New evidence is contributing to unraveling the mystery of the drastic worldwide decline in frog populations. The “plague
of frogs” may in fact be attributable to the use of popular herbicides.
Roundup killed three out of five species of frogs when the herbicide was tested in replicated wetland ecosystems (mesocosms), according to Rick Relyea of the University of Pittsburgh who published his findings in the journal Ecological Applications. The second most popular formula for eliminating unwanted vegetation in the United States, Roundup has been widely used both commercially and privately in gardens, croplands, and throughout forest communities.
Relyea created his study ecosystem from species found in northwestern Pennsylvania wetlands. Plankton, plants, and animals were collected and placed in cattle tanks. The number of each species was represented at naturally occurring densities. Animal species from a number of phyla and at different life-cycle stages were included: snails, dragonfly larva, spotted salamanders, and five species of toad and frog tadpoles. Each
mesocosm was then treated with one of four pesticides (two insecticides and two herbicides including Roundup) at the manufacturer’s recommended maximum dosages. Following a two week period each mesocosm was assessed for the impact of the
chemical. Contrary to Relyea’s expectations, the mesocosm treated with Roundup had dead frog tadpoles that were killed directly, not indirectly through the contamination of their plantlike food source, algae. Three species of frog tadpoles belonging to two different taxonomic families were eliminated while the rate of mortality was not significant for tadpoles of one frog and the one toad species included in the mesocosm.
Monsanto, the manufacturer of Roundup, challenged Relyea’s research on two counts. Firstly the company contended that the rate of chemical applied during the study was over and above the maximum recommended rate. Secondly, Monsanto objected to the use of the herbicide in a wetland environment stating that Roundup is marketed for use in terrestrial habitats. Relyea argued that the rate and concentration of chemical applied to the wetland ecosystem was realistic; this amount of herbicide had been measured in shallow wetlands following aerial applications to surrounding terrestrial areas.
Following this study, Relyea conducted similar tests using one third of the maximum concentration of Roundup. This proved lethal both to terrestrial and aquatic amphibian populations, with a lower percentage of the populations experiencing mortality (compared with the initial study).
The unanticipated consequences of human methods of environmental control will come back to “haunt us”. As a function of their highly permeable skin, amphibians are regarded as early barometers of environmental conditions. The health of our wetlands can, in part, be gauged by changes in amphibian populations. Our backyard frog is our “canary in a coal mine”. Heed the croaking!