Acute and Chronic Effects on Tadpoles ( Lithobates catesbeianus ) Exposed to Mining Tailings from the Dam Rupture in Mariana, MG (Brazil)

The mining sector has great importance to the economic activity in Brazil. However, it is also responsible for several environmental impacts such as the rupture of the Fundao dam (Mariana, Brazil) that resulted in the spillage of 50 million m3 of mining tailings in the Doce River Basin. This study evaluated the acute and chronic effects of Fundao tailings on growth, development, respiration rates, swimming performance, and avoidance behavior of Lithobates catesbeianus tadpoles. Results showed that 96-h exposure to different dilutions (10, 25, 50, 75, and 100%) of a stock solution containing mining tailings (50 g/L) caused no mortality of tadpoles; however, the most concentrated solution decreased the swimming speed of the animals. After 16 days, tadpoles exposed to 25, 50, and 100% treatments had both swimming speed and distance traveled reduced. Oxygen consumption was also decreased in tadpoles exposed to the 100% solution after 20 days. Avoidance test indicated that tadpoles avoided lower tailing concentrations, but a reduced avoidance response was attested to the higher concentrations, probably due to the toxic effects of the residues that prevented animals’ displacement. Chemical analysis confirmed the occurrence of cadmium (Cd), lead (Pb), iron (Fe), manganese (Mn), zinc (Zn), and aluminum (Al) in Fundao tailings and its presence in the mouth and inside the intestine of treated tadpoles indicated the ingestion of metals by these organisms. This study showed that even presenting low lethal toxicity, long-term exposure to mining tailings from Fundao dam caused morphophysiological and behavioral damage in tadpoles.