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The Tinto River estuary is highly polluted with the acid lixiviates from old sulphide mines. In this work the behaviour of dissolved and particulate trace metals under strong chemical gradients during a tidal cycle is studied. The pH values range from 4.4 with low tide to 6.9 with high tide. Precipitation of Fe and Al is intense during rising tides and As and Pb are almost exclusively found in the particulate matter (PM). Sorption processes are very important in controlling the mobility (and hence bioavailability) of some metals and particularly affect Cu below pH 6. Above pH ~ 6 Cu is desorbed, probably by the formation of Cu(I)–chloride complexes. Although less pronounced than Cu, also Zn desorption above pH 6.5 seems to occur. Mn and Co are affected by sorption processes at pH higher than ca. 6. Cd behaves conservatively and Ni is slightly affected by sorption processes. [ABSTRACT FROM AUTHOR]

The Tinto and Odiel rivers in southwest Spain drain the world's largest sulfide mineral formation: the Iberian Pyrite Belt which has been worked since 2,500 BC. The Tinto and Odiel estuarine zones include both an extensive area of salt marsh and an intensively industrialized urban area. As a consequence of pyrite oxidation, the Tinto and Odiel rivers are strongly acidic (pH < 3) with unusually high and quite variable metal concentrations. In this study, seasonally varying concentrations of dissolved major and trace elements were determined in the acid mine drainage affected estuary of the Ría de Huelva. During estuarine mixing, ore-derived metal concentrations exhibit excellent correlations with pH as the main controlling parameter. As pH increases, concentrations of dissolved ore-associated elements are attenuated, and this process is enhanced during the summer months. The decrease in Fe and Al concentrations ranged from 80 to 100 % as these elements are converted from dissolved to sediment-associated forms in the estuary. Coprecipitation/adsorption processes also removed between 60 and 90 % of the originally dissolved Co, Cu, Mn, Pb, Zn, and Th; however, Cd and Ni exhibited a greater propensity to remain in solution, with an average removal of approximately 60 %. On the other hand, As and U exhibited a different behavior; it is likely that these elements remain in dissolved forms because of the formation of U carbonates and soluble As species. Concentrations of As remain at elevated levels in the outer estuary (average = 48 μg L) which exceeds concentrations present in the Tinto River. Nevertheless, the estuary has recently witnessed improvements in water quality, as compared to results of several previous studies reported in the 1990s. [ABSTRACT FROM AUTHOR]

Abstract: The Tinto River shows very high concentrations of toxic elements and acidity from its source in the mining area to its mouth. In this paper, we studied the evolution of the levels of toxic elements during part of the Quaternary from the analysis of fluvial deposits that, forming terraces, were originated by the dynamics of the Tinto River. Using a detailed geomorphological cartography, up to nine terrace levels were differentiated in the lower sector of the basin, whose ages range from the Pleistocene to the Holocene. Sampling and geochemical analyses (major elements and trace) were carried out in six of these levels, in addition to sediments of the current flood plain. The results of these analyses do not show any bias from the mid Pleistocene (T8 — Terrace 8) to the early Holocene (T1). Moreover, these geochemical contents are similar to the average values obtained by other authors for the entire South-Portuguese Zone of the Iberian Massif. However, the current sediments of the Tinto River (T0) show a sharp increase in the levels of As, Cu, Pb and Zn compared to the rest, which indicates a serious increment of contamination by toxic elements. Although there are evidences on the existence of a natural process of oxidation of sulfides since the Miocene, the amounts of toxic elements released should be very small compared to those generated since the beginning of the mining activities in the Iberian Pyrite Belt. [Copyright &y& Elsevier]

