Page 380 - Industrial Ventilation Design Guidebook

5,3 TOXICITY AND RISKS INDUCED BY OCCUPATIONAL EXPOSURE TO CHEMICAL COMPOUNDS 335

5.3.6.5 Important Chemical Carcinogens
Polycyclic aromatic hydrocarbons have been classified as human carcino-
gens because they induce cancers in experimental animals and because smok-
ing and exposure to mixtures of chemicals containing polycyclic aromatic
hydrocarbons in the workplace increase the risk of lung cancer in exposed in-
dividuals. In experimental animals, benzo(a)pyrene induces cancer in different
204
organs depending on the route of administration. Furthermore, exposure to
polycyclic aromatic hydrocarbons commonly occurs in occupations related to
traffic (use of diesel engines in transportation and railways).
Tobacco smoke induces a myriad of deleterious health effects in exposed in-
dividuals. Carbon monoxide decreases oxygenation of tissues by erythrocytes,
nicotine causes vasoconstriction and disturbs circulation especially in the periph-
ery, e.g., in the placenta, and tar contains a number of carcinogenic compounds.
In addition, tobacco smoke irritates the mucous membranes in the respiratory
airways and eyes, depresses cilia in the bronchi, and also has immunosuppressive
effects. These effects may also contribute to the increased risk of lung cancer due
to smoking. Furthermore, all forms of smoking increase the risk of lung cancer.
The association between smoking and lung cancer is no longer open to debate;
there is a dose-effect relationship between the number of cigarettes smoked per
day and the magnitude of the risk, and an association between the duration of
smoking and the lung cancer risk. Also, an increased risk of bladder cancer and
kidney-pelvis cancer is associated with smoking. These observations are not sur-
prising because tobacco smoke contains many known carcinogens, such as
benzo(a)pyrene, at relatively high concentrations. 204
Asbestos fibers and arsenic compounds are also clear-cut human carcino-
205 206
gens. ' Today, substitutes of asbestos or insulation materials, notably
man-made vitreous fibres containing ceramic, glasswool, lockwool, and slog-
222
wool fibres are suspected human carcinogens, but further information is re-
quired before one can come to a final carcinogenic classification. Other
potentially important human carcinogens include reactive agents such as
formaldehyde and isocyanates.
IARC has also classified ethyl alcohol as a human carcinogen. The use of
ethyl alcohol is associated with increased risk of cancers of the oral cavity,
pharynx, larynx, esophagus, and liver. Ethanol is usually considered to be a
cocarcinogen which amplifies the effects of other carcinogens. For example,
the carcinogenic effects of tobacco smoke are amplified by ethyl alcohol. In
addition, ethyl alcohol is also genotoxic, and causes chromosomal aberra-
tions, sister chromatid exchanges, and point mutations in test systems where
ethyl alcohol can be metabolized. Thus, it seems likely that acetaldehyde, the
primary metabolite of ethyl alcohol, is the compound responsible for mutage-
nicity of ethyl alcohol. 207

5.3.6.6 Future Perspectives
In the future, the preventive role of toxicology will be emphasized. It
will be increasingly important to develop early indicators to monitor long-
term subtle exposures that predict deleterious effects that are known to
have a causal relationship with occupational exposures. In addition to col-
lection of blood and urine samples, also collection of cells from points of