Urinary p-nitrophenol as a biomarker of household exposure to methyl parathion

Methyl parathion (MP) is an organophosphate pesticide illegally applied to the interiors of many hundreds of homes throughout the United States by unlicensed pesticide applicators. Public health authorities developed a protocol for investigating contaminated homes and classifying their need for public health interventions. This protocol included environmental screening for MP contamination and 1-day biomonitoring (a.m. and p.m. spot urine samples) of household members for p-nitrophenol (PNP), a metabolite of MP. The variability of urinary PNP excretion under these exposure conditions was unknown. We collected a.m. and p.m. spot urine samples for 7 consecutive days from 75 individuals, who were members of 20 MP-contaminated households in the greater Chicago, Illinois, area, and analyzed them for PNP. We also assessed the ability of the 1-day sampling protocol to correctly classify exposed individuals and households according to their need for public health interventions, assuming that 1 week of sampling (14 urinary PNPs) represented their true exposure condition. The coefficient of variation of log urinary PNPs for individuals over the course of 7 days of a.m. and p.m. sampling averaged about 15%. Adjusting for urinary excretion of creatinine improved reproducibility of urinary PNPs among children but not among adults. The 1-day protocol correctly classified true risk category in 92% of individuals and 85% of households. The data contained in this study can be used to refine what is already a reasonable and effective approach to identifying MP-exposed households and determining the appropriate public health intervention.