Elutriate toxicity of soil contaminated with residues from an abandoned gold mine in Marayes (San Juan, Argentina) on Daphnia magna.

LAME YANINA; ROQUEIRO GONZALO; TAPIA, RAÚL.; MONETTA PABLO; YOUNG, BRIAN JONATHAN

Buenos Aires

Congreso; Congreso SETAC; 2015

The lack of a Closure Plan in abandoned mines causes environmental pollution due to the persistence of heavy metals and changes in the landscape. Toxicity test on aquatic species allow determining the toxic potency of substances dissolved in water. The aim of this study was to assess the toxicity of water from a tributary of Bermejo River and elutriates from soil contaminated with residues from an abandoned gold mine on Daphnia magna. Nine sampling sites in the town of La Planta (Marayes) were taken in summer (march): 3 samples of water on the riverbed of a tributary of the Bermejo River (3 km upstream, La Planta height, and 3 km downstream) and 6 samples of the first 20 cm of soil: 4 sites on the contamination plume, spaced every 700 m. (Sites 1, 2, 3 and 4), and two reference sites (2 km upstream and 2 km downstream from the Site 1). Water samples and elutriates were characterized by physicochemical determinations. Acute toxicity test were carried out using D. magna, according to a standard protocol. Experimental design consisted of 7 treatments by triplicate: six concentrations of each sample in the range of 0.01 to 100% and a control group. Ten neonates were exposed to 30 mL of sampling or control water in glass vessel for 48 h under controlled conditions (photoperiod 16L:8D; 21 ± 2°C). Number of immobile neonates was registered as endpoint. The contamination plume observed in the environment was characterized by a variation in color of soil and density of vegetation. No toxicity was observed in the samples of water (pH = 8.17 ± 0.30; electrical conductivity = 6320 ± 1134 mS/cm) nor in elutriates of the reference sites (pH = 8.37 ± 0.38; electrical conductivity = 558 ± 510 mS/cm). A decrease by 68% in the toxicity was observed between Site 1 (EC50 = 0.05%; NOEC = 0.01%; LOEC = 0.08%), point with mining residues, and Site 4 (EC50 = 68.35%; NOEC = 1%; LOEC = 25%), locate to 2100 m from Site 1. Toxicity was associated with the decrease in electrical conductivity (4120 to 233 mS/cm) and concentration of heavy metals (As, Bi, Cu, Zn, Pb, Co, Mn, Fe), and the increase in pH (2.86 to 4.76) across from the contamination plume. Results suggest that the changes in these parameters were related to the soluble elements from mining residues. However, water quality was no affected by the contamination plume at this sampling time.