Mutagenic activity of diallate and triallate determined by a battery of in vitro mammalian and microbial tests

Diallate and Triallate are carbamate herbicides used mainly for the pre-emergence control of wild oats in various crops. The genetic activity of these compounds was studied using a battery of microbial and mammalian in vitro tests. In the Salmonella/mammalian-microsome assay, Diallate and Triallate show dose-related increases without metabolic activation in strains TA1535, TA100 and TA98, indicating that these compounds cause both frameshift and base-substitution mutations. Mutagenicity of both herbicides was enhanced greatly by incubation with Aroclor 1254 induced rat-liver S9. Genetic activity in mammalian cells was determined using a number of in vitro tests with Chinese hamster ovary (CHO) cells combined with metabolic activation as described above. Both Diallate and Triallate caused dose-related decreases in colony-forming ability, with concomitant dose-related increases in the frequencies of cells with chromosome damage and in the number of sister-chromatid exchanges. However, only Diallate caused a reduction in DNA molecular weight as determined by alkaline sucrose gradient (ASG) sedimentation. DNA damage was negligible even at concentrations of Triallate that reduced colony-forming ability to zero. This suggests that the lesions in DNA detected by the ASG technique are not necessarily related to those that produce chromosomal damage. These data, taken together, strongly implicate both Diallate and Triallate as capable of causing mutations in mammals. However the risk to man in terms of inherited disease or cancer remains to be established by appropriate in vivo methodology.