A ‘microplastic bombshell’ – or why we must remain interested in (and worried about) microplastics

Of course, scientific debate about specific methodologies — especially within a developing field of study like Micro- and nanoplastics — can be helpful and productive, but there are serious concerns about how The Guardian has framed the discussion.

About headlines reframing The Guardian’s initial story 

Other media rapidly picked up on The Guardian’s reporting, and a familiar pattern of reinterpretation and recuperation took hold within days.

Of course, unsurprisingly some plastics industry outlets were among the first to report about The Guardian article. While some limited themselves to paraphrasing the original article, others were quick to state that “New research has cast doubts on claims concerning the scale of harm done to the human body due to the ingestion of microplastics and nanoplastics” or write that “Some scientists are casting serious doubt on high-profile studies claiming that microplastics are widespread throughout the human body”. Other online media made from this, that “Microplastics panic unravels”. And also mainstream media, like The Telegraph appear to follow this reading, declaring that “the Guardian [article suggests] that scientists may be overstating the health concerns”. Notably, in this regard, The Telegraph compares – apparently ‘overstated’ – ‘widespread fear’ of MNPs with tobacco and asbestos; … as if these health hazards turned out to be overstated…

To be clear, neither The Guardian nor the research to which it refers, say that there would be no MNP ending up in the human body. Nor do they question the potential health harm of such MNP – let alone that they would deny such harm to exist.

A closer look at The Guardian’s article and the academic literature it talks about

It must be emphasised that the person declaring the doubts to amount to a “bombshell” is – as The Guardian mentions – a chemist formerly working for the Dow Chemical company, which is one of the world’s biggest plastic producers. To be precise, this person worked his whole career in the chemical industry (24 years Dow and 4 years Union Carbide). Now in ‘semi-retirement’ he runs a YouTube channel which, in all nuance, can best be described as a merchants of doubt project.

Evidently, when that same chemist is the source of one of the criticisms cited, this is not without relevance, and The Guardian would have done well to mention it. The former Dow employee is the single author of a letter to the editors (Kuhlman 2022), criticising Leslie et al.’s (2022) research on MNPs in blood. True, this study by Leslie et al. is also among the 18 papers assessed by Rauert et al. (2025), as again mentioned by The Guardian. Though, confusingly, still another commentary talked about by the newspaper, Uppu et al. (2025) – which for its part criticises Hu et al.’s (2024) findings on microplastic presence in testis – instead refers to that same study by Leslie et al. (2022) in what can only be understood to be a more  favourable way.

This comment by Uppu et al. (2025) lists not less than seven ‘key concerns’ about the testis article. In that context, the authors directly cite ‘(Leslie et al. 2022)’ as a source (listed in full in their References) for both their first and third concern. Uppu et al. (2025) do not say anything more on why precisely ‘Leslie et al. (2022)’ is cited at these occasions: the reference just appears at the end of both comments one and three. Yet, to the best of my reading abilities, I can only understand that reference as either implying that the criticism is directly echoing similar concerns previously raised by Leslie et al. (2022); or that this paper instead is mentioned as an example of good practice – in contrast, that is, to the testis article by Hu et al. (2024) which is the focus of their comment.  Both explanations for the use of Leslie et al. (2022) as a reference are strange. As to the first, upon reading that publication, it is difficult to see how it gives any concrete substance in that sense. The second interpretation – that Leslie et al. (2022) would be cited here as an example of good practice – obviously would contradict both the criticism from Kuhlman (2022) and Rauert et al. (2025).

Adding to this confusion, it should be observed that, like Kuhlman (2022), also the commentary from Uppu et al. (2025) is not free from industry ties. First, as declared at the end, “Funding support for this article was provided by the American Chemistry Council”. Furthermore, the corresponding author, S.M. Hays, and the consulting companies he (co-)founded – Scipinion, and Summit Toxicology, L.L.P – have a history of collaboration with that same American Chemistry Council (ACC). On their website, Scipinion is mentioned once as a ‘collaborating organization’ (referring to an article co-written by S.M. Hays) while Summit Toxicology  L.L.P is mentioned not less than 34 times. Thereof, 33 results redirect to published scientific articles with the repeated involvement from S.M. Hays; and arguably all of which received ACC-funding (as many articles explicitly acknowledge).

