Jean-Louis Gonzalez

Impact of galvanic anode dissolution on metallic trace element concentrations in marine waters

Submerged harbor steel structures often employ cathodic protection using galvanic anodes to guard against corrosion. A laboratory experiment, with three different cathodic protection configurations by galvanic aluminum-based anodes, was performed to evaluate the potential metal transfer from the anodic alloy dissolution into the surrounding marine water. The anode dissolution rate is proportional to the imposed current demands and induced a significant Al, In, and Zn transfer in the dissolved and particulate fractions of the corrosion product layers covering the anode surface. These layers were poorly adherent, even under low hydrodynamic conditions. Consequently, at the anode vicinity, the suspended particle matter and dissolved fraction of surrounding marine waters showed strong enrichments in Al and Zn, respectively, the values of which could potentially affect the adjacent biota. After the anode activation period, however, the metal inputs from galvanic anode dissolution are rapidly diluted by seawater renewal. At regional scale, these metal fluxes should be negligible compared to river and wastewater fluxes. These results also showed that it is difficult to assess the impact of the anode dissolution on the concentrations of metals in the natural environment, especially for metals included in trace amounts in the anode alloy (i.e., Cu, Fe, In, Mn, and Si) in the aquatic compartment.

Mercury transformations and exchanges in a high turbidity estuary:: The role of organic matter and amorphous oxyhydroxides

The speciation and partition of mercury in a macrotidal estuary (Seine estuary, France) was studied in order to explore the role of the high turbidity zone (HTZ) in mercury transfer to the adjacent coastal waters. Water and particles were analyzed to determine the concentrations of various mercury species, including monomethylmercury and the inorganic fraction. The exchangeable particulate mercury, which varies with salinity, and the mercury fraction associated with the amorphous oxyhydroxides were evaluated. The distribution of dissolved mercury species during early mixing suggests non-conservative behavior of organically bound mercury at the head of the estuary. Mercury in the particles covaried positively with suspended particulate matter concentrations up to a threshold, which constitutes the typical mercury load of particles and deposited sediments of the HTZ. This distribution pattern is well explained by a dilution model: a slowly settling, low metal population of particle, characterized by relatively invariant turbidity, becomes admixed with a variable amount of higher metal content particles derived from the resuspension in the HTZ. In addition, in the HTZ, which acts as a degradation reactor for particulate organic matter, particulate mercury concentrations increase with increasing C:N ratios and amorphous oxyhydroxides particles. Mercury reaches the estuarine HTZ mainly associated with the riverine and marine particles, including organic matter and oxyhydroxides, which are temporarily trapped in the HTZ and mixed with autochthonous HTZ particles. The largest particles periodically settle and undergo diagenetic reactions and resuspensions, which lead to their mercury enrichment. Depending upon hydrodynamic conditions, mercury escapes seaward as fine particulate within the plume, partially associated with the oxyhydroxides. A surface complexation model reproduces most of the partitioning observed. In the dissolved phase the model simulation suggests that a very strong ligand must be present to explain the field observations.

Influence of the Gironde estuary outputs on cadmium concentrations in the waters: consequences on the Marennes-Oléron bay (France)

The Gironde, an estuary in Southwestern France, has been highly contaminated by cadmium for many years, and the results of the French mussel watch suggest that this contamination is not restricted to the estuary, but could be responsible for relatively high levels of Cd in the oysters from the Marennes-Oleron bay located nearby. This hypothesis has been evaluated through three cruises carried out in the Gironde estuary and plume, the Marennes-Oleron bay, and the Charente estuary, a river of minor importance that influences directly this bay. The field results from the Pertuis cruise (May 1991) and two others conducted in January and December of the same year show that the Gironde is an important source of dissolved cadmium for the bordering continental shelf (11 t year–1), while the Charente inputs are far lower (60 kg year–1). Dissolved Cd concentrations on the shelf vary according to the salinity, ranging from 0.76 nmol L–1 close to the Gironde to 0.15 nmol L–1 far from the shore. The field data as well as simulations from a 3D hydrodynamic model show that the Gironde plume reaches the Antioche Straits north of the Marennes-Oleron bay, and that the Charente plume is diluted in the bay by marine waters strongly influenced by the Gironde. This study confirms that the Gironde estuary is an important source of cadmium for the Marennes-Oleron bay.

