On the reaction kinetics and mutagenic activity of methylating and β-halogenoethylating gasoline additives

Poly (ADP-ribose) polymerase (PARP) is not involved in base excision repair but PARP inhibition traps a single-strand intermediate

Base excision repair (BER) represents the most important repair pathway of endogenous DNA lesions. Initially, a base damage is recognized, excised and a DNA single-strand break (SSB) intermediate forms. The SSB is then ligated, a process that employs proteins also involved in SSB repair, e.g. XRCC1, Ligase III and possibly PARP1. Here, we confirm the role of XRCC1 and PARP in direct SSB repair. Interestingly, we uncover a synthetic lethality between XRCC1 deficiency and PARP inhibition. We also treated cells with alkylating agent dimethyl sulfate (DMS) and monitored the SSB intermediates formed during BER. DMS-induced SSBs were quickly repaired in wild-type cells; while a rapid accumulation of SSBs was observed in cells where post-incision repair was blocked by a PARP inhibitor or by XRCC1 deficiency (EM9 cells). Interestingly, DMS-induced SSBs did not accumulate in PARP1 siRNA depleted cells, demonstrating that PARP1 is not required for efficient completion of BER. Based on these results we suggest no immediate role for PARP1 in BER, but that PARP inhibitors trap PARP on the SSB intermediate formed during BER. Unexpectedly, addition of PARP inhibitor 2 h after DMS treatment still increased SSB levels indicating ongoing repair even at this late time point.

Alkylating properties of dichlorvos (DDVP)

Dichlorvos (DDVP) is a methylating agent. In DNA from mice given 1.9 x 10(-6) mol/kg of DDVP, a degree of alkylation of guanine-N-7 amounting to 8 x 10(-13) mol methyl per g DNA, was found. From this, a rate of clearance of 29 hr-1 was estimated. This value is in reasonable agreement with the value (55 hr-1), calculated from published data on the concentration over time of DDVP in the brain after injection of the compound in mice. Applying a risk estimation on humans exposed to DDVP, the genetic risk connected with the methylating activity of DDVP is low or very low. Comparing the mutagenic effectiveness of DDVP with that of methyl methanesulfonate, indicates that DDVP is more effective than expected from reaction kinetic data. The possible contribution of the dichloroacetaldehyde formed in vivo from DDVP has to be evaluated before a complete risk estimate can be made for DDVP.

Mutagenicity and DNA repair of glycidamide-induced adducts in mammalian cells

Glycidamide (GA)-induced mutagenesis in mammalian cells is not very well understood. Here, we investigated mutagenicity and DNA repair of GA-induced adducts utilizing Chinese hamster cell lines deficient in base excision repair (BER), nucleotide excision repair (NER) or homologous recombination (HR) in comparison to parent wild-type cells. We used the DRAG assay in order to map pathways involved in the repair of GA-induced DNA lesions. This assay utilizes the principle that a DNA repair deficient cell line is expected to be affected in growth and/or survival more than a repair proficient cell. A significant induction of mutations by GA was detected in the hprt locus of wild-type cells but not in BER deficient cells. Cells deficient in HR or BER were three or five times, respectively, more sensitive to GA in terms of growth inhibition than were wild-type cells. The results obtained on the rate of incisions in BER and NER suggest that lesions induced by GA are repaired by short patch BER rather than long patch BER or NER. Furthermore, a large proportion of the GA-induced lesions gave rise to strand breaks that are repaired by a mechanism not involving PARP. It is suggested that these strand breaks, which might be the results from alkylation of the backbone phosphate, are misrepaired by HR during replication thereby leading to a clastogenic rather than a mutagenic pathway. The type of lesion responsible for the mutagenic effect of GA cannot be concluded from the results presented in this study.