Turning to the other studies and comments mentioned by The Guardian, we should wonder how exceptional and special the ‘challenges’ are. On closer look, all of it seems only part of the normal scientific process of debate and discussion among researchers (publication – comments – reply – …). And, overall, comments appear constructive rather than fundamentally critical of all findings.

True, one researcher has called the study by Nihart et al. (2025) on microplastics in the brain, ‘a joke’. Yet, for the good order, he did so on LinkedIn – arguably not the best-suited channel for well-reflected academic debate – and in one of the reactions on the post, his choice of words was disapproved of as not appropriate. I tend to agree with this. Especially on a sensitive topic such as the possible connection between plastic and human health, academics should guard themselves from polarising language that could all too easily be instrumentalised by the petrochemical industry. This is not to say that researchers cannot question others’ work (quite to the contrary) – including in the public sphere; only that it might be advisable to choose words carefully.

Of course, this does not mean that we can simply ignore the ‘Matters Arising’ (Monikh et al. 2025) which as mentioned by The Guardian, was published in response to Nihart et al. (2025). This commentary indeed highlights methodological limitations in the study, which – as it writes – “have general relevance for advancing robust and reproducible MNP detection in human biomonitoring studies”. However, while multiple issues are raised about the analytical technique used by Nihart et al. (2025), to my understanding, the commentary does not put into question the fact that MNPs have been found. Instead, it has questions about the considerably higher concentrations reported for brain samples compared to the liver and kidneys and reflects about the reasons why that might be. Rather than questioning “Human exposure to microplastics and nanoplastics (MNPs) [to be] an emerging concern with potential implications for health” – as the commentary opens – it calls for the scientific community to close ongoing gaps in analytical rigor within the field and as human biomonitoring of MNPs advances, to adopt harmonized practices that promote transparency, reproducibility and confidence in reported findings.

The same we observe with regard to the study by Marfella et al. (2024) on MNPs in atheromas and cardiovascular events. The way The Guardian presents things suggests more conflict than there is. The cited ‘criticism’ actually concerns one of five short ‘letters to the editor’ published together with a reply by the authors of the initial study.  Neither of this is clear from The Guardian’s coverage. Clicking on the provided hyperlink (“[…] criticised for not testing blank samples […]”) only allows the non-subscribed (i.e. non-paying) reader to see part of the first letter – arguably the most critical one. This hinders the public to get a true picture of the nature of the academic debate taking place.

• The first letter by Holda & Batko, raises the issue that “many factors suggest potential external plastic contamination of samples collected in [Marfella et al. (2024)]”. Though, as pointed out in the author’s reply, “the association between MNPs and the incidence of the primary outcome is unlikely to be ascribable to chance since eventual contamination would occur randomly (or in 100% of the samples) and not preferentially in samples obtained from patients who went on to have a clinical event”.
• The subsequent letter by Kalkman et al. asks if “endovascular devices with hydrophilic polymer coatings may also be a potential source of foreign-body embolization”. While in their reply the authors argue why according to them it is “unlikely that the presence of a coronary stent was the only driver of the presence of MNPs in this study”, they also recognise that “the correspondents’ hypothesis deserves to be explored in ad hoc studies”.
• As to the third letter by Ghirga et al., it reflects about the possible relationship with further environmental factors and the fact that “MNPs can attract and accumulate a variety of other contaminants […] [acting] as sponges for toxic metals, polycyclic aromatic hydrocarbons, and other hazardous chemicals”. The letter recognises that “the authors did not find differences in the incidence of MNPs in the plaque according to geographic area” but suggests that this cannot be excluded and such issues therefore are an area for future research; something Marfella et al. agree with in their reply.
• The fourth letter, by Wang & Tian asks about the possible pathway of MNPs, wondering if “[it is] possible that MNPs in the plaques originate from macrophages in the blood”; a possibility which the authors do not exclude, and which they see as a possible topic for further studies.
• The fifth letter by Hugh Glazier, finally, seems not so much directly connected with the initial study. Rather, the author takes it as an occasion to express his worries about the widespread use of single-use plastic in healthcare and the presence of MNPs in much used intravenous fluids.

