A study of 17 commonly used synthetic “permanent chemicals” has shown that these toxic substances can be easily absorbed through human skin.
New research, published today in International Environment demonstrates for the first time that a wide range of PFAS (perfluoroalkyl substances), chemicals that do not break down in nature, can cross the skin barrier and reach the body’s bloodstream.
PFAS are widely used in industries and consumer products, from school uniforms to personal care products, due to their water and stain repellent properties. While some substances have been banned by government regulations, others are still widely used and their toxic effects have not yet been fully investigated.
PFAS are already known to enter the body through other routes, such as by inhaling them or ingesting them through food or drinking water, and are known to cause adverse health effects, such as a decreased immune response to vaccination, deterioration of liver function and decrease in birth weight. .
It has commonly been thought that PFAS cannot cross the skin barrier, although recent studies have shown links between the use of personal care products and PFAS concentrations in human blood and breast milk. The new study is the most comprehensive assessment yet of the absorption of PFAS into human skin and confirms that most of them can enter the body through this route.
The study’s lead author, Dr Oddný Ragnarsdóttir, carried out the research while studying for her PhD at the University of Birmingham. He explained: “The ability of these chemicals to be absorbed through the skin has previously been ruled out because the molecules are ionized. It was thought that the electrical charge that gives them the ability to repel water and stains also made them unable to cross the skin membrane.
“Our research shows that this theory is not always true and that, in fact, absorption through the skin could be a major source of exposure to these harmful chemicals.”
The researchers examined 17 different PFAS. The compounds selected were among the most widely used and most studied for their toxic effects and other ways humans could be exposed to them. The most significant thing is that they correspond to chemical products regulated by the EU Drinking Water Directive.
In their experiments, the team used 3D models equivalent to human skin: lab-grown multilayer tissues that mimic the properties of normal human skin, meaning the study could be carried out without using any animals. They applied samples of each chemical to measure what proportions were absorbed, unabsorbed or retained within the models.
Of the 17 PFAS analyzed, the team found that 15 substances showed substantial dermal absorption: at least 5% of the exposure dose. At the exposure doses examined, bloodstream absorption of the most regulated PFAS (perfluorooctanoic acid (PFOA)) was 13.5% and an additional 38% of the applied dose was retained within the skin for possible absorption at long term in circulation.
The amount absorbed appeared to correlate with the length of the carbon chain within the molecule. Substances with longer carbon chains showed lower levels of absorption, while compounds with shorter chains that were introduced to replace longer carbon chain PFAS, such as PFOA, were more easily absorbed. The absorption of perfluoropentanoic acid, for example, was four times greater than that of PFOA (59%).
Study co-author Dr. Mohamed Abdallah said, “Our study provides the first insight into the importance of the dermal route as a route of exposure to a wide range of permanent chemicals. Given the large amount of PFAS in existence, it is important “Future studies aim to assess the risk of a broad range of these toxic chemicals, rather than focusing on one chemical at a time.”
Study co-author Professor Stuart Harrad, from the School of Geography, Earth and Environmental Sciences at the University of Birmingham, added: “This study helps us understand how important exposure to these chemicals can be through the skin and also what chemical structures might be They are absorbed more easily This is important because we see a shift in the industry towards chemicals with shorter chain lengths because they are thought to be less toxic however, the trade-off could be that we absorb; more of them, so we need to know more about the risks involved.”