Temporal variability in dynamic and colloidal metal fractions determined by high resolution in situ measurements in a UK estuary

Abstract

a b s t r a c tIn 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.

The Combined Effect of Dissolved Organic Carbon and Salinity on the Bioaccumulation of Copper in Marine Mussel Larvae

“…The Cu concentrations were chosen based on literature data on Cu toxicity in mussel larvae 18,30 and are environmentally realistic. 31 Two Cu concentrations were selected out of the five tested concentrations based on visual observation of the larval development.…”

“…In every salinity/DOC treatment, embryos were exposed to a control without added Cu and five different Cu concentrations. The Cu concentrations were chosen based on literature data on Cu toxicity in mussel larvae , and are environmentally realistic . Two Cu concentrations were selected out of the five tested concentrations based on visual observation of the larval development.…”

Trace Metal Partitioning in the Salinity Gradient of the Highly Stratified Estuary: A Case Study in the Krka River Estuary (Croatia)

“…For most metals (Cd, Pb, Ni, Mn, Fe, Al), an increase of the truly dissolved fraction from FWL (M1 and M2) to SWL (M5 and M6) was observed (Figure 2). For Cd, an increase of the truly dissolved species with salinity is usually ascribed to the competitive effect of chloride ions causing its release from particles [8,11]. For Pb, Mn, Fe and Al, an increase of the >5 µm size fraction was observed in the FSI (M2 and M3), indicating a close association of these metals.…”

“…Besides organic matter, Mn-and Fe-rich colloids can act as the principal sorptive carrier phase for some trace elements in estuarine waters (e.g., As, Pb and Zn) [7,9]. Colloids play an important role in the exchange processes of metals between the sediment and the water column [11]. The bridging of inorganic colloids by organic substances (humic substances and biopolymers) in an estuarine mixing area represents the major route for the aggregate formation and elimination of trace metals from the water column by sedimentation [3,12].…”

Evaluation of Analytical Instrumentation. Part XXVI: Instrumentation for Voltammetry

“…Determination of total dissolved metal concentrations in ltered and oxidised (i.e. organic matter removed) samples 21,23,26 Determination of the (operationally dened) labile dissolved metal fraction in fresh, ltered samples 7,8,27 In situ analysis of the (operationally dened) dynamic metal fraction in seawater 20,28 Determination of metal complexing capacity and complexing strength (log K 0 ) of natural organic ligands in fresh, ltered samples 22,[29][30][31] Determination of the free metal ion concentration. 32 The determination of organic compounds with voltammetric techniques is a wide eld and full coverage is beyond the scope of this report.…”