Clearly, nothing of this – neither the letters, nor the replies – puts into question the observation of MNPs in the human body or the possible harm they might cause there.

Further studies referred to by The Guardian are another publication on MNP in blood (Brits et al. 2024a), commented by Willhelmus et al. (2024) and a subsequent reply from the authors (Brits et al. 2024b); in arteries (Liu et al. 2024), with a letter to the editors about it by Sivan et al. (2024); and in bottled water (Qian-et al. 2024a) receiving criticism from Materić (2024) replied to by the authors in Qian-et al. 2024b.

Again the ‘challenges’, as The Guardian presents it, turn out to be not much else than the normal practice of collaborative scientific development in an evolving field of research. Yes, methodological questions are asked, points of attention raised, proposals for improvement made, …. But none of this therefore questions the presence of MPN and the health concerns this raises. To the contrary. Willhelmus et al. (2024), for instance, refer to microplastics as a topic “of a growing global concern” and recognise the need to further develop accurate identification and quantification of MNPs in biological tissue such as blood to determine the risk to health. It is in that sense that their letter goes into debate with Brits et al. (2024a-b). Also Sivan et al. (2024) are not denying that MNPs are found in the human body (even citing other literature in that regard), nor that these might be harmful to health. Instead, the letter wonders about how the migration of microplastics appears to be size-dependent, and whether organ absorption is influenced by the composition of the MNPs. And it reflects on analytical hurdles and the sensitivity of current equipment for the detection of MNP, and how to develop detection capabilities further.

True, in the case of the bottled water issue, Materić (2024) calls the quantitative assessment of nanoplastics by Qian et al. (2024a) ‘fundamentally unreliable’. Yet, notably in this case (as mentioned by The Guardian), the study’s authors were quick to respond, being quite as direct in expressing their disagreement with the criticism (in turn referring to its suggestions as ‘invalid’ and ‘mislead[ing]’). This should remind us: strong statements might well offer nice soundbites, though they easily risk getting disconnected from the context and content of the initial debate, and going on to live their own life at the disposal of anyone who wishes to use them in support of their own cause, whichever that might be.

Need for precaution: research on MNP in the human body – challenges remain, and that is normal (and does not mean we do not already know things, and they are worrying)

All of this is not to say that there are no challenges, problems, and shortcomings with research on MNPs in the human body. There certainly are, and that is normal; especially as this is a nascent field. Current analytic methods for the quantification of polymers in human biological matrices, such as blood, can still be confronted with multiple limitations and inaccuracies (as assessed by Rauert et al. (2025), talked about in The Guardian).  And it might even be that “at present, there is hardly any reliable information available on the actual distribution of microplastics in the body”, as The Guardian this time quotes Janzik et al. (2025). Yet, this does not mean that MNP do not enter the body , some of which “could reach the tissues or the bloodstream depending on their size and become systemically bioavailable”; this does not mean that by now it is not “considered certain that humans are exposed to microplastics via food, products, and the environment”, as the same article writes.

It might be that at present “no causal relation between [MNP] uptake and any health effects has yet been proven”, and that “Current evidence does not permit any definitive conclusion about the effects of microplastics”, but this does not deny that “Microplastics have been found in organs and tissues (e.g., placenta, atherosclerotic plaques)” – again from the same article. Plastics do contain numerous hazardous chemical compounds that inflict well-demonstrated harm, and microplastics are known to act as vectors transporting these health-harming chemicals into our bodies, as scientists’ responses to the ‘bombshell article’ reiterate yet again. That should be reason enough to worry and drive continuous research.

The fact that there might still be analytical uncertainties, knowledge gaps, many unknowns, … is not a reason for feeling reassured; and in no way is it proof of no harm as some are now quick to insinuate. Quite to the contrary. There is by now enough evidence that MNPs are ending up in our bodies, that some remain, and plausibly do cause harm. If anything, today’s uncertainties should be a call for intensifying inquiry. Yet also – and importantly – the development of such further research should not be an argument to delay action. On top of the many other environmental problems related to plastics, what we start to know about the possible health implications of MNPs is only more reason to urgently act and to drastically cap both production and consumption of plastic.