Growing use of nanoparticles raising questions for researchers

Paul Westerhoff portrait

ASU engineering professor Paul Westerhoff is among researchers taking a close look at the potential impacts of nanoparticles in products.

Posted on: August 14, 2012

As the use of nanoscale materials in consumer goods increases – including in food, personal care products and medicine – researchers are exploring the possible health and environmental impacts of exposure to nanoparticles.

More and more products contain titanium, silver or zinc that is nano-sized by being burned or crushed into an extremely fine dust and then used as ingredients in products or as a coating.

Such nanomaterials can make products more resilient and effective.

Among those leading research on the effects of nanoparticles is Paul Westerhoff, associate dean of research in Arizona State University’s Ira A. Fulton Schools of Engineering, and a professor in the School of Sustainable Engineering and the Built Environment.

A telling study on the subject co-authored by Westerhoff and published in the journal Environment Science and Technology raises many of the questions about nanoparticles use that are now the focus of news media reports such as a recent series in the Montreal Gazette.

Westerhoff is quoted extensively in one of the articles in the series: The Gazette (Montrealgazette.com)

Link to article: http://pubs.acs.org/doi/abs/10.1021/es204168d

Article abstract: Titanium dioxide is a common additive in many food, personal care, and other consumer products used by people, which after use can enter the sewage system and, subsequently, enter the environment as treated effluent discharged to surface waters or biosolids applied to agricultural land, incinerated wastes, or landfill solids. This study quantifies the amount of titanium in common food products, derives estimates of human exposure to dietary (nano-) TiO2, and discusses the impact of the nanoscale fraction of TiO2 entering the environment. The foods with the highest content of TiO2 included candies, sweets, and chewing gums. Among personal care products, toothpastes and select sunscreens contained 1% to >10% titanium by weight. While some other crèmes contained titanium, despite being colored white, most shampoos, deodorants, and shaving creams contained the lowest levels of titanium (<0.01 μg/mg). For several high-consumption pharmaceuticals, the titanium content ranged from below the instrument detection limit (0.0001 μg Ti/mg) to a high of 0.014 μg Ti/mg. Electron microscopy and stability testing of food-grade TiO2 (E171) suggests that approximately 36% of the particles are less than 100 nm in at least one dimension and that it readily disperses in water as fairly stable colloids. However, filtration of water solubilized consumer products and personal care products indicated that less than 5% of the titanium was able to pass through 0.45 or 0.7 μm pores. Two white paints contained 110 μg Ti/mg while three sealants (i.e., prime coat paint) contained less titanium (25 to 40 μg Ti/mg). This research showed that, while many white-colored products contained titanium, it was not a prerequisite. Although several of these product classes contained low amounts of titanium, their widespread use and disposal down the drain and eventually to wastewater treatment plants (WWTPs) deserves attention. A Monte Carlo human exposure analysis to TiO2 through foods identified children as having the highest exposures because TiO2 content of sweets is higher than other food products and that a typical exposure for a US adult may be on the order of 1 mg Ti per kilogram body weight per day. Thus, because of the millions of tons of titanium-based white pigment used annually, testing should focus on food-grade TiO2 (E171) rather than that adopted in many environmental health and safety tests (i.e., P25), which is used in much lower amounts in products less likely to enter the environment (e.g., catalyst supports, photocatalytic coatings).

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