Toxic PFAS chemicals are absorbed through human skin

New research, published in Environment InternationalFor the first time, it has been proven that a wide range of PFAS (perfluoroalkyl substances) – chemicals that do not decompose in nature – can penetrate the skin barrier and reach the body’s bloodstream.

PFAS are widely used in industries and consumer products, from waterproof clothing and school uniforms to personal care products, because they have water and stain repelling properties. While some substances have been banned by government regulation, others are still widely used and their toxic effects have not yet been fully investigated.

It is already known that PFAS enter the body through other routes, for example through breathing or through food or drinking water, and they are known to cause adverse health effects, such as a reduced immune response to vaccination, impaired liver function and low birth weight.

It has been generally believed that PFAS are unable to penetrate the skin barrier, however recent studies have shown a relationship between the use of personal care products and PFAS concentrations in human blood and breast milk. The new study is the most comprehensive assessment of the absorption of PFAS into human skin to date and confirms that most of them can enter the body via this route.

The study’s lead author, Dr Oddny Ragnarsdottir, carried out the research while she was studying for 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 is thought that the electrical charge that gives them the ability to repel water and stain also makes them unable to cross the skin membrane.

“Our research shows that this theory is not always true, and in fact, absorption through the skin may be a significant source of exposure to these harmful chemicals.”

The researchers examined 17 different PFAS. The compounds chosen were among the most widely used, and the most extensively studied for their toxic effects and other ways through which humans might be exposed to them. Most importantly, they conformed to chemicals regulated by the EU Drinking Water Directive.

In their experiments the team used 3D human skin equivalent models – multi-layered tissues grown in the lab that mimic the properties of normal human skin, meaning the studies could be carried out without using any animals. They applied samples of each chemical to measure what proportion was absorbed, engulfed or retained within the models.

Of the 17 PFAS tested, the team found that 15 substances showed substantial dermal absorption – at least 5% of the exposure dose. At the exposure dose tested, the most regulated PFAS (perfluoro octanoic acid (PFOA)) had an absorption of 13.5% into the bloodstream, while 38% of the applied dose remained intact within the skin for potential long-term absorption into the blood circulation.

The amount absorbed appeared to correlate with the length of the carbon chain within the molecule. Substances with longer carbon chains had lower levels of absorption, while shorter chain compounds that were introduced to replace long carbon chain PFAS such as PFOA were more easily absorbed. For example the absorption of perfluoro pentanoic acid was four times that of PFOA, i.e. 59%.

Study co-author Dr. Mohammed Abdullah said, “Our study provides the first insights into the importance of the dermal route as a route of exposure to a wide range of chemicals in perpetuity. Given the large number of existing PFAS, it is important that future studies aim to assess exposure to a broad range of these toxic chemicals, rather than focusing on one chemical at a time.”

Study co-author Professor Stuart Harrad, from the University of Birmingham’s School of Geography, Earth and Environmental Sciences, said: “This study helps us understand how important exposure to these chemicals through the skin can be and also which chemical structures may be most easily absorbed. This is important as we are seeing a shift in industry towards chemicals with shorter chain lengths as these are considered to be less toxic – although the disadvantage of this may be that we absorb more of them, so we need to know more about the risks involved.”

-Note: This news release was originally published University of Birmingham websiteSince it has been republished, it may differ from our style guide.

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