ALBERT

Description: 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. © 2002 Elsevier Science Ltd. All rights reserved.

Description: This work presents the optimisation, validation and field deployment of a voltammetric in situ profiling (VIP) system for the simultaneous determinations of dynamic Cd(II), Cu(II) and Pb(II) in estuarine and coastal waters. Systematic studies in NaNO3 (as a supporting electrolyte) and seawater, indicated that variations in ionic strength, pH and dissolved oxygen did not affect the response of the instrument, whereas an Arrhenius type temperature response was observed. The VIP instrument allows the determination of 2-3 samples h-1, and has a detection limit (defined as 3σ) in seawater for Cd(II): 23 pM, Cu(II): 1.13 nM, and Pb(II): 23 pM. The VIP system accurately measured the total dissolved concentrations of Cd(II), Cu(II) and Pb(II) in two certified reference materials; SLRS-3, a river water, and SLEW-2, an estuarine water. Field evaluation of the instrumentation and analytical methods was achieved through a series of surveys in the Plym Estuary (Devon, UK), from which environmental data are presented.

Description: Cathodic stripping voltammetry (CSV) is an analytical technique used for the analysis of low levels of analytes (principally trace metals and sulfur containing organic compounds) in aqueous solutions, and is based on the measurement of a reductive current response as a function of a potential scan towards more negative potentials. The technique is highly sensitive (limits of detection of 10− 10–10− 12 mol l− 1) because of the application of a preconcentrations step prior to the stripping step. During the preconcentration the analyte is collected on the surface of the working electrode (typically a mercury drop), often in the presence of an added electro-active ligand. The CSV technique has been used for automated measurements of trace metals in marine waters, but a key strength of CSV is in its use in trace metal speciation measurements in natural waters, in particular dissolved iron in marine waters.

Description: This paper presents the results of an inter-comparison exercise undertaken to test the reliability and performance of a voltammetric in situ profiling system (VIP system) and carried out by partners based in Italy, Sweden, Switzerland and the UK. The VIP system was designed to allow in situ simultaneous monitoring of the dynamic fractions (i.e. the maximum potentially bioavailable fractions) of Cu(II), Pb(II) and Cd(II) in natural waters at a frequency of 2-3 analyses h - 1. The four participating groups used the VIP systems under laboratory conditions to determine dissolved concentrations of Cu, Pb and Cd in river, estuarine and coastal water reference materials (SLRS-3/4, SLEW-2/3 and CASS3/4, respectively). The accuracy of the VIP method was comparable to that of established methodologies, including inductively coupled plasma mass spectrometry and voltammetric methods using mercury-electrodes. The VIP systems were also applied to determine the dynamic fractions of the target analytes in freshly collected samples ex situ, as well as in situ in contrasting European marine waters. There was good agreement between the concentrations of the dynamic metal fractions determined in laboratory analyses, and observed during the simultaneous deployment of up to five VIP instruments for periods of several hours in coastal waters. The simultaneous in situ deployment of two VIP instruments in an estuary showed a consistent analytical performance over several days of continuous operation. The results of this inter-comparison exercise show that the VIP system is a reliable submersible probe for accurate, sensitive and high resolution in situ monitoring of dissolved metal fractions in the picomolar (Cd, Pb) and nanomolar (Cu) concentration ranges. © 2009 Elsevier B.V. All rights reserved.

Description: Four surveys of the Huelva Estuary in southwest Spain and its sources, the Tinto and the Odiel Rivers, were carried out between 1996 and 1998. The surveys investigated the impact of metalliferous mining of sulfide-rich ores in the catchment area on metal speciation, metal concentrations in a macrophyte, and phytoplankton diversity and abundance. Chemical speciation measurements in the lower Tinto Estuary showed that metals were predominantly electrochemically labile (>99 of total dissolved Cu, Co, and Ni at 10 μM Cu, 424 nM Co, and 500 nM Ni, S = 28). Concentrations of Cu complexing ligands and free cupric ions Cu2+ in the Gulf of Cádiz ranged between 5.3 and 38 nM and 0.2-7.9 pM, respectively, with conditional stability constants of the ligands of log K′CuL = 11.7-12.6. At enhanced dissolved Cu concentrations in the lower Huelva Estuary, Cu complexing ligands were saturated with Cu, resulting in nanomolar Cu2+, which increased upstream. Metal tissue concentrations of the macrophyte Blindingia marginata were high, and a clear relationship between dissolved labile Cu and macrophyte tissue Cu concentrations was observed. A low biodiversity was observed in the Huelva system (Shannon-Wiener indices (H) typically 〈0.2). Nevertheless, the maximum biomass was observed in the lower Tinto Estuary, which showed high labile metal and nutrient concentrations and a low biodiversity (H 〈 0.02), thereby suggesting adaptation through evolutionary processes of the phytoplankton community to the harsh conditions. © 2007 American Chemical Society.

