Potential for Inhalation Exposure to Engineered Nanoparticles from Nanotechnology-Based Cosmetic Powders

Background: The market of nanotechnology-based consumer products is rapidly expanding, and the lack of scientific evidence describing the accompanying exposure and health risks stalls the discussion regarding its guidance and regulation. Objectives: We investigated the potential for human contact and inhalation exposure to nanomaterials when using nanotechnology-based cosmetic powders and compare them with analogous products not marketed as nanotechnology based. Methods: We characterized the products using transmission electron microscopy (TEM) and laser diffraction spectroscopy and found nanoparticles in five of six tested products. TEM photomicrographs showed highly agglomerated states of nanoparticles in the products. We realistically simulated the use of cosmetic powders by applying them to the face of a human mannequin head while simultaneously sampling the released airborne particles through the ports installed in the mannequin’s nostrils. Results: We found that a user would be exposed to nanomaterial predominantly through nanoparticle-containing agglomerates larger than the 1–100-nm aerosol fraction. Conclusions: Predominant deposition of nanomaterial(s) will occur in the tracheobronchial and head airways—not in the alveolar region as would be expected based on the size of primary nanoparticles. This could potentially lead to different health effects than expected based on the current understanding of nanoparticle behavior and toxicology studies for the alveolar region.

. Descriptive statistics of the size distributions of cosmetic powders by number during their application to human mannequin face as measured by the Aerodynamic Particle Sizer (APS). These size distributions are shown in Figure 5 Fig. 1. Size distributions of airborne cosmetic powders by mass during their application to human mannequin face as measured by the Aerodynamic Particle Sizer (APS): 0.6 -19.8 µm measurement size range. The data represent averages of three repeats with error bars representing ± one standard deviation based on these repeats. Nanotechnology-based cosmetic powders are shown in black symbols, regular ones are shown in white symbols.

Material Visibility with TEM
Only certain types of nanoparticles, e.g. certain metal, metal oxide, other inorganic and some organic nanoparticles absorb and scatter electrons enough to be visible in TEM micrographs (Egerton et al. 2004). Weak phase objects (mostly organic material) have low electron contrast and are consequently not visible in TEM images.

Mastersizer 2000's Operation
The laser light undergoes scattering, diffraction, and absorption by the airborne material, which results in varying intensities of the signal measured by large angle, focal plane, and backscatter detectors (Malvern Instruments Ltd 2011). The size, shape, and nature of the particles determine light scattering through reflection and refraction. The light resulting from diffraction depends solely on the geometric cross-section of the particle. Absorption is determined by the size and nature of the particles (Hackley et al. 2004). Mie theory is applied to determine particle size distribution.
The primary measurement unit is particle volume concentration. The instrument's software converts volume based scattering data into a particle size frequency distribution. For non-spherical particles, their size is reported as volume-equivalent diameter of a sphere.

Choice of the Inhalation Flow Rate
The U.S. EPA 1997 Exposure Factors Handbook (Table 5-14) recommends the used inhalation flow rate specifically for short-term exposures for our chosen user/activity profile. We believe that our choice of the recommended inhalation flow rate for shortterm exposures matches the type of inhalation exposure expected during cosmetic powder application (short-term exposure) and is the most realistic relative to the activity level expected during cosmetic powder application. This inhalation flow rate slightly exceeds the inhalation flow rates referenced for sedentary activity defined as sitting and standing (Table 5-6) and as car driving and riding (Table 5-7). We find it consistent with our referenced inhalation flow rate since application of a cosmetic powder would occur during both sitting or standing, but performing the physical activity required for the application of a product and the same application but during a visit to a public bathroom or a similar place of retreat where a cosmetic powder application process would follow physical movement that would be more intense than simply standing or sitting, which would result in a somewhat higher inhalation flow rate.

Electron Beam Sensitivity
When material is irradiated in TEM above a certain magnification setting (Carlo et al. 2002;Leapman and Sun 1995 ;Turgis and Coqueret 1999), higher electron beam power density per unit area of the sample results in physical and/or chemical alteration of the tested material (Egerton et al. 2004;Hobbs 1987). During the TEM analysis, this process can be observed visually. As mostly organic nanoparticles tend to be beam sensitive (Egerton et al. 2004), it can be concluded with some degree of certainty about organic or inorganic nature of nanoparticles in the tested products based on beam sensitivity.

Airborne Particle Measurement Results
The particle concentrations for 14.1 -700 nm size range as measured by the SMPS are shown in Figure 4 (main text). In the nanosize range (14.1 nm -98.2 nm), the highest concentration reached 3.4×10 4 cm -3 (at 14.1 nm for Regular Powder F). Below 25 nm, Nanopowders M and D and regular Powders F and E showed spikes of high nanoparticle concentration. The instability of the aerosol concentration over the course of cosmetic powder application to the face of the mannequin mimics the real life situation and is not unexpected. The impact of this instability on the results is discussed in the main article.
From ~100 nm to ~700 nm, concentration of Regular Powder E was the highest reaching the order of 10 5 cm -3 for ~300 -700 nm particles. Concentrations of the rest of the powders ranged from 7.2×10 -1 cm -3 (at 278.8 nm) to 1.3×10 3 cm -3 (at 661.2 nm) both for Nanopowder D. The background SMPS measurement and the clean brush control showed concentrations mostly below the detection limit of the instrument and are therefore not shown in Figure 4 (main text).
Results for 0.6-20 µm particles as measured by the APS are shown in Figure 5 (main text). In the size range from 0.6 to 1 µm, the lowest concentrations were observed during application of Regular Powders F and G, and Nanopowder M with concentrations reaching ~10 1 cm -3 , while the other three powders reached concentrations up to 10 3 cm -3 .
The concentration of Nanopowder M was the lowest for the rest of the size range and comparable to the level of the clean brush control.
In accumulation mode (1 -2.5 µm), moderate concentrations of particles were released during application of Powders F and G reaching only 6.5×10 1 and 4.2×10 2 cm -3 at 2.5 µm. The highest concentration in this range was from Regular Powder E reaching close to 10 4 cm -3 . For the Nanopowders D and K the concentrations were approximately 10 3 cm -3 .
In the coarse (2.5 -10 µm) and supercoarse (>10 µm) size modes, the highest concentrations were observed from Regular Powder E: it peaked at 7.8×10 3 cm -3 at 3 µm and decreased to approximately 1.3×10 1 cm -3 in the supercoarse mode. The particle concentration from nanopowders D and K and regular powders F and G were substantially higher than for Nanopowder M. At 2.5 µm size, their concentrations ranged from 6.9×10 1 cm -3 to 5.1×10 2 cm -3 . For larger particles, concentrations of these powders declined and separated a little bit more. At 10 µm, concentrations of these four powders ranged from 7.8×10 -1 cm -3 to 1.1×10 1 cm -3 .