Cal Baier-Anderson, Ph.D., is a Health Scientist.
When it comes to chemical exposures, workers are on the front line. Workers are usually the most likely to be exposed to harmful levels of chemicals, because they are the ones producing, processing, handling, sampling and measuring, transferring and transporting chemicals in larger and more concentrated quantities.
Throughout history, workers have been the canaries in the coal mines; the first to exhibit the health effects of hazardous chemical exposures, from scrotal cancer in chimney sweeps, to mesothelioma in shipyard and construction workers to liver cancer in vinyl chloride workers.
For these reasons, EDF has argued that workers handling or otherwise likely to be exposed to nanomaterials must be protected from harm (see our earlier posts here, here and here). Now, a new government study published in the respected journal Environmental Health Perspectives reveals that certain comfortable assumptions about nanomaterial laboratory safety may be downright wrong.
Increasing evidence indicates that carbon-based nanoparticles, such as carbon nanotubes and fullerenes, are a worker health concern because inhalation exposures in laboratory animals have been associated with lung damage (see these earlier posts).
Because of its small size, nanoscale carbon is difficult to contain in the workplace. During production, processing, sampling and measuring and transfer of nanomaterials, individual or aggregated nanoparticles can be dispersed into the air, where they could be inhaled by workers or escape into the environment.
The usual response is to say that laboratories should take certain steps to minimize both the release and exposure of nanoparticles, including avoiding handling materials in dry form and routinely requiring the use of personal protective equipment and specialized fume hoods.
Unfortunately, studies that document the effectiveness of these various control technologies are still largely lacking. Therefore, invoking such laboratory safety practices requires a leap of faith.
The new government study challenges one common assumption behind such prescriptions: that carbon nanoparticles suspended in liquid are less likely to become airborne. As carbon nanoparticles are not generally water-soluble, continuous stirring or sonication is required to prevent clumping. Alternatively, chemical dispersants can be added to the water. One study found that the organic acids naturally present in river water are an excellent dispersant, by reducing the tendency for carbon nanoparticles to clump. (An earlier post on our blog explored the implications of this study’s findings for the fate of nanoparticles released to the environment.)
The new study tested the extent to which dispersion to the air could occur from various liquid suspensions of nanoparticles, and also studied air dispersion during common activities involving dry forms of the materials, like weighing and transferring of carbon nanoparticles.
Some of the results are not surprising: weighing and transferring both carbon fullerenes and multi-walled carbon nanotubes (MWCNTs) in dry form released significant concentrations of nanoparticles into the air. Larger particles were also measured, but at lower concentrations.
The more surprising news was that sonication of fullerenes in distilled water, or MWCNTs in water containing natural organic acids, also led to significant airborne dispersion, with airborne concentrations not much lower than the activities involving handling if the materials in dry form!
Even more interesting: MWCNTs that have been modified to make them more water-soluble yield, in comparison to unmodified MWCNTs, far fewer airborne particles during weighing and transferring — but higher airborne concentrations during sonication!
Number of 300-nm particles/liter of air
|Weighing & transferring fullerenes||
|Sonicating fullerenes in distilled water||
|Weighing & transferring MWCNTs||
|Sonicating MWCNTs in water with organic matter||
|Weighing & transferring functionalized MWCNTs||
|Sonicating functionalized MWCNTs in water with organic matter||
Bottom line: The assumption that suspending carbon nanoparticles in water reduces the concentration of airborne particles, thereby reducing the chances of worker exposure, is at best overly simplistic.
One of the challenges of developing science-based policies is that we are always dealing with incomplete information. To move forward in the face of uncertainty requires that we make assumptions. Assumptions may be based on a combination of scientific information derived from a related issue, along with perceived common sense and conventional wisdom.
They also may be wrong. It is important that assumptions be tested as quickly and objectively as possible if we are to make sure that worker and public health are being adequately protected. (In an earlier blog post, my colleague Richard Denison challenges other points of conventional wisdom on nanoparticle aggregation.)
As noted in the new government study, “Conventional wisdom suggests that nanomaterials in liquid suspension generally pose lower inhalation risk to workers. However, CNMs [carbon nanomaterials] and other nanomaterials often agglomerate in aqueous suspension, requiring continuous mixing or sonication to deagglomerate nanomaterials. It is possible that this common laboratory process results in the release and dispersion of nanomaterials into the air via small water droplets.”
Kudos to these government scientists who tested this assumption and published the results. Now, let’s hope that laboratories that manufacture and handle nanoparticles take more aggressive action to ensure that nanoparticle releases are prevented and workers are fully protected.