Studies of transalkylation of phosphotriesters in DNA: reaction conditions and requirements on nucleophiles for determination of DNA adducts

Reactive compounds form adducts at several sites in DNA. One of these sites, the phosphate groups, forms phosphotriesters (PTE) which are both chemically stable and little repaired. A measurement of PTE in DNA could therefore be advantageous for the determination of doses in vivo of mutagens/cancer initiators. In this paper, the possibilities of utilizing the weakly alkylating properties of PTE for the transfer of adducts to strong nucleophiles have been investigated. Model compounds, thymidine 3'-[thymidine 5'-(methyl phosphate)], TpMeT, and thymidine 3'-[thymidine 5'-(2-hydroxyethyl phosphate)], TpHOEtT, were incubated with thiosulfate, a relatively strong nucleophile and the formation of dealkylated model PTE, thymidine 3'-(thymidine 5'-phosphate), TpT, was followed by HPLC. Transalkylation to thiosulfate or aniline of methyl PTE in DNA alkylated by [3H]N-methyl-N-nitrosourea was demonstrated. The methyl groups transferred, forming methyl thiosulfate and N-methylaniline, respectively, were determined by HPLC. These experiments demonstrate that it is possible to transfer alkyls from DNA phosphate to nucleophiles. Kinetic aspects of the transalkylation and requirement on nucleophiles for a practically useful method for determination of DNA adducts are discussed. Constants of reaction rates are presented.

Mutagenic synergism detected between dimethyl sulfate and X-rays but not found between N-methyl-N-nitrosourea and X-rays in the stamen hairs of Tradescantia clone BNL 4430

Mutagenic interactions with X-rays of two monofunctional alkylating agents, dimethyl sulfate (DMS) and N-methyl-N-nitrosourea (MNU), were studied in the stamen hairs of Tradescantia clone BNL 4430, a blue/pink heterozygote. The young inflorescence-bearing shoots with roots cultivated in the nutrient solution circulating growth chamber were used as tester plants. Synergism between two different mutagens was judged to have occurred when the mutation frequency observed after applying the two mutagens concurrently was statistically significantly higher than the mutation frequency expected from the additive effects of the two mutagens. Clear synergistic effects in inducing somatic pink mutations were detected with all combinations of doses of DMS and X-rays examined, even in a relatively low X-ray dose range (down to 299 mGy), resembling those confirmed earlier between ethyl methanesulfonate (EMS) and X-rays, but somewhat differing from the synergisms observed earlier between methyl methanesulfonate (MMS) and X-rays. On the other hand, no mutagenic synergism was detected between MNU and X-rays, even in a relatively high X-ray dose range (up to 862 mGy). The presence or absence of mutagenic synergisms of these alkylating agents with X-rays could be related to the action mechanism of each alkylating agent.

Mass spectrometric analysis of haemoglobin adducts formed by methyl bromide in vitro

An analytical procedure is described for the identification of the adducts formed by interaction of methyl bromide and haemoglobin. The reaction products of in vitro incubation of haemoglobin with methyl bromide have been characterised by electrospray mass spectrometry and gas chromatography-mass spectrometry. A prominent reactivity of several potential nucleophilic sites of haemoglobin was observed. Analogous results were recorded on blood samples of workers exposed to methyl bromide. The results obtained represent the basis for the complete structural characterisation of the modified haemoglobin and demonstrate the usefulness of the proposed analytical approach for the evaluation of alkylation degree and the identification of modified amino acids in proteins.

Toxicology of methyl bromide

Methyl bromide is widely used as an insecticidal fumigant in food supplies, warehouses, barges, buildings, and furniture. Its popularity as a fumigant is largely attributable to its high toxicity to many pests, the variety of settings in which it can be applied, its ability to penetrate the fumigated substances, and its rapid dissipation following application. Because of its frequent use around humans and human-related activities and its high acute toxicity, methyl bromide-related fatal accidents have occurred. The primary route for human exposure to methyl bromide is inhalation. In California, the most frequent cause of death from methyl bromide exposure in recent years has been unauthorized entry into structures under fumigation. The most frequently reported lesions included pulmonary edema, congestion, and hemorrhage. In recent years, a great deal of effort has been given to the characterization of the toxicity of methyl bromide because of its commercial value and its direct and indirect economic importance. Methyl bromide is acutely very toxic. Subchronically and chronically, the principal target site for methyl bromide appears to be the central nervous system. However, there was no evidence for carcinogenic activity of methyl bromide following the normal environmental exposure routes of inhalation or oral intake through residue on foods. Methyl bromide is clearly genotoxic in vitro and in vivo, as evidenced by the positive results from various tests. The mechanism of toxicity for methyl bromide is currently uncertain, although its alkylating property as well as the possibility of forming a reactive intermediate through metabolic transformation remain attractive hypotheses.

