Abiotic degradation of chlorinated ethanes and ethenes in water.

INTRODUCTION: Chlorinated ethanes and ethenes are among the most frequently detected organic pollutants of water. Their physicochemical properties are such that they can contaminate aquifers for decades. In favourable conditions, they can undergo degradation. In anaerobic conditions, chlorinated solvents can undergo reductive dechlorination. DEGRADATION PATHWAYS: Abiotic dechlorination is usually slower than microbial but abiotic dechlorination is usually complete. In favourable conditions, abiotic reactions bring significant contribution to natural attenuation processes. Abiotic agents that may enhance the reductive dechlorination of chlorinated ethanes and ethenes are zero-valent metals, sulphide minerals or green rusts. OXIDATION: At some sites, permanganate and Fenton's reagent can be used as remediation tool for oxidation of chlorinated ethanes and ethenes. SUMMARY: Nanoscale iron or bimetallic particles, due to high efficiency in degradation of chlorinated ethanes and ethenes, have gained much interest. They allow for rapid degradation of chlorinated ethanes and ethenes in water phase, but they also give benefit of treating dense non-aqueous phase liquid.

Application of the margin of exposure (MoE) approach to substances in food that are genotoxic and carcinogenic - example: 1-methylcyclopropene and its impurities (1-chloro-2-methylpropene and 3-chloro-2-methylpropene).

The chlorinated impurities of 1-methylcyclopropene possess weak mutagenicity and are carcinogenic in rodent bioassays. Dose-response modelling of the data for 1-chloro-2-methylpropene gave a BMDL10 for nasal carcinomas in male rats of 11 mg/kg-bw/day (after correction for the 5 days/week dosage schedule). No human exposure data are available and theoretical estimates had to be used to calculate the MoE. The MoEs ranged from 40,000 to 100,000,000 depending on the assumptions used in the exposure estimation.

Chemotherapy-induced bystander effect in response to several chloroethylnitrosoureas: an origin independent of DNA damage?

Chloroethylnitrosourea (CENU) chemotherapy is used for the treatment of melanoma tumors. The main mechanism of action of this anticancer agent is via DNA damage. We recently showed in murine experiments using a parental double B16 melanoma tumor model that, after treatment of primary tumors with cystemustine (CENU agent), untreated secondary tumors exhibited growth inhibition and metabolism disorders. The response of secondary untreated tumor was called the chemotherapy-induced bystander effect. To see whether chemotherapy-induced bystander effects were induced with other members of the CENU family, we compared three CENU(s) used in melanoma treatment: cystemustine, carmustine and fotemustine. Our results demonstrate that fotemustine, like cystemustine, but not carmustine induced a protective effect against secondary untreated tumors including alterations in phospholipid derivative and glutathione which are the metabolic signature of the bystander effect. From these data we may conclude that DNA damage to the primary tumor is not sufficient to explain chemotherapy-induced bystander effects.

Oral administration of dimethylvinyl chloride increases frequency of forestomach papillomas in Tg.AC mice.

This work was initiated to determine the potential for the Tg.AC mouse model to identify chemical carcinogens by an oral route of administration. Tg.AC v-Ha-ras transgenic mice were exposed to dimethyvinyl chloride (DMVC; 1-chloro-2-methylpropene), a structural analog of the human carcinogen vinyl chloride. In the National Toxicology Program 2-yr bioassay, DMVC induced tumors in the oral, nasal, and gastric epithelia of rats and mice. Initial studies were performed in female Tg.AC mice to determine an appropriate oral dose of DMVC to evaluate the potential for stratified gastric or oral epithelia of Tg.AC mice to serve as a target tissue for a transgene-dependent induced tumorigenic response. DMVC was administered to 13- to14-wk-old Tg.AC mice by gavage at doses of 0, 50, 100, and 200 mg/kg five times a week for 20 wk. The forestomachs of DMVC-treated Tg.AC mice had an increasing number of papillomas, which were associated with an increase in the dose of DMVC. The average numbers of papillomas per mouse per dose were 2.4, 7.6, 14.1, and 12.6 for the 0, 50, 100, and 200-mg/kg dose groups, respectively. The optimum papillomagenic dose of 100 mg/kg DMVC was established and administered for 5, 10, and 15/wk to investigate the kinetics of papilloma induction in Tg.AC mice. The average numbers of papillomas per animal were 1.8, 8.8, and 19.0 at 5, 10, and 15 wk, respectively. Reverse transcription-polymerase chain reaction assays determined that the v-Ha-ras transgene was transcriptionally active in all tumor tissues but not in nontumor tissues. In situ hybridization assays performed in conjunction with bromodeoxyuridine in vivo labeling localized the transgene-expressing cells of the forestomach papillomas to the proliferating cellular component of the tumors, as previously seen in skin papillomas of Tg.AC mice. The present results confirm that DMVC is tumorigenic and that oral routes of administration can be used to rapidly elicit a transgene-associated tumor response in the forestomach of Tg.AC mice.

