Do trace residues of industrial chemicals harm humans?
A new study published yesterday in the JOURNAL OF THE NATIONAL CANCER
INSTITUTE reports that breast cancer in American women is strongly
associated with DDE (a form of DDT) in their blood. Breast cancer
strikes 176,000 women in the U.S. each year, and each year 46,000 die
of it. DDE is a residue derived from the well-known pesticide, DDT. DDT
was banned in the U.S. in the early 1970s but trace residues are still
measurable nearly everywhere in the environment. Furthermore, DDT is
still heavily used today in many locations outside the U.S.
The principal author of the new study, Dr. Mary Wolff at the Mt. Sinai
School of Medicine in New York, says, "[Our] findings suggest that
environmental chemical contamination with organochlorine residues may
be an important etiologic [causal] factor in breast cancer. Given the
world-wide dissemination of organochlorine insecticides in the
environment and the food chain, the implications are far-reaching for
public health intervention worldwide."
The study shows that women with high levels of DDE in their blood have
a four-times-greater risk of breast cancer than women with low levels
of DDE in the blood. (In this case, "high" means 20 billionths of a
gram of DDE in each milliliter of blood and "low" means 2 billionths of
a gram in each milliliter of blood. There are 28.3 grams in an ounce,
and 4.7 milliliters in a teaspoon.)
The study group was selected from 14,290 New York City women who had
attended a mammography (breast x-ray) clinic and had each donated 30
milliliters of blood. Within the group of 14,290, 58 women who later
developed breast cancer were selected for a case-control study. The 58
"cases" were matched with 164 "controls," women from the large group
who did not have breast cancer but who were matched to the "case" women
in several key respects (such as age, menopausal status, and so forth).
All their blood samples were analyzed for DDE and PCBs. DDE is created
when DDT is metabolized (processed by a living organism that has eaten
it). PCBs are industrial chemicals originally used as insulators in
electrical equipment. PCBs were banned in the U.S. in 1976 but are
still measurable in all parts of the environment. (In the study, PCBs
were also associated with breast cancer but the association was not
statistically significant. There was one chance in 6 that the
association was due to random chance and statistical significance was
defined as one chance in 20, or less.)
For fifty years, the incidence of breast cancer in American women has
risen at a steady 1 percent per year. In 1940, an American woman's
lifetime risk of getting breast cancer was one in 16. Today it is one
in 8. (See Table 1, which shows the risk of breast cancer in the U.S.
today for women at various ages.) However, death from breast cancer has
remained steady throughout the past 20 years because of life-saving,
though brutal, treatment methods (chemotherapy, radiation therapy, and
No one doubts that something in the environment is responsible for the
rising incidence of breast cancer in the U.S. Japanese women have only
one-fifth as much breast cancer as American women; but when Japanese
women move to the U.S., they are stricken with breast cancer at U.S.
Since the 1960s, medical specialists have been trying to track down the
causes of breast cancer. Throughout the 1980s, most scientists believed
that a high-fat diet caused breast cancer. A study of diet and breast
cancer in 120,000 women has now discredited this theory and it has been
Researchers are now focused on the female hormones estrogen and
progesterone which, they suspect, may play a large role in breast
It has been known since the early 1970s that breast cancer is somehow
related to estrogen. Beginning at menarche (the onset of menstruation)
and continuing until menopause, a women experiences a sharply rising
and falling exposure, first to estrogen and then to progesterone, in a
repeating 4-week ovulation cycle.
Late menarche and early menopause (both of which reduce a woman's
lifetime exposure to estrogen) are both associated with reduced breast
cancer risk. In addition, women who have their ovaries removed early in
life and are therefore exposed to much less estrogen that other women,
rarely have breast cancer.
Furthermore, women who have "estrogen replacement therapy" (i.e., take
estrogen pills) have a 40 percent increased risk of breast cancer, and
women who use birth control pills have a 50 percent increased risk of
breast cancer. These clues all relate estrogen to breast cancer.
But the EXACT relationship is not understood.
In recent years, menarche in American women has been occurring at
earlier and earlier ages. (Chinese women reach menarche at age 17;
today U.S. women reach menarche at 12.8 years, on average, but 200
years ago North American women reached menarche at age 17.) The
declining age of menarche in U.S. women increases their lifetime
exposure to estrogen, which possibly increases their risk of breast
What is causing the declining age of menarche? Some scientists say
simply, improved nutrition. Others say it may be caused by industrial
chemicals in our food that mimic hormones and interfere with the
internal mechanisms that regulate our bodies. DDT, DDE, PCBs and dioxin
are examples of chemicals now known to mimic hormones and disrupt the
endocrine system of fish, birds and mammals, including humans.
