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.
(for more about Power Words, click here)
average (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.
cancer Any of more than 100 different diseases, each characterized by the rapid, uncontrolled growth of abnormal cells. The development and growth of cancers, also known as malignancies, can lead to tumors, pain and death.
cell The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.
chemical A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
environmental science The study of ecosystems to help identify environmental problems and possible solutions. Environmental science can bring together many fields including physics, chemistry, biology and oceanography to understand how ecosystems function and how humans can coexist with them in harmony. People who work in this field are known as environmental scientists.
epidermis The outermost layer of skin.
excrete To remove waste products from the body, such as in the urine.
graduate student Someone working toward an advanced degree by taking classes and performing research. This work is done after the student has already graduated from college (usually with a four-year degree).
hormone (in zoology and medicine) A chemical produced in a gland and then carried in the bloodstream to another part of the body. Hormones control many important body activities, such as growth. Hormones act by triggering or regulating chemical reactions in the body. (in botany) A chemical that serves as a signaling compound that tells cells of a plant when and how to develop, or when to grow old and die.
kidney Each in a pair of organs in mammals that filters blood and produces urine.
lipid A type of fat.
moisture Small amounts of water present in the air, as vapor. It can also be present as a liquid, such as water droplets condensed on the inside of a window, or dampness present in clothing or soil.
molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
obesity (adj. obese) Extreme overweight. Obesity is associated with a wide range of health problems, including type 2 diabetes and high blood pressure.
plastic Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.
pollutant A substance that taints something — such as the air, water, our bodies or products. Some pollutants are chemicals, such as pesticides. Others may be radiation, including excess heat or light. Even weeds and other invasive species can be considered a type of biological pollution.
resin A sticky, sometimes aromatic substance, often secreted by plants. It may also be the viscous starting ingredient for some plastics that will harden when heated or treated with light.
simulate To deceive in some way by imitating the form or function of something. A simulated dietary fat, for instance, may deceive the mouth that it has tasted a real fat because it has the same feel on the tongue — without having any calories. A simulated sense of touch may fool the brain into thinking a finger has touched something even though a hand may no longer exists and has been replaced by a synthetic limb. (in computing) To try and imitate the conditions, functions or appearance of something. Computer programs that do this are referred to as simulations.
tag (in biology) The attachment of a chemical to some food, pollutant or other material in such a way that it will glow or give off radiation. This allows scientists to see where it is in the body — or even within some individual cells.
taint To contaminate.
technology The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.
thermal Of or relating to heat
toxic Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.
toxicologist A scientist who investigates the potential harm posed by physical agents in the environment. These may include materials to which we may be intentionally exposed, such as chemicals, cigarette smoke and foods, or materials to which we are exposed without choice, such as air and water pollutants. Toxicologists may study the risks such exposures cause, how they produce harm or how they move throughout the environment.
waste Any materials that are left over from biological or other systems that have no value, so they can be disposed of as trash or recycled for some new use.
Journal: J Liu and J.W. Martin. “Prolonged exposure to bisphenol A from single dermal contact events.” Environmental Science & Technology. Vol. 51, p. 9940, September 5, 2017. doi: 10.1021/acs.est.7b03093.