Mutagenicity to Salmonella, Drosophila and the mouse bone marrow of the human antineoplastic agent fotemustine: prediction of carcinogenic potency

The antineoplastic agent fotemustine is shown to be a base-pair mutagen to Salmonella. Activity is more marked in the uvrB-proficient strain G46 than in the repair-deficient strain TA1535. This is consistent with its ability to cross-link DNA. Potent activity as a somatic and germ-cell mutagen to Drosophila was also observed. A potent clastogenic response was given by fotemustine in the mouse bone marrow following either oral gavage or intraperitoneal injection of a single dose of 5 mg/kg. In each of these respects it is shown to be indistinguishable from the structurally related antineoplastic agent and human carcinogen MeCCNU. It is concluded that fotemustine should be regarded as having clear potential to induce cancer in humans. Based on these data, including the preponderance of chromosome breakages over recessive lethal mutations in Drosophila, an estimated rodent carcinogenic potency (TD50) of between 15-150 mg/kg is suggested for fotemustine.

Characterization of the genotoxic action of three structurally related 1,2-dihaloalkanes in Drosophila melanogaster

The genetic activity profiles of three structurally related dihaloalkanes, 1,2-dibromoethane (DBE), 1,2-dichloroethane (DCE) and 1-bromo-2-chloroethane (BCE), were compared in germ cells and somatic tissue of Drosophila melanogaster. The two genotoxicity indices estimated after mutagen exposure of male germ cells were (i) the hypermutability index fexr-/fexr+, measured by the increased frequency of induced recessive lethals (RL) in a strain defective in DNA excision repair (exr-), as compared to the wild type (exr+); (ii) the relative clastogenicity index CL/RL, expressed by the ratio of chromosomal aberrations (CL; ring-X loss) to RL determined in exr+ strains. The fexr-/fexr+ index for DBE was 4-5 times higher than those for DCE and BCE, suggesting a difference in the types of premutagenic lesions produced by DBE in comparison to DCE and BCE. The relative clastogenicity indices for BCE (CL/RL = 0.29) and DCE (0.41) are similar to the value of 0.37 estimated for DBE in an earlier study, all indicating that the three compounds or their metabolites are incapable of forming DNA crosslinks. In somatic cells, after inhalation treatment of female larvae, the effectiveness for the induction of interchromosomal recombination decreased in the order BCE > or = DBE > DCE. It is concluded that in accordance with other studies also in Drosophila the glutathione-mediated pathway is the major cause of genotoxicity caused by DBE, DCE and BCE.

