How Well Do Gloves and Respirators Block Nanoparticles?

Health & Safety

The scientists who work on the front lines of research and manufacturing have long relied on standard protective equipment, such as respirators and gloves, as safeguards against potentially harmful substances. But no one is certain how effective these measures are against nanoparticles. The tiny particles could be small enough to slip past the fibers in a respirator's filter, or they could be so reactive that they penetrate the thin regions of a latex glove.

"There are still a lot of unknowns as to whether or not traditional protective measures work against nanoparticles," says Michael J. Ellenbecker, a professor of industrial hygiene at the University of Massachusetts, Lowell. Ellenbecker is one of a handful of researchers trying to find out just how effective protective equipment is for the thousands of workers who handle nanoparticles every day.

Ellenbecker and his colleague Kwangseog Ahn have been studying the efficacy of both latex and nitrile disposable gloves. In preliminary tests, they exposed gloves to bulk nanoalumina and nanoclay for one hour or, in a second, more rigorous test, shook the gloves in the presence of nanoparticles for one hour. Afterward, they examined the surface of the gloves, using scanning electron microscopy, to see if any of the material had gone through.

"We haven't found that particles penetrate gloves," Ellenbecker says, but, he adds, there was some evidence that the nanoparticles tend to accumulate in areas where the gloves are thinner. This phenomenon concerns the researchers. Where the gloves are thin, "it wouldn't take much force to push something through," Ellenbecker says.

Ahn and Ellenbecker are about to start experiments on new equipment that more closely simulates the stretching and pressure that gloves encounter when they're being worn. In the meantime, Ellenbecker says, "what we're recommending to labs is that if you're working with nanoparticles, you should wear latex or nitrile gloves."

In nanoparticle manufacturing, respirators are considered to be an essential piece of protective equipment, preventing workers from inhaling particulate matter. So scientists are studying the efficacy of the filter material used in respirators.

The National Institute for Occupational Safety & Health certifies respirators and over the years has accumulated plenty of data about how effective these filters are against many sizes of particulate matter. Despite this wealth of data, there's not much available about particles in the 3- to 20-nm range, according to NIOSH's Ron Shaffer.

So NIOSH teamed up with University of Minnesota researchers Seong-Chan Kim and David Pui to study particles in this size range. They found that several different types of commonly used filter materials effectively block the passage of silver particles 3 to 20 nm in diameter. In fact, the filters proved to be better at blocking the very smallest particles than they were at filtering particles in the 100-nm range.

There are, however, studies that suggest the filters are less effective for other nanoparticles. Sergey Grinshpun, a professor of environmental health at the University of Cincinnati, tested two types of N95 respirators, which are supposed to filter out 95% of the particles they encounter, under two different inhalation flow rates. He found that under certain conditions up to 7% of sodium chloride particles in the 30- to 70-nm range were getting through the respirators.

"Not all the respirators that are certified to be 95 provide 95% efficiency for all nanoparticles," Grinshpun concludes. Respirator filters are typically tested against 300-nm particles, a size that NIOSH determined years ago to be the most penetrating. But those tests, he explains, were based on data from uncharged filter material. Since then, respirator makers have shifted to using charged filter material. This shift, Grinshpun thinks, has resulted in a change in the most penetrating particle size.

All the health and safety researchers who spoke with C&EN stress that these studies are preliminary. They say more data are needed before they can declare protective equipment safe or unsafe. NIOSH's Shaffer, for example, points out that most respirator leaks don't come from the filters but from the face seal. "If you look at worker exposure, the biggest source of leakage is around the respirator seal because of poor face fit," he says.

A nanoparticle's chemistry, shape, and size are all likely to factor into its interaction with gloves or respirators, the health and safety scientists say. All these factors will need to be addressed in future research.