Release from Composites by Mechanical and Thermal Treatment - Safety of Nanomaterials along Their Lifecycle - page 270

melting point of 850°C for silver. SEM pictures of the silver residue, collected from
the crucible after an 850°C heating, showed that melting already occurred.
Walser et al. (2012) demonstrated the persistence of nano-objects in a munici-
pal solid-waste incineration plant. Walser et al. (2012) used nano-CeO 2 particles
due to low cerium background concentrations in the waste and the environment.
The nanoparticles were introduced (a) directly onto the waste before incineration
or (b) into the gas stream exiting the furnace. Samples were taken from the flue gas
and the residues of the combustion process and analyzed for cerium content. Nano-
objects were shown to survive the waste incineration process and were detected in
the fly ash and slag but not in the stack emissions. This suggests that no significant
nano-CeO 2 emissions can be expected from thermal waste treatment plants provided
that up-to-date flue gas cleaning systems are installed.
12.4 CONCLUSIONS AND RECOMMENDATIONS
Harmonized approaches are needed for various processes along the lifecycle to
enable risk assessors, regulators, and product developers to assess possible risks of
exposures for humans and the environment. The review of the different test methods
shows that release testing is feasible and also that not all test setups can deliver the
data needed to assess the exposure risk for a given release scenario. From the review
of aforementioned release studies, several general conclusions can be derived.
Conditions for harmonized testing: All general criteria for harmonized or stan-
dardized approaches certainly apply also for nano-objects release testing. They are
high accuracy, reproducibility, and comparability. Also all parameters of significant
influence for the results should be known and well defined. An additional require-
ment is the safety for the testing personnel. Affordability of the testing equipment
and easiness of use and cleaning are further criteria.
Data requirements for testing: The purpose of the release testing is to obtain
information for specific exposure scenarios, modeling of these exposures, and to
enable or at least facilitate exposure assessments linked to internal doses, for exam-
ple, for humans. This means that the test methods should allow the determination
of release rates, particle size distributions, and concentrations, as well as particle
morphologies, for those particles stemming from the nanomaterial.
General setup conditions for release testing: From the requirements previously
listed, it can be deduced that the use of enclosures facilitates the discrimination of
nano-objects from background particles. The placing of any testing equipment out-
side of the enclosure, especially electrical engines, also facilitates the discrimination
as well as determination of release rates. For most test setups some variability in test
parameters influencing, for example, the wear energy is advantageous to allow for
a better assessment of release probabilities. Another important asset of using enclo-
sures is the safety of the testing personnel, who is not directly exposed to the released
particles with possible hazardous properties.
Grouping of release processes: Release processes may be grouped as was done
in this chapter for mechanical and thermal processes. Sometimes these cannot be
clearly separated since mechanical treatments may also cause heat, like sanding or
milling, and hence those simulated release processes will cover both thermal and