Atrazine (1-chloro-3-ethylamino-5-isopropylamino-2,4,6-triazine) is a widely used herbicide in the United States. Atrazine is in a class of compounds that is known to mimic steroid hormones in a variety of animal species. Atrazine is used to stop pre- and post-emergence broadleaf and grassy weeds in major crops. Approximately 36 million kilograms of this substance are applied on U.S. farms yearly. It has been estimated that 225,000 kilograms of the herbicide become airborne and fall with rainfall as far as 1,000 kilometers from its source.
In a study under the direction of Dr. Tyrone Hayes of the Department of Integrative Biology at the University of California Berkeley, 40 male African clawed frogs were exposed to atrazine at a level of 2.5 parts per billion (ppb) in drinking water. This is at a level lower than the 3 ppb allowed in drinking water by the Environmental Protection Agency (EPA). As a result 30 of the frogs were chemically castrated. Interestingly enough, four of the treated frogs turned female and produced viable eggs despite being genetically male. Only six of the frogs resisted atrazine and displayed normal sexual function. This result was confirmed by additional studies. A possible candidate for the apparent sex change effect is the enzyme aromatase that triggers the production of the female hormone, estrogen causing male gonads to become ovaries.
On account of these disturbing data, the European Union has prohibited its use. The rationale for the continued use in the U.S.as stated by the Environmental Protection Agency (EPA) is, "The total or national economic impact resulting from the loss of atrazine to control grass and broadleaf weeds in corn, sorghum and sugar cane would be in excess of $2 billion per year if atrazine were unavailable to growers." In the same report, it added the "yield loss plus increased herbicide cost may result in an average estimated loss of $28 per acre" if atrazine were unavailable to corn farmers”
In summary, Atrazine is a common agricultural herbicide whose primary effects are reproductive and developmental. The study cited above indicates that for the organism studied, the frog, profound reproductive harm occurred at levels below what is currently allowed in drinking water. This is cause for concern especially in regard to the fact that atrazine is often found far from its original site of application.