There Are Probably No Nanoparticles in Your Food… At Least, Not Intentionally

Recently, Mother Jones posted an article about “Big Dairy” putting microscopic pieces of metal in food. Their main source is the Project on Emerging Nanotechnologies and its Consumer Products Inventory, a collaboration between the Wilson Center and Virginia Tech. Unfortunately, the Mother Jones piece seems to misunderstand how the CPI is meant to be used. But another problem is that the CPI itself seems poorly designed as a tool for journalists.

So what’s the issue? The Mother Jones piece mainly focuses on the alleged use of nanoparticles of titanium dioxide (TiO2) in certain foods to enhance colors, making whites whiter or brightening other colors. First, the piece makes an error in its description of TiO2 as a “microscopic piece of metal”. Titanium is a metal, but metal oxides are not, unless you consider rust a metal (which would also be wrong). But another issue is “microscopic”. Just because something is microscopic, which generally means smaller than your eye can see, doesn’t mean it’s a nanomaterial. The smallest thing you can see at a normal reading distance is about a tenth of a millimeter, which is 1000 times bigger than the 100 nanometer cut-off we typically use to talk about nanoparticles.

A clear glass dish holds a bright white powder.

Titanium dioxide is a vivid white pigment, even as macroscopic particles.

And that’s what confuses me most here. As you can see above, titanium dioxide is white as a powder, but in that form it’s several hundred nanometers wide at minimum, if not on the scale of microns (1000 nanometers). In fact, nanoparticles of TiO2 are too small to scatter visible light and so they can’t appear white. A friend reminded me how sunscreens have switched from large TiO2 particles to actual nanoparticles precisely because it helps the sunscreen go on clearer. I’m not naive enough to think food companies wouldn’t try to cut a buck to help improve and standardize appearances, but I also don’t think food scientists are dumb enough to pay for a version of a material they can’t fulfill the purpose they’re adding it for. So TiO2 is probably used in some foods, but not on a nanoscale that radically changes it’s health properties.

But I don’t entirely blame Mother Jones. The thing is, the main reason I had a hunch the article seemed wrong is because one of my labmates at UVA has been working with TiO2 nanotubes for the last three years, and I’ve seen his samples. If I didn’t know that, and I just saw PEN include TiO2 on its list of nano additives, I would be inclined to believe it. PEN saw the Mother Jones piece and another similar article and responded by pointing out that the inventory categorized their inclusion of TiO2 in the products as having low confidence it was actually used. But their source is an environmental science paper including actual chemical analyses of food grade TiO2, so why do they give that low confidence? Also, PEN claims the CPI is something the public can use to monitor nanotechnology in products, so maybe they should rethink how confident they are in their analysis if they want to keep selling it that way.

The paper CPI references in the TiO2 claim is interesting too. That paper actually shows that most of the TiO2 is around 100 nm (figure below). But like I said, that’s kind of pushing the limit on how small the particles can be and still look white. It might be that the authors stumbled across a weird batch, as they note that in liquid products containing TiO2, less than 5% of the TiO2 could go through filters with pores that were 450 nanometers wide. Does the current process used to make food grade TiO2 end up making a lot of particles that are actually smaller than needed? Or maybe larger particles are breaking down into the smaller particles that Weir sees while in storage. This probably does need more research if other groups can replicate these results.

A histogram showing the distribution of particle sizes of TiO2. Categories go from 40 nanometers to 220 nanometers in intervals of 10. The greatest number of particles have diameters of 90-100 or 100-110 nanometers.

Distribution of TiO2 particle sizes in food grade TiO2. From Weir et al, http://pubs.acs.org/doi/abs/10.1021/es204168d?journalCode=esthag

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