2 – CASE STUDY:
Environment and Reproductive Health
Special populations may be particularly susceptible to certain types of
risks. Thus on days of “ozone alert” (high trophoshpric ozone
due to traffic and weather conditions), older people and children are
asked to stay indoors. Another gropu at risk from specific environmtnal
agents are organisms – including human beings – during their
early developmental stages.
“Reproductive health” includes fertility, sexual function,
and fetal developmental health. We are just learning the effects of one
huge class of synthetic chemicals – organochlorines – and
their effects on fertility. DDT (Dichloro-diphenyl-trichloroethane) the
pesticide, has been shown to have the effect of estrogen given to young
male bids such as roosters. Young roosters treated with DDT are “feminized,”
with severely underdeveloped testes, and even combs. DES, Diethylstilbestrol,
invented the same year as DDT (1938) as DDT, was used to prevent miscarriages.
Given to women with history of miscarriages in early stages of pregnancy,
DES is a synthetic estrogen in1940’s and 50’s. Not thinking
of long-term effects, the chemical company that produced it advertised
it for all pregnancies, with a claim that it produced “bigger and
stronger babies,” a claim that had no evidence. Doctors also gave
DES for various other uses, such as suppressing milk production in new
mothers, for prostate cancer, gonorrhea, and even to limit the height
of teenage girls who were growing “too tall.”
In the ‘70’s it was discovered that female children of mothers
who had taken DES during pregnancy developed a rare vaginal cancer as
young women. Many of these women then had to undergo surgery to remove
their uterus and vagina to limit the spread of cancer. It is suspected,
but hard to prove that DES sons are at greater risk of various genital
defects, had abnormal sperm, and perhaps had greater risk of testicular
cancer as adults.
This stark case paints the picture of delayed effects from a critical
exposure during fetal development. While the placenta protects the mammalian
fetus to some extent, the period of organ development or organogenesis
called the fetal period is the most susceptible in terms of birth defects
(teratogenesis; terato=monsters). In humans, this period is for about
18-20 days since conception to about days 55-60 of gestation. This is
why doctors have developed the role of no lower abdominal x-rays, for
example, in young women, especially during the first 3 months of pregnancy.
Figure 6, from Wilson shows the degree of susceptibility to agents during
the prenatal developmental span of time.
6: Susceptibility to Teratogenesis
The type of malformation in the newborn changes depending on the time
of exposure, even for the same agent., or due to lack of nutrition. Drugs
and chemicals shown to be teratogenic in experimental mammals include:
aspirin, caffeine, antihistamine, anesthetics, antibiotics, steroids,
pesticides, ionizing radiation, nicotine, and alcohol. Fetal alcohol syndrome
affecting children on women who drank heavily during pregnancy manifest
in attention deficits and other nervous system problems manifested later
in the life of the offspring.
About 20-25% of developmental defects are known to be genetic. Known environmental
agents cause about 8% of defects. These include radiation; infections
(e.g. rubella virus, syphilis); maternal metabolic imbalance (e.g. diabetes,
vitamin deficiency); drugs; and environmental chemicals. The attention
to environmental chemicals is important because their effect may be subtle,
may interact with other categories, and are preventable.
Theo Colborn, Dianne Dumanosky, and John Myers, Our
Stolen Future. Plume (Penguin); NY, 1997
James G. Wilson, Environment and Birth Defects.
Academic Press; NY, 1973.