On December 12, 2025, the Organisation for Economic Co-operation and Development published a report entitled The Identification of Exposure Metrics for Use in Evaluation of Inhalation Exposure to Nano-Objects and their Aggregates and Agglomerates (NOAA) in the Workplace. The report presents a comprehensive overview, informed by a literature review, on methods for assessing and measuring inhalation exposure to nano-objects and their aggregates and agglomerates (NOAA) in workplace environments. According to the report, “while traditional mass-based assessments remain relevant, they often fail to capture the unique properties and potential risks of nanoscale materials.” The report notes that in many cases, metrics such as particle number concentration (PNC), surface area, or lung-deposited surface area (LDSA) provide a stronger correlation with toxicological effects than mass alone. Because no single metric is universally applicable, the report recommends a multi-metric approach to characterize different exposure scenarios accurately. The report also highlights the practical framework of a tiered approach, beginning with simpler screening (tier 1), followed by more targeted measurements with portable (real-time) instruments (tier 2), and, when necessary, comprehensive investigations (tier 3). Overall, the report “underscores the importance of selecting the right combination of metrics and methods to accurately assess airborne NOAA exposures in the workplace.”
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