Pick up a jar of chili powder, and the chances are it will contain a small amount of fumed silica – an engineered nanomaterial that’s been around for over half a century. The material – which is formed from microscopically small particles of amorphous silicon dioxide – has long been considered to be non-toxic. Amorphous silica is widely used as a flow agent in food powders – it’s what stops chili powder clumping together and sticking in the jar – and the Food and Drug Administration allows up to 2% by weight in food products. Yet recent research is beginning to question assumptions over the material’s safety.
In this month’s edition of the journal Nature Nanotechnology, I examine previous reviews of fumed silica safety, alongside two recent studies that suggest it may not be as benign as originally thought.
Fumed silica may be more toxic than thought
To cut a long story short, recent research suggests that there are toxic chemical groups that form on the surface of fumed silica during production, and that high exposure to sensitive parts of the body could be harmful. However, the weight of evidence from cell and animal studies suggests that ingesting small amounts of fumed silica is not harmful.
That’s the good news. But in many ways, this is just the backstory to a more challenging issue raised in the article – when surprising new insights emerge on possible material health risks, where does the responsibility lie for ensuring that new research is conducted on material safety, without this research influencing consumers and regulators before there is plausible justification for action?
Published research and public discourse
Newly published research is becoming increasingly influential in public discourse – academic institutions regularly publicize and push papers through press releases; peer review publications are becoming easier for anyone to access; and advocacy groups are getting more adept at promoting research that supports their cause. Yet in this highly laudable democratization of knowledge, there is a real danger of over-extrapolating interesting findings to ill-advised actions.
The problem is, not all research is equal when it comes to making decisions. In the case of fumed silica, Haiyung Zhang and colleagues demonstrated in 2012 that fumed silica is chemically more active than previously thought, and that it is capable of causing damage to specific cells under specific conditions. Then earlier this year, Meike van der Zande and colleagues showed that if rats are fed enough fumed silica, there was evidence of liver damage.
New research
Both of these studies are important in understanding the biology of fumed silica, and indicating where there may be unexpected and unforeseen risks. Yet in themselves they do not indicate risk to human health. Zhang and colleagues demonstrated higher than expected chemical activity in fumed silica and the ability of the material to damage specific cells under highly specific conditions, but did not indicate in any way what might happen when the material is plunged into the highly corrosive environment of the stomach. van der Zande and colleagues did look at ingestion in animals – but at massive concentrations: They observed fibrosis in the livers of some animals, but these rats were eating the equivalent of over five breakfast cereal servings of fumed silica per day, for three months. In contrast, there is extensive evidence that ingesting fumed silica at lower doses does not lead to observable health effects.
Research to decisions
And here’s the dilemma: It’s critically important that research like that of Zhang’s and van der Zande’s is carried out, so that we have a better idea of how these materials interact with our bodies, and researchers get a clearer sense of important and relevant research questions. But research like this is too tentative and premature to support decisions that can have profound impacts on lives and livelihoods.
How then can such research be encouraged, while ensuring it does not have undue influence in decision-making?
As I note in this month’s Nature Nanotechnology, responsibility for clarifying the distinction between discovery and action must fall in part on the scientific community. With increasing pressure to demonstrate the relevance of research, it’s all too easy to extrapolate from interesting findings to implied calls for action. Yet what is academically fascinating can quickly translate into unwarranted doubt and concern among constituencies, and from there to poorly conceived decisions. Rather, the privilege of scientific insight should come with the responsibility to use this insight with care and consideration.
Responsible research
In other words, responsible research must extend to taking some responsibility for how research findings are used and applied. Traditionally, the role of scientists in public discourse has often ended at the point of publication. Yet there’s increasing pressure to comment – either in the conclusions to papers or in associated press releases – on the actions consumers, policy makers and others should be making based on published research. And while I am a strong advocate for scientists engaging in public discourse, naive recommendations based on tentative data run the risk of doing more harm than good.
And fumed silica? As I conclude in the article,
Based on the available evidence, fumed silica in food is acceptably safe. It may be that future research leads to a re-evaluation of its safe use. But it would at this point be irresponsible to question its use on the grounds of a cell-based study that did not address behaviour in the gastrointestinal tract, and because the material falls under the umbrella of ‘engineered nanomaterials’. It would be equally irresponsible to curb research on the potential hazards and risks of fumed silica under the assumption that there is nothing else to discover about how it behaves in the body. And it would most definitely be irresponsible for researchers not to support consumers, policymakers, the media and others in understanding the distinction between exploratory research and that aimed at informing decisions.
Useful links:
Old materials, new challenges? Nature nanotechnology 9, 658-659. DOI: 10.1038/nnano.2014.196
The fumed silica Aerosil® (Evonic)
European Commission Joint Research Centre Synthetic Amorphous Silicon Dioxide (NM-200, NM-201, NM-202, NM-203, NM-204): Characterisation and Physico-Chemical Properties. JRC Scientific and Policy Reports, JRC 83506 (Publications Office of the European Union, 2013).
Code of Federal Regulations Title 21, Vol. 3, 21CFR172.480 (US FDA, 2013)
European Center for Ecotoxicology and Toxicology of Chemicals Synthetic Amorphous Silica (CAS No. 7631-86-9), JACC No. 51 (ECETOC, 2006)
Zhang, H. Y. et al. (2012) Processing Pathway Dependence of Amorphous Silica Nanoparticle Toxicity: Colloidal vs Pyrolytic J. Am. Chem. Soc. 134, 15790–15804. DOI: 10.1021/ja304907c
van der Zande, M. et al. (2014) Sub-chronic toxicity study in rats orally exposed to nanostructured silica. Part. Fibre Toxicol. 11, 8 (2014). DOI: 10.1186/1743-8977-11-8
Maynard, A. (2014) Is novelty overrated? Nature Nanotech. 9, 409–410. DOI: 10.1038/nnano.2014.116