Abstract: This work deals with the wash-out processes of evaporitic salts in the Tinto river in October 2005, with the arrival of the first rainfall after the summer. In order to monitor water levels and electrical conductivity, a datalogger was set up in the river, while sampling was performed by a portable autosampler. Thirty-two samples were selected for analysis for a wide range of elements by ICP-AES. Three different flood events, with a maximum discharge of 8.1m3/s, were monitored. River waters suffered from a dilution effect at the beginning of the first event, recording a concentration decrease of most elements, just before the wash-out of soluble salts precipitated during the summer took place. Wash-out processes provoked a sharp increase in most element concentrations coinciding with an intense decrease in Na and Sr. After the first event, there was strong enrichment of As, and to a lesser extent in Fe, Cr and Pb, due probably to the redissolution/transformation of Fe oxyhydroxysulfates. During the third event, evaporitic sulfate salts were depleted from riverbanks ending wash-out processes, and a decrease in most element concentrations was observed. Barium exhibited different behaviour to the rest of elements owing to the solubility control exerted by barite. Lead also showed a different pattern throughout the study period, its concentration decreasing due probably to its great affinity for coprecipitate on jarosite-group minerals, and increasing when schwertmannite precipitation is thermodynamically favoured. In October 2005, the Tinto river carried around 8100t SO4, 1300t Fe, 400t Al, 100t Zn and Cu, etc., highlighting the importance of wash-out processes of soluble salts in the Ría de Huelva ecosystem and metal fluxes into the Atlantic Ocean. [Copyright &y& Elsevier]

Abstract: The Tinto River estuary is one of the most contaminated coastal systems in the world due to the high amounts of pollutants this acidic river transports. The tidal influence and the fluvial discharges control the water mixing, which include a salt-induced process (that is typical of all estuaries) and an acid neutralization process (pH-induced mixing). These processes affect the geochemical behavior of uranium, which has a non-conservative pattern. Despite the high concentrations of dissolved uranium in the Tinto River, 234U/238U shows that uranium stems mostly from seawater (between 80 and 100%). Riverine uranium is adsorbed onto both Fe and Al precipitates when the acidic river water is mixed with seawater. Distribution coefficients (Kd) show that dissolved and particulate uranium are controlled by adsorption–desorption processes and the formation of carbonate complexes, both depending on pH. At low pH, uranium tends to be dissolved, and the adsorption by suspended particles is low. As the pH increases, the adsorption processes onto Fe and Al particles are more intense, increasing particulate uranium which reaches a maximum at pH 5.5, where the uranium solubility minimum occurs. At higher pH values, dissolved uranium increases by carbonate complexation. [Copyright &y& Elsevier]

Summary: The aim of this work is to study the hydrochemical variations during flood events in the Río Tinto, SW Spain. Three separate rainfall/flood events were monitored in October 2004 following the dry season. In general, concentrations markedly increased following the first event (Fe from 99 to 1130mg/L; Q max =0.78m3/s) while dissolved loads peaked in the second event (Fe=7.5kg/s, Cu=0.83kg/s, Zn=0.82kg/s; Q max =77m3/s) and discharge in the third event (Q max =127m3/s). This pattern reflects a progressive depletion of metals and sulphate stored in the dry summer as soluble evaporitic salt minerals and concentrated pore fluids, with dilution by freshwater becoming increasingly dominant as the month progressed. Variations in relative concentrations were attributed to oxyhydroxysulphate Fe precipitation, to relative changes in the sources of acid mine drainage (e.g. salt minerals, mine tunnels, spoil heaps etc.) and to differences in the rainfall distributions along the catchment. The contaminant load carried by the river during October 2004 was enormous, totalling some 770t of Fe, 420 t of Al, 100t of Cu, 100t of Zn and 71t of Mn. This represents the largest recorded example of this flush-out process in an acid mine drainage setting. Approximately 1000 times more water and 140–8200 times more dissolved elements were carried by the river during October 2004 than during the dry, low-flow conditions of September 2004, highlighting the key role of flood events in the annual pollutant transport budget of semi-arid and arid systems and the need to monitor these events in detail in order to accurately quantify pollutant transport. [Copyright &y& Elsevier]