USF Study Finds Common Fungicide Lethal for Frogs (Via HerpDigest)

USF Study Finds Common Fungicide Lethal for Frogs

Researchers trying to determine the cause of worldwide amphibian declines turn to popular fungicide.

By Vickie Chachere, USF News

TAMPA, Fla. (April 12, 2011) - Chlorothalonil, a common fungicide used around the world on farms and golf courses, has been found to be lethal to frog tadpoles at levels below what regulators have said are safe environmental concentrations, says a new University of South Florida study published in one of the nation's leading environmental journals.

In a study published in the journal Environmental Health Perspectives, USF biologists Taegan McMahon and Jason Rohr found that nearly every frog exposed to chlorothalonil in their study either died or suffered elevated stress hormone levels and changes in their immune cell counts, conditions which could weaken the animal and leave them vulnerable to parasites.

The finding could offer insight to a worldwide investigation of factors that might be causing widespread declines of amphibians, a taxon which many scientists view as a harbinger of potentially dangerous environmental conditions for other living creatures.

Chlorothalonil was known to suppress the immune systems of oysters and fish, but was relatively untested on amphibians before the USF study, conducted in conjunction with researchers from the University of Florida Gulf Coast Research and Education Center, Rowan University, and the Archbold Biological Station in Venus, Fla.

Unlike chlorothalonil, most previously tested pesticides have not directly killed frogs at or below expected environmental concentrations. The expected environmental concentration of a pesticide is a concentration expected to be found in a water body that is a standardized distance from an application site, is calculated using US Environmental Protection Agency (EPA) software, and is the concentration typically used by the US EPA to determine the safety of pesticides.

Lab tests showed that, at the expected environmental concentration, the fungicide was lethal to nearly 100 percent of the tadpoles in all four amphibian species tested. Moreover, concentrations of chlorothalonil four orders of magnitude below the expected environmental concentration were associated with significant mortality in two of the four amphibian species. Outdoor field experiments generally matched the findings of the laboratory experiments, suggesting that these results might be relevant to effects in nature.

The experiments also showed that the chemical was nonlinearly associated with mortality, stress hormones, and immunity: low and high concentrations caused significantly greater mortality and stress hormone levels than intermediate concentrations and controls, a dose-response consistent with endocrine disruption. In addition, for the survivors of low-dose chlorothalonil exposure, chlorothalonil concentration was inversely correlated with the number of immune cells in their liver, suggesting potential immunosuppresion of the surviving frogs.

Chlorothalonil is the most commonly used synthetic fungicide in the U.S., with some 14 million pounds being used predominantly on peanuts, strawberries, potatoes, tomatoes, and turf grass.

The fungicide is part of the same chemical family, organochlorines, as the pesticide DDT, which has been banned for decades but remains pervasive in the environment.

The U.S. Environmental Protection Agency has strict standards on the application of chlorothalonil, which is known to contaminate surface waters through runoff and soil erosion. Users are warned to not spray the fungicide near water. However, it should be noted that the concentrations tested in these experiments were based on appropriate product use.

The USF scientists are focusing their 2½-year research project on the effects of chlorothalonil on freshwater organisms. Chlorothalonil binds to glutathione, disrupting cellular respiration that can lead to cell death. "Cellular respiration is an essential process for almost all living things," said McMahon, a USF biology graduate student.

The researchers cautioned that their study has yet to determine the mechanism by which the fungicide affects frogs, only that its use raises red flags because levels expected to be found in the environment clearly have detrimental effects on amphibians, a taxon in global decline and an important biological indicator for the health of the environment. "We don't quite know its role in amphibian declines, but when the expected environmental concentration is associated with nearly 100 percent mortality across four amphibian species, it's a cause for concern," said Rohr, an assistant professor in USF's Department of Integrative Biology.

Bd Invades Everywhere (Via HerpDigest)

Bd Invades Everywhere
Smithsonoanian Tropical Research Inst. 1/31/10

Bd is a waterborne pathogen, and until recently, was thought to be limited by temperature, but the extent to which it persists and causes disease in amphibians at lower elevations in the neotropics is not known


A group of scientists led by Vanessa L. Kilburn of McGill University and including Roberto Ibáñez, director of STRI´s Amphibian Rescue and Conservation Center in Panama, Oris Sanjur and Eldredge Bermingham, also from STRI, Justin P. Suraci of Simon Frazer University and David M. Green of McGill, has just published an article in EcoHealth on the "Ubiquity of the pathogenic chytrid fungus, Batrachochytrium dendrobatidis, in anuran communities in Panama."

Batrachochytrium dendrobatidis (Bd) has been implicated as the main driver of many enigmatic amphibian declines in neotropical sites at high elevations.

Bd is a waterborne pathogen, and until recently, was thought to be limited by temperature, but the extent to which it persists and causes disease in amphibians at lower elevations in the neotropics is not known. It also is unclear by what mechanisms Bd emerged as a pathogenic organism; there is debate as to whether it is endemic to the region and for some reason its pathogenicity increased, or if it is a new pathogen to the region.

In this research, conducted in western Panama in 2006, several study sites were established along the epidemic gradient caused by Bd, including sites where the epidemic had not yet arrived, places right in the middle of the epidemic and others two and 10 years after the epidemic. Other sites were also established along an altitude gradient between 45 and 1,215 meters above sea level. 

After analyzing samples obtained from the skin of the frogs using quantitative PCR analyses to detect the fungus, the scientists found that there were infected frogs everywhere, including sites where the fungus arrived years ago, as well as lowland sites.

When comparing lowland frog abundance with previous years, the scientists also noticed a decline in frog diversity and abundance.

It is very difficult to know if Bd is an endemic organism or a new, recent arrival. However, based on the results of this study and current knowledge, the scientists maintain the idea that chytridiomycosis is new and invasive and that it is spreading all over the world.

Parasite Caused Frogs With Too Many Legs, Scientist Says

LOS LUNAS, N.M. -- Frogs in a Los Lunas pond are surfacing with either too many legs or too few, and one university researcher said he’s pinpointed the cause.


Worried viewers called Target 7 to find out if the water was contaminated and if it was harmful to humans.

Los Lunas officials didn’t know about the frogs until they were contacted by Target 7. Immediately, Parks and Recreation Director Michael Jaramillio closed off the pond and had the water tested.


Target 7 also conducted water tests, and reporter Anna Velasquez broke out in rashes after collecting samples.

Mason Ryan is an amphibian expert at the University of New Mexico who is investigating the frog deformities.

“In the big picture of the number of ponds and the number of frog species we have in this country, it's kind of a relatively rare event,” Ryan said.

Ryan said this is New Mexico’s first known case of bullfrog deformities. Out of the 178 frogs collected, he said 80 percent were deformed and all were juveniles.

“As with most stories in biology, it's a complex story with multiple things happening to cause this,” Ryan said.

Predators are responsible for the frogs that are missing legs, and a parasite called trematode caused three or more legs in some frogs, Ryan said.

“They have a complex life cycle where they go through a bird, into a snail, and they live in the water and then they enter the developing tadpole,” Ryan said.

Ryan said he believes something must have happened in the pond to trigger a spike in the parasite’s population.

“Our nitrogen level may have been high in the pond some time last year due to possibly and overspill of fertilizer,” Jaramillo said.


Jaramillo admits that a groundskeeper fertilized the grass around the pond and accidentally spilled some into the water.

“How much of it? They're thinking a couple pounds at the most, it wasn't like it was intentionally put in there,” Jaramillo said.

The amount of fertilizer was not enough to kill off the pond’s fish or other organisms, but may have been enough to cause the frogs’ deformities.