Emissions from Consumer Products Containing Engineered Nanomaterials over Their Lifecycle - Safety of Nanomaterials along Their Lifecycle - page 347

These studies about the behavior of the original sunscreen TiO 2 and the release
from commercial sunscreens show that the behavior of actually used ENM and
their behavior in their matrix (the sunscreen) are much more complicated than
the study of, for example, pure TiO 2 in water, see, for example, Ottofuelling et al.
(2011).
15.4 MODELING RELEASE AND ENVIRONMENTAL FATE
A handful of modeling studies have so far incorporated ENM release into the model
(Gottschalk and Nowack 2011). These studies modeled either the release of ENM
from products during the consumer use phase or the release throughout the whole
lifecycle of nano-products. The models vary how they conceptualize the release
of ENM. The studies can be categorized into top-down and bottom-up approaches
based on the release assessment frameworks used (Gottschalk and Nowack 2011).
The top-down approach is based on information on the use of certain products, and
uses a market fraction of nano-products and knowledge on the use of the product.
In the bottom-up approaches, data on the production of ENM is combined with
information on the distribution of the ENM to product groups. Some of the top-
down models consider only the ENM release from a very small set of nano-products
(Boxall et al. 2007; Blaser et al. 2008; Park et al. 2008; O'Brien and Cummins
2010). Some of the models using a bottom-up approach include the whole spectrum
of nano-products and an exhaustive assessment of all possible applications of ENM
(Mueller and Nowack 2008; Gottschalk et al. 2009; 2010b). In this approach an
inventory of all known commercially relevant nano-products using a specific ENM
is made and all these nano-products are categorized according to their potential to
release ENM.
Mueller and Nowack (2008) published the first modeling of ENM considering
ENM release from a whole lifecycle perspective. For nano-Ag, nano-TiO 2 , and car-
bon nanotubes (CNT) direct releases from the nano-products to air, water, soil, waste
incineration, sewage treatment plants, and landfills were modeled. Release processes
that were considered include, for example, abrasion during use and washing of tex-
tiles. Gottschalk and coworkers (Gottschalk et al. 2009; Gottschalk et al. 2010a;
Gottschalk et al. 2010b) extended this type of release modeling by replacing the sce-
nario analysis used by Mueller and Nowack (2008) with a probabilistic and stochas-
tic approach (Gottschalk et al. 2010a). The uncertainty and variability of the release
of ENM were considered by means of Monte Carlo algorithms. Release was calcu-
lated for nano-TiO 2 , nano-ZnO, nano-Ag, CNT, and fullerenes for the three regions,
United States, Europe, and Switzerland (Gottschalk et al. 2009). Figure 15.12 shows
an example of the material-flow diagrams which are the result of the modeling by
Gottschalk et al. (2009). It depicts the flows of nano-Ag in the EU, considering all
known applications of nano-Ag in products and incorporating release during pro-
duction, manufacturing, use, and disposal. The major release pathways were from
products into wastewater, caused by a high percentage of nano-Ag used in applica-
tions that have contact with water and the relatively high release of nano-Ag from
these nano-products.