Search

Recent studies indicate that aluminum (Al) could play an important role in the ocean carbon cycle by increasing phytoplankton carbon fixation and reducing organic carbon decomposition. However, how Al may influence the decomposition of organic carbon has not yet been explicitly examined. Here we report the effects of Al on carbon fixation by marine diatoms and their subsequent decomposition. By using radiocarbon as a tracer, the carbon fixation and decomposition of three model marine diatoms were examined in Aquil* media at different concentrations (0, 40, 200, and 2000 nM) of dissolved Al. Addition of Al enhanced net carbon fixation by the diatoms in the declining growth phase (by 9%–29% for Thalassiosira pseudonana, 15%–20% for T. oceanica, 15%–23% for T. weissflogii). Under axenic conditions the decomposition rates (d−1) of the diatom‐produced particulate organic carbon (POC) significantly decreased (by 21%–57% for T. pseudonana, 0%–41% for T. oceanica, 29%–58% for T. weissflogii) in the Al‐enriched treatments. In the presence of bacteria, the decomposition rates of T. weissflogii‐produced POC were still 37%–38% lower in Al‐enriched treatments compared to the control. Significant increases in cell size, cellular carbon content (pmol C/cell) and cellular carbon density (pmol C/μm3) of T. weissflogii were also observed in the Al‐enriched treatments compared to the control. The Al‐related increase in net carbon fixation and cell size, and the decrease in POC decomposition rate may facilitate carbon export to ocean depths. The study provides new evidence for the iron–aluminum hypothesis, which suggests that Al could increase phytoplankton uptake of atmospheric CO2 and influence climate change. [ABSTRACT FROM AUTHOR]

Abstract: Several cases have been described in the literature where different ligands enhanced lead (Pb) bioavailability over what would have been expected on the basis of equilibrium models such as the biotic ligand model (BLM). These exceptions compromise the development of BLMs for this metal, and mechanistic knowledge of the involved processes is still insufficient. The present study shows that the hydrophilic organic ligand citrate enhances Pb internalization by Chlamydomonas reinhardtii for both the wild and the wall‐less strains. Despite the high Pb internalization fluxes shown by this alga, which may be near the limits set by diffusion through the boundary layer, and its capacity to assimilate citrate (and potentially Pb‐citrate complexes), neither of these mechanisms could quantitatively account for the observed increase in Pb internalization in the presence of this ligand. However, algal‐driven pH increases in the boundary layer and concomitant changes in Pb speciation successfully explained the observed results. This study suggests that information on bulk solution chemistry is not enough to predict metal bioavailability for organisms that can substantially modify the chemical composition of their boundary layer, as observed for C. reinhardtii. [ABSTRACT FROM AUTHOR]

Abstract: Biomolecules involved in handling cytosolic metals in the liver of the yellow perch (Perca flavescens) were characterized in juvenile fish collected from 4 lakes constituting metal contamination gradients. Using size‐exclusion liquid chromatography coupled to an inductively coupled mass spectrometer, we determined metal distributions among ligands of different molecular weights in the cytosol, before and after a heat denaturation step designed to isolate metallothionein‐like peptides and proteins. Silver, Cd, and Cu found in the heat‐stable protein supernatants were indeed largely present as metallothionein‐like peptide complexes; but Co, Ni, and Tl, also present in the heat‐stable protein supernatants, did not coelute with metallothionein‐like peptides and proteins. This difference in metal partitioning is consistent with the known preference of “soft” metals such as Ag, Cd, and Cu(I) for thiolated ligands and the contrasting tendency of Co and Ni to bind to ligands with oxygen and nitrogen as donor atoms. Metal handling in the whole cytosol also reflected these differences in metal‐binding behavior. For Cd and Cu, the importance of the molecular weight pool that includes metallothionein‐like peptides and proteins increased relative to the other pools as the total cytosolic metal concentration ([M]cytosol) increased, consistent with a concentration‐dependent detoxification response. In contrast, for Ni and Tl the increase in [M]cytosol was accompanied by a marked increase in the high–molecular weight (670–33 kDa) pool, suggesting that hepatic Ni and Tl are not effectively detoxified. Overall, the results suggest that metal detoxification is less effective for Ni, Tl, and Co than for Ag, Cd, and Cu. Environ Toxicol Chem 2018;37:576–586. © 2017 SETAC [ABSTRACT FROM AUTHOR]

