Environmental Research Hormones in waters make frog female males

Why frog female suddenly become male
While experts warn again and again not to dispose of chemicals or drug residue in the drain, but too many people do not stick to it. Hormones and their breakdown products are released into the environment in various parts of the world. In the animal kingdom this has enormous consequences. Especially with amphibians.

Degradation products of hormones in waters
The residues of pesticides, other chemicals and medicines pollute the environment and people all over the world. Experts have warned against this for years. In many regions of the world, degradation products of hormones are repeatedly found in rivers and lakes.

A recent study, reported by the "Welt" online, shows that this can be dangerous for the animals living there. In the study, Chinese researchers investigated the effect of common aquatic substances on amphibians. They published their findings in the journal "Environmental Toxicology & Chemistry". It has been shown that a degradation product of the hormone testosterone, which can be found worldwide, makes it possible to produce female frogs - in concentrations that are already present in the environment, at least regionally.

Picture: molekuul.be - fotolia

Natural and man-made substances
According to the scientists, the gonads of tadpoles had developed different male characteristics in all females in experiments. Accordingly, not a single female showed exclusively female sexual characteristics. The hormone system controls the secretion of chemical messengers in the body - the hormones. These are essential for metabolism, growth and development. In the environment, there are many hormonally active substances, such as phytoestrogens in soy. Many others, however, are man-made substances, which come from pesticides, plastic materials or drugs. Researchers in Europe have noticed that such hormone-active chemicals threaten health.

Only males and mixed gender
The scientists from the Chinese Academy of Sciences in Beijing investigated the effects of 5-alpha-dihydrotestosterone (DHT), a degradation product of testosterone. This is used among other things by strength athletes, to cause more muscle growth. The researchers chose the water frog Pelophylax nigromaculatus as a laboratory animal. It is a widespread species in Asia, but its stock is currently waning significantly, especially in China. The tadpoles were placed in different aquaria with concentrations of 40, 400 or 4,000 nanograms of DHT per liter in the water. According to the researchers, the analysis of completed metamorphosis to the frog showed that in all ponds only males and animals of unequal sex, but not a single organically distinct females, were left.

Human hormones resembling chemicals
Human hormone-like chemicals are found throughout the world in many rivers, lakes and other waters. Just last year, a study showed that German and European waters are also more contaminated with chemicals than expected. A large part of the hormone-like substances comes from the wastewater, even sewage treatment plants are hardly filtering them out. Earlier studies had already shown what consequences female hormones or similar substances might have on aquatic life. For example, males fish with estrogen in the water, in extreme cases until complete sex reassignment. And also for male hormones (androgens), according to the Chinese researchers have already given some analysis. However, high concentrations in the microgram range were used, which would not occur in the environment at all.

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 test series with lower and medium concentration.

Not a single animal with female gender structures
It is said that the fact that even with 40 nanograms of DHT not a single animal showed exclusively female sex structures, indicates that even very low levels of the substance are effective. The interaction with other hormonal substances in the aquatic environment has not even been considered. Its overall effect may be one of several factors in the worldwide amphibious deaths. The chytrid fungus Batrachochytrium dendrobatidis, or Bd for short, is considered a major cause of this. However, factors such as the destruction of habitats, the introduction of pollutants and the spread of other pathogens also play an important role. (Ad)