Ecotoxicology of Manufactured Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 296

7.6 General Conclusions and Future Directions

As has been shown in this chapter, to date, very few ecotoxicity studies on manu-
factured nanoparticles have been conducted. With the exception of TiO 2 , even the
most basic aquatic ecotoxicity testing data set recommended for the regulation
of new materials (algae, invertebrate and fi sh) is not available in the scientifi c lite-
rature. In particular, there is a notable absence of terrestrial ecotoxicity data includ-
ing phytotoxicity.
Clearly a lot more work is required to address these defi ciencies. Firstly,
the development and application of validated toxicity testing protocols that can
be applied to new nanomaterials and formulations that enter the marketplace
is required. This will lead to the generation of basic toxicity testing data for a
range of manufactured nanomaterials allowing some assessment of hazards to
be made. Secondly, targeted research to identify the ecotoxicological properties
of manufactured nanoparticles needs to be carried out. This work should
encompass:

i. Research studies that address fundamental questions of how nanoparticle size,
shape and reactivity infl uence ecotoxicity. To address this important question it
is essential to conduct comparative studies that have appropriate bulk material
controls and also take into account the potential for nanoparticle dissolution to
contribute to toxicity. Nanoparticles do not form simple dispersions in solution
and may aggregate, dissolve or oxidise. This raises fundamental questions about
how we should interpret data from current toxicity tests with nanoparticles and
what is the most appropriate metric of dose.
ii. Given the widespread observations of nanoparticle aggregation in aqueous
solutions, understanding the toxicity of nanoaggregates and how they might
differ from stabilised nanoparticles is also important. Interactions between
nanoparticles and natural colloids leading to the formation of heterogeneous
structures may also occur in real waters and soil profi les which may well change
toxicity.
iii. The long term effects of low concentrations of manufactured nanoparticles on
organisms need to be studied, as they are not characterised by routine toxicity
testing, which often use test concentrations that are much higher than typical
environmental concentrations and short exposure durations. Long periods of
very low dose may be important. Sub-lethal effects studies and an understand-
ing of exposure pathways (e.g. importance of gut absorption of nanoparticles),
bioaccumulation and trophic transfer are also needed.
iv. Our focus is currently on relatively simple manufactured nanoparticles. As
nanotechnology evolves, the challenge will be to understand how the varied
range of composite materials and surface modifi ed particles affect toxicity.
Ecotoxicologists will need to keep pace with these exciting developments. In
our opinion, these challenges are best addressed by multidisciplinary teams in
which ecotoxicologists work alongside chemists, physicists, physiologists, life
cycle assessment specialists and the nanotechnologists designing these new
materials.