By Janet Raloff, Science News
Bisphenol A readily passes through skin, French scientists report. Best known as an estrogen-mimicking constituent of some plastics and resins, BPA is also found in a large share of cash register receipt paper in the United States and Europe, a trio of studies recently indicated. One of the three also showed that the powdery coating easily rubs off onto the hands.
"The new study is now unequivocal in showing that yes, BPA can go through human skin," says Frederick vom Saal of the University of Missouri-Columbia.
It may also explain why a survey due to appear in an upcoming issue of Environmental Health Perspectives found that among nearly 400 pregnant Cincinnati-area women, the highest BPA concentrations were in cashiers. However, Joe M. Braun and his coauthors note, "these results should be interpreted cautiously since estimates from cashiers were based on 17 women."
The French work, posted online in advance of print in Chemosphere, was conducted at INRA, the National Institute for Agricultural Research in France. Its Toulouse-based team has been investigating excised but still living skin tissue as an alternative to live animals for safety tests of cosmetics and other chemicals.
Toxicologist Daniel Zalko and his coworkers collected pig ears from slaughterhouses within five minutes of an animal being killed. In less than two hours, the tissues were in the lab where researchers removed the skin, cut it into tiny disks and cultured each in a dish.
The scientists applied BPA at various concentrations to the dry outer surface of the skin. The lowest concentration used would have delivered a dose of BPA that is in the ballpark of what could rub off onto an equivalent area of skin from handling receipt paper, Zalko says.
After three days more than half of the BPA had diffused through the skin and into the growth medium. In a living animal, Zalko says, the diffused chemical would likely be circulating in blood throughout the body.
Enzymes active in the skin transformed the majority of the BPA into metabolites known as conjugates, which have chemical "add-ons" to the main BPA molecule. BPA principally is converted into the compounds BPA glucuronide and BPA sulfate. Though such transformations are often assumed to render a chemical nontoxic, "that would be a false assumption," Zalko says, "because any compound that has been conjugated can be deconjugated."
To validate the value of pig skin as a human surrogate, Zalko's group also ran the BPA experiments using tiny samples of healthy human skin that had been removed from the abdomens of roughly 40-year-old women during various surgical procedures. Again, almost half of the BPA applied passed completely through the skin. And Zalko cautions that this pass-through rate might be conservative since the cultured human skin samples weren't as fresh—and therefore porous—as the pig ears had been.
Moreover, far less of the BPA exiting the human skin was conjugated compared with pig skin, and what had been transformed was less likely to be in the glucuronide form.
The role of metabolites in BPA's potential toxicity is complicated, vom Saal says, because the body can—and regularly does—conjugate and deconjugate compounds. "It's well known," for instance, "that the body is full of desulfating enzymes, which play a role regulating estrogen levels during pregnancy."
These new data reinforce concerns about store receipts, he adds, "because we know from many thermal papers that receipts can contain a heck of a lot of BPA." And that BPA is about as likely to rub off receipt paper as a coating of talcum powder would be, he says.
Vom Saal's team is just launching a study with volunteers to measure not only how much BPA people get on their hands from holding thermal receipt paper, but also whether the compound goes on to show up in their blood and urine. Those data could be available by the end of the year.
Meanwhile, the leading producer of thermal-receipt stock in the United States—Appleton Papers, which claims to have been BPA-free since 2006—is looking to help consumers identify its receipts. "Consumers have made it clear that they want an easy way to distinguish Appleton's receipt paper from our competitors' paper, which all contain BPA," says company vice president Kent Willetts. "We are preparing to launch a BPA-free receipt paper that can be quickly and easily distinguished from all others. We will rush that product to market and have it in retailers' hands in time for the holiday shopping season."