The researchers were looking into the causes of the declining populations of the West African clawed frog, or Xenopus tropicalis. It’s no secret that pesticides are endocrine disruptors, so they turned their attention to the pesticide linuron, which can make its way into the ponds where the frogs lay their eggs after being sprayed on nearby crops.
They exposed tadpoles to concentrations that matched those often found in the natural environment and compared them to control groups. They discovered that those tadpoles who were exposed to the linuron developed ovaries to a higher extent than testicles when compared to those in the control group. Moreover, by analyzing genetic expression in tadpoles, they discovered that the male-female sex ratio in these amphibians is shifting in favor of females.
The story gets worse as the frogs reach adulthood, with male fertility being seriously impaired and gender-specific features becoming noticeably more feminine. They believe this is because the pesticide is stopping the functioning of testosterone inside their bodies.
Project leader and Exotoxicologist Cecilia Berg said these results illustrate how pesticides cause permanent damage in frogs who are exposed when they’re just tadpoles. It supports past research that shows endocrine disruptors like pesticides have a negative effect on the animals. She points out that while the substance isn’t approved in Sweden, it is used in other parts of Europe and North America on crops like potatoes.
Frog populations around the world are already in danger of extinction, and interfering with their reproduction in this way could make the situation even worse. Experts believe that around 40 percent of our planet’s amphibian species are endangered, with habitat loss and pollution also contributing to the problem. An amphibian plague caused by a fungus has also played a role, putting an end to 100 different species. Meanwhile, German scientists warned an “ecological Armageddon” is coming after discovering insect populations fell by 75 percent in nature reserves in the country.
The results of this study could help shape pesticide policies in the EU and elsewhere. Dr. Berg commented that the European Commission is in the midst of taking measures to make pesticide risk assessment better. She’s encouraged by the European Food Safety Authority’s report that highlights the needs to assess pesticide risks to amphibians. The EU voted this spring to permanently ban a trio of pesticides that were found to pose a significant threat to bees.
It's not just frogs who are vulnerable to the endocrine disrupting effects of pesticides. Studies have also shown that the pyrethroid class of pesticides can cause boys to hit sexual maturity earlier, experience stunted growth, or note behavioral problems. It also raised their risk of testicular cancer as adults.
In addition, the popular herbicide atrazine has been found to destroy the human prostate gland, interfere with reproduction, create hormonal imbalances, and even cause early death. Why do we still allow our crops to be sprayed with these toxic chemicals?
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