Emissions from Consumer Products Containing Engineered Nanomaterials over Their Lifecycle - Safety of Nanomaterials along Their Lifecycle - page 336

15.2.2 a nalytiCal i ssues
A second subject that is relevant when studying release processes of nano-products
is the use of analytical methods to detect the released materials. In the simplest case
only total element concentrations are measured and thus no size-specific informa-
tion is obtained. Several studies investigating release of Ag from products used this
approach. These measurements do not distinguish between release of dissolved Ag
(after dissolution of the nano-Ag), release of nano-Ag, and release of larger agglom-
erates or other transformation products. Other studies used size-fractionation tech-
niques before analyzing the total concentration, and therefore additional information
on the size of the released materials could be obtained. Preferably the smallest filter
size is small enough that only dissolved compounds can pass through so that informa-
tion on dissolution can be obtained. This process is very important for some ENM,
for example, Ag or ZnO, because it may result in complete elimination of the particu-
late nature of the material. In certain cases, for example, for dissolved Ag + , methods
for analysis using ion-selective electrodes are available and thus direct determination
of the truly dissolved metals is possible. The direct coupling of size-fractionation
techniques with bulk-analytical techniques, for example, field flow fractionation with
ICPMS (Hagendorfer et al. 2010; Ulrich et al. 2012), is expected to provide additional
characterization data when this method is applied in the future to more release studies.
Many studies complement the bulk chemical analyses using electron microscopic
investigations which not only allow imaging the released particles but also enable the
element-specific characterization of single particles. This technique allows gaining
direct information on possible transformation reactions, a task that the other methods
are currently not able to carry out. All comprehensive release studies need to com-
bine a suite of different analytical techniques to quantify and characterize the release.
However, many of the few published studies did not employ the full spectrum of
possible methods and thus in many cases only fragmentary information on release
was obtained. The next section that presents the release studies in detail does not dis-
criminate any studies, mainly because in the present situation with only a few release
investigations each single study, even if just with minimal analytical methods, is able
to provide some much-needed information.

15.3 RELEASE STUDIES

15.3.1 t extiles
Nano-textiles are the nano-products that have been studied most often and there-
fore a detailed comparison between different studies is possible. Most of the stud-
ies targeted nano-Ag but one study also looked at TiO 2 -containing textiles (Windler
et al. 2012). Because different studies have analyzed various commercially available
textiles, it is possible to get an overview on the concentrations of nano-Ag in the
textiles (Figure 15.2).
Surprisingly there are many “nano-Ag textiles” that do not contain any measur-
able Ag, a fact that is observed in most studies. The majority of the textiles have
Ag concentrations below 100 mg/kg, however, a few have even concentrations in