Ecotoxicology of Manufactured Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 288

to 0.5 mg/l for a THF-derived product. Sub-lethal effects such as immobilisation
were often seen in a relatively short period (1 h). Experiments using fi ltered tita-
nium dioxide in the presence and absence of initial THF showed similar toxicities,
implying no effects due to residual THF. No data were reported for THF-treated
water in the absence of titanium dioxide.
In a study conducted using larval zebrafi sh, Danio rerio , Henry et al. (2007)
investigated changes in survival and gene expression after exposure to aggregates
of C 60 prepared by two methods: stirring and sonication of C 60 in water (C60- water);
and suspension of C 60 in THF followed by evaporation under reduced pressure,
resuspension in water and sparging with nitrogen gas (THF- C 60 ). Survival of larval
zebrafi sh was reduced in THF- C 60 and THF -water but not in C 60 - water. The great-
est differences in gene expression were observed in fi sh exposed to THF- C 60 and
most of these genes were similarly expressed in fi sh exposed to THF- water. Analyses
of THF- C 60 and THF -water by gas chromatography-mass spectrometry did not
detect THF but found THF oxidation products γ - butyrolactone and tetrahydro - 2 -

furanol. The toxicity of - butyrolactone (72 - hr LC 50 concentration 47 mg/l) indi-

cated that the toxicity effects in observed in the THF- C 60 treatment could have
resulted from

γ

-butyrolactone toxicity. The use of THF as a dispersing agent is a
controversial issue. For additional information on this topic, the review by Klaine
et al. (2008) is recommended.
The most defi nitive toxicity study to date, by Oberdorster et al. (2006a) , exam-
ined daphnids, the freshwater crustacean Hyalella , marine copepods and fathead
minnows using THF- free nano - C 60 preparations. Daphnia magna showed no acute
toxicity up to 35 mg/l. However, there was uptake of nanoparticles and sub-lethal
effects such as delays in moulting, reduced ability to produce offspring and some
mortality at concentrations as low as 2.5 mg/l. Acute toxic effects were absent with
Hyalella azteca at concentrations below 7 mg/l. Similarly, the marine copepod tested
showed no toxicity below 22.5 mg/l. In fathead minnow, no acute toxicity was seen
at 0.5 mg/l as already observed (Zhu et al. , 2006), and also no signifi cant biomarker
effects, based on traditional biomarkers of lipophillic exposure. Japanese medaka,
Oryzias latipes were less sensitive to nano-C 60 than fathead minnows. A comparison
of the responses of nano-C 60 and SWCNTs to fathead minnows indicated that the
latter show lesser biochemical or gene expression changes (Oberdorster et al. ,
2006a ).
It has been reported that bioaccumulation of nano-C 60 had been observed in the
gastrointestinal tract of Daphnia magna and other body compartments, with par-
ticles taken up as food. This uptake was enhanced with SWCNTs by coating the
nanotubes with lysophosphatidylcholine to make them dispersible in aqueous
media (Roberts et al. , 2007). Daphnids were shown to not only ingest the coated
nanotubes but to egest insoluble nanotubes, free of the coating, that subsequently
aggregated and precipitated.
The need to disperse CNTs for toxicity studies again raises the issue of environ-
mental relevance. Smith et al. (2007) chose to use a surfactant, sodium dodecyl
sulfate, to disperse SWCNTs for studying their toxicity to rainbow trout
( Oncorhynchus mykiss ). Their comprehensive study of physiological effects, showed
an absence of oxidative stress indicators, but rather the nanoparticles precipitated

γ