Can nanoplastics breach the blood brain barrier?

by Kushani Mendis

Plastic pollution has become one of the biggest global environmental challenges in recent years. Around 10% of plastics produced each year end up as waste in water bodies.¹ Approximately 30 million tons of plastics are released into the environment each year with impacts to soil, freshwater, groundwater, and surface waters that are of global concern.² The global demand for plastics is mainly driven by thermoplastics like polypropylene (PP, found in food storage containers), polyethylene (PE, found in plastic bags and food packaging including bottles, containers, and wraps), and polyvinyl chloride (PVC, found in water pipes). Other commonly used plastics include polystyrene (PS, found in foam packaging), expandable PS, and polyethylene terephthalate (PET, found in plastic water bottles and soda bottles).

Plastics are not just used for consumer products but also for making synthetic fibers, foams, coatings, adhesives, and sealants which are essential in various industries.⁴ Over time, plastics degrade into smaller fragments: you may have heard of microplastics, which range from 0.1 μm to 1 mm smaller than a width of a pencil tip), but they can also break down farther into nanoplastics, which are smaller than 100 nm in size( one thousandth the thickness of a sheet of paper)^2,4.  This breakdown occurs through biological, chemical, and physical processes. ² Biological processes happen when living organisms digest or metabolize plastics. Chemical processes happen when certain chemicals interact with the plastic and break it apart at a molecular level. Physical processes are caused by things like ultraviolet light, weather, and mechanical forces like the plastic simply scraping across dirt or rocks. As plastics degrade, they can break down into smaller and smaller pieces or particles.

What do these different kinds of degraded plastics mean for humans? Tiny particles like micro- and nano-plastics can easily get into our bodies in various ways. Many research studies have found plastics present in human bodies, including in the blood and brain, heart and kidneys, liver and lungs, human milk and placenta, and testicles and semen.⁵ For example, one study found >700 nm plastic particles in human blood, and another reported 2-12 μm microplastics in human breast milk.⁵  A single plastic teabag could generate approximately 11.6 billion microplastics and 3.1 billion nanoplastics in hot water.¹ Infant feeding bottles made of polypropylene have been found to release up to 16 million nano-/microplastic particles per liter in to  infant formula.⁶ Therefore, infants are at risk of plastic exposure from consuming formula prepared in polypropylene bottles. Nanoplastics can also be released into food and drink from food packages such as paper cups, instant noodle containers, and take-out boxes. When consumed, these nanoplastics can infiltrate bodily tissues through cellular internalization and may result in toxicological consequences.⁵

Simply put, nanoplastics can enter the human body through food, tap water, and plastic beverage bottles contaminated with microplastics and nanoplastics. Scientists have found seafood (mollusks—including mussels, oysters, and clams) and sea salt to be highly contaminated with nanoplastics. Furthermore, agricultural products such as fruits and vegetables can absorb nanoplastics through plant roots when grown in contaminated soil, allowing these particles to enter the human body upon consumption.⁵ And studies suggests the presence of plastics in the human body may cause health complications such as cognitive impairment, or neurodegenerative diseases like Alzheimer’s disease (AD) and Parkinson’s disease.^1,7,8 For example, in one study, human neuronal cells were found to internalize polyethylene nanoplastics (33 nm), and developed abnormalities following semi-acute (48 h, 22.5–1440 mg/L) and chronic (18 days, 22.5–360 mg/L) exposure. The internalization of nanoplastics was associated with altered gene expression and oxidative stress. Also at high concentrations (≥180 mg/L), more cells died.⁷

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The Blood-Brain Barrier

The blood-brain barrier (BBB) is a protective barrier that separates the brain from the blood. It is semi-permeable, meaning it carefully controls what enters and leaves the brain. This barrier allows essential nutrients and oxygen to pass through while blocking harmful substances, helping to maintain a stable environment for brain function. Scientists have found that nanoplastics can pass through the BBB by attaching to the membrane and getting endocytosed.⁵ Endocytosis is like a cell “eating” or “drinking.” The cell wraps around a molecule, pulls it inside, and forms a small bubble-like structure to transport it. This helps the cell take in nutrients, remove waste, or communicate with its environment.

