A risk assessment framework for self-management of poorly soluble low toxic nanomaterials

The safety of nanomaterials is still being debated and the risk should be assessed using the latest available information. As for poorly soluble low toxic (PSLT) nanomaterials, the US National Institute for Occupational Safety and Health estimated the occupational exposure limit (OEL) for titanium dioxide (TiO₂) based on a particle surface area (SA) metric. The Organisation for Economic Co-operation and Development (OECD) suggested a tiered exposure assessment approach. This article proposes a risk assessment framework for self-management of PSLT particles. Lung burden (described in SA units), which had positive correlation with low observed adverse effect levels for PSLT particles, is chosen as the dose metric. In-house OEL is determined for individual workplaces. For materials with limited data, we suggest evaluating in-house OEL by utilizing the no observed adverse effect level (NOAEL) for TiO₂, as a representative PSLT nanomaterial. As for the exposure assessment, workplace concentration is first measured with simple equipment (ex. optical particle counter, OPC), and respirator performance is taken into account if it is unavoidable as a last resort. This framework enables efficient risk assessment for PSLT particles by assuming worst cases for each step, and considering the particle characteristics and operational conditions in each workplace.