ROUTES OF ENTRY OF TOXIC AGENTS
Toxic chemicals can enter the body by various routes and the response to any
toxic agent may vary markedly depending on the specific route of entry. It is important
to understand the routes of entry since protecting the individual from toxic agents
depends on preventing exposure.
a. Inhalation. Inhalation is the most important route of entry for toxic agents.
Some toxic agents may produce acute effects that will be quickly recognized by the
person being exposed. Others may cause chronic effects that may take up to 25 years
to recognize, such as asbestosis from asbestos exposure.
b. Absorption. The most common occupational disease seen in the Army and
in the public sector is dermatitis. Effects on the skin and other sites of absorption are
primary irritation from contact, sensitization from repeated exposure, and systemic
poisoning from absorption.
c. Ingestion. Ingestion occurs as a result of eating or smoking with
contaminated hands, contaminated utensils, or in contaminated areas. Ingestion of
inhaled materials also occurs as a result of the natural cleaning action of the lungs.
Material is removed from the lungs by cilia and is deposited in the throat to be
d. Injection. Accidental injection occurs mainly during the administration of
drugs. Other injections may occur from the use of high pressure, air or liquid, such as in
spray painting, or from the rupture of high-pressure lines.
NATURAL BODY DEFENSES
a. The Respiratory System. The conducting portion of the respiratory system
provides a low resistance pathway for uniform distribution of gases to the air sacs in the
lungs, and it contains structures which "condition" the air and protect the lungs from at
least the largest of infectious or toxins particles in the atmosphere. Some of these
(1) Mucosa. The mucous surfaces of the nose protect nose breathers from
inhaling particles larger than 5 or 10 microns in diameter (a micron is one millionth of a
meter or approximately 1/25,000 inch). Soluble gases are largely removed by
absorption and the air is moistened and warmed (or cooled, in hot, dry conditions). In
addition, the smell receptors in the upper reaches of the nose may serve as a protective
(2) Cilia. The tracheobronchial system is lined with cilia (short hairs) that
constantly force mucus toward the larynx. When the mucus reaches the pharynx, it
may be expectorated but is usually swallowed. These "pulmonary clearance"