New analytical method for sensitive quantification of urinary 3-methyl-4-nitrophenol to assess fenitrothion exposure in general population and occupational sprayers

The measurement of blood cholinesterase (ChE) activities is adopted worldwide for biological monitoring of exposure to organophosphorus insecticides (OPs). Recent development of analytical chemistry has made sensitive quantification possible of non-specific OP metabolites, dialkylphosphates, in urine as a biomarker of low-level OP exposure. In this study, we established a method for quantification of urinary 3-methyl-4-nitrophenol (MNP), a specific metabolite of fenitrothion (FNT), and a parathion metabolite p-nitrophenol (PNP), using gas chromatography–mass spectrometry. The limits of detection of MNP and PNP were 0.3 and 0.5 μg/L, respectively. The method enabled the quantification of both free and conjugated metabolites. This method was actually applied to monitor human urine in summer and winter in FNT sprayers (N = 29 and 9, respectively) and control workers (N = 17 and 29, respectively). Geometric mean total MNP concentrations (μg/g creatinine) in the FNT sprayers (28.8 in summer and 8.6 in winter) were significantly higher than those of the controls (3.1 in summer and 2.3 in winter) in both seasons. Among the sprayers, total MNP concentrations in summer were significantly higher than in winter. In contrast, no significant difference in total PNP concentrations was observed between FNT sprayers (geometric mean 3.4 in summer and 3.0 in winter) and controls (3.6 in summer and 2.1 in winter). No seasonal difference was observed in each group. In conclusion, the present new method is sensitive enough for biological monitoring of FNT and parathion metabolites even in a non-spraying population.

► Urinary metabolites are exposure markers of organophosphorus insecticides.
► Fenitrothion is frequently used for malaria control and residential protection.
► 3-Methyl-4-nitrophenol is a specific urinary metabolite of fenitrothion.
► We established a sensitive method to measure 3-methyl-4-nitrophenol by GC–MS.
► Assessment of low-level fenitrothion exposure in general populations became possible.