Environmental Engineering Reference
In-Depth Information
Most cells of plants, algae, and fungi possess cell walls that constitute a primary
site for interaction and a barrier for the entrance of NMs into their cells. The diameter of
pores (5-20 nm) across the cell wall determines its sieving properties. However, the
NMs may cross the cell membranes using embedded transport carrier proteins or ion
channels (Navarro et al., 2008). In addition, consumption of organic compounds that
contain NMs is another mechanism for algae and fungi to take NMs (Fischer-Parton et
al., 2000).
17.3.1 Human Exposure to NMs
For NMs to be risk there must be both a potential for exposure and a hazard, such
as toxicity, that results from the exposure (Wiesner et al., 2006). Large concentrations of
NPs may be present in occupational environments, where human exposure is mainly
through the respiratory system and the skin. Numerous studies have been done on
worker exposure to NPs produced unintentionally in occupational environments. The
major routes into advanced organisms such as human beings are through uptake of NMs
by inhalation or ingestion (Dowling, 2004). The inhalation of NMs leads to the
deposition of NPs in the respiratory tract and lungs, resulting in lung-related diseases
such as asthma and bronchitis. The uptake and translocation of NMs also could lead to
the accumulation of NPs in the brain. Parak et al. (2002) reported that when quantum
dots are deposited on a collagen substrate where breast cancer cells are deposited on, the
cells incorporate the quantum dots that underlie them, which provides a rapid means for
assessing the cells' potential to metastasize or spread (as a cancer) from one part to the
other parts of the body. However, these quantum dot-based NMs may exert adverse
effects on the liver, nervous and cardiovascular systems.
Human exposure to NPs can occur through the gastrointestinal tract, and the skin,
where NPs may enter in through sweat glands and hair follicles. There are many
consumer products containing NPs already in the market that are applied to the skin,
such as cosmetics, suntan lotion and baby products that regulate and improve the
moisture, odor or color. There is some evidence that dermal exposure to NPs may lead to
direct penetration into the top layer of the skin and possibly into the blood stream
(Aitken et al., 2004). Skin exposure to cosmetics, sunscreens, and dust may result in the
uptake of NPs by human beings, as NPs smaller than 10 nm could enter into the hair
follicle and stratum corneum and, sometimes, the viable epidermis (Baroli et al., 2007).
NPs that are swallowed will sooner or later end up in the intestinal tract. According to a
report by the SwissRe, particles < 300 nm can reach the blood stream, while particles <
100 nm are also absorbed in various tissues and organs (Hett, 2004). As a general rule,
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