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Pesticides Feminizing Male Frogs, Impairing Reproduction

A new study conducted by a team of Swedish and British scientists has revealed that linuron, an endocrine-disrupting chemical used in pesticides, impairs the fertility of male frogs and causes tadpoles to develop ovaries rather than testicles, resulting in a skewed sex ratio where females frogs are more common than males.

Biodiversity is decreasing at an alarming rate globally, with amphibians being one of the most rapidly disappearing groups of animals. Current estimates suggest that nearly 40% of all documented amphibian species are threatened, largely due to habitat degradation and habitat loss, but other contributing factors include climate change, pollution and disease.

Many different pesticides are used in agriculture to control weeds and insect pests. These chemicals can leach through soils into groundwater or get washed off the surface of the soil with runoff, to contaminate ponds and other surface waterbodies where frogs congregate to breed. Some pesticides contain endocrine-disrupting chemicals which can disrupt hormone functioning of animals who are exposed to them.

Xenopus_tropicalis02

For the study, which focused on the endocrine disrupting affects of linuron on the West African clawed frog, the researchers exposed tadpoles to concentrations of the chemical similar to what they measured in ponds where the tadpoles naturally occurred. They found that when tadpoles where exposed to linuron they were more likely to develop ovaries than testicles. The scientists also found that the sex ratio became skewed, with a higher percentage of females in the population compared to males.

The researchers also found that once the tadpoles became adult frogs, fertility in males became impaired and some gender-specific features became more like that of female frogs. The researchers suggest a likely explanation for their observations is that chemicals used in pesticides inhibit the functioning of the male hormone testosterone, causing frogs to effectively become feminized.

The study was conducted in the Department of Environmental Toxicology at Uppsala University, whose laboratory specializes in testing the chemical affects on frogs throughout their lifecycle. By testing the affects of the pesticide on the West African clawed frog, the scientists have developed a system that can be used to test the affect of endocrine disrupting chemicals on other amphibians as well as other animal species. The results of this study highlight the importance of looking at the impacts throughout an animal's lifecycle to determine the affect of pesticide chemicals and other contaminants on the reproductive capacity of amphibians.

According to ecotoxicologist, Cecilia Berg, who lead the study, Sweden has not approved the use of the chemical linuron, however it is used in other countries in Europe, as well as in North America.

"The results of the study are important, since they contribute knowledge that risk assessment authorities in the EU can use as a basis for assessing the health and environmental risks of pesticides. The European Commission is currently taking several measures to improve pesticide risk assessment. A new report from the European Food Safety Authority (EFSA), for instance, points to the need to assess the risks of pesticide use to amphibians - something that isn't being done today," Berg says.

Considering that the pesticide is also used in the North America, the potential environmental health risks apply in the US too.  We recommend that the public use a water filter such as a berkey to remove potentially health damaging pesticides from their water to remove any potential disclosure.

Journal Reference

F. Orton, M. Säfholm, E. Jansson, Y. Carlsson, A. Eriksson, J. Fick, T. Uren Webster, T. McMillan, M. Leishman, B. Verbruggen, T. Economou, C. R. Tyler, C. Berg. Exposure to an anti-androgenic herbicide negatively impacts reproductive physiology and fertility in Xenopus tropicalis. Scientific Reports, 2018; 8 (1) DOI: 10.1038/s41598-018-27161-2

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