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PubMed1991

Validated methods for degrading hazardous chemicals: some halogenated compounds.

Two techniques were investigated for degrading a number of halogenated compounds of commercial and research importance. Reductive dehalogenation with nickel-aluminum alloy in potassium hydroxide solution was used to degrade iodomethane, chloroacetic acid, trichloroacetic acid, 2-chloroethanol, 2-bromoethanol, 2-chloroethylamine, 2-bromoethylamine, 1-bromobutane, 1-iodobutane, 2-bromobutane, 2-iodobutane, 2-bromo-2-methylpropane, 2-iodo-2-methylpropane, 3-chloropyridine, fluorobenzene, chlorobenzene, bromobenzene, iodobenzene, 4-fluoroaniline, 2-chloroaniline, 3-chloroaniline, 4-chloroaniline, 4-fluoronitrobenzene, 2-chloronitrobenzene, 3-chloronitrobenzene, 4-chloronitrobenzene, benzyl chloride, benzyl bromide, alpha,alpha-dichlorotoluene, and 3-aminobenzotrifluoride. The products were generally those obtained by replacing the halogen with hydrogen although concomitant reduction of the other groups was also observed. Bibenzyl was produced during the reduction of benzyl chloride, benzyl bromide, and alpha,alpha-dichlorotoluene. Refluxing with ethanolic potassium hydroxide was used to degrade iodomethane, chloroacetic acid, 2-fluoroethanol, 2-chloroethanol, 2-bromoethanol, 1-chlorobutane, 1-bromobutane, 1-iodobutane, 2-bromobutane, 2-iodobutane, 2-bromo-2-methylpropane, 2-iodo-2-methylpropane, benzyl chloride, benzyl bromide, 1-bromononane, 1-chlorodecane, and 1-bromodecane. The products were the corresponding ethyl ethers. 2-Methylaziridine was cleaved with nickel-aluminum alloy in potassium hydroxide solution to a mixture of isopropylamine and n-propylamine. In all cases, the compounds were completely degraded and only nonmutagenic reaction mixtures were produced.

Hazardous Substances↗

PubMed1999

Effect of Tn10/Tn5 transposons on the survival and mutation frequency of halogen light-irradiated AB1157 Escherichia coli K-12.

We show here that the Tn10/Tn5 transposon when inserted into the chromosome of strain AB1157 makes the bacteria more sensitive to and less mutable by halogen light irradiation. These effects are most probably caused by depletion of UmuD and UmuC proteins since: (i) transformation of the transposon-bearing bacteria with plasmids harbouring umuD'C (or umuDC) leads to recovery of the original survival and mutation frequencies; (ii) insertion of Tn10/Tn5 into chromosomal DNA has no effect on the level of mutation induced by ethyl methane-sulphonate treatment, a mutagen whose activity is umuDC-independent; (iii) the decline in survival is in about the same range for Tn10-bearing bacteria as for bacteria with deleted umuDC. However, whereas transformation of bacteria deleted in umuDC with plasmids carrying umuD'C/umuDC leads to full recovery of halogen light-induced mutability, recovery of survival is poor. This suggests that the mechanisms leading to umuDC-dependent mutagenesis and umuDC-dependent protection of cell survival are different. None of these effects occurs in bacteria bearing the Tn9 transposon in their DNA.

Bacterial Proteins↗

PubMed1987

The bone marrow clastogenicity of eight halogenated benzenes in male NMRI mice.

Eight widely used halogenated benzenes, including bromobenzene (BB), chlorobenzene (CB), three isomers of dichlorobenzene (DCB) and three isomers of trichlorobenzene (TCB) were tested for acute toxicity (LD50) and clastogenicity in 8-week-old NMRI mice by intraperitoneal administration. Four doses of each chemical (up to 70% of LD50) were tested for clastogenic activity. Each compound was administered in two equal doses, 24 h apart. Increased formation of micronucleated polychromatic erythrocytes, observed in femoral bone marrow, 30 h after the first injection, was considered to be due to the clastogenic activity of the test compound. All the halogenated benzenes tested were found to be clastogenic (P less than 0.01). The highest clastogenic activities were induced by m-DCB and BB. Among the three isomers of DCB, m-DCB significantly (P less than 0.05) induced more micronuclei than o-DCB or p-DCB. No significant differences were found between the clastogenic activities of TCB isomers.

