Population variability of phthalate metabolites and bisphenol A concentrations in spot urine samples versus 24- or 48-h collections.

Human exposure to phthalates and bisphenol A (BPA) can be assessed through urinary biomonitoring, but methods to infer daily intakes assume that spot sample concentrations are comparable to daily average concentrations. We evaluate this assumption using human biomonitoring data from Germany and the United States (US). The German data comprised three regional studies with spot samples and one with full-day samples analyzed for phthalate metabolites. The US data included: a study on DEHP metabolites and BPA involving eight persons supplying all urine voids (from which 24-h samples were constructed) for seven consecutive days; NHANES spot sample data on DEHP metabolites and BPA; and a regional study of children with 48-h samples analyzed for BPA. In the German data, measures of central tendency differed, but spot and 24-h samples showed generally comparable variance including 95th percentiles and maxima equidistant from central tendency measures. In contrast, the US adult data from the eight-person study showed similar central tendencies for phthalate metabolites and BPA, but generally greater variability for the spot samples, including higher 95th percentiles and maxima. When comparing children's BPA concentrations in NHANES spot and 48-h samples, distributions showed similar central tendency and variability. Overall, spot urinary concentrations of DEHP metabolites and BPA have variability roughly comparable with corresponding 24-h average concentrations obtained from a comparable population, suggesting that spot samples can be used to characterize population distributions of intakes. However, the analysis also suggests that caution should be exercised when interpreting the high end of spot sample data sets.