A study of 17 commonly used synthetic ‘forever chemicals’ has shown that these toxins can be easily absorbed through human skin.
New research, published in Environment International, proves for the first time that a wide range of PFAS (perfluoroalkyl substances) – chemicals that do not break down in nature – can penetrate the skin barrier and enter the body’s bloodstream.
PFAS are widely used in industries and consumer products, from waterproof clothing and school uniforms to personal care products, because of their water and stain repellent properties. Although some substances have been banned by government regulation, 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, for example by inhalation or ingestion through food or drinking water, and are known to cause adverse health effects such as reduced immune response to vaccination, reduced liver function and reduced birth weight. .
It is often thought that PFAS cannot penetrate 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 to date of PFAS absorption into human skin and confirms that most of them can enter the body via this route.
Lead author of the study, Dr Oddný Ragnarsdóttir, carried out the research during her PhD at the University of Birmingham. She explained: “The ability of these chemicals to be absorbed through the skin was previously dismissed because the molecules are ionised. It was thought that the electrical charge that gives them the ability to repel water and stains also prevented them from penetrating the skin membrane.
“Our research shows that this theory is not always correct and that skin absorption may in fact be a significant source of exposure to these harmful chemicals.”
The researchers examined 17 different PFAS. The selected compounds were among the most commonly used and most studied because of their toxic effects and other ways people can be exposed to them. Most importantly, they correspond to chemicals regulated by the EU Drinking Water Directive.
In their experiments, the team used 3D equivalent models for human skin: multi-layered laboratory tissue that mimics the properties of normal human skin, meaning the research could be conducted without the use of animals. They applied samples of each chemical to measure what proportions were absorbed, not absorbed, or retained in the models.
Of the 17 PFAS tested, the team found that 15 substances showed substantial absorption through the skin – at least 5% of the exposure dose. At the exposure doses studied, absorption into the bloodstream of the most regulated PFAS (perfluorooctanoic acid (PFOA)) was 13.5%, with an additional 38% of the administered dose retained in the skin for possible longer-term absorption into the circulation.
The amount absorbed seemed to correlate with the length of the carbon chain in the molecule. Substances with longer carbon chains showed lower levels of absorption, while shorter chain compounds introduced to replace PFAS with longer carbon chains, such as PFOA, were more easily absorbed. For example, the absorption of perfluoropentanoic acid was four times that of PFOA, namely 59%.
Co-author of the study, Dr Mohamed Abdallah, said: “Our research provides the first insight into the significance of the dermal route as a route of exposure to a wide range of perennial chemicals. Given the large number of existing PFAS, it is important that future studies focus on assessing the risk of a broad range of these toxic chemicals, rather than focusing on one chemical at a time.”
Co-author of the study, Professor Stuart Harrad, from the University of Birmingham’s School of Geography, Earth and Environmental Sciences, added: “This study helps us understand how important exposure to these chemicals through the skin can be and also which chemical structures are possible. most easily absorbed. This is important as we see a shift in the industry towards chemicals with shorter chain lengths as these are believed to be less toxic. However, the trade-off could be that we absorb more of it, so we need to know more about the risks associated with it. ”