Dip coating of air purifier ceramic honeycombs with photocatalytic TiO₂ nanoparticles: A case study for occupational exposure

Nanoscale TiO₂ (nTiO₂) is manufactured in high volumes and is of potential concern in occupational health. Here, we measured workers exposure levels while ceramic honeycombs were dip coated with liquid photoactive nanoparticle suspension and dried with an air blade. The measured nTiO₂ concentration levels were used to assess process specific emission rates using a convolution theorem and to calculate inhalation dose rates of deposited nTiO₂ particles. Dip coating did not result in detectable release of particles but air blade drying released fine-sized TiO₂ and nTiO₂ particles. nTiO₂ was found in pure nTiO₂ agglomerates and as individual particles deposited onto background particles. Total particle emission rates were 420 × 109 min⁻¹, 1.33 × 10⁹ μm² min⁻¹, and 3.5 mg min⁻¹ respirable mass. During a continued repeated process, the average exposure level was 2.5 × 104 cm⁻³, 30.3 μm² cm⁻³,<116 μg m⁻³ for particulate matter. The TiO₂ average exposure level was 4.2 μg m⁻³, which is well below the maximum recommended exposure limit of 300 μg m⁻³ for nTiO₂ proposed by the US National Institute for Occupational Safety and Health. During an 8-hour exposure, the observed concentrations would result in a lung deposited surface area of 4.3 × 10⁻³ cm² g⁻¹ of lung tissue and 13 μg of TiO₂ to the trachea-bronchi, and alveolar regions. The dose levels were well below the one hundredth of the no observed effect level (NOEL_1/100) of 0.11 cm² g⁻¹ for granular biodurable particles and a daily no significant risk dose level of 44 μg day⁻¹. These emission rates can be used in a mass flow model to predict the impact of process emissions on personal and environmental exposure levels.