Rapid and simultaneous analysis of trace metals (Cu, Pb and Cd) in seawater by potentiometric stripping analysis

Cellular and biochemical responses of the oyster Crassostrea gigas to controlled exposures to metals and Alexandrium minutum

Effects of simultaneous exposure of Pacific oyster, Crassostrea gigas, to both a harmful dinoflagellate that produces Paralytic Shellfish Toxins (PST), Alexandrium minutum, and cadmium (Cd) and copper (Cu), were assessed. Oysters were exposed to a mix of Cd-Cu with two different diets (i.e. A. minutum or Tisochrysis lutea) and compared to control oysters fed A. minutum or T. lutea, respectively, without metal addition. Metals and PST accumulations, digestive gland lipid composition, and cellular and biochemical hemolymph variables were measured after 4 days of exposure. Oysters exposed to Cd-Cu accumulated about thirty-six times less PSTs than oysters exposed to A. minutum alone. Exposure to Cd-Cu induced significant changes in neutral lipids (increase in diacylglycerol - DAG - and decrease in sterols) and phospholipids (decreases in phosphatidylcholine, phosphatidylethanolamine, cardiolipin and ceramide aminoethylphosphonate) of digestive gland suggesting that lipid metabolism disruptions and/or lipid peroxidation have occurred. Simultaneously, concentrations, percentages of dead cells and phenoloxidase activity of hemocytes increased in oysters exposed to metals while reactive oxygen species production of hemocytes decreased. Feeding on the harmful dinoflagellate A. minutum resulted in significant decreases in monoacylglycerol (MAG) and DAG and ether glycerides (EG), as well as significant increases in hemocyte concentration and phagocytic activity as compared to oysters fed T. lutea. Finally, the present study revealed that short-term, simultaneous exposure to Cd-Cu and A. minutum may induce antagonistic (i.e. hemocyte concentration and phagocytosis) or synergic (i.e. DAG content in digestive gland) effects upon cellular and tissular functions in oysters.

Variation patterns in individual fish responses to chemical stress among estuaries, seasons and genders: the case of the European flounder (Platichthys flesus) in the Bay of Biscay

The objective was to describe and model variation patterns in individual fish responses to contaminants among estuaries, season and gender. Two hundred twenty-seven adult European flounders were collected in two seasons (winter and summer) in four estuaries along the Bay of Biscay (South West France), focusing on a pristine system (the Ster), vs. three estuaries displaying contrasted levels of contaminants (the Vilaine, Loire and Gironde). Twenty-three variables were measured by fish, considering the load of contaminants (liver metals, liver and muscle persistent organic pollutants, muscle polycyclic aromatic hydrocarbons); the gene expression (Cyt C oxydase, ATPase, BHMT, Cyt P450 1A1, ferritin); the blood genotoxicity (Comet test); and liver histology (foci of cellular alteration-tumour, steatosis, inflammation, abnormal glycogen storage). Canonical redundancy analysis (RDA) was used to model these variables using gender, season and estuary of origin as explanatory variables. The results underlined the homogeneity of fish responses within the pristine site (Ster) and more important seasonal variability within the three contaminated systems. The complete model RDA was significant and explained 35 % of total variance. Estuary and season respectively explained 30 and 5 % of the total independent variation components, whilst gender was not a significant factor. The first axis of the RDA explains nearly 27 % of the total variance and mostly represents a gradient of contamination. The links between the load of contaminants, the expression of several genes and the biomarkers were analysed considering different levels of chemical stress and a possible multi-stress, particularly in the Vilaine estuary.

Responses of Pacific oyster Crassostrea gigas populations to abiotic stress in environmentally contrasted estuaries along the Atlantic coast of France

Genetic and ecophysiological responses of oyster, Crassostrea gigas, populations to environmental stress were investigated in three highly contaminated French estuaries (the Gironde, Loire and Vilaine) and compared to a control, the Belon estuary. A strong response in both metallothionein CgMT4 mRNA expression, as determined by semi-quantitative RT-PCR, and amount of protein, as determined by ELISA tests, was demonstrated in estuarine populations subjected to differential contamination, with an inhibition in the area most highly contaminated with metals. In these same estuarine populations, we found polymorphisms of the metallothionein CgMT4 gene and three other genes (glutamine synthetase--GS, delta-9 desaturase--D9 and phosphoglucomutase--PGM) involved in stress response of C. gigas. We showed that genetic differentiation was observed for MT4 and PGM genes in the Gironde estuary which is highly contaminated with metals. A strong seasonal effect was observed. Phenotype-genotype coupling revealed that one particular MT4 allele and one PGM allele seemed to be associated with metal sensitivity expressed as lower detoxification efficiency and higher metal bioaccumulation. The MT4 gene is a good physiological and genetic marker of stress response and susceptibility.

