Australia-first study finds ‘forever chemicals’ in human brain tissue

An Australia-first study has found fat-loving “forever chemicals” in the human brain, raising questions about how they got there and the potential health risks.

The study is the first to “definitively demonstrate” the presence of per- and polyfluoroalkyl substances (PFAS), a group of more than 14,000 man-made chemicals, in human brain tissue, according to neuroscientist and study co-author Dr Claire Shepherd.

Marina Suzuki, who is the lead author of the study and a PhD candidate at UQ’s Queensland Alliance for Environmental Health Sciences.Credit: Fleur Connick

“We’ve known for a long time that some of these chemicals accumulate in other organs in the body and the blood – and they’ve been linked to adverse health outcomes,” said Shepherd, who is also the director of the Sydney Brain Bank at Neuroscience Research Australia.

Although it has been suggested that exposure to PFAS may be associated with harmful effects on the brain, few studies have assessed the presence of PFAS in brain tissues.

“It’s the first study that’s definitively demonstrated it in the brain, beyond that can be accounted for by the blood,” Shepherd said.

The results surprised some experts because they suggest certain PFAS are capable of crossing the blood-brain barrier (BBB), a protective mechanism designed to shield the brain from harmful substances, and may be accumulating in the fatty tissue.

The paper, published in the Environmental Science & Technology journal this month, is the first part of a University of Queensland research project investigating chemical contamination and potential links to neurodegenerative diseases, specifically Parkinson’s Disease and Motor Neurone Disease.

While the presence of “forever chemicals” in the human brain is concerning, experts say the potential health effects remain uncertain and further research is essential.

Previous studies have detected PFAS in human and animal brains, but it is unclear whether the result was influenced by contaminated blood which can reside in the brain tissue after death, environmental scientist and lead author of the study Marina Suzuki said.

The new research confirms the presence of PFAS in the brain tissue itself.

To do this, researchers compared the concentrations of 43 different PFAS in brain tissue and blood serum samples from the same 10 individuals, whose age of death ranged from 56 to 79 years. The samples were provided by the Sydney Brain Bank.

“The results showed that the ratios varied across different PFAS, which means that the detection of PFAS in the brain cannot solely be explained by the contamination of blood in the brain tissues,” said Suzuki, who is also a PhD candidate at UQ’s Queensland Alliance for Environmental Health Sciences.

When it comes to preventing unwanted substances from infiltrating the brain and causing harm, the blood-brain barrier (BBB) is “extremely important”, neuroscientist and associate professor at UNSW Dr Gila Moalem-Taylor said.

“As a researcher working on ways to bypass the BBB in order to deliver therapeutics to the central nervous system, I was somewhat surprised by the findings of PFAS breaching the BBB because it normally blocks most harmful chemicals from entering the brain,” she said.

Neuroscientist and study co-author Dr Claire ShepherdCredit: Dominic Lorrimer

“The integrity of the BBB is essential for keeping the brain functioning normally, and disruption to this barrier is associated with neurological diseases.”

Moalem-Taylor, who was not involved in the study, said the ability of certain PFAS to bypass the BBB and accumulate in the brain tissue is “concerning because of its potential neurotoxic effects”.

PFAS are known as ‘forever chemicals’ because they are very persistent in the environment.

However, Suzuki said individual types of PFAS could behave differently depending on their structure and properties such as their chain length.

The study’s findings suggested that longer-chain PFAS, which have a higher number of carbons in their chemical structure, are more likely to enter the brain and potentially accumulate there compared to shorter-chain PFAS.

“Those results suggest that carbon chain length of PFAS might play a key role in determining the relative accumulation of PFAS in the brain,” Suzuki said.

Long-chain PFAS are typically lipophilic – in other words, they love fat – compared to short-chain PFAS that prefer water-based environments.

The brain is the fattiest organ in the human body, which means it will attract lipophilic chemicals such as long-chain PFAS.

Long-chain PFAS also pose more of a health concern due to their persistent and bioaccumulative properties, where they can build up in the human body over time and therefore be toxic at lower doses.

Of the 43 PFAS analysed in the study, 18 were detected in at least one serum or brain sample, including perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS) and perfluorohexane sulfonic acid (PFHxS).

The trio are the most well-known and studied “forever chemicals” – and are all considered to be toxic, long-chain types of PFAS.

For decades, they were widely used in consumer and industrial products, including fabric protectors, non-stick pans and food packaging.

Since 2009, global agreements have been reached to ban PFOS, PFOA and PFHxS by listing them under the United Nation’s Stockholm Convention.

In Australia, all three chemicals, along with 500 related substances, will effectively be banned by July 1 through their listing on the federal government’s Industrial Chemicals Environmental Management Standard.

PFAS have been detected extensively in the blood of people living in developed countries.

Some studies suggest the blood concentrations of PFOS, PFOA, and PFHxS in the Australian population have decreased significantly between 2002 and 2021, which coincides with implemented measures to reduce exposure.

The results show PFOS had the highest average concentration at 6.8 nanograms per millilitre (ng/mL) in the serum and 0.65 ng/mL in the brain samples.

One long-chain PFAS detected in 9 out of 10 brain samples was perfluoroundecanoic acid (PFUnDA).

Many everyday consumer products that used to contain PFOA and PFOS have now been widely replaced with longer-chain PFAS such as PFUnDA.

However, given the limited sample size, Suzuki said further studies with a larger sample size are required to fully understand the presence and accumulation of a wider range of PFAS in the human brain.

“This is an important study that adds evidence regarding PFAS penetration into the brain and shows their accumulation is based on the chemical structure of the compound,” Moalem-Taylor said.

“Since these chemicals are widely used, and since there is [emerging] evidence that PFAS can be neurotoxic, any studies that expand our knowledge about their presence in the brain are useful.”

However, Moalem-Taylor said it is important to acknowledge that the full extent of the health effects of specific PFAS compounds remains uncertain and ongoing research is essential to determine their long-term impact and inform appropriate regulatory actions.

“This study is a good starting point for evaluating which of these different PFAS have higher brain accumulation in older adults,” she said, adding that comparing PFAS accumulation in individuals from different age groups would be valuable.

“The authors’ conclusions are reasonable, and they have acknowledged the limitations of the study and the necessity to further investigate the impact of PFAS accumulation on neural health.”

Shepherd said this study is only the start of their investigation.

“The next step is: what are they doing there, and what are the consequences for brain health?”

The researchers will also be investigating how the PFAS can cross the BBB, whether the chemicals accumulate in the brain with age, and if there are any differences in patients who died from a neurodegenerative disease.

Fleur Connick received funding from the Copyright Agency’s Cultural Fund, through the Science Journalists Association of Australia (SJAA), as part of a one-month science journalist residency program at the University of Queensland’s Institute of Molecular Biology (IMB) that guarantees journalistic independence.

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