Matthieu Waeles

Speciation of dissolved copper within an active hydrothermal edifice on the Lucky Strike vent field (MAR, 37°N)

The objective of this study was to determine the concentrations of different fractions of dissolved copper (after filtration at 0.45 microm) along the cold part of the hydrothermal fluid-seawater mixing zone on the Tour Eiffel edifice (MAR). Dissolved copper was analyzed by stripping chronopotentiometry (SCP) after chromatographic C(18) extraction. Levels of total dissolved copper (0.03 to 5.15 microM) are much higher than those reported for deep-sea oceanic waters but in accordance with data previously obtained in this area. Speciation measurements show that the hydrophobic organic fraction (C(18)Cu) is very low (2+/-1%). Dissolved copper is present mainly as inorganic and hydrophilic organic complexes (nonC(18)Cu). The distribution of copper along the pH gradient shows the same pattern for each fraction. Copper concentrations increase from pH 5.6 to 6.5 and then remain relatively constant at pH>6.5. Concentrations of oxygen and total sulphides demonstrate that the copper anomaly corresponds to the transition between suboxic and oxic waters. The increase of dissolved copper should correspond to the oxidative redissolution of copper sulphide particles formed in the vicinity of the fluid exit. The presence of such a secondary dissolved copper source, associated with the accumulation of metal sulphide particles, could play a significant role in the distribution of fauna in the different habitats available at vents.

Measurements of trace concentrations of mercury in sea water by stripping chronopotentiometry with gold disk electrode: influence of copper

A stripping chronopotentiometric method, using a rotating gold disk electrode for mercury measurements in sea water is described. Compared with a same method using a stationary gold film electrode, this method has a eight times higher sensitivity and a detection limit of 5 ng l 1 after 10 min deposition time. Moreover, the time needed for gold plating is eliminated. Compared with other electrochemical methods capable of measuring mercury at low concentrations, the present method is more simplified with no degassing step and no need to use a medium-exchange procedure before the stripping step. These characteristics render the method easily practicable on board oceanographic vessels for ‘in situ’ measurements.

Simple and simultaneous determination of glutathione, thioacetamide and refractory organic matter in natural waters by DP-CSV.

Although reduced sulphur substances, such as thiol compounds, contain extremely reactive functional groups in the cell, and influence metal speciation and solubility, very few techniques have been developed to quantify such substances in natural waters. In this paper we present a novel method that allows for the simultaneous identification and quantification of glutathione (GSH), thioacetamide-like compounds (TA), and refractory organic matter (ROM) by differential pulse cathodic stripping voltammetry (DP-CSV). Organic compounds are initially deposited on a mercury drop electrode at 0.000 V, pH 1.95, in the presence of ~200 nmol L(-1) Mo(VI), and then stripped, creating reduction peak currents at specific potentials. Using a 60-s deposition time, limits of detection (LODs) are 1 nmol L(-1), 81 nmol L(-1) and 14 μg C L(-1) for GSH, TA and ROM, respectively. By increasing the deposition time to 300 s, LOD is decreased to 0.2 nmol L(-1), 22 nmol L(-1) and 2 μg C L(-1), respectively. This method has a number of advantages in terms of its rapidity, low cost, and relative simplicity (due to the lack of derivatization and pre-concentration steps) and is also an effective method for simultaneously analysing GSH, TA and ROM in water. When not mixed in solution, GSH, L-cysteine and N-acetyl-L-cysteine, as well as TA-like compounds and thiourea, can be detected and identified by measuring their peak potential and standard addition, due to the acidic pH, which also allows for a longer preservation of the filtered sample. The new method described in this paper was tested along an entire river-seawater gradient of the Aulne Estuary (Brittany, France) to assess its capability in terms of determining these natural organic compounds in various surface waters.

Dynamics and sources of reduced sulfur, humic substances and dissolved organic carbon in a temperate river system affected by agricultural practices

Although reduced organic sulfur substances (RSS) as well as humic substances (HS) are widely suspected to play a role in, for example, metal speciation or used as a model of dissolved organic carbon (DOC) in laboratory studies, reports of their quantification in natural waters are scarce. We have examined the dynamics and sources of reduced sulfur, HS and DOC over an annual cycle in a river system affected by agricultural practices. The new differential pulse cathodic stripping voltammetry was successfully applied to measure glutathione-like compounds (GSHs), thioacetamide-like compounds (TAs) and the liquid chromatography coupled to organic detector to analyze HS and DOC at high frequency in the Penzé River (NW France). The streamflow-concentration patterns, principal components analysis and flux analysis allowed discrimination of the source of each organic compound type. Surprisingly, the two RSS and HS detected in all samples, displayed different behavior. As previously shown, manuring practice is the main source of DOC and HS in this watershed where agricultural activity is predominant. The HS were then transferred to the river systems via runoff, particularly during the spring and autumn floods, which are responsible of >60% of the annual flux. TAs had a clear groundwater source and may be formed underground, whereas GSHs displayed two sources: one aquagenic in spring and summer probably linked to the primary productivity and a second, which may be related to bacterial degradation. High sampling frequency allowed a more accurate assessment of the flux values which were 280 tC y(-1) for DOC representing 20 kg C ha(-1) y(-1). HS, TAs and GSHs fluxes represented 60, 13, and 4% of the total annual DOC export, respectively.

Sulfide determination in hydrothermal seawater samples using a vibrating gold micro-wire electrode in conjunction with stripping chronopotentiometry.

