Ecotoxicology of Manufactured Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 294

normal development of the embryo into an adult. Single silver nanoparticles were
observed to move across the chorion, the protective membranous tissue that pro-
tects the embryo from the external environment. The chorionic pores were large:
500-700 nm in diameter. Lee et al. (2007b) also showed that single silver nanopar-
ticles made their way into the inner mass of the embryo. The single silver nanopar-
ticles were retained by the embryo as it matured into the adult and were found
embedded in different tissues as they developed, including the retina, brain, heart,
gill arches and tail. Maturation of the zebrafi sh embryo was normal at silver con-
centrations of 8 ng/l but was affected at higher silver doses. Different abnormalities
also occurred as dose increased. Fin abnormalities and spinal chord deformities
occurred at 19 ng/l. This was followed by malformation of the heart and swelling
of the yolk sac (edema) occurred at the next highest doses. At silver concentrations
of between 44-66 ng/l, swelling of the head and eye abnormalities occurred. Both
quickly resulted in death.

7.5.5 Copper

Griffi tt et al. (2007) studied the acute toxicity of soluble copper and 80 nm copper
nanoparticle suspensions (nanocopper) to the zebrafi sh Danio rerio . Nanocopper
was acutely toxic to zebrafi sh, with a 48-h LC 50 concentration of 1.5 mg/l. Rapid
aggregation of the copper nanoparticles occurred after suspension in water, result-
ing in 50-60% of the added mass leaving the water column. The study quantifi ed
the release of dissolved copper (which is highly toxic to fi sh) from the added
nanoparticles. The measured dissolved copper concentrations alone were insuffi -
cient to explain the mortality observed in the toxicity tests, clearly indicating the
direct involvement of the nanoparticles. Histological and biochemical analysis
revealed that the gill was the primary target organ for nanoparticulate copper. To
further investigate the effects of nanocopper on the gill, zebrafi sh were exposed to
100

g/l of nanocopper or to the concentration of soluble copper released by dis-
solution of the nanoparticles. Under these conditions, nanocopper produced differ-
ent morphological effects and global gene expression patterns in the gill than
dissolved copper, clearly demonstrating that the effects of nanocopper on gill are
not mediated solely by the particle dissolution and toxicity of dissolved copper. The
authors did not include a bulk particulate copper control, so the importance of
particle size remains to be evaluated. The chemical composition of the nanocopper
was not defi ned. Clearly, release of dissolved copper from the nanoparticles would
either involve oxidation of elemental copper followed by subsequent dissolution
of the ionic copper-containing oxidation products, or release of ionic copper that
may be sorbed to the surface of the nanoparticles.

µ

7.5.6 Quantum Dots

Quantum dots (QDs) are semiconductor nanocrystals ranging from 2 to 100 nm
diameter with unique optical and electrical properties. Structurally, QDs consist of
a metalloid crystalline core and a ' cap ' or ' shell ' that shields the core and renders
the QD bioavailable. QD cores consist of a variety of metal and metalloid com-
plexes, for instance, indium phosphitle, indium arsenide, gallium arsenide, zinc-