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Administrative data

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

There are several bacterial mutation assay data available for MBTS. Most of the bacterial mutation assays was negative (Monsanto Co. 1976, Goodyear 1980, Hinderer 1983, Crebelli 1984); whereas mutagenicity was indicated in one Ames assay with and without metabolic activation (NTP 1987). There are only limited mammalian cell data available for MBTS. No mutagenicity was noted in a limited mouse lymphoma assay (Monsanto Co. 1979); whereas a slight increase in mutation frequency was observed in another limited mouse lymphoma assay. Because of methodological deficiencies of both assays, the reliability of these findings is questionable. In a limited in vitro chromosome aberration assay, no clastogenic effects of MBTS were noted (Hinderer 1983). In a read across approach with MBT study data no mutagenicity was noted in mammalian cell test-systems. Some evidence of clastogenic effects in vitro were noted, however the relevance of these findings is questionable. No genotoxicity in vivo was indicated for MBT. Overall, taking into account the limited study data of MBTS and the supporting data of MBT no mutagenic activity is anticipated.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (negative)

Genetic toxicity in vivo

Description of key information

There are several bacterial mutation assay data available for MBTS. Most of the bacterial mutation assays was negative (Monsanto Co. 1976, Goodyear 1980, Hinderer 1983, Crebelli 1984); whereas mutagenicity was indicated in one Ames assay with and without metabolic activation (NTP 1987). There are only limited mammalian cell data available for MBTS. No mutagenicity was noted in a limited mouse lymphoma assay (Monsanto Co. 1979); whereas a slight increase in mutation frequency was observed in another limited mouse lymphoma assay. Because of methodological deficiencies of both assays, the reliability of these findings is questionable. In a limited in vitro chromosome aberration assay, no clastogenic effects of MBTS were noted (Hinderer 1983). In a read across approach with MBT study data no mutagenicity was noted in mammalian cell test-systems. Some evidence of clastogenic effects in vitro were noted, however the relevance of these findings is questionable. No genotoxicity in vivo was indicated for MBT. Overall, taking into account the limited study data of MBTS and the supporting data of MBT no mutagenic activity is anticipated.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (negative)

Additional information

In vitro data

The mutagenic potential of MBTS was evaluated in a bacterial mutagenicity test (Monsanto Co. 1976). Although the study is reliable the test design of the study does not comply with the current guideline with regard to the kind of tester strains used. Here, the tester strains Salmonella typhimurium TA 98, TA 100, TA 1535, TA 1537 and TA 1538 were used. Treatment by the plate incorporation method was done in presence or absence of metabolic activation (S9-mix). A concentration range of 0.1 µg/plate to 500 µg/plate was evaluated. In a pre-experiment toxicity at higher concentrations was indicated (no additional data given). No toxicity was indicated in the main experiment. No mutagenic response was noted in any of the tester strains used in presence or absence of metabolic activation (S9-mix). The authors concluded that the test substance did not induce a mutagenic response in any of the tester strains evaluated under the experimental conditions used.

This negative finding is confirmed by another bacterial mutation assay using Salmonella typhimurium tester strains TA 98, TA 100, TA 1535 and TA 1537 in presence and absence of metabolic activation (Goodyear 1980). In addition data from literature also indicated a non-mutagenic potential of MBTS in bacterial mutation assays (Hinderer 1983, Crebelli 1984). However, a positive response was noted with and without metabolic activation in another Ames assay (NTP 1987).

The mutagenic potential of MBTS was evaluated in two mouse lymphoma assays. Both assays are limited because the spontaneous mutation frequencies are below current recommendations and thus the validity of the test systems is questionable. In one of the assays no mutagenicity of MBTS was observed (Monsanto Co. 1979), whereas a weak mutagenic response were noted in the second assay with metabolic activation (Hinderer 1983). However, the validity of the results is questionable, because of the method deficiencies.

The clastogenic potential of MBTS was evaluated in an in vitro chromosome aberration assay with Chinese Hamster Ovary cells (CHO) (Hinderer 1983). However, the test is limited compared to current study designs. Cells were treated for 2 hours with the test substance MBTS in a concentration range of 0.313 µg/ml to 10 µg/ml. The cells were prepared and stained approximately 17 hours after test substance removal. 50 metaphases were analysed for each concentration. No increase in aberrant cells was noted in any of the treated cell cultures compared to the corresponding negative and solvent control.

There are only limited mammalian cell mutation assay data and only limited mammalian cell cytogenetic data available for MBTS. A read-across across is performed with data from MBT (benzothiazole-2-thiol) (see discussion endpoint summary toxicokinetics).

Read across MBT

The mutagenic potential of MBT was evaluated in a HGPRT assay with CHO cells (CMA 1984). A preliminary cytotoxicity assay was done with test substance concentrations of 0.03, 0.1, 0.33, 1.0, 3.3, 10.0, 33.33, 100.0, 333.3 and 1000 µg/ml with and without metabolic activation (S9-mix). Without metabolic activation cytotoxicity was indicated at 100, 333.3 and 1000 µg/ml; at 33.33µg/ml a survival of 58% was indicated. With metabolic activation cytotoxicity was noted at 1000 µg/ml; relative survival at 333.33µg/ml was 18 %. Based on the findings from the cytotoxicity assay a concentration range of 10 to 300µg/ml (with metabolic activation) and 1 to 50µg/ml (without metabolic activation) was evaluated in the mutation assay. No increase in the mutation frequency was observed. The authors concluded that the test substance MBT was negative under the experimental conditions used.