Recent studies have suggested that low-molecular-weight (LMW) ligands can enhance trace metal uptake by marine diatoms. We have extended this work to freshwater phytoplankton and have investigated Cd bioavailability in the presence of LMW thiols, with two green algae ( Chlamydomonas reinhardtii and Pseudokirchneriella subcapitata) and a cyanobacterium ( Anabaena flos-aquae). Using nitrilotriacetic acid (NTA) to hold the free Cd2+ concentration constant, we progressively added cysteine to the exposure medium and determined short-term Cd uptake rates for each organism; the Cd uptake rates remained constant and were unaffected even when the concentrations of the Cd-cysteine complexes exceeded that of the free Cd2+. Similar results were obtained with algae pre-acclimated to different nitrogen sources or low zinc concentrations, even though such treatments affect their ability to utilize amino acids or take up Cd. A lack of effect was also observed for the two green algae with penicillamine, mercaptosuccinic acid, dithiothreitol and glutathione. These results suggest that the Cd-thiol complexes do not contribute to Cd uptake. However, when the experiments were repeated with cysteine in the absence of NTA, at the same Cd2+ concentration, a significantly higher Cd uptake rate was observed in the presence of the L- or D-cysteine stereoisomers than in the presence of NTA. This enhancement of Cd uptake in the presence of cysteine alone was sensitive to the nitrogen nutrition of these microorganisms, and we suggest that the enhancement likely results from biologically-induced chemical oxidation of cysteine in the boundary layer adjacent to the algal cell. [ABSTRACT FROM AUTHOR]

Uptake of lipophilic metal complexes by freshwater algae has recently been shown to be pH dependent. Here we look at different physiological aspects that could influence the diffusion of the lipophilic Cd complex, Cd(diethyldithiocarbamate)20 (Cd(DDC)20), into algal cells at different exposure pH values. Changes in cell membrane permeability were assessed as a function of pH for three species of green algae [ Chlamydomonas reinhardtii P. A. Dang., Pseudokirchneriella subcapitata (Korshikov) Hindák, and Chlorella fusca var. vacuolata Shihira et R. W. Kraus] using two neutral, nonionic probes, fluorescein diacetate (FDA) and D-sorbitol. In parallel experiments, we exposed algae to inorganic Cd or to Cd(DDC)20 and monitored Cd intracellular metal distribution, together with phytochelatin synthesis. For the three algal species acclimated at pH 5.5 (w/wo DDC 1 μM) and exposed at this pH, their permeability to FDA and D-sorbitol was consistently lower than for algae growing at pH 7.0 and exposed at this pH ( P < 0.001). The ratio of the FDA hydrolysis rate measured at pH 7.0 with respect to the rate measured at pH 5.5 (both in the presence of DDC) correlated with the ratio of the Cd(DDC)20 initial internalization rate constant obtained at pH 7.0 versus that obtained at pH 5.5 (three algae species, n = 9, r = 0.85, P = 0.004). Our results strongly suggest that acidification affects metal availability to algae not only by proton inhibition of facilitated metal uptake but also by affecting membrane permeability. [ABSTRACT FROM AUTHOR]

Enzymes representing a variety of metabolic pathways were examined in yellow perch ( Perca flavescens) collected from a metal-contaminated region (Rouyn-Noranda, Québec, Canada) to determine which were most closely related to fish condition factor, pyloric caeca weight, and visceral lipid accumulation, as well to seek a better understanding of the influence of metal contamination on the physiology and biometrics of perch. Compared to laboratory fish, wild perch were under important energy restrictions. The condition factor of wild fish was correlated with indicators of aerobic metabolism (citrate synthase, cytochrome C oxidase), protein anabolism (nucleoside diphosphokinase), and indicators of lipid accumulation (glucose-6-phosphate dehydrogenase, visceral lipid index). Pyloric caeca weights were well correlated with indicators of protein anabolism, but only when both seasons were examined together, possibly indicating a lag in the response of enzymes to changes in diet. The addition of contaminant stress to existing energy restrictions led to changes in the relationships between enzymes and biometrics, reducing the predictive power of the models for perch in contaminated lakes. The present study broadens our knowledge of the impact of metal contamination on energy accumulation and tissue metabolic capacities in wild perch. Environ. Toxicol. Chem. 2011;30:2148-2156. © 2011 SETAC [ABSTRACT FROM AUTHOR]

