichloroethane (111-TCE), perchloroethylene (PER), or pentachlorethane (PCE) in an environmentally controlled chamber. All HC tested decreased the height of electrically induced cytosolic free Ca2+ ([Ca2+]i) transients in a concentration-dependent and reversible manner (IC50 0.15-18.06 mM) without significant effects on diastolic [Ca2+]i. The increase in [Ca2+]i induced by depolarization with 90 mM KCl was inhibited to a lesser degree. Investigations with thapsigargin (100 nM) and ryanodine (1 microM)-inhibitors of Ca2+ release from the sarcoplasmic reticulum-provided evidence that the tonic Ca2+ response after KCl depolarization depends mainly on sarcolemmal Ca2+ influx. The potency of the eight HC to inhibit Ca2+ dynamics in cardiomyocytes correlated with their octanol/water partition coefficients. Results support the hypothesis that alteration of Ca2+ dynamics in cardiomyocytes is a common mechanism of cardiotoxic HC actions.

Anesthetics↗
PubMed2001

PBPK modeling of canine inhalation exposures to halogenated hydrocarbons.

Human exposure guidelines for halogenated hydrocarbons (halons) and halon replacement chemicals have been established using dose-response data obtained from canine cardiac sensitization studies. In order to provide a tool for decision makers and regulators tasked with setting guidelines for egress from exposure to halon replacement chemicals, a quantitative approach, using a physiologically based pharmacokinetic model, was established that allowed exposures to be assessed in terms of the chemical concentrations in blood during the exposure. This model, which includes a respiratory tract compartment containing a dead-space region, a pulmonary exchange area, and a breath-by-breath description of respiratory tract uptake, allows successful simulation of exhaled breath concentrations of humans during the first minute of exposure to the anesthetics halothane, isoflurane, and desflurane. In the current study, the human model was modified with canine parameters and validated with data obtained from dog studies with halothane, isoflurane, desflurane, and CFC-11. With consideration of appropriate values for ventilation and cardiac output, the model successfully simulated data collected under a variety of exposure scenarios. The canine model can be used for simulating blood concentrations associated with the potential for cardiac sensitization. These target blood concentrations can then be used with the human model for establishing safe human exposure duration. Development of the canine model stresses the need for appropriate data collection for model validation.

Administration, Inhalation↗
PubMed1992

A gas-chromatographic determination of the ppb levels of volatile halogenated hydrocarbons in water for injections.

Some volatile halogenated hydrocarbons have been found in commercial large volume parenterals (LVPs) prepared from untreated or treated (disinfected) water. To monitor the presence of volatile halogenated hydrocarbons in the source water and also in the water for injections, a low cost and sufficiently simple procedure has been developed, specifically for the following components: 1,1,1 trichloroethane, 1,1,2 trichloroethylene, 1,1,2,2 tetrachloroethylene, carbon tetrachloride, chloroform, dichlorobromomethane and dibromochloromethane. A Head-space technique coupled with ECD-gaschromatography was used. The procedure is thoroughly discussed in the article, including the results of a ring test for a preliminary validation of this method.

Chromatography, Gas↗
PubMed1990

[Distribution pattern of chemical in surface waters as a reflexion of entry pattern--nonvolatile halogenated hydrocarbons].

The concentrations of some nonvolatile halogenated hydrocarbons in surface waters of an industrialized city and its surroundings are given. About 80% of the ballast isomers of hexachlorocyclohexane (alpha, beta and delta BHC) and of DDT and its metabolites are in the range of less than 5 micrograms l-1, whereas ca. 50% of lindane (gamma BHC) were found to be between 5 and 100 micrograms l-1. Starting form the remarks about the differential-diagnostic assessment of environmental concentrations conclusions as to the origin of hexachlorocyclohexane isomers are drawn with the help of their distribution pattern. A high part of the gamma isomer, compared with the ballast isomers means an application (e.g. against mosquitos). This fact may be supported if it coincides with the months typical for such an application. in contrast to this if you have high percentages of alpha, beta and delta hexachlorocyclohexane, it indicates a point source or diffuse inputs of technical BHC. If all four isomers are present on a comparable and very low level this may reflect a remobilization from the sediment.

DDT↗
PubMedDate not supplied

The use of stable isotopes to identify reactive metabolites and target macromolecules associated with toxicities of halogenated hydrocarbon compounds.

1. Halogenated compounds, such as the inhalation anaesthetics, halothane and enflurane, and the chemicals chloroform, carbon tetrachloride, and bromotrichloromethane can cause hepatotoxicity, nephrotoxicity, and inactivation of cytochromes P-450. Each of these toxicities is mediated by reactive metabolites. 2. Stable isotopes of hydrogen, carbon, chlorine and oxygen have been used in conjunction with mass spectrometry and n.m.r. spectrometry to identify the structures of these metabolites, to elucidate the mechanisms of their formation, and to characterize the structures of their macromolecular adducts. 3. In a number of cases, oxidative pathways of metabolism to toxic metabolites have been defined by kinetic deuterium isotope effects. 4. Recently, we have found that the trichloromethyl radical metabolite of bromotrichloromethane can activate myoglobin by causing the covalent cross-linking of haem to protein. The structure of a haem-myoglobin adduct has been defined by the use of stable isotope studies.

Animals↗
PubMed1998

In vitro assessment of the effect of halogenated hydrocarbons: chloroform, dichloromethane, and dibromoethane on embryonic development of the rat.

Halogenated hydrocarbons are widely used in industry, the laboratory, and in the home. In the present study three of these solvents--chloroform, dichloromethane, and dibromoethane--were examined for embryotoxic/teratogenic potential using rat embryo culture. The results showed that each of the solvents had a concentration-dependent embryotoxic effect on the developing rat embryo in vitro. The effect and no-effect concentrations (expressed in mumol/ml culture medium), respectively, for each of the halogenated hydrocarbons tested were: dibromoethane--0.33, < 0.18; chloroform--2.06, 1.05; dichloromethane--6.54, 3.46. The levels of chloroform and dichloromethane found to be embryotoxic in the present study were compared to reported blood levels attained following controlled human exposure. In the industrial situation, if the current exposure levels are adhered to, chloroform and dichloromethane appear to have little potential for reproductive toxicity in the human. Fatal or near fatal solvent levels would be required in the mother for the embryotoxic level to be reached. For dibromoethane, there are no reports following controlled human exposure presumably due to its carcinogenicity. In an attempt to elucidate the mechanism of embryotoxicity, histological studies were performed after exposure of rat embryos to an embryotoxic level of each of the halogenated hydrocarbons studied, for increasing time periods up to the standard 40-hour culture. Marked cell death in the neuroepithelium of the developing neural tube was a prominent feature in all embryos exposed to an embryotoxic level of these solvents for periods of 16 hours of longer.

Animals↗
PubMed1990

[Pollution of indoor air in large-scale kitchens and laundries by volatile halogenated hydrocarbons].

The study demonstrates that the agents used for dishwashing and in the central laundry are already slightly contamined with halogenated hydrocarbons and formaldehyde. Analyses of the washing lyes yield considerably higher concentrations of halogenated hydrocarbons. Especially in the dishwater a relatively high concentration of trichloromethane (chloroform) was detected. Obviously these halogenated hydrocarbons are also present in relatively high concentrations in the air of the corresponding working places. However, the concentrations of individual halogenated hydrocarbons and formaldehyde are clearly below the respective threshold limit values.

Air Pollutants, Occupational↗