Chemical mutagenesis testing in Drosophila. IX. Results of 50 coded compounds tested for the National Toxicology Program.

Fifty chemicals were tested for mutagenic activity in post-meiotic and meiotic germ cells of male Drosophila melanogaster using the sex-linked recessive lethal (SLRL) assay. As in the previous studies in this series, feeding was chosen as the first route of administration. If the compound failed to induce mutations by this route, injection exposure was used. One gaseous chemical (1,3-butadiene) was tested only by inhalation. Those chemicals that were mutagenic in the sex-linked recessive lethal assay were further tested for the ability to induce reciprocal translocations. Eleven of the 50 chemicals tested were mutagenic in the SLRL assay. These included bis(2-chloroethyl) ether, 1,4-butanediol diglycidyl ether, 1-chloro-2-propanol, dimethyl methylphosphonate, dimethyl morpholinophosphoramidate, dimethyloldihydroxyethylene urea, 2,2-dimethyl vinyl chloride, hexamethylphosphoramide, isatin-5-sulfonic acid (Na salt), isopropyl glycidyl ether, and urethane. Five of these, including 1,4-butanediol diglycidyl ether, 2,2-dimethyl vinyl chloride, hexamethylphosphoramide, isopropyl glycidyl ether, and urethane, also induced reciprocal translocations.

Metabolism of 1-chloro-2-methylpropene. Evidence for reactive chloroaldehyde intermediates.

Recent metabolism and disposition studies of 1-chloro-2-methylpropene (dimethylvinyl chloride) revealed cysteine and N-acetylcysteine conjugates of 3-chloro-2-methylpropenoic acid as the major metabolites. In the present studies we have investigated various steps in the metabolic pathway to determine which step was responsible for the observed trans (E)-stereochemistry of these metabolites. In vitro incubation studies of dimethylvinyl chloride with rat liver microsomes indicated cytochrome P-450-catalyzed aliphatic hydroxylation to be only stereoselective. Both (E)- and (Z)-3-chloro-2-methylpropenols formed in an identical ratio of 2:1 in incubations with microsomes from untreated male and female rats and phenobarbital-treated male rats. No alcohol formation was observed in incubations using microsomes from beta-naphthoflavone-treated male rats. Investigation of the subsequent conjugation reactions of sulfur nucleophiles with haloenoic carbonyl compounds showed that both (E)- and (Z)-3-chloro-2-methylpropenals reacted rapidly with N-acetylcysteine, the E-adduct being the sole product in either case. In contrast, the Michael reaction of the corresponding acids with N-acetylcysteine was very sluggish. Also, whereas the E-acid yielded exclusively the corresponding E-adduct, the Z-isomer afforded both Z- and E-conjugates in the ratio of 3:4. Glutathione S-transferases had poor activity towards conjugation of glutathione with these acids. Formation of only an E-glutathione conjugate could be observed from either the E- or Z-acid in these enzymatic reactions. Direct Michael reaction of glutathione with (E)-3-bromo-2-methylpropenoic acid, used in chemical synthesis of the conjugates, yielded both the E- and Z-adducts in the ratio of 95:5.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative metabolism and disposition of 1-chloro- and 3-chloro-2-methylpropene in rats and mice.