Metal contents in coastal waters of San Jorge Bay, Antofagasta, northern Chile: a base line for establishing seawater quality guidelines

We measured the concentration of 12 metals in coastal waters of seven sites of San Jorge Bay in Antofagasta (northern Chile), in order to relate the presence of metals with the different uses of San Jorge Bay coastal border, and to evaluate the quality of the bay's bodies of water according to the proposed current Chilean Quality Guide for trace elements in seawater (CONAMA 2003). The results suggest that the coastal water of San Jorge Bay has very good quality according to the proposed regulation mentioned above. However, the distribution of metals such as Cu and Pb along the bay's coast line evidences a notorious effect of the industrial activity, which would involve different behavior patterns for some trace elements in some bodies of water, suggesting that the levels indicated in the environmental guideline of the Chilean legislation do not represent pollution-free environments.

Responses of the European flounder Platichthys flesus to the chemical stress in estuaries: load of contaminants, gene expression, cellular impact and growth rate

European flounder responses to the chemical stress were assessed by a comparative approach on four estuaries displaying contrasted patterns of contamination. The contamination typology of the estuaries was investigated by individual measurements of contaminants in fish. Molecular and physiological responses were studied by gene expression, genotoxicity, neurotoxicity and growth rate. Fishes in contaminated estuaries were characterized by high levels of bioaccumulated contaminants, slow energetic metabolism and reduced growth rate, in contrast to the fish responses in the reference site. A seasonal effect was highlighted for contaminated flounder populations, with high PCB levels, high genotoxicity and elevated detoxification rate in summer compared with winter.

Simultaneous determination of zinc, cadmium and lead in environmental water samples by potentiometric stripping analysis (PSA) using multiwalled carbon nanotube electrode

The present paper has focused on the potential application of multiwalled carbon nanotube for the development of a new, simple and highly selective electrochemical method for simultaneous Zn (II), Cd (II) and Pb (II) monitoring in water samples (lake and effluent waters), by using potentiometric stripping analysis (PSA). The electrochemical method is based on simultaneous preconcentration/reduction of metal ions onto a multiwall carbon nanotube electrode at -1.3V (versus Ag/AgCl(sat)) in 0.3 mol L(-1) acetate solution containing 15 mg L(-1) Hg (II) ions during 180s, followed by subsequent chemical stripping. The analytical curve for all analytes covered the linear range varying from 58.4 up to 646.2 microg L(-1) with correlation coefficients higher than 0.981. The limits of detection for Zn (II), Cd (II) and Pb (II) were found to be 28.0, 8.4 and 6.6 microg L(-1), while the relative standard deviation (RSD) at 352 microg L(-1) was 5.6, 7.1 and 5.6% (n=5), respectively. The behavior of the simultaneous determination in the presence of following ions Co (II), Cr (III) and Cu (II) was affected by using the analyte:interferent ratio 1:10. Therefore, by using standard addition method, Zn (II), Cd (II) and Pb (II) ions in lake and effluent water samples were determined after the spiking procedure and the results were successfully compared with those obtained by atomic absorption spectrometry (AAS). The obtained results suggest that the proposed method can be applied as a simple and efficient alternative for the simultaneous monitoring of heavy metals in water samples, according to those established requirements from environmental organizations. In addition, this method demonstrates the powerful application of carbon nanotubes in the field of potentiometric stripping analysis.

Speciation of dissolved copper within an active hydrothermal edifice on the Lucky Strike vent field (MAR, 37 degrees 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.

