Nanotechnology White Paper - US Environmental Protection Agency

EPA Nanotechnology White Paper
33
oil refining processes, chemical and material manufacturing processes, chemical clean up
activities including the remediation of contaminated sites, releases of nanomaterials incorporated
into materials used to fabricate products for consumer use including pharmaceutical products,
and releases resulting from the use and disposal of consumer products containing nanoscale
materials (e.g., disposal of screen monitors, computer boards, automobile tires, clothing and
cosmetics). The fundamental properties concerning the environmental fate of nanomaterials are
not well understood (European Commission, 2004), as there are few available studies on the
environmental fate of nanomaterials. The following sections summarize what is known or can
be inferred about the fate of nanomaterials in the atmosphere, in soils, and in water. These
summaries are followed by sections discussing: 1) biodegradation, bioavailability, and
bioaccumulation of nanomaterials, 2) the potential for transformation of nanomaterials to more
toxic metabolites, 3) possible interactions between nanomaterials and other environmental
contaminants; and 4) the applicability of current environmental fate and transport models to
nanomaterials.
3.3.1 Fate of Nanomaterials in Air
Several processes and factors influence the fate of airborne particles in addition to their
initial dimensional and chemical characteristics: the length of time the particles remain airborne,
the nature of their interaction with other airborne particles or molecules, and the distance that
they may travel prior to deposition. The processes important to understanding the potential
atmospheric transport of particles are diffusion, agglomeration, wet and dry deposition, and
gravitational settling. These processes are relatively well understood for ultrafine particles and
may be applicable to nanomaterials as well (Wiesner et al., 2006). However, in some cases,
intentionally produced nanomaterials may behave quite differently from incidental ultrafine
particles, for example, nanoparticles that are surface coated to prevent agglomeration. In
addition, there may be differences between freshly generated and aged nanomaterials.
With respect to the length of time particles remain airborne, particles with aerodynamic
diameters in the nanoscale range (