Limitations of pesticide genotoxicity testing using the bacterial in vitro method

The results of genotoxicity assessment of 115 technical grade pesticide products (61 names) with the Ames test and mammalian erythrocyte micronucleus test in vivo are presented. In most cases, unidirectional results were found. However, some pesticides belonging to classes of neonicotinoids, derivatives of phenylurea, glycine and phenoxycarboxylic acids showed genotoxic effects only under in vivo conditions. All observed effects were statistically significant and dose-depended but were only slightly beyond the upper limit of the historical negative control. Pendimethalin (dinitroaniline pesticide) showed positive results only in Ames test. Furthermore, the limitations of Ames test related to the high cytotoxicity of pesticides against bacterial cells were shown (e.g. bipyridylium derivatives, chlorothalonils, dithiocarbamates, quinones, phenyl pyridinamines and sulphonylureas). But many pesticides possessing the highest cytotoxic activity against bacterial cells have shown low toxicity in vivo (MTD > 2000 mg/kg b.w.). On the other hand, all of the tested neonicotinoids, organophosphates, pyrethroids, phenoxycarboxylic acid derivatives were highly toxic to mice but non-cytotoxic against microbial cells. Triazole pesticides exerted toxicity to the target organ (bone marrow). Therefore, these findings suggest that genotoxicity assessment using at least two methods is needed for reliable evidence of the safe use of pesticides.