Animals↗

PubMed1991

An association between mutagenicity of the Ara test of Salmonella typhimurium and carcinogenicity in rodents for 16 halogenated aliphatic hydrocarbons.

Sixteen halogenated aliphatic hydrocarbons were assayed for genotoxicity using the Ara mutagenicity assay with Salmonella typhimurium. Seven substances (1,2-dibromo-3-chloropropane, 1,2-dibromoethane, 1,2-dichloroethane, vinyl bromide, hexachloro-1,3-butadiene, iodoform and vinilydene chloride) were mutagenic at non-lethal doses. Comparatively, nine compounds (chloroform, carbon tetrachloride, 1,1,1-trichloroethane, 1,1,2-trichloroethane, tetrachloroethylene, trichloroethylene, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane and hexachloroethane) were non-mutagenic after being assayed both in the presence and absence of metabolic activation with a rat liver microsomal fraction (S9). All negative compounds (except hexachloroethane) gave a lethal response, which could be an indication that bacteria were adequately exposed. The concordance between mutagenicity in the Ara test and carcinogenicity in rodents for this group of halogenated hydrocarbons was (31%) significantly lower than the concordance (72%) previously found in the Ara test with respect to a wider range of chemical classes. This result is in agreement with data reported for other genotoxicity assays. The presence of non-genotoxic carcinogens versus genotoxic non-carcinogens is discussed as a possible explanation. Five positive compounds (1,2-dibromo-3-chloropropane, 1,2-dibromoethane, 1,2-dichloroethane, vinyl bromide and hexachloro-1,3-butadiene) were analyzed for a quantitative relationship between carcinogenic potency in rats and the potency of response in the Ara mutagenicity test. This was possible because the Ara test, for volatile compounds (such as vinyl bromide), did not require the use of special vaporization techniques, which are difficult to evaluate quantitatively for mutagenic activity. A highly significant correlation was found between the mutagenic efficiencies of the five compounds in the Ara test and their carcinogenic potencies in rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2005

5-halogenated pyrimidine lesions within a CpG sequence context mimic 5-methylcytosine by enhancing the binding of the methyl-CpG-binding domain of methyl-CpG-binding protein 2 (MeCP2).

Perturbations in cytosine methylation signals are observed in the majority of human tumors; however, it is as yet unknown how methylation patterns become altered. Epigenetic changes can result in the activation of transforming genes as well as in the silencing of tumor suppressor genes. We report that methyl-CpG-binding proteins (MBPs), specific for methyl-CpG dinucleotides, bind with high affinity to halogenated pyrimidine lesions, previously shown to result from peroxidase-mediated inflammatory processes. Emerging data suggest that the initial binding of MBPs to methyl-CpG sequences may be a seeding event that recruits chromatin-modifying enzymes and DNA methyltransferase, initiating a cascade of events that result in gene silencing. MBD4, a protein with both methyl-binding and glycosylase activity demonstrated repair activity against a series of 5-substituted pyrimidines, with the greatest efficiency against 5-chlorouracil, but undetectable activity against 5-chlorocytosine. The data presented here suggest that halogenated pyrimidine damage products can potentially accumulate and mimic endogenous methylation signals.

5-Methylcytosine↗

PubMedDate not supplied

Torchiere-style halogen floor lamps: a need for fire safety awareness.