Dissolved and particulate metals (Fe, Zn, Cu, Cd, Pb) in two habitats from an active hydrothermal field on the EPR at 13 degrees N

The distribution of Fe, Cu, Zn, Pb, Cd between the dissolved (<2 microm) and the particulate (>2 microm) fractions was measured after in-situ filtration in two hydrothermal habitats. The total metal concentration ranges exhibit a clear enrichment compared with the seawater concentration, accounting for the hydrothermal input for all the metals considered. Iron is the predominant metal (5-50 microM) followed by Zn and Cu. Cd and Pb are present at the nM level. At the scale studied, the behavior of temperature, pH and dissolved iron is semi-conservative whereas the other dissolved and particulate metals are characterized by non-conservative patterns. The metal enrichment of the >2 microm fraction results from the settlement and accumulation of particulate matter close to the organisms, acting as a secondary metal source. The enrichment observed in the dissolved fraction can be related to the dissolution or oxidation of particles (mainly polymetallic sulfide) or to the presence of small particles and large colloids not retained on the 2 microm frit. SEM observations indicate that the bulk particulate observed is characteristic of crystalline particles settling rapidly from the high temperature smoker (sphalerite, wurtzite and pyrite), amorphous structures and eroded particles formed in the external zone of the chimney. Precipitation of Zn, Cu, Cd and Pb with Fe as wurtzite, sphalerite and pyrite is the main process taking place within the area studied and is semi-quantitative. The distribution of the dominant observed fauna has been related to the gradient resulting from the dilution process, with the alvinellids worms colonizing the hotter and more variable part of the mixing zone, but also to the metallic load of the mixing zone. Dissolved and particulate metal concentrations are therefore necessary abiotic factors to be studied in a multiparametric approach to understand the faunal distribution in hydrothermal ecosystems.

Dissolved iron analysis in estuarine and coastal waters by using a modified adsorptive stripping chronopotentiometric (SCP) method

An electrochemical method based on adsorptive stripping chronopotentiometry (SCP) with a rotating mercury film electrode has been developed for the determination of dissolved iron (III) at subnanomolar concentrations in estuarine and coastal waters. The detection limit was 0.11 nM after adsorption time of 60s. Compared to the other chronopotentiometric methods available for dissolved iron measurement in natural and estuarine waters, the procedure described here exhibits a 15-fold better sensitivity. Therefore, it allows one to accurately quantify concentrations commonly found in estuarine and coastal waters. Moreover, by using the speciation scheme proposed by Aldrich and van den Berg (Electroanalysis 10 (1998) 369), several forms could be measured, i.e. reactive iron (Fe R) and reactive iron (III) (Fe(III) R), or estimated, i.e. complexed iron (Fe C) and reactive iron (II) (Fe(II) R). The method described here is reliable, fast, inexpensive and compact. It was applied successfully to the study of the chemical speciation of dissolved iron along the salinity gradient of the Aulne estuary (Brittany-France).

Electroanalytical determination of cadmium(II) and lead(II) using an in-situ bismuth film modified edge plane pyrolytic graphite electrode

A highly sensitive and simple electroanalytical methodology is presented using an in-situ bismuth film modified edge plane pyrolytic graphite electrode (BiF-EPPGE) which is exemplified with the simultaneous determination of cadmium(II) and lead(II). Square-wave anodic stripping voltammetry is utilised with the effects of several experimental variables studied. Simultaneous additions of cadmium(II) and lead(II) were investigated where two linear ranges between 0.1-100 and 0.1-300 microg/L and also detection limits of 0.062 and 0.084 microg/L were obtained, respectively. The method was then successfully applied to the simultaneous determination of cadmium(II) and lead(II) in spiked river water, where recoveries of 100.5 and 98% were obtained, respectively. This electroanalytical protocol using edge plane pyrolytic graphite electrodes is one of the simplest methodologies to date using non-mercury based electrodes and is simpler and cheaper than alternatives such as carbon nanotube electrode arrays, suggesting the use of edge plane pyrolytic graphite electrode for routine sensing.

