Variability of urinary excretion of pyrethroid metabolites in seven persons over seven consecutive days--implications for observational studies.

Concentration of urinary metabolites is frequently used for biomonitoring of exposure to synthetic pyrethroids, the class of non-persistent insecticides. These chemicals are currently widely used in agriculture, households and public health all over the world. Most of them are easily metabolized in mammals and in the form of metabolites excreted in urine. The concentration in urine is thus susceptible to significant variations, even within a short period of time. In this study, temporal changes in urinary metabolites concentrations in seven subjects (four females and three males aged: 24-71) were monitored over seven consecutive days. All urine voids (281 in total) were collected and analyzed for cis- and trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-carboxylic acid (cis-Cl2CA and trans-Cl2CA), cis-3-(2,2-dibromo-vinyl)-2,2-dimethylcyclo-propanecarboxylic acid (Br2CA) and 3-phenoxybenzoic acid (3PBA) using a validated gas chromatography ion-trap mass spectrometry method. Only 3PBA was detectable in more than 60% of the collected samples enabling a reliable statistical analysis. Statistical analysis was performed to evaluate temporal variability in urinary excretion of 3PBA over the studied period. Both volume and creatinine (Cre) adjusted concentrations were evaluated with the latter one being the most reliable. Among all samples, first morning voids (FMV) were the least reproducible (interclass correlation coefficient - ICC, 0.551 and 0.350 for volume and creatinine adjusted concentrations, respectively). Spot and reconstructed 24-h samples were more reproducible in this study. ICC values for ng/mL concentrations were 0.599 and 0.681 (in spot and 24-h samples) and 0.846 and 0.796 for μg/g creatinine concentrations. Results of this study suggest fairly constant short-term exposure to pyrethroids metabolized to 3PBA among the urban population in Poland. Creatinine adjustment should be performed in epidemiological studies and spot or multiple spot samples should be preferentially collected for the highest reliability of the measurement.