Gas-chromatography mass-spectrometry determination of phthalic acid in human urine as a biomarker of folpet exposure
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Agricultural workers are exposed to folpet, but biomonitoring data are limited. Phthalimide (PI), phthalamic acid (PAA), and phthalic acid (PA) are the ring metabolites of this fungicide according to animal studies, but they have not yet been measured in human urine as metabolites of folpet, only PA as a metabolite of phthalates. The objective of this study was thus to develop a reliable gas chromatography–tandem mass spectrometry (GC–MS) method to quantify the sum of PI, PAA, and PA ring-metabolites of folpet in human urine. Briefly, the method consisted of adding p-methylhippuric acid as an internal standard, performing an acid hydrolysis at 100 °C to convert ring-metabolites into PA, purifying samples by ethyl acetate extraction, and derivatizing with N,O-bis(trimethylsilyl)trifluoro acetamide prior to GC–MS analysis. The method had a detection limit of 60.2 nmol/L (10 ng/mL); it was found to be accurate (mean recovery, 97%), precise (inter- and intra-day percentage relative standard deviations <13%), and with a good linearity (R 2 > 0.98). Validation was conducted using unexposed peoples urine spiked at concentrations ranging from 4.0 to 16.1 μmol/L, along with urine samples of volunteers dosed with folpet, and of exposed workers. The method proved to be (1) suitable and accurate to determine the kinetic profile of PA equivalents in the urine of volunteers orally and dermally administered folpet and (2) relevant for the biomonitoring of exposure in workers.
KeywordsPhthalic acid Phthalamic acid Folpet Human urine Biological monitoring
We thank Gregory Plateel for his assistance in method adjustment and Patricia Stephan, Christine Arnoux, and Christine Kohler for their technical assistance. The project was funded by the ANSES (Agence Nationale de Sécurité Sanitaire de l’alimentation, de l’environnement et du Travail). Aurélie Berthet also received a scholarship from the Institut de recherche Robert-Sauvé en santé et sécurité du travail du Québec.
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