Biologists have spent the last decade trying to answer a question largely ignored by mainstream agriculture: is Roundup particularly toxic to frogs?
Two Canadian studies, published in 2012, have moved scientists closer to a satisfactory answer, but a definitive result remains elusive, says a University of Ottawa biologist who specializes in fish and frogs.
“I don’t think we have the clear answer yet, but it is clear that the (frog) species makes a difference and the water (pH) makes a difference,” said Vance Trudeau, a research chair in neuroendocrinology.
“It’s really tough (to answer). Some studies are very clear that there are major impacts (on frogs). Others are showing there is less of an impact…. It really comes down to what species of frog you’re talking about…. Some frog species have different sensitivities to these toxins.”
North American scientists began to look seriously at glyphosate formulations and frogs in the early 2000s, after several lab studies showed that surfactants in the formulations are deadly to tadpoles.
For instance, Trent University biologists and Bruce Pauli, chief of ecosystem health research with the National Wildlife Research Centre in Ottawa, exposed tadpoles to Roundup Transorb, glyphosate and a surfactant added to glyphosate formulations called polyethoxylated tallowamine (POEA).
Surfactants, or detergents, are added to glyphosate formulations because they break down the waxy coating on plant leaves, which allows glyphosate to penetrate the plant tissue.
Pauli and his colleagues found that glyphosate alone wasn’t toxic to northern leopard frog tadpoles, but the surfactants caused reproductive and growth malfunctions.
“Tadpoles exposed to either POEA or Roundup Original showed tail and growth abnormalities, a decrease in successful metamorphosis and an increased percentage of intersex frogs,” biologists wrote in a 2004 paper.
Looking back at the study, Pauli said the results weren’t surprising.
“(It) confirmed what other studies had already showed. If you have glyphosate formulated product with that surfactant in it, it’s the surfactant causing the toxicity.”
Some biologists condemned Pauli’s lab experiments as unrealistic when his research and other papers were published. They claimed the laboratory exposure rates were much higher than rates found in natural settings, such as sloughs and marshes.
To address the doubts surrounding lab studies, biologists began testing glyphosate formulations in wetlands and other natural settings.
Scientists at the Long Term Experimental Wetlands Area in Gagetown, N.B., used curtains to separate a wetland into halves. One half was dosed with a glyphosate formulation and the other half was not to determine if the chemical affects frogs at the larval and tadpole stages.
Dean Thompson, a research scientist with Natural Resources Canada who collaborated with University of Guelph and University of New Brunswick researchers on several such studies in Gagetown, said the results are consistent and clear.
“That is, under typical environmental exposure scenarios of the glyphosate-based herbicide products we have studied, toxic effects on sensitive amphibian larvae or juveniles frogs are improbable.”
For example, Chris Edge, who worked with Thompson, wrote in a paper published last year in Environmental Toxicology and Chemistry that there is “little evidence that application of the glyphosate-based herbicide VisionMAX has a negative effect on L. clamitans (frog larvae) abundance or growth.”
However, Trudeau said the science isn’t quite that black and white. It depends on the species of frog, the pH of the water and the type of surfactant in the glyphosate formulation.
In a 2012 experiment that divided ponds in half, Trudeau and his colleagues concluded that Roundup Weathermax did not have major effects on tadpole numbers.
However, there was evidence of endocrine disruption, or interference with hormonal systems in the immature frogs.
Trudeau said experiments have shown that the pH of the water alters the toxicity of the surfactants. They are less toxic in neutral or acidic water, but in basic water the “toxicity goes way up,” he added.
As well, certain surfactants are more hazardous to frogs than others, but it’s difficult for scientists to test particular surfactants because glyphosate formulations are proprietary.
“We know that the Roundup (Original) surfactant is polyethoxylated tallowamine (POEA),” Pauli said.
“We don’t know, for instance, (what’s) in the Weathermax. We assume it’s a POEA, but we don’t know.”
Pauli said the science that shows surfactants are toxic to frogs at certain exposure levels means chemical companies should switch to less hazardous surfactants.
“There should be some mechanism whereby you could change the formulation a little bit to reduce the aquatic toxicity or eliminate the aquatic toxicity.”
Trudeau agreed, noting biologists need to know more about the surfactants and the ag industry should use “the one that is the least dangerous.”
Pauli said mitigating the risk of glyphosate formulations is a significant biological issue, because ponds, sloughs and ditches are the only habitat for frogs in intensive agricultural areas.