Subject: Facts versus fears - DDT
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Date: Fri, 11 Jan 2013 21:46:51 -0800

Facts versus fears: DDT

Extract from the American Council on Science and Health publication "Facts
Versus Fears" - Edition 3, June 1998. © American
Council on Science and Health - all rights reserved.

DDT, 1962
Background

DDT (dichlorodiphenyltrichloroethane) was first synthesized in
1877,1 but it was not until 1940 that a Swiss chemist discovered that
it could be sprayed on walls and would cause any insect to die within the next
six months, without any apparent toxicity to humans.2 DDT’s
effectiveness, persistence, and low cost (only 17 cents per pound) resulted in
its being used in antimalarial efforts worldwide. It was introduced into
widespread use during World War II and became the single most important
pesticide responsible for maintaining human health through the next two decades.
The scientist who discovered the insecticidal properties of DDT, Dr. Paul
Müller, was awarded the 1948 Nobel Prize in Physiology and
Medicine.3

The Scare

In 1962 Rachel Carson’s lyrical yet scientifically flawed book Silent
Spring was released. The book argued eloquently but erroneously that
pesticides, and especially DDT, were poisoning both wildlife and the environment
and also endangering human health. The emotional public reaction to Silent
Spring launched the modern environmental movement.4 DDT became
the prime target of the growing anti-chemical and anti-pesticide movements
during the 1960s. Reasoned scientific discussion and sound data on the favorable
human health effects of DDT were brushed aside by environmental alarmists who
discounted DDT’s enormous benefits to world health with two allegations: (1) DDT
was a carcinogen, and (2) it endangered the environment, particularly for
certain birds.

In 1969 a study found a higher incidence of leukemia and liver tumors in mice
fed DDT than in unexposed mice.5 Soon, too, environmentalists were
blaming the decline in populations of such wild bird species as the osprey and
peregrine falcon on the contamination by DDT of their environment. A number of
states moved to ban DDT, and in 1970 the U.S. Department of Agriculture
announced a plan to phase out all but essential uses.6

The Reaction

Numerous scientists protested that the laboratory-animal studies flew in the
face of epidemiology, given that DDT had been used widely during the preceding
25 years with no increase in liver cancer in any of the populations among whom
it had been sprayed. And when the World Health Organization (WHO) investigated
the 1969 mice study, scientists discovered that both cases and controls had
developed a surprising number of tumors. Further investigation revealed that the
foods fed to both mice groups were moldy and contained aflatoxin, a
carcinogen.7 When the tests were repeated using noncontaminated
foods, neither group developed tumors. In 1970 the National Academy of Sciences
declared, “In little more than two decades, DDT has prevented 500 million human
deaths due to malaria, that would otherwise have been
inevitable.”8

Additionally, the evidence regarding the effect of DDT on eggshell thinning
among wild birds is contradictory at best. The environmentalist literature
claims that the birds threatened directly by the insecticide were laying eggs
with thin shells. These shells, say the environmentalists, would eventually
become so fragile that the eggs would break, causing a decline in bird
populations, particularly among raptors (birds of prey).

In 1968 two researchers, Drs. Joseph J. Hickey and Daniel W. Anderson,
reported that high concentrations of DDT were found in the eggs of wild raptor
populations. The two concluded that increased eggshell fragility in peregrine
falcons, bald eagles, and ospreys was due to DDT exposure.9 Dr. Joel
Bitman and associates at the U.S. Department of Agriculture likewise determined
that Japanese quail fed DDT produced eggs with thinner shells and lower calcium
content.10

In actuality, however, declines in bird populations either had occurred
before DDT was present or had occured years after DDT’s use. A comparison of the
annual Audubon Christmas Bird Counts between 1941 (pre-DDT) and 1960 (after
DDT’s use had waned) reveals that at least 26 different kinds of birds became
more numerous during those decades, the period of greatest DDT usage. The
Audubon counts document an overall increase in birds seen per observer from 1941
to 1960, and statistical analyses of the Audubon data confirm the perceived
increases. For example, only 197 bald eagles were documented in
194111; the number had increased to 891 in 1960.12

