Toxicity of Vertimec® 18 EC (active ingredient abamectin) to the neotropical cladoceran Ceriodaphnia silvestrii

• The acute EC50-48 h for immobilization was 1.47 μg a.i./L.
• The chronic NOEC-8 d for survival and fertility were 169 and 84 ng a.i./L, respectively.
• Mesocosm water treated with Vertimec had lower toxicity than expected from laboratory bioassay toxicity data.
• Ceriodaphnia silvestrii is a suitable species for ecotoxicity testing in the tropics.

The aim of the present study was to evaluate the toxicity of abamectin to the neotropical cladoceran Ceriodaphnia silvestrii. To this end, acute and chronic bioassays were conducted with the commercial formulation Vertimec® 18 EC. In addition, the toxicity of water samples taken from a microcosm experiment evaluating the effects of a single application (144 μg a.i./L) and two applications (2 × 36 μg a.i./L) of Vertimec® 18 EC, in the presence or absence of a tadpole species (Lithobates catesbeianus), was also assessed. The acute LC50-48 h for immobilization was 1.47 μg a.i./L and chronic NOEC-8 d for survival and fertility (number of neonates per female) were 169 and 84 ng a.i./L, respectively. Irrespective of the presence of tadpoles, water samples from the microcosms applied with the single concentration of 144 μg a.i./L remained toxic until the end of the experiment, even when samples were diluted 32 times with culture medium. Water in the repeated pesticide treatment showed a similar toxic response after both applications. Toxicity of water samples from the microcosms was lower than that expected based on the generated LC50 values, which is explained by a potential reduced bioavailability of the test compound resulting from absorbance to organic material. Potential side-effects on C. silvestrii related with the use of Vertimec® 18 EC in Brazil and the suitability of this species for tropical toxicity testing are discussed.