Spatiotemporal changes in cadmium contamination in the Seine estuary (France)

Cadmium (Cd) is among the major contaminants in the Seine estuary. In the biota, the RNO (Réseau National d’Observation, the French Mussel-Watch) has shown that Cd concentrations in mussels living at the mouth of the estuary are related to changes in inputs to this area of phosphogypsum, a calcium sulphate that is a by-product of the phosphoric acid naturally enriched with Cd. In the water column, Cd concentrations at several key estuary sites show a very marked trend toward decreased contamination in the particles as well as in the dissolved phase. The behavior of Cd in the estuary has been studied between 1991 and 1998 in the framework of the scientific program Seine-Aval. This program has highlighted punctual Cd inputs in the estuarine water column. The partition of Cd between the dissolved and the particulate phase, previously described in various estuaries, is characterized by an intense phenomenon of solubilization in the mixing zone freshwater-seawater, but the colloidal Cd fraction remains low along the whole salinity gradient, about 5% to 10% of the apparent dissolved fraction. Although the decrease of inputs induced a fall of Cd concentrations in the water column, laboratory experiments show that the estuarine particles are far from being exhausted in Cd. Despite continuous efforts to reduce the urban and industrial inputs into the estuarine and coastal waters, the Seine estuary still remains very contaminated by Cd.

Relation between metal concentration in water and metal content of marine mussels (Mytilus galloprovincialis): impact of physiology.

The present study constitutes an in situ investigation of metal kinetics within soft tissue of mussels (Mytilus galloprovincialis), which solves the problem of the decoupling of the effect of animal physiology and metal bioavailability in water. Field experiments were conducted to measure uptake and elimination kinetics for four metals (Hg, Pb, Cd, and Cu) in three Mediterranean sites with different contamination and nutritive levels. At each site, metal concentrations were monitored in soft tissues of mussels and in the surrounding waters. The experimental conditions were completely characterized: Lazaret Bay (located between Nice and Marseille, France) is a hot spot for Hg (6.3 ng/L) and Pb (163 ng/L) concentrations and is an oligotrophic, stable site; Bages Lagoon (located to the west of Montpellier, France) is particularly contaminated by Cd (1.5 ng/L) and Cu (1.5 microg/L) and is a mesotrophic site where variability of trophic and physicochemical parameters is significant; and Port-Cros Island (located in the Hyeres National Park, France) is considered to be a reference site. Those kinetics permit us to decouple physiological, chemical, and environmental interactions. After normalizing mussel metal content for similar physiological conditions, application of the local weighted regression (LOWESS) statistical treatment shows a parallelism between the time trends of metal concentrations in the bivalve and metal concentrations in water. The results enabled us to obtain in situ kinetic parameters and realistic bioaccumulation factors. Their logarithmic values were 4.6 for Hg, 4.3 for Pb, 4.9 for Cd, and 3.9 for Cu. The importance of physiological processes such as spawning is discussed as a factor influencing the bioaccumulation factor. This information may be useful in refining monitoring tools for risk assessment and, more generally, in environmental management strategies.

Evaluation of diffusive gradients in thin-films (DGTs) as a monitoring tool for the assessment of the chemical status of transitional waters within the Water Framework Directive.

In this contribution, the potential use of diffusive gradients in thin-films (DGTs) for the chemical evaluation of transitional water bodies within the Water Framework Directive (WFD) has been studied. The water metal concentration has been evaluated in 13 estuaries in the southeastern Bay of Biscay. The DGTs were deployed in triplicate at two stations in each estuary, delimiting the tidal influence. The DGT results were in the ranges of 2-1570 ng L(-1) for cadmium, 66-515 ng L(-1) for copper, 30-3650 ng L(-1) for nickel and 0.8-95.5 μg L(-1) for zinc. The DGTs provided reliable average labile metal concentrations in highly dynamic systems that were comparable with DGT measurements in coastal and estuarine waters worldwide. In addition, it was possible to discriminate those estuaries more susceptible to environmental impacts, being consistent with the historical contamination of each estuary. Based on the obtained results, a sampling strategy for the monitoring of transitional water bodies using DGTs is proposed.

