RESUMEN
Synthetic pyrethroids, chlorpyrifos, and neonicotinoids are representatives of non-persistent insecticides ubiquitously used against insects all over the world. Their widespread use causes prevalent exposure to these compounds, which may be hazardous to human health. The insecticides have short biological half-lives and are mostly excreted in urine within 24 h after entering the human body; thus, the urinary concentration of their metabolites is highly dependent on the time elapsed between exposure and sample collection. Considering the within-day fluctuations in urinary concentration, one randomly collected sample may cause misclassification of long-term exposure. We evaluated the variability of excretion of eight insecticide metabolites in 24-h urine samples collected from 14 volunteers once or twice per month over 12 consecutive months. High detection frequency above 70% for non-specific metabolites of pyrethroid, chlorpyrifos, and neonicotinoids confirmed widespread exposure to these insecticides in the studied population. A long-term variability of exposure was assessed based on intraclass correlation coefficient (ICC). We found relatively low variability of excretion for non-specific pyrethroid metabolites and 3,5,6-trichloro-2-pyridinol (ICC > 0.75), but poor repeatability for 6-chloronicotinic acid. Constantly higher ICCs were observed for daily excretion than for unadjusted concentrations. Seasonal differences were observed for 3,5,6-trichloro-2-pyridinol and 6-chloronicotinic acid, with the highest and the lowest median concentration, respectively, in the summer. Due to high ICC values and lack of seasonal variations, one 24-h urine sample was considered sufficient to characterize long-term excretion of non-specific pyrethroid metabolites in non-occupationally exposed population. In addition, we calculated the daily intake (DI) for cypermethrin, permethrin, deltamethrin, and chlorpyrifos. The estimated DI values were mostly below the acceptable daily intake, which indicates that the evaluated exposure is non-hazardous to the population.