Size/Shape – Property Relationships of Non - Carbonaceous Inorganic Nanoparticles and their Environmental Implications - Environmental and Human Health Impacts of Nanotechnology - page 98

(i) Titanium dioxide and other photoactive semiconductor nanoparticles (e.g.
CdSe, PbS, MoS 2 ). Titanium dioxide and zinc oxide nanoparticles are already
available in commercial sunscreen creams and multiple applications are being
developed using semiconductor nanoparticles, including sensors, cells for solar
power, water-splitting for hydrogen gas generation, air cleaners, and so on. A
recent report on exposure modelling of manufactured nanoparticles in the
environment (in Switzerland) indicated that nano-TiO 2 is a substance of
concern (Mueller and Nowack, 2008).
(ii) Silver nanoparticles. Silver nanoparticle coatings are already on many com-
mercially-available products (e.g. bandages, clothing) as antibacterial barriers.
While Mueller and Nowack's (2008) environmental modelling, mentioned
above, concluded that nano-sized silver pose little risk in Switzerland based
upon present data, the widespread use of nano-sized silver calls for additional
study.
(iii) Nano zero-valent iron particles. As these nanoparticles have proven to be
effective at decomposing halogenated organics in the fi eld, their continued and
potentially increasing use is likely.
Aside from knowing entry routes of nanoparticles into the environment, research-
ers will need to build a comprehensive knowledge base linking aspects of nanopar-
ticle structure or chemistry (e.g. size, shape, coating, composition) to their behaviour
in a simulated or actual environmental system. This is important because an enor-
mous number of nanoparticle types are possible and it will be impossible to test
every single one of them. Understanding trends in nanoparticle behaviour provides
the ability to predict how different nanoparticles behave based upon their charac-
teristics, even in the absence of hard data for a particular nanoparticle. Science
policy makers and regulatory agencies will fi nd this ability to predict behaviour
especially useful.
Towards the goal of linking nanoparticle structure and chemistry to behaviour,
it is necessary for studies to use exceptionally well characterized nanoparticles. In
addition to particle size and composition, features such as particle shape, coatings
and aggregation state should be carefully measured or controlled if possible.
Researchers should also account for any known impurities. Preferably, in any study
connecting nanoparticle characteristics to behaviour, nanoparticle features should
be varied carefully. For example, in a study of size dependence in nanoparticles,
researchers should strive to maintain the same morphology, aggregation state and
coatings between different sizes. If this is not possible due to synthetic limitations,
the other varying characteristics must be taken into account when interpreting
data. Given the need for well characterized, pure nanoparticles, it may behove
environmental scientists to synthesize and characterize their own materials or to
collaborate with nanochemistry specialists.
In addition to beginning studies with well defi ned, well characterized nanopar-
ticles, if possible it is important to be able to characterize the nanoparticle structure
and chemical state throughout the study. Nanoparticles may change during the
study, altering their morphology, degrading (e.g. oxidizing), aggregating or losing
coatings. Such changes will doubtless alter the physical and chemical behaviour of