Metrics and instruments used to assess occupational exposure to nanomaterials: A scoping review

Quantitative assessment of occupational exposure to nanomaterials in workplaces is crucial. This task faces many challenges, notably the lack of an agreed-upon metric for measuring and characterizing exposure. This scoping review examines research on exposure assessment, focusing on the metrics used to evaluate occupational exposure. In accordance with PRISMA-ScR reporting recommendations, databases PubMed, Scopus, and Web of Science were searched without initial time limit up to September 23, 2026. The inclusion criteria were articles quantitatively assessing airborne nanoscale particles in occupational or workplace relevant settings. The following data were extracted and descriptively analyzed: measurement metrics, instruments, tasks, sampling strategies, background assessment, and assessment purposes. From the 3867 records identified, 215 studies were included, of which number based measurements were reported in 195 (90.7%), particle size distributions in 164 (76.3%), mass related outcomes in 149 (69.3%) and airborne surface area measures in 69 (32.1%); categories overlapped. Fifty three studies reported lung deposition related surface area measures. Direct reading instruments characterized particle concentration and size patterns whereas collection based sampling and offline analyses provided complementary chemical and morphological information. Differences in background assessment, sampling location, instrument outputs and the distinction between directly measured and derived metrics complicated comparisons. The frequency of reporting does not determine the metric validity, health relevance, or comparative suitability. The choice of what metric to adopt depends on the material, occupational task, and assessment purpose. In addition, both online and offline measurements should be taken when appropriate, and reports need to be consistently compared to facilitate improved exposure characterization and interpretation.