Evaluation of growth, biochemical and bioaccumulation parameters in Pelophylax perezi tadpoles, following an in-situ acute exposure to three different effluent ponds from a uranium mine

Mining activities invariably produce metal contaminated effluents. Depending on factors such as pH and metal concentration the toxicity of the effluent may vary. To assess the effects of three characteristically different effluent ponds from a deactivated uranium mine, with toxicologically relevant data, an in situ exposure with Pelophylax perezi tadpoles, was conducted. Tadpoles were exposed to the three effluent ponds, ranked by increasing order of metals concentrations (REF, M1, M2). Survival, growth, metal accumulation, antioxidant enzymes (catalase, glutathione peroxidase and glutathione reductase) and lipid peroxidation (LPO) were determined in tadpoles. As well, physical and chemical variables of the effluents were measured. Death percentage in the effluents was 3.17 (REF), 9.84 (M1) and 42.86% (M2) and was not coincident with metal accumulation which was highest in tadpoles exposed to M1, while metal contents in M2 tadpoles were quite similar to those recorded in REF tadpoles. However, high mortality in M2 was attributed to the extremely low pH (≈ 3.77). From the three effluents M2 tadpoles had the lowest growth and the antioxidant enzymatic activity was only affected in the case glutathione peroxidase (GPx) with significantly higher activity in M1, being in accordance with the highest accumulation of metals. LPO, usually associated with metal accumulation, had the following pattern M1. > REF. > M2. Overall, effluent toxicity in tadpoles exposed to M2 effluent seems to be primarily an effect of pH while in M1 toxicity is mainly owed to high metal concentrations. The effluent acidity seems to reduce metal accumulation probably due to damage in the integument, affecting ion uptake. The results obtained bring a better understanding of the toxicological processes that local P. perezi population is subjected to, mainly in the early life stages. Furthermore this study highlights the influence of pH in the toxicity of metal rich effluents.Authors wish to acknowledge EDM for their collaboration. Sérgio M. Marques was supported by a PhD grant (ref. SFRH/BD/38282/2007) from Fundação para a Ciência e Tecnologia (Portuguese Ministry of Science, Technology and Higher Education). This research is part of the projects Engenur (ref. PTDC/AAC-AMB/114057/2009) funded by the Portuguese Government (Program Ciência - Inovação 2010) and by the European Social Fund. This research was also partially funded by FSE and POPH funds (Programa Ciência 2007).publishe