Synergist - March 2010

Of course, by the title, you knew we were talking about nanomaterials. But did you know that nanomaterials turn everything you know about industrial hygiene upside down? The very founda- tions of the profession, which you worked so hard to master, are pulled out from under you. And nanomaterials make the gold standard of our profession, the quantitative science of exposure assessment, look pretty rusty.

Quantitative measurements of nanomaterials are possible, but the instruments are generally very expensive, and getting an appropriate workplace personal exposure measurement can be very difficult, if not impossible. The potential for worker exposures, however, is very real, as evidenced by a recent publication reporting worker exposures to polyacry-late nanoparticles in a Chinese factory (Song et al. 2009).

With something this complex and challenging, how does a concept as simple as control banding save the day? Many industrial hygienists know of control banding from its application in the COSHH (Control of Substances Hazardous to Health) Essentials toolkit from the British Health and Safety Executive. Considerable disagreement about COSHH Essentials and its value for risk assessments exists in the published research. But almost all the experts agree that control banding can be useful when no OELs are available (Zalk and Nelson 2008).

This aspect of control banding—its utility with uncertainty—led international experts to recommend it for nanomaterials. However, since this recommendation was only theoretical, we took on the challenge of developing a working toolkit, the control banding (CB) Nanotool (see Zalk et al. 2009 and Paik et al. 2008), as a means to perform a risk assessment and protect researchers at the Lawrence Livermore National Laboratory.

Dealing with Uncertainty While engineered nanomaterials have potentially endless benefits for society, the very properties that make them so useful to industry could also make them dangerous to humans and the environment. The uncertainties and unknowns with nanomaterials include the contribution of their physical structure to their toxicity, significant differences in

their deposition and clearance in the lungs when compared with their parent material, a lack of agreement on the appropriate indices for exposure to nanomaterials, and a dearth of background information on exposure scenarios or at-risk populations.

Our insufficient background knowledge of nanomaterials can be traced partly to the lack of risk assessments historically performed in the industry. A recent survey indicated that 65 percent of companies working with nanomaterials are not doing any nanomaterials-specific risk assessments; instead, companies are focusing on traditional parent material methods for industrial hygiene (Helland et al. 2009). The number of peer-reviewed publications that address environmental, health and safety aspects of nanomaterials has increased over the last few years, but the percentage of these that address practical methods to reduce exposure and protect workers is orders of magnitude lower.

Our intent in developing the CB Nanotool was to create a simplified approach that would protect workers while unraveling the mysteries of nanomaterials for experts and non-experts alike. Since a large part of the toxicological effects of both the physical and chemical properties of nanomaterials were not only unknown but changing logarithmically with the continued growth in nanomaterials research, we needed to account for this lack of information as part of the CB Nanotool’s risk assessment.

We chose a standardized 4x4 risk matrix (see Figure 1) as our starting point, working with the severity parameters on one axis and the probability parameters on the other. The development of the severity axis was the hardest part of our effort. It required the dissection of nanomaterials and their physicochemical properties, which are often unknown; adding information on the parent material, which is far more available; and somehow scoring these input factors in a manner that appropriately weighted each factor.

We decided to give unknown input
factors a score of 75 percent of the points
corresponding to the highest rating for
each category. Assigning maximum
points for unknowns would have
branded nearly every nanomaterial as
extremely dangerous, necessitating the
highest level of control. Balancing a
conservative approach with a reason-
able scientific estimate was the best
way not to stifle research ingenuity,
yet still protect workers. The probability
axis, which fits well with traditional
industrial hygiene knowledge, was much
easier to develop and score. The details
of the CB Nanotool go far beyond this,
but we give the basics below.

Severity Factors

Based on the literature available prior to publication of the CB Nanotool, the factors below were considered to determine the overall severity of exposure to nanomaterials. The research and logic behind both the composition and scoring distribution of these factors can be found in our publications (see Zalk et al. 2009 and Paik et al. 2008). These factors influence the ability of particles to reach the respiratory tract, deposit in various regions of the respiratory tract, penetrate or be absorbed through skin, and systemically elicit biological responses. The division of severity factor points taken cumulatively is 70 percent for the nanomaterial and 30 percent for the parent material. Research to date does not contraindicate the potential for engineered nanomaterials to be more toxic than their parent materials.

The following factors contribute to nanomaterials severity. (NM stands for nanomaterial; PM for parent material.)

Surface chemistry NM: Surface chemistry is known to be a key factor influencing the toxicity of inhaled particles. Points are assigned based on knowledge of whether the surface activity of the nanoparticle is high, medium or low.

High............. 10 Medium........... 5 Low.............. 0 Unknown . . . . . . . . 7. 5

Particle shape NM: Points are assigned based on the shape of the particle. The highest rating is given to fibrous or tubu-lar-shaped particles based on toxicological studies. Particles with irregular shapes (anisotropic) have higher surface areas than isotropic or spherical particles and therefore are given the next highest rating.