Environmental ▼News More evidence that herbicides feminize amphibians ecent reports have suggested Cane toads don’t have much of that exposure to the herbicide a fan club. This big, ugly, invasive atrazine is altering sexual despecies secretes a white slime poivelopment in frogs (Environ. Sci. sonous to many pets. Although Technol. 2002, 36, 444A). Now Florida researchers report that male toads living near sugar cane fields in Florida show signs of feminization, which may be linked to herbicide runoff. Sugar cane fields have the highest usage of triazine herbicides, such as atrazine, per acre in the United States, according to U.S. Geological Survey endocrinologist Tim Gross, who led the research team. “We wanted to study the worst case of environmental exposure, and it looks like we found something,” he says. Gross and graduate student Krista McCoy presented their findings on November 17 at the Society of Environmental Toxicology and Chemistry meeting in Salt Lake City, Utah. Although preliminary, the research lends credence to Cane toads living near Florida sugar cane fields University of Berkeley enall had female markings. docrinologist Tyrone Hayes’ hypothesis that atrazine is affecting cane fields support several amthe sexual development of amphibphibian species, the researchers ians, according to several frog spechose the cane toad because males cialists familiar with the work. have a nonfunctional rudimentary The researchers studied the ovary called a Bidder’s organ, giant, or cane toad (Bufo marinus), which may make them sensitive to which normally has easy-to-idenenvironmental contaminants that tify markings differentiating males affect sexual differentiation, acand females—the females are darkcording to McCoy. Cane toads also er and mottled while the males are metamorphose in the spring when a single bland color. However, all of atrazine concentrations can reach the toads living near the cane fields as high as 30–35 parts per billion that the researchers examined had in surface waters near the cane female coloration. In addition, fields. about 30% of the male toads found From early April until June 2002, at the contaminated sites were McCoy collected toads from two hermaphrodites. sugar cane research sites just north 46 A ■ ENVIRONMENTAL SCIENCE & TECHNOLOGY / FEBRUARY 1, 2003
U.S. GEOLOGICAL SURVEY
R
of the Everglades. She also collected 25 toads from a control site on the University of Miami campus. Roughly half of the female-colored toads from one of the sugar cane fields turned out to have male gonads. But about 30% of these males were hermaphrodite—they also had either a mass of developing eggs or a developing ovary. Histological examination, while not yet completed, confirms the observations, according to Gross. The researchers acknowledge that they do not know how much atrazine, or any other chemicals, these toads were exposed to during the crucial period when the animals metamorphosed. But there is every reason to think that atrazine exposure levels were high, says Gross. The hermaphrodite males appeared to have normal plasma sex steroid concentrations, but their levels of vitellogenin, a biomarker for environmental estrogens, resembled those of female toads. The vitellogenin levels suggest that an external estrogen mimic could be responsible for the effects documented by the Florida group, says Gross, who acknowledges that atrazine has not been reported to act in this way. “This work raises more questions than answers,” he says, adding that the findings are consistent with the previous work of both Hayes and Texas Tech experimental toxicologist James Carr. “Carr finds an effect at atrazine concentrations that are similar to what we see in the field and to what we think the toads were exposed,” he says. Gross plans to follow up the research, which was funded by atrazine manufacturer Syngenta, with controlled laboratory experiments and fieldwork on other species. —REBECCA RENNER © 2003 American Chemical Society
