J. Zhang, R. He, G. Mainelis
Keywords: nanospray, deposition, resuspension, exposure
Summary:Nanotechnology-based consumer sprays are widely available and are used as deodorizers, surface cleaners, and multiple other purposes. Our earlier research reported that relatively high concentrations of nanoparticles and their agglomerates are released from the nanotechnology-based sprays during their use and become available for inhalation. This project continues the investigation into the fate of particles released from such products, namely their deposition on the floor and resulting resuspension due to walking. For this study, we selected two Ag-containing and two Zn-containing spray products which generate relatively high mass concentration when applied. The products were applied in a 5 x 9 x 8 ft^3 chamber with controlled background particle concentration. After spraying for 5 min, the spray was allowed to settle, and experimenter walked on the floor and measured the resuspension rate and size distribution at static locations 0.288 m and 1.1 m above the floor, as well as with the mobile instrument measuring particles in the experimenter’s breathing zone. The experiments were performed on the carpet and vinyl flooring, and the particles from the same spray were resuspended every 24 h until the resuspended particle mass concentration reached the maximum value. Filter samples were also collected to analyze the morphology and chemical composition of the resuspended particles. To mimic particle resuspension by children, we used a remote-controlled robot carrying particle instruments. The sprayed particle mass concentration ranged from 0.3 to 58.2 mg/m^3 and the floor-deposited mass density (loading) ranged from 0.00022 x 10^4 to 1.0 x 10^4 mg/m^2. The resuspended particle concentration ranged from 5.2 µg/m^3 to 61 µg/m^3, depending on the product. When the robot was used to resuspend particles, the resuspended mass concentration ranged from 3.8 µg/m^3 to 9.5 µg/m^3. We found that the particle resuspension rate due to walking ranged from 10^-1 to 10^-6 h^-1 across the products and floor types, and it reached the peak value 24 h or 48 h after spraying. As could be expected, the large particles representing agglomerates of sprayed nanoparticle and their agglomerates resuspended the easiest. Interestingly, there was a higher concentration of 0.4 – 15 µm from the dynamic instrument than from the static one at 1.1 m above the floor. The resuspension pattern from both the carpet and vinyl surface was the same, but the resuspension rate from the carpet was an order of magnitude higher than that from the vinyl. The resuspended particles and their agglomerates showed the presence of various metals, including Ag and Zn as was advertised in product composition. Our data show that when nanotechnology-enabled consumer products are used in homes, the sprayed particles deposit on floors and can be resuspended thus becoming available for inhalation. The extent of the resuspension depends on the flooring type, the product, as well as the activity causing the resuspension, i.e., walking by an adult or a child.