Torchiere-style halogen lamps pose a significant fire hazard. The 500-W halogen bulb in these lamps can generate temperatures as high as 1200 degrees F. Factors related to the design of the lamp also contribute to the fire risk. The Consumer Products Safety Commission has issued various warnings and recalls on these lamps because of a significant number of fire-related incidents and deaths. The impact of these recalls on a random sample of consumers was investigated. A survey of these participants revealed that 60% of lamp owners and nonowners were unaware of the recalls. The majority of respondents were also not aware of the risks of injury, the extreme bulb temperatures, or safety measures designed for these lamps. There is a need for increasing community awareness and education to reduce the fire hazards associated with this product.

Burns↗

PubMed1995

Cancer incidence among Finnish workers exposed to halogenated hydrocarbons.

Epidemiologic studies and long-term carcinogenicity studies in experimental animals suggest that some halogenated hydrocarbons are carcinogenic. To investigate whether exposure to trichloroethylene, tetrachloroethylene, or 1,1,1-trichloroethane increases carcinogenic risk, a cohort of 2050 male and 1924 female workers monitored for occupational exposure to these agents was followed up for cancer incidence in 1967 to 1992. The overall cancer incidence within the cohort was similar to that of the Finnish population. There was an excess of cancers of the cervix uteri and lymphohematopoietic tissues, however. Excess of pancreatic cancer and non-Hodgkin lymphoma was seen after 10 years from the first personal measurement. Among those exposed to trichloroethylene, the overall cancer incidence was increased for a follow-up period of more than 20 years. There was an excess of cancers of the stomach, liver, prostate, and lymphohematopoietic tissues combined. Workers exposed to 1,1,1-trichloroethane had increased risk of multiple myeloma and cancer of the nervous system. The study provides support to the hypothesis that trichloroethylene and other halogenated hydrocarbons are carcinogenic for the liver and lymphohematopoietic tissues, especially for non-Hodgkin lymphoma. The study also documents excess of cancers of the stomach, pancreas, cervix uteri, prostate, and the nervous system among workers exposed to solvents.

Adult↗

PubMed1999

Evidence that halogenated furanones from Delisea pulchra inhibit acylated homoserine lactone (AHL)-mediated gene expression by displacing the AHL signal from its receptor protein.

Acylated homoserine lactone (AHL)-mediated gene expression controls phenotypes involved in colonization, often specifically of higher organisms, in both marine and terrestrial environments. The marine red alga Delisea pulchra produces halogenated furanones which resemble AHLs structurally and show inhibitory activity at ecologically realistic concentrations in AHL bioassays. Evidence is presented that halogenated furanones displace tritiated OHHL [N-3-(oxohexanoyl)-L-homoserine lactone] from Escherichia coli cells overproducing LuxR with potencies corresponding to their respective inhibitory activities in an AHL-regulated bioluminescence assay, indicating that this is the mechanism by which furanones inhibit AHL-dependent phenotypes. Alternative mechanisms for this phenomenon are also addressed. General metabolic disruption was assessed with two-dimensional PAGE, revealing limited non-AHL-related effects. A direct chemical interaction between the algal compounds and AHLs, as monitored by 1H NMR spectroscopy, was shown not to occur in vitro. These results support the contention that furanones, at the concentrations produced by the alga, can control bacterial colonization of surfaces by specifically interfering with AHL-mediated gene expression at the level of the LuxR protein.

4-Butyrolactone↗

PubMed1988

Purification and characterization of a bacterial dehalogenase with activity toward halogenated alkanes, alcohols and ethers.

An enzyme that is capable of hydrolytic conversion of halogenated aliphatic hydrocarbons to their corresponding alcohols was purified from a 1,6-dichlorohexane-degrading bacterium. The dehalogenase was found to be a monomeric protein of relative molecular mass 28,000. The affinity for its substrates was relatively low with Km values for short-chain haloalkanes in the range 0.1-0.9 mM. The aliphatic dehalogenase showed a much broader substrate range than has been reported for halidohydrolases so far. Novel classes of substrates include dihalomethanes, C5-C9 1-halo-n-alkanes, secondary alkylhalides, halogenated alcohols and chlorinated ethers. Several of these compounds are important environmental pollutants, e.g. methylbromide, dibromomethane, 1,2-dibromoethane, 1,3-dichloropropene, and bis(2-chloroethyl)ether. The degradation of chiral 2-bromoalkanes appeared to proceed without stereochemical preference. Optically active 2-bromobutane was converted with inversion of configuration at the chiral carbon atom, suggesting that the dehalogenase reaction proceeds by a nucleophilic substitution involving a carboxyl group or base catalysis.

