Titanium dioxide nanoparticles in food and personal care products

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-) TiO(2), and discusses the impact of the nanoscale fraction of TiO(2) entering the environment. The foods with the highest content of TiO(2) 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 TiO(2) (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 TiO(2) through foods identified children as having the highest exposures because TiO(2) 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 TiO(2) (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).

Figure 1

SEM images of E171 (left) and P25 (middle) TiO₂. The sample on the right is from the dissolved hard coating on a chewing gum (Trident White) after it was placed in water and the supernatant filtered onto a 20-nm filter; samples were confirmed by EDX to be titanium and oxygen.

Figure 2

Normalized Ti concentration in food products. For the top 20 products (upper), error bars represent the standard deviation from samples digested in triplicate. The bar-and-whisker diagram (lower) for all products shows the minimum and maximum values as whiskers and the lower-quartile, median, and upper-quartile as the box.

Figure 3

Histogram of the average daily exposure to TiO₂ for the US population (Monte Carlo simulation). Error bars represent the upper and lower boundary scenarios.

Figure 4

Total titanium concentration for PCPs. Black bars are sunscreens with TiO₂ listed on the label. Grey bars are toothpastes with TiO₂ listed on label. Open bars are for products whose labels did not reference TiO₂.