- WASHINGTON (Reuters) - The
most popular weedkiller in the United States can give male frogs female
sex organs and other attributes, researchers said on Monday, in a study
that could shed light on the global decline in amphibian populations.
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- Very low levels of the herbicide atrazine can cause male
frogs to grow female sex organs and curtail their croaks -- key to attracting
mates in the frog world -- a team at the University of California Berkeley
found.
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- The frogs appear normal on the outside, but often have
both male and female sex organs, the researchers said, adding that the
findings may help explain the amphibian population decline.
-
- The decline worries scientists because amphibians such
as frogs respond to environmental dangers before other species.
-
- "Atrazine is the most commonly used herbicide in
the U.S. and probably the world," the researchers wrote in their report,
published in the Proceedings of the National Academy of Sciences. "It
can be present at several parts per million in agricultural runoff and
can reach 40 parts per billion in precipitation."
-
- Such a common pollutant would reach many animals as well
as humans, so the team, led by Tyrone Hayes, tested its effects on the
African clawed frog Xenopus laevis.
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- They put tadpoles into water laced with levels of atrazine
much lower than allowed by the U.S. Environmental Protection Agency, and
found that the weedkiller had serious effects on 16 percent of them.
-
- These genetically male frogs had testicles and ovaries,
and many had testicles that did not function properly and contained eggs
and sperm. Their levels of testosterone were much lower than normal.
-
- The male frogs also had much smaller larynxes than normal,
which could affect their ability to croak and attract mates, Hayes' team
reported.
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- The researchers determined that atrazine is an endocrine
disruptor -- a class of chemicals that disrupts the hormones in the body.
Many pesticides fall into this category and it is one of the qualities
that can make them dangerous.
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- "We hypothesize that atrazine ... promotes the conversion
of testosterone to estrogen," they wrote.
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- "This widespread compound and other environmental
endocrine disruptors may be a factor in global amphibian declines."
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- Environmentalists responded with alarm.
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- "This research is further proof that this pesticide
is a major threat to public health and the environment," the Natural
Resources Defense Council said in a statement.
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- "EPA's tap water standard for atrazine is 3 parts
per billion -- 30 times higher than the level at which these dramatic sexual
side effects occurred. At higher levels, the frogs developed additional
health problems," it added.
-
- "This rigorous scientific study reinforces what
we and other scientists have been saying for years -- atrazine is a dangerous
pesticide," the council's Jennifer Sass said. "It's no surprise
that it's been banned by many European countries."
-
- She said the study had implications for humans, especially
children who have not reached puberty.
-
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