2-Chlorocinnamaldehyde and 2-bromocinnamaldehyde, compounds of practical interest, for example, as bacteriocides and fungicides or for utilization in light sensitive layers, were tested in the Ames preincubation test with various Salmonella typhimurium strains, and in the SOS chromotest with Escherichia coli PQ 37.2-Chlorocinnamaldehyde was clearly mutagenic in strain TA 100 (6081 revertants/mumol) and in strain TA 98 (3050 revertants/mumol) without S9 mix, and was clearly positive in the SOS chromotest (SOSIP = 0.181). 2-Bromocinnamaldehyde was a strong mutagen in strain TA 100 (105, 500 revertants/mumol), in strain TA98 (41567 revertants/mumol) and in strain TA 1538 (15825 revertants/mumol), and also unambiguously mutagenic in strain TA 1535 (2110 revertants/mumol) without S9 mix. The SOSIP in the SOS chromotest was 1.5. Addition of S9 mix led to a marked decrease in the mutagenic activity of 2-bromocinnamaldehyde in all strains tested. In the case of strain TA 1535, mutagenic activity was abolished or not significant in the presence of S9 mix. The possible primary mechanisms underlying these mutagenic effects are discussed. Frame-shift activity of these halocinnamaldehydes can be explained by their planar structure.

2-Chloroacrolein and 2-bromoacrolein are very potent direkt mutagens not requiring metabolic activation in Salmonella typhimurium strains TA 100 and TA 1535. Mutagenic activities decrease with increasing degree of methyl substitution at carbon atom C-3 of the acrolein moiety from 2-chloroacrolein via 2-chlorocrotonaldehyde to 2-chloro-3,3-dimethylacrolein. With 2-chloroacrylonitrile equivocal results are obtained in strain TA 100 without S9-mix and unequivocal with S9-mix. In the SOS-chromotest the 2-chloroenals are also very strong genotoxins and the structure-activity relationships found in the Ames test are clearly confirmed. 2-Chloroacrylonitrile is not positive in the SOS-chromotest. The mutagenic mechanisms are discussed, and indications are provided that genotoxicity/mutagenicity depends on formation of DNA adducts, e.g., 1,N-2-cyclic deoxyguanosine adducts.