Environmental Risks of Nanomaterials - Nanotechnologies for Water Environment Applications - page 596

the smaller the particles are, the more of them are absorbed and the deeper into the body
they can go (Helland, 2004).
The most critical concern of health and environmental effects occurs when NPs
are aerosolized. Aerosolized NPs can enter the human body via inhalation. Uptake and
translocation of NMs into the gastrointestinal tract can occur after taking food, drinks,
and medicine. For instance, vitamin E NPs (~100 nm) are used in beverages and stable
in the solution (Chen et al., 2006). Sources of NMs from food may be from: (a) food
manufacturing; (b) food packaging, (c) the presence of vitamins and minerals; and (d)
the food chain from eating crops, meat or fish containing NMs. The degree of
contamination of the human food chain by NMs will depend on water quality and
whether or not NMs contaminate agricultural land for farming. Ingestion of aquatic
organisms such as fish and shellfish (e.g., molluscs and crustaceans) may cause an
accumulation of NPs in human body. For instance, molluscs are known to accumulate
suspended particle and sediment-associated pollutants (Galloway et al., 2002). Because
some of the NMs may be adsorbed onto natural particulates, these mollusks are
preferred candidates for uptake of manufactured NPs released into the environment.
Accidental spillages of NPs may also result in direct human exposure to NMs via
skin contact, inhalation of atmospheric aerosols, drinking of contaminated water, or
ingestion of contaminated vegetables and foodstuffs (Donaldson et al., 2000).
Physicochemical characteristics, such as surface area or size, acidity, and metal content,
of NMs may have possible adverse health effects.
17.3.2 Toxic Effects of NMs on Living Organisms
Particle toxicology is a mature science based on the mechanisms of lung injury
by inhaled particles (Oberdörster et al., 2005a). Inhaled NMs are efficiently deposited by
diffusion in all regions of the lung. Inhaled or instilled ambient NMs can induce
pulmonary inflammation, oxidative stress, and distal organ involvement. Research
results show that occupational exposure to quartz, mineral dust particles, and asbestos
fibers induce oxidative injury, inflammation, fibrosis, cytotoxicity, and mediator release
from lung target cells (Nel, 2005). Recent hazardous evaluations of NMs focused mainly
on damage to lung tissue after inhalation. Oxidative stress (the production of damaging
oxygen radicals) is likely involved in cytotoxicity. Oxidative stress refers to a state in
which glutathione (GSH) is depleted while oxidized glutathione (GSSG) accumulates
(Halliwell and Gutteridge, 1999). Mechanistic hypotheses can explain the biology of
oxidative stress by proteomics and genomics tools (Xiao et al., 2003). Clinical and
experimental studies indicate that an ability to generate reactive oxygen species (ROS)
play a role in the ability of NPs to induce lung injury (Oberdörster et al., 2005b). There
is a direct relationship between the surface area, ROS-generating capability, and
proinflammatory effects of NMs in the lung. ROS generation and oxidative stress can