Engineered Nanomaterials as Emerging Contaminants in Water - Nanotechnologies for Water Environment Applications - page 560

Many pollutants have transitioned from being an emerging contaminant of
concern in water and drinking water (Figure 16.1). Among these are (a) nutrient control
from wastewater treatment plants into watersheds, (b) formation of disinfection
byproducts, including trihalomethanes, during drinking water treatment, (c) presence
and need to inactivate the pathogen Cryptosporidium in drinking water, (d) formation of
bromate as an ozonation disinfection byproduct during water treatment, (e) occurrence
of trace levels (parts per billion or trillion) of endocrine disruptors, pharmaceuticals and
personal care products (EDC/PPCPs) in water (Colborn et al., 1996; Kolpin et al., 2002).
With the advent of nanotechnology as a major research initiative for developed
countries, our society is recognizing the potential of NMs to occur in waterways and
pose potential risks to aquatic ecosystems and humans (Colvin, 2003; Savage and
Diallo, 2005; Maynard et al., 2006; Powers et al., 2006; Thomas et al., 2006; Wiesner et
al., 2006; Davies and Rejeski, 2007; Nowack and Bucheli, 2007; Scheufele et al., 2007).
A concern exists that NMs, because of their size and high surface area to mass
aspect, pose a risk to bacteria, aquatic organisms, higher trophic organisms and humans.
There are bewildering numbers and varieties of NMs each with unique physico-chemical
properties, including unique shape, size, surface area, surface charge, electronic,
photonic and magnetic properties, tendency to aggregate, hydrophobicity, lipophilicity,
and with coated NMs the ability to interact with biological membranes and
macromolecules. Cytotoxicity of carbon NMs has been observed at a relatively low
dose (Jia et al., 2005). Positive cytotoxicity and genotoxicity of water-soluble C 60
aggregates (n-C 60 ) has been reported (Zakharenko et al., 1997; Sayes et al., 2004; Sayes
et al., 2005; Dhawan et al., 2006). Organic acid capped CdSe/CdTe quantum dots are
toxic to cells due to Cd 2+ released from their cores and/or reactive oxygen species
formed via photooxidation processes (Derfus et al., 2004; Cho et al., 2007). Metal oxide
NMs (e.g., Fe 2 O 3 , TiO 2 and ZnO) can also cause cytotoxicity response, such as
inflammatory response and cell membrane leakage (Tran et al., 2000; Brunner et al.,
2006; Jeng and Swanson, 2006). Bacteria and virus can be inactivated in the presence of
NMs, although their efficacy varies as a function of aggregation status and surface
charge (Adams et al., 2006; Badireddy et al., 2007; Fang et al., 2007). NMs in air may
enter into human body by inhalation. Hand-mouth contact with NMs can produce high
ingestion exposure. NMs also are likely to penetrate into hair follicles, enter the skin and
be taken up by lymphatic system (Tinkle, 2005). NMs can be transported in human body
and be easily distributed to all organs (Oberdorster, 2000; Behrens et al., 2002; Kreyling
et al., 2002; Oberdorster et al., 2004; Gilmour et al., 2004). Because of these known
risks and potential unknown dangers, there is an emerging concern about the release,
occurrence and treatment of NMs in aquatic systems.
Five grand challenges were identified in 2006 to form a framework for
understanding the implications of nanotechnology (Maynard et al., 2006):