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April 22, 2016
Is nanoscale silver leaving your workers blue? Training can help

Nanomaterials are ordinary materials, divided into very tiny particles—a nanoparticle will have one or more external dimensions in the nanoscale size range of 1 to 100 nanometers (nm).

They may have the same molecular formula as larger particles or bulk amounts of the same substance, but because of their size, they can act very differently. Reducing a substance to nanoparticles can change almost everything about the way it behaves, including its toxicological profile.

One substance whose nanoparticle form is proving to have many uses is silver. The National Institute for Occupational Safety and Health (NIOSH) recently published a Draft Current Intelligence Bulletin on the health effects of occupational exposure to silver nanomaterials, identifying possible risks and recommending control measures. If your workers are exposed to silver nanoparticles, here’s what they need to know.

Practice Tip

Workers may not see argyria and argyrosis as serious health effects, but they might feel differently if you tell them the conditions are irreversible.

Background on silver nanoparticle safety

Who needs to be trained? Silver, silver compounds, and silver nitrate are all found on California’s Hazardous Substances List (8 CCR 339). Workers who are occupationally exposed to these substances must be trained under both California Labor Code Section 6361 and General Industry Safety Orders Section 5194, the hazard communication standard.

Why train workers in silver nanoparticle hazards? Silver can cause changes to the kidneys and liver, and nanoparticle silver may have health effects that are not yet identified. Workers need to be aware of their risk and how to protect themselves.

Basics of silver nanoparticle safety

Instructions to Trainer: Give workers a visual comparison of the size of nanoparticles compared to larger particles and an overview of how this can affect their activity in the body (for example, nanoparticles can be more easily absorbed through the skin and into the bloodstream).

How can you tell that you have been overexposed to silver at work? It turns your skin and mucous membranes bluish, a condition called argyria, and can also turn the whites of your eyes bluish-gray, a condition called argyrosis.

Ordinarily, silver is not highly toxic, but some substances that are not usually very toxic have been shown to be far more toxic in nanoscale form. Silver is of concern because the use of silver nanoparticles is increasing. About 20 tons of silver nanomaterials were produced in the United States in 2010, and about 500 tons were produced worldwide in 2014. Much of the increased production is used in medical and consumer products like electronics and textile coatings.

Studies in animals and cells have shown that the way silver behaves in the body depends upon physical-chemical properties, including solubility, particle size, and particle shape—properties that are different in nanoscale materials. Studies in animals and in lab-grown cells have shown that silver nanoparticles may indeed have greater toxicity than larger silver particles.

Inhalation studies in rats have shown lung, liver, and kidney damage that doesn’t normally occur in silver exposures, as well as accumulations of silver in major organs and tissues. In vitro studies have shown that exposure to nanoscale silver wires may cause greater lung damage than exposure to more rounded particles.

Limiting exposure

Cal/OSHA has set a permissible exposure limit (PEL) of 10 micrograms/m3 for silver metal dust and soluble compounds. The limit was adopted to protect against argyria and argyrosis, but NIOSH has determined that it’s the best protective limit available at the present time against nanoscale silver exposures.

To keep your exposure below this limit, NIOSH recommends that you:

  • Protect your skin. Silver nanoparticles can enter the body through the skin, especially broken skin. Wear protective clothing and gloves made of nonwoven textiles whenever you’re working with silver particles.
  • Protect your lungs. Avoid handling silver nanomaterials in powdered form, and don’t create dusty conditions. If you could be exposed to inhalable silver nanoparticles, wear the provided respiratory protection.
  • Know what you work with. Know which job tasks and materials involve exposure to silver nanomaterials. Those jobs will require exposure control measures, safe work practices, and personal protective equipment (PPE).
  • Store materials properly. Silver nanomaterials, including those suspended in liquids or in powder form, should be stored in tightly sealed containers whenever possible. Don’t handle these materials in open containers.
  • Clean your work area. At the end of each shift, you should clean your work area with a HEPA vacuum or wet wipes. Don’t dry sweep the area or clean it with compressed air.
  • Keep food and drink separate. Don’t eat or drink in your work area.
  • Wash your hands. Wash your hands before eating, smoking, or leaving the worksite.
  • Shower and change. You don’t want to take potentially harmful substances home on your clothes, so shower and change after work, and leave your contaminated clothing in the provided area.
  • Clean up spills. It’s important to know where the spill cleanup kit is located and how to use it. Cleaning up a spill requires additional PPE and training.

Conclusion

Nanoparticles behave differently than substances in larger particles or aggregate form, so you may have to use more or different strategies to protect yourself from their hazards. Don’t make the mistake of thinking that the particle size is insignificant. Smaller particles can be far more toxic than larger ones.

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