Francis Ribeyre

Interspecific comparison of cadmium and zinc contamination in the organs of four fish species along a polymetallic pollution gradient (Lot River, France).

The impact of cadmium (Cd) and zinc (Zn) discharges related to an old zinc ore treatment facility in the Lot River (France) was investigated in four fish species (the chub: Leusciscus cephalus, the roach: Rutilus rutilus, the perch: Perca fluviatilis and the bream: Abramis brama). The organisms were sampled in four stations along the polymetallic contamination gradient. Cd and Zn analysis were carried out in five organs (gills, posterior intestine, liver, kidneys and skeletal muscle) in order to highlight the potential pathways of uptake, storage and elimination of metals. The results indicate a very strong Cd contamination in fish collected downstream from the metal source. The kidneys have the highest cadmium concentrations, but the gills and the intestine, as exchange organs, present the largest variations between the stations in close relation with the contamination gradient. Cd concentrations measured in the liver vary only slightly among the sampling stations. Unlike the trends observed for Cd, Zn levels in fish populations are strongly regulated and do not follow ambient Zn concentrations. The concentrations measured vary also according to fish species, for both Cd and Zn. This study shows that the trophic habits can explain the interspecific differences in Cd bioaccumulation. Zn levels observed for each species in non-contaminated populations also help to understand metal bioaccumulation patterns in polluted sites, suggesting that the determinism of interspecific differences is constitutive.

Seasonal variations of metallothionein concentrations in the asiatic clam (Corbicula fluminea)

Natural variations of metallothionein (MT) concentrations in the Asiatic clam Corbicula fluminea were analyzed over a 1-year period in specimens collected from an unpolluted site (Cazaux-Sanguinet lake, southwest France). Sampling was carried out from November 1994 to December 1995, one to three times per month, according to the season. At each sampling time, lake temperature was measured and concentrations of MTs, Cd, Hg, Zn and Cu were determined in the whole soft body and in four organs or tissue samples. A histological study was conducted simultaneously to follow the development of the gonads in relation to the reproductive cycle of this bivalve. Results showed very high fluctuations in MT concentrations over the whole year, with a maximum value measured in the middle of May and ratios of around 4 at the whole organism level between extreme MT values. The tissue compartment presenting the most important variations was the visceral mass, which contains the gonads. Metal accumulation in the organisms did not seem to be involved among the factors likely to account for these variations in MT concentrations; metal concentrations remained at low and relatively constant levels throughout the whole year. The histological study revealed one spawning period from late May to the middle of June, appearing just after the MT “peak,” with maximum incubation of the embryos in the gills in late June. Because MT biosynthesis can be induced by hormonal secretions implicated during reproductive phenomena, the variations in MT concentrations appeared to be directly related to the biological cycle of this freshwater mollusc rather than to the direct or indirect effects of metal bioaccumulation.

Comparative study of mercury accumulation in dolphins (Stenella coeruleoalba) from French Atlantic and Mediterranean coasts

Total mercury concentrations (Hgt) have been determined in liver, kidneys, skeletal muscle, melon, stomach and intestine of 35 specimens of Stenella coeruleoalba stranded on French Atlantic and Mediterranean coasts. Very high mercury levels, with concentrations reaching 80 mg Hgt kg(-1) fresh weight (FW) in muscle and about 1500 mg Hgt kg(-1) FW in liver tissue, were observed. Liver has the highest concentration, followed by muscle and kidney. The lowest concentrations were found in the melon. The levels observed in the Mediterranean specimens are among the highest observed in marine organisms and confirm previous reports of high mercury levels in marine mammals from the Mediterranean. Comparison between Hgt accumulation levels in these two geographic groups of dolphins shows that Mediterranean individuals have much higher concentrations than specimens from the Atlantic. These differences provide additional confirmation for the higher Hgt concentrations observed previously in other pelagic species (tuna, sardine, anchovy, etc.) from the Mediterranean Sea. Taking into consideration the pelagic habitat of the dolphin and the local influence of anthropogenic mercury sources it seems reasonable to assume that the main source of the high mercury concentrations observed in Mediterranean biota is natural mercury deposits located in many regions of the Mediterranean basin.

