Impact of urine preservation methods and duration of storage on measured levels of environmental contaminants

Abstract

Collection of urine samples in human studies involves choices regarding shipping, sample preservation, and storage that may ultimately influence future analysis. As more studies collect and archive urine samples to evaluate environmental exposures in the future, we were interested in assessing the impact of urine preservative, storage temperature, and time since collection on nonpersistent contaminants in urine samples. In spiked urine samples stored in three types of urine vacutainers (no preservative, boric acid, and chlorhexidine), we measured five groups of contaminants to assess the levels of these analytes at five time points (0, 24, 48, and 72 h, and 1 week) and at two temperatures (room temperature and 41C). The target chemicals were bisphenol A (BPA), metabolites of organophosphate (OP), carbamate, and pyrethroid insecticides, chlorinated phenols, and phthalate monoesters, and were measured using five different mass spectrometry-based methods. Three samples were analyzed at each time point, with the exception of BPA. Repeated measures analysis of variance was used to evaluate effects of storage time, temperature, and preservative. Stability was summarized with percent change in mean concentration from time 0. In general, most analytes were stable under all conditions with changes in mean concentration over time, temperature, and preservative being generally less than 20%, with the exception of the OP metabolites in the presence of boric acid. The effect of storage temperature was less important than time since collection. The precision of the laboratory measurements was high allowing us to observe small differences, which may not be important when categorizing individuals into broader exposure groups.

Distributions and determinants of urinary biomarkers of organophosphate pesticide exposure in a prospective Spanish birth cohort study

“…Additionally, there was a long time lag between collection of samples and analysis. The low concentrations observed in this population could be related with this limitation; in fact, Hoppin et al [39] observed that urinary TCPY concentrations decreased with the time elapsed since collection at room temperature; however, our samples were frozen at −20 °C immediately after collection and this drop in OP metabolite concentrations is expected not be so important. Our FFQ covered average intakes during the 3 months before the sampling, when the half-life of these compounds is shorter.…”

Association between Pregnancy Loss and Urinary Phthalate Levels around the Time of Conception

“…Therefore, it is not surprising that we found associations between phthalate exposure and pregnancy loss only when we included the sample taken a few days before conception, because we did not expect delayed effects on implantation and embryonic development. Even when measured close to the event of interest, there could have been misclassification of the exposure due to the interday variation in the urinary concentration of these compounds (Fromme et al 2007) and imprecision of the analysis (Hoppin et al 2006). In our study, the coefficient of variation of concentrations obtained in quality control samples varied between 7% and 34% [see Supplemental Material, Table 1 (http://dx.doi.org/10.1289/ehp.1103552)].…”

Within-person variability in urinary phthalate metabolite concentrations: measurements from specimens after long-term frozen storage

“…Phthalate metabolites are considered chemically stable (Barr et al, 2005; Hoppin et al, 2005; Wittassek et al, 2007), but there are no data comparing measurements taken on the same urine specimens more than 20 years apart. Our results support their long-term stability.…”