A stripping chronopotentiometric (SCP) method with a gold film electrode for determining inorganic arsenic species in seawater

An electrochemical method based on stripping chronopotentiometry (SCP) with a gold film electrode has been developed for determining arsenic in seawater. The detection limits were 0.053 ppb (0.71 nM) and 0.022 ppb (0.29 nM) for total inorganic As (As(T)) and As(III) after deposition times of 60 and 150 s, respectively. Compared to other stripping chronopotentiometric methods that use a gold macroelectrode to perform measurements of arsenic in seawater, the procedure described here exhibits better sensitivity and a fourfold shorter deposition time. Among the SCP methods, our procedure had proven its ability to analyse arsenic(III) in seawater. It therefore allows the concentrations of the various arsenic inorganic species in seawater--i.e. As(T), As(III) and As(V)--to be analysed. The proposed method is reliable, inexpensive and compact. It was successfully applied to the study of arsenic speciation along the salinity gradient of the Penzé estuary (NW France).

Determination of dissolved iron(III) in estuarine and coastal waters by adsorptive stripping chronopotentiometry (SCP)

An adsorptive stripping chronopotentiometric (SCP) method has been developed for quantification of dissolved iron in estuarine and coastal waters. After UV-digestion of filtered samples the Fe(III) ions in non-deoxygenated samples were complexed with solochrom violet RS (SVRS). The complexes were then accumulated by adsorption on the surface of a mercury-film electrode. The stripping step was performed by applying a constant current of -17 microA. Sensitivity and detection limit were 15 ms nmol(-1) L (270 ms microg(-1) L) and 1.5 nmol L(-1) (84 ng L(-1)), respectively, for 60-s electrolysis time. Compared with the only other chronopotentiometric method available for measurement of iron in natural waters, our procedure is fifty times more sensitive in a quarter of the electrolysis time. It therefore enables detection of the concentrations currently found in estuarine and coastal waters. The method was successfully used to study the behaviour and seasonal variations of dissolved iron in the Penzé estuary, NW France.

Physiological cost of tolerance to toxicants in the European flounder Platichthys flesus, along the French Atlantic Coast

Physiological and genetic responses of flounder Platichthys flesus populations were investigated along the French Atlantic Coast in one moderately contaminated estuary (Ster) and three contaminated estuaries (Seine, Loire and Gironde). The focus of this study was to explore the relationship between stress resistance and energetic trade-offs, in order to detect possible differential physiological capacities or performances between individuals carrying particular alleles or genotypes (allozyme data) characterised as "tolerant" or "sensitive". A general reduction of the relative fecundity, the growth rate and the condition factor was highlighted in contaminated fish populations, suggesting that survival in such polluted systems implies energetic costs for fish thus reducing the energy available for particular functions. A lower observed heterozygosity was also detected in contaminated populations with respect to the Ster, suggesting a general decrease in genetic variability in response to chemical stress (with an exception for the Seine estuary). This study confirmed the previously detected relationship between PGM 85, AAT1 95 alleles and reduced DNA damage in contaminated fish [Marchand, J., Tanguy, A., Laroche, J., Quiniou, L., Moraga, D., 2003. Responses of European flounder Platichthys flesus populations to contamination in different estuaries along the Atlantic coast of France. Mar. Ecol. Prog. Ser. 260, 273-284] and furthermore suggested that, reduced fecundity and condition factor associated to the individuals carrying the previous alleles, were also reflecting the cost of resistance to stress in polluted populations. The cost of tolerance to stress as well as the high gene flow from neighbouring populations less exposed to contamination may explain the apparently moderate increase of the suspected "tolerant" alleles in contaminated flounder populations.

Respiratory adaptations to the deep-sea hydrothermal vent environment: the case of Segonzacia mesatlantica, a crab from the Mid-Atlantic Ridge

Segonzacia mesatlantica (Crustacea; Decapoda; Brachyura) is the only endemic crab species known from the Mid-Atlantic Ridge (MAR) hydrothermal vents. Known from all explored sites in the Atlantic, its wide distribution makes this species a model to study physiological adaptation, and specifically respiratory strategies. Native haemocyanin (Hc) comprises four non-covalent associations in equilibrium formed by monomers, hexamers, dodecamers and octadecamers made up of approximately 75 kDa polypeptide chains. Four different amino acid chains are observed with a molecular mass ranging from 75,234 to 75,972 Da. Experiments carried-out under pressure suggested that the percentage of monomer increased in the haemolymph under hypoxic condition. We have also observed a shift of the proportion of the two dodecamer series, suggesting a rapid modification of the Hc phenotype between hypoxic and hyperoxic conditions. Native Hc possesses a high oxygen affinity ( P50 = 2.2 Torr at 15 degrees C and pH 7.5), a large Bohr effect (Deltalog P50 / DeltapH approximately -2.7) and a slightly reverse temperature effect (DeltaH = +17.19 kJ mol(-1). The composition of Segonzacia haemolymph is similar to that of other littoral species except for the large enrichment in free copper and zinc. As for other species from hydrothermal vent sites, Segonzacia haemolymph possesses a higher buffer capacity than littoral species. Moreover, species from the hydrothermal vent decapods from Pacific hydrothermal vent that encounter higher CO2 content in their environment have a higher buffer capacity than Atlantic vent species. The results presented are discussed in relation with the physico-chemical characteristics of the hydrothermal vent environment.