Fundamental roles of biological barriers in mercury accumulation and transfer in freshwater ecosystems (analysis at organism, organ, cell and molecular levels)

In the framework of an ecotoxicological approach to the processes of bioaccumulation and transfer of Hg in freshwater systems, we present a synthesis of our experimental studies concerning the interactions between inorganic Hg and MeHg and biological barriers- at organism and organ levels : three biological models are selected: fish (Salmo gairdneri), burrowing mayfly nymphs (Hexagenia rigida) and rooted macrophytes (Elodea densa, Ludwigia natans). Results show strong specificities of the biological barriers (gills, intestine, roots, ...) towards metal fixation and absorption, closely related to the chemical form of the metal, the contamination sources (water, sediments or food) and the physico-chemical characteristics of the medium ;- at cell and molecular levels : biophysical study of Hg fixation on membrane reveals a new binding site on the phospholipids, the primary amine group on serine and ethanolamine polar heads, jointly with the SH groups of proteins ; Hg(II) induces a strong rigidification of the phospholipidic bilayers. Inorganic Hg and MeHg transports through model membranes (BLM) are essentially due to diffusion of neutral chloride species. These interactions between Hg compounds and membranes are strongly dependent on Hg chemical speciation (pH and pCl effects).

Effects of the phenylurea herbicide isoproturon on periphytic diatom communities in freshwater indoor microcosms

The toxic effects of the phenylurea herbicide Isoproturon -IPU: (3-(4-isopropylphenyl)-1, 1-dimethylurea)-were studied on the colonization of periphytic diatom communities, within indoor microcosms consisting of a mixed biotope (water column and natural sediment) and two biological species-rooted macrophyte cuttings (Elodea densa) and benthic bivalve molluscs (Corbicula fluminea). The periphyton, essentially composed of diatoms, was collected on artificial substrata (glass slides) in the upper layers of the water column, after two periods of exposure (34 and 71 days). IPU was initially added in the water or in the sediment compartment, at two nominal concentrations (L1 and L2 levels) for each contamination source-5 and 20 microg litre(-1) and 100 and 400 microg kg(-1) in sediment (w/w) respectively. The effects of IPU on the density and community structure of periphytic diatoms are described. A marked reduction in the diatom density was observed after 34 days exposure to the lower concentration of IPU in the water (5 microg litre(-1)). For the L2 levels, the very small number of live cells present did not permit quantification of the diatom density. After 71 days, recovery in community parameters occurred for the two contamination levels of the sediment and water column sources. Samples collected in the experimental units contaminated with the L2 levels were dominated by heterotrophic and smaller diatom species, such as Sellaphora seminulum. Data treatment based on factorial discriminant analysis enabled us to distinguish the different contamination conditions, with only 11 species from the 130 taxa identified.

Dynamics of cadmium and mercury compounds (inorganic mercury or methylmercury): uptake and depuration in Corbicula fluminea. Effects of temperature and pH

The kinetics of cadmium, inorganic mercury and methylmercury bioaccumulation and decontamination were studied in the Asiatic clam (Corbicula fluminea). The contamination phase was studied over a 14-day period, and the decontamination phase over 30 days. A further analysis of the decontamination kinetics of Cd and MeHg was carried out over a 120-day period. Combinations of two modalities, of temperature 12 and 24°C, and of pH 6.0 and 8, enabled us to quantify the actions of these two abiotic factors and also their interactions on metal depuration. During the exposure period, the concentration changes as a function of time clearly revealed a plateau tendency for the cadmium, and this was apparent as from time 4 days; in the case of the Hg(II), however, the trend was almost linear. Against these two results, the methylmercury revealed no pronounced saturation phenomenon, despite very high mercury concentrations in the soft body parts. After 30 days of decontamination, no loss of Cd or Hg was observed in the molluscs previously contaminated with Cd or with MeHg. When this study was continued for 120 days, however, we observed decontamination rates of 25% for the Cd and 40% for the MeHg. For the inorganic mercury, the average decrease in burdens measured in the soft body parts was 30% after 30 days decontamination. The temperature and pH factors had no significant effect on the decontamination processes at the organism or at the organs levels, despite the wide differences between the modalities of the two factors (12 and 24°C, pH 6.0 and 8.0).