Mechanisms of carcinogenicity of methyl halides

Methyl chloride, bromide, and iodide are used as methylating agents. These compounds are mutagenic in short-term tests and do not require activation by exogenous S9 mix. In DNA-binding studies performed in rats and mice, 14C-labeled methyl chloride was given by inhalation, and methylation of DNA bases was examined. The compound did not lead to specific DNA adducts. In particular, methylation of DNA bases was not observed. In contrast, methyl bromide and methyl iodide, upon oral and inhalation administration to rats and mice, caused systemic DNA methylation. Specifically, 3-methyl-adenine, 7-methyl-guanine, and O6-methyl-guanine were formed. Long-term inhalation bioassays have been performed in rats and mice with methyl chloride and methyl bromide. Methyl chloride induced renal tumors, but only in male mice at the highest concentration tested (1000 ppm). Under these special conditions, a number of secondary effects occur subsequent to glutathione depletion in the target tissue, resulting in DNA damage (DNA-protein cross-links and probably DNA single-strand breaks). The particular coincidence of secondary high-dose effects precludes a risk extrapolation to man. Methyl bromide did not induce tumors in rats and mice when administered by inhalation. However, experimental data point to a possible local carcinogenic effect on the rat forestomach when the compound is given by gavage. A factor that accounts for the discrepancy between systemic DNA methylation and apparent noncarcinogenicity upon inhalation might be the preference of 7-N over O6 methylation of guanine. An extrapolation of the negative rodent inhalation bioassay of methyl bromide to man might be problematic because rodents metabolize methyl bromide very quickly whereas in humans there is a particular subpopulation that only poorly metabolizes the compound ("nonconjugators"). Such individuals can be characterized by incubation of erythrocytes with methyl chloride or methyl bromide and measurement of the substrate decline. Methyl iodide has been tested, with positive outcome, in early carcinogenicity bioassays not based on modern methodology. However, these results, along with the proven systemic methylating potency of methyl iodide, argue in favor of a carcinogenic effect of the compound.

Micronucleated reticulocyte induction by ethylating agents in mice

Six model ethylating agents were tested for clastogenic potency by means of a new technique of the micronucleus assay with mouse peripheral blood cells using acridine orange (AO)-coated slides, to evaluate the test. The alkylating agents were: N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG), N-ethyl-N-nitrosourea (ENU), diethylsulfate (DES), ethyl methanesulfonate (EMS), epichlorohydrin (ECH) and ethylene dibromide (EDB). The animals were given a single intraperitoneal injection of the following doses of the chemicals: ENNG and ENU, 25, 50 and 100 mg/kg; EMS and DES, 100, 200 and 400 mg/kg body weight. For EDB and ECH, the doses were 50, 100 and 200 mg/kg, given twice, 24 h apart. Before and after the injection, blood samples were taken from the tails at 24-h intervals up to 72 h and preparations were made on AO-coated slides. For each dose group, 4 animals were used and 1000 reticulocytes were examined per slide for the presence of micronuclei. At the optimum induction time of 48 h, ENU induced micronucleated reticulocytes (MNRETs) at all 3 doses. ENNG and EMS induced MNRETs significantly at 2 dose levels each and DES only at the highest dose. ECH and EDB failed to induce MNRETs. On the basis of the dose of chemical needed to double the spontaneous frequency, the order of clastogenic potency was ENU greater than ENNG greater than EMS greater than DES. The results obtained compared favorably with those from other in vivo methods. The present technique proves to be simple, flexible and relatively sensitive. Shifts in the optimum induction peak in individual animals and by some chemicals can be picked up easily which is important when testing weak mutagens and chemicals with an unknown mechanism of action.

Mutagenic activity of promutagens in plants: indirect evidence of their activation

This review summarizes data concerning mutagenic activity of promutagens in various plant in vivo assays. These data are compared with the present knowledge about the metabolism of xenobiotics and activation of promutagens in plants obtained by biochemical studies and by the separation of the activation process from the genetic endpoints assayed for the mutagenicity. The article documents a differential response of plant species in the endogenous transforming of various classes of promutagens into mutagens. Attention is devoted to the following types of promutagens: nitrosamines, polycyclic aromatic hydrocarbons and aromatic amines, aflatoxins, pyrrolizidine alkaloids, diallate, styrene, vinylchloride, ethanol, cycasin, nitrofurans, sodium azide, s-triazine herbicides, 1,2-dibromoethane and maleic hydrazide.

