Cypermethrin- and Glyphosate-Based Pesticides: Synergy in Tadpoles and Antagonism in Fish.

J.C. BRODEUR; M. SANCHEZ; S. MALPEL; B. ANGLESIO; M.F. D'ANDREA; M.B. POLISERPI

Workshop; 41st Aquatic Toxicity Workshop; 2014

The herbicide glyphosate and theinsecticide cypermethrin are key pesticides of modern management in soy andcorn cultures.  Although these pesticidesare likely to co-occur in ephemeral ponds or aquatic systems supportingamphibian and fish wildlife, the toxicological interactions prevailing inmixtures of these two pesticides have been little studied.  The current study evaluated the toxicity ofequitoxic and non-equitoxic binary mixtures of glyphosate- andcypermethrin-based pesticides to the fish, Cnesterodondecemmaculatus, and to tadpoles of the commonSouth American toad, Rhinella arenarum. In the experiments with tadpoles, twodifferent combinations of commercial products were evaluated: GlyphosateAtanor® + Cipermethrin Xiper25® and Glyphosate Glifoglex®+ Cypermethrin Glextrin®.  Equitoxicand non-equitoxic mixtures were significantly synergic in both combinations ofcommercial products. The magnitude of the synergy was constant at aroundtwofold for all tested proportions of the Glyphosate Glifoglex® +Cypermethrin Glextrin® mixture, whereas the magnitude of the synergyvaried between 4 and 9 times in the Glyphosate Atanor® +Cipermethrin Xiper25® mixture. Lethal concentrations 50 (LC50) obtained in terms of toxic units (TU)for the equitoxic mixtures were 0.47 y 0.58 TU for the two combinations ofproducts tested, respectively.  For theirpart, experiments with fish were realized with mixtures of Glyphosate Glifoglex®+ Cypermethrin Glextrin® only.  In this case, both equitoxic and non-equitoxicmixtures were significantly antagonistic; the magnitude of the antagonismvarying between 1.56 and 7.36, depending on the proportions tested.  The LC50 obtained for equitoxic mixture infish was 1.52 TU.  These resultshighlight the need to include both amphibian and mixture toxicity testing inthe regulatory requirements for the registration of pesticide products.