At Hawk Mountain, Pennsylvania, teams of ornithologists made daily counts of
migrating raptors for over 40 years. The counts—published annually by the Hawk
Mountain Sanctuary Association—reveal great increases in most kinds of hawks
during the DDT years. The osprey counts increased as follows: in 1946, 191; in
1956, 288; in 1967, 457; and in 1972, 630.13 In 1942 Dr. Joseph
Hickey—who in 1968 would blame DDT for bird population decline—reported that 70
per-cent of the eastern osprey population had been killed by pole traps around
fish hatcheries.14 That same year, before DDT came into use, Hickey
noted a decline in the population of peregrine falcons.15

Other observers also documented that the great peregrine decline in the
eastern United States occurred long before any DDT was present in the
environment.16,17 In Canada peregrines were observed to be
“reproducing normally” in the 1960s even though their tissues contained 30 times
more DDT than did the tissues of the midwestern peregrines allegedly being
extirpated by the chemical.18 And in Great Britain, in 1969, a
three-year government study noted that the decline of peregrine falcons in
Britain had ended in 1966 even though DDT levels were as abundant as ever. The
British study concluded that “There is no close correlation between the decline
in population of predatory birds, particularly the peregrine falcon and the
sparrow hawk, and the use of DDT.”19

In addition, later research refuted the original studies that had pointed to
DDT as a cause for eggshell thinning. After reassessing their findings using
more modern methodology, Drs. Hickey and Anderson admitted that the egg extracts
they had studied contained little or no DDT and said they were now pursuing
PCBs, chemicals used as capacitor insulators, as the culprit.20

When carefully reviewed, Dr. Bitman’s study revealed that the quail in the
study were fed a diet with a calcium content of only 0.56 percent (a normal
quail diet consists of 2.7 percent calcium). Calcium deficiency is a known cause
of thin eggshells.21–23 After much criticism, Bitman repeated the
test, this time with sufficient calcium levels. The birds produced eggs without
thinned shells.24

After many years of carefully controlled feeding experiments, Dr. M. L. Scott
and associates of the Department of Poultry Science at Cornell University “found
no tremors, no mortality, no thinning of eggshells and no interference with
reproduction caused by levels of DDT which were as high as those reported to be
present in most of the wild birds where ‘catastrophic’ decreases in shell
quality and reproduction have been claimed.”23 In fact, thinning
eggshells can have many causes, including season of the year, nutrition (in
particular insufficient calcium, phosphorus, vitamin D, and manganese),
temperature rise, type of soil, and breeding conditions (e.g., sunlight and
crowding).25

In the years preceding the DDT ban, the National Academy of
Sciences,26,27 the American Medical Association, the U.S. Surgeon
General,28 the World Health Organization,29 and the Food
and Agriculture Organizations of the United Nations30 had been among
those who spoke out in support of the continued use of DDT as a disease fighter
and crop protectant.

In 1971 authority over pesticides was transferred from the Department of
Agriculture to the newly formed Environmental Protection Agency (EPA). In April
1972, after seven months of testimony, Judge Edmund Sweeney stated that “DDT is
not a carcinogenic hazard to man. . . . The uses of DDT under the regulations
involved here do not have a deleterious effect on freshwater fish, estuarine
organisms, wild birds, or other wildlife. . . . The evidence in this proceeding
supports the conclusion that there is a present need for the essential uses of
DDT.”31

Two months later EPA head William Ruckelshaus—who had never attended a single
day’s session in the seven months of EPA hearings, and who admittedly had not
even read the transcript of the hearings— overturned Judge Sweeney’s decision.
Ruckelshaus declared that DDT was a “potential human carcinogen” and banned it
for virtually all uses.32

Conclusion

The ban on DDT was considered the first major victory for the
environmentalist movement in the U.S. The effect of the ban in other nations was
less salutary, however. In Ceylon (now Sri Lanka) DDT spraying had reduced
malaria cases from 2.8 million in 1948 to 17 in 1963. After spraying was stopped
in 1964, malaria cases began to rise again and reached 2.5 million in
1969.33 The same pattern was repeated in many other tropical— and
usually impoverished—regions of the world. In Zanzibar the prevalence of malaria
among the populace dropped from 70 percent in 1958 to 5 percent in 1964. By 1984
it was back up to between 50 and 60 percent. The chief malaria expert for the
U.S. Agency for International Development said that malaria would have been 98
percent eradicated had DDT continued to be used.34

