Study suggests link between agricultural chemicals and frog decline

Feb 04, 2009
Study suggests link between agricultural chemicals and frog decline

(PhysOrg.com) -- Around the world, amphibian populations are in decline, and scientists have not been able to figure out why. Now a study of leopard frogs in Pennsylvania has identified a possible culprit, and the ramifications are troubling, according to a Penn State ecologist.

Research conducted primarily at Penn State's Russell E. Larson Agricultural Research Center at Rock Springs in the summer of 2007 — described in a recently published article in the journal Nature — suggests that chemical pollution can increase often-deadly trematode (parasitic flatworm) infections in a declining amphibian species.

"Like canaries used to gauge the safety of air in coal mines, amphibians are thought to be the 'canaries' in our freshwater environments, and reductions in their health can warn that subsequent species declines might be in store," says Hunter Carrick, associate professor of aquatic ecology in Penn State's College of Agricultural Sciences, who was one of the lead investigators in the study.

"The scientific findings point to worrisome synergisms between two commonly used agro-chemicals that, when combined, can produce a lethal effect to frog populations at concentrations that are often observed in wetland ecosystems."

The study looked at atrazine, a widely used herbicide, and phosphate, a primary ingredient in fertilizers. "When combined, they accounted for 74 percent of the variation in larval trematode abundance in the frogs,” says Carrick.

These agrochemicals increase trematode infections by augmenting snail intermediate hosts (phosphorus) — the source of trematodes that infect amphibians -- and suppressing amphibian immune responses (atrazine), explains Jason Rohr, assistant professor of integrative biology at the University of South Florida, who was the principal investigator in the research. Rohr was a postdoctoral fellow in Penn State's College of Agricultural Sciences during much of the project, which was funded by grants from the National Science Foundation, the U.S. Department of Agriculture and the Environmental Protection Agency.

According to Rohr, identifying the main risk factors and predictors for disease in amphibians is important. The study showed that atrazine and phosphate concentrations in wetlands they investigated were the best of more than 240 plausible predictors of trematode abundance in frogs. In a manipulative experiment conducted with 300-gallon tanks outdoors at Penn State's Larson Agricultural Research Center, Rohr and colleagues verified that atrazine and phosphate increased snail abundance, caused amphibian immuno-suppression and elevated amphibian trematode loads.

"At concentrations commonly occurring in freshwater ecosystems, atrazine and phosphate can be drivers of amphibian trematode infections, raising concerns about the role of these chemicals in amphibian declines," concludes Rohr. "Reducing atrazine and phosphate inputs to wetlands might remediate these often-debilitating amphibian trematode infections."

Atrazine and phosphate might not be the only chemicals affecting disease risk, notes Carrick. "Many chemicals can be immuno-suppressive, and standard toxicity tests used to register chemicals in the United States and Europe are conducted on isolated individual organisms, often ignoring interactions with other species, such as their parasites," he says. "Thus, our findings are likely the tip of the iceberg for pollution-induced disease emergence in both humans and wildlife."

Leopard frogs are a species of concern in Pennsylvania because of the marked decline in their population, Carrick points out. Scientists had been unable to explain their shrinking numbers, suspecting growth in predator populations, habitat degradation or climate change. "Now we have shown that these chemicals combine to increase infections in amphibians, and this is a plausible explanation for their decline," he says.

"The scope of this research is unique," explains Carrick. "We used 72 cattle tanks to create experimental wetland environments for the frogs, and we administered 18 different chemical treatments using off-the-shelf pesticides — four replicate tanks each. They were surrogates for small ponds, and we seeded each with a food web representative of those that naturally occur in wetlands here in the mid-Atlantic region."

The study results should be an eye-opener for society, Carrick contends, because atrazine and phosphate are common, widely used ingredients in off-the-shelf pesticides and fertilizers, respectively. And phosphorus can be prevalent in animal and human waste.

"We need to be asking, are we are putting things into the environment that work together to make big ecological differences?" he says. "Chemicals in nonlethal doses may not be dangerous alone, but we could be underestimating the threat that common compounds pose when combined."

Provided by Pennsylvania State University

Explore further: Risks from extreme weather are 'significant and increasing'

add to favorites email to friend print save as pdf

Related Stories

Recommended for you

Education is key to climate adaptation

12 hours ago

Given that some climate change is already unavoidable—as just confirmed by the new IPCC report—investing in empowerment through universal education should be an essential element in climate change adaptation ...

India court slams Delhi's worsening air pollution

22 hours ago

India's environment court has slammed the government over the capital's horrendous air pollution, which it said was "getting worse" every day, and ordered a string of measures to bring it down.

User comments : 7

Adjust slider to filter visible comments by rank

Display comments: newest first

GrayMouser
2 / 5 (4) Feb 04, 2009
What is the cost of reducing phosphates and atrazine compared to killing off the nematodes and their carriers?
Soylent
5 / 5 (1) Feb 04, 2009
What is the cost of reducing phosphates and atrazine compared to killing off the nematodes and their carriers?


The cost of reducing phosphates is reduced agricultural yields where too little was applied(reducing excess application, e.g. through precision farming or runoff control may be a cost reduction).

The cost of quitting phosphates completely is the starvation of at least half of all humans alive today.
Big_Oil_Sockpuppet
2.3 / 5 (6) Feb 04, 2009
More alarmist crap. Who cares about frogs anyway?
theophys
3.7 / 5 (3) Feb 05, 2009
More alarmist crap. Who cares about frogs anyway?

I care about frogs. They are absolutely delicious and must be protected for the sake of lovers of French food worldwide.
lengould100
2.3 / 5 (3) Feb 05, 2009
What is the cost of reducing phosphates and atrazine compared to killing off the nematodes and their carriers?


The cost of reducing phosphates is reduced agricultural yields where too little was applied(reducing excess application, e.g. through precision farming or runoff control may be a cost reduction).

The cost of quitting phosphates completely is the starvation of at least half of all humans alive today.


No worries, as world reseerves of phosphate are set to run out very shortly at present rates of use...
Velanarris
3 / 5 (4) Feb 06, 2009
No worries, as world reseerves of phosphate are set to run out very shortly at present rates of use...

Ok then....

In a manipulative experiment conducted with 300-gallon tanks outdoors at Penn State's Larson Agricultural Research Center
Using the term "Manipulative experiment" probably wasn't the best.

Other than that I'm all for pollution and run off control. Run off control is really something that should be under environmental engineering and should always remain at the forefront of our thoughts when it comes to agriculture.

Even if you don't care about frogs you should probably realize that they're very necessary for controling disease carrying insect populations.
MikeB
not rated yet Feb 08, 2009
The authors of this study are hard at work on their new novel, Silent Swamp. I'm getting a little teary eyed just thinking about it.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.