Biomedical Engineering Reference
In-Depth Information
dissolved fraction of emitted silver, while Meyer et al.
37
assumed that 100%
of the nanosilver contained in the socks was released. Using the character-
ization factors available for colloidal silver, both studies concluded on the
minor contribution from the releases of nanosilver to ecotoxicity-related
impacts over the entire life cycle. In a third study, Eckelman et al.
29
com-
pared the freshwater ecotoxicity impacts caused by the production of carbon
nanotubes and those caused by their emissions to the environment. Using
the USEtox model,
7, 5 9
the characterization factor for carbon nanotubes was
determined on the basis of existing literature and assuming two scenarios—
realistic and worst-case—with regard to emission, fate, transport, and effects
in the freshwater environment. In the unrealistic worst-case scenario, the
ecotoxicity exerted by carbon nanotubes in freshwater was approximately
equivalent to the ecotoxicity caused during the production of the nanotubes,
while it ranged three orders of magnitude lower under the realistic scenario.
Although other exposure routes have not been investigated in these stud-
ies, like exposure of workers and users to nanosilver or carbon nanotubes
during the production, use, or disposal stage, these results tend to lower the
anticipated risks related to the use of nanomaterials. These studies, dating
from 2011 to 2012, also constitute signals that the field of LCA has started to
bridge the gaps in the life cycle toxicity assessment of nanoparticles.
11.2.4 Limitations in Application of LCA in Studies
Despite the fact that all the identified LCA studies claim to perform an LCA—
sometimes improperly termed “life cycle analysis”—only a few meet the
holistic dimensions of LCA in both the completeness of the life cycle (scope
of the studies) and the breadth of impact coverage (impact assessment).
11.2.4.1 Goal and Scope of Studies
One major shortcoming of the LCA studies lies in the extent to which the life
cycle perspective is encompassed. To fulfill its purpose and avoid environ-
mental problem shifting, an LCA should include all life cycle stages. However,
as Figure 11.5 shows, a large number of studies are mere cradle-to-gate studies,
thus stopping after the production stage. Less than half of them include the
use stage, while only 20% go to complete the life cycle up to its disposal stage.
This choice in the system boundaries has large implications on the results
obtained throughout the study and on their interpretation by LCA practition-
ers. Eventually, it is the whole decision-making process that ends up being at
stake—let us see how.
Cradle-to-gate studies typically use functional units defined by either (i) a
mass of produced nanomaterials or (ii) a mass of manufactured nanoproduct.
Let us first take case (i). This situation has led many studies to compare the
impacts caused by producing a given mass of nanomaterials with those from
producing a same mass of conventional materials such as aluminum or steel.
