Kermit to Kermette?
Does the Herbicide Atrazine Feminize Male Frogs?
by
Frank J. Dinan
Department of Chemistry and Biochemistry
Canisius College, Buffalo, NY
by
Frank J. Dinan
Department of Chemistry and Biochemistry
Canisius College, Buffalo, NY
Atrazine is the most widely used herbicide in the United States. The U.S. Department of Agriculture reports that approximately 70 million pounds were used in the United States in 1995. Not surprisingly, atrazine is a very common contaminant of ground and surface waters. The U.S. Centers for Disease Control’s Agency for Toxic Substances reports that when atrazine enters the environment, its life on land is measured in days to months. However, atrazine decomposes only slowly in water, where it can last for much longer times (Agency for Toxic Substances and Disease Registry, 2003). Since the use of atrazine is banned in Switzerland, Denmark, Sweden, Germany, France, and Norway, questions about its safety have inevitably been raised. Earlier studies had shown that atrazine induces (causes) the production of aromatase, an enzyme that converts androgens (male sex hormones) into estrogens (female sex hormones). These studies suggest that the herbicide may act as a chemical castration agent and may be linked to the decline in the population of amphibians that has been observed worldwide. This process and the structures of the chemicals involved in it are shown diagrammatically below:
In 1997, the U.S. Environmental Protection Agency (EPA) was in the process of considering the renewal of the Syngenta Corporation’s (atrazine’s Swiss manufacturer, and one of the world’s largest chemical companies) license to continue the use of atrazine in the United States, atrazine’s largest market. To provide the needed safety data to the EPA, Syngenta employed Tyrone Hayes, a professor at the University of California at Berkeley, to investigate atrazine’s safety.
Professor Hayes began his investigation by growing frog larvae in water samples that he had collected from ponds and streams in areas of the Midwest. Some of these areas used atrazine extensively, whereas others reported little or no use of atrazine. Hayes grew the larvae in water samples that contained a wide range of atrazine concentrations until they developed into sexually mature frogs. Larvae were used since the presence of atrazine could potentially have a significant effect on their sexual maturation and on the biosynthesis of the male sex hormone, testosterone. This hormone must be present in appropriate concentrations for the normal sexual development of male frogs.
Hayes published his findings in articles that appeared in prestigious scientific journals. The data that Hayes gathered show the effect of atrazine on hermaphroditism (the presence of both male and female sexual organs) in male frogs. These data are shown below in graphical form. Note that the first chart compares the concentration of atrazine in the water in which the tadpoles were grown to the percent of gonadal abnormalities found in male frogs, whereas the second chart reports the amount of atrazine to which each tadpole was exposed, the dose. The non-linear nature of the atrazine concentration and dose ranges reflects the way in which the author reported these data in the original literature (Hayes, 2004). Note that one microgram per liter is equivalent to one part per billion.
Date Posted: 03/20/06 nas
Image Credit: Frog photograph copyright © Adam Lukasiewycz.
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