Inhalation of methyl bromide gas induces mitotic recombination in somatic cells of Drosophila melanogaster

The fumigant methyl bromide was evaluated for genotoxicity in the somatic wing-spot assay of Drosophila melanogaster. Third instar larvae trans-dihybrid for mwh and flr3 were exposed to varying concentrations (0-16 mg/l) of the gas for 1 h. Following this exposure via inhalation, the larvae were placed into vials containing Instant Medium. 7 days after the exposure, the adult flies in the vials were collected, and their wings were scored under 400X magnification for the presence of clones of cells possessing malformed wing-hairs. Such clones appeared as mwh-flr3 twin spots and single spots of either mwh or flr3 phenotype. Exposure to methyl bromide was found to result in the positive induction of both twin spots and large (greater than 2 cells) single spots. For each endpoint, a significant exponential association was obtained between concentration and frequency of spots per wing. Methyl bromide was found to be a negative inducer of small (1-2 cells) single spots at all concentrations except 16 mg/l where a positive effect was observed. Because twin spots arise exclusively from mitotic recombination, methyl bromide was identified as having recombinogenic activity in the somatic tissue of Drosophila larvae.

Mutagenicity of methyl bromide in a series of short-term tests

Methyl bromide is commonly used as a soil fumigant in greenhouses. In the framework of a toxicological evaluation, it was tested for possible genotoxic properties in two bacterial test systems (the fluctuation test using Klebsiella pneumoniae and the plate test using Salmonella typhimurium TA100 and TA98), two systems using mammalian cells in vitro (forward mutations at the TK and HPRT loci in L5178Y mouse lymphoma cells and unscheduled DNA synthesis in primary rat-liver cells) and in the sex-linked recessive lethal test using Drosophila melanogaster. Methyl bromide was active in all tests except the DNA-repair assay. The results indicate a relatively low mutagenic efficiency of the compound, as expected from its alkylating properties.

Induction of somatic segregation by halogenated aliphatic hydrocarbons in Aspergillus nidulans

8 halogenated aliphatic hydrocarbons were assayed for their ability to induce somatic segregation in the mould Aspergillus nidulans. Induction of haploidization, mitotic non-disjunction and mitotic crossing-over was studied in heterozygous colonies exposed to the tested chemicals through the detection and phenotypic analysis of segregated sectors. The results obtained show that 1,2-dibromoethane induced all kinds of segregated sectors; 1,2-dichloroethane, allyl chloride, 2-chloroethanol, 2,2-dichloroethanol and 2,2-dichloroacetaldehyde significantly increased the frequency of haploid sectors and diploid non-disjunctional sectors; chloroform and 1,2-dichloropropane were ineffective.

International Commission for Protection Against Environmental Mutagens and Carcinogens. Dosimetry of genotoxic agents and dose-response relationships of their effects

Dose-response relationships and determination of dose of mutagens and carcinogens are summarized and discussed on the basis of conceptual and kinetic aspects. Different dose definitions may be referred to steps in the chain of events from exposure (or emission) to observed effects. A system is applied to show the influence of various processes on the kinetics of the transfers between consecutive steps. The same system illustrates processes influenced by protraction and fractionation of dose, synergists, comutagens/cocarcinogens, heritable factors, etc. The response at a given dose is expected to depend on the product of consecutive transfer functions. An application of general rules of chemical kinetics shows that when a chemical is introduced at a sufficiently low level, all processes affecting the transfers and therefore the transfer functions themselves become first-order, provided the induction status of enzymes and the cell-division rate remain constant. Under the same conditions, dose-response relationships are expected to be linear, i.e. without "safe" thresholds. However, present knowledge of the kinetics of repair at low levels of DNA damage and of the kinetics of induction of repair functions is not enough complete to be decisive. These considerations and the fact that observed dose-response data in some cases indicate the existence of thresholds but in others appear able to reject the threshold hypothesis lead to the conclusion that, generally, dose-response curves are most probably linear down to dose zero. However, certain mutagens/carcinogens give rise to lesions repaired so effectively that quasi-thresholds appear in certain subpopulations or organs.