The negative finding in the HGPRT assay was confirmed in another mammalian cell mutation assay. No significant increase in mutation frequency was noted in a mouse lymphoma assay (WTR 1997).

In a chromosome aberration assay with CHL cells an induction of polyploidy cells and endoreduplications were noted after treatment with 0.2 µg/ml MBT. The frequency of polyploidy cells and endoreduplications was 3.6% and 6.2 % without metabolic activation and 2 % and 0.4 % with metabolic activation, respectively. No endoreduplications were noted in the solvent control (Matsuoka 2005). Furthermore, in a limited chromosome aberration assay with CHO cells an increase in aberrant cells were noted (NTP 1988). However, the findings are questionable because of significant chemically induced cell cycle delay, which presumably indicated high toxicity. In addition, in a limited sister chromatid exchange (SCE) assay a relative increase in SCE’s was noted in presence of metabolic activation (NTP 1988). However, the relevance of this finding is questionable because of presumed high toxicity indicated by a significant chemically induced cell cycle delay and the lacking of a dose-response relationship.

In vivo data

There are no data available for in vivo genotoxicity of MBTS. In vivo genotoxicity data from MBT was used in a read across approach (see discussion endpoint summary toxicokinetics).

Read across with MBT

The genotoxic potential of MBT was evaluated in an in vivo micronucleus assay with CD-1 mice (4 males and 4 females per group) (CMA 1984). Single dose group animals received 300 mg/kg of MBT and multiple dose group animals received MBT in a split dose regimen with two doses of 300 mg/kg each, separated by 24 hours. The positive control article triethylenemelamine was administered intraperitoneally to a separate group of mice (4 males and 4 females) at a dose of 0.5 mg/kg. Thirty hours after treatment the positive control animals were sacrificed. The negative control animals were given two doses of corn oil separated by 24 hours and sacrificed 48 hours after the first dose. Single Dose Group I and Single Dose Group II were sacrificed at 30 and 48 hours, respectively after a single injection. Multiple Dose Group I and Multiple Dose Group II were given two doses of the test article separated by 24 hours and sacrificed at 48 and 72 hours, respectively after the initial injection. Systemic availability of the test substance was indicated by occurrence of clinical signs after application. The following signs were observed at the first dose: prostration, hypoactivity, hypernea, ptosis, tremors upon stimulation and an occasional animal exhibited a loss of righting. Observations at 4 and 24 hours following the first dose included ptosis with no other visible signs in all treated animals. No mortality occurred in the study. The results for test article MBT were negative in the micronucleus test at a dose level of 300 mg/kg in the single dose groups and with a second dose of 300 mg/kg in the multiple dose group administered in a split dose regimen. The test material did not produce a statistically significant increase in the number of micronuclei per 1000 polychromatic erythrocytes in the treated versus the control group. In addition to these criteria, all animals administered MBT were within the normal historical range of spontaneous micronuclei incidence.

The test substance MBT was evaluated in a dominant lethal test in Sprague-Dawley rats (CMA 1989). Male rats were treated with 0, 2500, 8750, or 15000 ppm MBT in the diet. Following a 13 week treatment each male was housed with two virgin female rats per week for two weeks. All females with evidence of mating from each group were sacrificed on gestation day 13 for determination of dominant lethal effects. MBT produced dose-related toxicity in male rats treated with 8750 and 15000 ppm in the diet. Toxicity was limited to reduced body weights and food consumption. When the rats were serially mated over two weeks after 13 weeks of treatment, no dominant lethal effect was observed.


Short description of key information:
There are several bacterial mutation assay data available for MBTS. Most of the bacterial mutation assays was negative (Monsanto Co. 1976, Goodyear 1980, Hinderer 1983, Crebelli 1984); whereas mutagenicity was indicated in one Ames assay with and without metabolic activation (NTP 1987). There are only limited mammalian cell data available for MBTS. No mutagenicity was noted in a limited mouse lymphoma assay (Monsanto Co. 1979); whereas a slight increase in mutation frequency was observed in another limited mouse lymphoma assay. Because of methodological deficiencies of both assays, the reliability of these findings is questionable. In a limited in vitro chromosome aberration assay, no clastogenic effects of MBTS were noted (Hinderer 1983). In a read across approach with MBT study data no mutagenicity was noted in mammalian cell test-systems. Some evidence of clastogenic effects in vitro were noted, however the relevance of these findings is questionable. No genotoxicity in vivo was indicated for MBT. Overall, taking into account the limited study data of MBTS and the supporting data of MBT no mutagenic activity is anticipated.

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

No classification is required according to the classification criteria of regulation no. 1272/2008 (GHS).