Biomedical Engineering Reference
In-Depth Information
It can also be noted from these models that the disposal stage, and notably
recycling, is not fully represented. Only two studies have addressed recy-
cling but in an incomplete manner, primarily because of the adopted system-
oriented perspective. Mueller and Nowack
84
have defined the amount of
nanomaterials generated from recycling process as “leaving the system”
without further consideration, for example, exported outside the system
boundaries (Switzerland). Gottschalk et al.
86,87
have raised the difficulty to
quantify the amount of nanomaterials leaving a certain recycling process
and has consequently assumed that all particles entering the recycling com-
partment were eliminated in the model (either combusted or incorporated
in new materials). The authors of both studies have advanced that sewage
sludge, wastewater, and waste incineration of nanoproducts were the major
pathways through which nanoparticles enter the environment. However,
with the likelihood of recycling to become a major concern for exposure to
nanoparticles in the future (see Section 11.2.4), this demonstrates that further
research is still needed to cover the life cycle emissions of nanoparticles in a
comprehensive manner.
11.3.2.2 Inventory for Nanoproduct-Specific Processes and Potential Releases
The nanoproduct-specific processes, for example, the insertion of the nano-
materials in a matrix during the manufacture of the nanoproduct or the
grinding of the nanoproduct in view of its recycling, are processes for which
little consistent data are currently available (see Section 11.2.4). In addition,
the difficulties to quantify nanoparticle releases (see above Section 11.3.2.1)
have compelled LCA practitioners to narrow down their ambitions and
merely identify “potential” releases in qualitative manner, relying on the fact
that the magnitude of the emissions is strongly dependent on (i) the location
of the nanomaterials in the product and its structure, and/or (ii) the type
of external pressures that the product undergoes during its life cycle.
74,76, 89,90
These two major data shortcomings in the settings of complete life cycle
inventories are discussed below for each life cycle stage.
Material extraction
is the life cycle stage that is least affected by the spe-
cific issues of nanoparticles as, depending on the type of nanoparticle (e.g.,
metal oxide, carbon), the specific extraction processes will in most cases cor-
respond to those used in any LCA; no releases of engineered nanoparticles
occur at this stage.
Transport
of nanomaterials or nanoproduct might lead to accidental emis-
sions through leakage or damage of the transport packaging; however, con-
tinuous emissions during this stage are unlikely for most products.
Manufacturing
of nanomaterials (synthesis) can be done through a variety
of production pathways, which can be distinguished into top-down (start-
ing from bulk materials) and bottom-up (starting from atomic or molecular
level) approaches. These approaches can be further distinguished into wet
(using solvents and liquid reagents in lithography or chemical coprecipitation)
