BEIJING, Feb. 28 (Xinhuanet) -- One reason up to
a third of the world's frog species are in danger of extinction may be
estrogen-like pollutants in the environment that turn male tadpoles into
females, according to a new study.
Two species of frogs in an Uppsala University, Sweden
laboratory were exposed to levels of estrogen similar to those detected in
natural bodies of water in Europe, the United States and Canada.
The population of the two groups receiving the
heaviest dose of estrogen became 95 percent female in one case, and 100 percent
in the other.
"The results are quite alarming," said co-author
Cecilia Berg, a researcher in environmental toxicology. "We see these dramatic
changes by exposing the frogs to a single substance. In nature there could be
lots of other compounds acting together."
The results revealed the percentage of females in two
control groups was under 50 percent -- not unusual among frogs -- the sex ratio
in three pairs of groups maturing in water dosed with different levels of
estrogen were significantly skewed.
Even tadpoles exposed to the weakest concentration of
the hormone were, in one of two groups, twice as likely to become females.
Earlier studies in the United States, Berg explained,
linked a similar sex-reversal of Rana pipiens male frogs -- one of the two
species used in the experiment -- in the wild to a pesticide that produced
estrogen-like compounds.
"Pesticides and other industrial chemicals have the
ability to act like estrogen in the body," Berg said. "That is what inspired us
to do the experiment," she said referring to her collaborator and lead author of
the article, Irina Pettersson, also a researcher at Uppsala.
The other species examined was the European common
frog, Rana temporaria.
Some of sex-altered males became fully functioning
females, but other had ovaries but no oviducts, making them sterile, Berg
explained.
The study does not measure the potential impact of
pollutant-driven sex change for frog species, but the implications, said Berg,
are disquieting.
"Obviously if all the frogs become female it could
have a detrimental effect on the population," she said.
The only immediate remedy, she continued, would be to
improve sewage treatment in areas where frogs and other amphibians might be
affected to filter out estrogen concentrations coming from contraceptive pills
and from industrial pollutants.
(Agencies)