Estimation of genetic risks of alkylating agents. VI. Exposure of mice and bacteria to methyl bromide

Methyl bromide was studied in a forward mutation system of E. coli to evaluate the relationship between dose and mutagenic response. The compound had a high toxicity and a low mutagenic efficiency, as expected from the high s value. The mutagenic effectiveness was estimated to be 1 mutation per 10(8) surviving bacteria per mM . h, in reasonable agreement with expectation from reaction kinetic data. To study the possibilities of using hemoglobin alkylation for an estimation of DNA alkylation in vivo, mice were treated with 14C-labeled methyl bromide. The degree of alkylation of DNA, determined in liver and spleen, was considerably lower than expected (200 and 20 times, respectively) from the degree of alkylation of hemoglobin and from the relative reactivities of DNA and hemoglobin towards methyl bromide in vitro. when hemoglobin alkylation is used for quantitative risk estimations, a correction factor has to be applied by taking into account the difference between the dose in red blood cells and the dose in the compartments of DNA.

Alkylating properties and genetic activity of 4-vinylcyclohexene metabolites and structurally related epoxides

The mutagenicity of the epoxides 4-vinyl-1,2-epoxycyclohexane, 4-epoxyethyl-1,2-epoxycyclohexane, 4-epoxyethyl-1,2-dihydroxycyclohexane, 1,2-epoxycyclohexane and styrene oxide was assayed on the TA100 strain of S. typhimurium and V79 Chinese hamster cells. In the latter cell system, both point mutation (6-thioguanine resistance) and chromosomal damage (anaphase bridges and micronuclei) were scored. Genetic effects were related to the alkylating properties of the epoxides. For this purpose, alkylation of 4-(p-nitrobenzyl)pyridine (NBP) and sodium-p-nitrothiophenolate (NTP) was measured and values for the substrate constant (s) were calculated. 4-Epoxyethyl-1,2-epoxycyclohexane, 1,2-epoxycyclohexane and styrene oxide, characterized by the highest reactivity toward NBP and by an s value in the vicinity of 1, were mutagenic in all test systems. 4-Vinyl-1,2-epoxycyclohexane and 4-epoxyethyl-1,2-dihydroxycyclohexane, characterized by lower NBP reactivity and higher s value (1.30-1.38), did not induce reversion in S. typhimurium or 6-thioguanine-resistant mutants in V79 cells, but were as effective as the 3 other compounds in the induction of chromosomal damage.

Potential carcinogenic and mutagenic industrial chemicals. I. Alkylating agents

A variety of alkylating agents, acylating agents, peroxides, halogenated derivatives, and nitrogen derivatives have been reviewed, principally in terms of their synthesis, areas of utility, stability, distribution, reactivity, levels of exposure, population at risk, metabolism, carcinogenicity, and mutagenicity.

Determination of reaction rate constants for alkylation of 4-(p-nitrobenzyl) pyridine by different alkylating agents

The rate constants have been determined for the reaction between some different alkylating agents and 4-(p-nitrobenzyl) pyridine (NBP) in methanol. These constants have been compared with those for alkylation of aniline in water. All the constants were lower in methanol than in water but in different degrees. The rate constants of the different alkylating agents have been calculated at a nucleophilic strength n=2. The genetic risk defined as the degree of alkylation of a nucleophile (n=2) is equivalent to the rate constant kn=2 and the target dose. The dependence of the genetic risk on the rate constant (kn=2) is discussed.

Genetic effects of dimethyl sulfate, diethyl sulfate, and related compounds

DMS and DES are monofunctional alkylating agents that have been shown to induce mutations, chromosomal aberrations, and other genetic alterations in a diversity of organisms. They have also been shown to be carcinogenic in animals. As an alkylating agent, DMS is a typical SN2 agent, attacking predominantly nitrogen sites in nucleic acids. DES is capable of SN1 alkylations as well as SN2 and thereby causes some alkylation on oxygen sites including the O6-position of guanine which is thought to be significant in mutagenesis by direct mispairing. The mutagenicity of DMS is better explained in terms of indirect, repair-dependent processes. With respect to both alkylating activity and genetic effects, striking similarities are found between DMS and MMS and between DES and EMS. In most systems where they have been tested, both DMS and DES are mutagenic. Results of many of the mutagenesis studies involving these compounds and other alkylating sulfuric acid esters are summarized in Tables 6, 7, 8, 9 and 10 of this review. Most data are consistent with these agents acting primarily as base-pair substitution mutagens. In the case of DES, strong specificity for G.C to A.T transitions has been reported in some systems but has not been clearly supported in some others. Low levels of frameshift mutations of the deletion type are also likely. In addition to the induction of mutations, recombinogenic and clastogenic effects have been described.

