How worried should you be about microplastics?

Let’s start off with a fact: you do not, no matter what you’ve heard, eat a credit card’s worth of microplastics each week. At least, not in the course of a normal human diet. But this popular claim has raised alarm, especially as it has been followed by a flurry of studies that have found microplastics accumulating everywhere – even on the highest mountains, in the deepest ocean trenches and in the most remote polar regions – as well as in human heart tissue, livers, kidneys, breast milk and the bloodstream. If they are all over the place, and we can show in some scientific studies that they can lead to some sort of harm, that’s cause for major concern, right? Well, no, not necessarily.

The reason microplastics are effectively everywhere is that plastic is truly a marvel. The advent of the first plastic, Bakelite, in the early 20th century ushered in an age of materials manufactured on demand instead of being harvested from nature. As plastics became thinner and cheaper, they spread far and wide, revolutionising food packaging, electronics and medical devices, to name just a few things. But their durability has a downside. Tiny particles have been shedding into the environment for more than a century, and they last a long time, which is why they’ve been found in the body tissues and bloodstream of animals up and down the food chain – including us – and in many things we consume, such as salt, beer and drinking water.

So yes, microplastics are probably in you. But don’t fret just yet. When we think about any kind of pollutant in the body, we need to consider several things. Firstly, there is the question of size, and for microplastics, there is a huge range. Then there’s what dosage would show any effect. And finally, whether that effect is actually harmful. As many of the studies involve animals, we also need to ask whether those animal studies can reasonably apply to the average human.

The credit card claim

For microplastics, many of the most worrisome headlines in the news in the past few years have been vague about the size of the microplastics in question, or have relied on studies using outlandishly large doses which are unlikely to reflect day-to-day reality.

The big claim that went viral, and has seemingly stuck around, was that on average every person on the planet is ingesting as much as 5 grams of microplastics per week – or the equivalent of a credit card’s worth. It came from a 2019 study that used some really shoddy maths, and it’s simply not true unless you’re taking a very unusual approach to curbing your spending.

The study in question was financed by the World Wildlife Fund in partnership with the University of Newcastle. It was a review combining the findings of 59 previous studies on microplastics found in food and water. The problem is that some of the studies only measured the number of microplastic particles in a sample and others measured the mass of microplastics. This meant that the researchers had to rely on estimation in order to compare the two types of study. For example, they estimated the mass of microplastic particles found in drinking water using measurements from ocean water and particle counts per litre from drinking water. But microplastics in the ocean and our drinking water aren’t necessarily the same – if the average size of a microplastic particle in the ocean is much larger than those in filtered drinking water, the ultimate calculation will be inflated. Subsequent studies looking at the same data found that it was.

So, no, we don’t consume 5 grams of microplastics each week – it is likely far, far less. In fact, one study found that most of the world’s population ingests just 0.0041 milligrams per week, which is 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 plough through a credit card’s worth of plastic. If you’re immortal, go ahead and worry.

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

Fresh concerns have also been raised in the past few weeks over the quality of studies looking at the amount of microplastics in the body. For instance, some studies vaporise tissue samples and then analyse the fumes for the presence of microplastics. However, when fat is vaporised it can produce similar molecules, creating a false positive.

What do microplastics do in the body?

But all of that only addresses the amount of microplastics we consume. What they are doing to us is another question, and one we don’t have really solid answers for yet. Some evidence points to behavioural changes and inflammation in mice exposed to microplastics. But the highest dose given to those 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 microplastics exposure affected the expression of 86 genes and induced oxidative stress in the pancreas, which is caused when there aren’t 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 much higher than people are typically exposed to, or use larger microplastic particles than are likely to be taken up by the human body. The report also notes that microplastics circulate through our organs differently than they do in rodents, making it difficult to translate findings to humans.

Preliminary studies in humans do exist, and one recent study found that microplastics can accumulate in plaques along with fats, cholesterol and blood cells. In people who had these plastic-infused plaques, researchers saw a higher rate of heart attack and stroke – but we can only say these were correlated, and not that the microplastics themselves caused these outcomes.

Understanding what microplastics are doing to our bodies is complex. Yes, they contain chemicals that could disrupt our body processes, but when assessing the risk, we can’t assume that 100 per cent of those chemicals leach into our bodies instantaneously. Research has shown that when we assume an average amount of leaching in our gut, for example, it results in negligible increases in chemical concentration in the surrounding tissue. And these chemicals don’t necessarily increase over your lifetime, because they can also leach out of your tissues and exit through your faeces.

Concerns have been raised that other toxins attached to microplastics could be brought into the body. Or they could interfere with immune responses, or cause cell damage or inflammation. But do they cause these effects more than, say, other kinds of air pollution, sun exposure, eating excess sugar or getting a cold? We simply don’t know.

It is understandable to think that microplastics could possibly be dangerous to our health, and we should find out whether they really are. It is a claim that feeds into our doomerism feelings about the pollution happening all around us. And just because we don’t consume a credit card’s worth of plastic every week doesn’t mean the underlying concerns aren’t valid. But the field is still young, and we don’t 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.