Actinomycetales↗

PubMed1988

Substrate specificity, regiospecificity and stereospecificity of halogenation reactions catalyzed by non-heme-type bromoperoxidase of Corallina pilulifera.

Many organic compounds were found to be substrates for halogenation reactions catalyzed by the non-heme-type bromoperoxidase found in the red alga Corallina pilulifera. Anisole, 1-methoxynaphthalene and thiophene were converted to o and p-bromoanisoles, 1-methoxy-4-bromonaphthalene and 2-bromothiophene respectively. Regiospecificity of the enzymatic bromination of anisole was tested and found to be the same as in the chemical reaction with NaOBr. The enzyme also acted on substituted alkenes such as styrene, cyclohexene, trans-cinnamic acid, trans-cinnamyl alcohol and cis-propenylphosphonic acid, to give the respective bromohydrin compounds or decarboxylated bromo compound. These bromohydrin compounds were always mixtures of stereoisomers. In the light of the above findings together with the previous studies concerning the halogenation mechanism, the bromoperoxidase of C. pilulifera was considered to have no specific restriction site for these substrates.

Alcohols↗

PubMed2001

Halogenated furanones from the red alga, Delisea pulchra, inhibit carbapenem antibiotic synthesis and exoenzyme virulence factor production in the phytopathogen Erwinia carotovora.

The plant pathogen Erwinia carotovora regulates expression of virulence factors and antibiotic production via an N-3-oxohexanoyl-L-homoserine lactone (3-oxo-C6-HSL) dependent quorum sensing mechanism. The marine alga Delisea pulchra produces halogenated furanones known to antagonise 3-oxo-C6-HSL activity. We have tested the effects of a halogenated furanone on the production of carbapenem, cellulase and protease in E. carotovora. Despite differences in the regulatory mechanisms controlling carbapenem and exoenzyme production each was inhibited by the algal metabolite. We present evidence to suggest that the furanone dependent inhibition of carbapenem production is a result of the disruption of the 3-oxo-C6-HSL dependent expression of the carABCDEFGH operon.

4-Butyrolactone↗

PubMed1990

Activities and mechanisms of action of halogen-substituted flavanoids against poliovirus type 2 infection in vitro.

The effects of some halogen-substituted flavanoids (dichloroflavan, halogenated isoflavans, and isoflavenes) on poliovirus type 2 infection was examined. Only two isoflavenes exhibited a significant inhibitory activity on the virus-induced cytopathic effect and plaque formation. In a single cycle of viral replication, both compounds reduced the viral yield by approximately 90%. The presence of the isoflavenes from the beginning of infection or during the adsorption period only prevented the shutoff of host translation and viral RNA and protein synthesis, suggesting that the drugs blocked an early step of viral replication. Indeed, both isoflavenes were not virucidal, did not protect virus infectivity from heat inactivation, and had no measurable effect on the binding of virus to cells, viral penetration, and uncoating of the viral RNA. In contrast, both compounds significantly reduced the infectivity of free viral RNA. The possibility that compounds interfere with poliovirus replication at a very early stage of translation of the input RNA is discussed.

Flavonoids↗

PubMed2001

Enhancement of fluoroquinolone activity by C-8 halogen and methoxy moieties: action against a gyrase resistance mutant of Mycobacterium smegmatis and a gyrase-topoisomerase IV double mutant of Staphylococcus aureus.

