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
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
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.
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.
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.
Tubular, fibrous. . . . . 10
Anisotropic . . . . . . . . 5
Compact/spherical . . . 0
Unknown . . . . . . . . 7. 5