Parathion synergists

The Australian patents also contain descriptions of analogs, which include nitro-phenyl thiophosphates possessing more than one nitro group. Many of the analogs are biologically active, and several exhibit high activities comparable with parathion. The o-nitrophenyl isomer, which is present to some extent in crude parathion, is substantially less active than the p-nitrophenyl isomer (parathion itself). These patents disclose a synergistic effect of the ortho isomer with parathion. 

Low synergistic ratios indicating antagonism by PBO (ratios from 0.15 to 0.33) were obtained with aldrin, parathion, malathion, aminocarb, and mexacarbate. PBO strongly synergized allethrin (SR 102). Assays where synergism was weak or absent... 

The oxidation, which is the bioactivation reaction, is inhibited by piperonyl butoxide, whereas the demethylation reaction catalyzed by glutathione transferase is not inhibited. Piperonyl butoxide is therefore an antagonist to methyl-parathion, but a synergist to most other pesticides, including carbamates and pyrethroids. Pyrethrins are very quickly detoxified by oxidation of one of the methyl groups, catalyzed by the CYP enzymes. 

The herbicide atrazine is not toxic to midge (Chironomus tentans) larvae but has a strong synergistic effect on several organophosphorus insecHcides such as chlorpyrifos and parathion-methyl, but not to malathion. The increased rate of oxidahon to the achve toxicants, the oxons, is suggested as one of the mechanisms, and the level of CYP enzymes is elevated. Figure... 

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