Page 337 - Industrial Ventilation Design Guidebook

5.3 TOX1CITY AND RISKS INDUCED BY OCCUPATIONAL EXPOSURE TO CHEMICAL COMPOUNDS 293

to acids or alkalies, in the cornea may seriously damage the visual system, Acid
and alkali burns of the eye have to be washed immediately for at least 30 min
with water. 41
A special feature of the iris is its autonomic innervation. Sympathetic acti-
vation widens the aperture of the iris whereas impulses from the parasympa-
thetic nervous system decrease the aperture size. Therefore adrenergic agonists
and anticholinergic compounds both increase the aperture of the iris, i.e.,
cause mydriasis, and antiadrenergic and cholinergic agonists decrease it, i.e.,
cause miosis. The iris can thus be considered an excellent mirror reflecting the
balance of the autonomic nervous system in the body. 140
The eye has its own hydraulic system, and disturbances in it may cause se-
rious damage to the eye. The normal eye pressure is 22 mm Hg, but when the
pressure increases to 28-30 mm Hg, the optic nerve is squeezed and becomes
hypoxic. This increase in the eye pressure may be due to acids or alkali caus-
ing inflammation in the anterior chamber of the eye, blocking the outflow of
aqueous humor back into the systemic circulation.
The lens is an avascular transparent tissue surrounded by an elastic, col-
lagenous capsule. Disturbances in the normal metabolism of the lens and rup-
ture of the lens alter its optical characteristics, and may cause cataract, i.e.,
reduced transparency of the lens. For example exposure to a herbicide, 2,4-
dichlorophenol, may cause cataract."
The retina is the part of the eye that belongs to the nervous system. Rods
and cones are the photoreceptors of the retina that synapse with the cells in
the bipolar layer in the retina, and these cells, in turn, make connections
with ganglion cells. The metabolism of retina is very active and, therefore,
the retina is sensitive to toxic insults. For example, natural retinols that were
being used in skin therapies have provoked retinal damage, perhaps by re-
placing the retinoids of the photoreceptors. Hyperbaric oxygen can also
cause serious retinal damage in immature newborn children that have had
107 137
respiratory difficulties. '
Methanol intoxication can cause blindness due to damage to ganglion
cells in the retina. The blindness results from the accumulation of formalde-
hyde and formic acid, which are metabolites of methanol. Chemical com-
pounds can also damage the visual cortex, for example, visual damage was
observed among the victims of organic mercury intoxication in Japan (the
107 137
fishermen of Minamata Bay). '
Pulmonary Toxicity
The lungs are an important port of entry for toxic compounds into the
body, and also an important target organ for chemical compounds. Gas ex-
change is the most important function of the lungs—oxygen enters the circu-
lation through the lungs, and carbon dioxide and other products of
metabolism are exhaled. In addition, the lungs are an important metabolizing
organ. Lungs possess a number of non-specific defense systems, such as
sneezing and coughing, active movement of the cilia of the pulmonary epithe-
lial cells, and secretion of mucus in the airways. In addition, there are a num-
ber of specialized phagocytic cells such as neutrophils, eosinophits and
macrophages, that destroy foreign particles through phagocytosis, i.e., they