This story was originally published by the Guardian and appears here as part of the Climate Desk collaboration

High-profile studies reporting the presence of microplastics throughout the human body have been thrown into doubt by scientists who say the discoveries are probably the result of contamination and false positives. One chemist called the concerns “a bombshell.”

Studies claiming to have revealed micro and nanoplastics in the brain, testes, placentas, arteries and elsewhere were reported by media across the world, including the* Guardian*. There is no doubt that plastic pollution of the natural world is ubiquitous, and present in the food and drink we consume and the air we breathe. But the health damage potentially caused by microplastics and the chemicals they contain is unclear, and an explosion of research has taken off in this area in recent years.

However, micro- and nanoplastic particles are tiny and at the limit of today’s analytical techniques, especially in human tissue. There is no suggestion of malpractice, but researchers told the Guardian of their concern that the race to publish results, in some cases by groups with limited analytical expertise, has led to rushed results and routine scientific checks sometimes being overlooked.

The* Guardian* has identified seven studies that have been challenged by researchers publishing criticism in the respective journals, while a recent analysis listed 18 studies that it said had not considered that some human tissue can produce measurements easily confused with the signal given by common plastics.

There is an increasing international focus on the need to control plastic pollution but faulty evidence on the level of microplastics in humans could lead to misguided regulations and policies, which is dangerous, researchers say. It could also help lobbyists for the plastics industry to dismiss real concerns by claiming they are unfounded. While researchers say analytical techniques are improving rapidly, the doubts over recent high-profile studies also raise the questions of what is really known today and how concerned people should be about microplastics in their bodies.

‘The paper is a joke’

“Levels of microplastics in human brains may be rapidly rising” was the shocking headline reporting a widely covered study in February. The analysis, published in a top-tier journal and covered by the Guardian, said there was a rising trend in micro- and nanoplastics (MNPs) in brain tissue from dozens of postmortems carried out between 1997 and 2024.

One of the team behind the letter was blunt. “The brain microplastic paper is a joke,” said Dr Dušan Materić, at the Helmholtz Centre for Environmental Research in Germany.

However, by November, the study had been challenged by a group of scientists with the publication of a “Matters arising” letter in the journal. In the formal, diplomatic language of scientific publishing, the scientists said: “The study as reported appears to face methodological challenges, such as limited contamination controls and lack of validation steps, which may affect the reliability of the reported concentrations.”

One of the team behind the letter was blunt. “The brain microplastic paper is a joke,” said Dr Dušan Materić, at the Helmholtz Centre for Environmental Research in Germany. “Fat is known to make false-positives for polyethylene. The brain has [approximately] 60 per cent fat.” Materić and his colleagues suggested rising obesity levels could be an alternative explanation for the trend reported in the study.

Materić said: “That paper is really bad, and it is very explainable why it is wrong.” He thinks there are serious doubts over “more than half of the very high impact papers” reporting microplastics in biological tissue.

Prof Matthew Campen, senior author of the brain study in question, told the Guardian: “In general, we simply find ourselves in an early period of trying to understand the potential human health impacts of MNPs and there is no recipe book for how to do this. Most of the criticism aimed at the body of work to date (ie from our lab and others) has been conjectural and not buffeted by actual data.

“We have acknowledged the numerous opportunities for improvement and refinement and are trying to spend our finite resources in generating better assays and data, rather than continually engaging in a dialogue.”

‘Bombshell’ doubts

But the brain study is far from alone in having been challenged. One, which reported that patients with MNPs detected in carotid artery plaques had a higher risk of heart attacks and strokes than patients with no MNPs detected, was subsequently criticised for not testing blank samples taken in the operating room. Blank samples are a way of measuring how much background contamination may be present.

Another study reported MNPs in human testes, “highlighting the pervasive presence of microplastics in the male reproductive system”. But other scientists took a different view: “It is our opinion that the analytical approach used is not robust enough to support these claims.”

This study was by Prof Campen and colleagues, who responded: “To steal/modify a sentiment from the television show Ted Lasso, ‘[Bioanalytical assays] are never going to be perfect. The best we can do is to keep asking for help and accepting it when you can and if you keep on doing that, you’ll always be moving toward better.’”

Further challenged studies include two reporting plastic particles in blood – in both cases the researchers contested the criticisms – and another on their detection in arteries. A study claiming to have detected 10,000 nanoplastic particles per litre of bottled water was called “fundamentally unreliable” by critics, a charge disputed by the scientists.

The doubts amount to a “bombshell”, according to Roger Kuhlman, a chemist formerly at the Dow Chemical Company. “This is really forcing us to re-evaluate everything we think we know about microplastics in the body. Which, it turns out, is really not very much. Many researchers are making extraordinary claims, but not providing even ordinary evidence.”

While analytical chemistry has long-established guidelines on how to accurately analyse samples, these do not yet exist specifically for MNPs, said Dr Frederic Béen, at Vrije Universiteit Amsterdam: “But we still see quite a lot of papers where very standard good laboratory practices that should be followed have not necessarily been followed.”

These include measures to exclude background contamination, blanks, repeating measurements and testing equipment with samples spiked with a known amount of MNPs. “So you cannot be assured that whatever you have found is not fully or partially derived from some of these issues,” Béen said.

Biologically implausible

A key way of measuring the mass of MNPs in a sample is, perhaps counterintuitively, vaporising it, then capturing the fumes. But this method, dubbed Py-GC-MS, has come under particular criticism. “[It] is not currently a suitable technique for identifying polyethylene or PVC due to persistent interferences,” concluded a January 2025 study led by Dr Cassandra Rauert, an environmental chemist at the University of Queensland in Australia.

