Carlos Vale

Halogenated Compounds from Marine Algae

Marine algae produce a cocktail of halogenated metabolites with potential commercial value. Structures exhibited by these compounds go from acyclic entities with a linear chain to complex polycyclic molecules. Their medical and pharmaceutical application has been investigated for a few decades, however other properties, such as antifouling, are not to be discarded. Many compounds were discovered in the last years, although the need for new drugs keeps this field open as many algal species are poorly screened. The ecological role of marine algal halogenated metabolites has somehow been overlooked. This new research field will provide valuable and novel insight into the marine ecosystem dynamics as well as a new approach to comprehending biodiversity. Furthermore, understanding interactions between halogenated compound production by algae and the environment, including anthropogenic or global climate changes, is a challenging target for the coming years. Research of halogenated metabolites has been more focused on macroalgae than on phytoplankton. However, phytoplankton could be a very promising material since it is the base of the marine food chain with quick adaptation to environmental changes, which undoubtedly has consequences on secondary metabolism. This paper reviews recent progress on this field and presents trends on the role of marine algae as producers of halogenated compounds.

Histological biomarkers in liver and gills of juvenile Solea senegalensis exposed to contaminated estuarine sediments: A weighted indices approach

Young juvenile Solea senegalensis were exposed to three sediments with distinct contamination profiles collected from a Portuguese estuary subjected to anthropogenic sources of contamination (the Sado estuary, western Portugal). Sediments were surveyed for metals (cadmium, chromium, copper, nickel, lead and zinc), a metalloid (arsenic) and organic contaminants (polycyclic aromatic hydrocarbons, polychlorinated biphenyls and a pesticide, dichloro-diphenyl-trichloroethane plus its metabolites), as well as total organic matter, redox potential and particle fine fraction. The fish were exposed to freshly collected sediments in a 28-day laboratorial assay and collected for histological analyses at days 0 (T(0)), 14 (T(14)) and 28 (T(28)). Individual weighted histopathological indices were obtained, based on presence/absence data of eight and nine liver and gill pathologies, respectively, and on their biological significance. Although livers sustained more severe lesions, the sediments essentially contaminated by organic substances caused more damage to both organs than the sediments contaminated by both metallic and organic contaminants, suggesting a possible synergistic effect. Correlation analyses showed that some alterations are linked, forming distinctive histopathological patterns that are in accordance with the severity of lesions and sediment characteristics. The presence of large eosinophilic bodies in liver and degeneration of mucous cells in gills (a first-time described alteration) were some of the most noticeable alterations observed and were related to sediment organic contaminants. Body size has been found to be negatively correlated with histopathological damage in livers following longer term exposures. It is concluded that histopathological indices provide reliable and discriminatory data even when biomonitoring as complex media as natural sediments. It is also concluded that the effects of contamination may result not only from toxicant concentrations but also from their interactions, relative potency and sediment characteristics that ultimately determine bioavailability.

Seasonal variation of Zn, Pb, Cu and Cd concentrations in the root-sediment system of Spartina maritima and Halimione portulacoides from Tagus estuary salt marshes

Concentrations of Zn, Pb, Cu and Cd have been determined in leaves, stems and roots of Spartina maritima and Halimione portulacoides from the Tagus estuary salt mash (Corroios) and in the sediments between their roots. Biological materials and sediments were sampled every 2 months, between July 1991 and July 1992. Root biomass increased from July to September and from January to March. The greatest metal concentrations occurred in the roots, with lowest levels in January and increasing levels during the growth periods. Zn, Pb and Cu in sediments exhibited a corresponding change in concentrations, reaching maximum in January and subsequently decreasing in spring. The ratios between metal concentrations in the root and in sediments were higher for H. portulacoides when compared to S. maritima, whose roots are surrounded by a more acidic and reduced sediment environment. It was concluded, therefore, that H. portulacoides is a more effective accumulator of metals than S. maritima, and both root-sediment systems exhibited a seasonal variation of metal concentrations.

