Cuban tree frog

A Cuban tree frog, the type studied by University of South Florida researchers who found that exposure to a common herbicide early in life makes frogs more susceptible to a fatal fungal infection. (University of Southern Florida / October 25, 2013)

Frogs exposed to the commonly used herbicide atrazine early in life are particularly susceptible to a skin fungus linked to vanishing amphibians around the world, according to a new University of South Florida study.

Amphibians might need to be exposed to atrazine only briefly as larvae to cause persistent increases in their risk of chytrid fungus mortality, according to the study published in the new edition of Proceedings of the Royal Society B.

Batrachochytrium dendrobatidis is a chytrid fungus that was first identified in 1998 and is thought to have originated in Japan. It causes a thickening of the skin, which impairs gas exchange and the animal's ability to absorb water, triggering rapid mass die-offs of frog populations.

“Our findings suggest that reducing early-life exposure of amphibians to atrazine could reduce lasting increases in the risk of mortality from a disease associated with worldwide amphibian declines,” Jason Rohr, co-author of the study, said.

The findings are consistent with earlier studies at other research facilities showing that atrazine can affect the behavior, growth, immunity and survival of mammals, fish and amphibians.

An estimated 76.4 million pounds of atrazine are applied annually in the United States, about 86% of it used to treat corn, according to the U.S. Environmental Protection Agency.

The study led by Rohr and Lynn Martin, associate professors of integrative biology at USF, tested the short-term and long-term effects of exposure to concentrations of the chemical typically found in the environment on Cuban tree frogs, both in the tadpole stage and after they had metamorphosed.

Although atrazine exposure early in life had no significant effects on survival in the absence of the fungus, the risk of death was two times more likely for individuals exposed to both the chemical and the fungus, according to the study.

The increase in mortality was caused by a reduction in the frogs’ tolerance of infection, according to the study. In addition, the researchers found no evidence of recovery from early-life exposure to atrazine.

In an interview, Rohr said, “The findings suggest that folks in the medical sciences should take a hard look at minimizing encounters with potential stressors early in life to decrease long-term disease risks.”

louis.sahagun@latimes.com