A hormone-mimicking chemical that coats some cash-register receipt can linger in the body for a week or more, a new study finds. Its data show that skin contact with this BPA may expose people to its effects for longer than if it had been eaten.
Short for bisphenol A (Bis-FEE-nul A), BPA is used to make some plastics, dental sealants and resins used in food packaging. It also is an ingredient in a coating on the thermal paper used in some cash-register receipts. Parts of that coating will darken when exposed to heat. This is how cash registers can print out receipts without using ink.
Researchers worry that BPA may harm health. It mimics natural hormones that help control many body activities. It’s been linked to cancer, obesity and heart disease.
Studies have shown that BPA can get into the body when a person eats or drinks something tainted with it. But skin is a less-studied exposure route into the body.
“People are often surprised when I tell them that we can absorb chemicals through the skin,” says Jonathan Martin. One of the study’s authors, he works at Stockholm University in Sweden. As a toxicologist, he studies how people are exposed to and react with potentially toxic materials.
Previous studies had shown that if someone swallows BPA, the body will excrete most of it within hours. That’s good, because it gives the chemical little time to disturb the body’s normal processes. But researchers have understood little about what happens once BPA is absorbed through the skin.
Jiaying Liu is a graduate student at the University of Alberta in Edmonton, Canada. With Martin, she set out to study how the body handles BPA when it is absorbed through the skin. They wanted to know how skin exposures differ from those that occur by mouth.
By hand or by mouth
To find out, Liu and Martin coated slips of paper with BPA. This was to simulate receipt paper. But there’s a potential problem. BPA is such a common chemical that most people have small amounts of it passing through their body on any given day. To deal with this, the researchers chemically attached another molecule — what’s known as a tag — to the BPA.
This tag was a chemical that emits small amounts of radioactivity. Scientists can track this radioactivity to identify where BPA is as it passes through the body. That tag also distinguish the BPA used in these tests from any other BPA that someone encountered from another source.
The researchers asked six adult men to hold the BPA-coated paper in their hands for five minutes. Afterward, these volunteers put on rubber gloves for another two hours. The gloves made sure that any BPA on their hands would not accidentally get in their mouths. After that, the men removed the gloves washed their hands with soap.
Over the next several days, the researchers measured how much of the tagged BPA came out in the mens’ urine. This showed how quickly the body was processing and removing the chemical. (Waste products, including BPA and other toxic chemicals, are filtered out of the bloodstream by the kidneys. The body then excretes these wastes in the urine.)
Later, the researchers asked the volunteers to come back to the lab. This time, each man ate a cookie laced with the tagged BPA. Each cookie contained about four times more BPA than what’s consumed each day by the average person in Canada (where the study took place). Then the researchers measured the chemical’s release in urine over the next few days.
As expected, the ingested BPA passed out of the body pretty quickly. Liu and Martin estimate that the men lost more than 96 percent of the cookies’ BPA within 12 hours.
In contrast, BPA from the paper stayed in the mens’ bodies for much longer. More than two days after they had washed their hands, their urine levels of BPA were as high as on day one. Half the men still had detectable traces in their urine one week later.
The researchers shared their findings September 5 in Environmental Science & Technology.
Understanding the skin barrier
Gerald Kasting says the new data by Liu and Martin make sense when you think about the skin’s chemistry. A cosmetic scientist, Kasting works at the University of Cincinnati in Ohio. There, he studies how different chemicals move through the skin.
Skin acts as a barrier between the body and outside world. The outer layer of skin is called the epidermis. It’s made of stacked, flattened layers of cells. They contain fatty molecules, called lipids, which repel water.
This water-repellant layer helps prevent the body from losing too much moisture. It also helps keep out dirt and other foreign substances.
Some chemicals, including BPA, can become trapped in the outer layer of skin cells. Each day, the body sheds some of these cells. That allows some of the BPA to slough off too. But tiny amounts of the pollutant may remain stuck in the skin. These can slowly seep into the blood and circulate around the body.
The new study “is a positive step” in understanding BPA’s potential to cause harm as a result of skin exposures, says Kasting. Studies with women and people of different ages would be useful, he says, to see if they respond similarly to the men studied here.
Knowing that BPA from skin contact stays in the body is just the first step, the researchers note. For now, Liu argues, “We can’t say from this study whether it is dangerous to handle store receipts.” That’s because they didn’t look for evidence of harm. Future studies, she says, should investigate that.