Health Effects
Human health effects caused by exposure to toxic substances fall into two categories: short-term
and long-term effects. Short-term effects (or acute effects) have a relatively quick onset (usually
minutes to days) after brief exposures to relatively high concentrations of material (acute
exposures). The effect may be local or systemic. Local effects occur at the site of contact
between the toxicant and the body. This site is usually the skin or eyes, but includes the lungs if
irritants are inhaled or the gastrointestinal tract if corrosives are ingested. Systemic effects are
those that occur if the toxicant has been absorbed into the body from its initial contact point,
transported to other parts of the body, and cause adverse effects in susceptible organs. Many
chemicals can cause both local and systemic effects.
Long-term effects (or chronic effects) are those with a long period of time (years) between
exposure and injury. These effects may occur after apparent recovery from acute exposure or as a
result of repeated exposures to low concentrations of materials over a period of years (chronic
exposure).
Health effects manifested from acute or chronic exposure are dependent upon the chemical
involved and the organ it effects. Most chemicals do not exhibit the same degree of toxicity for
all organs.
Usually the major effects of a chemical will be expressed in one or two organs. These organs are
known as target organs which are more sensitive to that particular chemical than other organs.
The organs of the body and examples of effects due to chemical exposures are listed below.
Respiratory Tract. The respiratory tract is the only organ system with vital functional elements
in constant, direct contact-with the environment. The lung also has the largest exposed surface
area of any organ on a surface area of 70 to 100 square meters versus 2 square meters for the skin
and 10 square meters for the digestive system.
The respiratory tract is divided into three regions: (1) Nasopharyngeal--extends from nose to
larynx. These passages are lined with ciliated epithelium and mucous glands. They filter out
large inhaled particles, increase the relative humidity of inhaled air, and moderate its
temperature. (2) Tracheobronchial--consists of trachea, bronchi, and bronchioles and serves as
(Created 12/02)
UNL Environmental Health and Safety · (402) 472-4925 · http://ehs.unl.edu
conducting airway between the nasopharyngeal region and alveoli. These passage ways are lined
with ciliated epithelium coated by mucous, which serves as an escalator to move particles from
deep in the lungs back up to the oral cavity so they can be swallowed. These ciliated cells can be
temporarily paralyzed by smoking or using cough suppressants. (3) Pulmonary acinus--is the
basic functional unit in the lung and the primary location of gas exchange. It consists of small
bronchioles which connect to the alveoli. The alveoli, of which there are 100 million in humans,
contact the pulmonary capillaries.
Inhaled particles settle in the respiratory tract according to their diameters:
• 5-30 micron particles are deposited in the nasopharyngeal region.
• 1-5 micron particles are deposited in the tracheobronchial region.
• Less than 1 micron particles are deposited in the alveolar region by diffusion and
Brownian motion.
In general, most particles 5-10 microns in diameter are removed. However, certain small
inorganic particles, settle into smaller regions of the lung and kill the cells which attempt to
remove them. The result is fibrous lesions of the lung.
Many chemicals used or produced in industry can produce acute or chronic diseases of the
respiratory tract when they are inhaled (Table 5). The toxicants can be classified according to
how they affect the respiratory tract.
• Asphyxiants: gases that deprive the body tissues of oxygen
• Simple asphyxiants are physiologically inert gases that at high concentrations displace
air leading to suffocation. Examples: nitrogen, helium, methane, neon, argon.
• Chemical asphyxiants are gases that prevent the tissues from getting enough oxygen.
Examples: carbon monoxide and cyanide. Carbon monoxide binds to hemoglobin 200
times more readily than oxygen. Cyanide prevents the transfer of oxygen from blood to
tissues by inhibiting the necessary transfer enzymes.
• Irritants: chemicals that irritate the air passages. Constriction of the airways occurs and
may lead to edema (liquid in the lungs) and infection. Examples: hydrogen fluoride,
chlorine, hydrogen chloride, and ammonia.
• Necrosis producers: Chemicals that result in cell death and edema. Examples: ozone and
nitrogen dioxide.
• Fibrosis producers: Chemicals that produce fibrotic tissue which, if massive, blocks
airways and decreases lung capacity. Examples: silicates, asbestos, and beryllium.
• Allergens: Chemicals that induce an allergic response characterized by
bronchoconstriction and pulmonary disease. Examples: isocyanates and sulfur dioxide.
• Carcinogens: Chemicals that are associated with lung cancer. Examples: cigarette
smoke, coke oven emissions, asbestos, and arsenic.
Not only can various chemicals affect the respiratory tract, but the tract is also a route for
chemicals to reach other organs. Solvents, such as benzene and tetrachloroethane, anesthetic
gases, and many other chemical compounds can be absorbed through the respiratory tract and
cause systemic effects.
(Created 12/02)
UNL Environmental Health and Safety · (402) 472-4925 · http://ehs.unl.edu
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