Medicines in the environment affect frogs
Frogs are more sensitive to hormone-disturbing environmental pollutants than was previously believed. New research results from MistraPharma show that male tadpoles can have their fertility reduced, or be transformed to females.
Large quantities of medicines are released with drain water and found in streams all over the world. There are indications that they affect organisms that live in water. For example, the estrogen in birth-control pills is associated with reproduction disturbances in wild fish. But in general little is known about how wild animals are affected by pharmaceuticals. Reduced fertility
Irina Gyllenhammar, with MistraPharma, has studied how two different pharmaceuticals — ethinylestradiol and clotrimazole (a fungicide used in shampoo and ointments) — affect the reproduction system in frogs. Her recently-published doctoral thesis shows that low concentrations of ethinylestradiol cause reduced fertility and sex reversal in frogs. “The results show that frogs are more sensitive to estrogen-like environmental pollutants than was previously believed," says Gyllenhammar.
Ovaries
When tadpoles swim in water with low concentrations of ethinylestradiol, the male frogs develop ovaries instead of testicles. Irina Gyllenhammar has demonstrated this in two frog species: the European common frog and the West African clawed frog. It is during the larval stage that reproductive organs begin to develop in frogs; a process that is steered by the hormone system. The males that were exposed to ethinylestradiol but still developed testicles had reduced fertility as adults. “They fertilized fewer eggs when they mated than the unexposed males, and they even had reduced quantities of sperm in their testicular tubes. Many female frogs that were exposed had no oviducts, which made them sterile," she says.
Model species
The fungicide clotrimazole caused disturbed hormone production in the West African clawed frog. The activity in the estrogen-producing enzyme changed in ovaries, testicles and the brain. The most important conclusion of Gyllenhammar´s thesis is that the reproductive capacity of wild frogs may be negatively influenced by hormone-disturbing environmental pollutants. Her thesis also shows that the West African clawed frog is a suitable model species for studying the effects of environmental pollutants on the reproductive system.