Molecular identification and expression of heat shock cognate 70 (hsc70) and heat shock protein 70 (hsp70) genes in the Pacific oyster Crassostrea gigas

The 70-kDa heat shock protein (Hsp) family is composed of both environmentally inducible (Hsp) and constitutively expressed (Hsc) family members. We sequenced 2 genes encoding an Hsp70 and an Hsc70 in the Pacific oyster Crassostrea gigas. The Cghsc70 gene contained introns, whereas the Cghsp70 gene did not. Moreover, the corresponding amino acid sequences of the 2 genes presented all the characteristic motifs of the Hsp70 family. We also investigated the expression of Hsp70 in tissues of oysters experimentally exposed to metal. A recombinant Hsc72 was used as an antigen to produce a polyclonal antibody to quantify soluble Hsp70 by enzyme-linked immunosorbent assay in protein samples extracted from oysters. Our results showed that metals (copper and cadmium) induced a decrease in cytosolic Hsp70 level in gills and digestive gland of oysters experimentally exposed to metal. These data suggest that metals may inhibit stress protein synthesis.

Structural and functional properties of hemocyanin from Cyanagraea praedator, a deep-sea hydrothermal vent crab

Cyanagraea praedator (Crustacea: Decapoda: Brachyura) is an endemic species of the East Pacific Rise hydrothermal vents, living in the upper part of black smoker chimneys. Because we were seeking species that have made respiratory adaptations to the hydrothermal environment, we looked at Cyanograea hemocyanin (Hc) and determined its quaternary structure and the oxygen-binding properties in relation to temperature, pH, and lactate. C. praedator Hc is composed of dodecamers and hexamers, with dodecamers formed by the perpendicular association of two hexamers. The composition of these polymers was determined by electrophoresis and, for the first time, by electrospray mass spectrometry. Dodecamers and hexamers are composed of six subunits common to the two forms, with molecular mass ranging from 75,008 Da to 75,534 Da. In addition, we found two dodecamer-specific subunits, at 75,419 Da and 75,629 Da. The native hemocyanin possesses a high oxygen affinity (P(50) varies between 4 and 10 Torr at pH 7.5, 15 degrees C) and a large Bohr coefficient (Delta log P(50)/DeltapH approximately -1.8). Oxygen affinity is not affected by lactate or, surprisingly, temperature between 5 degrees C and 35 degrees C (DeltaH = 1.16 kJ/mol(1) 5-35 degrees C). Dialysis of native hemolymph elicited a significant increase in Hc-O(2) affinity (DeltaP(50) = 2.5 Torr at pH 7.5), an effect opposite the usual trend observed for crustacean hemocyanins. In this article these functional properties are interpreted in relation to characteristics of the environment.

Cloning and characterization of a gene coding for a novel metallothionein in the Pacific oyster Crassostrea gigas (CgMT2): a case of adaptive response to metal-induced stress?

Cases of heavy metal resistance acquisition have already been demonstrated in eukaryotes, which involve metallothionein (MT) gene duplication or amplification mechanisms. We characterized in a marine bivalve, Crassostrea gigas, a gene coding for an unusual MT, which has never been described in other species. Our results illustrate a unique case of exon duplication and rearrangement in the MT gene family. The particular organization of the third exon of this gene allows the synthesis of a MT that presents a higher metal ion binding capacity compared to previously described MTs. The formation of a supplementary third structural beta-domain is proposed to explain results obtained in in vitro experiments. Differences in the metal responsive element (MRE) copy number and MRE core sequence observed in the promoter of CgMT2 also suggest differential regulation of CgMT2 transcription and possible implication in the detoxification processes.