Jesús Perez-Peña

Binding of Cu(II) to the surface and exudates of the alga Dunaliella tertiolecta in seawater

The adsorption process and the organic matter interaction between the marine phytoplankton specie Dunaliella tertiolecta and copper ions were investigated by differential pulse anodic stripping voltammetry. Suspensions of living algae in natural Gran Canaria (Islas Canarias) seawater were titrated with Cu(II) as a function of pH, temperature, and salinity. The acid-base properties of the surface of the alga in a 0.7 M NaCI solution were characterized and interpreted as if the surface contained carboxylic acid groups (pK a,1 = 4.92 ± 0.16) and amino groups (pK a,2 = 6.28 ± 0.09, pK a,3 = 10.06 ± 0.10). The binding constant for the weaker ligands of the Gran Canaria seawater increased from 8.60 ± 0.03 to 9.30 ± 0.12 when 2.2 x 10 7 cell L -1 was added to 0.45-μm filtered seawater. The rate of uptake was found to occur in two steps. The adsorption equilibrium data correlate well with a two-site model which considers the algal surface as one which possesses two major functional groups : high-affinity binding and low-affinity binding. The high-affinity constant was of the same order of magnitude as the complexing capacity of the exudates excreted by the algae, showing that extracellular ligands play an important role in decreasing the concentration of the free metal concentration. Changes in the temperature, salinity, and pH of the seawater solution modified both the adsorption of metal and the amount of complexed copper.

Pb2' interactions with the marine phytoplankton Dunaliella tertiolecta

Metal ions become adsorbed to algal surface groups and complexed to organic material released by algae at all growth stages influencing their distribution in the seawater. In this study, the differential pulse anodic stripping voltammetry (DPASV) technique was used to evaluate the adsorption and the interaction between the exudates excreted by the marine algae Dunaliella tertiolecta and Pb2+. The adsorption process has been studied in seawater as a function of pH (2 to 8), temperature (5 to 45 °C), salinity (5 to 36), biomass and the presence of a second metal, copper. The rate of adsorption was found to occur in two steps: first a relatively fast adsorption step (10 min) and second, a slow, diffusion-controlled uptake into the cells. A two-site model which considers the presence of two major functional groups, namely: high-affinity binding and low-affinity binding was used to fit the experimental data. The values for the stability constants of Pb2 on these two groups were log ∗KH,1S = 8.40 ± 0.18 and log ∗KH,2S = 7.25 ± 0.31. The high-affinity constant similar to the complexing capacity of the exudates (log ∗KMe2+ = 8.40 ± 0.05) produced by the alga showing that extracellular ligands play an important role in buffering the concentration of the free metal concentration. A decrease in the temperature and salinity result in lower adsorption of Pb2+ to the algae and a higher complexation of lead with the exudate. The presence of copper decreases the lead complexation to the algal surface by 70%.

Aluminium distributions in Central East Atlantic waters (Canary Islands)

Abstract DASA-reactive aluminium and nutrients have been determined on a grid located in Central East Atlantic waters (Canary Islands) during early spring. The sample area shows major features of biogeochemical interest, such as elevated aeolian (dust) inputs from the Sahara desert, proximity to upwelling areas (150–200 km) and mesoscale features induced by the effect of the islands on the course of the Canary Current. The aluminium distributions show a marked latitudinal E-W gradient. The low values towards the east are explained by the intrusion of cold waters originated in the upwelling region off northwest Africa, where aluminium is scavenged by organic matter. High values towards the west suggest aeolian inputs that may stretch to below the seasonal thermocline. Nutrients are shown to be inefficient to trace these features, as they are quickly used by biological uptake. The mesoscale circulation south of the islands produces cyclonic and anticyclonic eddies that, respectively, rise and sink the thermocline over 60 m. Aluminium appears to be a useful tracer for this mixing process as well as for the intrusion of cold waters coming from the eastern boundary.

The influence of zinc, aluminum and cadmium on the uptake kinetics of iron by algae

The uptake of iron by the marine diatom Thalassiosira weissflogii and the green algae Dunaliella tertiolecta in seawater has been investigated. Computations were made of the rate constants for the binding of iron to specific cell surface-associated transport ligands and the subsequent slow active uptake into the cytoplasm of the cells. Although both algae transport Fe, the sorption constants and the kinetic parameters are markedly different and temperature dependent. The sorption constants, which are one order of magnitude higher for T weissjlogii versus D. tertiolecta (2.5 X 10m9 1 cell-’ vs. 2.2 X lo-” 1 cell-‘) at 2X, give us a measure of the theoretical number of transport sites needed by each cell. The effects on the iron speciation and on the rate of iron uptake due to the addition of different concentrations of Zn(II), Al(II1) and Cd(D) have also been determined. The results confirm that while iron is taken up via specific sites on the cell surfaces, synergistic and antagonistic effects on the iron rate uptake for T. weissflogii and D. tertiolecta, respectively, have been found and evaluated. 0 1997 Elsevier Science B.V.

