The decline of frog populations world-wide has stirred dispute in the
media. Like other environmental problems beset with uncertainties, the
simultaneous disappearance of frog populations from every continent
offers the media a vehicle for venting philosophical views,
environmental and anti-environmental. (Just as the anti-
environmentalists now have their own funders, they also have their own
favorite media and writers.)
The NEW YORK TIMES pins frog loss on ozone depletion and resultant
increases in ultraviolet sunlight striking the Earth. At the other
end of the philosophical spectrum, Boyce Rensberger, an anti-
environmentalists' favorite with the WASHINGTON POST, suggests that
environmentalists caused the frog loss when they forced government to
ban a pesticide that formerly controlled a fungus that is now running
rampant worldwide, killing off frog populations.
The ozone layer in the stratosphere--6 to 30 miles above the earth's
surface--filters out deadly ultraviolet radiation from the sun. Many
chemicals, but chiefly DuPont's chlorofluorocarbons, diminish Earth's
ozone shield, allowing increased ultraviolet light to strike the Earth.
The TIMES reported studies showing that ultraviolet light is increasing
on parts of the Earth and that reproduction of some frogs and toads is
diminished by exposure to ultraviolet light. Rensberger responded with
a theory of his own.
For some time now, Rensberger and the WASHINGTON POST have been selling
the idea that ozone depletion, although real, has never harmed anyone
or anything and is getting better all the time. Rensberger puts his
name on stories carrying headlines such as "After 2000, Outlook for the
Ozone Layer Looks Good" and "Decline of Ozone-Harming Chemicals
Suggests Atmosphere May Heal Itself." And he writes things like, "In
fact, researchers say, the problem [of ozone loss] appears to be
heading toward solution before they can find any solid evidence that
serious harm was or is being done." Blaming frog loss on ozone appears
to ruffle Rensberger's philosophical feathers.
Rensberger's theory that the ozone layer will fix itself before anyone
or anything is hurt is more wishful thinking than science reporting.
Rensberger himself says that the ozone "holes" over the North and South
poles will not go away until the year 2050 at the earliest. Even this
prediction is optimistic because it assumes worldwide compliance with
the Montreal Protocol, a 1987 international agreement to stop using
DuPont's ozone-destroying chlorofluorocarbons in cooling systems. A few
countries, such as China, India, Indonesia, and those of the former
Soviet Union --representing 47% of the world's population --have said
they can't afford to comply with the Protocols. Whether they will or
not remains to be seen.
Even if everyone phases out chlorofluorocarbons right on schedule, U.S.
Environmental Protection Agency (EPA) is sticking with its April, 1991,
estimate of the skin cancers that ozone loss will cause. During the
next 50 years, EPA says, ozone loss will cause 12 million skin cancers
in the U.S. and 200,000 deaths. Worldwide, a billion (a thousand
million) skin cancers are expected to result from ozone loss, including
17 million deaths, over the next 50 years.
Rensberger's new theory on frog loss seems philosophically consistent
with the anti-environmental perspective, but more than a little
implausible all the same. HOMO SAPIENS --modern humans --have been on
Earth for 60,000 years. Most chemical pesticides have been around
for 50 years or less. Frogs have successfully inhabited the Earth for
at least 200 million years. Rensberger's theory, that during the
past two decades frogs somehow became dependent on human pesticides for
their survival, is --to put it politely --pretty silly.
The scientific concern about frog disappearances emerged during the
First World Congress of Herpetology at Cambridge, England in 1989.
Herpetology is the study of reptiles (snakes, lizards, turtles) and
amphibians (salamanders, toads and frogs).
At the Congress, in the hallways and during coffee breaks, scientists
compared notes and realized that in Colorado and Costa Rica, in
Australia and Africa, frogs are disappearing. Whole species being
studied in the '60s and '70s simply disappeared during the '80s.
The International Union for the Conservation of Nature (IUCN) by 1991
organized a Declining Amphibian Populations Task Force (DAPTF), located
at Oregon State University in Corvallis. Late last year the Task Force
published, THE STATUS OF AMPHIBIAN POPULATIONS; A COMPILATION AND
ANALYSIS. This authoritative report leaves little doubt that
amphibians--particularly frogs--are disappearing from locations all
over the globe, though the full dimensions of the problem of course
What's responsible for the declines? Journalists like simple answers
and perhaps scientists do too. But there seem to be multiple complex
causes for the loss of amphibians worldwide. The DAPTF lists the
1) "The overwhelmingly reported cause of declines is habitat
destruction, disturbance and fragmentation," says the DAPTF status
report. In other words, condominiums, parking lots, and shopping malls
are the culprit reported most often. Humans are wrecking wildlife
habitat in a frenzy of what the anti-environmental movement calls
2) A close second is pollution --pesticides, acid rain, and other
3) Third is the introduction of non-native species of predatory fish,
which disturb the ecological balance of lakes and streams.
4) Drought and flood --both of which seem to be increasing, worldwide,
perhaps in response to global warming (see RHWN #300 AND #301) --are
taking their toll on amphibian populations.