A rapid electrochemical stripping chronopotentiometric procedure to determined sulfide in unaltered hydrothermal seawater samples is presented. Sulfide is deposited at -0.25 V (vs Ag/AgCl, KCl 3M) at a vibrating gold microwire and then stripped through the application of a reductive constant current (typically -2 μA). The hydrodynamic conditions are modulated by vibration allowing a short deposition step, which is shown here to be necessary to minimize H(2)S volatilization. The limit of detection (LOD) is 30 nM after a deposition step of 7s. This LOD is in the same range as the most sensitive cathodic voltammetric technique using a mercury drop electrode and is well below those reported previously for other electrodes capable of being implemented in situ.

The removal of colloidal lead during estuarine mixing: seasonal variations and importance of iron oxides and humic substances

In the present study, seven colloidal fractions of lead (Pb) were analysed along the mixing zone of the Penze estuary over the Year 2009, with the aim to provide some insight into the mechanism that removes the metal from the 300 kDa) and was removed in the salinity range 0-10 from all of the size fractions where it was significantly found. Because the colloidal fractionation of Pb was strongly linked to that of iron (Fe) and humic substances (HS), the removal of Pb in the mixing area must occur under flocculation of organomineral complexes. A key period corresponding to the first strong autumnal precipitations was also revealed in the present work. At this time of the year, the mobilisation of Pb (and Fe) from catchment soils is enhanced by the mobilisation of HS and the metal is associated with smaller colloids (30-300 kDa).

On the control of copper colloidal distribution by humic substances in the Penzé estuary

In this study, we investigated the variations of colloidal Cu in a temperate macrotidal estuarine system (Penzé, NW France). The originality of this work resides on examining seven colloidal/dissolved fractions at seven different periods of the year whereas previous studies on estuaries generally considered two or three fractions and were focused on a unique survey. A high proportion of Cu (∼90%) was generally found as colloids (5 kDa-0.45 μm) throughout the salinity gradient with divergent size distributions being observed over the seasonal cycle. This consisted essentially in two contrasted periods, i.e. winter-spring with a greater association of Cu with high molecular weight (HMW) compounds (50 kDa-0.45 μm) and summer-autumn with Cu being found mainly as low molecular weight (LMW) forms (5-50 kDa). The comparison of Cu with humic substances (HS) data allowed to us to highlight the importance of the pedogenic refractory organic matter in controlling the concentrations and the size distribution of Cu in the estuary. In the mixing zone, Cu behaved conservative in autumn and winter but important additions of HMW compounds were observed in spring in the lower estuary as the result of particulate organic matter degradation in the sediment. Although HS appears to be the background chelators of Cu in the systems, the strong benthic inputs occurring in spring may be of different (biotic) origin and may be in part responsible for the higher association of Cu with HMW compounds.

Cadmium in the waters off South Morocco: Nature of particles hosting Cd and insights into the mechanisms fractionating Cd from phosphate

In this study we report the distributions of total dissolvable cadmium and particulate cadmium from 27 stations in southern Moroccan coastal waters (22-30°N) which is part of the North-West African upwelling system. These distributions were predominantly controlled by upwelling of the North Atlantic Central Waters (NACW) and uptake by primary production. Atmospheric inputs and phosphogypsum slurry inputs from the phosphate industry at Jorf Lasfar (33°N), recently estimated as an important source of dissolved cadmium (240 tCd year−1), are at best of minor importance for the studied waters. Our study provides new insights into the mechanisms fractionating cadmium from phosphate. In the upper 30 m, the anomalies observed in terms of Cd:P ratios in both the particulate and total dissolvable fractions were related to an overall preferential uptake of phosphate. We show that the type of phytoplanktonic assemblage (diatoms vs dinoflagellates) is also a determinant of the fractionation intensity. In sub-surface waters (30-60 m), a clear preferential release of P (vs Cd) was observed indicating that remineralization in oxygen minimum zones is a key process in sequestering Cd. This article is protected by copyright. All rights reserved.

Stream chemical dynamic and metal accumulation in a temperate watershed affected by agricultural practices (Penzé, NW France)†

RATIONALE Understanding the fate of metals in agricultural land is an important issue for agronomic sustainability. This study aimed at quantifying the export/retention of metals in a temperate watershed subject to important manuring activities. METHODS The chemical composition of the Penzé stream was examined at high resolution during a 1-year study in 2012. After immediate on-site filtration, here demonstrated as necessary to avoid modification of the dissolved-particulate partition, the concentrations of 21 elements were determined using inductively coupled plasma (ICP) optical emission spectrometry and ICP mass spectrometry. This dataset was extended with the local atmospheric deposition of several metals (Cd, Cr, Cu, Pb, Ni and Zn) monitored on a monthly basis. RESULTS Two groups were distinguished according to the evolution of the concentrations during floods. Some major cations (Na, Ca, Mg, Sr, K, Ba) and nitrate followed counter-clockwise hysteresis patterns originating from the dilution of the enriched groundwaters by surface waters. Conversely, Al, Fe, Mn, Ti, V, Cr, Co, Ni, Cu, Zn, Cd, Pb and U displayed high dissolved concentration increases at the early stage of floods due to washing out of the enriched soils. CONCLUSIONS The comparison of stream output fluxes for the two main inputs for the watershed, i.e. atmospheric deposition and manure spreading, indicates that the vast majority of the Cu and Zn (>99 and 96%, respectively), mainly originating from pig manure, is accumulated in the watershed. The accumulation rates for other metals were >60% for Ni and Cr, >75% for As and >90% for Pb and Cd.