Feb. 27, 2007 — Frogs that began life as male tadpoles can be changed into females by estrogen-like pollutants similar to those found in the environment, according to a new study.
The results may shed light on one reason up to a third of frog species around the world are threatened with extinction. The study is set to appear in the journal Environmental Toxicology and Chemistry in May.
In a laboratory at Uppsala University in Sweden, scientists exposed two species of frogs to levels of estrogen similar to those detected in natural bodies of water in Europe, the United States and Canada.
The results were startling: whereas 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.
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.
