Comparative evaluation on the biological monitoring of exposure to parathion and its methyl analog

The effects of both parathion and methyl parathion on the inhibition of plasma cholinesterase were elaborated in a rat model employing a modified isocratic reverse-phase HPLC method coupled with UV detection for the determination of the urinary metabolite p-nitrophenol (U-4NP), A linearity of r2 > 0.995 was found for a standard curve ranging from 0.06 to 0.96 mu g/mL with a % relative error of less than or equal to +/- 10% and a recovery of 89 +/- 2%. The % CV at all levels was less than or equal to 11%. A linear correlation was observed between the oral administration of parathion and methyl parathion for both the percent inhibition of cholinesterase as well as the urinary elimination of 4NP, It is tentatively recommended that an U-4NP of 2.0 mg/g creatinine be established as a biological exposure index (BEI) for methyl parathion.