Abstract
The herbicide atrazine is one of the most commonly applied pesticides in the world. As a result, atrazine is the most commonly detected pesticide contaminant of ground, surface, and drinking water. Atrazine is also a potent endocrine disruptor that is active at low, ecologically relevant concentrations. Previous studies showed that atrazine adversely affects amphibian larval development. The present study demonstrates the reproductive consequences of atrazine exposure in adult amphibians. Atrazine-exposed males were both demasculinized (chemically castrated) and completely feminized as adults. Ten percent of the exposed genetic males developed into functional females that copulated with unexposed males and produced viable eggs. Atrazine-exposed males suffered from depressed testosterone, decreased breeding gland size, demasculinized/feminized laryngeal development, suppressed mating behavior, reduced spermatogenesis, and decreased fertility. These data are consistent with effects of atrazine observed in other vertebrate classes. The present findings exemplify the role that atrazine and other endocrine-disrupting pesticides likely play in global amphibian declines.
Keywords: amphibian decline, endocrine disruption, pesticide, sex reversal
Atrazine is one of the most widely used pesticides in the world. Approximately 80 million pounds are applied annually in the United States alone, and atrazine is the most common pesticide contaminant of ground and surface water (1). Atrazine can be transported more than 1,000 km from the point of application via rainfall and, as a result, contaminates otherwise pristine habitats, even in remote areas where it is not used (2, 3). In fact, more than a half million pounds of atrazine are precipitated in rainfall each year in the United States (2).
In addition to its persistence, mobility, and widespread contamination of water, atrazine is also a concern because several studies have shown that atrazine is a potent endocrine disruptor active in the ppb (parts per billion) range in fish (4, 5), amphibians (6–12), reptiles, and human cell lines (5, 13–15), and at higher doses (ppm) in reptiles (16–18), birds (19), and laboratory rodents (20–28). Atrazine seems to be most potent in amphibians, where it is active at levels as low as 0.1 ppb (6–10). Although a few studies suggest that atrazine has no effect on amphibians under certain laboratory conditions (29, 30), in other studies, atrazine reduces testicular volume; reduces germ cell and Sertoli cell numbers (11); induces hermaphroditism (6, 8, 10); reduces testosterone (10); and induces testicular oogenesis (7–9, 31). Furthermore, atrazine contamination is associated with demasculinization and feminization of amphibians in agricultural areas where atrazine is used (32) and directly correlated with atrazine contamination in the wild (7, 9, 33, 34).
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