Page 350 - Industrial Ventilation Design Guidebook

306 CHAPTER 5 PHYSIOLOGICAL AND TOXICOLOGICAL CONSIDERATIONS

There are undifferentiated stem cells of the blood elements in the bone
marrow that differentiate and mature into erythrocytes, (red blood cells),
thrombocytes (platelets), and white blood cells (leukocytes and lympho-
cytes). The production of erythrocytes is regulated by a hormone, erythro-
poietin (see the section on kidney toxicity), that is synthetized and excreted
by the kidney. An increase in the number of premature erythrocytes is an
indication of stimulation of erythropoiesis, i.e., increased production of
erythrocytes in anemia due to continuous bleeding.

Toxic Effects on the Blood-Forming Tissues Reduced formation of eryth-
rocytes and other elements of blood is an indication of damage to the bone
marrow. Chemical compounds toxic to the bone marrow may cause pancy-
topenia, in which the levels of all elements of blood are reduced. Ionizing
radiation, benzene, lindane, chlordane, arsenic, chloramphenicol, trinitro-
toluene, gold salts, and phenylbutazone all induce pancytopenia. If the
damage to the bone marrow is so severe that the production of blood ele-
ments is totally inhibited, the disease state is termed aplastic anemia. In the
occupational environment, high concentrations of benzene can cause
aplastic anemia. 158
Platelets are essential as the first line of defense in clot formation to
stop bleeding. Platelets gather quickly around the damaged vessel wall and
clump together with fibrin filaments to form a clot that prevents bleeding.
Platelets also become activated by exposure to adrenaline, thrombin, and
collagen. Drugs and chemicals that disturb normal functioning of the bone
marrow also decrease the number of circulating platelets, a state termed
thrombocytopenia. Vinyl chloride is an example of a chemical which may
cause this kind of disturbance.
Specialized phagocytes (i.e., actively phagocytizing cells of the immune
system) include granulocytes (neutrophils, eosinophils, and basophils),
monocytes, and macrophages, which often originate from circulating
monocytes. Many environmental factors may decrease the number of these
cells. Ionizing radiation and several drugs may cause granulocytopenia.
Erythrocytes can be degraded if they are exposed to chemical compounds,
the end result being hemolytic anemia. Hemolytic anemia reduces the ca-
pacity of blood to carry oxygen, and thereby prevents oxygenation of vari-
ous tissues, especially the central nervous system and the heart, organs that
are particularly sensitive due to their large oxygen need. Aniline and ni-
trobenzene cause hemolytic anemia, and several other nitrocompounds
also induce this effect. Phenols and propylene glycol are also capable of in-
'
ducing hemolytic anemia. 158 159
Toxicity to the Skin
The skin is the largest organ in the human being. In particular, the surface
layer of the outer epidermis, the stratum corneum, usually provides quite good
protection against chemical compounds. Nevertheless, the skin is an impor-
tant entry route for chemical compounds into the body.
Skin has several protective mechanisms in addition to its thick epidermis
that prevent many chemical compounds from penetrating it. Eccrine (sweat)