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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.
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