Airborne reactive oxygen species (ROS) is associated with nano TiO2 concentrations in aerosolized cement particles during simulated work activities

Photocatalytic cement is self-cleaning due to the addition of titanium dioxide (TiO2) nanoparticles, which react with sunlight (UV) and produce reactive oxygen species (ROS). Construction workers using photocatalytic cement are exposed not only to cement particles that are irritants but also to nano TiO(2)and UV, both carcinogens, as well as the generated ROS. Quantifying ROS generated from added nano TiO(2)in photocatalytic cement is necessary to efficiently assess combined health risks. We designed and built an experimental setup to generate, under controlled environmental conditions (i.e., temperature, relative humidity, UV irradiance), both regular and photocatalytic cement aerosols. In addition, cement working activities-namely bag emptying and concrete cutting-were simulated in an exposure chamber while continuously measuring particle size distribution/concentration with a scanning mobility particle sizer (SMPS). ROS production was measured with a newly developed photonic sensing system based on a colorimetric assay. ROS production generated from the photocatalytic cement aerosol exposed to UV (3.3.10(-9) nmol/pt) was significantly higher than for regular cement aerosol, either UV-exposed (0.5.10(-9) nmol/pt) or not (1.1.10(-9) nmol/pt). Quantitatively, the level of photocatalytic activity measured for nano TiO2-containing cement aerosol was in good agreement with the one obtained with only nano TiO(2)aerosol at similar experimental conditions of temperature and relative humidity (around 60%). As a consequence, we recommend that exposure reduction strategies, in addition to cement particle exposures, also consider nano TiO(2)and in situ-generated ROS, in particular if the work is done in sunny environment

Characterization of nanoparticles in aerosolized photocatalytic and regular cement

Photocatalytic cement containing nano-TiO2 has been introduced to the construction industry because of its biocidal and self-cleaning properties. Although, TiO2 is classified as possibly carcinogenic to humans, the cancer risk among cement workers is currently unknown. This is partly because an assessment of exposures to airborne photocatalytic cement is missing. We characterized airborne photocatalytic cement in an experimental aerosolization set-up and compared it to regular cement. Aerosolized nanoparticle size distributions and concentrations were measured with a scanning mobility particle sizer (SMPS) and a portable aerosol spectrometer (PAS). Particle morphology was analyzed with a scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Energy dispersive X-ray analysis (SEM-EDX) was used for elemental determination. The aerosolized photocatalytic cement powder contained 5% nanosized particles in number concentration while regular cement had only a negligible amount. Airborne photocatalytic cement concentration was 14,900 particles per cubic centimeter (pt/cm3) with a geometric mean diameter (GMD) of 249 nm (geometric standard deviation; GSD ±2 nm). Airborne regular cement concentration and GMD (GSD) were 9,700 pt/cm3 and 417 nm (±2 nm), respectively. Photocatalytic cement contained 18.5 times more airborne nano-TiO2 (37%) compare to bagged powder (2%). Aerosolized photocatalytic cement had a significantly smaller particle size distribution and greater particle concentration compared to regular cement. Both types of cement had 99% of the particles with sizes less than 1 μm. Nano-TiO2 was directly aerosolized from the cement, followed with a coagulation/agglomeration process. Future studies should evaluate workers’ exposures associated with the use of photocatalytic cement. Copyright © 2019 American Association for Aerosol Research</p

Airborne nano-TiO 2 particles: an innate or environmentally-induced toxicity ?

Titanium oxide (TiO2) is a known photocatalyst, able to produce reactive oxygen species (ROS) when exposed to UV light. TiO2 phototoxicity has been abundantly demonstrated in aqueous solutions. Little is known; however, about its phototoxicity as an aerosol, particularly in the nano-size particle range. An experimental setting was developed to measure the oxidation capacity of TiO2 NP with or without exposure to UV light. TiO2 NP were generated using a Collison nebulizer, carried through a diffusion dryer and exposed to UV using the collimated beam of a solar light simulator. Their oxidation capacity was measured on-line via a photonic sensor based on multiscattering absorbance enhancement (MAE) strategy. The oxidative potential of aerosolized TiO2 nanoparticles is exacerbated by exposure to UV light. The oxidative response is affected by humidity and reaches its maximum in the 70%-90% relative humidity range. Gaseous hydrogen peroxide (H2O2) was found to be the predominant oxidative specie. Our results suggest that the use of TiO2 nanoparticles in outdoor environments or close to artificial UV sources lead to an involuntary exposure to ROS, to an extent greater than previously known. It raises also concerns about other environmental pollutants known to be UV photosensitive