Analysis and Characterization of Manufactured Nanoparticles in Aquatic Environments - Environmental and Human Health Impacts of Nanotechnology - page 249

• Sewage treatment simulation testing
• Identifi cation of degradation product(s)
• Further testing of degradation product(s) as required
• Abiotic degradability and fate
• Hydrolysis, for surface modifi ed nanomaterials
• Adsorption - desorption
• Adsorption to soil or sediment
• Bioaccumulation potential.

Several of these properties are not directly applicable or relevant for NPs, while
others are extremely challenging to accurately determine.
To accommodate all analytical requirements, strategies need to be developed and
methods optimised for characterization of NPs (free, deposited, aggregated) and
dissolution products in a range of complex matrixes (soil, sediment, sewage sludge,
and biological tissue). Hence, it is not only advanced analytical instrumentation that
is required but, as importantly, sampling, handling, storage protocols, extraction and
digestion methods also need to be optimized and validated. Again, this list refl ects
the driving force to accommodate nanomaterials under existing regulation rather
than primarily based on scientifi c grounds on which NP-specifi c properties need to
be determined. For example, most NPs are not inherently biodegradable, although
to some extent they can dissolve, and the dissolution rate may be enhanced or
decreased by external factors. More importantly, many of the tests build on the
assumption that the nanomaterials are driven by chemical equilibrium processes
(e.g. the sorption tests and octanol-water partitioning), and this is scientifi cally
unfounded for NPs. Nanoparticle dispersions are inherently unstable (although
maybe meta-stable) and the kinetically controlled processes are chemically
irreversible.

6.3.3 Exposure Characterization in Effect Assessment Experiments

Analysis of the actual exposure situation in the effect experiments is necessary as
a third characterization tier due to the often unstable state of engineered NPs in
aqueous dispersions in general, and in the water chemistry of ecotoxicology media
in particular. But since the effects experiments require many replications and the
analytical capabilities are not necessarily at hand in the biological laboratories, it
is important to carefully consider the requirements for appropriate metrics during
the course of the experiments. Powers et al. (2007) suggest that physico - chemical
characterization should be ideally carried out on the nanomaterials as-received,
as-dosed (in the exposure medium), as interacting with the organisms with possible
changes induced by mucus and excudates, and, fi nally, as present in the organisms
(post mortem analysis). This corresponds to the strategy being outlined here and
is also similar to some of the standardization working group discussions. There may
also be a concentration dependence on some of the properties; therefore, dose-
response experiments should be individually characterized to determine such
dependency.
Although the need was not recognized in the pioneering studies of nanoecotoxi-
cology, characterization is now starting to be implemented in most effects