33
2.3 Exposure Pathways of Nanomaterials
Knowledge of exposure stages of nanoparticles is of great importance in terms of
risk assessment and evaluation. The exposure of nanoparticles can take place via
inhalation, ingestion, skin absorption, or injection (Hansen 2012). When human is
exposed to nanoparticles, the circulation and their fate vary, depending on the exposure form. In order to comprehend their circulation and fate in the body, these pathways should be elucidated. Below is given a concise way of these pathways.
Inhaled nanoparticles in the air come into contact with body via nasal cavity or
oral cavity. After pharynx and larynx, they follow the course of trachea which is
covered with tiny hair, cilia. The back-and-forth movement of the cilia protects
body against invaders by carrying mucus up and out. Finally, they arrive at the lobes
of the lungs via bronchial tubes. The lobes involve small spongy sacs called alveoli
where exchange of oxygen and carbon dioxide occurs. The alveolar walls are tiny
and composed of epithelial cells and tiny blood vessels called pulmonary capillaries. Thus, all of the parts of respiratory system are likely to be under the threat of
exposure. Nanomaterials such as paints and coatings, skin care sprays, sunscreen
sprays, food additives and colorings can cause pulmonary inflammation (Viswanath
and Kim 2016). Particles with smaller diameter can diffuse more easily into the lung
than larger diameter particles (Hoet et al. 2004). de Lorenzo (1970) investigated
silver-coated colloidal gold nanoparticles with a size of 50 nm using squirrel monkeys and reported that these nanoparticles can be accumulated in olfactory bulb (de
Lorenzo 1970). Accumulation of gold nanoparticles leads to intestinal epithelial cell
cytotoxicity. This occurs by mitochondria membrane depolarization and the outcomes give information about the relationship between the size of gold nanoparticles, potential cytotoxicity, and their gastrointestinal uptake (Yao et al. 2015).
Another research carried on rats revealed that 13C nanoparticles with a size of
35 nm inhaled were found in olfactory bulb and an increase in the amount of
nanoparticles was observed as the exposure duration was prolonged (Oberdörster
et al. 2004).
The second route of entry, assimilation via the peripheral nervous system, is
achieved by retrograde axonal transport. A number of viruses are known to be able
to travel via the trigeminal nerve to the semilunar ganglion in the middle of cranial
fossa. Herpes viruses can use both anterograde and retrograde axonal transport via
branches of the trigeminal nerve (Chaudhuri and Kennedy 2002). Non-biological
nanoparticles have also been observed to undergo retrograde axonal transport from
the peripheral nervous system. Hunter and Dey demonstrated the uptake of rhodamine labelled microspheres of 20–200 nm in rats (Hunter and Dey 1998).
There are many reports about nanoparticles inhaled and their side effects.
Oberdöster et.al reported that carbon nanoparticles in the range of 20–29 nm was
accumulated in the rat liver within 30 minutes’ duration of inhalational exposure
(Oberdörster et al. 2004). This indicates rapid translocation of nanoparticles
(Hansen 2012).
2 Nanomaterials and Human Health
2.3 Exposure Pathways of Nanomaterials
Knowledge of exposure stages of nanoparticles is of great importance in terms of
risk assessment and evaluation. The exposure of nanoparticles can take place via
inhalation, ingestion, skin absorption, or injection (Hansen 2012). When human is
exposed to nanoparticles, the circulation and their fate vary, depending on the exposure form. In order to comprehend their circulation and fate in the body, these pathways should be elucidated. Below is given a concise way of these pathways.
Inhaled nanoparticles in the air come into contact with body via nasal cavity or
oral cavity. After pharynx and larynx, they follow the course of trachea which is
covered with tiny hair, cilia. The back-and-forth movement of the cilia protects
body against invaders by carrying mucus up and out. Finally, they arrive at the lobes
of the lungs via bronchial tubes. The lobes involve small spongy sacs called alveoli
where exchange of oxygen and carbon dioxide occurs. The alveolar walls are tiny
and composed of epithelial cells and tiny blood vessels called pulmonary capillaries. Thus, all of the parts of respiratory system are likely to be under the threat of
exposure. Nanomaterials such as paints and coatings, skin care sprays, sunscreen
sprays, food additives and colorings can cause pulmonary inflammation (Viswanath
and Kim 2016). Particles with smaller diameter can diffuse more easily into the lung
than larger diameter particles (Hoet et al. 2004). de Lorenzo (1970) investigated
silver-coated colloidal gold nanoparticles with a size of 50 nm using squirrel monkeys and reported that these nanoparticles can be accumulated in olfactory bulb (de
Lorenzo 1970). Accumulation of gold nanoparticles leads to intestinal epithelial cell
cytotoxicity. This occurs by mitochondria membrane depolarization and the outcomes give information about the relationship between the size of gold nanoparticles, potential cytotoxicity, and their gastrointestinal uptake (Yao et al. 2015).
Another research carried on rats revealed that 13C nanoparticles with a size of
35 nm inhaled were found in olfactory bulb and an increase in the amount of
nanoparticles was observed as the exposure duration was prolonged (Oberdörster
et al. 2004).
The second route of entry, assimilation via the peripheral nervous system, is
achieved by retrograde axonal transport. A number of viruses are known to be able
to travel via the trigeminal nerve to the semilunar ganglion in the middle of cranial
fossa. Herpes viruses can use both anterograde and retrograde axonal transport via
branches of the trigeminal nerve (Chaudhuri and Kennedy 2002). Non-biological
nanoparticles have also been observed to undergo retrograde axonal transport from
the peripheral nervous system. Hunter and Dey demonstrated the uptake of rhodamine labelled microspheres of 20–200 nm in rats (Hunter and Dey 1998).
There are many reports about nanoparticles inhaled and their side effects.
Oberdöster et.al reported that carbon nanoparticles in the range of 20–29 nm was
accumulated in the rat liver within 30 minutes’ duration of inhalational exposure
(Oberdörster et al. 2004). This indicates rapid translocation of nanoparticles
(Hansen 2012).
2 Nanomaterials and Human Health