5) Eutrophication of ponds (excessive growth of plants, which depletes
oxygen in the water) caused by the modern farming practice of over-
In the last three years, two new causes, perhaps related, have been
6) The immune systems of some populations of frogs and toads have
somehow been damaged, perhaps by chemical contaminants, perhaps in
combination with extremes of weather and temperature. Animals with
damaged immune systems may fall prey to bacteria and viruses that they
might otherwise withstand.
7) And most recently Robert Stebbins, emeritus professor of zoology at
University of California at Berkeley, has suggested that amphibian
population declines may be caused by environmental pollutants that
mimic estrogens and disrupt the endocrine and immune systems of
amphibians. Stebbins presented his views in a paper at the Second World
Congress of Herpetology in Adelaide, Australia in January and they will
appear again in this month's issue of FROGLOG, the journal of the DAPTF
in Corvallis. Stebbins will examine his hypothesis further in a
chapter of his new book, A NATURAL HISTORY OF AMPHIBIANS, to be
published this year by Princeton University Press, he said in an
interview. He wonders aloud whether frogs aren't particularly
susceptible to damage by hormone-mimicking, endocrine-disrupting
chemicals for some or all of the following reasons:
1) Most or all hormone-mimicking chemicals are soluble in fat;
2) Frogs absorb environmental chemicals through their highly permeable
skin, as well as via digestion;
3) The change from tadpole to frog may release toxins that have been
stored in fat;
4) When emerging from hibernation to breed, amphibians draw heavily on
fat reserves, which may release fat-stored toxins;
5) Females draw upon fat reserves to create the yolk of their eggs,
perhaps again releasing fat-stored toxins into their systems.
6) The dramatic physical change from tadpole to frog is hormone-driven
and thus could be susceptible to interference by environmental
pollutants (xenoestrogens, or xenobiotics) that mimic hormones.
7) During the change from tadpole to frog, the creature stops eating,
stressing its whole system.
Of course no one knows what's really going on in nature. Scientists
produce fragments of information, then try to see patterns among the
fragments. What patterns a reporter sees depends upon where he or she
stands on one basic question that separates environmentalists from
anti-environmentalists: can humans continue to rearrange and
contaminate ecosystems everywhere without ultimately destroying the
ability of the Earth to support human life? Those with an abiding faith
might answer, "Humans are not threatening anything serious. Even if
frogs ARE disappearing, we'll simply learn to live without them. All is
Environmentalists, on the other hand, are likely to stand with
biologist Rachel Carson who in SILENT SPRING (1962) wrote,
"...[T]he new chemicals come from laboratories in an endless stream;
almost 500 annually find their way into actual use in the United States
alone. The figure is staggering and its implications are not easily
grasped --500 new chemicals to which the bodies of men and animals are
required somehow to adapt each year, chemicals totally outside the
limits of biologic experience.
"These sprays, dusts, and aerosols are now applied almost universally
to farms, gardens, forests and homes. Can anyone believe it is possible
to lay down such a barrage of poisons on the surface of the earth
without making it unfit for all life?"
 Carol Kaesuk Yoon, "Thinning Ozone Layer Implicated in Decline of
Frogs and Toads," NEW YORK TIMES March 1, 1994, pg. C4, citing J.B Kerr
and C.T. McElroy, "Evidence for Large Upward Trends of Ultraviolet-B
radiation Linked to Ozone Depletion," SCIENCE Vol. 262 (November 12,
1993), pgs. 1032-1034. See also Mario Blumthaler and Walter Ambach,
"Indication of Increasing Solar Ultraviolet-B Radiation Flux in Alpine
Regions," SCIENCE Vol. 248 (April 13, 1990), pgs. 206-208.
 Boyce Rensberger, "Sunlight and Fungus As Amphibian Hazards,"
WASHINGTON POST March 7, 1994, pg. A3.
 Boyce Rensberger, "After 2000, Outlook for the Ozone Layer Looks
Good," WASHINGTON POST April 15, 1993, pg. A1. And: Boyce Rensberger,
"Decline of Ozone-Harming Chemicals Suggests Atmosphere May Heal
Itself," WASHINGTON POST Aug. 26, 1993, pg. A10.
 Bernard G. Campbell, HUMANKIND EMERGING. SIXTH EDITION. (New York:
HarperCollins, 1992), pg. 438.
 Emily Yoffe, "Silence of the Frogs," NEW YORK TIMES MAGAZINE
December 13, 1992, pgs. 36-38, 64, 66, 76.
 C. Carey, "Hypothesis Concerning the Disappearance of Boreal Toads
from the Mountains of Colorado," CONSERVATION BIOLOGY Vol. 7 No. 2
(1993), pgs. 355-362.
 Loralei Saylor, "The Endocrine Connection," FROGLOG No. 9 (March,
1994). FROGLOG is published by the Declining Amphibian Populations Task
Force of the The International Union for the Conservation of Nature
(IUCN) at 200 S.W. 35th Street, Corvallis, Oregon 97333; telephone
Descriptor terms: anti-environmental movement; wise use; frogs;
amphibians; toads; pesticides; fungi; fish; species loss; ozone
depletion; ultraviolet light; solar radiation; washington post;
international union for the conservation of nature; declining amphibian
populations task force; robert stebbins; boyce rensberger; immune
system disorders; endocrine disrupters; hormones; estrogen; fat;
reproductive health; reproduction; rachel carson; silent spring;