Let’s start off with a fact: you do not, no matter what you’ve heard, . 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 , in the and in the most – 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 – – and in , such as salt, beer and drinking water.

Exposure to microplastic makes animals want to eat it more

Over multiple generations, small nematode worms began preferring microplastic-contaminated food over cleaner options, which could have consequences for ecosystem health

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 that are unlikely to reflect day-to-day reality.

The , 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.

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

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, 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 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 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 ÎçŇą¸ŁŔű1000ĽŻşĎ Organization warned 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 . 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.

Microplastics aren’t floating on only the surface of the ocean. A global survey of the tiny particles reveals they are prevalent throughout the water column – even at the deepest depths – which could affect the ocean’s ability to remove carbon from the atmosphere.

“It’s millions and millions of metric tonnes of this stuff throughout the interiors of the ocean,” says at Florida Atlantic University.

Mincer and his colleagues have reviewed microplastic measurements taken over the past decade from nearly 2000 sites around the world. While most microplastic measurements focused on the shallow surface of the ocean, the dataset included samples from a range of depths, including the deepest parts of the ocean.

They found that microplastics have been recorded virtually everywhere people have looked for them. That includes the Mariana trench, where more than 13,000 microplastic particles per cubic metre were measured nearly 7 kilometres down.

The researchers were surprised to see that the smallest particles are distributed almost evenly throughout the water column – not sinking or floating at the surface, but suspended. “We expect to find plastics at the bottom of the ocean, and at the top of the ocean. But not everywhere,” says at Northeastern University in Massachusetts.

They also found that the polymers in these plastics account for a significant proportion of the carbon particles floating around. At depths of 2000 metres, where there is less biological activity than nearer to the surface, they make up as much as 5 per cent of the carbon.

Free newsletter

Sign up to The Earth Edition

Sign up to newsletter

The ecological consequences of this are largely unknown, but one concern is that buoyant plastic consumed by plankton could reduce the volume of carbon that sinks to the depths in their faecal pellets and dead bodies. That could hamper the ocean’s ability to take up CO₂ from the atmosphere via the biological carbon pump, says Stubbins. However, he points out that we are far from being able to estimate the size of this effect. “We’re just now discovering the extent of plastics across the ocean,” he says.

“It can’t be ignored any longer by chemists or biologists trying to sort out how vast chunks of the oceans work,” says at the University of California Santa Barbara. He says the survey helps explain disagreements between estimates of the millions of tonnes of plastic flowing into the ocean and the amount actually measured there. “It didn’t disappear, unfortunately. It’s distributed in microplastic form across the water column,” he says.

People with artery plaques containing microplastics are more likely to have a heart attack or stroke than those with plastic-free plaques, suggesting microplastics may contribute to heart disease.

Microplastics form when sunlight, water and other agents erode plastics into fragments less than 5 millimetres long. At this size, the particles can make their way into our bodies and blood through food, water and even the air we breathe. Yet, little is known about their potential health effects.

So, at IRCCS MultiMedica, a hospital in Italy, and his colleagues looked for evidence of microplastics in artery plaques from 257 adults. All of them underwent surgery between August 2019 and August 2020 to have the plaques removed from arteries carrying blood to the brain.

Chemical analysis detected plastics in plaques from 150 of the participants. Using a microscope, the researchers could see jagged particles in the plaques as well – visible evidence of the microplastics. The team then monitored the study participants until July 2023 and found that during this period, those whose plaques had contained microplastics had an elevated risk of heart disease and death. On average, they were more than four times as likely to die or have a heart attack or stroke as participants with plastic-free plaques, suggesting microplastics contribute to cardiovascular disease.

However, these findings only establish a link between microplastics and heart disease, rather than proving microplastics are the cause, says Prattichizzo. He and his colleagues couldn’t discount the possibility that other confounding factors might underlie the association such as diet or air pollution. They did, however, find high levels of inflammatory molecules in plastic-containing plaques. This might suggest that microplastics in the bloodstream exacerbate inflammation, which increases the risk of heart attacks and stroke, he says.

“Plastics contain a lot of different chemicals that we know can adversely impact health, so I’m not surprised that we are starting to see increasing evidence of health effects,” says at the University of California, San Francisco.

Free newsletter

Sign up to ÎçŇą¸ŁŔű1000ĽŻşĎ Check

Sign up to newsletter

“Plastic production is steadily increasing and is projected to continue increasing, so we must know how [and] if any of these molecules affect our health,” says Prattichizzo.