In addition, from 1960 to 1974 WHO screened about 2,000 compounds for use as
antimalarial insecticides. Only 30 were judged promising enough to warrant field
trials. WHO found that none of those compounds had the persistence of DDT or was
as safe as DDT. (Insecticides such as malathion and carbaryl, which are much
more toxic than DDT, were used instead.) And—a very important factor for malaria
control in less developed countries—all of the substitutes were considerably
more expensive than DDT.35

[Insertion: See the human toll of not using DDT here.
Ends.]

And what of the charges leveled against DDT? A 1978 National Cancer Institute
report concluded—after two years of testing on several different strains of
cancer-prone mice and rats—that DDT was not carcino-genic.36 As for
the DDT-caused eggshell thinning, it is unclear whether it did, in fact, occur
and, if it did, whether the thinning was caused by DDT, by mercury, by PCBs, or
by the effects of human encroachment.16,37 And as recently as 1998
researchers reported that thrush eggshells in Great Britain had been thinning at
a steady rate 47 years before DDT hit the market; the researchers placed the
blame on the early consequences of industrialization.38

Regardless of whether DDT, exclusive of other chemicals, presented a threat
to bird populations, it remains in the news. DDT has a long half-life, and
residues sometimes persist for years in certain environments. Also, DDT is an
organochlorine. Some organochlorines have been shown to have weak estrogenic
activity, but the amounts of naturally occurring estrogens in the environment
dwarf the amounts of synthetic estrogens.39 A recent article in the
journal Environmental Health Perspectives suggested that the ratio of
natural to synthetic estrogens may be as much as 40,000,000 to
1.40

In addition, Dr. Robert Golden of Environmental Risk Studies in Washington,
DC, reviewed the research of numerous scientists and concluded that DDT and DDE
(a breakdown product of DDT) have no significant estrogenic
activity.41

The 1996 book Our Stolen Future speculated on a link between DDT and
breast cancer, noting that DDE has been found in some breast
tumors.42 Recently, charges have been made associating DDT and DDE
with breast cancer—specifically, the finding that women with breast cancer had
higher levels of DDE in their blood than did women without breast
cancer.43 However, elevated blood DDE could quite plausibly be a
result of the mobilization of fat from storage depots in the body due to weight
loss associated with breast cancer. Breast cancer thus may be a risk factor for
elevated DDE, rather than DDE’s being a risk factor for breast
cancer.44

In a 1994 study published in the Journal of the National Cancer
Institute, researchers concluded that their data did not support an
association between DDT and breast cancer.45 The researchers did note
that breast cancer rates are higher than the national average in many places in
the northeastern United States; but the data also indicated that the higher
levels could be accounted for by nonenvironmental factors among women living in
these regions—factors such as higher socioeconomic status and deferral or
avoidance of pregnancy, both of which increase the risks of breast cancer by up
to twofold.45,46

In October 1997 the New England Journal of Medicine published a large,
well-designed study that found no evidence that exposure to DDT and DDE
increases the risk of breast cancer.47 In the accompanying editorial
Dr. Steven Safe, a toxicologist at Texas A&M University, stated, “weakly
estrogenic organochlorine compounds such as PCBs, DDT, and DDE are not a cause
of breast cancer.”48 Dr. Sheila Zahm, deputy chief of the
occupational epidemiology branch at the National Cancer Institute, agrees that
the body of evidence that DDT can cause breast cancer “is not very
compelling.”49

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Desowitz R. The Malaria Capers: More Tales of Parasites and People,
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Hickey JJ, Anderson DW. Chlorinated hydrocarbons and eggshell changes in
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Bitman J, Cecil HC, Harris SJ, Gries GF. DDT induces a decrease in
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The 42nd Annual Christmas Bird Census. Audubon Magazine. 1942; 44:1–75.

The 61st Annual Christmas Bird Census. Audubon Field Notes. 1961; 15(2):
84–300.

Taylor JW. Summaries of Hawk Mountain migration of raptors, 1934 to 1970.
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