Combined effects of water pH and salinity on the bioaccumulation of inorganic mercury and methylmercury in the shore crab Carcinus maenas

Abstract Tissue mercury concentrations were analysed in the whole organism and various organs of the euryhaline shore crab Carcinus maenas after 3 and 15 days of exposure to inorganic mercury (Hg(II)) and methylmercury (MeHg) at a nominal concentration of 1 μgHg l−1. Chemical speciation of the metals was varied by using four pH/salinity conditions (combinations between pH 7.0 and 8.5/salinity 560 and 140 mM NaCl). In all conditions, the results showed a particularly important Hg accumulation in gill tissue, smaller levels in the carapace and internal organs, and very low concentrations in circulating haemolymph. For Hg(II), accumulation was generally favoured at low salinity, but the data revealed complex pH/salinity interactions. Positive correlations were found between tissue metal levels and the abundance of some inorganic Hg species: HgCl2, HgCl−3, Hg2+, HgCl+, indicating that chemical speciation may be an important factor governing metal uptake. The balance of evidence favours HgCl2 and CH3HgCl as the most bioavailable species for uptake of Hg(II) and MeHg, respectively.

Mercury accumulation in the burrowing mayfly hexagenia rigida (ephemeroptera) exposed to CH3 HgCl or HgCl2 in water and sediment

The accumulation of Hg and its distribution within nymphs of the burrowing mayfly Hexagenia rigida (Ephemeroptera) were investigated experimentally by exposure of nymphs to radiolabelled Hg in laboratory microcosms containing water and sediment. Mercury was introduced into the experimental units either in the overlying water (twice-daily additions) or in the sediment (single addition prior to introduction of the nymphs). At the whole animal level, Hg accumulation varied according to the chemical form of the Hg added and the contamination source. When added in an organic form (CH3HgCl), Hg was accumulated to a greater extent than when added in an inorganic form (HgCl2); the ratio of accumulation between the two compounds exceeded 60 (organic/inorganic exposure) when Hg was introduced via the sediment but was only about 2 when Hg was added to the overlying water. The distribution of Hg among the various body parts of the nymphs indicated that the Hg burdens in two major target organs—the gills and the gut—depended strongly on the initial contamination source. When Hg was added via the sediment, the contribution of the gut to the total body burden (43% for inorganic Hg, 18% for methyl-Hg) was much greater than that of the gills (3 and 5%, respectively). In contrast, when Hg was added to the overlying water, the contribution of the gills to the total body burden (49% for inorganic Hg, 20% for methyl-Hg) exceeded that of the gut (8 and 17%, for the two forms, respectively).

Experimental study of bioaccumulation and effects of the herbicide isoproturon on freshwater rooted macrophytes (Elodea densa and Ludwigia natans)

Abstract Bioaccumulation and effects of the herbicide Isoproturon (IPU) on two freshwater rooted macrophytes Elodea densa and Ludwigia natans were studied after direct exposure via the water column in indoor microcosms. Three complementary experiments were set up, based on two [IPU] ranges (0–1000 and 0–100 μg.L−1 - 6 points/range) and on a chronological approach (1.5, 4, 9 and 21 days). The results showed a significant growth inhibition of the E. densa cuttings for an [IPU] close to 10 μg.L−1 Oxygen concentrations in the medium were weakly but significantly reduced after 24 h exposure to 2 μg.L−1 IPU bioaccumulation revealed a clear saturation process in the low range of [IPU] in the water, with maximal BCF values close to 60 at 2 μg.L−1.

Experimental study of mercury transfer between artificially contaminated sediment (CH3HgCl) and macrophytes (Elodea densa)

Abstract The quantification of metal transfer routes from a natural sediment enriched with methylmercury (4 mg · Hg kg −1 fresh weight) to Elodea densa , shows a high mercury accumulation in the plant organs (leaves, stems and roots). The experimental approach developed shows that, in the long term (28 days), root absorption of the organic compound (direct route) represents the dominating vector of metal accumulation in the plant, the leaves being the principal organ for storage. Two mechanisms, far less important from a quantitative point of view, are superimposed in this direct transfer: contamination by the water, linked to the releasing phenomenon at the interface ‘water-sediment’, during the initial exposure phase (4 days), and inter-plant transfers resulting from decontamination processes, acting together with direct metal accumulation in the E. densa .