Navigating the minefield of airborne nanoparticle exposure
The issue is raised in the current edition of Nature Nanotechnology by Vladimir Murashov of the National Institute for Occupational Safety and Health (NIOSH), and former NIOSH-director John Howard. But the question has been bubbling along for some time.
And it’s an important one. Uncertainty over safe workplace practices is bad news for nanotech businesses trying to do the right thing—especially small start-ups that don’t have the resources to work out their own bespoke solutions. It’s not much better for regulators—as the gap between emerging technologies and solid information on their safe use widens, how do you craft new approaches to protecting people’s health and the environment?
Back in 2007, the Environmental Defence Fund and DuPont released their Nano Risk Framework… The Framework places a heavy emphasis on pragmatic exposure-based decision-making. In a nutshell, the message was: Use the best information available. And when that runs out, use every trick in the book to come up with the best possible benchmarks for qualitatively managing risk—until better information is available. And do all this under “reasonable worst-case” assumptions.
But the Nano Risk Framework stops short of providing practical guidelines on developing benchmarks for exposure assessment.
This gap was neatly filled by a guidance document from BSI Inc—the British Standards Organization—in January 2008. The “Guide to safe handling and disposal of manufactured nanomaterials” (BSI PD 6699-2:2007) takes the bold step of recommending starting exposure values for four different classes of nanomaterials—benchmarks for establishing exposure decision-points in the absence of anything else. PD 6699-2 refers to them as Benchmark Exposure Levels, and couches them in enough caveats to make the most hardened lawyer proud. A better moniker might have been Lifeline Exposure Levels—because they quite literally throw a lifeline to anyone completely at sea when it comes to making practical decisions on making sense of airborne nanomaterial exposure measurements.
But the Benchmark Exposure Levels are based on assumptions and speculation, not hard science. And while they are firmly grounded in recommendations within the Nano Risk Framework—using available information and reasonable worst-case solutions—they are, in the long-run, no substitute for quantitative risk assessment.
This is one of the main concerns that Murashov and Howard have about the BSI guidelines in their Nature Nanotechnology commentary. They argue that exposure limits should be based on generally accepted principles of risk assessment—and I agree with them. But something is needed in the interim while these limits are established, otherwise the whole emerging technology enterprise is on dodgy ground!
This is exactly what the Nano Risk Framework and PD 6699-2 address, and hopefully what additional guidance from organizations like the International Standards Organization, and even government agencies, will grapple with.
But this brings us back to the original question—how low is low enough? Because recommendations like “keep exposures as low as reasonably practicable” simply don’t cut the mustard without some sense of how to evaluate exposure, and what the numbers mean.
PD 6699-2 makes a good stab at helping industries develop internal pragmatic guidelines on how to use airborne exposure measurements when working with new nanomaterials. Earlier this year, I took a stab at assessing the validity and utility of the Benchmark Exposure Limits for BSI—the full assessment is available here (PDF, 168 KB). My conclusions: the benchmark levels are far from perfect, but they are a great starting point.
Assuming that most readers will have better things to do than read through the 12-page assessment, here are the conclusions:
If effective health and safety plans are to be implemented in research laboratories and workplaces generating and using nanomaterials, guideline exposure limits are essential. In the absence of further information, the benchmark exposure levels presented in BSI PD 6699-2:2007 appear reasonable. Furthermore, the context surrounding the levels—which is clearly stated in the document—allows people following the recommendations to adapt the levels to their specific circumstances, depending on the best available information. In other words, they are not binding, but rather present a clear starting point for an informed process of setting relevant exposure levels. And thus, where evidence exists to suggest that the benchmark exposure levels are overly stringent or not measurable for a given material, it is left to the discretion of the person setting the levels to adjust the accordingly.
These suggested levels are not a substitute for workplace exposure limits, and do not remove the need for targeted research leading to the development of evidence-based limits. But until such levels are developed, they fulfil a role that is essential to underpinning the development of safe and successful nanotechnologies. As such, BSI should be applauded for publishing them.
The bottom line here is that industry needs practical guidelines on safe workplace practices where hard information on risks is lacking, and at some point this will mean grasping the bull by the horns and providing advice on how to measure exposures, and what the numbers mean.
Giving meaning to the numbers might simply require establishing rules of thumb for developing bespoke exposure levels. Or it might require clear benchmark exposure levels to be suggested for different classes of materials (with suitable caveats of course). Either way, there will be exposure data, and people will want to know what they mean, and what action to take as a result.
In the long run however, hard data are still needed to underpin quantitative and authoritative risk assessment that will supersede interim qualitative measures. And this of course means there needs to be a research plan, plenty of funding, and a willingness to translate new information into informed oversight.
But that is a story for another day…