M. Teresa S.D. Vasconcelos

Macrobenthic community in the Douro estuary: relations with trace metals and natural sediment characteristics.

The relationship between macrobenthic community structure and natural characteristics of sediment and trace metal contamination were studied in the lower Douro estuary (Portugal, NW, Iberian Peninsula), using an innovative threefold approach (SQG, Sediment Quality Guidelines), metal normalization to Fe, and macrobenthic community structure. This study allowed detection of a clear signature of anthropogenic contamination, in terms of Zn, Cu, Pb, and Cr in the north bank of the estuary, which experiences high urban pressure. Using the SQG approach, metal concentrations above ERM (effects range-median) were observed only at one sampling station, but several stations had levels above ERL (effects range-low). The macrobenthic community had a low diversity, with only 19 species found in the entire estuarine area, dominated by opportunistic species. The granulometric distribution of the sediments (estimated from the combination of organic matter, Fe and Al) seemed to be the major structuring factor for the communities, establishing the natural macrobenthic distribution pattern. The metals (Zn, Cu, Pb, and Cr) seemed to act as a disturbing factor over the natural distribution, with deleterious consequences for the macrobenthic communities.

Allelopathy in freshwater cyanobacteria.

Freshwater cyanobacteria produce several bioactive secondary metabolites with diverse chemical structure, which may achieve high concentrations in the aquatic medium when cyanobacterial blooms occur. Some of the compounds released by cyanobacteria have allelopathic properties, influencing the biological processes of other phytoplankton or aquatic plants. These kinds of interactions are more easily detectable under laboratory studies; however their ecological relevance is often debated. Recent research has discovered new allelopathic properties in some cyanobacteria species, new allelochemicals and elucidated some of the allelopathic mechanisms. Ecosystem-level approaches have shed some light on the factors that influence allelopathic interactions, as well as how cyanobacteria may be able to modulate their surrounding environment by means of allelochemical release. Nevertheless, the role of allelopathy in cyanobacteria ecology is still not well understood, and its clarification should benefit from carefully designed field studies, chemical characterization of allelochemicals and new methodological approaches at the “omics” level.

Influence of the nature of the exudates released by different marine algae on the growth, trace metal uptake and exudation of Emiliania huxleyi in natural seawater

Marine phytoplankton are known to release metal complexing ligands but little is known about the effect of exudates on the biological behaviour of the different microorganisms, including their toxicity and influence on trace metal availability. In this study,cultures ofEmiliania huxleyigrownin filtered seawater,enriched withnitrate andphosphateaswellasits ownexudates and those ofPhaeodactylum tricornutum,Porphyraspp. andEnteromorphaspp.,were used to investigate the effectsofalgal exudates on algal growth, uptake (extracellular adsorption plus intracellular uptake) of Cu, Pb, Cd, Zn, Fe, Mn, Ni and Co, and extent of exudation. Cathodic and anodic stripping voltammetry (CSVand ASV) were used to determine metals, both in the medium and taken up by the algae, and total complexing organic ligands in the medium. Among these ligands, thiol compounds (cysteine-like and glutathione-like) were quantified in the exudates of different origins and during the growth of E. huxleyi in media enriched with them. An improvement of the final cell yield of E. huxleyi was caused by the addition of Enteromorpha exudates (the richest inglutathione-likecompounds),andgrowthinhibition(adecreaseoffinalcellyieldandgrowthrate)wascausedbytheadditionof P. tricornutum exudates (the richest in cysteine-like compounds). The nature and concentration of the organic compounds present in the culture medium also influenced trace metal uptake and the concentration and composition of the exudates produced by E. huxleyi. Therefore, it can be speculated that a bloom of a species of algae that produces large amounts of specific exudates may favour or inhibit the local growth of other algal species and, in an extreme situation, change the biodiversity. D 2002 Elsevier Science B.V. All rights reserved.

