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3 I 6 CHAPTER 5 PHYSIOLOGICAL AND TOXICOLOGICAL CONSIDERATIONS
Fetal alcohol syndrome (FAS) was only defined in 1973, even though harmful ef-
fects of ethyl alcohol on the fetus have been known for a long time. During the past
25 years, the estimates of the dose required to damage the fetus have decreased, and
today the consumption of ethyl alcohol during pregnancy is not recommended at all.
The incidence of FAS has been found in different epidemiological studies to be about
2-7 cases/1000 live births. 177
FAS is normally characterized by growth retardation, anomalies of the head
and face, and psychomotor dysfunctions. Excessive consumption of ethyl alcohol
may lead to malformations of the heart, extremities, and kidneys. Since consump-
tion of ethyl alcohol is socially acceptable and prevalent even in pregnant women,
the risks associated with the use of ethyl alcohol are remarkable. However, it
should be kept in mind that there are several chemical compounds in the occupa-
tional environment that may also cause malformations even at low doses. The oc-
cupationally-important known human teratogens include methyl mercury, ethyl
alcohol, PCB compounds, tobacco smoke, lead, TCDD, 2,4,5-T, carbon monox-
ide, nitrogen dioxide, gasoline, and fluoride. 167
5.3.4.6 Carcinogens and Mutagens
A mutagen is a chemical that can induce alterations in the DNA. Mutations
occurring in germ cells are inheritable and may lead to genetic diseases. If muta-
tions take place in somatic cells, carcinogenesis may be initiated.
The International Agency for Research on Cancer (IARC) classifies carcino-
gens into five groups: human carcinogens (Category I), probable human carcino-
gens (Category 2A), possible human carcinogens (Category 2B), not classified
(Category 3), and compounds with no evidence of carcinogenicity for humans
(Category 4). Before an agent can be classified as a human carcinogen, there must
be sufficient epidemiological evidence for a causal association between exposure
to this agent and cancer. Probable human carcinogens include agents for which
the epidemiological evidence is more limited and/or animal test carcinogenicity ev-
idence is available. A compound is classified as possible human carcinogen when
there is limited evidence of animal carcinogenicity. If the animal evidence is inade-
quate, the agent belongs to the not classified category. The final category includes
agents with no evidence of carcinogenicity as determined by adequate animal test-
ing or epidemiological studies. By the year 1993, IARC had classified the carcino-
genicity of 763 chemical compounds, groups of chemical compounds, and
mixtures of chemical compounds. Of these, 58 were placed in Category 2A, and
205 compounds were placed in Category 2B. The number of chemical com-
pounds belonging to Category 3 was 405, and only one compound was classified
as Category 4. These figures reveal some of the difficulties associated with the as-
sessment of the carcinogenicity of chemical compounds: (1) usually only a limited
number of studies on the carcinogenicity of chemicals are available; (2) human
carcinogenicity is difficult to demonstrate; and (3) experimental or epidemiologi-
cal evidence of the lack of carcinogenicity is practically impossible to obtain. This
is the reason for not having a "not carcinogenic in humans" category in the IARC
150
classification. Some of the difficulties in assessing the carcinogenicity of chemi-
178
cal compounds are discussed below. Table 5.21 lists categories of human car-
cinogens according to IARC.