Nanoscale silver particles are some of the most widely used nanomaterials in commerce, with numerous uses in consumer and medical products. Workers who produce or use silver nanomaterials are potentially exposed to those materials in the workplace. Previous authoritative assessments of occupational exposure to silver did not account for particle size. The National Institute for Occupational Safety and Health (NIOSH) assessed potential health risk from occupational exposure to silver nanomaterials by evaluating more than 100 studies of silver nanomaterials in animals or cells. In studies that involved human cells, silver nanomaterials were associated with toxicity (cell death and DNA damage) that varied according to the size of the particles. In animals exposed to silver nanomaterials by inhalation or other routes of exposure, silver tissue concentrations were elevated in all organs tested. Exposure to silver nanomaterials in animals was associated with decreased lung function, inflamed lung tissue, and histopathological (microscopic tissue) changes in the liver and kidney. In the relatively few studies that compared the effects of exposure to nanoscale or microscale silver, nanoscale particles had greater uptake and toxicity than did microscale particles. To date, researchers have not reported health effects in workers exposed to silver nanomaterials.
To assess the risk of adverse health effects from occupational exposure, NIOSH evaluated the data from two published subchronic (intermediate duration) inhalation studies in rats. These studies revealed lung and liver effects that included early-stage lung inflammation and liver bile duct hyperplasia. NIOSH researchers used the data from these studies to estimate the dose of silver nanoparticles that caused these effects in rats. They then calculated the corresponding dose that would be expected to cause a similar response in humans, accounting for uncertainties in those estimates. From this evaluation, NIOSH derived a recommended exposure limit (REL) for silver nanomaterials (<100 nm primary particle size) of 0.9 micrograms per cubic meter (μg/m3) as an airborne respirable 8-hour time-weighted average (TWA) concentration. In addition, NIOSH continues to recommend a REL of 10 μg/m3 as an 8-hour TWA for total silver (metal dust, fume, and soluble compounds, as Ag). NIOSH further recommends the use of workplace exposure assessments, engineering controls, safe work procedures, training and education, and established medical surveillance approaches to protect workers.
CURRENT INTELLIGENCE BULLETIN 70 Health Effects of Occupational Exposure to Silver Nanomaterials [PDF – 12 MB]
NIOSH [2021]. Current Intelligence Bulletin 70: health effects of occupational exposure to silver nanomaterials. By Kuempel E, Roberts JR, Roth G, Dunn KL, Zumwalde R, Drew N, Hubbs A, Trout D, and Holdsworth G. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2021-112, https://doi.org/10.26616/NIOSHPUB2021112.
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