Biomonitoring with benthic macroalgae and direct assay of heavy metals in seawater of the Oporto coast (Northwest Portugal)

The concentrations of dissolved Cd, Cu, Hg and Pb in seawater and algae (Enteromorpha spp. and Porphyra spp.) were determined in parallel on three beaches located in the Oporto coast (Portugal), during 8 successive months, comprising periods of low and high biological productivity. The concentrations of dissolved metals in seawater varied markedly during the sampling period and exhibited seasonality. The concentrations of Cd were high in autumn and winter, but low in spring. The concentrations of Cu and Hg were high in autumn, low in winter and peaked in May. The concentrations of Pb were low in autumn and winter, and also peaked in May. It is likely that biological activity was, at least partially, responsible for the observed seasonal changes. The mean concentrations of dissolved metals in seawater were similar to those reported for polluted and industrialized european coastal areas. Metal concentration factors, calculated month-to-month for each alga, metal and site, varied markedly during the sampling period, indicating that concentration factors based on single or few determinations could be misleading. On the contrary, mean concentration factors (calculated by dividing the mean metal concentration in the algae by the mean metal concentration in seawater) were relatively constant at all three sites, indicating that in the Oporto coast, Enteromorpha spp. can be used to estimate the mean concentration of dissolved Cd, Cu and Hg in seawater, and Porphyra spp., the mean concentration of Cd, Cu and Pb. However, considering that future estimates of the concentrations of these metals in seawater should be based on determinations of the metal contents in Enteromorpha spp. and Porphyra spp. carried out on several occasions spanning a considerable period of time, the use of these algae as monitors of heavy metal pollution can have limited practical advantages over the direct assay of the metals in seawater.

Evaluation of n-substituted aminosulfonic acid pH buffers with a morpholinic ring for cadmium and lead speciation studies by electroanalytical techniques

Abstract The electrochemical behavior of cadmium and lead metal ions was investigated in the presence of different pH buffers [3-(N-morpholino)-2-hydroxypropanesulfonic acid (MOPSO), 2-(N-morpholino)ethanesulfonic acid (MES) and 3-(N-morpholino)propanesulfonic acid (MOPS)] by various methods [differential pulse anodic stripping voltammetry (DPASV), differential pulse polarography (DPP) and cyclic voltammetry (CV)]. The complexation and/or adsorption properties of these pH buffers were also examined. Conclusions about the possible influences of these pH buffers on the speciation studies of cadmium and lead metal ions are drawn. MES, MOPSO and MOPS can be suitable pH buffers for determination of both metals by DPP and DPASV as they do not complex these metals and do not modify to a significant extent the reversibility of the electrochemical processes under the experimental conditions used.

Cyanobacteria Metal Interactions: Requirements, Toxicity, and Ecological Implications

The environmental health-related relevance of cyanobacteria is primarily related to their ability to produce a wide range of toxins, which are known to be hazardous to many organisms, including human beings. The occurrence of cyanobacterial blooms has been related to eutrophic surface water. In the bloom-forming process the levels of phosphorus and nitrogen have been well documented but information regarding concentrations of other chemicals (inorganic, organo-metallic, and organic) is still incipient. Several contaminants, like trace metals, elicit a variety of acute and chronic toxicity effects, but cyanobacteria also have the capability to accumulate, detoxify, or metabolize such substances, to some extent. The role of cyanobacterial exudates has been proved a means of both nutrient acquisition and detoxification. In addition, cyanobacteria are effective biological metal sorbents, representing an important sink for metals in aquatic environment. Understanding the fundamental physicochemical mechanisms of trace metal bio-uptake by cyanobacteria in natural systems is a step towards identifying under what conditions cyanobacterial growth is favored and to ascertain the mechanisms by which blooms (and toxin production) are triggered. In this review the cyanobacterial interactions with metals will be discussed, focusing on freshwater systems.

