Microplastics are everywhere. We drink them in our water, we eat them in our food, we breathe them in our air, leading to – so we are told – alarming levels of plastic accumulating in our tissues.

So it was somewhat of a shock this week when the Guardian published a “bombshell” article suggesting that scientists may be overstating the health concerns. The award-winning journalist Damian Carrington, a champion of green issues, accepted that he himself had warned of the dangers, but said there was mounting concern over the technology used to detect tiny pieces of plastics in the body.

The article followed a recent letter published in Nature Medicine which questioned the analytical techniques used to detect microplastics in human tissue, warning they lacked controls and validation. One of the signatories, Dr Dusan Materic, of the Helmholtz Centre for Environmental Research in Germany, argued that fat in the body can give a false positive for polyethylene, and said the obesity epidemic could be behind the perceived rise in bodily plastic.

Most studies ‘are not scientifically convincing’

Dr Fazel Monikh, of the University of Padua, Italy, another signatory, who has spent a decade working on the detection of nanomaterials in biological samples, says he has never come across the kinds of microplastics reported in recent studies. “When particulate materials enter a living organism, including the human body, they undergo biotransformation,” he tells The Telegraph.

“Even if one were to assume the highly unlikely scenario in which an intact particle reaches a protected compartment, such as the brain, and is then successfully detected, it would not retain the appearance shown in most of the reported data.

“For these reasons, most of the presented results and their interpretation are not scientifically convincing to me, nor to my colleagues who are experts in this field.”

Microplastics were first detected in the human body in 2018 when Austrian scientists analysed stool samples of people in eight countries – including Britain – and found every one contained the tiny particles. Such research is not in doubt, and there is good evidence that humans do ingest tens of thousands of plastic particles each year. The sticking point is whether these become embedded in tissues, causing long-term harm.

The problem seems to lie in the tinier versions of microplastics, known as nanoplastics.

Officially, microplastics are no larger than 5mm in size (the size of a grain of rice or smaller) whereas nanoplastics are 1nm to 1,000nm in size (as small as bacteria) and are a lot harder to detect. In recent years, studies have claimed to have found these miniscule particles in nearly every human organ and tissue, including the lungs, liver, kidneys, heart, brain, placenta, testicles, bone marrow and blood.

It is feared that these tiny intruders carry toxic chemicals which cause inflammation and cell damage, as well as disrupting hormones, damaging microbes in the gut, lowering IQ, decreasing fertility and increasing the risk of cardiovascular disease, cancer, heart attacks and strokes. The paper which sparked the recent Nature Medicine rebuttal letter claimed to have found microplastics and nanoplastics in the brain, which the scientists behind it linked to dementia.

Such studies have sparked a wave of eco-anxiety, with people switching to plastic-free tea bags and ditching water bottles, kitchen sponges, polyethylene chopping boards and non-stick saucepans.

Methodological concerns

But there are concerns that because microplastics are so prevalent in the environment it is difficult to tease out whether they really are getting into human tissue, or if samples are just contaminated during the process of collecting and analysing them. Lab testing should include “blanks” – control samples of clean water or inert material processed like real samples to detect contamination – but many studies do not.

Fay Couceiro, professor of environmental pollution at the University of Portsmouth says: “I don’t think that there is any doubt that there are microplastics in us – they are everywhere and we are breathing and eating them daily, so that they are in us is inevitable.

“I think the question raised is more about where in the body they are stored and what quantity there is.

“Some studies – particularly those based on humans – don’t follow the full standard methodologies used in environmental sampling around blanks, replicates and recovery checks.”

With large microplastics, scientists can easily spot particles under a microscope and then fire a laser at them to see if they are plastic. But with nanoplastics, scientists must burn the particle and measure the gases emitted, which is less reliable and still in its infancy as a technique.

This unreliability of testing has made researchers more sceptical about the more alarmist findings. An abstract presented at the European Society of Human Reproduction and Embryology last year showing microplastics in human reproductive fluids was met with raised eyebrows among scientists.

“Many previous scary-sounding headlines on microplastics in blood and food have turned out to be measurement errors,” warns Oliver Jones, professor of chemistry at RMIT University, Melbourne, referring to reports that preceded last year’s findings.

Likewise, separate claims that microplastics had been found in human blood in 2022 were criticised by a US chemist as being “consistent with incidental or accidental contaminations”, in a letter to the Environmental International journal.

Even Dr Philipp Schwabl, of the Medical University of Vienna, who found the original evidence of microplastics in human bodies is unsure about their health impacts. “The question of how harmful these little foreign plastic bodies truly are remains open to me and thus constitutes a crucial field of environmental biology that remains to be scientifically elucidated,” he says.

‘It is still a serious issue’

Yet despite the testing issues, many experts are still convinced microplastics are causing harm.

Prof Philip Landrigan, a paediatrician and epidemiologist at Boston College in the US, led a recent review into microplastics for the Lancet, and says people should not dismiss the dangers. “The Guardian article is accurate in pointing out that there is work to be done in refining, standardising and harmonising the analytical techniques for examining microplastics in tissue samples,” he says.

“There is a need especially to distinguish microplastics from lipids [fats]. But the Guardian is wrong in implying that this whole area of science is rubbish.

“The presence of microplastics in the human body needs to be taken seriously, even if we don’t yet know all the ways in which they may harm health. They cannot be wished away.”

The Medical University of Vienna recently developed a new imaging technique which can detect plastics without needing to burn up samples. They say it reduces contamination risk and allows scientists to find direct correlations between tissue samples and disease.

And Dr Matthew Campen, of the University of New Mexico, lead author of the brain study that was challenged in Nature Medicine, said his team had hosted a microplastics conference in the last few days in which “convincing” new evidence had been presented of particles in cerebrospinal fluid. “Our paper is actually very clear on where uncertainties lie and how these may impact the interpretation of results,” he added. “We are 100 per cent confident that nanoplastics are in the brain.”

Prof Lukas Kenner, deputy director of the Department of Pathology at the Medical University of Vienna, says: “The concerns raised are understandable but a blanket dismissal of the entire body of evidence is not scientifically justified.

“While early studies certainly had methodological limitations, the field has advanced rapidly.

“There is now good evidence that microplastics can enter and accumulate in the human body, and growing experimental evidence that they are biologically active rather than inert.”

For now, it seems the scientific community is split on the true impact of microplastics and it may be several years before consensus is reached on the harms. The debate over the extent to which they enter and remain in human bodies will be a key part of those discussions.

While some fear that plastics could be the modern-day equivalent of asbestos, lead or tobacco, it may be that the particles are processed or ejected by the body before they do long-term damage.

Prof Christian Dunn, an expert in microplastic pollution at Bangor University in Wales, says: “When it comes to nanoplastics I think we’re still pushing the boundaries as to what we can confidently detect.

“The extent of how much of this plastic is entering and accumulating in our organs, and the damage this is doing to us, is still up for scientific discovery.”