Structure activity relation for some 1,4-benzodiazepinones: correlation between rate constants for reduction by sodium borohydride and antileptazol ED50

Significant correlation in 11 different 1,4-benzodiazepinones has been established between log k2 (the second order rate constant for the reduction of the "azepinones" by sodium borohydride) and their ED50 against leptazol-induced seizures in mice. The results suggest a possible involvement of the carobnyl group at the receptor site.

Mutagenic effects of petrol in Drosophila melanogaster I. Effects of benzene and 1,2-dichloroethane

Commercial petrol and two of its components, benzene and 1,2-dichloroethane, were tested for mutagenicity in Drosophila melanogaster. The chemicals were given to larvae through their food supply. A genetically unstable sexlinked test system caused by a transposable genetic element was used. Mutagenicity was measured by the frequency of somatic mutations for eye pigmentation. Commercial petrol and 1,2-dichloroethane showed mutagenic activity. With the system used, benzene did not show any mutagenic activity. The high frequency of mutations induced by 1,2-dichloroethane indicate the existence in Drosophila of a metabolic activating system.

The mutagenic effect of 1,2-dichloroethane on Salmonella typhimurium I. Activation through conjugation with glutathion in vitro

One of the main components in the waste products from vinyl chloride industries (EDC-tar), is ethylene dichloride (1,2-dichloroethane). This compound has been tested for mutagenicity on Salmonella typhimurium TA 1535. It is concluded that 1,2-dichloroethane gives a weak direct mutagenic effect, which is enhanced by addition of the postmitochondrial liver fraction (S-9). This activation is NADPH-independent and non microsomal. It is caused by a factor in the soluble fraction (115 000 g supernatant). This activation was further enhanced by the addition of glutathione but not by the addition of L-cysteine, N-acetyl-L-cysteine or 2-mercaptoethanol. No activation was observed when glutathione was added in the presence of a totally denaturated S-9 fraction or in the absence of this fraction. Activation of 1,2-dichloroethane was also found in the presence of glutathione and glutathione S-transferase A and C but not with glutathione S-tranferase B. A synthetic conjugate S-(2-chloroethyl)-L-cysteine gave a strong direct mutagenic effect at concentrations where no effects were seen with 1,2-dichloroethane. It is thus concluded that 1,2-dichloroethane is activated by conjugation to glutathione. Another main component in EDC-tar, 1,1,2-trichloroethane, was not mutagenic under any of our experimental conditions. For comparison 1,2-dibromoethane was also tested and gave a stronger direct mutagenic effect than 1,2-dichloroethane. Like the latter 1,2-dibromoethane was also activated by a NADPH-independent process.

Mutagenicity of waste products from vinyl chloride industries

The by-product from vinyl chloride production, EDC-tar, is a complex mixture of mainly short-chained chlorinated aliphatic hydrocarbons. This mixture has been tested for mutagenicity by means of Ames' Salmonella/mammalian microsome method. Since most of the components in the tar are poorly soluble in water, three agents were used as solvents or emulsifier: ethanol, DMSO, and Tween 80. The results with all these agents showed that EDC-tar contains direct as well as indirect mutagenic constitutents. It could be concluded that the mutagenic effect observed in the test could not be due to any significant extent to one of the main components, ethylene dichloride (1,2-dichloroethane). This substance showed a weak mutagenic effect, but only at higher concentrations than could be available in the highest concentration tested of the tar. Although the microsomal system enhanced the mutagenicity both of the EDC-tar and of 1,2-dichloroethane, this enhancement was dependent on NADPH in the case of EDC-tar but independent of NADPH with 1,2-dichloroethane. The Salmonella/mammalian microsome method seems to be a suitable tool for both mutagenicity screening of complex chemical mixtures and identification of mutagenic constituents in such mixtures.

