Determinação da toxicidade aguda de atrazina em pós-larva de tilápia-do-nilo.

Resumo: A atrazina e um herbicida amplamente utilizado nas culturas agricolas. Por ser classificado como bioacumulativo e nao biodegradavel e frequentemente encontrado no meio aquatico, podendo ocasionar toxicidade aos peixes. O presente estudo teve como objetivo determinar a CL50, em 96 horas, da atrazina em pos-larva de tilapia-do-nilo Oreochromis niloticus, assim como avaliar a influencia de diferentes concentracoes deste herbicida no crescimento dos animais e nos parâmetros de qualidade da agua. Foram utilizadas 147 pos-larvas de tilapia com peso medio inicial de 8,5±1,0 mg, aclimatadas por 48 horas, com cada aquario teste contendo sete pos-larvas, mantidas em jejum durante o experimento. Os parâmetros de qualidade de agua (pH, oxigenio dissolvido, temperatura, condutividade, dureza e amonia total) foram medidos diariamente. As pos-larvas foram submetidas as seguintes concentracoes de atrazina 2, 4, 8, 16 e 32 mg L-1,alem de um tratamento controle (sem atrazina) e outro controle com acetona, que foi utilizado para auxiliar a dissolver a atrazina. Analises biometricas foram realizadas no inicio e ao fim do experimento. A concentracao letal media (CL50) em 96 horas da atrazina para tilapia foi de 17,87 mg L-1. Foram constatadas diferencas significativas (p<0,05) para peso e crescimento final, pH e oxigenio dissolvido que foram responsivos ao aumento da concentracao de atrazina e estao relacionados com os efeitos toxicos deste herbicida para as pos-larvas de tilapia. ? Abstract: Atrazine is an herbicide widely used in agricultural crops. Because it is classified as bioaccumulative and not biodegradable it is often found in the aquatic environment and may cause toxicity to fish. The objective of the present study was to determine the LC50 in 96 hours of the atrazine in Nile tilapia Oreochromis niloticus post-larvae, as well as to evaluate the influence of different concentrations of this herbicide on the fish growth and the water quality parameters. A total of 147 post-larvae of tilapia with initial mean weight of 8.5 ± 1.0 mg, acclimated for 48 hours, with each aquarium test containing seven post-larvae, were fasted during the experiment. The water quality parameters (pH, dissolved oxygen, temperature, conductivity, hardness and total ammonia) were measured daily. The post-larvae were submitted to the following concentrations of atrazine 2, 4, 8, 16 and 32 mg L-1, in addition to a control treatment (without atrazine) and another with acetone, which was used to help dissolve the atrazine. Biometric analyzes were performed at the beginning and at the end of the experiment. The 96-hour median lethal concentration (LC50) of atrazine for tilapia was 17.87 mg L-1. There were significant differences (p < 0.05) for weight and final growth, pH and dissolved oxygen that were responsive to the increase of atrazine concentration and are related to the toxic effects of these herbicides to the post-larvae of tilapia.