The increasing prevalence of antibiotic resistance among bacterial pathogens prompted a microbiological study of fluoroquinolone structure-activity relationships with resistant mutants. Bacteriostatic and bactericidal activities for 12 fluoroquinolones were examined with a gyrase mutant of Mycobacterium smegmatis and a gyrase-topoisomerase IV double mutant of Staphylococcus aureus. For both organisms C-8 halogen and C-8 methoxy groups enhanced activity. The MIC at which 99% of the isolates tested were inhibited (MIC(99)) was reduced three- to fivefold for the M. smegmatis mutant and seven- to eightfold for the S. aureus mutant by C-8 bromine, chlorine, and methoxy groups. With both organisms a smaller reduction in the MIC(99) (two- to threefold) was associated with a C-8 fluorine moiety. In most comparisons with M. smegmatis the response to a C-8 substituent was similar (within twofold) for wild-type and mutant cells. In contrast, mutant S. aureus was affected more than the wild type by the addition of a C-8 substituent. C-8 halogen and methoxy groups also improved the ability to kill the two mutants and the respective wild-type cells when measured with various fluoroquinolone concentrations during an incubation period equivalent to four to five doubling times. Collectively these data help define a group of fluoroquinolones that can serve (i) as a base for structure refinement and (ii) as test compounds for slowing the development of fluoroquinolone resistance during infection of vertebrate hosts.

Anti-Infective Agents↗

PubMed1983

Transformations of 1- and 2-carbon halogenated aliphatic organic compounds under methanogenic conditions.

Several 1- and 2-carbon halogenated aliphatic organic compounds present at low concentrations (less than 100 micrograms/liter) were degraded under methanogenic conditions in batch bacterial cultures and in a continuous-flow methanogenic fixed-film laboratory-scale column. Greater than 90% degradation was observed within a 2-day detention time under continuous-flow methanogenic conditions with acetate as a primary substrate. Carbon-14 measurements indicated that chloroform, carbon tetrachloride, and 1,2-dichloroethane were almost completely oxidized to carbon dioxide, confirming removal by biooxidation. The initial step in the transformations of tetrachloroethylene and 1,1,2,2-tetrachloroethane to nonchlorinated end products appeared to be reductive dechlorination to trichloroethylene and 1,1,2-trichloroethane, respectively. Transformations of the brominated aliphatic compounds appear to be the result of both biological and chemical processes. The data suggest that transformations of halogenated aliphatic compounds can occur under methanogenic conditions in the environment.

Anaerobiosis↗

PubMed1983

Transformations of halogenated organic compounds under denitrification conditions.

Trihalomethanes, carbon tetrachloride, 1,1,1-trichloroethane, 1,2-dibromoethane, chlorinated benzenes, ethylbenzene, and naphthalene at concentrations commonly found in surface and groundwater were incubated under anoxic conditions to study their transformability in the presence of denitrifying bacteria. None of the aromatic compounds showed significant utilization relative to sterile controls at initial concentrations from 41 to 114 micrograms/liter after 11 weeks of incubation. Of the halogenated aliphatic compounds studied, transformations of carbon tetrachloride and brominated trihalomethanes were observed after 8 weeks in batch denitrification cultures. Carbon from the decomposition of carbon tetrachloride was both assimilated into cell material and mineralized to carbon dioxide. How this was possible remains unexplained, since carbon tetrachloride is transformed to CO2 by hydrolysis and not by oxidation-reduction. Chloroform was detected in bacterial cultures with carbon tetrachloride initially present, indicating that reductive dechlorination had occurred in addition to hydrolysis. The data suggest that transformations of certain halogenated aliphatic compounds are likely to occur under denitrification conditions in the environment.

Anaerobiosis↗

PubMed1980

p-Cymene pathway in Pseudomonas putida: selective enrichment of defective mutants by using halogenated substrate analogs.