On the reaction kinetics in water of 1,3-propane sultone and 1,4-butane sultone: a comparison of reaction rates and mutagenic activities of some alkylating agents

To determine correlations between the biological action pattern and chemical reactivity of alkylating agents, the rate constants for reactions of 1,3-propane sultone and 1,4-butane sultone with a series of nucleophiles at 37 degrees C have been determined. Previously published data on the mutagenicity of the two sultones and of some alkyl methanesulfonates and dialkyl sulfates towards Schizosaccharomyces pombe have been used in the evaluation of the dependence of mutagenic effectiveness on chemical reactivity. It is of interest to note that the mutagenic effectiveness of the two sultones, if expressed per alkylating event at a certain low nucleophilicity is the same as that of e.g. methyl methanesulfonate and ethyl methanesulfonate.

The mutagenicity of chloroethylene oxide, chloroacetaldehyde, 2-chloroethanol and chloroacetic acid, conceivable metabolites of vinyl chloride

Previous investigations have shown that the carcinogen vinyl chloride causes base-pair substitution in the bacterium Salmonella typhimurium. The ability of four conceivable metabolites-chloroethylene oxide, chloroacetaldehyde, 2-chloroethanol and chloroacetic acid-to cause base-pair substitution directly in Salmonella typhimurium TA1535 has been compared. The main comparison was performed at initial concentrations from 0.1 to 1.5 mM. In this region, however, a mutagenic effect was observed only with chloroethylene oxide and chloroacetaldehyde, the former being approximately 20 times more effective than the aldehyde when compared on a molar basis.2-Chloroethanol and chloroacetic acid were studied also at higher concentration (1 mM-1 M), and a weak mutagenic response was found with 1 M 2-chloroethanol solution. With chloroacetic acid no enhancement of the mutation frequency could be detected. Chloroethylene oxide was found to be approximately 450 times more effective as a mutagen than chloroacetaldehyde when the comparison is based on exposure doses, defined as the time-dependent concentrations of the compounds in the treatment solutions, integrated between the times of onset and termination of treatment. Similarly, chloroethylene oxide was 10,000-15,000 times more effective as a mutagen than ethylene oxide, used as a positive control.

Industrial mutagens and potential mutagens I. Halogenated aliphatic derivatives

The halogenated aliphatic hydrocarbons represent one of the most important categories of industrial chemicals from a consideration of volume, use categories, environmental and toxicological considerations and hence most importantly, potential population risk. The major halocarbons reviewed, primarily in terms of their occurrence, utility, stability, distribution, and levels of exposure as well as their metabolism, carcinogenicity and mutagenicity included: vinylchloride, vinylidene chloride, trichloroethylene, perchloroethylene, ethylene dichloride, ethylene dibromide, chloroprene, chloroform, carbon tetrachloride, fluorocarbons (trichlorofluoromethane and dichlorodifluoromethane), epichlorohydrin, halohydrins (2-chloro- and 2-bromoethanol) and haloethers (bis(chloromethyl); chloromethyl'-methyl; bis(2-chloroethyl)-and bis(2-chloroisopropyl)ether. In many instances, data were not available to assess world production, populations at risk and degrees of exposure. With the exception of vinylchloride, vinylidene chloride, epichlorohydrin and 2-halo ethanols, there is an acknowledged paucity of definitive mutagenicity data concerning the majority of halogenated hydrocarbons. Their ubiquitous distribution, and in a number of cases, their carcinogenicity both in man and animals, dictates the urgent need to more exhaustively investigate their potential mutagenicity.