Nanotech respiratory risk: Do tiny particles mean big danger?
They may be small, but their potential is enormous. Nanoparticles are being developed that could “starve” tumors1, make perishable food last longer, create gold-flecked luxury fabrics2 and even - some day - enable your shoes to power your cell phone.3
While researchers are busy exploring the commercial applications of nanotechnology, less attention is being given to determining the possible health implications of working with particles whose extraordinarily small size causes them to behave in strange, sometimes unpredictable ways.
Do the unique properties that make them so useful also make them uniquely dangerous?
And, since the most likely avenue of exposure is airborne, will existing respiratory protection be effective in nanotechnology processing and manufacturing environments?
Take a precautionary approach
Although subatomic particles are more biologically active than larger particles of the same composition, scientists are not sure what that means in terms of their possible effects on human health. Studies suggest that exposure to nano-sized particles contributes to pulmonary problems like lung disease and decreased lung function, but whether that link is to the engineered particles used in nanotechnology remains to be seen.4
Under what circumstances might exposure occur?
Experts believe that while nanomaterial-enabled products are unlikely to pose a risk, some of the processes used to manufacture them (i.e., formulating and applying nanoscale coatings; or machining, sanding, drilling, cutting or grinding nanomaterials) could release respirable-sized nanoparticles. Cleaning and disposing of materials from dust collection systems could also result in exposure to nanoparticles.4
While researchers work on developing ways to accurately assess the health risks of nanotechnology, the National Institute for Occupational Science and Health (NIOSH) recommends taking a precautionary approach to respiratory protection.
Develop a risk management program
NIOSH says a nanotechnology risk management program should include:
- Evaluating potential nano hazards in the workplace, using existing chemical, toxicology and health information;
- Assessing the workers’ tasks to determine the potential for exposure; and
- Training workers in the proper handling of nanomaterials.
The industrial hygiene hierarchy of controls calls for reducing exposure by changing an employee’s work practices - when feasible - followed by the use of engineering controls like portable vacuum cleaners and exhaust ventilation systems with high-efficiency particulate air (HEPA) filters.
“Respirators would come last on that list if the other methods aren’t successful at reducing exposure to your target level or they’re not an option for whatever reason,” said Dr. Ron Shaffer, Chief of the Research Branch of NIOSH’s National Personal Protective Technology Lab (NPPTL).
But will existing respirators be effective with nanomaterials?
Despite the difficulties of studying particles that are only slightly larger than molecules, Shaffer and his colleagues have produced data that answers that question.
“It is hard to generate, control and measure particles that are less than a hundred nanometers in size,” Shaffer conceded. “So until there was really a need to do that kind of research, I don’t think anybody had really tried to do it.”
Shaffer and other scientists have conducted extensive studies on filtration, leakage and respiratory protection performance5, coming up with findings that offer useful information for safety professionals.
Use RSL guidelines
“What we can say from the data that we’ve published is that the selection guidelines that NIOSH has used still would hold,” said Shaffer. “We’re still recommending that companies use the respirator selection logic (RSL).6 There is nothing about nanoparticles that would suggest that you need to change the practices of how you select respirators for your employees.”
RSL is a decision-making tool developed by NIOSH to help employers choose the right kind of respirators for their workplaces by taking them through a series of questions on how and in what environments the respirator will be used, and with what types of contaminants. The RSL takes into account the Assigned Protection Factors (APF) developed by OSHA to indicate the level of protection that a respirator or a class of respirators is expected to provide.
Shaffer said APFs simplify the task of choosing a respirator. “If you pick a NIOSH-approved respirator of a certain type, we can say how much performance that type of respirator should have. The burden on the employer to provide adequate protection for their employees is minimized. They don’t have to make measurements inside respirators. They just need to make general exposure assessment measurements.”
Expect inward leakage
However, even the correct respirator can’t completely eliminate exposure to nanomaterials or any other contaminant. “While you’re wearing a respirator, even one that’s been properly selected and you’ve been fit tested on, you can still get some exposure into the lungs,” said Shaffer. Such exposure, known as “inward leakage,” occurs when particles penetrate through the filter or through face seal leakage.
“Very small gaps can create opportunities where particles can go around the filter and directly through that gap between your face and your respirator,” Shaffer said, pointing out that it is particularly difficult to get a strong seal around the nose and chin. Fit testing can minimize the gaps, but not completely eliminate them.
Those gaps are taken into account in the APF risk assessments given to different types of respirators.
Traditional rules are valid
Research being conducted according to the National Nanotechnology Initiative Strategic Plan - developed by the National Science and Technology Council - is expected to lead to a greater understanding of the environmental, health and safety impacts of nanotechnology development.
In the meantime, Shaffer is able to offer industrial hygienists some reassurance. “Yes, nanoparticles are unique,” he says. “They have some wonderful properties - that’s why scientists like studying them. Some of those properties may lead them to be more hazardous, but at the same time, some of the traditional rules that we use for filtering out particles and controlling worker exposures are still valid.”
1 Nanotechnology brings scientists one step closer to a universal treatment for cancer. Nanotechnology Now. March 21, 2011. At: www.nanotech-now.com.
2 Thin Films and Nanotechnology applications. NANO Magazine, Issue 14. January 25, 2010. At: www.nano.org.uk.
3 Energy-harvesting rubber sheets could power pacemakers, mobile phones. UnderstandingNano.com. January 2011. At: www. understandingnano.com.
4. Approaches to Safe Nanotechnology, NIOSH document No. 2009–125, March 2009.
5. An Overview of NIOSH Nanotechnology Research and an Update on the Efficacy of Personal Protective Equipment for Reducing Worker Exposure to Nanoparticles by Dr. Ron Shaffer, presented at the Commercialization of Nanomaterials Conference, Nov. 12, 2007.
6. NIOSH Respirator Selection Logic 200. NIOSH Publication No. 2005-100. Online at: www.cdc.gov/niosh/docs.