Plastic brain ASLM

The plastic brain: the potential neurotoxicity of microplastics

It seems impossible to imagine a world without plastic. Plastic is one of the materials most used by us in our everyday lives. In fact, it’s so prevalent in everyday life today it’s considered one of the defining features of the Anthropocene. That’s why the current era of Earth’s history is frequently referred to as “Plasticene,” or the Plastic Age.1

Life in the plasticene: how microplastics are formed

On my way to work I grab a take-away coffee, and after enjoying the caffeine hit, I thoughtlessly discard my cup in the bin. While this is the end of my morning indulgence, this is just the start of my coffee cup’s plastic cycle.

My coffee cup is part of the 368 million tons of plastic that are produced each year, 60% of which are disposed of as plastic litter, often after just a single use.2,3 Once discarded in the bin, a combination of biological, physicochemical and weathering forces go to work, and the result is plastic fragments that were once my morning coffee cup.

Microplastics (plastic particles with a diameter between 100nm and 5mm) and nanoplastics (particles with a diameter below 100nm) are formed.4 These tiny particles contaminate the soil, are blown away by the wind, washed into rivers and finally into the sea, where approximately 10% of all plastic waste ends up.5  They are joined by the so-called primary microplastics, which we flush down our sinks every day. These are the plastic particles deliberately added to products, often advertised as “microbeads.” They’re common in personal care products such as toothpaste, detergents, ‘scrub’ facial cleansers, and makeups.6,7

Parts of our 6.3 billion tons of plastic waste degrade constantly and make their way into our terrestrial and marine ecosystems.2 Worldwide, invisible plastic particles now contaminate oceans, rivers, soil, sediment, and dust.8

The question is, could there be plastic in us? And, if so, how are we ingesting it and what consequences does this have for our health?

Occurrence of plastic in human tissues

In 2019, Schwabl et al.9 found humans are indeed ingesting plastics, or at least, that they’re coming out the other end. The team examined stool samples and found about 20 microplastics between 50μm and 500μm per 10g of human stool. But is it possible that some (smaller) particles make their way into our body?

This question was answered a year after Schwabl et al.’s study, when the first human study using colectomy samples showed that microplastics were ubiquitously present in human colon tissue. Researchers found 28 plastic particles per gram colon tissue.10

Again, one year later, the first published evidence of microplastic’s presence in the human placenta was released. These particles had a size of 5 -10μm, which is compatible with transportation via the bloodstream. For reference, a red blood cell has a diameter of 8μm.11 That plastic particles can travel in either blood or lymphatic systems to the liver, spleen and lymph nodes was already known from research on the wear of knee and hip prostheses.12

Uptake via food: human is a “plastivore”

We now know plastic is present in many types of food. Firstly, due to the extreme contamination of oceans, seafood is the most studied food in relation to plastic makeup.  Recent calculations show we consume up to 55,000 microplastics per year from seafood alone.13 The bad news is even if you don’t eat seafood, you’re unfortunately not spared from consuming plastic.

Plastic is found in both bottled and tap water,14 sea salt, beer, honey, and milk.15 But it doesn’t stop here. Plastic can be absorbed by the roots of plants, transporting from there to the edible, supra-terrestrial parts, shown by studies on crops such as wheat, barley, oats, and rice.16,17

How much plastic could end up on your plate was recently investigated by Australian researchers who studied the plastic contamination of store-bought rice. It was estimated that we ingest 3.7mg plastic with each 100g serve of rice. Washing the rice reduced the amount somewhat, indicating packaging is contributing to the contamination.18

Unfortunately thus far, many staple foods, including fruit, veg, and meat haven’t been investigated. But if we trust the estimation (based on the food items that have been researched) by Senathirajah et al.19, we could consume up to 13kg of microplastics by age 50.

The unexpected source of microplastics: My takeaway coffee contains millions

Besides plastic in food itself, a major source of contamination is plastic leakage from packaging, especially when plastic is used to carry hot food items.

An ordinary plastic takeaway coffee cup releases about 1.4 million plastic particles per ml.20 If you do the maths, this translates to 350 million particles per 250ml cup. Disposable paper cups seem to be even worse, with one study detecting 10.2 million microplastic particles per ml leachate after 15 min of soaking in 85-90 C hot water.21

And tea drinkers, beware: a research team from McGill University in Canada found that a single plastic teabag at brewing temperature released about 11.6 billion micro-plastics and 3.1 billion nano-plastic particles into the water. Therefore, only two cups of tea per day could expose you to 29.4 billion plastic particles.22

The bottom line is: you could be ingesting hundreds of thousands of millions of microplastics just by simply using one plastic item every day.20

Uptake via inhalation: another major way into the body

Besides dietary intake, inhalation is another major pathway of human plastic exposure. Not surprising, as we are all familiar with the mineral fibre asbestos, that can be found in lung tissue. What about plastic fibres? The first study about plastic fibres in lung tissue, and, notably in lung cancers, was published in 1998,23 unfortunately it did not receive too much attention within the scientific community at this time.

