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Atrazine and Frogs

by aseligmann — last modified Jul 05, 2010 12:00 AM
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Atrazine, the number two agricultural herbicide in America, may be a major player in the decline of the northern leopard frog, according to research recently published in the journal Nature.

Atrazine, the number two agricultural herbicide in America, may be a major player in the decline of the northern leopard frog, according to research recently published in the journal Nature.

In Minnesota wetlands, northern leopard frogs are suffering from debilitating infections caused by parasitic flatworms called trematodes. A survey of wetland ponds found that atrazine contamination was the best predictor of trematode infections. Atrazine outranked 240 other environmental factors that were evaluated. When atrazine and phosphate (from fertilizers) were found together in pond water, there was an greater abundance of trematodes.

Researchers conducted follow-up experiments in huge tanks that recreated wetland pond environments, with some tanks containing atrazine at levels that mimicked the low levels expected in the environment. Study results showed that atrazine increased the abundance of trematode infections in tadpoles in two ways.

First, atrazine had a direct toxic effect by suppressing two types of immune responses in the tadpoles. These, immune responses are important in fighting trematode infections.

Second, atrazine led to an increase in the number of snails, which are the source, or intermediate host, of trematodes that affect frogs. The increase in the snail population was due to atrazine reducing one type of algae that floats on the pond surface. That reduction increases sunlight and nutrients for a different type of algae that grows lower down. The expanded growth of the second type of algae, which is a food source for snails, fuels growth of snail populations that host trematodes. The population growth results in greater exposure of tadpoles to trematodes. In the model wetlands, test tanks treated with a single dose of atrazine, ended up with four times as many snails as untreated tanks.

The lead author of the study, Jason Rohr, emphasized that studies identifying underlying drivers of infection could be used in efforts to improve survival of declining frogs or amphibian populations worldwide. In the case of the northern leopard, trematode infections in northern leopard frogs could be reduced by reducing the use of atrazine and phosphate in areas where these frogs live - especially near heavily treated Midwest corn and soybean fields.

Rohr also noted that EPA's pesticide registration process requires tests that examine only one organism at a time. These tests will never uncover problems exemplified by the atrazine-trematode link involving interactions between multiple organisms.

 


SOURCE

Agrochemicals increase trematode infections in a declining amphibian species.
Jason R. Rohr. October 30 2008. Nature vol.455 no.7217 pp.1235-1239.
Abstract available at: http://www.nature.com/nature/journal/v455/n7217/full/nature07281.html

NEWS STORY

Farm chemicals can indirectly hammer frogs
Janet Raloff. November 22 2008. Science News vol.174 no.11 p. 12.
http://www.sciencenews.org/view/generic/id/38161/title/Farm_chemicals_can_indirectly_hammer_frogs_