Prior posts have noted that BPA (an estrongen mimic) is found not only in certain plastics (about which there is much nashing of teeth), but the main vector may very well be thermal cash register receipts. Well, get ready for its cousin, BPS, and the newest vector, paper money. Holy greenbacks, Batman. (Well, maybe. More below.) Two small investigations in the last 18 months have identified the presence of BPA on the money of the U.S. and 20 other nations. Now researchers report the presence of BPS (bispenol S) on not only many of these currencies, but also on 13 other types of paper products.
Now things get ironic (this is a surprise?). When experiments demonstrated that BPA (an ingredient in plastic foodware and food-contact materials) could function like the body's primary female sex hormone, manufacturers began hunting for less bioactive alternatives. After its search, the largest U.S. maker of thermal-receipt paper switched to BPS from the BPA it had relied upon for its thermal "ink." Structurally (think topology), the two bisphenols bear a strong similarity, which may explain why manufacturers have been able to functionally swap one for the other (at least in some applications). It now turns out that their biological activity is also similar, which given their topology should not be a surprise.
Depending on which of two assays it used, a research arm of the European Commission now finds that BPS is either comparable to BPA in its estrogenicity or about a tenth as strong. For perspective, the body's natural hormone is roughly 10,000-times as potent as BPA in activating estrogen-sensitive genes. The EU's new potency tests were conducted in isolated cells growing in a dish. So it's hard to translate the new findings into effects that might be expected if BPS were ingested or passed through the skin. Cellular effects of hormonal substances tend to rely on the docking of those compounds with the receptors on a cell's surface (thus the importance of topology, or the shape of the molecule -- see http://en.wikipedia.org/wiki/Topology_(chemistry)).
But, as toxicologists note, this is just the molecular initiating event. There then follows effects at the cellular, tissue, and organ level, which then yields what is called the "observed effect." Thus, it is this chain of causation that is important in assessing impact. For example, a report last December found that BPA (at concentrations close to human exposures) risks desynchronizing contractions in heart tissue. Unlike effects that usually commence when BPA is carried by an estrogen receptor from a cell's surface to its nucleus (where genes can be activated) the mechanism of heart rhythm disruption appeared to take place especially quickly and at the cell's surface. This new mechanism may explain why BPA, normally orders of magnitude weaker than estrogen, rivaled the natural hormone's potency in heart cells. Thus, while the estrogenic effects may be weaker than the natural hormone in some cells, at least in heart cells it may be equivalent. One thus has to be careful when talking about "equivalents" because it depends on the cell, tissue, and organ affected. As of the date of the publication of the report on BPS, studies had not been done on the impact of BPS on heart cells to see if it triggered effects akin to those of BPA. Topology might incline one to say but of course it will, but (of course) the question is more complex than that.
Anyway, just like thermal receipts turned out to be the major vector for BPA exposure (while everyone focused on plastics), it turns out that since BPS has replaced BPA in thermal paper, the thermal paper is now a major source of exposure to BPS. Like this is a surprise...not. The compound showed up in all 91 receipts printed with thermal inks that the researchers collected in the United States as well as all 20 that it sampled from Japan, Korea, and Vietnam. Concentrations ranged from near the limit of detection up to 22 parts per thousand (a very high level) and tracked the type of BPA levels previously seen in thermal papers.
In the new study, where BPS was high, BPA tainting was low, consistent with a recent swapping of one for the other. The chemists also identified BPS in 87% of the 52 banknotes it sampled, representing 21 countries. Of course, greenbacks too came up positive. In fact, the only nondetects were the currencies from Egypt, South Africa, and the United Arab Emirates. The suspicion of the researchers was that most BPS found on money was the result of banknotes rubbing against thermal receipts (perhaps in a wallet or purse) or through a transfer from the fingers of the powdery BPS-residues picked up while handling thermal paper. [Think you have heard of this effect before? Well you have, when it turned out that most Greenbacks had cocaine residues, which really messed with "evidence" that had been used in drug prosecutions. No, Alan Greenspan's dollars did not demonstrate that he was a coke dealer.]
BPS also showed up in business cards, napkins, toilet paper, food cartons, mailing envelopes, magazines, and brochures. The only sampled products free of the contaminant (although this was based on small sample sizes) were paper towels and computer-printer paper. Based on the miniscule concentrations seen in most non-thermal papers, the researchers believe that the likely source in these is a recycling of BPS-inked thermal receipts into other types of paper; when these researchers calculated likely human exposures, thermal receipts were very high compared to every other type of paper. After accounting for contamination levels and the likely exposure people have to various paper types, the researchers concluded that thermal papers accounted for at least 7,600-times more BPS exposure than the next most contaminated paper type.
Now, another irony. EPA convened last year a working group to look for replacements for BPA in thermal paper. The rumor-mill was that BPS was under consideration. The report is now overdue. Perhaps they have seen the data on BPS, and will have to start over. Telle est la vie.
The studies on the various issues addressed in this post can be found at: http://www.sciencedirect.com/science/article/pii/S0887233312000847; http://pubs.acs.org/doi/abs/10.1021%2Fes300876n; http://pubs.acs.org/doi/abs/10.1021/es200977t; http://www.epa.gov/dfe/pubs/projects/bpa/index.htm; http://endo.endojournals.org/content/early/2011/12/07/en.2011-1772.abstract; www.national-toxic-encephalopathy-foundation.org/bpamalemice.pdf; & http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0025455.