Characterizing workplace exposures to nano-TiO2 in Singapore: potential risks and mitigation strategies

Engineered nanomaterials (ENMs), particularly nano-titanium dioxide (nano-TiO2), are widely used across industries in Singapore, raising concerns about potential worker exposure. This study aimed to quantify occupational exposures and emissions at workplaces handling nano-TiO2, assessing work practices, usage patterns and workplace controls.

Occupational exposure to nano-TiO2 was assessed across 7 workplaces (laboratories, manufacturing, downstream application, and recycling). Methods for characterizing personal exposure included personal gravimetric sampling (NIOSH 0600), elemental analysis (NIOSH 7300), and scanning electron microscopy (SEM), while real-time particle number concentration (PNC) monitoring was done to understand the particle distribution in the workplace environment during the tasks performed. Workplace observations included measurement of dimensions of the work area, existing control measures (engineering, administrative, and personal protective equipment), nature of nano-TiO2 handling practices, forms, quantities, particle size, and state changes of the nano-TiO2 used.

Personal exposure samples were collected from 30 workers across workplaces. These include: 7 in laboratory, 10 in manufacturing, 6 in spraying, and 7 in shredding/recycling. Of these, 3 samples, collected during bulk loading and spraying activities, exceeded the NIOSH recommended exposure limit (REL) for ultrafine nano-TiO2 (0.3 mg/m3). Electron microscopy analysis of the samples exceeding the NIOSH REL for ultrafine nano-TiO2 during spraying revealed that the nano-TiO2 particles were predominantly in the size range of 80 to 147 nm. Respirable dust concentration and PNC were positively correlated for higher-risk activities, with peak PNC observed at the workplaces where spraying applications were performed.

To our knowledge, this is the first study evaluating nano-TiO2 workplace exposure in Singapore. Exposure levels were generally low, likely due to prevalence of small-scale and research-based applications but varied significantly across workplaces for activities such as spraying, bulk loading and manufacturing. Singapore's current regulatory approach (TR 73) establishes exposure limits but lacks specific guidance on control measures. A more holistic regulatory framework is needed, providing tailored recommendations for diverse workplace exposure scenarios.