Cadmium forms neutral, lipophilic CdL20 complexes with diethyldithiocarbamate (L = DDC) and with ethylxanthate (L = XANT). In a synthetic solution and in the absence of natural dissolved organic matter (DOM), for a given total Cd concentration, uptake of these complexes by unicellular algae is much faster than the uptake of the free Cd2+ cation. The objective of the present study was to determine how this enhanced uptake of the lipophilic CdL20 complexes was affected by the presence of natural DOM (Suwannee River humic acid, SRHA). Experiments were performed with Cd(DDC)20 and Cd(XANT)20 at two pH values (7.0 and 5.5) and with the three chlorophytes [ Chlamydomonas reinhardtii P. A. Dang., Pseudokirchneriella subcapitata (Korshikov) Hindák, Chlorella fusca var. vacuolata Shihira et R. W. Krauss]. Short-term uptake (30-40 min) of the CdL20 complexes was followed in the absence and presence of SRHA (6.5 mg C · L−1). Acidification from pH 7.0 to 5.5 decreased CdL20 uptake by the three algae, in the presence or absence of humic acid (HA). The dominant effect of the HA was to decrease Cd uptake, due to its interaction with the CdL20 complexes in solution. However, if uptake of the free CdL20 complexes was compared in the presence and absence of HA, in four of eight cases initial uptake rate constants ( ki) were significantly higher ( P < 0.05) in the presence of the HA, suggesting the operation of an interfacial effect of the HA at the algal cell membrane, favoring uptake of CdL20. Overall, the experimental results suggest that neutral metal complexes will be less bioavailable in natural waters than they are in synthetic laboratory media in the absence of natural DOM. [ABSTRACT FROM AUTHOR]

Objectives/Hypothesis: Repair of the skull base still begins with a direct repair of the dural defect. We present a new button closure for primary repair of the dura for high flow defects. Study Design: Retrospective review. Methods: We reviewed our 20 cases of primary button grafts and compared the results to the previous 20 high-flow open-cistern cerebrospinal fluid (CSF) cases. Subjects were excluded if they had no violation of the arachnoid space or potential for low-flow CSF leak. The button is constructed so that the inlay portion is at least 25% larger than the dural defect, and the onlay portion is just large enough to cover the dural defect. The two grafts are sutured together using two 4-0 Neurolon sutures and placed with the inlay portion intradurally and the onlay portion extradurally. Results: The button graft repair of open-cisternal defects had a drop in CSF leak complications to 10% (2/20), and these two leaks were repaired with the button technique as the salvage surgery. This is a significant improvement over the 45% leak rate in the prebutton graft group (P < .03). In our button graft group we used nasoseptal flaps on 16/20 repairs, and 1/2 repairs that leaked in the button group did not have a nasoseptal flap. Lumbar drains were used in ∼38% in both groups (P = .83). Conclusions: The button graft can be used in conjunction with the nasal septal flap or as a stand-alone repair with good results reducing the postoperative leak rate to 10% for high-flow CSF repairs. Laryngoscope, 2010 [ABSTRACT FROM AUTHOR]

We conducted a reciprocal transfer of nymphs of the burrowing mayfly Hexagenia limbata between two rivers harboring populations of this insect that differed in their cadmium (Cd) concentrations. We measured Cd uptake and loss rates simultaneously in the held at several levels of biological organization: in the gut and body of whole nymphs as well as in three subcellular fractions. The most marked changes in Cd concentrations occurred in the insect's gut, where Cd was largely associated with heat-stable proteins, a fraction that includes the metal-binding protein metallothionein. Because most of the Cd that entered nymphs was detoxified in this manner, we would not expect it to have direct toxic effects; however, it would be readily transferred to higher trophic levels. Our data on subcellular partitioning suggest that there is a fast-exchanging pool of Cd bound to heat-stable proteins such as metallothionein and a slow-exchanging pool bound to either or both of the remaining fractions (heat-denatured proteins; remainder, which includes exoskeleton and granules). Nymphs of H. limbata responded rapidly to changes in bioavailable Cd, which suggests that they would be useful for monitoring changes in ambient Cd for weeks or months in the field. A one-compartment model successfully explained the changes we observed in nymph Cd values. Furthermore, values of the modal constant for Cd loss were close to those reported for Hexagenia rigida in the laboratory, which suggests that accumulation patterns observed in the laboratory can be representative of those measured in nature. [ABSTRACT FROM AUTHOR]