A recent 2-year carcinogenicity study found that gavage administration of 3-chloro-2-methylpropene (CMP), containing 5% 1-chloro-2-methylpropene (dimethylvinyl chloride, DMVC), caused forestomach neoplasms in rats and mice. Similar chronic studies revealed that DMVC caused forestomach neoplasms in both rats and mice; neoplasms of the nasal and oral cavities were observed in rats but not in mice. In the current studies we have investigated the metabolic basis of these differences. Daily doses of 150 mg/kg of 2-[14C]DMVC or 2-[14C]CMP were administered to rats for 1, 2, or 4 consecutive days. One daily dose of 150 mg/kg of DMVC was administered to mice. Both DMVC and CMP were rapidly metabolized; however, CMP was cleared at a slightly lower rate. Rats exhaled approximately 25 and 10% of the DMVC and CMP as CO2, respectively. Mice exhaled 25% of the DMVC as CO2. Rats expired 30% of the administered DMVC unchanged in the 24 hr after dosing compared to only 7% of the administered CMP. Mice expired 5% of the administered DMVC in the same time period. This observation may explain the occurrence of tumors in the nasal and oral cavities of rats treated with DMVC but not in rats treated with CMP or in mice treated with DMVC in 2-year carcinogenicity studies. The 24-hr urinary excretion in rats was 35% of the administered DMVC compared to 58% of CMP. Mice excreted 47% of the administered DMVC in 24 hr in the urine. An unusual urinary metabolite of DMVC, 2-amino-6-methyl-4-thia-5-heptene-1,7-dioic acid, was identified.(ABSTRACT TRUNCATED AT 250 WORDS)

Review of experimental carcinogenesis by compounds related to vinyl chloride.

The experimental carcinogenesis results in six compounds related to vinyl chloride are reported. Vinylidene chloride, given by inhalation, was carcinogenic in male CD-1 mice, male CD rats, Sprague-Dawley rats and male Swiss mice. Trichloroethylene, given by gavage and inhalation, was carcinogenic in the B6C3F1 mice. When given by gavage, perchloroethylene was carcinogenic in the B6C3F1 mice, and dichloroethane was carcinogenic in Osborne-Mendel rats and B6C3F1 mice. Dibromoethane, given by gavage and inhalation, was carcinogenic in B6C3F1 mice, F344 rats and Osborne-Mendel rats. Finally, epichlorohydrin was carcinogenic in male Sprague-Dawley rats and B6C3F1 mice.

Prenatal susceptibility to carcinogenesis by xenobiotic substances including vinyl chloride.

The carcinogenicity of vinyl chloride for experimental animals when administered transplacentally is reviewed in comparison with known transplacental carcinogens, including those that, like vinyl chloride, are dependent on enzyme-mediated metabolic conversion to a reactive intermediate in maternal or fetal tissues. Vinyl chloride is converted by mixed-function oxidases to the reactive metabolite chlorooxirane, the carcinogenicity of which is also reviewed. Vinyl chloride is unequivocally a transplacental carcinogen for the rat. No evidence exists, however, to support the hypothesis that exposure of male rats to vinyl chloride or any other carcinogen confers an increased risk of tumor development on their progeny. Many structural analogs of vinyl chloride, i.e., substituted ethylenes, are also carcinogenic for adult animals, and can with confidence likewise be predicted to be effective transplacental carcinogens.

Review of epidemiologic study results of vinyl chloride-related compounds.

Epidemiologic study results addressing the carcinogenicity of six compounds related to vinyl chloride (vinylidene chloride, trichloroethylene, perchloroethylene, carbon tetrachloride, ethylene dibromide and epichlorohydrin) are reviewed. The study results suggest an increased carcinogenic risk among workers exposed to epichlorohydrin and to dry cleaning and degreasing solvents. Although several studies report no significant excess of cancer mortality, an evaluation of the design of these investigations demonstrates that these negative cohort studies consisted of populations of insufficient sample size and latency to permit any meaningful conclusions regarding carcinogenic risk. Therefore, experimental studies must be relied upon to determine whether several of these substances pose a potential carcinogenic risk to humans. Available evidence indicates that all of these substances have demonstrated a carcinogenic response in experimental animals and most are mutagenic in experimental test systems.