Several classes of mutants of Pseudomonas putida (JT810) defective in the utilization of p-cymene as sole carbon source have been isolated. Selective enrichment of the mutants and for strains putatively cured of a degradative plasmid was achieved by incubation of cells in minimal growth media containing p-cymene (or p-cumate) and various halogenated analogs of the growth substrates or pathway intermediates. Analogs which led to successful enrichments included: p-chlorotoluene, p-bromotoluene, alpha-chloro-p-xylene, and p-iodobenzoate. A mutant strain, PpJT811, constitutive for the p-cymene pathway gave significantly greater enrichments of defective mutants than the wild-type parent PpJT810 after incubation with the halogenated analogs. It is suggested that the defective mutants are enriched because of the genetic alterations they possess, which confer immunity to a lethal synthesis performed by transformation of the analogs in clones possessing an intact p-cymene pathway. A nomenclature for the genetic organization of p-cymene pathway is described.

Biotransformation↗

PubMed1985

Reconstituted halogenated hydrocarbon pesticide and pollutant mixtures found in human tissues: effects on the immature male Wistar rat after short-term exposure.

Halogenated hydrocarbon insecticides and polychlorinated biphenyl (PCB) mixtures are routinely detected as residues in human adipose tissue, serum, and milk. Based on average values observed in analytical studies, reconstituted halogenated hydrocarbon pesticide mixtures and PCB mixtures were prepared and administered to immature male Wistar rats. The mixtures were administered at dose levels which approximate the concentrations which would be absorbed by an infant suckling for 180 days (low dose, L), and at three higher dose levels (2 X L, 10 X L, and 100 X L). The pesticide mixture contained isomeric hexachlorocyclohexanes, dieldrin, heptachlor epoxide, oxychlordane, trans-nonachlor, hexachlorobenzene, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane, and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene; the reconstituted PCB mixture contained 13 of the major congeners which have been identified in human milk samples. Administration of the L dose level of the pesticide (0.95 mg/kg), PCB (0.45 mg/kg), and pesticide plus PCB mixture (0.95 + 0.45 mg/kg, respectively) in corn oil on days 1 and 3 did not significantly alter hepatic drug-metabolizing enzyme activities or elicit any observable pathological damage 6 days after the first exposure. In contrast, administration of the higher dose levels of this mixture elicited a dose-dependent induction of several hepatic drug-metabolizing enzymes. Moreover, despite the short duration of exposure to these chemicals, the rats treated with the higher doses (10 X L and 100 X L) of these mixtures exhibited mild alterations in thyroid architecture, changes in hepatocellular nuclei including variations in chromatin distribution, vesiculation of larger nuclei, and frequent appearance of pyknotic shrunken nuclei.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Interaction of Cl- and other halogens with Cl- transport systems in rabbit cortical collecting duct.

We have reported that in the rabbit cortical collecting duct (CCD) we can identify electrophysiologically three distinct cell types; the collecting duct (CD) cell and the alpha- and beta-intercalated (IC) cell. To further characterize the Cl- transport properties of each cell type, we examined the interaction between Cl- and other halogens or SCN- in the isolated and perfused CCD by intracellular microelectrode impalement. The rapid depolarization of the basolateral membrane potential (VB) caused by replacement of bath Cl- with each anion revealed that the sequences of apparent halogen selectivity for the basolateral Cl- conductance were similar in all three cell types. The ranking of Cl- > Br- > F- > I- corresponds to the sequence 5 of Eisenman's series, indicating "strong" interaction of the anions with the selectivity site. The basolateral Cl- conductance of these three cell types may share common characteristics, although I- permeability is less in IC cells than in CD cells. Hyperpolarization of the basolateral membrane of the beta-IC cell upon reduction of luminal Cl- reflects alterations in either Cl- entry across the apical membrane, or Cl- exit across the basolateral membrane, or both. Luminal Cl- replacement with each anion showed that the sequence of the hyperpolarization of the basolateral membrane was I- >> cyclamate = SCN- > F- > Br-, suggesting that I-inhibits either apical Cl- entry or basolateral Cl- exit. On the other hand, in the CD cell reduction of the perfusate Cl- by replacement with each anion caused the basolateral membrane to hyperpolarize with a different ranking: cyclamate = F- > I- = SCN- > Br-.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