Evaluación de la Toxicidad del Biodiésel en renacuajos de Rana Toro Lithobates catesbeianus (Shaw, 1802)

Abstract

Fossil fuels like diesel generate pollution; therefore the use of alternative fuels, such as biodiesel and their mixtures, which are considered less toxic, is being promoted. Bull frog L. catesbeianus (Shaw, 1802) is considered a sensitive bioindicator for aquatic pollution in its early life stages. The objective of this work was to evaluate and compare the toxicity of diesel, biodiesel (B100) and a mixture (B20), in tadpoles of this species. Two tests were performed (acute and sublethal) using the soluble fraction of the three fuels. Both bioassays included a 96 h exposure period and a month recovery lapse. Fifty percent of the exposure solution was renewed every 48 h. The concentrations used in the acute toxicity test were: 0.00, 0.06, 0.12, 0.25, 0.50 and 1.00 % for each fuel, (with three replies). Two hundred and forty animals (five per chamber) were used and mortality was recorded. Mortality at 96 h did not reach 50%, however, an LC50-96h of 2.85% resulted with the diesel soluble fraction; and a LC1-96h of 2.273%. This allowed the selection of 0.06 and 0.12% concentrations for the sublethal toxicity tests; 246 organisms (12 per camera) were included. Metabolic stress (oxygen consumption and nitrogen excretion) and oxidative stress (catalase activity) were analyzed on days one, two, four (exposure period), 15 and 30 (recovery phase). On days two and 15, fuels increased nitrogenous excretion and decreased the O:N ratio, reflecting important metabolic stress. However, on day 15 only animals exposed to 0.06% diesel and 0.06% blend showed high nitrogenous excretion and metabolic stress, although less than on day two. Oxidative stress was detected in the 0.12% soluble fraction of diesel and blend the day four, on the day 30 the effect was observed in all concentrations, except in biodiesel at 0.06% concentration. In conclusion, while biodiesel and the blend were less toxic than diesel, the damage persisted in both tests through the recovery period. Therefore, it is suggested to carry out immediate and medium-term evaluations in case of a spill.