Pieter Johnson, Center for Limnology
It seems like frogs just can't catch a break. Scientists have been warning us about the global decline in amphibian populations for years. Habitat destruction, disease and chemicals are commonly cited as causes of destruction. Then we found out that triclosan, an antibacterial ingredient in soap and toothpaste, is killing them. And if that's not enough, just a few weeks ago we found out that humans are eating our little green friends to the edge of oblivion.
The journal Nature recently reported on a study that digs a little deeper into the demise of the northern leopard frog.
Researchers from seven different U.S. universities and government organizations studied the northern leopard frog (Rana pipiens) in wetlands across Minnesota. They were looking for causes of limb malformation and population decline. The study suggests that agrochemicals, combined with parasitic infestation, was the culprit.
The study sought factors associated with the abundance of larval trematodes [parasitic flatworms] in the frogs. An abundance of these parasites can be debilitating, causing limb malformation, kidney damage and death. Of more than 240 plausible predictors of trematode infection — ranging from the presence of various plant and animal species to agrochemicals and habitat geography — two stood out: the herbicide atrazine and the fertilizer, phosphate. Atrazine and phosphate are principal agrochemicals for corn and sorghum production, and together they accounted for 74% of the variation in trematode abundance.
What the researchers found was that atrazine augmented snail numbers which act as an intermediary host of the trematodes at the same time it suppressed the frog's immunity to trematode invasion. The chemical was banned in the EU in 2004, but is still widely used in the U.S.