Differential information from blood vs urine levels in studies of endocrine disruptors

Abstract

Background: The plastic monomer bisphenol A (BPA) is a good example of a short lived and rapidly metabolized chemical with endocrine disrupting activities. Numerous studies show associations between exposures and health outcomes based on linking urinary levels of BPA to the adverse health outcome. However, these studies provides no information regarding the proportion of chemical that is bioavailable in blood after exposure or the duration during which the chemical is bioavailable prior to being conjugated in the liver and excreted in urine by the kidneys. Aims: 1) To discuss the advantages and disadvantages of measuring exposures in epidemiology studies via urine measurements verses blood levels, and 2) to discuss whether estimates of human exposure to biologically active levels of BPA can be measured in blood, and 3) to discuss if measurement of total BPA in spot urine samples can be used to accurately determine actual exposure. Methods: I will review recent findings regarding the exquisite sensitivity of human and animal tissues and systems to BPA toxicity. I will also present the results of the NIEHS sponsored round robin to define methods and approaches to accurately measure BPA in human serum. Conclusions: There is a need in epidemiology studies for both measurement of urine levels of environmental chemicals and measurements in blood as these measurements provide important non-overlapping information. In the case of BPA, measurement of free BPA in blood is necessary to answer the question of whether there are levels of bioactive BPA in humans that could lead to health problem: data that cannot be ascertained from urine measurements. In addition urine measurements and back-calculations from spot urine levels may not provide accurate assessment of actual exposures.