“I do think it is a problem in the entire field,” Rauert told the Guardian. “I think a lot of the concentrations [of MNPs] that are being reported are completely unrealistic.”

“This isn’t a dig at [other scientists],” she added. “They use these techniques because we haven’t got anything better available to us. But a lot of studies that we’ve seen coming out use the technique without really fully understanding the data that it’s giving you.” She said the failure to employ normal quality control checks was “a bit crazy”.

Py-GC-MS begins by pyrolysing the sample – heating it until it vaporises. The fumes are then passed through the tubes of a gas chromatograph, which separates smaller molecules from large ones. Last, a mass spectrometer uses the weights of different molecules to identify them.

The problem is that some small molecules in the fumes derived from polyethylene and PVC can also be produced from fats in human tissue. Human samples are “digested” with chemicals to remove tissue before analysis, but if some remains the result can be false positives for MNPs. Rauert’s paper lists 18 studies that did not include consideration of the risk of such false positives.

Rauert also argues that studies reporting high levels of MNPs in organs are simply hard to believe: “I have not seen evidence that particles between 3 and 30 micrometres can cross into the blood stream,” she said. “From what we know about actual exposure in our everyday lives, it is not biologically plausible that that mass of plastic would actually end up in these organs.”

“It’s really the nano-size plastic particles that can cross biological barriers and that we are expecting inside humans,” she said. “But the current instruments we have cannot detect nano-size particles.”

Further criticism came in July, in a review study in the Deutsches Ärzteblatt, the journal of the German Medical Association. “At present, there is hardly any reliable information available on the actual distribution of microplastics in the body,” the scientists wrote.

Fresh blood

Plastic production has ballooned by 200 times since the 1950s and is set to almost triple again to more than a billion tonnes a year by 2060. As a result, plastic pollution has also soared, with 8bn tonnes now contaminating the planet from the top of Mount Everest to the deepest ocean trench. Less than 10 per cent of plastic is recycled.

An expert review published in the Lancet in August called plastics a “grave, growing and underrecognised danger” to human and planetary health. It cited harm from the extraction of the fossil fuels they are made from, to their production, use and disposal, which result in air pollution and exposure to toxic chemicals.

In recent years, the infiltration of the body with MNPs has become a serious concern, and a landmark study in 2022 first reported detection in human blood. That study is one of the 18 listed in Rauert’s paper and was criticised by Kuhlman.

But the study’s senior author, Prof Marja Lamoree, at Vrije Universiteit Amsterdam, rejected suggestions of contamination. “The reason we focused on blood in the first place is that you can take blood samples freshly, without the interference of any plastics or exposure to the air,” she said.

“I’m convinced we detected microplastics,” she said. “But I’ve always said that [the amount estimated] could be maybe twice lower, or 10 times higher.” In response to Kuhlman’s letter, Prof Lamoree and colleagues said he had “incorrectly interpreted” the data.

Prof Lamoree does agree there is a wider issue. “It’s still a super-immature field and there’s not many labs that can do [these analyses well]. When it comes to solid tissue samples tissues, then the difficulty is they are usually taken in an operating theatre that’s full of plastic.”

“I think most of the, let’s say, lesser quality analytical papers come from groups that are medical doctors or metabolomics [scientists] and they’re not driven by analytical chemistry knowledge,” she said.

Scaremongering

Improving the quality of MNP measurements in the human body matters, the scientists said. Poor quality evidence is “irresponsible” and can lead to scaremongering, said Rauert: “We want to be able to get the data right so that we can properly inform our health agencies, our governments, the general population and make sure that the right regulations and policies are put in place.

“We get a lot of people contacting us, very worried about how much plastics are in their bodies,” she said. “The responsibility [for scientists] is to report robust science so you are not unnecessarily scaring the general population.”

Rauert called treatments claiming to clean microplastics from your blood “crazy” – some are advertised for £10,000. “These claims have no scientific evidence,” she said, and could put more plastic into people’s blood, depending on the equipment used.

Materić said insufficiently robust studies might also help lobbyists for the plastics industry downplay known risks of plastic pollution.

The good news, said Béen, is that analytical work across multiple techniques is improving rapidly: “I think there is less and less doubt about the fact that MNPs are there in tissues. The challenge is still knowing exactly how many or how much. But I think we’re narrowing down this uncertainty more and more.”

Prof Lamoree said: “I really think we should collaborate on a much nicer basis – with much more open communication – and don’t try to burn down other people’s results. We should all move forward instead of fighting each other.”

‘On the safe side’

In the meantime, should the public be worried about MNPs in their bodies?

Given the very limited evidence, Prof Lamoree said she could not say how concerned people should be: “But for sure I take some precautions myself, to be on the safe side. I really try to use less plastic materials, especially when cooking or heating food or drinking from plastic bottles. The other thing I do is ventilate my house.”

“We do have plastics in us – I think that is safe to assume,” said Materić. “But real hard proof on how much is yet to come. There are also very easy things that you can do to hugely reduce intake of MNPs. If you are concerned about water, just filtering through charcoal works.” Experts also advise avoiding food or drink that has been heated in plastic containers.

Rauert thinks most of the MNPs that people ingest or breathe in are probably expelled by their bodies, but said it can’t hurt to reduce your plastics exposure. Furthermore, she said, it remains vital to resolve the uncertainty over what MNPs are doing to our health: “We know we’re being exposed, so we definitely want to know what happens after that and we’ll keep working at it, that’s for sure.”