Lessons Learned from Unintentional Aerosols - Safety of Nanomaterials along Their Lifecycle - page 106

terminology is that particles ranging from 2.5 to 10 µm are coarse, particles less
than 2.5 µm are regarded as fine, and particles less than 0.1 µm are ultrafine. Thus,
particles classified as ultrafine in the air pollution literature are nanoparticles. These
nanoparticles emitted from cars, trucks, and stationary sources are of concern
because they may increase the probability of heart attacks, aggravation of asthma,
and resulting in increases in visits to emergency rooms and hospitals, especially by
individuals with pre-existing cardiopulmonary disease (Smith et al. 2006).
In a recent editorial, Grigg emphasized how air pollution relating to traffic affects
the growth of lungs in utero , early in childhood, and throughout adolescence (Grigg
2012). Concerns are increasing as more and more of the world's population moves
from rural to urban areas.
Gong and colleagues have utilized concentrated ambient UFPs to measure health
effects in humans utilizing chamber studies. Exposures were associated with sig-
nificant reductions in arterial oxygen saturation as well as pulmonary function
(e.g., EFV-1) (Gong et al. 2008). However, evidence of inflammation was absent,
and the responses of subjects who had asthma compared to normals were similar.
Comparable studies were also carried out in the EPA lab in Chapel Hill. Modest
pulmonary function and cardiovascular changes were noted.
There are also profound consequences of natural aerosols on weather and other
environmental problems. These natural atmospheric aerosols degrade visibility and
may affect human health, as discussed earlier. Importantly, they also influence cli-
mate by reflecting and absorbing radiation from the sun. Especially, they have a key
role in the formation of clouds. The size and the chemical makeup of these droplet
nuclei influence weather and must be better studied in the laboratory and in environ-
mental measurements (Zhang 2010).
In terms of biologic responses, it is interesting that as particles dissolve, they will
inevitably go through a nanoparticle phase. For example, particles that are one or two
microns in diameter undergoing gradual dissolution will pass through a stage when
they are less than 100 nm on their way to complete dissolution. This is yet another
reminder of a long history of human exposures to nanoparticles.
5.6 CONCLUSION
There is compelling evidence that although some engineered nanoparticles are novel
and human exposures have not occurred before, many nanoparticles are not new.
Polydisperse aerosols such as diesel particulates, silica dust, welding fume, and
tobacco smoke contain abundant nanoparticles.
Typically, nanomaterials contribute the minority to exposure end-dose in terms
of mass (almost always less than 10%), but they may dominate in terms of particle
number and surface area. A challenge is that there is abundant literature showing
health effects relating to PM 2.5 , but there is little data on the extent to which these
responses are attributable to the ultrafine fraction.
A challenge for the future is to learn as much as we can from these “his-
toric particles.” What properties do they have which are shared with “new”
nanoparticles? Moreover, to what extent is the toxicity of familiar polydispersed
materials attributable to the nanoparticle fraction? The field of unintentional