Exposure via the Respiratory Tract

Respiratory tract exposure is the most common and widely studied pathway of particulate matter invasion [14, 32, 35, 51, 84], and the same is true for nanomaterials. The inhalation of airborne natural particulate matter or engineered nanomaterials may lead to serious toxic effects for example, the prolonged exposure and uptake of these materials in the human lung can cause chronic obstructive pulmonary disease and pulmonary morbidity, both of which may lead to death [32]. Therefore, it is crucial to understand how these materials enter and reside in 

10% in the tracheobronchial region. None of these nanomaterials can reach the alveolar region, as the smallest nanomaterials can easily be exhaled from the alveolar interstitial region, without deposition. Although the size-related deposition efficiency is complicated, the evidence is clear that it is particle size that determines the rates of decomposition and consequent particle-induced toxicity. 

In addition to size, the solubihty of particles is also important with regards to their deposition site. Typically, water-soluble particles are readily absorbed in all parts of the respiratory tract, whereas insoluble particles will remain inside the lung, due to their long retention time [85]. 

As particulate matters and synthetic nanomaterials are deposited in the respiratory system, they are further translocated to other organs via several pathways. The first step for the translocation is endocytosis or transcytosis [35], after which particulate matters and nanomaterials will be further transported to other organs via the blood, lymphatic drainage or, in very rare cases, the sensory nervous system [86]. The particle size, shape and surface properties greatly affect these processes. 

the endocytosis of particulate matters and nanomaterials is size- dependent, with smaller particles more easily taken up by epithelial cells than larger particles. Thus, nanomaterials are more readily translocated via endocytosis or transcytosis. 

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Since we are considering here the toxic effects of plastic materials on humans in their everyday life our main interest will he in the two exposure types mentioned above, which are the most common, namely, exposure via the respiratory tract (inhalation exposure) and exposnre by percutaneous absorption (through the skin) and perocular absorption (through the eyes). 

A substance that demonstrates the potential to induce cancer, to produce short- and longterm disease or bodily injury, to affect health adversely, to produce acute discomfort, or to endanger life of humans or animals resulting from exposure via the respiratory tract, skin, eye, mouth, or other routes in quantities that are reasonable for experimental animals or that have been reported to have produced toxic effects in humans. 

From the literature, statistically relevant toxicological data for acute toxicity testing (e. g., LCS(), LD50, dermal) are based on the exposition of 6 animals (minimum) with a control group of 6. Normally, several doses are used, one at a time, starting from close to the no-effect level (e. g., via the respiratory tract for a defined time). After exposure the animals are observed... 

Exposure to inhaled formaldehyde via the respiratory tract is usually to molecular formaldehyde vapor, whereas exposure by other routes is usually to formalin. Exposure to formaldehyde vapor can occur in industrial settings. In recent years, a great deal of concern has arisen over the potential for exposure in buildings to formaldehyde vapor evolved from insulating foams that were not properly formulated and cured or when these foams bum. Hypersensitivity can result from prolonged, continuous exposure to formaldehyde. Furthermore, animal experiments have shown formaldehyde to be a lung carcinogen. 

Type I, or immediate immune, response involves the body s production of immunoglobulin E (IgE) antibodies in lymphatic tissue that bind to the surface of mast cells and basophils and prime them for action. The antibodies are produced in B lymphocytes during the period of sensitization. Sensitization occurs as the result of exposure to appropriate antigens through the respiratory tract, dermally, or by exposure via the gastrointestinal tract. Subsequent cross-linking of the antibodies... 

Exposure to fungal spores is ubiquitous and, therefore, of pivotal importance for the development of mycoses acquired via the respiratory tract. This situation has also led to increased public awareness of the importance of indoor air quality and to the emergence of aerobiology, which has established itself as a major environmental academic discipline (Levetin and Homer). 

Almost all inhaled chlorine (>90%) is absorbed via the respiratory tract, in both humans and animals (Abdel-Rahman et ah, 1983 Nodelman and Ultman, 1999a,b Morris et al., 2005). Humans absorbed >95% of an inhaled bolus of 0.5-3 ppm chlorine in the upper airway and <5% in the lower airway, regardless of the mode of breathing or respiratory flow rate (Nodelman and Ultman, 1999a,b). Chlorine that is absorbed is not subject to metabolic biotransformation and is distributed widely throughout the body and joins the pool of chloride ions. Rats that were orally administered HO Cl in distilled water excreted the majority of C1 in the urine (36.43%) and feces (14.80%) over a 96h post-exposure period (Abdel-Rahman et al., 1983). 

Aspergillus is an ubiquitous, thermotolerant saprophyte with worldwide distribution. This dimorphic fungus derives its name from its resemblance to a brush used for sprinkling holy water (1). It is commonly found in moist soil and decomposing environment. The exposure to Aspergillus spores or conidia is universal and is acquired primarily via the respiratory tract (2). 

Available information from human exposures indicates that airborne americium-containing particles are deposited in the respiratory tract, cleared to some extent via mucociliary action, and swallowed or expelled (Edvardsson and Lindgren 1976 Fry 1976 Newton et al. 1983 Sanders 1974 Toohey and Essling 1980). Descriptions of human respiratory tract models that can be used for radiation protection also include relevant information regarding biokinetics of inhaled particles (ICRP 1994b, 1995 NCRP 1997). Quantitative data are not available, however. Supporting animal studies include inhalation exposure to aerosols of americium (Buldakov et al. 1972 DOE 1978 Gillett et al. 1985 Sanders and Mahaffey 1983 Talbot et al. 1989 Thomas et al. 1972) or intratracheal instillation of americium compounds (Moushatova et al. 1996). 

Weeks et al. (1963) reported that 80% of the 1,1-dimethylhydrazine administered via endotracheal tube to anesthetized mongrel dogs was retained in the respiratory tract. It was unclear if the retention was monitored only for the 51-64 min duration of exposure. 

Probably the vanadium compound to which people are most likely to be exposed is vanadium pentoxide, V205. Exposure normally occurs via the respiratory route, and the pulmonary system is the most likely to suffer from vanadium toxicity. Bronchitis and bronchial pneumonia are the most common pathological effects of exposure skin and eye irritation may also occur. Severe exposure can also adversely affect the gastrointestinal tract, kidneys, and nervous system. 

The presence of DAAB as a dye contaminant in cosmetics and food products could result in low level exposures via the oral and dermal routes. Occupational exposure may occur through inhalation and dermal contact where these chemicals are produced or used as a chemical intermediate and polymer additive. DAAB is harmful to the respiratory tract, skin, and eyes. Most exposures to the general population are typically through consumption of food and use of cosmetics containing DAAB impurities. 

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