Power considerations in studies of reproductive effects of vinyl chloride and some structural analogs.

We review the evidence examining the relation of reproductive function and exposure to vinyl chloride and selected structural analogs. Investigation of these compounds for possible reproductive effects has focused on paternal exposure, a much less well studied route than maternal exposure. Drawing on animal models, we discuss what is known about the possible reproductive consequences of exposure to the father as well as to the mother. In evaluating the studies of reproductive outcome in relation to vinyl chloride or analogs, we consider what biologic model may have been tested and whether there was statistical power to detect moderate increases in risk. Parameters influencing statistical power are reviewed, and recommended sample sizes are set out which would insure sufficient power, in future studies, to detect adverse effects.

Rat hepatic vinyl chloride metabolites induce gene conversion in the yeast strain D7RAD in vitro and in vivo.

We have tested the genetic activity of gaseous vinyl chloride in vitro and in vivo using the gene-conversion system (trp5-12/trp5-27 leads to TRP+) in the yeast strain D7RAD. To induce, in vitro, TRP+ convertants with 2.5% gaseous vinyl chloride, a rat-liver microsomal system for metabolic activation of the vinyl chloride and dividing yeast cells are required. Neither a deficiency in excision repair (rad3) nor in the error-prone repair pathway (rad6) increased the vinyl-chloride-induced conversion frequencies compared with the repair-competent D7RAD strain. When logarithmically growing cells of the D7RAD strain were injected intravenously into male Wistar rats which inhaled 1% vinyl chloride in air for 24 h, a significant enhancement of the TRP+ conversion frequencies was found compared with that in cells re-isolated from untreated rats. These results indicate that vinyl chloride metabolites from the metabolizing hepatocytes diffuse into yeast cells, which accumulate in the liver capillaries. This supports the hypothesis that the endothelial cells of the liver sinuses, which have hardly any metabolic activity, but give rise to vinyl-chloride-induced hemangiotheliomas (rare type of liver tumor), are transformed by diffusible metabolites of the procarcinogen vinyl chloride.

Chemical characterization of 465 known or suspected carcinogens and their correlation with mutagenic activity in the Salmonella typhimurium system.

Since chemicals exhibiting mutagenic activity pose a potential hazard to their users, there is increasing acceptance of mutagenicity testing as an integral part of a premarketing toxicological evaluation of chemicals. In vitro testing has gained much notoriety as quick and relatively inexpensive means to assess the mutagenic potential of chemicals. However, the innovative use of microsomes to simulate metabolism has not changed the fact that in vitro activation cannot duplicate faithfully the metabolism that occurs in vivo. This shortcoming will express itself by the production of false negatives and possibly false positives during mutagenicity screening. This assertion is also borne out by a reanalysis of the ability of known animal carcinogens to cause mutations in the generally recognized premier in vitro system, the Salmonella-S-9 system. Although previous studies have suggested that a high percentage (greater than 85%) of all carcinogens will be mutagenic in this system, with no indication that false negatives are associated with certain chemical types, these findings are of uncertain practical value due to the limited number of chemical types that were considered. An analysis of 465 compounds with known or suspected carcinogenic activity indicates that about 58% have been adequately tested in Salmonella, that the testing has concentrated on certain chemical types and has neglected others, and that some categories of carcinogens exhibit individual correlations that are unsatisfactorily low by any standard. Poorly detected categories of carcinogens include: azonaphthols; carbamyls and thiocarbamyls; phenyls; benzodioxoles; polychlorinated aromatics, cyclics, and aliphatics; steroids; antimetabolites; and symmetrical hydrazines. Nonstandard procedures are necessary to optimize the testing of chemicals that are bactericidal, that are volatile, or that cross-link DNA. False negatives appear to arise for two reasons: an inability to devise an in vitro activation system that can be reliably used in a standard way; and an inability to detect the entire spectrum of mutational events that can lead to the induction of cancer.