Modelling of pollutant behaviour in estuaries: Application to cadmium in the Loire estuary

A one-dimensional multivariate mathematical model was used to study the behaviour of cadmium in a macrotidal estuary. Dissolved and particulate Cd were computed using a complexation model to solve the thermodynamic equations governing balances between free ion Cd2+ and various ligands (chloride, sulfate and hydroxide ions). Suspended matter is also considered as a ligand, characterised by an adsorption constant linking free ion Cd2+ activity to concentrations of sorbed cadmium on suspended matter. The models sensitivity study, which was applied to the Loire estuary, shows that results can be highly dependent on: (1) the adsorption constant; (2) the initial conditions determining cadmium concentrations in particulate matter at the start of each simulation; (3) the longitudinal distribution of salinity and suspended matter. The above data is often badly evaluated, introducing many uncertainties as to the results and their interpretation. The number of degrees of freedom becomes too high to permit a proper validation. However, this type of approach does allow for a rapid evaluation of the variables controlling the evolution of a given pollutant in an estuary. The results obtained show that the application and validation of a model simulating pollutant behaviour require: (1) validation of the distribution of master variables (salinity and suspended matter (S.M.) in the case of Cd); (2) relatively precise evaluation of: either the initial conditions if the simulation time scale is short, or of boundary conditions and various inputs into the estuary if the model is capable of simulating the systems evolution over a long period of time (several months).

Diatom artificial medium (DAM): a new artificial medium for the diatom Haslea ostrearia and other marine microalgae

Artificial media are used in physiological studies of microalgae to maintain consistent conditions from one experiment to another and these media must be adapted to the needs of the organism studied. The artificial medium, in this case named diatom artificial medium (DAM), was designed to maintain long-term cultures of Haslea ostrearia and 19 other planktonic microalgae, and to allow physiological studies related to metal metabolism. The biomass and biochemical composition of H. ostrearia grown in the DAM and in a modified Provasoli medium were compared to assess the suitability of this new artificial medium for the culture of this diatom. The DAM provided sufficient nutrients to allow H. ostrearia to grow as efficiently as in the enriched seawater medium, without negative impact on metabolism. The DAM was tested with 19 other microalgae in order to widen its potential use, and 18 of the 19 showed a good adaptation to this medium. The chemical speciation of metals (Cd, Cu, Pb, Zn) was assessed using a speciation mathematical model. The presence of EDTA resulted in the total complexation of the trace metals implying that they were present in a sole chemical species in the DAM.

Modeling of cadmium speciation and dynamics in the Seine Estuary (France)

A complexation model (MOCO) was used to describe cadmium (Cd) speciation during estuarine transit in the Seine estuary. This model was developed from field data. Laboratory experiments based on the use of109Cd enabled checking of certain model simplifications and hypotheses and evaluation of parameters which could not be measured directly. MOCO was coupled with a 3D multivariable hydrosedimentary model (SAM3D) to simulate Cd dynamics in the estuary. These results were compared with measurements (dissolved and particulate Cd) obtained during cruises representative of various hydrodynamic conditions. The purpose of this article is to present the modeling approach used, and its expected applications and limits.

PARTICULATE CD AND HG FLUXES TO THE SEDIMENT IN THE MARENNES-OLERON BAY : ORIGIN AND EVOLUTION

Abstract The location of one of the largest oyster centres in France in the Marennes‐Oleron Bay instigated the study of two toxic metals: cadmium and mercury, most likely originated from the Charente Estuary. Analyses of particulate metallic inputs in sediments (60 kg Cd and 35 kg Hg/yr) and radiochronological data showed that outputs from the Charente river (20 kg Cd and 12 kg Hg/yr) alone could not account for the high metallic contents recorded in the bay. This metallic input could be due to the presence of an exterior source to the bay.