Environmental research: hormones in water cause female frogs to become males

Environmental research: hormones in water cause female frogs to become males

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Why female frogs suddenly become male
Experts repeatedly warn against not disposing of chemicals or medication residues in the drain, but far too many people do not adhere to them. In this way, hormones and their breakdown products are released into the environment in different regions of the world. In the animal kingdom this has enormous consequences. Especially with amphibians.

Degradation products of hormones in water
The residues of pesticides, other chemicals and medicines pollute the environment and people all over the world. Experts have been warning about this for years. In many regions of the world, hormone degradation products repeatedly end up in rivers and lakes.

A recent study, which the “Welt” reports online, shows that this can be dangerous for the animals living there. In the study, Chinese researchers examined the effect of substances commonly found in water on amphibians. They published their results in the journal "Environmental Toxicology & Chemistry". It was shown that a degradation product of the hormone testosterone found in water worldwide makes male frogs masculine - and in concentrations that are already present in the environment, at least regionally.

Natural and man-made substances
According to the scientists, the gonads of tadpoles had developed different degrees of male expression in all females. Accordingly, not a single female has only shown female sexual characteristics. The hormone system controls the release of chemical messenger substances from the body - the hormones. These are essential for metabolism, growth and development. There are numerous hormonally active substances in the environment, such as phytoestrogens in soy. However, many others are artificially manufactured substances that come from pesticides, plastic materials or medicines. Researchers in Europe discovered years ago that such hormone-active chemicals threaten health.

Only males and mixed gender
The scientists from the Chinese Academy of Sciences in Beijing examined the effects of 5-alpha-dihydrotestosterone (DHT), a testosterone breakdown product. This is used by strength athletes, among other things, to cause more muscle growth. The researchers chose the water frog Pelophylax nigromaculatus as the experimental animal. It is a species that is widespread in Asia, but its population is currently declining significantly regionally, especially in China. The tadpoles were placed in various aquariums with concentrations of 40, 400 or 4,000 nanograms of DHT per liter in the water. According to the researchers, the analysis after the metamorphosis to the frog showed that in all tanks there were only males and animals of different sexes, but not a single organically clear female.

Chemicals similar to human hormones
Chemicals similar to human hormones can be found in many rivers, lakes and other bodies of water worldwide. Just last year, a study showed that German and European waters are also more chemically contaminated than expected. A large part of the hormone-like substances comes from the wastewater, even sewage treatment plants hardly filter them out. Earlier studies had shown what consequences female hormones or similar substances can have on aquatic life. For example, male fish with estrogen remain in the water, in extreme cases up to complete sex change. According to the Chinese researchers, there have already been some analyzes for male hormones (androgens). However, high concentrations in the microgram range were used that did not occur in the environment.

In a study in China, concentrations of 39 to 55 nanograms per liter in surface waters and 326 to 621 nanograms per liter in wastewater were measured for 5-alpha-dihydrotestosterone. This corresponds to the two series of experiments with low and medium concentration.

Not a single animal with female gender structures
It is said that the fact that even at 40 nanograms of DHT no single animal showed exclusively female sex structures indicates that very low levels of the substance are effective. The interaction with other hormonal substances in water has not yet been taken into account. Their overall impact may be one of several factors in the worldwide amphibian death. The chytrid mushroom Batrachochytrium dendrobatidis, or Bd for short, is considered a major cause of this. But factors such as habitat destruction, pollutant entry and the spread of other pathogens also play an important role. (ad)

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