Fate and Transport of Nanomaterials in Aquatic Environments - Nanotechnologies for Water Environment Applications - page 513

derivatives could cross the external cellular membrane, and it localizes preferentially to
the mitochondria (Foley et al., 2002). Nano-Ceo is substantially more toxic than highly

soluble derivatives such as Cj, Na +2 " 3 [C6oO7-9(OH)i2-i5] 2 " 3 ", and Ceo(OH)24; sparingly
soluble fullerenes may cause damage to cellular membranes even at relatively low
concentrations, and the resulting toxicity may diminish as the fullerene cage becomes
more fully derivatized and water soluble (Sayes et al., 2004). SWNTs can inhibit the
growth of human HEK293 cells by inducing cell apoptosis and decreasing cellular
adhesion ability. HEK293 cells exhibit active responses to SWNTs such as secretion of
some 20-30 kd proteins to wrap SWNTs, aggregation of cells attached by SWNTs and
formation of nodular structures (Cui et al., 2005). Kang et al. (2007) reported that, after
incubated for 60 min, the percentage of inactivated E. coli K12 cells was 79.9 ± 9.8% on
highly purified pristine SWNT aggregates averaged and 86.8 ± 6.8% on a SWNT-coated
filter, which was significantly higher the average of the free-swimming cells (7.2 ±
2.4%) and the control (7.2 ± 2.4% without SWNT). In addition, the viability of the free-
swimming cells was independent of the SWNT whereas cells on SWNT aggregates
always exhibited a substantial loss of viability. These results indicate that physical
contact between cells and NMs is critical.

Interaction of water-soluble semiconductor QDs (cadmium selenide capped with
a shell of zinc sulfide, complete with biotin surface functionality) with super coiled
DNA resulted in DNA damage. Plasmid damage was observed in assays run with DNA
isolated from dots at time 0, indicating immediate modification upon mixing the dots
and the DNA (Green and Howman, 2005). Incubating agglomerates of 77-nm elemental
carbon (EC) and 21 nm TiCh particles with alveolar macrophages (one of many types of
white blood cells) would result in arachidonic acid (AA) and the cyclooxygenase (COX)
products. NPs (e.g., the mixed carbon NPs, SWNT, multiple wall NT, the standard urban
particulate matter) activate human platelets and stimulate them to aggregate, or clump
together; the same NPs stimulated blockage of the carotid artery in the rat model
(Science Blog, 2005). These four types of NPs were shown to activate the glycoprotein
integrin receptor on platelets that is vital to their aggregation. Ceo, known as "bucky
ball" was the exception, showing no effect on human platelet aggregation and very little
effect on rat thrombosis (Science Blog, 2005). Reactive MgO NPs and halogen (C\i,
Br2) adducts of these MgO NPs were reported to change Gram-positive and Gram-
negative bacteria as well as spores in the cell membranes, resulting in the death of the
cells. It is proposed that abrasiveness, basic character, electrostatic attraction, and
oxidizing power (due to the presence of active halogen) combine to promote these
biocidal properties (Stoimenov et al., 2002).

The third set of evidence is obtained from studies on toxic effects of NPs in
different host organisms (see Table 15.8). Although Kostarelos et al. (2007) reported
that cellular uptake of ^CNTs is independent of functional group and cell type, the
toxicity of different ^CNTs on different cells was not reported. Oberdorster (2004)