Avaliação genotóxica de herbicidas imidazolinonas em células somáticas de Drosophila melanogaster

Abstract

In the present study, five analogue herbicides, namely Imazapyr (IMZR), Imazapic (IMZC), Imazethapyr (IMZT), Imazamox (IMZX) and Imazaquin (IMZQ), were evaluated for genotoxicity (mutagenic and recombinagenic activity) in the wing somatic mutation and recombination test (SMART) of Drosophila melanogaster. They are classified as imidazolinone (IMI) pesticides and their mode of action is to inhibit acetohydroxyacid synthesis (AHAS) an enzyme involved with the biosynthesis of the amino acids leucine, isoleucine and valine. For this purpose, two crosses were used: the standard (ST) cross and the high-bioactivation (HB) cross. The latter is characterized by high CYP450-dependent activation capacity awarding increased sensitivity to promutagens and procarcinogens. Three-day-old larvae were exposed to chronic feeding (48 h) to four different concentrations of these herbicides (2.5; 5.0; 10.0 and 20.0 mM). For the evaluation of genotoxic effects, the frequencies of spots per individual in the treated series were compared to the concurrent negative control series (ultra pure water). In the ST-cross, imazamox showed positive result only for large single spots (20.0 mM IMZX) and weak positive results for total spots (10.0 and 20.0 mM IMZX), while Imazaquin showed positive results only for large single spots (5.0 and 20.0 mM IMZQ) and a weak positive result for total spots (20.0 mM IMZQ). In the HB-cross, only Imazamox (5.0 mM IMZX) showed a weak positive result for small single spots, what suggest the involvement of CH2OCH3 radical and quinolinic ring in the genotoxicity, respectively, of Imazamox and Imazaquin herbicides. Imazapyr, Imazapic and Imazethapyr gave negative results with both crosses of the wing spot test. The positive control urethane caused an increase in the number of all types of spots in both ST- and HB- crosses. In conclusion, the results of chronic treatments performed at high doses (toxicity was observed at higher doses) indicate that, under these experimental conditions, the few positive results observed suggest the involvement of CH2OCH3 radical and quinolinic ring in the genotoxicity, respectively, of Imazamox and Imazaquin herbicides and the involvement of CYP450 enzymes in IMI herbicide detoxification. Nevertheless, further research is needed to discern the genotoxic potential of IMI herbicides active ingredients and their formulations and the involvement of CH2OCH3 radical and quinolinic ring in the genotoxicity of Imazamox and Imazaquin herbicides.