Teflubenzuron

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

Ames test: negative

HPRT: negative

Chromosomal aberration test: negative

UDS assay: negative

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Genetic toxicity in vivo

Description of key information

in vivo MNT: negative

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Additional information

Genotoxicity in vitro:

The test substance was tested in vitro in two independent Ames tests, an HPRT test, a chromosomal aberration test and an UDS assay.

 

In an Ames test similar to OECD guideline 471, the test substance was tested in the Salmonella strains TA 1537, TA 1538, TA 98, TA 100 and TA 1535 at doses up to 5000 µg/plate with and without metabolic activation. Two independent experiments were performed with 4 plates per experimental condition. No cytotoxicity was observed except for TA 100 at concentrations of 5000 µg/plate, however precipitation was observed in all bacterial strains starting at 1250 µg/plate. No increased reverse mutation rate was observed in any strain at any of the doses tested. However, several methodological weaknesses were identified: the purity of the test substance was not stated and the bacterial strains did not include a strain to detect oxidizing or cross-linking mutagens. Further, only a plate incorporation test was performed.

To evaluate the mutagenicity in the Ames test, another study report can be taken into consideration. In a protocol according to the Japan MAFF guidelines and under GLP, the test substance was tested in Salmonella strains TA 100, TA 1535, TA 98, TA 1537, TA 1538 and E.coli WP2uvrA at doses up to 5000 µg/plate. While only one experiment was conducted, it included two plates per dose. According to the report, no genotoxicity was observed, however no details on cytotoxicity or precipitation on the test substance were available.

Taking the information from both studies together, it can be concluded that the test substance was not mutagenic under the conditions of the Ames test as described.

 

In order to clarify mutagenicity in mammalian cells, an HPRT test was conducted according to OECD guidelines and under GLP. V79 cells were incubated with test substance at concentrations up to 50 µg/ml (which was the highest achievable concentration without precipitation) with and without metabolic activation. Two independent experiments were performed, no reproducibly increased mutation rate was observed. Therefore, the test substance was considered not mutagenic under the conditions of this assay.

 

In vitro clastogenicity was assessed with a chromosomal aberration test according to OECD and EPA guidelines and under GLP. V79 cells were incubated with up to 50 µg/ml test substance (highest achievable concentration without precipitation) with and without metabolic activation for 4 hours. Analysis time points were 7, 18 and 28 hours after start of treatment. Four cultures were used for each test condition, a repetition was considered not necessary due to the clearly negative results observed. No increases in aberrant cells were observed in treated cultures as compared to the concurrent controls at any time point analyzed. The positive and negative / solvent controls were considered valid. Therefore, the test substance was not clastogenic under the conditions of this assay.

 

Finally, a UDS assay was conducted similar to OECD guideline 482 and under GLP. Primary rat hepatocytes were isolated and incubated with the test substance up to 100 µg/ml (highest achievable concentration without precipitation) and 3H-labeled thymidine for 3 hours. Addition of a metabolic system was considered not necessary since freshly isolated primary hepatocytes have sufficient metabolic capacity. After incubation, the nuclei were isolated, lysed and the DNA extracted. The respective radioactivity was measured in each sample (6 per experimental condition). No increased radioactive signal was detected in treated samples as compared to the concurrent controls while a clearly elevated radioactive signal was provided by the positive control. Therefore, the substance was considered not genotoxic in this UDS assay.

 

 

Genotoxicity in vivo:

In an in vivo micronucleus test according to OECD guideline 474 and GLP, the test substance was administered by gavage at doses of 5000 mg/kg bw to groups of NMRI mice (6 per sex and dose). Sampling of the bone marrow and subsequent analysis was conducted in 5 animals per sex and dose at 24, 48 and 72 hours following test substance administration. The following microscopic evaluation reported the micronuclei frequency in 1000 PCE per animal as well as the PCE/NCE ratio.

Following administration of the test substance, no mortality was observed and the animals did not show clinical signs. In test substance-treated animals, no changes in PCE/NCE ratio and no increases in micronuclei were observed, while the positive control treated animals showed a clear and significant increase in micronuclei as well as changes in PCE/NCE ratio.

Proof of systemic exposure with the test substance was not investigated in this study, however bioavailability data on the test substance is available and indicates that while the oral bioavailability is limited, systemic exposure is achieved at the doses tested in this assay.

 

 

Justification for classification or non-classification

Based on the data available and taking into consideration the criteria laid down in regulation (EC) 1272/2008 (CLP), no classification for genotoxicity is warranted.