Acute toxicity of pyrethroid-based insecticides in the Neotropical freshwater fish Brycon amazonicus

Pyrethroids are insecticides widely used in agriculture to control ectoparasites and biological vectors. They can reach the water bodies by leaching and or runoff. Fishes are highly sensitive to pyrethroids and the nervous system sensibility and the deficient drug metabolism are the clues but the toxicity mechanisms are yet unclear. The acute toxicity assays allow evaluating the potential, environmental risks of specific pesticides. Type II pyrethroids are becoming widely used and there is no law concerning the limits of use to this kind of pesticide in Brazil. The LC50;96h was evaluated for three pyrethroid based-insecticides (PBI): cypermethrin, deltamethrin and λ-cyhalothrin in fish Brycon amazonicus. The LC50;96h for the cypermethrin based-insecticide (CBI) was 36 μg L-1; for deltamethrin based-insecticide (DBI) was 2.6 μg L-1; and for λ-cyhalothrin (LBI) was 6.5 μg L-1. During the tests some behavioral alterations were registered just after the exposure; they were more evident at the highest xenobiotics concentrations. These alterations were indicative of asphyxia and nervous system damages. The three insecticides are highly toxics to B. amazonicus and the degree of toxicity is: deltamethrin> λ-cyhalothrin> cypermethrin. The behavioral alterations observed are worrying since long-term exposure to sublethal concentrations can affect survival and reproductive ratios.