Study confirms forever chemicals are absorbed through the skin

Researchers at the University of Birmingham have revealed that a wide range of PFAS (perfluoroalkyl substances) — chemicals which do not break down in nature — can permeate the skin barrier and reach the body’s bloodstream.

The team’s research, published in the journal Environment International, has been described as the most comprehensive assessment yet undertaken of the absorption of PFAS into human skin and confirms that most of them can enter the body via this route.

PFAS are used widely in industries and consumer products from waterproof clothing and school uniforms to personal care products because of their water- and stain-repellent 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.

PFAS are already known to enter the body through other routes, for example being breathed in or ingested via food or drinking water, and they are known to cause adverse health effects such as a lowered immune response to vaccination, impaired liver function and decreased birth weight. But it has commonly been thought that PFAS are unable to breach 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 ability of these chemicals to be absorbed through skin has previously been dismissed because the molecules are ionised,” said lead author Dr Oddný Ragnarsdóttir, who carried out the research while studying for her PhD. “The electrical charge that gives them the ability to repel water and stains was thought to also make them incapable of crossing the skin membrane.

“Our research shows that this theory does not always hold true.”

The researchers investigated 17 different PFAS that are among those most widely used, and most widely studied for their toxic effects and other ways through which humans might be exposed to them. Samples of each chemical were applied to 3D human skin equivalent models — multilayered laboratory-grown tissues that mimic the properties of normal human skin — to measure what proportions were absorbed, unabsorbed or retained within the models.

Of the 17 PFAS tested, the team found 15 substances showed substantial dermal absorption — at least 5% of the exposure dose. At the exposure doses examined, absorption into the bloodstream of the most regulated PFAS (perfluoro octanoic acid, or PFOA) was 13.5%, with a further 38% of the applied dose retained within the skin for potential longer-term uptake into circulation.

The amount absorbed seemed 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, like PFOA, were more easily absorbed. Absorption of perfluoro pentanoic acid, for example, was four times that of PFOA at 59%.

“This study helps us to understand how important exposure to these chemicals via the skin might be, and also which chemical structures might be most easily absorbed,” said study co-author Professor Stuart Harrad. “This is important because we see a shift in industry towards chemicals with shorter chain lengths because these are believed to be less toxic; however, the trade-off might be that we absorb more of them, so we need to know more about the risks involved.”

“Given the large number of existing PFAS, it is important that future studies aim to assess the risk of broad ranges of these toxic chemicals, rather than focusing on one chemical at a time,” added study co-author Dr Mohamed Abdallah.

Image credit: iStock.com/swissmediavision