Influence of a low molecular weight metabolite (citrate) on the toxicity of cadmium and zinc to the unicellular green alga Selenastrum capricornutum: An exception to the free-ion model

International audienceToxicities of Cd and Zn to the chlorophyte Selenastrum capricornutum were determined in synthetic media buffered by 100 µmol*l -1 of NTA (FRAQ(NTA)) or citrate (FRAQ(CIT)), or in unbuffered FRAQUIL medium (FRAQ). Metal speciation in these exposure media was adjusted so as to maintain constant free concentrations of C 2+, Mg 2+ and Me(z+) even while the free Zn 2+ or Cd 2+ concentrations were varied. The growth response of the algae to variations in free Zn 2+ and free Cd 2+ was similar in FRAQ and FRAQ(NTA) media, but algal sensitivity to free Zn 2+ or free Cd 2+ increased markedly in FRAQ(crr) medium. Addition of Zn to FRAQ, FRAQ(NTA) or FRAQ(CIT) media (0.02-2 µmol*l -1 free Zn 2+) caused a decrease in the algal growth rate, but the algae remained in exponential growth just as long as in the control (72 h). Similar results were obtained for exposures to Cd in FRAQ or FRAQ(NTA) media (0.01-0.9 µmol*l -1 free Cd 2+), but additions of Cd to FRAQ(CIT) yielded anomalous growth curves (heightened sensitivity to Cd 2+ at low Cd levels; shortened period of exponential growth at high Cd levels). Short-term (6 min) intracellular uptake of radiolabelled 109Cd was measured in the three media containing the same free Cd 2+ concentration (0.25 µmol*l -1). Uptake of cadmium was more than 2-fold higher in FRAQ(CIT) than in the other two media. Under the same conditions, the algae could be shown to accumulate citrate; the measured uptake rate (83 pmol citrate m -2*s -1) was about 4 times greater than that of Cd in the presence of citrate (21 pmol Cd*m -2*s -1) - the citrate transporter would only have to be fooled once every four transport events to account for the enhanced cadmium uptake in the presence of citrate. Our results clearly show that the bioavailability of Cd and Zn diverges from the predictions of the Free-Ion Model in the presence of a low molecular weight metabolite such as citrate - accidental or piggy-back uptake of the metal-ligand complex across the biological membrane is a plausible explanation for this enhanced availability.Toxicities of Cd and Zn to the chlorophyte Selenastrum capricornutum were determined in synthetic media buffered by 100 µmol*l -1 of NTA (FRAQ NTA) or citrate (FRAQ CIT), or in unbuffered FRAQUIL medium (FRAQ). Metal speciation in these exposure media was adjusted so as to maintain constant free concentrations of Ca 2+, Mg 2+ and Me z+ even while the free Zn 2+ or Cd 2+ concentrations were varied. The growth response of the algae to variations in free Zn 2+ and free Cd 2+ was similar in FRAQ and FRAQ NTA media, but algal sensitivity to free Zn 2+ or free Cd 2+ increased markedly in FRAQ CIT medium. Addition of Zn to FRAQ, FRAQ NTA or FRAQ CIT media (0.02-2 µmol*l -1 free Zn 2+) caused a decrease in the algal growth rate, but the algae remained in exponential growth just as long as in the control (72 h). Similar results were obtained for exposures to Cd in FRAQ or FRAQ NTA media (0.01-0.9 µmol*l -1 free Cd 2+), but additions of Cd to FRAQ CIT yielded anomalous growth curves (heightened sensitivity to Cd 2+ at low Cd levels; shortened period of exponential growth at high Cd levels). Short-term (6 min) intracellular uptake of radiolabelled 109Cd was measured in the three media containing the same free Cd 2+ concentration (0.25 µmol*l -1). Uptake of cadmium was more than 2-fold higher in FRAQ CIT than in the other two media. Under the same conditions, the algae could be shown to accumulate citrate; the measured uptake rate (83 pmol citrate*m -2*s -1) was about 4 times greater than that of Cd in the presence of citrate (21 pmol Cd*m -2*s -1) - the citrate transporter would only have to be fooled once every four transport events to account for the enhanced cadmium uptake in the presence of citrate. Our results clearly show that the bioavailability of Cd and Zn diverges from the predictions of the Free-Ion Model in the presence of a low molecular weight metabolite such as citrate - accidental or piggy-back uptake of the metal-ligand complex across the biological membrane is a plausible explanation for this enhanced availability

