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Let’s start with the facts. Despite what you may have heard, you’re not eating a credit card’s worth of microplastics every week. At least not in the normal human eating process. But this popular claim has become alarming, especially as a series of studies have found microplastics accumulating everywhere, including in our highest mountains, deepest ocean trenches, and most remote polar regions, as well as in our heart tissue, liver, kidneys, breast milk, and bloodstream. If they were everywhere and scientific studies showed that they could cause some harm, that would be a big cause for concern, right? No, not necessarily.
The reason microplastics are present virtually everywhere is because plastics are truly amazing. The advent of Bakelite, the first plastic, in the early 20th century ushered in an era in which materials were manufactured on demand rather than extracted from nature. As plastics became thinner and cheaper, they became widespread, revolutionizing food packaging, electronics, medical devices, just to name a few. However, durability has its drawbacks. Fine particles have been released into the environment for more than a century and persist for long periods of time. Therefore, it is present in the body tissues and bloodstream of animals up and down the food chain, including us, and even in many of the things we consume, such as salt, beer, and drinking water.
Yes, microplastics are probably inside you. But don’t worry yet. When thinking about all types of pollutants in the body, there are several things to consider. First, there is the issue of size, and in the case of microplastics, the range is very wide. The next question is at what dose does it take effect? And finally, whether the effects are actually harmful. Since much of the research involves animals, we also need to ask whether those animal studies can be reasonably applied to the average human.
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When it comes to microplastics, many of the most alarming headlines in the news over the past few years have been vague about the size of the microplastics in question, or relied on studies that used unusually high doses that don’t seem to reflect everyday reality.
A big claim that spread quickly and still seems to stick is that every person on the planet ingests an average of 5 grams of microplastics per week, which is the equivalent of one credit card. This comes from a 2019 study using some very sloppy math, and it’s simply not true unless you take a very specific approach to controlling your spending.
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According to one study, most of the world’s population consumes just 0.0041 milligrams per week, which is less than a grain of salt.
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The research in question was funded by the World Wildlife Fund in partnership with Newcastle University. This review combined the results of 59 previous studies on microplastics in food and water. The problem is that some studies only measured the number of microplastic particles in a sample, while others measured the mass of microplastics. This meant that researchers had to rely on estimates to compare the two types of studies. For example, they used measurements from seawater and the number of particles per liter from drinking water to estimate the mass of microplastic particles found in drinking water. However, microplastics in the ocean and our drinking water are not necessarily the same. If the average size of microplastic particles in the ocean is much larger than microplastic particles in filtered drinking water, the final calculation would be inflated. A subsequent study looking at the same data found that to be the case.
So, no, we don’t consume 5 grams of microplastics every week. Probably much less. In fact, one study found that most of the world’s population consumes just 0.0041 milligrams per week, which is less than a grain of salt. At that rate, it would take more than 1.2 million weeks, or more than 23,000 years, to mine a credit card’s worth of plastic. If you’re immortal, worry about it.
The same researchers conducted simulations to predict that each person accumulates an average of 12.2 milligrams of microplastics over their lifetime, but only 41 nanograms are actually absorbed by the body.
New concerns have also emerged in the past few weeks about the quality of research examining the amount of microplastics in the body. For example, some studies vaporize tissue samples and analyze the smoke for the presence of microplastics. However, when fat evaporates, similar molecules are produced, which can lead to false positives.
What do microplastics do in the body?
But all of this only corresponds to the amount of microplastics we consume. What they are doing to us is another question, about which we still don’t have a sure answer. Some evidence points to behavioral changes and inflammation in mice exposed to microplastics. However, the highest dose given to these mice was 1 gram per day, which is an astronomical number for the human body, let alone the mice. A study in pigs using 1 gram per week found that exposure to microplastics affected the expression of 86 genes and induced oxidative stress in the pancreas. Oxidative stress is caused when the body does not have enough antioxidants to remove unstable molecules that cause cell damage. But again, the dosage is unrealistic. In fact, the World Health Organization warned in a report in 2022 that most animal studies use much higher concentrations of microplastics than humans are normally exposed to, or microplastic particles larger than those likely to be ingested by humans. The report also notes that microplastics circulate through our organs differently than in rodents, making the results difficult to extrapolate to humans.
Preliminary studies in humans exist, and a recent study found that microplastics can accumulate in plaques along with fat, cholesterol, and blood cells. Researchers found that people with plaques injected with these plastics had higher rates of heart attacks and strokes. But all we can say is that these were correlated, not that microplastics themselves caused these results.
Understanding how microplastics affect our bodies is complex. Yes, they contain chemicals that can disrupt our body’s processes, but when assessing risk, we cannot assume that 100% of those chemicals will leach into our bodies instantly. For example, studies have shown that assuming average leaching rates in the intestines, the increase in chemical concentrations in surrounding tissues is negligible. And because these chemicals can leach out of your tissues and be excreted through your feces, they don’t necessarily increase over your lifetime.
Concerns have been raised that other toxins attached to microplastics could be introduced into the body. Alternatively, they may interfere with the immune response or cause cell damage and inflammation. But do they cause these effects more than, say, other types of air pollution, sun exposure, excess sugar intake, or the common cold? We simply don’t know.
It’s understandable to think that microplastics can pose a risk to our health, but we need to know if they are really dangerous. This is an argument that feeds our fatalistic feelings towards the pollution happening around us. And just because we don’t consume as much plastic as a credit card each week doesn’t mean the underlying concerns aren’t valid. However, this field is still in its infancy, and there is still no rigorous data on the effects of microplastics in the body. So until more solid research is done on the effects of microplastics, I’ll spend my time worrying about other things.
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