Nanoparticles in food products
Over the past couple of years a number of articles have been posted claiming that we’re eating more food products containing nanoparticles than we know (remember this piece from a couple of weeks ago?). One of the latest appeared on The Guardian website yesterday with the headline “Activists take aim at nanomaterials in Dunkin’ Donuts” (thanks to @HilarySutcliffe for the tip-off). While I’m sympathetic to the desire for consumers and consumer groups to know what’s going into food products, what caught my eye in this case is an analysis of the amount of nanoparticles in donuts that I just couldn’t make sense of. So I indulged in a bit of nano-donut math.
As You Sow ask for nano-clarity
First thought, the Guardian piece draws on the environmental group As You Sow’s campaign to raise awareness and transparency of the use of nanomaterials in food products, and their recent shareholder resolution to Dunkin’ Brands (who own Dunkin’ Donuts). This resolution requested that Dunkin’ identify products that may contain nanomaterials, and prepare a report assessing the risks of using these substances in foods. (18.7% of shareholders voted for the resolution).
This resolution was in turn
based on based in part on a 2013 report from As You Sow that asked a commercial test lab (Analytical Sciences LLC) to measure the quantity of titanium dioxide (TiO2) nanoparticles in various donut product covered in powdered sugar. [Updated November 16 2014]
Testing donuts for nanoparticles
Ten types of donuts were tested, seven of which listed TiO2 as an ingredient, and nine showed the presence of TiO2. Where TiO2 was detected, quantities measured ranged from 19 µg TiO2 per gram of coating (19 ppm) to 75 µg TiO2 per gram of coating (75 ppm). I’m assuming here that just the coating was tested, as this is where the TiO2 would most likely be used as a whitening agent.
For two of the donut types (Hostess Donettes and Dunkin’ Donuts Powdered Cake Donut), Analytical Sciences LLC separated out the TiO2 nanoparticles from the donuts’ sugar coating, and passed them through a series of filters to measure the mass of particles between certain sizes. They then measured the quantity of TiO2 passing through a filter with 10 nm pores – this was reported as the the amount of TiO2 nanopaticles that were 10 nm in diameter or less in the two donut products.
According to the analysis,
one serving size of Hostess Donettes (three small donuts) would result in the ingestion of 13.8 mg of TiO2 in the nanoparticle size of less than 10 nm, while one serving (one donut) of a Dunkin’ Donut Powdered Cake Donut would result in the ingestion of 8.9 mg of TiO2 less than 10 nm in size.
It’s these figures that caught my eye – they’re massive! [Note: since this post was published As You Sow have reviewed the figures and revised the report]
To give you an idea how massive, here’s the math:
Doing the nano-donut math
If we assume that the Dunkin’ Brands are using approved food grade TiO2 – and there’s no reason why they shouldn’t be, as this is what’s FDA-approved for use, and it contains particles big enough to whiten food (ultra small particles don’t work as a whitener) – it’s possible to calculate what mass of particles would be expected below 10 nm. Using data from a recent paper in the journal Environmental Science and Technology, the Mass Median Diameter of food grade primary particles (based on particle mass) is around 168 nm, and the geometric Standard Deviation of the size distribution is around 1.44. This means that when the size distribution of the individual particles is plotted on a logarithmic axis (the standard approach for analyzing powders), the peak of the mass distribution will be around 168 nm, and 95% of the powder’s mass will lie between particles greater than 81 nm in diameter and less than 348 nm in diameter.
From this, it’s possible to calculate the mass of primary particles smatter than 10 nm that would be expected in food grade TiO2 powder. Doing the math, this comes out at something less that a trillionth of a percent of the powder’s mass being associated with particles smaller than 10 nm! (Note update at the end of this piece)
This is not a typo (I triple checked) – for a lognormal distribution with a Mass Median Diameter of 168 nm and a Geometric Standard Deviation 1.44, less than one trillionth of a percent of the powder will be associated with particles smaller than 10 nm.
In other words, if a Dunkin’ Donut Powdered Cake Donut contained 8.9 mg of TiO2 particles smaller than 10 nm, it would have to have been doused with over 1 million tons of sugar coating! (Note update at the end of this piece)
Clearly something’s wrong here – either Dunkin’ Donuts are not using food grade TiO2 but a nanopowder with particle so small they would be no use whatsoever in the sugar coating (as well as being incredibly expensive, and not FDA approved). Or there’s something rather wrong with the analysis!
If it’s the latter – and it’s hard to imagine any other plausible reason for the data – it looks like As You Sow ended up using rather dubious figures to back up their stakeholder resolution. I’d certainly be interested in more information on the procedures Analytical Sciences used and the checks and balances they had in place, especially as there are a number of things that can mess up a particle analysis like this.
So how many nanoparticles are there in a donut?
Just to round things out here, knowing the rough size distribution of food grade TiO2 does allow an estimation of the likely nanoparticle content in donut sugar coating.
Based on the Yang et al. data cited above, he mass percentage of primary particles smaller than 100 nm in pure food grade TiO2 powder will be around 8% (although powders will vary). Assuming the TiO2 is added to the donut sugar coating at the approved 1% level, the coating could contain around 0.08% by mass TiO2 particles smaller than 100 nm.
This is not insignificant. These estimates do need to be tempered by the reality that the particles will clump together into much larger agglomerates. But even so, it seems food grade TiO2 does contain a decent amount of material in the nanoparticle size range – just not nearly as much as As You Sow would have you think.
Yang et al. Characterization of Food-Grade Titanium Dioxide: The Presence of Nanosized Particles (2014) Environmental Science and Technology DOI: 10.1021/es500436x
The math behind the analysis – http://2020science.org/2014/07/14/nanoparticle-donut-math-crunching-numbers/
Update July 13: Headings added
Update July 14: My bad, I made a slight error in the size distribution calculation first time round. This has been corrected in the article above. Originally, I cited the estimated Mass Median Diameter (MMD) of the TiO2 particles as 167 nm, and the Geometric Standard Deviation (GSD) as 1.6. Correcting an error in the Excel spreadsheet used to calculate the distribution (these things happen!) led to a revised estimate of MMD = 168 nm and a GSD of 1.44. These may look like subtle differences, but when calculating the estimated particle mass below 10 nm, they make a massive difference. With the revised figures, you’d expect less than one trillionth of a percent of the mass of the TiO2 powder to be below 10 nm!! (the original estimate was a tenth of a millionth of a percent). In other words – pretty much nothing! The full analysis can be found here.
Update November 16 2014. Based on this post, As You Sow checked the data from Analytical Sciences LLC and revised the report accordingly. This is noted above.