The Inhalation of Air Contaminants

Air contaminants are exogenous substances in indoor or outdoor air, and include both particulates and gaseous contaminants that may cause adverse health effects in humans or animals. In addition, they may affect plant life and impact on the global environment by changing the atmosphere of the Earth [5]. Various physical, chemical and dynamic processes may generate air pollution leading to the emission of gases, particulates, or mixtures of these, into the atmosphere [6]. Whilst major attempts have been made to reduce emissions from both stationary and mobile sources, millions of people today face excessive air pollution in both occupational and urban environments [7, 8]. Many industrial and commercial activities release toxic contaminants in gas, vapor or particulate forms, and occupational and environmental health problems can potentially arise where such releases are not controlled properly. Moreover, air contaminants today are not limited to the urban environment, nor to the industrial workplaces, but may

104 | 4 Novel In-Vitro Exposure Techniques for Toxicity Testing and Biomonitoring Table 4.1 Types of airborne contaminants (from [3, 9, 10]).

Type Properties

Gas These are substances that exist in a gaseous state at room temperature and pressure. Only by the combined effects of increased pressure and decreased temperature, can gas be changed to a liquid or perhaps solid state. Processes that involve high temperature, such as welding operations and exhaust from engines, can potentially generate toxic gases such as oxides of carbon, nitrogen or sulfur.

Vapor This is the gaseous phase of a substance that ordinarily is in a liquid or solid state at room temperature and pressure. Vapor can convert to a liquid state either by increasing pressure and/or reducing temperature. Several occupational practices may produce toxic vapors, such as charging and mixing liquids, painting, spraying, and dry cleaning or any other activities which involve volatile solvents or chemicals.

Dust This is a small solid particle, usually produced by different mechanical processes such as grinding, cutting, sawing, crushing, screening, or sieving. Dust particles may originate from organic materials. Dust particles have a nonspherical shape, with a wide range of sized from a few nanometers (nanoparticles) to larger particles of > 100 |xm.

Fiber This is an elongated or long solid particle with an aspect ratio (length:width) more than 3 : 1. There are two types of fibers: natural (e.g., asbestos), and synthetic or man-made (e.g., glass) fiber. Asbestos is the most important natural fiber, as it can induce asbestosis and lung cancer in workers who have experienced heavy exposure.

Fume This is a solid aerosol produced by combustion, sublimation or condensation of vaporized materials. Metallic fumes usually form in air due to the oxidation of metallic vapors. Fume particles are spherical and extremely fine, usually < 0.1 |xm diameter, though the size can increase by aggregation or flocculation as the fume ages. High-temperature operations such as arc-welding, torch-cutting and metal smelting can generate extremely fine metal oxide fumes.

Smoke This is a complex compound that involves solid and liquid aerosols, gases and vapors that usually result from the incomplete combustion of organic materials. For example, tobacco smoke contains thousands of chemical substances, most of which are toxic or carcinogenic. Although primary smoke particles are between 0.01 and 1 |xm diameter, they can aggregate and produce extremely larger particles known as soot.

Mist This is a suspended spherical liquid droplet formed by mechanical dispersing of a bulk liquid such as spraying and atomizing. Mist droplets have their parent liquid properties with a wide range of sizes, ranging from a few to more than 100 |xm. All processes involving high-pressure liquids which can potentially generate mists, such as paint-spraying, need to be adequately controlled. Other examples of mists include oil mists in cutting and grinding operations, acid mists in electroplating, and acid or alkali mists from pickling operations.

Fog This is a suspended spherical liquid droplet aerosol (similar to mist), but it is formed by the condensation of vapor phase on particle nuclei of the air. The size of fog droplets (1-10 |xm) is less than that of mists.

be common indoor air contaminants present in office workplaces, schools, and hospitals.

Based on their physical properties, airborne contaminants can be classified as two main types:

• Gases and vapors or dissolved air contaminants.

• Aerosols or suspended air contaminants.

The term "aerosol" refers to both liquid droplets and solid particles suspended in the air such as dust, fiber, smoke, mist, and fog. These terms can be defined as shown in Table 4.1.

Three main routes of exposure to chemicals are inhalation, dermal absorption, and ingestion [11]. Inhalation is considered to be the most important means by which humans are exposed to airborne chemicals. The severity of toxic effects of inhaled chemicals is influenced by several factors such as the type of air contaminant, airborne concentration, size of airborne chemical (for particles), solubility in tissue fluids, reactivity with tissue compounds, blood-gas partition coefficient (for gases and vapors), frequency and duration ofexposure, interactions with other air toxicants, and individual immunological status [9-12]. The site of deposition/action of inhaled toxicants will determine, to a great extent, the ultimate response of the respiratory tract to inhaled chemicals. After inhalation, airborne contaminants may be deposited in different regions of the respiratory tract including the nasopharyngeal, tracheobronchial and pulmonary regions.

The major physiological function ofthe respiratory tract is the transfer of oxygen to the blood and removal of carbon dioxide as a metabolic waste product. The human respiratory tract has a very large surface area ofapproximately 140 m , and a high daily exchange volume in excess of10 m [13-16]. In addition, the membrane between air and blood in the gas exchange region is extremely thin (ca. 0.4-2.5 p,m) [17, 18]. As well as olfactory, gas exchange and blood oxygenation functions, the respiratory system has evolved to deal with xenobiotics and airborne materials such as those usually occurring in the air environment [17]. However, this system cannot always deal adequately with the wide range of airborne contaminants that may occur in urban, and particularly occupational, environments [10]. As a result, the respiratory system is both a site of toxicity for pulmonary toxicants, and a pathway for inhaled chemicals to reach other organs distant from the lungs and to elicit their toxic effects at these extrapulmonary sites. Responses to inhaled toxicants range from immediate reactions to long-term chronic effects, and from specific impacts on single tissue to generalized, systemic effects [9, 12].

A Disquistion On The Evils Of Using Tobacco

A Disquistion On The Evils Of Using Tobacco

Among the evils which a vitiated appetite has fastened upon mankind, those that arise from the use of Tobacco hold a prominent place, and call loudly for reform. We pity the poor Chinese, who stupifies body and mind with opium, and the wretched Hindoo, who is under a similar slavery to his favorite plant, the Betel but we present the humiliating spectacle of an enlightened and christian nation, wasting annually more than twenty-five millions of dollars, and destroying the health and the lives of thousands, by a practice not at all less degrading than that of the Chinese or Hindoo.

Get My Free Ebook


Post a comment