Abstract
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 420×109min−1, 1.33×109μm2min−1, and 3.5mgmin−1 respirable mass. During a continued repeated process, the average exposure level was 2.5×104cm−3, 30.3μm2cm−3, <116μgm−3 for particulate matter. The TiO2 average exposure level was 4.2μgm−3, which is well below the maximum recommended exposure limit of 300μgm−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 4.3×10−3cm2g−1 of lung tissue and 13μg of TiO2 to the trachea-bronchi, and alveolar regions. The dose levels were well below the one hundredth of the no observed effect level (NOEL1/100) of 0.11cm2g−1 for granular biodurable particles and a daily no significant risk dose level of 44μgday−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.
Highlights
The air that we breathe contains a diverse mixture of gaseous and particulate matter (PM) pollutants released from natural and anthropogenic sources (Streets et al, 2009; Karagulian et al, 2015)
People spend 80 to 90% of their time indoors, where the quality of air is driven by pollutant source and loss mechanisms, including indoor emission sources in close proximity to occupants, outdoor pollutants that are transported indoors via ventilation and infiltration, pollutant deposition to indoor surfaces, and filtration, among others (e.g. Hussein et al, 2013)
Disease burden due to ambient air pollution exposure is mainly associated with PM10 (D50 ≤ 10 μm), PM2.5, ozone (O3), and nitrogen oxide (NOX) pollutants where PM2.5 is considered the most harmful component for human health (Landrigan et al, 2018; GBD, 2017a, 2017b; Butt et al, 2017; Environmental Agency (EEA), 2018; HEI, 2017; WHO, 2016; Lehtomäki et al., 2018)
Summary
The air that we breathe contains a diverse mixture of gaseous and particulate matter (PM) pollutants released from natural and anthropogenic sources (Streets et al, 2009; Karagulian et al, 2015). For a short-term exposure, Achilleos et al (2017) found a 0.89% increase in all-cause respiratory mortality per 10 μg m-3 increase in PM2.5, and for long-term PM2.5 exposure, the theoretical minimum for No-Observable Adverse Effect Level (NOAEL) ranges from 2.5 to 5.9 μg m-3 (GBD, 2017b) This is clearly lower than the WHO air quality guidelines for PM2.5 of 25 μg m-3 for a 24-hour mean and 10 μg m-3 for the annual mean (WHO, 2016). There is increasing evidence that PM1 (D50 ≤ 1 μm) or ultrafine particulate matter (UFP; D50 ≤ 0.1 μm) might have stronger associations to health effects at similar mass concentration (Seaton et al, 1995; Peters et al, 1997; Oberdörster, 2001; Donaldson et al, 2001; Nel, 2005; Politis et al, 2005; Chen et al, 2017) Chemical reactions, such as oxidation in ambient air, can change the compositions of the gaseous and PM pollutants and affect their toxicity (2016) showed that freshly generated diesel and gasoline engine exhaust UFPs are inherently more toxic than PM 123 that has lost surface-adhered volatile gases by aging
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