Factors affecting the accuracy of bisphenol a and bisphenol A-monoglucuronide estimates in mammalian tissues and urine samples

Bisphenol A (BPA) (CAS Number 80-05-7; EINECS Number 201-245-8) is used in the production of plastics having food contact applications. Some biomonitoring studies have reported free BPA in blood or urine of humans. Since complete first-pass metabolism of orally administered BPA to BPA-monoglucuronide (BPA-G) occurs in humans, the presence of free BPA in human specimens raises questions as to the origin and/or possible sources of the free BPA. We hypothesized that BPA-G instability during specimen collection and analysis contributes to the presence of free BPA in the biological samples. Investigation of the in vitro hydrolysis of BPA-G in blood plasma, tissue homogenates, and diluted urine from laboratory rats and in aqueous/organic solutions commonly used for extraction in BPA analyses lent support to the hypothesis of BPA-G instability as a possible source of free BPA determinations in the biological specimens. Hydrolysis of BPA-G occurred at neutral pH and room temperature in diluted urine and in rat placental or fetal tissue homogenates at room temperature. Hydrolysis of BPA-G in aqueous/organic solutions began within minutes at pH 2 and 80 degrees C. BPA-G was degraded to an unidentified compound in a urine/water mixture or when stored in a 25/75 mixture of urine/acetonitrile at pH 9 at either 22 or 80 degrees C. Based upon these experiments, it was concluded that methods demonstrating BPA-G stability or accounting for its instability during analysis are warranted in studies designed to measure free BPA in biological specimens.