The genetic toxicology of Kathon biocide, a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one.

Kathon biocide, an aqueous solution containing a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one in an approximate ratio of 3:1, was tested for mutagenic activity in Salmonella typhimurium, L5178Y mouse lymphoma cells in culture and Drosophila melanogaster. Tests also were conducted for chromosome aberrations in vivo on mouse bone marrow cells, for DNA damage/repair in primary rat hepatocytes in culture, and for morphological transformation in C3H 10T1/2 cells in culture. Kathon biocide produced point mutations in the absence of a rat-liver metabolizing system in bacteria (strain TA 100) and mammalian cells in culture. In the presence of rat-liver metabolizing system a 10-fold higher concentration was required to induce point mutations in mammalian cells in culture. No mutagenic activity was observed with the metabolizing system and S. typhimurium. Negative results were obtained in the sex-linked recessive lethal assay in Drosophila, the in vivo cytogenetic assay in mice, the unscheduled DNA synthesis assay in cultured rat hepatocytes, and the in vitro cell transformation assay.