Metal Remobilisation during Resuspension of Anoxic Contaminated Sediment: Short-Term Laboratory Study

The sediments of the Tagus estuary North Channel arecharacterised by high concentrations of trace metals andmonosulphides. During dredging operations Cd, Cu and Pb wereanalysed in water and suspended sediments collected 50 to 100 m around the dredging point. Concentrations in bothfractions fluctuated randomly: 2–3 fold for Cd and Cu and 10 for Pb. Since sampling in the dredging point reflectsintegration of rapid chemical reactions, a short-termlaboratory experiment was conducted to follow the geochemicalalterations occurring in the highest turbidity sites. Theexperiment was monitored as a function of time over a period of4 hr in short time intervals. Dissolved oxygen, pH, EH,AVS, SO42-, Cl- and metals were monitored in theslurry samples. Iron, Mn, Cd, Pb and Cu were determined in thedissolved fraction (<0.45 μm), in the reactive solid phaseand in the total fraction. Resuspension resulted in asignificant release of Fe, Mn, Cd, Cu and Pb from the solids.Following the release Pb and Cu were almost totally scavengedin the 4 hr by the newly precipitated Fe oxyhydroxides, while more than 50% of the mobilised Cd remained in the dissolved fraction. The less efficient removal of Cd from solution implies a prolonged availability of this metal in the environment.

Suspended sediment fluctuations in the Tagus estuary on semi-diurnal and fortnightly time scales

Abstract Nine multi-ship synoptic surveys of the distribution of suspended sediment, each survey including the distribution at both low and high tide, were carried out over a 12-month period in the mesotidal Tagus estuary in Portugal. Additional measurements of the semi-diurnal fluctuations of suspended sediment concentration and current strength were made at fixed stations during a neap and a spring tide. During the study period, the river discharge of water and suspended sediment remained below the mean annual discharge and did not show a pronounced seasonal fluctuation. A turbidity maximum, defined as an area with suspended sediment concentrations greater than 50 mg l −1 , was absent during neap tides (1·3-m amplitude), but appeared and grew in both extent and turbidity as the tidal amplitude increased. The turbidity maximum was fully developed during spring tides (> 3-m amplitude) with concentrations greater than 50 mg l −1 throughout the entire estuary. Maximum concentrations, reaching as much as 1000 mg l −1 during spring tides, were always found in the inner shallow bay region of the estuary. In contrast to the salinity distribution, which fluctuated between partly stratified during neap tides and well mixed during spring tides, the vertical distribution of suspended matter in the turbidity maximum zone was always stratified with the highest concentrations near the bottom. The semi-diurnal fluctuation of the suspended sediment concentration was negligible during neap tides, but attained magnitudes during spring tides that were comparable to the fortnightly fluctuation. The fluctuation in suspended matter concentration is interpreted as a fortnightly erosion-sedimentation cycle, caused by a cyclic variation in the strength of the bottom currents. Superimposed on this fortnightly cycle is a semi-diurnal cycle. The amount of material involved in these cycles is equivalent to one years input of suspended sediment by the Tagus river during normal discharge conditions.

Stock and losses of trace metals from salt marsh plants.

Pools of Zn, Cu, Cd and Co in the leaf, stem and root tissues of Sarcocornia fruticosa, Sarcocornia perennis, Halimione portulacoides and Spartina maritima were analysed for a Tagus estuary (Portugal) salt marsh. Pools of Cu and Cd in the salt marsh were higher in spring/summer, indicating a net uptake of these metals during the growing season. Standing stocks of Zn, Cu, Cd and Co in the leaf and stem biomass of S. fruticosa, S. perennis and H. portulacoides showed a strong seasonal variation, with higher values recorded in autumn. The metal-containing leaves and stems that shed in the autumn become metal-containing detritus. The amount of this material washed out from the total marsh area (200 ha) was estimated as 68 kg of Zn, 8.2 kg of Cu, 13 kg of Co and 0.35 kg of Cd. The high tidal amplitude, a branched system of channels and semi-diurnal tidal cycle greatly favour the export of the organic detritus to adjoining marsh areas.

