Part Human, Part Plastic – How Microplastics Impact Health

By Hannah Vonberg

Ecosystem degradation and pollution have long been recognized as a major harmful impact that human life has had on the planet. Pollution comes in many forms, but the most prominent one, especially in aquatic and marine systems, are plastics. Plastics have become essential in our everyday lives, with their use ranging from packaging to electronics, clothes, and industrial processes; even toothpaste and chewing gum often contain plastics. However, plastics are not always visible to the eye. For these, the term ‘microplastics’ was coined about 18 years ago. In less than two decades, microplastics have seemingly ‘appeared’ everywhere, and have most recently been discovered in the blood and lungs of living humans. This article will give an overview of what there is to know about microplastics, before highlighting these new studies linking microplastics to the human body, and outlining some possible implications of these findings.

Microplastics (MPs) have not been uniformly defined in the literature. Two characteristics are clear, though: MPs are a group of plastic particles and fibers, and they are small. Definitions pin down their size from 1.6 micrometers up to 10 millimeters; the most common convention is to lump all plastic particles smaller than 5 millimeters together as MPs (see the interesting graphic in this article for more information). Particles below 1 micrometer in size are often termed ‘nanoplastics’, leading to some more definitional problems as for where microplastics begin and end. Classifications usually divide primary and secondary microplastics. The former, called microbeads, are industrially produced in their small size, and are contained by many cosmetics (e.g. facial cleansers or toothpaste). The latter are created through the process of fragmentation which results from a break-down of macroplastics items (larger pieces of plastic, e.g. food packaging). Due to these different creation processes, MPs come in many shapes, sizes, and colors. It also becomes evident just how diverse the sources of MPs are, as they range from industrial waste to decade-old broken down fishery debris to household wear-and-tear (clothes or tires). Ultimately, one thing links all these forms of MPs together: sooner or later they find their way into the environment and become distributed mainly through aquatic systems (rivers, currents, rain, groundwater, etc.). MPs are small enough to get everywhere. Rain in the Pyrenee mountains, arctic snow, the deep sea, and the tissue of seafood are some of the more unexpected places in which scientists were able to isolate MPs.

But why is this problematic? The biggest reason is uncertainty. As this field of research is relatively new, we simply do not know enough to make certain claims about MPs and their impacts. However, given our track record regarding the environment, it would be overly optimistic to assume that there won’t be any negative consequences whatsoever from MPs pollution. In this sense, findings on the potential toxicity of MPs are very concerning. Furthermore, MPs have been found in animal tissue and are known to cause, among other issues, developmental anomalies. This has created a need to contain MPs so they do not enter the human body. Sewage treatment plants have managed to remove up to 99.9% of MPs from wastewater, but this is not as good of a development as we may think. The sludge that remains after the cleaning process contains all the MPs, and is essential for agricultural use in many countries. This way, MPs re-enter the water cycle and the food web. MPs are small enough to be taken up (and often get mistaken for food sources due to their shapes and colors) by organisms at the bottom of the food chain. Then, they can slowly move up in trophic levels, through the entire food web to larger aquatic animals (e.g. fish) and terrestrial animals (in this case even humans). We, and every other living organism, are dependent on the food web and the water cycle. Plastic particles have been found in 83% of tap water samples collected across six regions on five continents. And the problem is growing daily, with every single unit of plastics and microbeads we produce and discard.

In March and April 2022, MPs were found in humans for the first time in two independent studies. The first one, conducted by the Vrije Universiteit Amsterdam in The Netherlands, found MPs particles in human blood. The study shows that 77% of blood donors (17 out of 22) carried MPs in their blood in a size and concentration that was quantifiable (though both these factors varied among participants). Different types of plastics were found in the samples, but the most common type in this study was PET – a material used in e.g. single-use water bottles. These findings are spectacular for the reason that the researchers managed to overcome the measurement issues previous studies have encountered due to MPs’ small size. Blood vessels are unlikely to contain and circulate particles larger than 7 micrometers, a particle size that becomes difficult to pin down and isolate (as opposed to for example marine MPs debris, which is often much larger, ~ 5 millimeters). Health concerns about these findings could not be tied to the subjects themselves, but previous lab experiments have proven before that MPs pose a danger to human cells, possibly causing clogging and even cell death. If MPs can travel the bloodstream, it is likely that they can make it into human organs. What impacts that might have remains unclear.

This is where the second new study, published a few days ago, comes in. This experiment was led by the Hull York medical school in the UK, and proves the existence of MPs in the lungs of healthy living adults. In this study, 39 MPs were found in 11 out of 13 lung tissue samples, an astonishing 84.6%. Common particles were PET and polypropylene, some of the most widely spread materials when it comes to MPs. What is interesting about these findings is the fact that a high MPs concentration was found even in the lower part of the lung, where airways are smaller. The researchers expected this part of the lung to stay mostly untouched, as the ‘large’ MPs particles should be filtered out or trapped before getting this deep. Yet, the particles were there. MP particles have been found in lungs of cadavers before, but never before in healthy, living lung tissue – a major breakthrough in MPs research. Airborne MPs, a category often neglected in the news, thereby become a major player in future human health considerations and air pollution.

Together, these studies demonstrate that MPs are small enough to enter the human bloodstream and accumulate in organs. Their irregular and often jagged shape can cause serious damage to cells, and a large accumulation of particles could potentially lead to the clogging of vessels, and the smallest particles may even pass the blood-brain barrier. Since more testing is necessary to determine the precise impact of MPs in the human body, implications for health remain mostly unclear. One thing to keep in mind is that both studies work with relatively small sample sizes. This could possibly skew the results and accentuates the need for follow-up studies under similar and more diverse conditions. However, the numbers are concerning even in these small samples. The authors of both studies urge the scientific world to expand research in this area to create a clearer picture of the extent and impacts of MPs in the human body and on the larger environment.

Solutions to plastic pollution are usually two-fold: technical and political. Technical solutions include innovative ways of filtering and safely discarding MPs, e.g. through wastewater treatment and infiltration basins. Political solutions typically target the problem through laws and market regulation, such as the recent ban of several items made of single-use plastics by the EU. But much work remains to be done in terms of research, as well as public education on MPs and their environmental and health impacts.

MPs, a major driver of increasing plastic pollution, are to be taken seriously. They make their way through the most complicated and intricate systems on earth, and have been detected in water, air, soil, and living organisms. The human body poses no different case in this context. We know dangerously little about the impacts of these tiny particles, but we do know they are likely here to stay, and to increase in number, unless we start targeting plastic pollution in a more efficacious manner.

Edited by Uilson Jones & Teun van Dieten, artwork by Hannah Vonberg