Nanoparticles – One Word: A Multiplicity of Different Hazards
Twelve leading scientists have published a memorandum in the journal Nanotoxicology, in an effort to draw attention to how the term "nanoparticles" is being used indiscriminately, particularly in the titles of scientific papers and statements to the press.
They cite, as a recent example, a paper that linked nanoparticles to seven very serious cases of occupational lung and pleural injury, two of which resulted in death, in China. The article's title, "Exposure to nanoparticles is related to pleural effusion, pulmonary fibrosis and granuloma", they say, is dangerously misleading, and draws a link between generic nanoparticles and the observed effects. The title indicates that a new, causative link between nanoparticles and severe, even fatal, lung condition, has been identified, when, the scientists argue, this conclusion is premature and requires more data to support such a link. The writers of the memorandum respectfully remind the scientific community, and all who publish and review papers on the human health impacts of engineered nanomaterials, to consider the following: "[E]nsure that all descriptions of nanoparticle hazards recognize the intrinsic heterogeneity of the nanoparticle hazard and discuss the uncertainty of alleged causality; Ensure that there is a convincing and scientifically sustainable link between any nanoparticle exposure and any pathological outcomes putatively associated with that exposure; and, Ensure that sufficient physical and chemical characterization data are provided on the nanoparticles in question to support valid data interpretation and comparison."
We, the undersigned, would like to draw the attention of the nanotoxicology community to how the term “nanoparticles” is being somewhat indiscriminately used, especially in the titles of scientific papers and in statements to the press. This has been common in the past without stating the nature of the nanoparticle being studied. Five years into serious hazard-based toxicology of manufactured nanoparticles and 20 years into the toxicology of environmental ultrafines, we know that there is a clear spectrum of toxicity associated with nanoparticles, and that failing to differentiate between different chemistries, sizes, shapes and other attributes can cause confusion. We can no more generalize about ‘nanoparticles’ than we can about ‘particles’ more widely.
No self-respecting researcher would dream of publishing results showing, for example, that quartz was a genotoxin under the title ‘Particles are genotoxic’. Generalizations like these are unhelpful and unscientific, and potentially dangerous in the wrong hands. Exactly the same applies for research into the toxicology and potential impacts of nanoparticles. Yet in 2009, papers are still appearing that explore the activity of a small range of nanoparticle types, yet uses the term ‘nanoparticle’ in its broadest sense in the title as though it was a generically useful term representing one class of hazard.
This issue has been highlighted by a recent paper that linked nanoparticles in the most general sense to seven very serious cases of occupational lung and pleural injury occurring in China (Song et al. 2009). The exposures were not characterized, but histological assessment of lung biopsies and pleural fluid indicated the presence of nanoparticles with an unidentified origin or chemistry. Despite a lack of information on the nature of the nanoparticles, the research was published under the title ‘Exposure to nanoparticles is related to pleural effusion, pulmonary fibrosis and granuloma’.
While it is possible that the observed nanoparticles could have played a role in the health effects reported amongst the seven workers, it is our contention that the link drawn between generic nanoparticles and the observed effects is unjustified, and is dangerously misleading. The type of severe lung injury described as a result of this exposure has never been seen with any conventional nanoparticle exposure except possibly Teflon fumes which were nanoparticulate in nature but which contained highly toxic free radicals. The magnitude, nature and composition of the occupational exposures in the Chinese incident were not measured; neither was the composition of the nanoparticles found in biological samples. The exposure was chemically very complex, consisting of sprayed polyacrylate particles and thermo-degradation products of polystyrene. Toxic gaseous species may well have adsorbed onto nanoparticle surfaces. The workers were spraying large quantities of polyacrylate powder in a small, unventilated space – inhalation exposure to which is well-documented to cause a range of injurious effects in rat lungs (Zondlo 2002). In short, the study offers only tentative evidence for an association between exposure to a specific category of nanoparticles and the health effects observed; it does not provide any evidence for generic nanoparticle hazard.
In our opinion the authors and the reviewers of the paper were remiss in publishing it with the existing title. As a clinical study, the authors were limited in their ability to reconstruct exposures or to assess the nature of the material the workers were exposed to. However, given these limitations, they would have been advised to present their findings with appropriate caveats, and not to have implicated generic nanoparticles where no implication was justified. At a minimum, the authors should have identified the composition of the nanoparticles found in biological samples – a simple, yet important step toward interpreting their observations. As it stands, the paper brings into question the peer review process that led to its publication, and raises the spectre of misinformed public dialogue on nanoparticle toxicity.
We acknowledge, of course that the reporting of severe and unusual respiratory disease amongst seven workers, leading to two deaths, is very important. There is a long history of publishing clinical studies of this nature in the peer-reviewed literature. Yet, this does not excuse an unjustified focus on generic nanoparticles as the causative agent in the paper, or in the paper’s title
This paper appeared in a reputable scientific respiratory journal, supposedly identifying a new causative link between nanoparticles and an evolving severe, even fatal, lung condition. In our opinion this conclusion is at the very least premature and requires much more data in support of the link to the nanoparticle exposure given the concomitant chemical exposure. Indeed, it remains entirely possible that the nanoparticles were an epiphenomenon and had no relation to the reported pulmonary toxicity. As a result, the paper does little to advance the state of the science. Yet by publishing it – and by issuing a press release emphasizing the speculated association between “nanoparticles” and pulmonary disease, the journal has promulgated the myth of generic nanoparticle toxicity, and potentially misled the public and the media into believing there is some reason to fear “nanoparticles”.
The scientific community is still learning how to best approach an understanding of the potential risks associated with new and emerging nanomaterials. Yet there is growing consensus that generic nanoparticles are not a toxicologically unique class of material, and that there is a danger of ill-informed studies slowing down scientific progress, while encouraging misinformed dialogue and decision-making. In the light of the Song et al. paper, we seek to respectfully remind all researchers who publish and review papers on the human health impacts of engineered nanomaterials, and who communicate with the media, the public and decision-makers, to bear this in mind and to:
- Ensure that all descriptions of nanoparticle hazards recognize the intrinsic heterogeneity of the nanoparticle hazard and discuss the uncertainty of alleged causality;
- Ensure that there is a convincing and scientifically sustainable link between any nanoparticle exposure and any pathological outcomes putatively associated with that exposure; and
- Ensure that sufficient physical and chemical characterization data are provided on the nanoparticles in question to support valid data interpretation and comparison.
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