Accumulation and biological cycling of heavy metal in four salt marsh species, from Tagus estuary (Portugal)

Pools of Zn, Cu, Cd and Co in leaf, stem and root tissues of Sarcocornia fruticosa, Sarcocornia perennis, Halimione portulacoides and Spartina maritima were analyzed on a bimonthly basis, in a Tagus estuary salt marsh. All the major concentrations were found in the root tissues, being the concentrations in the aboveground organs neglectable for sediment budget proposes, as seen by the low root-aboveground translocation. Metal annual accumulation, root turnovers and cycling coefficients were also assessed. S. maritima showed the higher root turnovers and cycling coefficients for most of the analyzed metals, making this a phytostabilizer specie. By contrast the low root turnover, cycling coefficient and low root necromass generation makes S. perennis the most suitable specie for phytoremediation processes. Although the high amounts of metal return to the sediments, due to root senescence, salt marshes can still be considered sinks of heavy metals, cycling heavy metals mostly between sediment and root.

Accumulation of Mercury in Sea Bass from a Contaminated Lagoon (Ria de Aveiro, Portugal)

This work reports the distribution of total mercury (Hg) in Dicentrarchus labrax (sea bass) and in material collected in plankton nets from an inner basin contaminated with the effluent from a chlor-alkali plant, and in other locations of a coastal lagoon (Ria de Aveiro, Portugal). Mercury concentrations were higher in material collected in 200 than in 63 μm mesh net. Mercury in seston decreased pronouncedly with the distance to the industrial source (1.3–0.015 μg g−1 on a wet weight basis), and was higher at low tide than at high tide. This indicates that mercury is exported from the contaminated basin through the first levels of the estuarine chain. Mercury was analysed in muscle, liver, gills and stomach content of sea bass. Specimens captured in the contaminated basin showed higher accumulation of mercury: levels in muscle and liver of young specimens exceeded 1 μg g−1 and 2 μg g−1, respectively; gills and stomach content also presented higher concentrations. Mercury increased more drastically in liver than in muscle of specimens exposed to high contamination, changing the liver/muscle Hg ratio. Although juveniles exhibited higher concentrations in the contaminated basin than in other areas, there is an age effect on the accumulation of mercury in sea bass at the contaminated basin. Occasionally, intermediate concentrations were found in specimens captured in other areas of the lagoon.

Study of the Ria Formosa ecosystem : benthic nutrient remineralization and tidal variability of nutrients in the water

Exchange of nutrients across the sediment-water interfaces of Ria Formosa was studied in the laboratory. In the field, water samples were collected (i) fortnightly, at low and high tide over one year, and (ii) semi-diurnally, over three neap-spring tidal cycles in winter. Results from both laboratory experiments and field collection were quite variable. Higher liberation rates of silicates, phosphates and ammonium occurred in chambers whose bottom was formed by mixtures of mud and sand covered by vegetation with clams. The bottom took up nitrates from the overlying water. Nutrient variations in the lagoon water were controlled both seasonally and tidally. Higher concentrations of silicates were found at low tide independently of the season; phosphates in spring/summer at low tide; nitrates in winter/spring at high tide. Tidal flushing appears to be an important removal-mechanism in this lagoon.

Effect of plants on sulphur geochemistry in the Tagus salt-marshes sediments

Depth distributions of salinity, pH, Eh, sulphate (SO 4 2- ), thiosulfate (S 2 O 3 2- ), sulphite (SO 3 2- ), hydrogen sulphide (H 2 S) and acid volatile sulphides (AVS) were measured seasonally in pore waters of vegetated and non-vegetated sediments of a Tagus salt-marsh colonized by Spartina maritima. Near-bottom water was also analyzed. The vertical distributions obtained in both sites were compared. The vegetated site was more acid (6.0-7.0) and oxidative (reaching + 360 mV vs. H), and presented higher SO 4 2- concentrations (10-31 mM). At depth of higher root density, AVS and H 2 S levels were low (0.1-53 μmol g -1 and < 0.1-0.5 μM, respectively) in comparison to vegetated sediments (30-225 μmol g -1 and 0.5-17 μM). S 2 O 3 2- was only detected in anoxic non-vegetated sediments (11-54 μM) and concentrations increased with depth. Differences of sulphur speciation between the two sites were recorded during all seasons as result of Spartina activity almost the entire year.