Dr. Patricia Whitten at Emory University in Atlanta, Ga., has examined
historical records extending back 200 years in several countries. Dr.
Whitten's concludes that improved nutrition cannot account for all the
changes in human reproduction that are observable in the historical
record. She believes that hormone-mimicking industrial chemicals in the
environment provide a more satisfactory explanation.
The debate over menarche has real consequences in the kinds of research
that scientists are doing. Scientists who believe hormone-mimicking
industrial chemicals may play an important role are doing the kinds of
studies reported today in the JOURNAL OF THE NATIONAL CANCER INSTITUTE,
examining hormone-mimicking chemicals like DDT in relation to breast
On the other hand, those who believe improved nutrition provide
sufficient explanation for the change in menarche tend to ignore
external influences, such as environmental chemicals. Malcolm Pike at
University of Southern California (USC) School of Medicine has emerged
as a leader of this school of thought. Pike argues as follows:
nutrition is the cause of reduced age of menarche; nutrition is
unlikely to worsen, so we're stuck with reduced age of menarche and
therefore with increased exposure to estrogen. Pike is experimenting
with a technical fix, giving women additional chemicals
(pharmaceuticals) to block their natural production of estrogen, then
giving them controlled doses of estrogen, to maintain their chemical
balance artificially. SCIENCE magazine reported January 29, 1993 that,
"To the extent it's possible to see a trend emerging in the 1990s, this
anti-estrogen strategy appears to be a leading contender." Dr. Walter
Willett at Harvard University's School of Public Health is in Pike's
camp. He says, "In the end, I think we're going to have to go with a
pharmacological fix." SCIENCE comments "There may be some reluctance to
support such experiments because people feel they are 'unnatural.'"
But, says Willett, "our whole lifestyle is unnatural."
Dr. Wolff's new study does not definitively prove that chemical
residues cause breast cancer. The number of "cases" is small.
Additional research will be needed. Nevertheless, an editorial in the
JOURNAL OF THE NATIONAL CANCER INSTITUTE yesterday said, "Because the
findings of Wolff [and associates] may have extraordinary global
implications for the prevention of breast cancer, their study should
serve as a wake-up call for further urgent research."
--Peter Montague, Ph.D.
 Mary S. Wolff and others, "Blood Levels of Organochlorine Residues
and Risk of Breast Cancer," JOURNAL OF THE NATIONAL CANCER INSTITUTE
Vol. 85 (April 21, 1993), pgs. 648-652.
 Eliot Marshall, "Search for a Killer: Focus Shifts From Fats to
Hormones," SCIENCE Vol. 259 (January 29, 1993), pgs. 618-621. See also,
Eliot Marshall, "The Politics of Breast Cancer," SCIENCE Vol. 259
(January 29, 1993), pgs. 616-617.
 Everyone interested in chemicals that mimic hormones must read Theo
Colborn and Coralie Clement, editors, CHEMICALLY-INDUCED ALTERATIONS IN
SEXUAL AND FUNCTIONAL DEVELOPMENT: THE WILDLIFE/HUMAN CONNECTION
[Advances in Modern Environmental Toxicology Vol. XXI] (Princeton,
N.J.: Princeton Scientific Publishing Co., 1992).
 Patricia L. Whitten, "Chemical Revolution to Sexual Revolution:
Historical Changes in Human Reproductive Development," in Theo Colborn
and Coralie Clement, cited above, pgs. 311-334.
 David J. Hunter and Karl T. Kelsey, "Pesticide Residues and Breast
Cancer: The Harvest of a Silent Spring?" JOURNAL OF THE NATIONAL CANCER
INSTITUTE Vol. 85 (April 21, 1993), pgs. 598-599.
A Woman's Risk of Developing Breast Cancer Today in the U.S.
By age 25: one in 19,608 By age 30: one in 2525 By age 35: one in 622
By age 40: one in 217 By age 45: one in 93 By age 50: one in 50 By age
55: one in 33 By age 60: one in 24 By age 65: one in 17 By age 70: one
in 14 By age 75: one in 11 By age 80: one in 10 By age 85: one in 9
Ever: one in 8
Source: See footnote 2.
Descriptor terms: pesticides; ddt; dde; breast cancer; morbidity;
mortality; mary wolff; mt sinai school of medicine; new york, ny;
females; hormones; estrogen; endocrine disrupters; menarche; menopause;
estrogen replacement therapy; birth control pill; patricia whitten;