Prior posts have noted in detail the results of various studies of the impacts of BPA on various test media (e.g., animals). Prior posts have described the ongoing public debate over BPA and its listing and then delisting as a reproductive toxicant under California's Proposition 65. A recent post described testing done on newborns in a neonatal ICU, and their substantially large exposure to BPA, as demonstrated by the sampling of urine. Now a study challenges the accuracy of past human blood samples for BPA. The study indicates that the amount attributed to the average general population is in error by perhaps three orders of magnitude.
In experiments rodents received 7 doses of BPA daily from conception through birth and subsequently into early adulthood. Amounts ranged from "very low" (2.5 micrograms per kilogram of body weight, in the range of probable human exposure) to doses 100-times higher. The researchers reported not seeing adverse effects in the low range, and that they detected none of the active form of the chemical in animals receiving less than 80 micrograms per kilogram of body weight per day. Blood levels were below the limits of detection.
As yet unpublished studies have indicated that studies in rodents and monkeys demonstrate the rapid breakdown of ingested BPA into inactive substances. However, as recently reported, infants have been shown to be much less efficient are breaking down BPA than adults.
Researchers argue that because urine levels were at a particular point in the 28 thousand individuals sampled, the corresponding blood levels should be in the parts per trillion range. Such levels are not detectable given current analytical capabilities. Since they were not undetectable in various studies, the researchers state that the sampled population must have been exposed to unusually high amounts, or that the samples were contaminated during the sampling or analytical process.
Critics point out that more than 25 studies have measured blood BPA levels, and thus it is unlikely all were wrong. They state that just because the researchers state that urine/blood relationship must be of a particular sort does not mean that such an assertion is scientifically correct.
This debate will continue. Stay tuned.
Studies and conference reports relevant to this issue can be found at: http://aaas.confex.com/aaas/2013/webprogram/Paper8721.html; http://aaas.confex.com/aaas/2013/webprogram/Paper8728.html; http://aaas.confex.com/aaas/2013/webprogram/Paper8725.html; http://aaas.confex.com/aaas/2013/webprogram/Paper8720.html; http://toxsci.oxfordjournals.org/content/85/2/823.full; http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2944084/; http://endo.endojournals.org/content/early/2011/12/07/en.2011-1772.abstract; http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2920080/.