Thankfully, there is now a renewed interest regarding the inhalation of plastic particles, with many studies showing higher plastic concentrations in indoor air and dust as compared to outdoors.24 The biggest shedders of plastic particles in the indoor environment are carpet floors, with crawling toddlers having the highest exposure rates according to a study conducted in Sydney. 25

Three toxic effects of plastic particles

So, what makes plastic toxic? Plastic particles can exert toxic effects in three ways: First, due to the plastic particle itself, which, the smaller the easier it can penetrate biological barriers. In tissues, microplastics are considered foreign bodies and can trigger local immunoreactions.26 However, it seems that substances that are released from plastic can considerably contribute to its toxicity.

One source of leachate are the chemicals which are deliberately added to plastic, to give plastic its desired properties. These include for example flame retardants, plasticisers, stabilisers or colorants.27,28 Most of these additive chemicals have been well documented to cause adverse health effects in humans, in particular endocrine disruption, also reproductive toxicity, neurotoxicity, hepatotoxicity and cancer.29

Plastic particles are also great at absorbing and concentrating pollutants from the environment. In fact, plastic is so great at this, that it is used in analytical chemistry in a process called solid phase extraction for this purpose.  The problem is, once contaminated plastic particles have made their way into the human body, the pollutants in these plastic particles can be released when in contact with bodily fluids. Not surprisingly, these pollutants can reach concentrations many orders of magnitude higher than those detected in the surrounding environment.8,30,31

Indirect evidence for neurotoxicity

Some authors suggest that microplastics may have toxic effects on the brain, because in-vivo studies on animals shave shown that microplastics can impact neuronal function and behaviour. Plastic could be directly toxic to nerve cells or could impact the gut-brain axis.32,33

Looking at fish, micro and nanoplastics can accumulate in inner organs and are able to cross the blood brain barrier. Fish with nanoparticles in their brains showed not only changes in behaviour, but also had an altered shape of their cerebral gyri and changes in neurotransmitter concentrations. 34–36

And what about mammals? In mice, plastic microparticles accumulated in inner organs after they were taken up with water. As a result, researchers observed a disturbance of energy and lipid metabolism, oxidative stress 37 and increased permeability of the gut.38 Furthermore, researchers observed that blood biomarkers of neurotoxicity were altered. This means that microplastic exposure could have adverse effects on neurotransmission,37or in other words, disturb the way nerve cells communicate with each other.

Of course, man is not mouse or fish in this respect, but could human exposure to plastic equally result in systemic uptake, accumulation in the brain and disturb the function of nerve cells? This is an absolute possibility, as studies have proven that nanoparticles of 0.1 to 10μm in size can cross the blood brain barrier and are consecutively taken up by brain cells.39,40

So how do human brain cells react when they are exposed to nano-plastics in a petri dish? Cell cultures react to plastic with oxidative stress and inflammation, a reaction which has been linked to various neurodegenerative diseases such as Alzheimer’s or Parkinson’s disease. Furthermore, if the plastic is allowed to absorb toxins (as it would in real world conditions), the harmful effect on brain cells increases.41

Researchers have started to compare plastic nanoparticles with metallic nanoparticles with similar chemical behaviour. This is because they are much better researched in terms of neurotoxicity. Although it is a bit like comparing apples with pears, metallic nanoparticles indicate which effects could be possible.31,33

In animals, exposure to such particles leads to damage of nerve cells due to oxidative stress, and activation of microglia (these are local immune cells of the brain).42 Moreover, human studies show that exposure to pollutants in nano-size can accumulate in the vagus nerve (that’s the information “highway” between the gut and the brain, the core of the gut-brain axis) and contribute to neurodegeneration: Children who were exposed to these particles showed early changes of Alzheimer’s disease in their brains.43,44

Through the same mechanisms, and depending on individual susceptibility, microplastics could contribute to the increasing incidence of neurodegenerative diseases.26

Little research, big questions

At the moment, we have very limited information on whether plastic can harm our brain. Data regarding potential toxicity for now come exclusively from experiments on cellular cultures and animals, and from comparisons with other nanoparticles. Therefore, any indications of potential risks for human health have to be extrapolated from these results. This means that there are many open questions remaining- which will hopefully be answered in the years to come.

There is, however, sufficient evidence to support a precautionary approach in dealing with microplastic exposures. For my part, I have stocked up on reusable coffee cups.

Suggestions to minimise plastic intake

  • Avoid consuming hot food/beverage from plastic material
  • If you have to use plastic containers, use them for the minimal possible time (pour into another container, shorten mealtime)20
  • Don’t cut/stir food in plastic takeaway containers
  • Opt for reusable non-plastic coffee cups for your takeaway
  • Wash rice before cooking (or any other plastic packaged food where possible)18
  • Avoid using teas in plastic teabags
  • Frequent vacuum cleaning can reduce indoor plastic dust 25
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  22. Hernandez LM, Xu EG, Larsson HCE, et al. Plastic Teabags Release Billions of Microparticles and Nanoparticles into Tea. Environmental Science & Technology 2019; 53: 12300–12310.
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This article has been written for the Australasian Society of Lifestyle Medicine (ASLM) by the documented original author. The views and opinions expressed in this article are solely those of the original author and do not necessarily represent the views and opinions of the ASLM or its Board.

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