Page 301 - Industrial Ventilation Design Guidebook

5.3 TOXiCITY AND RISKS INDUCED BY OCCUPATIONAL EXPOSURE TO CHEMICAL COMPOUNDS 257

manual tasks nowadays. Thus, relatively few possibilities for substitution are
left in individual workplaces. One rather common exception does exist; very
fine powders can often be replaced with granular or liquid products. All possi-
bilities to replace solvent-based products with water-based alternatives have
not yet been utilized. However, one must be aware of the possible novel risks
involved with the use of the new products; for example, when acid-cured fur-
niture paints and lacquers, which released formaldehyde, have been replaced
with acrylic resins, skin sensitization has become more common among furni-
ture painters.
Since process disturbances do take place, and accidental releases are
possible, even from processes closed under normal conditions, the plants
where highly toxic or sensitizing substances are in use or may be generated
should be provided with continuous monitoring and alarm systems in the
critical areas.
5.3.2.2 Exposure Routes
The exposure routes include the lungs, i.e., inhalational exposure, the
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skin, i.e., dermal exposure, and the mouth, i.e., oral exposure. ' Inhalation
is usually considered to be the most important route for occupational expo-
sure. Some chemicals are also absorbed via the skin or damage (irritation or
sensitization) to the skin, and thereby amplify their own absorptions. Poor
personal hygiene may result in oral exposure from eating or smoking with
dirty hands. Toxic effects also often depend on the exposure route. The effects
of irritating agents occur at the contact site. On the other hand, many com-
pounds are distributed widely in the body and the target organ may be situ-
ated far from the entry site. Compounds may become concentrated in certain
organs. The organ with the highest concentration is, however, not necessarily
the target organ; for example, lead is accumulated in the bones but its most se-
vere effects appear in the central nervous system. Many lipophilic carcinogens
are accumulated in the adipose tissue but the cancer does not usually develop
there but rather in the target organs, such as the liver, the kidneys, or the
5 J>5 57
1. ungs. ' ~
Inhalational Exposure
Gases, vapors, mists, and dusts are mainly absorbed into the body
through the lungs. Lipid-soluble vapors, especially those of solvents, and
gases reach the alveolar space without any difficulty from where they pass
through the respiratory tract, and diffuse readily across alveolar lining to
reach the systemic circulation. Passive diffusion is based on a concentration
gradient between alveolar air and the blood. The rapidity of the saturation
of the blood with gaseous compounds largely depends on the blood and
lipid solubility of the gas. Highly blood- and lipid-soluble compounds reach
saturation slowly whereas vapors and gases with low blood- and lipid-solu-
58 60
bility rapidly become saturated in the blood. " Also, water-solubility and
reactivity greatly affect penetration through the lung. Very water-soluble
and reactive compounds tend to dissolve in the mucus in the upper respira-
tory airways, or react with proteins in the mucus, and only a small portion
of the dose of such compounds ever reaches the alveolar region of the lungs.
Examples include sulfur dioxide and formaldehyde. Especially, the latter