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,3 TOXICITY AND RISKS INDUCED BY OCCUPATIONAL EXPOSURE TO CHEMICAL COMPOUNDS 26 I

fiber diameter and length are important determinants of their behavior in the
airways. The effect of particle size on the fate of particles is discussed in more
detail in sections 3.1 and 5.2. 50

5.3.2.4 Physiological Determinants of Exposure
Anthropologic features of humans, their physical activities, ventilation ca-
pacities, and the state of their circulation all affect exposure to chemical com-
pounds. Some of the physiological determinants of exposure will be dealt with
below. Exercise typically increases cardiac output, facilitates circulation, in-
creases the minute volume of ventilation, is associated with vasodilation of the
skin circulation, and increases perspiration and secretory activity of the sweat
glands. All of these changes tend to facilitate the absorption of chemicals
through multiple routes.

Inhalational Exposure
During exercise, both minute ventilation and cardiac output increase dra-
matically. Whereas minute ventilation averages 7-10 L/min at rest for an aver-
age person of about 70 kg, it can increase to 160 L or more/min during intense
exercise, and be 25^40 L/min with moderate exercise. This has a considerable
direct effect on exposure through the lungs. For example, when young persons
were exposed to ra-xylene at a concentration of 100 ppm, the concentration of
ra-xylene in their venous blood reached a level of 19 jjimol/L whereas after a
moderate exercise at 100 W, a concentration of 100 jxmol/L was reached in
their blood. Thus, the exercise caused about a five-fold increase in the concen-
tration of w-xylene in the blood compared to values in sedentary subjects even
65
though the ambient air xylene concentration was the same. The increase was
approximately equivalent to the change in minute ventilation (which was four
to six fold). Increased cardiac output and thereby increased circulation helped in
maintaining the concentration gradient between the alveolar space and the
66 67
blood and thereby facilitated pulmonary absorption of w-xylene. '

Dermal Exposure
Exercise also increases skin circulation and perspiration, which both en-
hance dermal penetration of compounds into the body. Furthermore, skin le-
sions, such as wounds and dermatitis, can increase the permeability of the skin
to chemicals. Also, exposure of the skin to solvents and removal of skin fat in-
crease dermal penetration of a number of compounds. Compounds penetrate
the skin more readily in places where the skin is thin, like the face, hands and
scrotum. Increased dermal blood flow due to exercise facilitates the penetra-
615 67
tion of the skin by chemicals. ""
Considerable protection against dermal exposure can be achieved by using
the appropriate protective clothing, such as overalls, rubber gloves, and boots.
For example, protective clothing provided 80-95% protection when workers
52 54 57
manually handled ethylenebisdithiocarbamate fungicides in agriculture. ' - It
would seem that a similar protection against dermal exposure can be achieved
in agriculture and industry in general. Figure 5.33 shows that urinary excretion
of ethylenethiourea mainly depends on dermal absorption of the parent com-
pound, raaneb (a dithiocarbamate) because a delay can be seen before the start