Ecotoxicology of Manufactured Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 287

greater adsorption of the positively charged C 60 derivative. Inhibitory concentra-
tions for this derivative were relatively high at 10 mg/l. The likelihood of reaching
such concentrations in an aquatic system needs to be considered in assessing the
risk of impacts.
Fang et al. (2007) demonstrated that the Gram-negative bacterium Pseudomonas
putida responded to oxidative stress from nano-C 60 by changing membrane com-
position, decreasing the amount of unsaturated fatty acids in favour of cyclopro-
pane fatty acids. Similar adaptive changes in membrane composition and behaviour
were observed for the Gram-positive B. subtilis at concentrations of C 60 as low as
0.01 mg/l.
In soil systems, the addition of an aqueous suspension of nano-C 60 (1 mg/kg) or
as C 60 in granular form (1000 mg/kg) was shown to have little impact on soil micro-
bial communities or on microbial processes (Tong et al. , 2007). This is possibly not
surprising given the high concentrations needed to have effects in aquatic systems.
The environmental impacts of SWCNTs in effl uents reaching estuarine systems
were examined using the estuarine meiobenthic copepods Amphiascus tenuiremis
(Templeton et al. , 2006). The impacts were critically dependent on the presence of
impurities, as found elsewhere and discussed earlier. Purifi ed SWCNTs showed no
effects, whereas unpurifi ed nanotubes showed increased effects on life cycle mortal-
ity in microplate exposures conducted over 35 days. These effects included increased
mortality, reduced development rate and success, and reduced fertilisation success
at 10 mg/l, but no deleterious effects at 1.6 mg/l. Signifi cantly, a manufacturing by-
product, a soluble fl uorescent fraction, showed chronic toxicity at sub-mg/l concen-
trations. The mechanism of toxicity was not examined but it was postulated that
ingestion of nanoparticles may have resulted in physical disruption of feeding
appendages, penetration of the gut wall, and/or active uptake followed by oxidative
stress.
One of the most cited studies on C 60 impacts on aquatic organisms is that by
Oberdorster (2004) on juvenile large-mouth bass. The study found oxidative damage
in the form of lipid peroxidation in the brains of the juveniles after a 48-h exposure
to 0.5 mg/l of uncoated C 60 nanoparticles. Total glutathione levels were also depleted
in the gills. These fi ndings followed the work of Foley et al. (2002) showing that a
water soluble fullerene derivative (C 61 (COOH) 2 ) was able to cross cell membranes
and reinforced the fears that engineered nanoparticles, many of which are redox
active, represented a major environmental threat (Colvin, 2003).
As noted earlier, ' water - soluble ' nano - C 60 can be prepared from THF soluble
fractions mixed with water. Even after the THF is notionally removed by evapora-
tion, some can remain. It was shown that fathead minnow ( Pimephales promelas )
exposed to aqueous solutions of 0.5 mg/l of nano-C 60 prepared from THF solutions
showed 100% mortality within 18 hours (Zhu et al. , 2006 ). Nano - C 60 prepared by
water stirring showed no toxic effects, although there was increased lipid peroxida-
tion in the brain tissue and gills, together with increased expression of CYP2 family
isozymes in the liver compared to controls. Similarly, an order of magnitude greater
toxicity of the THF - derived C 60 was observed with Daphnia magna . At the same
time, a second study of Daphnia magna by Lovern and Klaper (2006) found that
for C 60 samples sonicated in water for 30 minutes, the LC 50 was 7.9 mg/l compared