Spatial evolution of an AMD stream in the Iberian Pyrite Belt: process characterization and control factors on the hydrochemistry

This paper presents hydrochemical data of an AMD stream in the Iberian Pyrite Belt, obtained from its source, in the Poderosa Mine Portal, till its confluence at the Odiel River. The main objective is to establish potential interdependent relations between sulfate and metals’ loads and the following physical-chemical variables: pH, electric conductivity (EC), redox potential (EH), and dissolved oxygen (O2). All the parameters show a global increasing tendency since the tunnel’s exit to the confluence at Odiel River. The TDS and EC are two relevant exceptions. They behave similarly, showing a decreasing trend and a strong inflection that describes a minimum immediately after the discharging point. The spatial analysis combined with statistical tools put in evidence the typical AMD processes and the respective physical-chemical implications. Inputs with distinctive hydrochemical signatures impose relevant modifications in the Poderosa creek waters. This indicates low hydrochemical inertia and high vulnerability to external stimulus.Financial support for this research was provided by DGCICYT National Plan, project CGL2010-21268-C02-01 and the Andalusian Autonomous Government Excellence Projects, Project RNM-6570

UV digestion of seawater samples prior to the determination of trace metals using flow injection with chemiluminescence detection

A purpose built UV digestion system was successfully used for the breakdown of Cu complexing organic ligands in seawater samples, prior to total dissolved Cu determination using flow injection with chemiluminescence detection (FI-CL) and on-line micro-column preconcentration/matrix removal. Residual dissolved organic carbon (DOC) was quantified using a DOC analyser. Humic acid (1.8–7.2 mg l?1 C) in ultra high purity (UHP) water was completely broken down within 4 h in all batch experiments (125 and 400 W lamps; with and without 15 mM H2O2 and, as expected, was more rapid with the 400 W lamp, in the presence of H2O2, and for lower humic acid concentrations. UV digestion experiments with seawater showed that the residual DOC concentration after batch UV treatment (4 h) was <0.08 mg l?1 C compared with >0.32 mg l?1 C after on-line irradiation (residence time 11.2 min). Therefore, the batch method was more efficient than on-line UV digestion at breaking down added humic acid and naturally present organic compounds in seawater. However, the release of Cu from metal complexing organic matter in seawater and estuarine water was the same using both on-line and batch UV digestion (sample irradiation residence time: 5.6 min and 8 h, respectively). UV digestion is, therefore, a contamination-free approach for seawater pretreatment prior to micro-column preconcentration and FI-CL determination of total dissolved Cu and should also be applicable to the selective determination of the total dissolved fractions of other trace metals in seawater (e.g. Co, Fe, Mn)

Metal behaviour in an estuary polluted by acid mine drainage: the role of particulate matter

The concentrations of dissolved and suspended particulate Cd, Cu and Zn have been determined in water samples obtained during two axial transects of the Rio Tinto-Huelva Ria system in south-west Spain, which is severely impacted by acid mine drainage. Although the metal concentrations in both phases were elevated, dissolved metals were dominant and, in the upper estuary, constituted >99% of total metal in the water column. Dissolved metals behaved non-conservatively on each transect, with maximum concentrations in the low salinity region. There was no evidence of metal adsorption within the turbidity maximum zone, despite the high specific surface areas of resuspending particles. Measurements of electrophoretic mobility showed that the suspended particulate matter (SPM) had a positive surface charge in the salinity range 0–4, where the waters had a pH<3. Desorption experiments were carried out in which SPM from the turbidity maximum zone was resuspended in coastal seawater. The desorption of the metals was monitored for 24 h, using anodic stripping voltammetry (ASV) to detect the variation in total dissolved Cd, Cu and Zn and the species of Cu and Zn. Total dissolved Cd concentrations doubled during the incubation period, whereas the concentration of total dissolved Cu declined and that of Zn remained rather constant. The ASV-labile fraction of dissolved Cu and Zn showed an initial sharp release followed by a slower uptake. However, desorption was shown to be a minor source of dissolved metals and made little contribution to the non-conservative behaviour in the low salinity zone. The results are used to predict the effects of acid mine drainage on estuarine ecology

Determination of dissolved organic nitrogen in natural waters using high temperature catalytic oxidation

Studies on nitrogen in natural waters have generally focussed on dissolved inorganic nitrogen (DIN), primarily because of relative ease of analysis and the important influence of DIN on water quality. Advances in analytical techniques now permit the systematic study of dissolved organic nitrogen (DON), and this work has shown that DON is quantitatively significant in many waters. This article describes the sampling and analytical protocols required for rapid, precise and reliable determinations of DON, involving high-temperature catalytic oxidation (HTCO), coupled to chemiluminescence detection. This approach simultaneously determines dissolved organic carbon (DOC) and total dissolved nitrogen (TDN), and DON is derived by subtraction of DIN measured by colorimetry. The DON determination is simple to perform, exhibits excellent precision (<1 for C and 1.5 for N) and is applicable to a wide range of natural waters. © 2003 Published by Elsevier B.V

Voltammetric in situ measurements of trace metals in coastal waters

Developments in instrument miniaturisation and automation have resulted in the manufacture of portable electrochemical instrumentation for continuous trace-metal measurements from the banks of estuaries and on board ships. The most recent developments in flow cells with gel-coated iridium (Ir) micro-electrode arrays have resulted in submersible in situ voltammetric probes that allow long-term trace-metal monitoring at sub-nanomolar concentrations in coastal waters. This article overviews the design and the application of field-deployable voltammetric instrumentation for trace-metal monitoring. © 2003 Published by Elsevier B.V

Influence of sorption processes by Fe oxides and algal uptake on Arsenic and Phosphate cycle in an acidic estuary (Tinto river, Spain)

Inorganic arsenic and phosphate distributions have been studied in the acidic mixing zone of the Tinto river in November 1996, June 1997, and April 1998. This mixing zone receives high inputs of As, PO3?4 and Fe in relation with acid mine drainage and run-off from phosphogypsum waste. In the early stage of mixing the dissolution of detritic Fe phases (pyrite and oxides) releases Fe and As to water. This process is counterbalanced by removal due to precipitation of Fe-oxides and Fe-organic complexes and algae fixation. In autumn, the amount of algae is negligible and a release of As, Fe and PO3?4 to the dissolved phase was observed. As a consequence, high As and PO3?4 concentrations are registered in the water (up to 43 nM for As and 330 M for PO3?4). In spring, the removal dominates in relation with high algae productivity. As a result As and PO3?4 are depleted in the dissolved phase in spring compared to autumn and high concentrations of As (up to 1530 g g?1 and 700 g g?1 in June and in April, respectively) were observed in the suspended particulate matter. In autumn dissolved As is correlated with Fe whilst in spring As behaves in a similar way as PO3?4