Is your brain full of plastics?

October 12, 2021

Written by: Vanessa B. Sanchez

What if I told you that you could be swallowing a credit card’s worth of plastic every day^1,2?

Everything we eat, drink, or breath contains “nanoplastics” and/or “microplastics” which are super tiny particles of plastic that are smaller than 0.1 microns and/or 5 millimeters, respecitvely¹. According to a team of scientists from the University of Newcastle, Australia, we “ingest an average of around 2,000 microplastic particles a week^1,2”. This number seems overwhelmingly concerning, but how does it affect our well-being? Most importantly, how does consumption of microplastics affect our brain?

Well, not to shock you, but there hasn’t been much research done on the effects of microplastics on the brain. The earth’s oceans contain over 5.25 trillion macro and micro pieces of plastic, so scientists have studied the neurotoxicity of plastic uptake primarily in fish and crabs^3,4. In two independent studies, Japanese rice and red tilapia fish that were exposed to a large dose of polystyrene nanoplastics for 7 or 10 days were found to have these nanoplastics in their gills, testis, liver, and blood. Interestingly, nanoplastics were also found in their brains, suggesting that they have the capacity to pass through the blood brain barrier (BBB)^4-6. The BBB prevents any unwanted “villains” in the blood, like germs, from crossing over to where your brain and neurons reside – kind of like the brain’s protective sheath.

There is a lot of evidence that the uptake of nanoplastics coincides with altered activity of important enzymes in the fish brain. Specifically, nanoplastic consumption has been associated with the inhibition of Acetylcholinesterase (AChE) and an increase of superoxide dismutase (SOD) activity^4-6. AChE is a protein that terminates signaling between neurons at synapses (the connection between two neurons) by breaking down the neurotransmitter acetylcholine. If AChE is inhibited, then acetylcholine will begin to accumulate and impede neuron communication, which can lead to symptoms of agitation, muscle weakness and paralysis¹¹. Moreover, SOD is an important antioxidant defensive protein whose goal is to break down free radicals (harmful oxygen molecules) and prevent damage to your body¹². If nanoplastics are being taken up and ending up in your brain, you would hope SOD’s activity is increased because it is working hard to break down of potentially harmful free radicals! Not to mention, studies in zebrafish models also showed that nanoplastics relate to a decrease in AChE and increase in SOD, and the fish in this study also exhibited altered motor behavior and seizures.

You may be wondering- has anyone studied these neurotoxic effects in non-sea creatures?

Surprisingly, little to none. To date, only two studies on the neurotoxic effects of micro- and/or nano-plastics have been conducted in rodents⁴. For 7 days, adult mice were given high doses of polystyrene microplastics through oral gavage – a technique that involves passing a feeding needle through the mouth into the esophagus. After 7 days, these microplastics were taken up and found in the gut, liver, and kidneys. Unlike the studies in fish that found an inhibition of brain AChE, AChE activity was increased in the liver of rodents⁷. This study suggested that these changes could potentially reflect changes in neurotransmitter levels, but future work will have to examine the brain to know for sure.

Even more alarming, just this year a study found that microplastics have been found in placentas of unborn babies⁸. A baby’s brain and nervous system begin to grow six weeks into pregnancy and continue to grow until about the age of 25. Additionally, scientists have reported that babies who are fed from plastic bottles swallow approximately 3 million microplastics in a day! Scientists currently have very little idea what the side effects of these microplastics are on brain development and overall brain health. Clearly, research on microplastics uptake and neurotoxicity must be intensified and should be demanded by the public.

Our society can continue to push for more sustainable, biodegradable, and compostable products, but it is going to take a long time until companies convert to plastic-free packaging. In the meantime, the best things we can do as individuals is to be mindful of the products we purchase, try to reduce our plastic intake, and recycle. The less plastic we use, the less ends up polluting our environment, therefore, reducing the amount of nanoplastics in our bodies and hopefully, our brains.

References:

1. Gerretsen, sabelle. (2019, June 17). You could be swallowing a credit card’s weight in … – CNN. You could be swallowing a credit card’s weight in plastic every week. Retrieved October 1, 2021.
2. de Wit, W., & Bigaud, N. (2019). No plastic in nature: assessing plastic ingestion from nature to people.

3. Parker, L. (2015). Ocean trash: 5.25 trillion pieces and counting, but big questions remain. National Geographic, 11, 2015.

4. Prüst, M., Meijer, J., & Westerink, R. H. (2020). The plastic brain: neurotoxicity of micro-and nanoplastics. Particle and fibre toxicology, 17, 1-16.

5. Kashiwada, S. (2006). Distribution of nanoparticles in the see-through medaka (Oryzias latipes). Environmental health perspectives, 114(11), 1697-1702.

6. Ding, J., Zhang, S., Razanajatovo, R. M., Zou, H., & Zhu, W. (2018). Accumulation, tissue distribution, and biochemical effects of polystyrene microplastics in the freshwater fish red tilapia (Oreochromis niloticus). Environmental pollution, 238, 1-9.

7. Deng, Y., Zhang, Y., Lemos, B., & Ren, H. (2017). Tissue accumulation of microplastics in mice and biomarker responses suggest widespread health risks of exposure. Scientific reports, 7(1), 1-10.

8. Ragusa, A., Svelato, A., Santacroce, C., Catalano, P., Notarstefano, V., Carnevali, O., … & Giorgini, E. (2021). Plasticenta: First evidence of microplastics in human placenta. Environment international, 146, 106274.

9. Li, D., Shi, Y., Yang, L., Xiao, L., Kehoe, D. K., Gun’ko, Y. K., … & Wang, J. J. (2020). Microplastic release from the degradation of polypropylene feeding bottles during infant formula preparation. Nature Food, 1(11), 746-754.
10. Colovic, M. B., Krstic, D. Z., Lazarevic-Pasti, T. D., Bondzic, A. M., & Vasic, V. M. (2013). Acetylcholinesterase inhibitors: pharmacology and toxicology. Current neuropharmacology, 11(3), 315-335.
11. Younus, H. (2018). Therapeutic potentials of superoxide dismutase. International journal of health sciences, 12(3), 88.

Photo by Nariman Mesharrafa on Unsplash