Sub-cellular partitioning of essential and non-essential metals in a freshwater mollusc, Pyganodon grandis, collected in the field along a polymetallic environmental gradient

The cellular alterations normally induced by metals at high concentrations can be prevented by detoxification processes [1] such as sequestration into cellular compartments (calcium concretions, lysosomes, etc.) or their binding to specifie cellular ligands like metallothionein [2]. The aim of this project was to study and compare the subcellular partitioning of three metals (Cd, Cu, Zn) in gills of a freshwater mollusc, Pyganodon grandis, collected along a polymetallic environmental gradient (nine lakes in the Rouyn-Noranda area, Abitibi, QC, Canada). Differential centrifugation was used to partition metals among different subcellular fractions. In the gills, along the environmental metal gradient, total tissue metal concentrations were positively correlated with concentrations in the granule fraction; gill tissues contained high amounts of calcium concretions, which acted as preferential sites for sequestration of the three metals. An increase in Cd concentration was observed in the heat stable proteins fraction (including metallothionein), but not in the heat-denatured proteins fraction, suggesting that Cd-induced cell injury could be prevented by the involement of multiple cellular compartments in a protective role

Metal (Ag, Cd, Cu, Ni, Tl, and Zn) Binding to Cytosolic Biomolecules in Field-Collected Larvae of the Insect Chaoborus

International audienceWe characterized the biomolecules involved in handling cytosolic metals in larvae of the phantom midge (Chaoborus) collected from five mining-impacted lakes by determining the distribution of Ag, Cd, Cu, Ni, Tl, and Zn among pools of various molecular weights (HMW: high molecular weight, \textgreater670-40 kDa; MMW: medium molecular weight, 40-\textless1.3 kDa; LMW: low molecular weight, \textless1.3 kDa). Appreciable concentrations of nonessential metals were found in the potentially metal-sensitive HMW (Ag and Ni) and LMW (Tl) pools, whereas the MMW pool, which includes metallothioneins (MTs) and metallothionein-like proteins and peptides (MTLPs), appears to be involved in Ag and Cd detoxification. Higher-resolution fractionation of the heat-stable protein (HSP) fraction revealed further differences in the partitioning of nonessential metals (i.e., Ag = Cd ≠ Ni ≠ Tl). These results provide unprecedented details about the metal-handling strategies employed by a metal-tolerant, freshwater animal in a field situation. © 2016 American Chemical Society

Impacts of habitat contamination on the health of declining American and European eel populations

International audienceThis research project is a joint initiative of researchers from Québec and France. Its general objective is to examine the relationships between pollution, both inorganic and organic, and the health of Atlantic eels in the Gironde and the St Lawrence estuaries

Impact of soil properties on critical concentrations of cadmium, lead, copper, zinc and mercury in soil and soil solution in view of ecotoxicological effects

Concern about the input of metals to terrestrial ecosystems is related to (i) the ecotoxicological impact on soil organisms and plants (Bringmark et al. 1998; Palmborg et al. 1998) and also on aquatic organisms resulting from runoff to surface water and (ii) the uptake via food chains into animal tissues and products, which may result in health effects on animals and humans (Clark 1989). Effects on soil organisms, including microorganisms/macrofungi and soil fauna, such as nematodes and earthworms, are reduced species diversity, abundance, and biomass and changes in microbe-mediated processes (Bengtsson and Tranvik 1989; Giller et al. 1998; Vig et al. 2003). Effects on vascular plants include reduced development and growth of roots and shoots, elevated concentrations of starch and total sugar, decreased nutrient contents in foliar tissues, and decreased enzymatic activity (Prasad 1995; Das et al. 1997). A review of these phytotoxic effects is given by Balsberg-Påhlsson (1989). Effects on aquatic organisms, including algae, Crustacea, and fish, include effects on gill function (Sola et al. 1995), nervous systems (Baatrup 1991), and growth and reproduction rates (Mance 1987). Environmental quality standards or critical limits, often also denoted as Predicted No Effect Concentrations, or PNECs, for metals in soils and surface waters related to those effects serve as a guide in the environmental risk assessment process for those substances