Partitioning of hydrochlorinated pesticides to chitin in seawater: Use of a radial-diffusion model to describe apparent desorption hysteresis

Abstract Desorption hysteresis has been reported frequently in the literature, with several theories advanced to explain the cause of this phenomenon. Batch experiments were performed to observe sorption-desorption behaviour of endrin and heptachlor epoxide onto chitin in seawater as a function of chitin concentration, temperature and salinity. For full range of solids concentrations, sorption was described by a single linear partition coefficient. Desorption hysteresis was found at low chitin concentrations for endrin, increasing both at low temperatures and high salinity values. Results of these experiments were interpreted with a radial-diffusion sorption rate model. Model predictions of the desorption experiments showed that slow desorption rates explained most of the apparent hysteresis. The “salting effect” in marine systems makes partition coefficients ∼ 0.2 log unit higher than comparable partition coefficents measured in freshwater.

Dissolved/Dispersed Hydrocarbons in Sea Water, Determined by Infrared and Fluorescence Spectroscopy

Abstract Samples of sub-surface (1m) and surface water were collected in the harbour of Las Palmas. These have been analyzed by infrared and by fluorescence spectroscopy in order to provide information on the levels of hydrocarbons generally present in the area. With the infrared method, the absorbance at 2925cm−1 has been measured and the values are given as API mixture equivalents. For the determination of total hydrocarbons by fluorescence spectroscopy, both the single-wavelength excitation fluorescence spectra which were used for the determination of the total concentration and the synchronous excitation spectra which give more structural information were recorded. The concentrations are given as chrysene equivalents. In all cases, high concentration levels of oil were detected. The results obtained from the two methods have been explained based upon the meteorological and oceanographic conditions.

Binding of lead to P. Tricornutum and T. Weissflogii cultures in seawater

Titrations using differential pulse anodic stripping voltammetry (DPASV) to detect electroactive lead were carried out in Phaeodactylum tricornutum and Thalassiosira weissflogii seawater cultures to determine the extent of lead complexation with both dissolved ligands and cell surface groups. Adsorption and complexation parameters in a heterogeneous model were determined as a function of pH, temperature, and salinity and cell concentration by using a new iterative method. Lead forms high stable complexes in seawater and organically complexed lead fraction constitutes a significant portion of the total lead. Higher affinity for lead is observed by the surface groups of T. weissflogii in respect to P. tricornutum showing that the functional groups of T. weissflogii are more specific in the presence of 100 nM Cu(II) in solution.

Lindane adsorption-desorption on chitin in seawater

Abstract The adsorption and desorption processes by solid materials are important in determining the movement and fate of pesticide compounds in aquatic systems. Chitin is one of the constituents of natural organic matter and may serve as a model organic phase for studying the pesticide adsorption-desorption in marine systems. The lindane adsorption-desorption to chitin has been studied as a function of chitin concentration (2.5 gl−1 to 12.5 gl−1), temperature (5 to 45°C), pH (1.5 to 8) and salinity (15‰ to 36‰). Both, Freundlich and linear isotherms for the adsorption and desorption processes were used to represent the experimental data. Two-site Langmuir isotherm can describe well the measured sorption isotherm. The adsorbent-concentration effect and the adsorption-desorption hysteresis show the existence of different classes of site with different accessibility. Thus, the adsorption-desorption reaction of lindane is the result of more than a single mechanism. An increase in temperature (ΔH = −4.0 ± 0.7...

SEASONAL VARIATION OF ALUMINIUM AND ZINC CONTENT IN CYSTOSEIRA ABIES-MARINA

The paper describes a fast and simple electrochemical method to measure aluminium and zinc in algae. It is applied to measure their seasonal variation at two communities of Cystoseira abies‐marina (GMELIN) C. Agardh (Fucales, Cytoseiraceae) in the Canary Islands. Our results show high seasonal variability for both metals, concentrations increase during late summer and fall while decrease in late winter and spring. Both the cycle of the plant and the environmental conditions produce an effect on metal concentration in the tissue. Thus, the use of Cystoseira abies‐marina as metal bioindicator requires knowledge of the natural cycle of the plant and calibration of the environmental effects.

The nonreversibility of adsorption-desorption of dieldrin and lindane on chitin in seawater

Abstract Adsorption and desorption of dieldrin and lindane on chitin were investigated in seawater batch tests as a function of chitin concentration, temperature, pH and salinity. For chitin concentrations ranging from 0.5 g l−1 to 12.5 g l−1, the pesticide concentrations were varied from 4 μgl−1 to 65 μg−1 for dieldrin and from 40 μl−1 to 680 μg l−1 for lindane. Both dieldrin and lindane show adsorption-desorption hysteresis at low chitin concentration. At high chitin concentrations (m > 6.25 g l−1 for dieldrin and m > 10 gl−1 for lindane) both pesticides exhibit reversible behaviour. However, only lindane adsorption is affected by chitin concentration. These types of behaviour remain fixed in prewashed chitin. However, an increase in the temperature and a decrease in the salinity made the process become reversible. A resistant-reversible two component model has been applied to account for these types of behaviour and provides a way to explain most of the observed effects by defining mass independent dis...