NIOSH Derives New REL for Occupational Exposure to Silver Nanomaterials
NIOSH has derived a new recommended exposure limit (REL) for occupational exposure to silver nanomaterials: 0.9 μg/m3 measured as an airborne respirable 8-hour time-weighted average (TWA) concentration. The new REL applies to silver nanomaterials with a primary particle size of 100 nanometers or less. Current Intelligence Bulletin 70, which was published in May and focuses on the health effects of occupational exposure to silver nanomaterials, explains how NIOSH researchers estimated the risks to workers based on animal data from inhalation studies in rats. In those studies, researchers observed adverse lung and liver effects, including early-stage lung inflammation and liver bile duct hyperplasia, in rats following inhalation exposure to nanoscale silver particles. According to NIOSH, these responses are relevant to workers and led the agency to determine that it was “reasonable and prudent to establish a REL for nanoscale silver.” In addition to following the new REL, NIOSH recommends that employers use workplace exposure assessments, engineering controls, safe work procedures, training and education, and established medical surveillance approaches to further protect workers.
NIOSH advises continued use of its existing REL of 10 μg/m3 as an 8-hour TWA for total silver (metal dust, fume, and soluble compounds, as silver). NIOSH’s REL for total silver is the same as OSHA’s permissible exposure limit for silver. The new current intelligence bulletin explains that the REL and PEL for total silver are based on preventing workers from developing argyria—bluish-gray pigmentation to the skin and mucous membranes—and argyrosis, or bluish-gray pigmentation to the eyes.
“When the current REL of 10 μg/m3 for total silver was developed, it did not include a specific evaluation of silver nanomaterials,” the NIOSH document reads. “More recent studies in animals and cells have shown that the fate and biologic activity of silver are affected by physical-chemical characteristics such as particle size, shape, solubility, and surface properties.”
To learn more, see Current Intelligence Bulletin 70, available from NIOSH’s website.