Amphibian Roundup Herbicide Kills More Than Weeds
Frog Species are Rapidly Dying Off
DEBORAH K. RICH / San Francisco Chronicle 23jul2005
adult wood frog
On a walk this past wet spring, I lifted a chunk of rotting log, hoping to uncover a termite or beetle for my 2-year-old son, who crouched expectantly alongside me. I started when my eyes met those of a large pink salamander. I don't know what kind it was, but it stared at me so steadfastly, and its moist, translucent skin so contrasted with the flashes of feathers and fur and with the waxy needles and ragged bark around us, that my perception of the whole forest shifted. I walked slowly and carefully when we moved on, as a guest in a friend's church does. My son reached up to hold my hand.
I should have stared at the salamander longer. Evidence is mounting that human activities have accelerated the speed of species extinction. We're losing 3,000 species a year now, and may lose tens of thousands a year in the near future. If the predictions prove true, half of earth's species may face extinction over the next hundred years.
Amphibians are becoming extinct at a faster rate than birds or animals. The World Conservation Union lists 427 amphibian species on the brink of extinction and suggests that this figure is on the low side because 1,294 amphibian species are too poorly known to assess. The Union calls the unassessed species "data deficient."
The decline of at least half of the amphibians can be attributed directly to over-harvesting and habitat loss. But the other half is rushing toward the brink for unknown reasons. The Union calls their pending extinction "enigmatic decline."
"Enigmatic-decline species have never previously been recorded at a level comparable to that currently observed in amphibians," reported the World Conservation Union in 2004.
I hope the pink enigma that my son and I saw isn't on the brink list. Its patch of urban forest is just three blocks long and ringed by a school, a nicely landscaped shopping center and a uniform cleaning shop. Close quarters.
Rick Relyea's study, published earlier this year in Ecological Applications and highlighting the toxicity of Roundup Weed and Grass Killer to amphibians, serves to remind us that the chemicals we use at home and in commercial agriculture often have unforeseen effects on amphibians.
Pesticides and Amphibians: The Importance of Community Context - Relyea et al / Ecological Applications 1jul2005
Relyea, assistant professor of aquatic ecology, toxicology, evolution and behavior at the University of Pittsburgh, evaluated the effects on algae and aquatic organisms in near-natural settings of four common pesticides: two insecticides, Sevin and malathion, and two herbicides, Monsanto's Roundup and 2,4-D. To simulate pond ecosystems, Relyea filled 30 polyethylene tanks with 1, 000 liters of water each, then added zooplankton and phytoplankton from local ponds. A few days later, he began adding the macro-organisms of pond ecosystems: tadpoles, snails, damselflies, hemipterans (an order of insects that undergo incomplete metamorphosis), dragonflies, beetles and spotted salamander larvae, all in densities that reflect those found in nature. Finally, he added the pesticides to his ponds in amounts that simulated those that might be present after an aerial overspray.
Not unexpectedly, Relyea found that the insecticides reduced the diversity and number of insects. Interestingly, he found that very low doses of the insecticides increased the survival of tadpoles, probably because of the high mortality of the dragonflies, beetles and hemipterans, all tadpole predators. Perhaps most surprisingly, Relyea discovered that Roundup, designed to kill plants, exterminated two frog species, and nearly exterminated a third, reducing tadpole "richness" by 70 percent. Many of the deaths occurred in the first 24 hours after the addition of the Roundup.
Relyea found the same results using Roundup in subsequent tests. "Collectively, the available data indicate that, contrary to conventional wisdom, current application rates of Roundup can be highly lethal to many species of amphibians," writes Relyea in his paper "The Impact of Insecticides and Herbicides on the Biodiversity and Productivity of Aquatic Communities." The federal National Science Foundation funded Relyea's research.
Relyea's review of the literature on Roundup toxicity suggests that it is the surfactant, the carrier chemical in Roundup, rather than the herbicide's "active" chemical, glyphosate, that caused the high mortality rates he observed. "The surfactant system enables the products to adhere to the surface of leaves so the active ingredient can penetrate," says Monsanto in its "History of Monsanto's Glyphosate Herbicides." Surfactants fall under "inactive ingredients" on pesticide labels, and the EPA generally does not test their toxicity.
Monsanto acknowledges the toxicity of the surfactant used in its Roundup brand herbicides to aquatic animals and says that is why Roundup formulations are not registered for direct water applications. When Roundup does enter water, Monsanto believes that the risk to aquatic organisms is minimal because of studies indicating that the surfactant dissipates rapidly once in water.
Relyea grants that Roundup herbicides are intended for terrestrial use but cites multiple studies by independent researchers of the presence of Roundup in aquatic habitats, primarily because of "inadvertent (or unavoidable) aerial overspray." Although pesticide applicators may take care to avoid large bodies of water when spraying fields and clear-cut forest swaths, it is often the small temporary pools of water, only 6 inches or so deep and easily overlooked, that are most important for amphibian populations. Temporary basins of water don't support fish (predators of tadpole and larvae) and so offer amphibian offspring a better chance of survival than do permanent bodies of water. Even when not directly sprayed, surface waters large and small are frequently contaminated by pesticides carried in irrigation runoff.
This news about Roundup and amphibians is a mix of bad and good. Bad because Roundup herbicides have become ubiquitous now that Monsanto has genetically modified corn, soybeans, cotton and canola to be "Roundup Ready" — able to withstand applications of glyphosate herbicides while the weeds around them wither.
"Roundup agricultural herbicides remain the world's No. 1 selling herbicides. Monsanto intends to maintain its market leadership and brand position for Roundup agricultural herbicides," says Monsanto in its 2004 Annual Report.
The good half of the news lies in the fact that Roundup herbicides are convenience items -- we knew how to farm and garden before Roundup's release in 1974 -- and the decision of whether to use them remains ours.
Despite its formidable powers of persuasion, Monsanto can't force farmers to plant Roundup Ready crops, nor to apply its companion glyphosate herbicide. The 85 million to 90 million pounds of glyphosate used by U.S. farmers in 2001 was a matter of choice. (The EPA tracks pesticide use by pounds of active ingredient, rather than pounds of final product containing both active and inactive ingredients.)
Neither can Monsanto reach out and toss a gallon jug of Roundup into my cart as I roll it down the aisle at the hardware store. Yet, of the 12.3 million pounds or so of glyphosate purchased in California in 2003, about 6 million pounds, or roughly half, were probably used by you or me or our neighbors.
Those of us who haven't bet the farm on Roundup can stop using it tomorrow. We could do it without scheduling a single EPA hearing or review, without enacting any legislation and without risking the unknown effects of the new and improved Roundup formulations that are sure to emerge on the heels of Relyea's studies.
How many amphibians will we save? I don't know. But it only took one to put me in my place when I was out walking with my son.