the American Cancer Society, indicating that the mortality rates of childhood
cancer have declined by about 47% since 1975.
20
The association of pesticides and related chemicals with various illnesses
and death has attracted a wide attention and much study. Of particular
concern are chlorinated hydrocarbon-based pesticides and dioxin. For
instance, accidents during the manufacture of the herbicide 2,4,5-trichlorophenoxy acetic acid (2,4,5-T) and polychlorinated phenol derivatives have
caused acute dioxin poisoning of plant workers and populations in several
countries.
As is widely known, 2,4,5-T and related dioxin-contaminated defoliants
were used extensively in Vietnam from 1961 to 1969. Among the major toxic
effects attributed to dioxins is liver cancer. Between 1956 and 1961 (the year in
which spraying of the herbicides began), 159 cases of primary hepatic cancers
were recorded among 5492 cancers in the Hanoi area, while between 1962 and
1968, 791 primary hepatic cancers were observed in a total of 7911 cancers.
This change represented a more than three-fold increase in the proportion of
primary cancer of the liver.
22
2.3.3 BIRTH DEFECTS
It is estimated that approximately 3% of all live births in the U.S. have
significant birth defects.
23 This represents about 100,000 congenital anomalies
in a total of 3 million live births annually. Congenital malformations are the
leading cause of infant mortality in the U.S. Furthermore, studies show that
the presence of any malformation diagnosed during the first year after birth
increased mortality 18-fold for white infants. Clearly, enormous financial costs
and emotional suffering are associated with these malformations.
The etiologic nature of the majority of congenital malformations in infants
is largely unknown. It has been estimated that about 5 to 10% of all birth
defects are due to an in utero exposure to a known teratogenic agent or
maternal factor. Intrauterine growth retardation can be caused by a number of
agents, including hypoxia (a deficiency of oxygen reaching the tissues of the
body), drugs, x-ray irradiation, maternal endocrine and nutritional factors, and
environmental chemicals. Many chemical species are known to be teratogenic,
i.e., capable of causing birth defects. These chemicals include various organic
solvents, pesticides, dioxins, several heavy metals (such as lead, cadmium, and
mercury), and others. Many human epidemiological data support the claim
that environmental chemicals are an important factor responsible for inducing
teratogenicity.
2.3.4 REPRODUCTIVE DAMAGE
An increasing number of studies have shown that a variety of toxicants can
induce detrimental effects on reproductive systems in animals and humans. For
instance, reproductive damage in seagulls and other wildlife presented some of
the first clues about the adverse effects of DDT.
24 Organochlorines have also
24
Environmental Toxicology
[16:55 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-002.3d]
Ref: 4365 MING-HO YU Chap-002 Page: 24 13-30
cancer have declined by about 47% since 1975.
20
The association of pesticides and related chemicals with various illnesses
and death has attracted a wide attention and much study. Of particular
concern are chlorinated hydrocarbon-based pesticides and dioxin. For
instance, accidents during the manufacture of the herbicide 2,4,5-trichlorophenoxy acetic acid (2,4,5-T) and polychlorinated phenol derivatives have
caused acute dioxin poisoning of plant workers and populations in several
countries.
As is widely known, 2,4,5-T and related dioxin-contaminated defoliants
were used extensively in Vietnam from 1961 to 1969. Among the major toxic
effects attributed to dioxins is liver cancer. Between 1956 and 1961 (the year in
which spraying of the herbicides began), 159 cases of primary hepatic cancers
were recorded among 5492 cancers in the Hanoi area, while between 1962 and
1968, 791 primary hepatic cancers were observed in a total of 7911 cancers.
This change represented a more than three-fold increase in the proportion of
primary cancer of the liver.
22
2.3.3 BIRTH DEFECTS
It is estimated that approximately 3% of all live births in the U.S. have
significant birth defects.
23 This represents about 100,000 congenital anomalies
in a total of 3 million live births annually. Congenital malformations are the
leading cause of infant mortality in the U.S. Furthermore, studies show that
the presence of any malformation diagnosed during the first year after birth
increased mortality 18-fold for white infants. Clearly, enormous financial costs
and emotional suffering are associated with these malformations.
The etiologic nature of the majority of congenital malformations in infants
is largely unknown. It has been estimated that about 5 to 10% of all birth
defects are due to an in utero exposure to a known teratogenic agent or
maternal factor. Intrauterine growth retardation can be caused by a number of
agents, including hypoxia (a deficiency of oxygen reaching the tissues of the
body), drugs, x-ray irradiation, maternal endocrine and nutritional factors, and
environmental chemicals. Many chemical species are known to be teratogenic,
i.e., capable of causing birth defects. These chemicals include various organic
solvents, pesticides, dioxins, several heavy metals (such as lead, cadmium, and
mercury), and others. Many human epidemiological data support the claim
that environmental chemicals are an important factor responsible for inducing
teratogenicity.
2.3.4 REPRODUCTIVE DAMAGE
An increasing number of studies have shown that a variety of toxicants can
induce detrimental effects on reproductive systems in animals and humans. For
instance, reproductive damage in seagulls and other wildlife presented some of
the first clues about the adverse effects of DDT.
24 Organochlorines have also
24
Environmental Toxicology
[16:55 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-002.3d]
Ref: 4365 MING-HO YU Chap-002 Page: 24 13-30