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Mixture of Corn Pesticides Harms Frogs

by aseligmann — last modified Jul 13, 2010 12:00 AM
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Tyrone Hayes an amphibian biologist at the University of California, jolted the pesticide industry when he demonstrated that tiny amounts of the widely used herbicide atrazine cause tadpoles' sexual development to go awry. Now he and his research team have published another important finding: a mixture of pesticides often used when growing corn in the Midwest causes more problems for frogs, again at stunningly low concentrations.

Tyrone Hayes an amphibian biologist at the University of California, jolted the pesticide industry when he demonstrated that tiny amounts of the widely used herbicide atrazine cause tadpoles' sexual development to go awry. Now he and his research team have published another important finding: a mixture of pesticides often used when growing corn in the Midwest causes more problems for frogs, again at stunningly low concentrations.

Hayes's team exposed leopard frog tadpoles to a mixture of the four herbicides, two fungicides, and three insecticides that were used to grow corn on a typical Nebraska farm. The concentration of each herbicide was 0.1 parts per billion, a concentration the researchers describe as "ecologically relevant." [i.e. Water collected from Nebraska farmland had previously been tested for contamination. Each herbicide was detected in the water at this tiny amount.] The experiment showed that the mixture of pesticides caused a range of problems. Almost two-thirds of the pesticide-exposed tadpoles died before becoming frogs. They took longer to reach the transition from tadpole to frog, and they were smaller when they became frogs.

In addition, the researchers determined pesticide exposure damaged the immune system of the frogs. Over two-thirds of the frogs raised in pesticide-contaminated water suffered from a bacterial disease. Hayes and his team then looked at the thymus, an organ that is an important part of the immune system, in the pesticide-exposed frogs. They found that more than a quarter of these frogs had a damaged thymus, an injury that did not occur in unexposed frogs.

Biologists around the world have noticed that "amphibian populations are declining globally at an alarming rate." It seems likely that there are many causes of this decline, but Hayes suggests that pesticide mixtures may need to be added to the list: "Estimating ecological risk and the impact of pesticides on amphibians using studies that examine single pesticides at high concentrations, only, may lead to gross underestimations of the role of pesticides in amphibian declines."

Reference: Hayes, T.R. et al. 2006. Pesticide mixtures, endocrine disruption, and amphibian declines: Are we underestimating the impact? Environ. Health Perspect. 114(Suppl 1):40-50.
http://www.ehponline.org/docs/2006/8051/abstract.html

 


This article was originally published as:

Cox, C. 2006. A mixture of corn pesticides harms frogs. Journal of Pesticide Reform 26(1):4