Let’s Get Small

June 19, 2011

My friend Mike from Edinburgh writes expressing some concern about nanomaterials in food. I blogged about nanotechnology over a year ago, but Mike has a question that may be of more general interest.

Some of my colleagues are concerned about the welfare implications for lab animals used in testing for such risks, and we are also wondering whether there is any cause for concern about the welfare of farm animals if (or when) such materials are used in their feed. Can you give me a view on these issues? Are nanomaterials already in use in either food or feed, or likely to be so in the near future?

I get asked questions like this all the time. Well, maybe not while I’m riding the bus or shopping for orange juice, but I have been asked a version of this question four or five times already this year. So I’m using the blogosphere to post an answer.

In reference to your question, Mike, my short answer would be that I am unaware of any reason for concern. The long answer is quite long.

On the one hand, many water soluble substances effectively become nanomaterials when dissolved in water (or the bloodstream, as it were), though the surface tension of the fluid itself regulates their movement through body tissues somewhat. Hence it would be false to say that there are no nanomaterials used in food. That is not what anyone is worried about, but it is akin to the way that people worried that genes were appearing in food for the first time after they heard about GMOs.

The most intractable risk debates in nanotechnology involve engineered nanoparticles: carbon nanotubes and other durable structures whose novelty and irregularity challenge classic toxicological methods. No engineered nanoparticles are being intentionally used in food or feed in so far as I know. They are being used in things like tires, so we can’t guarantee that they don’t get into food, and I do think that there is some basis for being concerned about this, but I’m assuming that this, too, is not really germane to the question you asked. I’m assuming your question is about the intentional introduction of nanoparticles into food.

That brings me to a middle group. These include 1) nano or near-nano sized particles of natural non-soluble substances like silver, zinc oxide etc.; 2) nozzles that produce fine mists of nano-sized droplets of liquids that will more rapidly penetrate the surface of a leaf, skin or hide; and 3) nano-thin layers of fats, oils, sugars, and clays that can be used either as barriers (like on a food package) or as capsules. All of these are being used in the food industry, and could potentially be used in feed, though I have not heard of this.

Unlike engineered nanoparticles, tests on these nanomaterials are amenable to classic toxicological methods. This means, on the one hand, that they DO NOT represent a major challenge to regulatory methods and procedures. On the other hand, this fact does not in itself imply that they are safe. They are as likely (but no more likely) to be safe as any other chemical or substance that is used as a food additive, as an aid in processing or as an ingredient. So with this important group, it is entirely possible that there is room for concern, but it would be misleading to say that the basis for concern lies in the fact that they are nanomaterials. The concern would be tied to the possibility of classic dose-related toxic responses, and to the question of whether current regulatory capabilities are adequate to the task with which they are charged.

Now we are almost done, except that since chemical reactions occur on the surface of particles, the mass of the particle is a much less reliable indicator of reactivity (including toxicity) than surface area. However, it is much easier to determine mass than surface area–you just weigh it. So many toxicological standards in common use are calibrated to mass, rather than surface area. This is probably fine if you are a talking about stuff you measure out in spoonfuls, but when particles get very small (and certainly well before they get to the nano scale) surface to mass ratios start to vary enormously, and mass no longer serves as an adequate proxy for surface area.

SO it would be quite irresponsible to use a mass-based toxicity standard to estimate a dose-response relationship for particles at even the micro scale, much less the nanoscale. Generally, food chemists and regulators know this. But would the food or feed industry ever think about doing something that people in the know generally believe to be “quite irresponsible”? I leave that question to you. Form your own opinion.

Again, I’m not sure that it’s the nano-thing that we should be worried about here, so I’m going to stick with my short answer even if my now long, arcane and somewhat qualified answer to your question of whether there is anything to be concerned about may seem less than comforting.

Paul B. Thompson is the W.K. Kellogg Professor of Agricultural, Food and Community Ethics at Michigan State University

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