Atrazine, the most commonly used herbicide in the world, has been found to disrupt the reproductive cycles of the African clawed frog and may offer a partial solution to the global decline in amphibian species.
Atrazine is the most common herbicide used world-wide and, consequently, it is also the most commonly detected herbicide residue found in ground and surface water, as well as in our drinking water. Atrazine is a known “disruptor” of endocrine functioning (the endocrine system secrets and regulates hormones and proteins that are vital for proper growth) and it remains biologically active even in low concentrations.
In a recent study, male frogs of the genus Xenopus were exposed to low atrazine levels and became “demasculinized”
In a March 2010 paper published on the Proceedings of the National Academy of Science website, researchers (Hayes et al) conducted their study to determine the effects of the pesticide on the reproductive system of an African frog species, Xenopus laevis. This particular species was chosen because past studies showed the chemical compound disrupted the larval stage of the amphibian.
In this study, adult males of the species were exposed to Atrazine (in low but ecologically relevant quantities). Atrazine-exposed males became “demasculinized (chemically castrated) and completely feminized as adults.”
Ten percent of the exposed population developed into viable females which were able to copulate with (unexposed) males and produce viable eggs. According to results published in the paper, the majority of exposed, male frogs developed “depressed testosterone, decreased breeding gland size, demasculinized/feminized laryngeal development, suppressed mating behavior, reduced spermatogenesis, and decreased fertility.”
The results from this study were consistent with observations of atrazine effects in other amphibian species. Other pesticides are also shown to act as endocrine-disruptors.
Massive Declines of Amphibian Species
Over the past two decades, many amphibian species (such as frogs and salamanders) have suffered dramatic declines throughout the world. These declines have been associated with a type of chytrid fungus (BD) or with exposure to habitats that are favorable to the fungus. Whether or not the two factors — the atrazine and fungus exposure — are working in combination somehow, or, if they represent two separate forces acting on different populations of amphibians around the world, remains a mystery.
The African Clawed Frog
An entirely aquatic frog, The African clawed frog (Xenopus laevis; common name platanna), has no tongue, teeth or true ears. Instead, the frog possesses lateral lines of specialized cells running the length of its body and underside which allow it to sense movements in its environment. Found throughout Africa but concentrated in South Africa, the frog can grow up to 5 inches (12 cm) in length. It is a scavenger and will consume almost any type of organic waste or decaying matter. Of the 14 species of Xenopus, Xenopus gilli is the most endangered.
Reference for this article: Atrazine induces complete feminization and chemical castration in male African clawed frogs (Xenopus laevis), Proceedings of the National Academy of Sciences (PNAS 2010 107 (10) 4612-4617; published ahead of print March 1, 2010, doi:10.1073/pnas.0909519107)
Photo Credit: USGS