Cu and Pb accumulation by the marine diatom Thalassiosira weissflogii in the presence of humic acids

Abstract

Environmental context.Dissolved organic matter protects aquatic microorganisms from toxic metals by complexing and decreasing the concentration of the biologically reactive species such as free metal ions. However, there are some cases of enhancement of toxic effects when humic acids are present, which is thought to be due to effects of adsorbed humic acids on cell membranes. For a marine diatom, humic acids adsorbed to cell surfaces enhanced metal adsorption, whereas intracellular metal contents decreased as a result of metal binding by humic acids. These findings suggest that the diatom wall, the frustule, presents a barrier against direct effects of adsorbed humic acids on the plasma membrane. Abstract.Metal complexation by dissolved organic matter, as humic acids, is considered to decrease metal bioavailability by lowering the free metal ion concentration. However, dissolved organic matter adsorption on cell surfaces can modify cell membrane properties, which can also influence metal uptake. Copper and lead accumulation and internalisation by the marine diatom Thalassiosira weissflogii were studied in the absence and presence of humic acids, and adsorption of humic acids to cell surfaces was evaluated. Both Pb and Cu intracellular concentrations decreased in the presence of humic acids according to labile metal concentrations measured by anodic stripping voltammetry, whereas total (intracellular plus adsorbed) metal content was enhanced in the presence of humic acids, probably owing to enhanced metal plus humics adsorption to cell surfaces. The results of the present work stress the importance of differentiating between intracellular and total cellular metal in bioavailability studies, and suggest that the silica frustule of diatoms represents a barrier against humic acids effects on cell membranes.

Determination of trace metals accumulated and internalized by marine phytoplankton; interferences with colloidal organic matter

“…HA decrease Cu and Pb internalization by the algae, and this decrease is higher at higher HA concentrations. This is in accordance with the decrease in free Cu and Pb caused by complexation with HA, as measured by anodic stripping voltammetry [36]. This effect, in agreement with the free ion activity model, is supported by many other studies in the case of Cu [29,37], but contrast with the observed enhancing effect of HA on Pb uptake and toxicity to marine invertebrates [38].…”

“…It is known that HA adsorbed to cell membranes can modify membrane properties, as membrane potential or membrane permeability [39,40], and enhance the uptake of some inorganic elements, as Na þ [41], or Pb 2þ [38,40]. The fact that this enhancing effect on Pb uptake was not observed for T. weissflogii is discussed in our previous paper [36], where it is proposed that the silica frustule of the diatom protects against the adsorption of HA on the cell membrane.…”

Lead Bioavailability to Freshwater Microalgae in the Presence of Dissolved Organic Matter: Contrasting Effect of Model Humic Substances and Marsh Water Fractions Obtained by Ultrafiltration

“…The presence of colloidal material, isolated from a Swiss wastewater treatment plant effluent, also enhanced Pb uptake by C. kessleri (Worms et al 2010). In contrast, for the diatom T. weissflogii, the cellular Pb content decreased in the presence of DOM (Sanchez-Marin et al 2010a). DOM from terrestrial and riverine origin enhanced Pb toxicity for sea urchin embryos, the mussel Mytilus sp.…”

Updated species sensitivity distribution evaluations for acute and chronic lead toxicity to saltwater aquatic life

“…Uptake of Pb by M. edulis gills was significantly lower when the exposure medium was supplemented with fulvic acid and Suwannee River DOM . In a marine diatom ( Thalassiosira weissflogii ), humic acid did not alter the amount of Pb that was internalized, although humic acid concentrations were positively related with adsorption of Pb to the exterior of the cell wall of the diatom . Nogueira et al observed that enzyme activity in embryonic Mytilus galloprovincialis was altered during 48‐h exposures to several types of natural organic matter but that the addition of metals (including Pb) did not generally alter enzyme activity beyond the effect of organic matter alone.…”