The effects of humic substances and low pH on short-term Cd uptake byPseudokirchneriella subcapitata(Korshikov) Hindak andChlamydomonas reinhardtiiDang were investigated under defined exposure conditions. The uptake experiments were run in the presence of either a synthetic organic ligand (nitrilotriacetate) or natural organic ligands (Suwannee River fulvic or humic acid). An ion-exchange method was used to measure the free Cd2+ concentrations in the exposure solutions. At pH 5, measured free Cd2+ concentrations agreed with estimations made using the geochemical equilibrium model WHAM, but at pH 7 the model overestimated complexation by both Suwannee River fulvic and humic acids compared with the ion-exchange measurements. Consistent with the metal internalization step being rate limiting for overall short-term uptake, intracellular Cd uptake was linear for exposure times less than 20 min at pH 5 or pH 7 for both algal species. After taking into account complexation of Cd in solution, Suwannee River humic substances had no additional effects on cadmium uptake at pH 7, as would be predicted by the free ion model. This absence of effects other than complexation persisted at pH 5, where the tendency of humic substances to adsorb to the algal cell surface is favored. Changes in pH strongly influenced Cd uptake, with the intracellular flux of Cd being at least 20 times lower at pH 5 than at pH 7 forP. subcapitata. Our results support models such as the free ion model or the biotic ligand model, in which humic substances act indirectly on Cd uptake by reducing the bioavailability of Cd by complexation in solution. [ABSTRACT FROM AUTHOR]

Silver bioavailability in the presence of chloride was estimated from short-term (≤60 min) uptake experiments with two green algae, Pseudokirchneriella subcapitata and Chlorella pyrenoidosa. In the first experiment, silver uptake was monitored under two concentration regimes in which total dissolved silver ([Ag]tot) and [C1] were manipulated to maintain [Ag+] at a constant value (10 nM). Comparable uptake rates were measured for both treatments despite the dramatic changes in [C1] and [Ag]tot. In the second experiment, ambient [Ag]tot was held constant (10 or 115 nM), but [C1] was varied (0.005-50 mM) to explore the whole range of silver chloro-complexes. Intracellular silver varied markedly along the [C1] gradient and exhibited a clear, positive correlation with ambient [Ag+] for both algae. We conclude that the biotic ligand model reliably describes silver bioavailability in the presence of chloride for the two test algae and that its applicability depends on the relative magnitudes of silver fluxes through the unstirred diffusion layer and across the cell membrane, with the latter being affected by the presence or absence of a Cu(I) transporter. In the presence of chloride, no evidence was found for the internalization of silver via anion transport or passive diffusion of the neutral mono-chloro-complex, AgCl0. [ABSTRACT FROM AUTHOR]

Larvae of the insect Chaoborus are used to monitor cadmium (Cd) in lakes. We set out to determine if this animal possesses a metallothionein-like protein to which its Cd could be bound and if the concentrations of such a protein are correlated with those of Cd in the insect and in lakewater. To achieve our goals, we collected water and larvae of several Chaoborus species from 10 lakes situated along an environmental Cd gradient. We found that all of the Chaoborus species possess a metallothioneinlike protein and that concentrations of the protein and of Cd differed among species. Concentrations of the metallothionein-like protein were directly related to those in Chaoborus and in lakewater. These direct relationships support the use of Chaoborus larvae as a Cd biomonitor. [ABSTRACT FROM AUTHOR]

Short-term (<1 h) silver uptake by the green alga Chlamydomonas reinhardtii was measured in the laboratory in defined inorganic media over a range of silver and chloride concentrations. For a low, fixed, free Ag+ concentration (e.g., 8 nM), silver uptake increases markedly (up to ∼43) as a function of the chloride concentration (5 μM→4 mM C1-); the free-ion model would have predicted a constant silver uptake rate. No evidence could be found for the passive diffusion of the neutral AgC1-0 complex or for the facilitated uptake of the anionic AgCl-2 complex. The enhanced uptake observed in the presence of chloride is related to the very high silver uptake rates demonstrated by the test alga, which lead to diffusion limitation in the boundary layer surrounding the algal cell. In such a situation, metal accumulation is proportional to the total metal concentration (i.e., to the concentration gradient between the bulk solution and the algal surface). At higher silver concentrations (e.g.,≥10-7M), diffusion in the phycosphere is no longer rate limiting, the chloride stimulation disappears, and silver uptake is sensitive to the free-ion concentration. However, such a high concentration of silver is not likely to be encountered in the environment, even in wastewater effluents. [ABSTRACT FROM AUTHOR]