Description: Nutrient (nitrate, phosphate, silica) and dissolved metal (Al, Cu, As, Cd, Ni, Zn, Fe, U) distributions were studied in the mixing zones of the Tinto and Odiel rivers which drain the South Iberian pyrite belt. Phosphate distribution is strongly influenced by discharges from the fertiliser industry, especially in the Tinto mixing zone. The increase of silica content in this zone is related to a release of biogenic silica from diatoms. Nitrate concentrations which are influenced by urban and industrial effluents showed an important maximum in the early stages of mixing in the Tinto (as do the metals). Compared to the Odiel river, the metal concentrations in the Tinto river reached higher values in relation to more intensive mining activities. Dissolved Fe, Mn, Al, Cu, Cd and Zn concentrations were correlated in the mixing zones of both rivers. This suggests that they have the same source and are subjected to the same controlling processes in the estuary. A maximum concentration for these metals was observed in the early stage of mixing in the Tinto and reflects a decrease of redox in a low pH (〈3) environment. Downstream in the Odiel system, metals showed a slight removal. Dissolved uranium, present at a low level (0.05 μmol l-1) in the rivers, is introduced by the phosphate fertiliser industry in the estuary and trapped in sedimentation areas. As a consequence, waters of the Gulf of Cadiz have a U content similar to that of the open seawater. Copyright (C) 1999 Elsevier Science B.V. All rights reserved.

Description: The Rio Tinto and Rio Odiel drain the Iberian Pyrite Belt, an important metal-rich sulphide deposit. The rivers are highly acidic (pH 2.2-3.6) and have milli-molar SO4 and Fe concentrations and micro-molar Co, Cu, Mn and Zn concentrations. Observed dissolved metal levels were at a maximum during autumn and early winter surveys (e.g. Rio Tinto: 460-856 μM Cu), and lower in late winter, spring and summer (121-175 μM Cu). This variability is attributed to the production of concentrated acid mine drainage (AMD) during periods of enhanced microbial activity at higher temperatures in summer, and a subsequent run-off of the AMD into the rivers with the first rain in the autumn. Lower temperatures and dilution by winter floods resulted in a reduction of river metal concentration towards the end of the wet season. Metal distributions in the estuarine mixing zones of the Tinto and Odiel were governed by the acidity. The lack of metal transfer from the dissolved to the particulate phase in the low salinity region is attributed to the electrostatic repulsion between the metal cations and positive charges on particle surfaces, and/or to the protonation of adsorption sites at low pH. Dissolved Pb was an exception and showed marked removal in the low salinity zone at low pH (pH 2.5), due to its particle reactive nature. The gross metal fluxes from the Rio Tinto and Rio Odiel are important on a global scale, for example amounting to 8.1 and 1.6 of the estimated global riverine dissolved Zn and Cu fluxes. The fluxes of metals from the estuary contribute to enhanced dissolved metal concentrations observed in the Gulf of Cadiz. © 2003 Elsevier Ltd. All rights reserved.

Description: In recent environmental legislation, such as the Water Framework Directive in the European Union (WFD, 2000/60/EC), the importance of metal speciation and biological availability is acknowledged, although analytical challenges remain. In this study, the Voltammetric In situ Profiler (VIP) was used for high temporal resolution in situ metal speciation measurements in estuarine waters. This instrument simultaneously determines Cd, Cu and Pb species within a size range (ca〈4. nm) that is highly relevant for uptake by organisms. The colloidal metal fraction can be quantified through a combination of VIP measurements and analyses of total dissolved metal concentrations.VIP systems were deployed over tidal cycles in a seasonal study of metal speciation in the Fal Estuary, southwest England. Total dissolved concentrations were 4.97-315. nM Cu, 0.13-8.53. nM Cd and 0.35-5.75. nM Pb. High proportions of Pb (77 ± 17) and Cu (60 ± 25) were present as colloids, which constituted a less important fraction for Cd (37 ± 30). The study elucidated variations in the potentially toxic metal fraction related to river flow, complexation by organic ligands and exchanges between dissolved and colloidal phases and the sediment. Based on published toxicity data, the bioavailable Cu concentrations (1.7-190. nM) in this estuary are likely to severely compromise the ecosystem structure and functioning with respect to species diversity and recruitment of juveniles. The study illustrates the importance of in situ speciation studies at high resolution in pursuit of a better understanding of metal (bio)geochemistry in dynamic coastal systems. © 2011 Elsevier Ltd.

Description: The increasing environmental pressures on estuarine and coastal waters call for improved monitoring techniques of chemical constituents to aid management decisions. Automated stripping voltammetry is a suitable technique for continuous, near real-time monitoring of trace metals in marine systems. This contribution describes the application of voltammetric monitoring techniques in estuarine and coastal waters of the UK and Spain. The high spatial and temporal resolution of the data obtained, allows a thorough interpretation of the trace metal sources and behaviour. Future trends in this field research include submersible sensors which can be remotely deployed for a period of several weeks.