Ecotoxicology of Manufactured Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 281

' insoluble '. A dialysed suspension of nanoparticulate zinc oxide was as toxic to the
freshwater alga Pseudokirchnerilla subcapitata as a suspension of bulk zinc oxide
or an equivalent concentration of zinc chloride in water. Failure to test for solubility
effects might have led to the erroneous conclusion that a suspension of nanopar-
ticulate zinc oxide was toxic to the alga.
The photocatalytic activity of nanoparticles can be an additional contributor
to their toxicity. Adams et al. (2006a, 2006b) showed that the antibacterial activity
(to Bacillus subtilis and Escherichia coli ) of both TiO 2 and SiO 2 increased signifi -
cantly in the presence of UV light. Laboratory tests should incorporate some
assessment of photolytic effects so that they can be related to real effects in the
environment.
In some cases it is necessary to characterise effects due to impurities introduced
during the manufacturing process. As will be discussed later, the presence of impuri-
ties in carbon nanotubes (Templeton et al. , 2006) was found to result in enhanced
toxicity compared to purifi ed samples.
Whilst it is appropriate for toxicity testing to determine the concentrations of
nanoparticles causing effects on organisms, which can often be at concentrations
far higher than ever encountered in the environment, the effect of long-term expo-
sure to low concentrations of nanoparticles should not be neglected. Chronic, low
dose exposure may invoke mechanisms of toxicity that are not observed in short-
term laboratory toxicity tests.

7.5 Review of Ecotoxicity Studies

7.5.1 Overview

In this section, the aquatic ecotoxicology studies (algae, invertebrates and fi sh)
conducted to date are summarised. A comprehensive tabulation of ecotoxicity data
for nanoparticles is provided in Table 7.2. It is clear that there are many data gaps
and a complete absence of ecotoxicity data for nanomaterials such as gold, silver,
cerium oxide, nanoclays and quantum dots. The effects of nanoparticles on a range
of bacterial cultures are also discussed in the ensuing sections. These data have been
included as bacteria are important constituents of ecosystems carrying out many
vital processes. In our opinion, the effects of nanoparticles on such organisms
should not be overlooked. This view was also expressed by Klaine et al. (2008) , who
noted the importance of bacteria in ecosystems as providers of key environmental
services such as primary productivity, waste decomposition and nutrient cycling. An
understanding of nanoparticle toxicity to bacteria is therefore an important con-
sideration when evaluating nanoparticle impacts on environmental systems.
By far the most used aquatic invertebrate test organism is the water fl ea, Daphnia
magna . Aside from acute toxicity tests, behaviour tests with fi ltered fullerenes have
also been conducted. Daphnia exhibited behavioural responses, with juveniles
showing an apparent inability to swim down from the surface and adults demon-
strating sporadic swimming and disorientation (Lovern and Klaper, 2006). Exposure