Toxicities of cadmium (Cd) and zinc (Zn) to the green alga Selenastrum capricornutum Printz were determined over 72 h in defined synthetic media buffered by citrate (FRAQCIT ; [citrate] = 100 μM or 5 μM) or nitrilotriacetate (FRAQNTA ; [NTA] = 5 μM). Algal sensitivity to free Cd2+ or free Zn2+ in FRAQCIT was much higher than in FRAQNTA. In parallel experiments, short-term intracellular uptake of radiolabeled 109Cd was measured as a function of time (0–30 min) in FRAQCIT and FRAQNTA; for a given free Cd2+ concentration (8, 250, or 610 nM), intracellular accumulation of Cd was consistently higher in FRAQCIT than in FRAQNTA. Under the same conditions, the alga accumulated 14C-labeled citrate almost linearly over a 2-h period. Loss of 109Cd from algal cells that had been prelabeled with the radionuclide occurred slowly, and the loss rate was insensitive to the presence or absence of citrate, indicating that the overall permeability of the algal membrane to Cd was unaffected by citrate. The enhanced bioavailability of Cd in the presence of citrate could be explained by membrane transport of a charged Cd–citrate complex, presumably by accidental transport. [ABSTRACT FROM AUTHOR]

The transformation of bauxite to alumina, the first step in the production of metallic aluminum (AI), generates AI-rich effluents. One installation is located near Jonquiere (QC, Canada), with the effluentsbeing discharged into the Saguenay River. We undertook an integratedgeochemical and ecotoxicological study to determine if these Al discharges affected the receiving water. In the spring, summer, and autumn of 1997, samples of river water were collected from stations upstream and downstream of the effluent outfalls and from a regional reference site. Samples were analyzed for A1 (e.g., particulate and dissolved Al, total monomeric and organic monomeric Al, dissolved polymeric Al) and for parameters known to affect Al speciation (pH, SO4 fluoride, dissolved organic carbon). Parallel samples were used for ambient toxicity tests with fathead minnow and Ceriodaphnia dubia.Concentrations of total Al (231-596 Mu g/L) and dissolved Al (112-344 Mu g/L) at downstream stations were 1.1 to 3.7 times higher than those at the station immediately upstream. Average levels of total and dissolved A1 exceeded the Quebec provincial criterion of 87 Mu g acidrecoverable Al/L, even at sites upstream of the plant. Inorganic monomeric Al at downstream stations ranged from 22 to 88 Mu g/ L. With the exception of a single elevated value observed at one downstream site, inorganic monomeric Al levels were <75 Mu g/ L. Other studies in soft neutral-pH waters have shown that no toxic effects occur at this concentration of inorganic monomeric Al. None of the river water samples from stations 300 m downstream from the outfalls caused significant toxicity to C. dubia or fathead minnows. We suggest that expressing guidelines as monomeric inorganic Al would offer a more useful basis for comparison with ambient Al concentrations. [ABSTRACT FROM AUTHOR]

Uptake of lipophilic metal complexes by freshwater algae has recently been shown to be pH dependent. Here we look at different physiological aspects that could influence the diffusion of the lipophilic Cd complex, Cd(diethyldithiocarbamate)20 (Cd(DDC)20), into algal cells at different exposure pH values. Changes in cell membrane permeability were assessed as a function of pH for three species of green algae [ Chlamydomonas reinhardtii P. A. Dang., Pseudokirchneriella subcapitata (Korshikov) Hindák, and Chlorella fusca var. vacuolata Shihira et R. W. Kraus] using two neutral, nonionic probes, fluorescein diacetate (FDA) and D-sorbitol. In parallel experiments, we exposed algae to inorganic Cd or to Cd(DDC)20 and monitored Cd intracellular metal distribution, together with phytochelatin synthesis. For the three algal species acclimated at pH 5.5 (w/wo DDC 1 μM) and exposed at this pH, their permeability to FDA and D-sorbitol was consistently lower than for algae growing at pH 7.0 and exposed at this pH ( P < 0.001). The ratio of the FDA hydrolysis rate measured at pH 7.0 with respect to the rate measured at pH 5.5 (both in the presence of DDC) correlated with the ratio of the Cd(DDC)20 initial internalization rate constant obtained at pH 7.0 versus that obtained at pH 5.5 (three algae species, n = 9, r = 0.85, P = 0.004). Our results strongly suggest that acidification affects metal availability to algae not only by proton inhibition of facilitated metal uptake but also by affecting membrane permeability. [ABSTRACT FROM AUTHOR]