Can PAHs influence Cu accumulation by salt marsh plants

The presence of polycyclic aromatic hydrocarbons (PAHs) may change the mechanisms of metal uptake, thus influencing kinetics and extent of metal phytoextraction. Studies on the subject are scarce, particularly for salt marsh plants. The aim of this work was to investigate the effect of PAHs on the uptake of Cu by Halimione portulacoides, a plant commonly found in salt marshes. Experiments were carried out in the laboratory, either in hydroponics (sediment elutriate) or in sediment soaked in elutriate, which were prepared with sediment and water from a salt marsh of the Cavado river estuary (NW Portugal). Groups of H. portulacoides (grown in a greenhouse) were exposed to those media during six days. Cu2+ (as Cu(NO3)2), 10(2) and 10(4) microg l(-1), was added to the media as well as 1.6 microg l(-1) of the sixteen EPA priority PAHs (0.1 microg l(-1) of each PAHs). Cu was assayed in solutions, sediments and different plant tissues before and after experiments. After exposure, photosynthetic efficiency and levels of chlorophylls were also measured, indicating that plant stress indicators were identical in all plants independently of the media to which the plants were exposed. PAHs influenced both the soluble Cu fraction and Cu uptake by plants. The amounts of metal accumulated in both roots and stems were significantly higher when the 10(4) microg l(-1) of Cu enriched elutriate was amended with PAHs. Thus, results suggest that PAHs may modify Cu solubility, the Cu sorption by plants and/or the passive penetration of Cu into the root cells. Therefore, the combined effects of different types of pollutants should be taken in consideration when studying the remediation potential of plants, namely in terms of phytoextraction.

Extraction and preconcentration techniques for chromatographic determination of chlorophenols in environmental and food samples

Methods for chlorophenols (CPs) determination (with low limits of detection) that can be applied to real environmental samples (waters, sediments, soils, biological tissues) and food are reviewed. Special emphasis is given to sampling, storage conditions and the application of preconcentration techniques for the determination of CPs using chromatographic methods. Solid phase extraction, solid phase microextraction, stir bar sorptive extraction, liquid phase microextraction, dispersive liquid-liquid microextraction, liquid-liquid-liquid microextraction and purge and trap methods are considered. Methods for microwave and ultrasonic extraction of CPs from solid matrices are also focused.

N-(2-Carboxyethyl)chitosans: regioselective synthesis, characterisation and protolytic equilibria

N-(2-Carboxyethyl)chitosans were obtained by reaction of low molecular weight chitosan with a low degree of acetylation and 3-halopropionic acids under mild alkaline media (pH 8-9, NaHCO3) at 60 degrees C. The chemical structure of the derivatives obtained was determined by 1H and 13C NMR spectroscopies. It was found that alkylation of chitosan by 3-halopropionic acids proceeds exclusively at the amino groups. The products obtained are described in terms of their degrees of carboxyethylation and ratio of mono-, di-substitution and free amine content. The protonation constants of amino and carboxylate groups of a series of N-(2-carboxyethyl)chitosans were determined by pH-titration at ionic strength 0.1 M KNO3 and 25 degrees C.

Speciation of Cu, Pb, Cd and Hg in waters of the Oporto coast in Portugal, using pre-concentration in a Chelamine resin column 1☆

Abstract Sea water was collected monthly between January and March 1996 from the shore of the Oporto coast at three different representative sampling points and speciation of Cu, Pb, Cd and Hg were carried out. For the purpose, total particulate (retained on a 0.45 μm pore-size filter), particulate sorbed to inorganic matter, total dissolved, and dissolved and operationally labile metal was discriminated. The filters were digested by microwaves. The filtered water was pre-concentrated on a microcolumn of Chelamine, eluted with 5 ml of 2 mol l −1 HNO 3 and analysed by flame atomic absorption spectrometry (F-AAS) or mercury cold vapour (MCV-AAS) for Hg. Spike recovery percentages did not differ significantly ( P >0.05) from 100% for any metal studied. The organic matter (OM) destruction was performed by UV photolysis. For quality control of the results, determination of Cu, Pb and Cd total dissolved concentration by differential pulse anodic stripping voltammetry was also performed; for Hg only the pre-concentration in the column was changed to partial evaporation of the sea water, followed by MCV-AAS. No statistically significant difference was observed between the results provided by the comparative methods. Online pre-concentration with Chelamine showed to be expeditious and effective for extraction of the heavy metals in coastal waters. The distribution of each metal in the different fractions, including ascertainment of significant correlation between pairs of metal fractions and the respective partition coefficients, is discussed.