Growth and survival of five amphibian species exposed to combinations of pesticides.

The global decline of amphibians has sparked interest in the role that pesticides may play. Pesticides in nature typically exist in combinations, but given the vast number of chemicals used, most toxicological experiments necessarily have examined one pesticide at a time. I examined how four commercial formulations of pesticides (diazinon, carbaryl, malathion, and glyphosate) affected the survival and growth of five larval amphibian species (Rana pipiens, R. clamitans, R. catesbeiana, Bufo americanus, and Hyla versicolor) when alone (at 1 or 2 mg/L of active ingredient) and in pairwise combinations (1 mg/L of each pesticide). At 1 mg/L, the pesticides reduced survival in 5% of the 20 species-pesticide comparisons and reduced growth in 35% of the comparisons. At 2 mg/L, the pesticides had more widespread effects, reducing survival in 35% of the 20 species-pesticide comparisons and reducing growth in 70% of comparisons. Combined pesticides occasionally caused lower survival and growth than either pesticide alone, but the effects were never larger than the more deadly of the two pesticides alone at 2 mg/L. This suggests that the impact of combining these four pesticides is similar to that predicted by the total concentration of pesticides in the system.