Lessons Learned from Unintentional Aerosols - Safety of Nanomaterials along Their Lifecycle - page 105

concentrations of coal dust and especially smaller particles, including increasing
numbers of nanoparticles.
5.4.5 n on -a nthroPogeniC s ourCes
Like their sister engineered nanomaterials, unintentional nanomaterials deposited in
the deep lungs interact with surfactant film and are subject to phagocytosis by resi-
dent alveolar macrophages. Because of their small size, the receptors used may dif-
fer from those used by larger particles. Nevertheless, nanoparticles generally appear
in the cell within intracellular vesicles. Peculiar to nanoparticles is their occasional
appearance in the cell cytoplasm or even in the nucleus in a nonmembrane bound
fashion (Geiser et al. 2005, Rothen-Rutishauser et al. 2006).
Important sources of unintentional aerosols are particles coming from volcanoes,
forest fires, soil colloids (e.g., silicate clay), viruses, and sea spray. Also relevant is
radon progeny. Radon gas decays into metal ions and they attach to particles already
present in indoor air, especially persistent nanoparticles.
The most prominent source of unintentional nanoparticles created in the atmo-
sphere represents condensation of gas phase molecules. This process is called nucle-
ation and is particularly important for sulfuric acid and other compounds of low
volatility which condense to small particles when they reach a critical concentration
in the atmosphere. This is a process comparable to the formation of rain as water
vapor condenses into cloud drops (Andreae 2013).
Polydisperse aerosols come from volcanic eruptions around the world and can
travel for thousands of kilometers. For example, see Revuelta et al.'s (2012) research
that measures volcanic dust in Spain, which originated 3000 km away in Iceland.
Mather et al. (2004) discuss the importance of volcanic eruptions as a source of
atmospheric gases and particles, and provide detailed information about concen-
tration and particle size of two volcanoes in Chile. Typically, the technology used
is not well designed to produce complete information on UFPs. They do report
that the volcanic plumes are bimodal in size and that the two maxima have radii
of 0.1-0.2 and 0.7-1.5 μm. Clearly, the smaller sized maximum includes particles
smaller than 0.1 μm.
5.5 BIOLOGIC AND ENVIRONMENTAL RESPONSES
Pinkerton et al. deliberately produced nanoparticles of soot and showed that expo-
sure to these particles early in neonatal development has long-term consequences
on lung growth (Pinkerton et al. 2004). This is achieved by eliciting changes in cell
division at critical sites in the airways during periods of rapid post-natal develop-
ment. They speculate that these changes have “life-long consequences.”
Nanoparticles, including unintentional ones, may be more toxic because of
molecular adsorption of toxins to the particle surfaces. Given the fact that the small
particles have greater surface areas per unit mass, their potential to carry toxins may
be greater.
There is increasing evidence that ambient nanoparticles have consequences and
may be more toxic than larger particles in the fine and coarse mode. The current