Study Finds DDT's Legacy
* Women Exposed to Pesticide Prenatally Have More Trouble Getting
Pregnant Decades Later
who were exposed while still in the womb to the pesticide DDT are
more likely to experience delays in getting pregnant, according
to a study of California mothers and daughters published today in
an international medical journal.
report by the Public Health Institute in Berkeley is the first scientific
evidence that DDT that collects in women's bodies can affect their
female offspring many years later, when they reach adulthood and
attempt to reproduce.
findings support a controversial theory that pesticides and other
environmental contaminants that mimic sex hormones are altering
human fertility and health.
was used worldwide in the 1940s through 1960s for pest control.
Banned in the United States and most of the world, it is still used
in parts of Africa, Southeast Asia, South America and Latin America
to control malaria-carrying mosquitoes. Many Americans still have
the pesticide and its byproducts in their bodies, and they continue
to be exposed through produce grown in tropical countries, as well
as fish caught in some U.S. waters, particularly in the Los Angeles
Berkeley team measured the pesticide in stored blood that had been
drawn between 1960 and 1963 from new mothers in the Oakland area.
Then the researchers questioned the daughters of those women to
calculate how long it had taken them to conceive.
the basis of responses from 289 women, the scientists found that
the length of time it took for the women to get pregnant correlated
strongly with the amount of DDT in their mother's blood, according
to the study, which was published in the British journal Lancet.
their surprise, the scientists also found that a common breakdown
product of DDT seemed to have the exact opposite effect: The more
DDE in the mothers, the less time it took for the daughters to become
say that the unexpected, mixed results of the new study show that
hormone-disrupting chemicals work in a complicated way on human
bodies that no one yet understands. The results indicate that a
woman's fertility can be altered in sometimes inexplicable ways
by what her mother was exposed to decades earlier.
raises the specter that the chemical cocktail we are all exposed
to is altering our human reproductive capability," said the
study's lead researcher, Barbara Cohn, director of the Center for
Research on Women's and Children's Health at the Public Health Institute,
which is one of the largest nonprofit public health agencies in
study found that, after 13 months of trying, about 75% of all the
women in the study were pregnant. But for the group with higher
than median DDT and lower DDE, only 65% were pregnant. For the group
with higher than median DDE and lower DDT, 83% were pregnant.
it is reassuring that possible harmful effects of DDT may be reduced
by its conversion to DDE, women still experienced delays in becoming
pregnant," Cohn said.
apparent counteractive effect of DDE could explain why there have
been no reported widespread fertility problems in the generation
of women exposed in the womb to the pesticide. DDT converts slowly
into its metabolite DDE in the body and in the environment.
the U.S., children born between the late 1950s and the late 1960s
probably had the highest exposures to the pesticide of any generation.
People are exposed to the compounds, which can last for decades
in soil or at the bottoms of oceans and rivers, mainly through food.
The chemicals are stored in a woman's fat over her lifetime and
cross into the placenta during pregnancy, exposing the fetus.
real message of our study is that the human system is vulnerable
to these chemicals," Cohn said.
every increase of 10 parts per billion of DDT in the mother's blood,
the daughter's probability of pregnancy within a cycle fell 32%.
But for every 10-ppb increase in DDE, the probability of pregnancy
conclusions are conflicting. We just don't have a way of understanding
it, " said Dr. Harry Fisch, a fertility expert at Columbia
Presbyterian Medical Center in New York who was not involved with
suspects that an explanation lies in the differing hormone-disrupting
abilities of the two compounds. DDE is a potent blocker of male
hormones called androgens; DDT mimics estrogen. Perhaps blocking
androgens in some women increases their fertility and offsets the
effect of the DDT.
Robert Taylor, director of the Center for Reproductive Sciences
at University of California, San Francisco, called the study quite
remarkable because it involves mothers and daughters. He said the
good news is that the body seems capable of changing DDT to a form
that does not harm offspring. "This suggests that we were fortunate
to have evolved in a way that lets us dodge some of these potentially
toxic bullets," he said.
researchers warned in their report that, although they adjusted
their data for several factors that affect fertility, such as age,
frequency of intercourse and alcohol use, "other factors could
confound our findings."
scientists agree that many pesticides and industrial chemicals mimic
the effects of estrogen or block testosterone. Studies of lab animals
and wildlife have already linked many chemicals, including DDT and
its metabolites, to infertility, birth defects and other reproductive
problems. But there has been little information about humans.
study recently reported that men exposed to pesticides have as much
as a 30-fold reduction in sperm quality.