Response of the antioxidant and detoxifying system in the anuran tadpole (Leptodactylus latrans) exposed to the organochlorine insecticide endosulfán.

BACH, N.; BAVIERA, M.; MARINO, D.J.; NATALE, G.S.; RONCO, A.E.; CARRIQUIRIBORDE, P.

Bombinhas

Congreso; XI Congresso Brasileiro de Ecotoxicologia; 2010

Sociedad Brasilera de Ecotoxicologia

The effect of the organochlorine insecticide endosulfan on the activity of EROD, GST, and CAT was assessed in tadpoles of the South-American anuran, Leptodactylus latrans. Larvae (35-38 Gosner Stages) were exposed under laboratory conditions during 48hs to 0, 10, 20 µg endosulfan L-1 and 1.5 µM β-naphthoflavone (EROD positive control) using a semi-static system (media replacement every 24hs). Treatments were run by triplicate using 15 individuals per replica. DMSO was the vehicle and the same concentration was used in all groups. Water samples were collected every 24hs after each replacement for chemical analysis (CG-EC). Livers of each organism were sampled at 8, 24, and 48hs, immediately frozen in dry ice, and kept at -80 °C until tissue homogenization and biochemical analysis. EROD (ethoxyresorufin-O-deethylase) activity was assessed following the method of Quabius et. al 2002. GST (glutathione-S-transferase) was conducted using the method of Stephensen et. al 2002. CAT (catalase) was performed using the method of Vlahogianni et. 2007. Concentration of endosulfán in the water decreased 97% during the 24hs between replacement, and isomer ratio alfa/beta shift from 1.37 to 0.60 indicating a selective uptake by the organisms. Significant mortalities respect to controls were registered only at the highest tested concentration, with values of 58% and 72% after 24 and 48hs respectively. Spontaneous rate of response was near 10% and the cause was the drowning of the organisms after metamorphosis. Metamorphic rate was not significantly affected among treatments. The EROD activity (mean ± SD) in control group was 178.4 ± 15.4 pmol min-1 mg prot-1. Though, EROD activity in positive controls showed a 2.2-fold induction respect to the non-exposed group, no significant effects were observed with endosulfan concentration or exposure time (p<0.05). The time course of the experiment significantly affected the GST activity of the tadpoles, but no statistical differences were observed with the concentration of endosulfan. The activity of CAT showed a significant induction in tadpoles exposed to the highest concentration of endosulfán (54.0 % increases) and β-naphthoflavone (42.0 %), but only after 48hs of exposure. The study showed that the studied biological responses are not good early warning signals to assess effects induced by endosulfán in Leptodactylus latrans, since only CAT was affected but at concentrations that caused lethality. On the basis of previous experiments, different responses in the studied biomarkers are expected among tadpoles of different anuran species.