How worried should you be about microplastics?

Let’s start with a fact: you don’t eat, whatever you’ve heard, a credit card’s worth of microplastics every week. At least, not as part of a normal human diet. But this popular claim sparked concern, especially since it was followed by a series of studies that showed microplastics were accumulating everywhere – even in the highest mountains, in the deepest ocean trenches and in the most remote polar regions – as well as in human heart tissue, liver, kidneys, breast milk and the bloodstream. If they’re everywhere, and we can demonstrate in some scientific studies that they can cause some sort of harm, that’s very concerning, right? Well no, not necessarily.

The reason microplastics are indeed everywhere is because plastic is truly a marvel. The advent of the first plastic, Bakelite, in the early 20th century ushered in an era of materials made on demand instead of harvested from the wild. As plastics have become thinner and cheaper, they have become widespread, revolutionizing food packaging, electronics and medical devices, to name just a few things. But their durability has a downside. Tiny particles have been spreading in the environment for over a century and last a long time. This is why they have been found in the body tissues and blood of animals throughout the food chain – including us – and in many products we consume, such as salt, beer and drinking water.

So yes, microplastics are probably in you. But don’t worry just yet. When we think about any type of pollutant found in the body, there are several things we need to consider. First there is the question of size, and for microplastics the range is very wide. Then there is the dosage that would produce an effect. And finally, if this effect is really harmful. As many studies involve animals, we must also ask whether these animal studies can reasonably be applied to the average human.

Credit card claim

When it comes to microplastics, most news headlines in recent years have been vague about the size of the microplastics in question, or relied on studies using extremely high doses that are unlikely to reflect everyday reality.

The big claim that went viral, and seems to persist, is that on average, each person on the planet ingests up to 5 grams of microplastics per week, the equivalent of the value of a credit card. This comes from a 2019 study that used some really shoddy calculations, and it’s simply not true unless you take a very unusual approach to cutting your spending.

The study in question was funded by the World Wildlife Fund in partnership with the University of Newcastle. This was a review combining 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 and 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 estimated the mass of microplastic particles found in drinking water using measurements from seawater and the number of particles per liter from drinking water. But the microplastics found in the ocean and in our drinking water are not necessarily the same: if the average size of a microplastic particle in the ocean is much larger than that found in filtered drinking water, the final calculation will be inflated. Subsequent studies of the same data found this to be the case.

So no, we’re not consuming 5 grams of microplastics every week – it’s probably a lot less. In fact, one study found that most of the world’s population ingests just 0.0041 milligrams per week, or less than a grain of salt. At that rate, it would take you more than 1.2 million weeks, or more than 23,000 years, to go through the plastic equivalent of a credit card. If you’re immortal, go ahead and worry.

The same researchers ran simulations to predict that on average, each person will accumulate 12.2 milligrams of microplastics over their lifetime, but that only 41 nanograms will actually be absorbed by the body.

New concerns have also been raised in recent weeks about the quality of studies investigating the amount of microplastics in the body. For example, some studies vaporize tissue samples and then analyze the fumes for the presence of microplastics. However, when fat is vaporized, it can produce similar molecules, creating a false positive.

What do microplastics do in the body?

But all this only concerns the amount of microplastics we consume. What they do to us is another question, for which we don’t have any really solid answers yet. Some evidence indicates behavioral changes and inflammation in mice exposed to microplastics. But the highest dose given to these mice was 1 gram per day, which is astronomical for a human body, let alone a mouse. A study in pigs used 1 gram per week and found that exposure to microplastics affected the expression of 86 genes and induced oxidative stress in the pancreas, caused when there are not enough antioxidants in the body to get rid of unstable molecules that lead to cell damage. But again, the dosage is unrealistic. In fact, in 2022, the World Health Organization warned in a report that most animal studies use concentrations of microplastics far higher than people are typically exposed to, or use microplastic particles larger than those likely to be absorbed by the human body. The report also notes that microplastics circulate in our organs differently than in rodents, making it difficult to translate the findings to humans.

Preliminary studies in humans exist, and a recent study found that microplastics can accumulate in plaques along with fats, cholesterol and blood cells. In people who had these plastic-infused patches, researchers saw a higher rate of heart attacks and strokes – but we can only say that there is a correlation between these two phenomena, not that the microplastics themselves are causing these results.

Understanding the effect of microplastics on our bodies is complex. Yes, they contain chemicals that could disrupt our body’s processes, but when we assess risk, we cannot assume that 100% of these chemicals will instantly seep into our body. Research has shown that when we assume an average amount of leaching in our gut, for example, it results in a negligible increase in chemical concentration in the surrounding tissues. And these chemicals don’t necessarily increase over the course of your life, because they can also leach out of your tissues and pass out through your stool.

Concerns have been raised that other toxins linked to microplastics could be introduced into the body. Or they could interfere with immune responses or cause cellular damage or inflammation. But do they cause these effects more than, for example, other types of air pollution, sun exposure, excessive sugar consumption or a cold? We just don’t know.

It’s understandable to think that microplastics could be dangerous to our health, and we should find out if they really are. It is a statement that fuels our catastrophic feeling about the pollution that surrounds us. And just because we don’t spend the equivalent of a credit card each week doesn’t mean the underlying concerns are unfounded. But the field is still young and we do not yet have rigorous data on the effects of microplastics in the body. So I would spend my time worrying about other things until we have more solid research on the effects of microplastics.