Crossing the Line: Microplastics Breach the Blood-Brain Barrier

It’s no secret that plastic has become ubiquitous in our daily lives, from the packaging of our food to the clothes we wear. Recent research has revealed that microplastics, tiny fragments resulting from our plastic-dominated world, are not just contaminating our oceans and soil—they're infiltrating our bodies and crossing the blood-brain barrier, suggesting potential impacts on the nervous system. This discovery opens a new frontier in our understanding of human health risks. 

What are microplastics and why should you care?

Microplastics are tiny plastic particles less than 5mm in size, often invisible to the naked eye. They come from two main sources:

1. The breakdown of larger plastic items exposed to environmental factors like sunlight and wave action.
2. Manufactured microplastics, such as microbeads used in cosmetics or fibers shed from synthetic clothing.

The blood-brain barrier is a highly selective, semipermeable border of cells that prevents solutes in the circulating blood from non-selectively crossing into the extracellular fluid of the central nervous system. This barrier is a vital defense mechanism that protects our brain from potentially harmful substances.

Recent studies on microplastics and the blood-brain barrier

Studies from 2024 confirm the presence of microplastics in human brain tissue, but they also suggest that the brain may be particularly susceptible to microplastic accumulation compared to other organs.

Research published in September 2024 by Professor Dr. Thais Mauad and Dr. Luis Fernando Amato-Lourenco from the University of Sao Paulo and Freie University Berlin found microplastics in the olfactory bulb of deceased residents in Sao Paulo, Brazil. This study, which examined samples from 15 individuals, identified plastic fibers and particles in 8 out of 15 samples. Their findings include:

• The most common plastic found was polypropylene, which is unsurprising as it is one of the most widely produced plastics globally. 
• Larger nano and microplastics may be able to pass through the blood-brain barrier. Nanoplastics are defined as plastics with dimensions ranging from 1 nm to 1 μm, while microplastics are defined as plastics less than or equal to 5 mm. It was previously assumed that only nanoplastics smaller than 1 micron were able to pass the blood-brain barrier. 
• The olfactory pathway appears to be a potential major entry route for plastic into the brain, implying that breathing in air with higher levels of microplastics such as indoor environments could be a significant source of plastic pollution in the brain.

In addition, a study published earlier this year by researchers from the Office of the Medical Investigator in Albuquerque, New Mexico, compared microplastic accumulation in kidneys, livers, and brains from autopsy samples collected in 2016 and 2024. Their findings raise concerns, including:

• Brains exhibited higher concentrations of microplastics than liver or kidney samples (9 up to 0.48% by weight).
• All organs showed significant increases in microplastic concentrations from 2016 to 2024, indicating a potential rise in microplastic pollution.
• Polyethylene was the predominant polymer found, with a higher relative proportion in brain samples compared to liver or kidney.

What are the potential health implications?

Researchers have already observed adults with higher concentrations of microplastics in the heart were at higher risk for stroke or heart attack. Thus, the presence of microplastics in the brain raises several concerns. In particular, researchers are working to understand the capacity of such particles to be internalized by cells and alter how our bodies function, potentially leading to disruptions in normal brain function and cellular processes. There is also concern about the interaction of microplastics with organs in children, with the research suggesting that exposure during critical developmental periods could lead to definitive alterations in adult life, potentially affecting cognitive function, behavior, and overall brain health.

 In a related study, Dr. Lukas Kenner found that cancer cells in the gut can spread at an accelerated rate after contact with microplastics, indicating that the presence of microplastics in the body could potentially exacerbate existing health conditions or contribute to the development of new ones. Furthermore, microplastics may act as a conveyor of additional contamination into the human body as they may also contain chemicals such as per- and polyfluoroalkyl substances, or PFAS, lead, and other chemical compounds embedded within or on the surface of the microplastic.

Who is most at risk?

Due to the ubiquitous nature of microplastics, it is assumed that everyone is potentially at risk. However, certain groups may be more vulnerable:

• Children: Because of their developing organs and systems, children may be particularly susceptible to the effects of microplastics. Their smaller body size also means that a given amount of microplastic exposure represents a proportionally larger dose compared to adults.
• People with occupational exposure: People working in industries that produce, recycle, dispose or handle large amounts of plastic may be at higher risk of inhaling or ingesting microplastics.
• Urban dwellers: Given that indoor environments appear to be a significant source of microplastic exposure to the brain, people living in urban areas with less ventilation and more synthetic materials may face higher exposure levels.
• Individuals with pre-existing conditions: Those with compromised immune systems or existing health issues may be more susceptible to the potential negative effects of microplastic accumulation.
• Underserved communities: People living in underserved communities and people of color are often disproportionately burdened by environmental contamination at the household and community level for a myriad of reasons, such as living in closer proximity to particulate pollution. 

What can we do to protect ourselves?

While it's challenging to completely avoid microplastics in our current plastic-dominated world, there are steps we can take to reduce our exposure:

• Minimize use of plastic products, especially single-use items. For example, use a reusable glass or stainless steel water bottle or coffee mug when you’re on the go when possible.
• Choose natural fiber clothing over synthetic materials. Synthetic fabrics like polyester, nylon, and acrylic shed microfibers during washing and wearing.
• Filter drinking water at your household kitchen tap and limit use of plastic water bottles.
• Avoid heating food in plastic containers and using plastic cutting boards.
• Reduce dust in your home. Regular cleaning through vacuuming and dusting along with the use of air purifiers can help reduce indoor microplastic pollution.

The push for policy change

As the evidence of microplastics' impact on human health grows, so does the push for policy changes.

In November 2024, the final round of negotiations for a UN Global Plastics Treaty will take place in South Korea. NGOs and scientists are calling for urgent action, especially with these new findings about microplastics in the brain. The Plastic Health Council, a group of leading scientists dedicated to researching the impact of micro, nano-plastics and chemicals on human health, is arguing for an alternative treaty that would reduce the production volumes of plastics, eliminate all but truly essential single-use plastic items, and require testing of all chemicals used in plastics.

There's a growing call for the precautionary principle to be applied to plastic production and use, given the potential harm to human health. The precautionary principle forms the basis of many modern environmental regulations and urges caution with new technologies where there is lack of scientific consensus on the long-term potential for harm from these technologies (see Principle 15 of the United Nations Rio Declaration on Environment and Development).

Need for additional research and proactive measures can occur in tandem

In 2019, the World Health Organization stated that while microplastics are ubiquitous in our environment, there was no evidence to conclude an impact to human health. In 2024, the United States Food and Drug Administration concluded that “Current scientific evidence does not demonstrate that levels of microplastics or nanoplastics detected in foods pose a risk to human health due to lack of harmonization in microplastic research methodology and the many research gaps left to explore.”

While finding microplastics in the human brain is a cause for concern, it also further highlights the need to determine the impacts of these particles to the human body. As research continues individuals can take proactive steps to voluntarily minimize plastic use, stay informed, and support policies that protect our health and environment from the growing threat of microplastic pollution.

RTI is actively working to address the issue of plastic pollution through waste management practices globally. Additionally, work is being done to develop standard reference materials for nanoplastics and testing the human health effects of microplastics within in vitro cell models.