Amphibians Under Fire

frogAll across the globe, amphibian species are in trouble. Currently, about one-third of all amphibians are either extinct or endangered due to habitat degradation and loss, disease, and exposure to chemicals used in agricultural practices. The extent of the latter had not been comprehensively quantified until now, thanks in part to researchers Nick Baker and Tiffany Garcia from the Department of Fisheries and Wildlife at Oregon State University, along with Betsy Bancroft from Southern Utah University.

Together they have conducted a meta-analysis of the effects of pesticides and fertilizers on amphibians. Their analysis, published in the journal Science of the Total Environment, shows a wide range of negative effects on amphibians. Effects include increased mortality, increased susceptibility to disease, decreased size at metamorphosis, and decreased swimming speed and endurance.

The researchers analyzed 111 studies to gauge the impacts of 16 classes of contaminants on amphibian species. They found that effects varied among chemical classes and among different amphibian species, but ultimately found significant negative impacts on survival and growth rates.

Six chemical classes were reported to have negative impacts on amphibian survival. Among these are organophosphates, triazines, and phosphonoglycines—three of the most prevalent chemicals used in the United States, with a total of 180 million pounds used each year. Organophosphates and phosphonoglycines were also found to have negative impacts on amphibian growth. The negative impacts of the application of huge volumes of these chemicals are amplified by the timing of their use. Application during the spring breeding season increases the likelihood of exposure to the chemicals during the fragile larval stage of amphibian development. Exposure to chemicals at this stage profoundly impact amphibian health and survival to adulthood.

The researchers report that small changes in chemical application may reduce negative impacts on amphibians. Precise application techniques could reduce the amount of chemicals needed, as well as the amount that runs off the land into aquatic habitats. In addition, limited application during breeding seasons could reduce the negative impacts on amphibian larvae. More research is needed on the indirect effects of chemicals on amphibians, and on chemical interactions within the environment, but it is clear that changes must be made if we want to protect amphibian species on the brink.

By Kristin Daly