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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.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).
Despite the wealth of data from larvae and newly metamorphosed amphibians, the ultimate impacts of atrazine’s developmental effects on reproductive function and fitness at sexual maturity, which relate more closely to population level effects and amphibian declines, have been unexplored. In the present study, we examined the long-term effects of atrazine exposure on reproductive development and function in an all-male population of African clawed frogs (Xenopus laevis), generated by crossing ZZ females (sex-reversed genetic males) to ZZ males (SI Materials and Methods). The advantage of using this population is that 100% of the animals tested were genetic males. As a result, all hermaphrodites and females observed are ensured to be genetic males that have been altered by endocrine disruption. We examined sex ratios, testosterone levels, sexual dimorphism, reproductive behaviors, and fertility in males exposed to 2.5 ppb atrazine throughout the larval period and for up to 3 years after metamorphosis.
