ABSTRACT
In the majority of insecticide formulations, such as organophosphorus diazinon and trichlorfon and carbamate carbofuran, water is used as a vehicle. Chemical stability of these pesticides has been evaluated as a function of their aqueous solution pH, using Drosophila melanogaster bioassay and acetylcholinesterase inhibition test. Degradation of the insecticides has been evaluated in solutions at pH 6.0; 7.8 and 10.5, maintained at 25.0º C. The percent mortality of drosophilas exposed to insecticides demonstrated that structural transformations of insecticide molecules were higher at pH 10.5 and lower at 6.0. Data on acetylcholinesterase inhibition, in different time intervals, indicate that whereas carbofuran is the direct agent responsible for the variation of the enzymatic inhibition levels, in the case of trichlorfon it is due to its more toxic metabolite dichlorvos; no information on structural modifications in diazinon was attained through this toxicity parameter. Observed results lead to conclude that the knowledge about the pesticides behavior as a function of pH of their aqueous solutions or suspensions is important for reducing insecticide activity loss and also for controlling eventual intoxication problems due to toxicity enhancement.
KEY WORDS:
Diazinon; trichlorfon; carbofuran; acetylcholinesterase; median lethal concentration; structure-activity relationships.
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