Fluometuron

Endpoint summary

Additional information

The test substance, fluometuron, was tested for mutagenic potential in the mouse lymphoma L5178Y cell mutation test (Clive & Spector 1975). In this in vitro system it is possible to detect and quantify forward mutation from a wild type cell, which is heterozygous at the thymidine kinase locus (TK +/-), to the homozygous thymidine kinase deficient form (TK -/-). The agent used to select for the mutant phenotype is the thymidine analogue trifluorothymidine (TFT). TK -/- mutants, unlike the TK +/- form, are resistant to the otherwise lethal effects of TFT. The experimental methods employed are based on those published by Clive et al (1979), Amacher, Paillet and Ray (1979), Amacher et al (1980), Amacher and Turner (1980), Cole, Arlett and Green (1976) and Cole et al (1983).

Since many substances do not exert their mutagenic effect until they have been metabolised by enzyme systems not available in cultured cells, the test substance and the cells are incubated in the absence and the presence of a supplemented liver fraction (S9 mix) prepared from animals previously treated Aroclor 1254.

The study “Key_Clare_2003_Fluometuron mammalian cell mutation assay” was designed to comply with the following guidelines:

OECD Guidelines for Testing of Chemicals No. 476: "Genetic Toxicology: In vitro mammalian cell gene mutation tests", 1997. US EPA (1998) Health Effects Test Guidelines. OPPTS 870.5300 In vitro mammalian cell gene mutation test. EPA 712-C-98-221.

Commission Directive 2000/32/EC Annex 4E - B17 Mutagenicity - In vitro mammalian cell gene mutation test. No. L136, 65.

Fluometuron, dissolved in dimethyl sulphoxide, did not demonstrate mutagenic potential in this in vitro cell mutation assay, under the experimental conditions described.

The study “Key_Ogorek, B._1987_Salmonella/Mammalian-microsome mutagenicity test” "was designed to assess the mutagenic potential of Fluometuron in a bacterial system. The study was conducted in compliance with the following guidelines: OECD Guidelines for the Testing of Chemicals. (1997) Genetic Toxicology: Bacterial Reverse Mutation Test, Guideline 471. EC Commission Directive 2000/32/EC Annex 4D-B.13/14. Mutagenicity – Reverse mutation test in bacteria. No. L 136/57. US EPA (1998) Health Effects Test Guidelines. OPPTS 870.5100 Bacterial reverse mutation test. EPA 712-C-98-247.

The in vitro technique described by Ames and his co-workers (Ames, McCann and Yamasaki 1975, Maron and Ames 1983) enables the mutagenic effect of a test substance to be determined by exposing specially selected strains of Salmonella typhimurium to the test substance. Normally S. typhimurium is capable of synthesising the essential amino acid, histidine, but the mutant strains used in this test are incapable of this function. When these strains are exposed to a mutagen, reverse mutation to the original histidine independent form takes place in a proportion of the population. These are referred to as revertants, and are readily detected by their ability to grow and form colonies on a histidine deficient medium (supplemented with biotin, since these strains are also incapable of biotin synthesis).

A technique based on similar principles has also been described by Green (1984). This system employs mutant strains of Escherichia coli that are incapable of synthesising the amino acid, tryptophan, which is required for growth.

The strains used carry additional mutations that render them more sensitive to mutagens. The S. typhimurium strains have a defective cell coat, which allows greater permeability of test substances into the cell. All the strains are deficient in normal DNA repair processes. In addition, three of them possess a plasmid (pKM101) which introduces an error-prone repair process, resulting in increased sensitivity to some mutagens.

Many substances do not exert a mutagenic effect until they have been metabolised by enzyme systems not available in the bacterial cell. Therefore, the bacteria and test substance are incubated in both the absence and presence of a supplemented liver fraction (S9 mix) prepared from rats previously treated with a substance (Aroclor 1254) known to induce a high level of enzyme activity.

Fluometuron, showed no evidence of mutagenic activity in the strains of Salmonella typhimimurium used in this bacterial system.

Conclusion

The in vitro tests gave negative results. Fluometuron did not demonstrate mutagenic potential in the in vitro tests.

Short description of key information:
Genetic toxicity: Mammalian cell mutation (in vitro): negative - no mutagenic potential (Mouse lymphoma L5178Y), (EU 2000/32/EC Annex 4E-B17 (2000) = OECD 476 (1997) = US EPA OPPTS 870.5300 (1998))
Genetic toxicity: Salmonella/Mammalian-microsome mutagenicity test (in vitro): negative - no mutagenic potential (Histidine dependent auxotrophic mutants strains TA1535, TA1537, TA98 and TA100 of Salmonella typhimurium), OECD 471 (1983)

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

According to the CLP Regulation criteria for classification and labelling of dangerous substances fluometuron (CAS 2164 -17 -2) is not classified as mutagenic.