Thermal paper used in till receipts is a source of BPA. Credit: M. Flippo

Two studies have thrown the controversial compound bisphenol A (BPA) back into the limelight. One study found that the chemical is readily absorbed through the skin, while a second study found that people who routinely touch BPA-laden till receipts have higher than average levels of the chemical in their bodies. Taken together, the findings strengthen calls for tougher regulation of the chemical, which is widely used in plastics manufacturing.

BPA is detectable in most people in Western countries. Animal studies have confirmed that high doses are harmful, but some evidence that it may also be harmful at low doses has yet to convince regulators to take decisive action against the compound.

The chemical mimics the effects of oestrogen in the body, so health concerns are especially pressing for pregnant women and some scientists also advise against the use of babies' bottles that contain BPA.

BPA is commonly used in food and drink packaging, where the molecule is usually locked in as part of a complex polymer. However, concerns have also been raised over its presence in the thermal paper used mainly in till receipts. In thermal paper the compound exists as a free monomer, which makes it easier for the body to absorb than other forms found in food packaging.

Daniel Zalko, a toxicologist at the French National Institute for Agricultural Research in Paris, and his colleagues have shown that free BPA can indeed be 'efficiently' absorbed through the skin. The findings, published in Chemosphere1, could help to explain why BPA levels in the general population appear to be higher than doses theoretically received through food and drink.

It would be smart to advise pregnant women to avoid or wash their hands after touching till receipts. Daniel Zalko , French National Institute for Agricultural Research, Paris

To investigate levels of skin exposure, the researchers took radioactively labelled BPA and observed the movement of radioactivity through pig ear skin — a widely used model for human skin. They repeated their experiments with smaller samples of human skin.

In the pig model, about 65% of the BPA diffused through the skin. For human skin around 46% diffused through. Both types of tissue were also able to metabolize BPA.

The findings suggest that till receipts should be handled with caution, says Zalko. "In the same way we advise people not to use polycarbonate-based baby bottles, it would be smart to advise pregnant women to avoid or wash their hands after touching these sorts of papers."

Problem on paper

Zalko and his team's findings are supported by another study that took a contrasting approach. Joe Braun, an epidemiologist at Harvard University in Boston, Massachusetts, and his group looked at the urine concentrations of BPA in 389 pregnant women, and broke these data down by occupation2.

Cashiers — who handle far more receipts than the general population — had the highest prenatal BPA concentrations in their urine at 2.8 micrograms per gram. By contrast, teachers had 1.8 micrograms per gram and industrial workers had 1.2 micrograms per gram.

Previous studies in factory workers exposed to BPA found even higher levels. One study3 linking BPA exposure to reduced sexual function in men found that one-quarter of workers had levels above 467 micrograms per gram.

Although there were only 17 cashiers in his sample, Braun says that he is "pretty confident" of the finding, not least because of Zalko's work. "It's reasonable to assume BPA can be absorbed through the skin," he says.

Braun notes that for people who handle only a couple of receipts a day, thermal paper is unlikely to be a major source of exposure. Pregnant women working as cashiers should be careful though, he suggests. "I would err on the side of caution and avoid exposure we think might be harmful."