November 11, 2008
FOR IMMEDIATE RELEASE
Contact: Morgan Kelly
[412-624-4356 (office); 412-897-1400 (cell); [EMAIL PROTECTED]
Pitt Research Finds That Low Concentrations of Pesticides Can Become Toxic
Mixture
Concentrations of 10 most popular pesticides that fall within EPA
safe-exposure levels, when combined, cause 99 percent mortality in leopard
frog tadpoles
PITTSBURGHTen of the worlds most popular pesticides can decimate amphibian
populations when mixed together even if the concentration of the individual
chemicals are within limits considered safe, according to University of
Pittsburgh research published Nov. 11 in the online edition of Oecologia.
Such cocktails of contaminants are frequently detected in nature, the
paper notes, and the Pitt findings offer the first illustration of how a
large mixture of pesticides can adversely affect the environment.
Study author Rick Relyea, an associate professor of biological sciences in
Pitts School of Arts and Sciences, exposed gray tree frog and leopard frog
tadpoles to small amounts of the 10 pesticides that are widely used
throughout the world. Relyea selected five insecticidescarbaryl,
chlorpyrifos, diazinon, endosulfan, and malathionand five
herbicidesacetochlor, atrazine, glyphosate, metolachlor, and 2,4-D. He
administered the following doses: each of the pesticides alone, the
insecticides combined, a mix of the five herbicides, or all 10 of the poisons.
Relyea found that a mixture of all 10 chemicals killed 99 percent of leopard
frog tadpoles as did the insecticide-only mixture; the herbicide mixture had
no effect on the tadpoles. While leopard frogs perished, gray tree frogs did
not succumb to the poisons and instead flourished in the absence of leopard
frog competitors.
Relyea also discovered that endosulfana neurotoxin banned in several
nations but still used extensively in U.S. agricultureis inordinately
deadly to leopard frog tadpoles. By itself, the chemical caused 84 percent
of the leopard frogs to die. This lethality was previously unknown because
current regulations from the U.S. Environmental Protection Agency (EPA) do
not require amphibian testing, Relyea said. His results showed that
endosulfan was not only highly toxic to leopard frogs, but also that it
served as the linchpin of the pesticide mixture that eliminated the bulk of
leopard frog tadpoles.
Endosulfan appears to be about 1,000-times more lethal to amphibians than
other pesticides that we have examined, Relyea said. Unfortunately,
pesticide regulations do not require amphibian testing, so very little is
known about endosulfans impact on amphibians, despite being sprayed in the
environment for more than five decades.
For most of the pesticides, the concentration Relyea administered (2 to 16
parts per billion) was far below the human-lifetime-exposure levels set by
the EPA and also fell short of the maximum concentrations detected in
natural bodies of water. But the research suggests that these low
concentrationswhich can travel easily by water and, particularly, windcan
combine into one toxic mixture. In the published paper, Relyea points out
that declining amphibian populations have been recorded in pristine areas
far downwind from areas of active pesticide use, and he suggests that the
chemical cocktail he describes could be a culprit.
The results of this study build on a nine-year effort by Relyea to
understand potential links between the global decline in amphibians, routine
pesticide use, and the possible threat to humans in the future. Amphibians
are considered an environmental indicator species because of their unique
sensitivity to pollutants. Their demise from pesticide overexposure could
foreshadow the fate of less sensitive animals, Relyea said. Leopard frogs,
in particular, are vulnerable to contamination; once plentiful across North
America, including Pennsylvania, their population has declined in recent
years as pollution and deforestation have increased.
Relyea published a paper in the Oct. 1 edition of Ecological Applications
reporting that gradual amounts of malathionthe most popular insecticide in
the United Statesthat were too small to directly kill developing leopard
frog tadpoles instead sparked a biological chain of events that deprived
them of their primary food source. As a result, nearly half the tadpoles in
the experiment did not reach maturity and would have died in nature. Relyea
published papers in 2005 in the same journal suggesting that the popular
weed-killer Roundup® is extremely lethal to amphibians in concentrations
found in the environment. News releases about Relyeas previous work are
available on Pitts Web site at www.news.pitt.edu
The paper can be found on the Oecologia Web site at
www.springerlink.com/content/3420j3486k108805/ or by contacting Morgan Kelly.
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