One study on mice models has shown that exposure to nanoplastics increases the permeability of the BBB. This means that substances that would normally be blocked by the BBB could pass into the brain, triggering inflammatory responses. Furthermore, the studies that investigated the neurotoxicity of one type of nanoplastics showed that nanoplastics crossing the BBB activates microglia (a type of clean-up cell in the brain and central nervous system).¹¹ Microglia are a key part of the immune defense system in the brain which respond to pathological events. Additionally, findings suggest that the synergistic interactions of nanoplastics with other biomolecules can trigger neurotoxicity.¹ Overall, nanoplastics exposure can lead to increased production of reactive oxygen species (ROS)⁸ which may cause oxidative stress, inflammation, and DNA damage⁵. These in turn can cause long-term effects such as increasing the incidence of neurodegenerative diseases like Alzheimer’s disease.¹

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Detection methods

Scientists have been working for a long time to learn about the health consequences of nanoplastics in humans and the environment. One of the most fundamental challenges of nanoplastics research is simply being able to detect the nanoplastics in our blood and other tissues. Because these particles are less than 100 nm, we need specialized instruments to see them. Research shows that nanoplastics have a greater potential than microplastics to cause harm because they are so small that they can actually get inside of individual cells.⁵ And as we’ve discussed in previous blog posts, the high ratio of surface area to volume makes nanoparticles (including nanoplastics) more reactive than larger particles.¹² Accurately quantifying and characterizing the nanoplastics infiltrating our bodies requires multiple complementary detection techniques. For example, researchers use a technique called pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) to identify and measure the levels of micro- and nanoplastics in tissue samples.¹³ This method involves digesting organic tissue with potassium hydroxide, separating the plastic particles using an ultracentrifuge, heating the collected plastic, and using a mass spectrometer to analyze the gas emissions to identify and quantify different polymers.⁵ However, the Py-GC/MS method has limitations. It can be difficult to detect certain plastics like polyethylene and polyvinyl chloride. Also, the digestion process can create residues that might interfere with the analysis. Py-GC/MS also does not provide information about the nanoparticle shape and size. Other techniques like Raman spectroscopy and machine learning approaches also have been used in detection of nanoplastics.¹¹

Techniques like fluorescence microscopy and electron microscopy are helpful but pose a challenge in spotting the tiny plastic particles in tissue samples. The nanoplastics are more difficult than other materials to detect using electron microscopy because they actually don’t have a ton of electrons! (They’re not “electron dense” like gold and other metallic materials that make great electron microscope subjects.)

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Key takeaways

While the full scope of the impact of nanoplastics on human health and the environment is still being uncovered, the research is clear: nanoplastics pose a significant threat that cannot be ignored. The projected doubling of global plastic production by 2050⁵ underscores the urgent need for action. These tiny particles are not just a distant concern; they are already infiltrating our bodies, with studies finding them in human blood, breast milk, and even the brain. The potential health consequences, including neurodegenerative diseases and other serious conditions, are alarming!

Using environmentally friendly alternatives to plastics can significantly benefit human health and environmental sustainability. The responsibility is not only with the global scientific community but also with the corporate sector. Global corporate responsibility in reducing plastic usage can take many forms. Just a few examples:

• Sustainable packaging: Invest in biodegradable, recyclable, or reusable packaging to minimize plastic waste.
• Supply Chain Optimization: Reduce plastic use in logistics and transportation by using eco-friendly alternatives.
• Product Innovation: Develop plastic-free or minimal-plastic products to reduce reliance on traditional plastics.
• Recycling Programs: Implement take-back programs for plastic products and support global recycling initiatives.
• Corporate Partnerships: Collaborate with governments and NGOs to drive large-scale plastic reduction initiatives.
• Consumer Education: Raise awareness and encourage responsible consumption through campaigns and incentives.

I hope this post has contributed to the consumer education piece of the puzzle. However, there is also reason for optimism. The growing awareness of the problem is driving innovation and change. Companies are starting to invest in sustainable packaging, optimize their supply chains, and develop plastic-free alternatives.¹⁴ Furthermore, scientific research is continually advancing our understanding of health and environmental impact of nanoplastics, and also designing sustainable polymers that can replace conventional plastics.^16,17 The responsibility for addressing this challenge lies not only with the scientific community but also with corporations and consumers alike. By supporting companies committed to reducing plastic waste, advocating for stronger regulations, and making conscious consumer choices, we can collectively mitigate the risk posed by nanoplastics. This is not just about protecting our own health but also safeguarding the health of future generations and the planet. The time to act is now, to ensure a healthier, more sustainable world for all.

References

1. Gou, X.; Fu, Y.; Li, J.; Xiang, J.; Yang, M.; Zhang, Y. Impact of Nanoplastics on Alzheimer’s Disease: Enhanced Amyloid-β Peptide Aggregation and Augmented Neurotoxicity. Journal of Hazardous Materials 2024, 465, 133518. DOI: 10.1016/j.jhazmat.2024.133518.
2. Teng, M.; Zhao, X.; Wang, C.; Wang, C.; White, J. C.; Zhao, W.; Zhou, L.; Duan, M.; Wu, F. Polystyrene Nanoplastics Toxicity to Zebrafish: Dysregulation of the Brain–Intestine–Microbiota Axis. ACS Nano 2022, 16 (5), 8190–8204. DOI: 10.1021/acsnano.2c01872.
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