Serum levels of unconjugated bisphenol A are below 0.2 ng/ml in Swedish nursing women when contamination is minimized

In this study serum levels of bisphenol A (BPA) were investigated in primiparous women from Uppsala County, Sweden, sampled 3 weeks after delivery 1996-2011, in both yearly pools of serum (n = 39, temporal trend study) and in 208 individual samples also present in the pools. Possible contamination risks of BPA from blood sampling equipment and sample tubes, as well as from handling of the samples were evaluated. The unconjugated form of BPA was analyzed using a UPLC-MS/MS method with a limit of quantification (LOQ) of 0.2 ng/ml. The results show that the levels of unconjugated BPA generally were = 0.2 ng/ml were found in 12% of the individual samples and in 21% of the trend samples. However, in reanalyses of individual serum samples from the same aliquot or from new aliquots, samples with BPA levels >= 0.2 ng/ml in the first analysis did not have quantifiable BPA levels. Moreover, 11% of BPA spiked calibration samples (over 200) had higher levels than could be explained by the random error of the method. Thus BPA contamination of the biobanked samples probably occurred randomly during sample handling, pooling and processing. Equipment used for sampling of children and repeated blood sampling were leaking BPA. The results show the difficulties in analyzing compounds where samples are easily contaminated from exogenous sources. It also points out that it is questionable to use biobanked samples unless absence of BPA contamination from the sampling and storage materials, and during handling of the samples, can be proven. (C) 2013 Elsevier Ltd. All rights reserved.