Last fall I wrote a post about bisphenol-A (BPA) in which I questioned the science behind the banning of the chemical in Canada and certain other countries.
Last month, in an epub ahead of print article in the Journal of Toxicological Science, a group out of the Pacific Northwest National Laboratory in Richland, WA, have released a study examining the effect of high dietary BPA exposure.
24-Hour Human Urine and Serum Profiles of Bisphenol A During High Dietary Exposure.
Teeguarden JG, Calafat AM, Ye X, Doerge DR, Churchwell MI, Gunawan R, Graham M.
By virtue of its binding to steroid hormone receptors, BPA (unconjugated monomer) is hypothesized to be estrogenic when present in sufficient quantities in the body, raising concerns that widespread exposure to BPA may impact human health. To better understand the internal exposure of adult humans to BPA and the relationship between the serum and urinary pharmacokinetics of BPA, a clinical exposure study was conducted. Blood and urine samples were collected ∼hourly over a 24-hour period from twenty adult volunteers who ingested 100% of one of three specified meals comprising standard grocery store food items for breakfast, lunch, and dinner. The volunteers’ average consumption of BPA, estimated from the urinary excretion of total BPA ((TOT)BPA=conjugated BPA + BPA), was 0.27 μg/kg body weight (range, 0.03-0.86), 21% greater than the 95(th) percentile of aggregate exposure in the adult U.S. population. A serum time course of (TOT)BPA was observable only in individuals with exposures 1.3-3.9 times higher than the 95(th) percentile of aggregate U.S. exposure. (TOT)BPA urine concentration T(max) was 2.75 hours (range, 0.75-5.75 hours) post meal, lagging the serum concentration T(max) by ∼1 hour. Serum (TOT)BPA area under the curve per unit BPA exposure was between 21.5 and 79.0 nM•hr•kg/μg (TOT)BPA. Serum (TOT)BPA concentrations ranged from ≤ limit of detection (LOD, 1.3 nM) to 5.7 nM and were, on average, 42 times lower than urine concentrations. During these high dietary exposures, (TOT)BPA concentrations in serum were below the LOD for 86% of the 320 samples collected and BPA concentrations were determined to be ≤ LOD.
The study examined the blood and urine concentrations of BPA following, meals that exceeded the 95th percentile of exposure in the adult population of the USA. In 86% of the serum samples, BPA concentrations were lower than the limit of detection i.e. undetectable, and were only found in those with exposure 1.3-3.9 times higher than the 95th percentile.
In an interview, Teegarden stated:
“In a nutshell, says Teeguarden, “we can now say for the adult human population exposed to even very high dietary levels, blood concentrations of the bioactive form of BPA throughout the day are below our ability to detect them, and orders of magnitude lower than those causing effects in rodents exposed to BPA.”
One of the principle opponents of the BPA banning movement, Richard Sharpe added:
What this also means, says Professor Richard Sharpe, Principal Investigator at the Independent Medical Research Center’s Center for Reproductive Health in Britain, and a member of the WHO (World Health Organisation)/FAO (Food and Agriculture Organisation) “expert committee for evaluation of the health risks and research priorities on bisphenol A,” is that Teeguarden’s findings show “the majority of effects observed in animal studies are probably not relevant to humans because they involved much higher BPA exposures.”
This study also attempted to avoid any potential contamination of the samples.
“I don’t know of any biomonitoring studies that make repeated measures of blood and urine BPA in humans under controlled conditions, as we did,” says Teeguarden. “Most, if not all, of the other studies take single blood or urine samples. Our findings contrast those studies that claim much higher levels of bioactive BPA in human blood, levels that are unexpected based on our clear understanding of exposure, absorption and elimination in humans and other primates. The simplest explanation for this major discrepancy, one that has been confirmed repeatedly by independent laboratory experiments, is that inadvertent contamination occurred during sample collection or processing.”
I am comfortable in saying that we can expect considerable criticism of this study, some claiming industry bias and some being legitimate criticism of the study design and analysis. One of the things that jumped out at me was the limitation of the analysis to 24 hours. I do not know the elimination rate of BPA, nor do I know the cumulative effect of longer term exposure to the chemical. Also under debate is the effect on humans of this exposure.
However, this study does reinforce the opinion of the WHO and many regulatory bodies around the world. The battle continues.