Common pollutant in drinking water linked to brain damage and cognitive impairment

New research has found that prolonged exposure to low concentrations of per- and polyfluoroalkyl substances—known as PFAS—can disrupt brain function, damage neurons, and impair memory and behavior in mice. The findings, published in the Journal of Hazardous Materials, add to growing evidence that these “forever chemicals” may pose significant risks to brain health, even at levels currently found in drinking water and the environment.

PFAS are a large group of synthetic chemicals widely used for their resistance to water, grease, and heat. They are found in countless everyday products, including nonstick cookware, food packaging, waterproof clothing, carpet treatments, and firefighting foam. Because they do not easily break down, PFAS persist in soil, water, air, and living organisms.

Exposure can occur through drinking contaminated water, eating fish or dairy products from affected areas, inhaling dust, or using items treated with PFAS, such as certain cosmetics, dental floss, and cleaning products. Waste sites, chemical plants, and military facilities are major sources of contamination, and biosolids from wastewater treatment—used as fertilizer—can spread PFAS into food systems and surface waters.

Due to their widespread use and persistence, PFAS have been detected in the blood of most people in the United States. While most exposures are relatively low, they can become concentrated and accumulate over time. Some occupational groups, such as firefighters and chemical manufacturing workers, face higher risks. Public health surveys and environmental testing have revealed PFAS contamination in public and private drinking water systems, especially near industrial sites and military bases.

Despite the growing scientific consensus that PFAS can cause harm, efforts to regulate these chemicals have faced repeated delays and rollbacks. The Environmental Protection Agency took early steps during the Trump administration to address PFAS pollution, developing an action plan in 2019 that included limiting PFOS and PFOA in drinking water and beginning the process of classifying them as hazardous substances under the Superfund law. These efforts advanced during the Biden administration, which finalized enforceable limits for six PFAS in water and continued research into health risks.

But in 2025, under a new EPA leadership, enforcement of these drinking water standards was postponed until 2031, and other rules are now under review. Grants for PFAS-related research have been cut, and internal scientific capacity has been restricted amid proposed agency-wide budget reductions. These actions have raised concern among scientists and advocates who fear that existing protections could be weakened just as new findings point to more widespread and serious risks.

The latest study on mice, conducted by researchers in China, sought to simulate real-world exposure by administering a PFAS mixture through drinking water over a period of seven weeks. The mixture included 17 different PFAS compounds at concentrations between 0.2 and 20 micrograms per liter—similar to what has been reported in surface water near contamination sites.

After the exposure period, the researchers found that four chemicals—PFPeA, PFHpA, 6:2 FTS, and PFOS—accumulated in the mice’s brains at levels higher than in their blood. These compounds were able to cross the blood-brain barrier and reach concentrations high enough to potentially interfere with brain activity.

To assess brain function, the team recorded electrical signals from the brain using electroencephalography. They observed changes in two key types of brain waves: beta waves, which are linked to attention and memory, were reduced, while gamma waves, associated with higher cognitive processing, increased. These shifts in brainwave patterns became more pronounced at higher exposure levels.

The behavioral effects were also significant. In open field tests, exposed mice showed signs of anxiety and reduced exploration. They traveled shorter distances and avoided the central area of the testing arena. In memory tests, mice took longer to explore new environments and were less able to distinguish between familiar and novel objects. These behaviors suggest deficits in memory, attention, and emotional regulation.

Microscopic analysis of the hippocampus, a brain region involved in memory formation, revealed signs of neuron death and structural damage in the exposed groups. Damage in this area is consistent with the types of memory and behavior impairments observed.

To understand the biological changes behind these outcomes, the researchers conducted chemical and genetic analyses of brain and blood samples. They found that PFAS exposure disrupted several metabolic pathways. Levels of key neurotransmitters and their precursors—including glutamate, aspartate, and tryptophan—were reduced. These molecules are vital for synaptic signaling and emotional regulation. At the same time, inflammatory markers in the brain were elevated, pointing to an immune response that could further disrupt normal brain function.

The study also identified changes in gene expression related to neurotransmitter systems, including those involving acetylcholine, GABA, and oxytocin. One notable finding was increased activity in the oxytocin signaling pathway, which may represent a compensatory response to chemical injury or inflammation. Previous studies have linked disruptions in this system to emotional and cognitive changes in animals and humans.

The results suggest that long-term, low-level exposure to PFAS mixtures can impair brain function through multiple mechanisms: chemical accumulation in brain tissue, interference with neurotransmitter systems, activation of inflammatory pathways, and changes in gene expression. The combination of behavioral, chemical, and genetic findings provides a comprehensive picture of PFAS neurotoxicity under environmentally relevant conditions.

The authors note that while the study was conducted in male mice and may not directly translate to humans, mice are widely used as models in neuroscience and toxicology. The range of PFAS used in the experiment reflects the types commonly found in contaminated water sources, offering insights into what effects humans might experience under similar exposure.

The findings from the new mouse study echo concerns raised by recent human research. A separate study published in the same journal earlier this year examined the effects of PFAS exposure during early pregnancy on children’s development. Researchers analyzed blood samples from more than 1,600 pregnant women in Shanghai and found that higher levels of perfluorooctanoic acid (PFOA) were associated with a greater likelihood of autistic traits in their children by age four.

Another compound, PFHxS, showed stronger effects in children who were genetically predisposed to autism. These effects appeared more pronounced in boys than in girls, and some associations were influenced by whether mothers took folic acid before pregnancy.

Taken together, these studies suggest that some PFAS compounds may have harmful effects on the developing brain, especially when exposure occurs during critical periods of growth. While human data remains limited and sometimes inconsistent, both animal and epidemiological research point toward the possibility that PFAS can disrupt neurotransmitters, alter gene expression, and contribute to behavioral changes.

Despite advances in research, regulatory action on PFAS continues to face political and industrial resistance in the United States. In recent months, the EPA has delayed key provisions related to drinking water standards and reporting requirements for PFAS use. Industry groups, including chemical manufacturers, have challenged regulations in court, and new leadership at the agency has requested multiple pauses to reevaluate policies, citing the need for scientific review.

At the same time, budget cuts have hampered the agency’s ability to carry out independent PFAS research. Several university grants aimed at studying PFAS in food systems and agriculture were canceled earlier this year, raising concerns about the agency’s commitment to understanding and managing PFAS exposure.

Researchers involved in the mouse study say their findings add to the growing body of evidence that PFAS exposure is not only widespread but potentially harmful to the brain. They emphasize the need for continued public health protections, environmental monitoring, and scientific investigation.

The study, “Neurotoxic effects of per- and polyfluoroalkyl substances (PFAS) mixture exposure in mice: Accumulations in brain and associated changes of behaviors, metabolome, and transcriptome,” was authored by Qiurong He, Qingkun Yang, Lin Wu, Yuhang He, Ni Zeng, and Zhenglu Wang.