Relyea initially conducted the experiment to see whether the Roundup® would have an indirect effect on the frogs by killing their food source, the algae. However, he found that Roundup®, although an herbicide, actually increased the amount of algae in the pond because it killed most of the frogs.
“It’s like killing all the cows in a field and seeing that the field has more grass in it–not because you made the grass grow better, but because you killed everything that eats grass,” he said.
Previous research had found that the lethal ingredient in Roundup® was not the herbicide itself, glyphosate, but rather the surfactant, or detergent, that allows the herbicide to penetrate the waxy surfaces of plants. In Roundup®, that surfactant is a chemical called polyethoxylated tallowamine. Other herbicides have less dangerous surfactants: For example, Relyea’s study found that 2,4-D had no effect on tadpoles.
“We’ve repeated the experiment, so we’re confident that this is, in fact, a repeatable result that we see,” said Relyea. “It’s fair to say that nobody would have guessed Roundup® was going to be so lethal to amphibians.”
From a UPMC press release.