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Abstract: After having estimated the patterns of flow to the ocean and found some seasonal and tidal differences, mainly with regard to the relative importance of dissolved and particulate fractions, mercury partitioning at the interface between a contaminated lagoon and the Atlantic Ocean was investigated during four tidal cycles in contrasting season and tidal regimes. Mercury was found to be located predominantely in the particulate fraction throughout the year, contributing to its retention within the system. Seasonal conditions, variations in marine and fluvial signals and processes affecting bed sediment resuspension influenced the character and concentration of suspended particulate matter in the water column. Variation in the nature, levels and partitioning of organic carbon in the particulate fraction affected levels of particulate mercury as well as mercury partitioning. These results highlight the dominant role of suspended particulate matter in the distribution of anthropogenic mercury and reinforce the importance of competitive behavior related to organic carbon in mercury scavenging. [ABSTRACT FROM AUTHOR]

In the presence of metal stress, plants can resort to a series of tolerance mechanisms. Therefore field studies should be undertaken in order to evaluate the real role of these mechanisms in stress coping. The aim of this paper was to clarify the biochemical processes behind mercury tolerance in Halimione portulacoides (L.) Aellen (Caryophyllales: Chenopodiaceae) collected in a mercury contaminated salt marsh. Different fractions of mercury were separated: buffer-soluble (mainly cytosolic) and insoluble mercury (mainly associated with membranes and cell walls). The amounts in each fraction of metal were compared and related to metal distribution within plant organs. Protein–mercury complexes were isolated and analysed for their thiol content in order to assess wether the tolerance of this salt marsh plant was associated with the induction of metal chelation by phytochelatins. Overall, the mercury tolerance strategies of the plant are likely to involve root cell wall immobilization as a major mechanism of metal resistance, rather than metal chelation in the cytosolic fraction. Nevertheless, phytochelatins were demonstrated to chelate mercury under environmental exposure. [Copyright &y& Elsevier]

Mercury concentrations were quantified in Halimione portulacoides (roots, stems and leaves) as well as in sediments from eight Portuguese estuarine systems, covering seventeen salt marshes with distinct degrees of mercury contamination. The concentration of mercury in the sediments ranged from 0.03 to 17.0μgg−1. The results show that the accumulation of mercury differed according to the organ of the plant examined and the concentration of mercury in the sediments. Higher mercury concentrations were found in the roots (up to 12.9μgg−1) followed by the leaves (up to 0.12μgg−1), while the stems had the lowest concentrations (up to 0.056μgg−1). A linear model explained the relation between the concentrations of mercury in the different plant organs: roots and stems , stems and leaves and roots and leaves . However, the results show that the variation of mercury concentration in the roots versus mercury concentration in the sediments was best fitted by a sigmoidal model . Mercury accumulation in the roots can be described in three steps: at a low range of mercury concentrations in the sediments (from 0.03 up to 2μgg−1), the accumulation of mercury in roots is also low reaching a maximum concentration of 1.3μgg−1; the highest rates of mercury accumulation in the roots occur in a second step, until the concentrations of mercury in the sediments reach approximately 4.5μgg−1; after reaching this maximum value, the rate of mercury accumulation in the roots slows down leading to a plateau in the concentration of mercury in the roots of about 9.4μgg−1, which corresponds to a mercury concentration in the sediments of about 11μgg−1. A linear model explained also the accumulation of mercury in leaves versus the mercury concentration in the sediments . Differences in responses of roots and leaves are explained by the dynamics of the plant organs: old roots are mineralised in situ close to new roots, while leaves are renewed. Previous studies have already shown that H. portulacoides is a bioindicator for mercury and the results from this work sustain that H. portulacoides may also be used as a biomonitor for mercury contamination in salt marshes. Nevertheless, caution should be taken in the application of the models, concerning the life cycle of the species and the spatial variability of the systems. [Copyright &y& Elsevier]

The present study intends to increase the knowledge on the mobility of mercury in a salt marsh colonised by Halimione portulacoides. Mercury distribution in the sediment layers and its incorporation into the plant biomass were assessed, as well as the potential export of mercury from the contaminated area to the adjacent environment. Mercury pools in the sediments ranged from 560 to 943mgm−2 and are largely associated with the solid fraction, with just a small amount being associated with the pore waters. Estimated diffusive fluxes of reactive mercury ranged from 1.3 to 103ngm−2 d−1. Despite the above ground biomass values being comparatively higher than below ground biomass values, the mercury pools were much higher in the root system (0.06–0.16mgm−2 and 29–102mgm−2, respectively). The annual bioaccumulation of mercury in above ground tissues was estimated in 0.11mgm−2 y−1, while in below ground biomass the values were higher (72mgm−2 y−1). The turnover rates of H. portulacoides biomass suggest higher mercury mobility within the plant rhizosphere. Taking into account the pools of mercury in above ground biomass, the export of mercury by macro-detritus following the “outwelling hypothesis” is not significant for the mercury balance in the studied ecosystem. The mercury accumulated in the below ground part of the plant is quite mobile, being able to return to the sediment pool throughout the mineralisation process. [Copyright &y& Elsevier]

This study was carried out in the Laranjo basin (Ria de Aveiro, Portugal), an area impacted by mercury discharges. Liza aurata oxidative stress and biotransformation responses were assessed in the liver and related to total mercury (Hgt) concentrations. A seasonal fish survey revealed a sporadic increase in total glutathione (GSHt) and elevated muscle Hgt levels, although Hg levels did not exceed the EU regulatory limit. As a complement study, fish were caged for three days both close to the bottom and on the water surface at three locations, and displayed higher Hgt levels accompanied by increased GSHt content and catalase activity as well as EROD activity inhibition. The bottom group displayed higher hepatic Hgt and GSHt contents compared with the surface group. Globally, both wild and caged fish revealed that the liver accumulates higher Hgt concentrations than muscle and, thus, better reflects environmental contamination levels. The absence of peroxidative damage in the liver can be attributed to effective detoxification and antioxidant defense. [Copyright &y& Elsevier]

Abstract: During four decades, the Ria de Aveiro was subjected to the loading of mercury from a chlor-alkali industry, resulting in the deposition of several tons of mercury in the sediments. The present study evaluates the impact of this disturbance and the recovery processes, temporally and spatially, by means of examining the richness of the species of salt marsh plants and mercury concentrations in sediments over the last fifty years. The temporal assessment showed that the mercury loading induced a shift in the species composition of the salt marsh from a non-disturbed salt marsh with higher species richness to an alternative state dominated by Phragmites australis. The horizontal assessment, through a mercury gradient, presents the same trend, indicating that P. australis is the species most tolerant to higher mercury concentrations, comparative to Halimione portulacoides, Arthrocnemum fruticosum, Triglochin maritima, Juncus maritimus and Scirpus maritimus. After the reduction of mercury discharges in 1994, the salt marsh shows a slowly return path recovery response. The hysteresis in the response results in the temporal gap between the reduction in mercury concentrations in the sediment and the salt marsh species richness response, comparatively to the existing diversity in the local reference marsh. [Copyright &y& Elsevier]

Abstract: Determinations of dissolved reactive and total dissolved mercury, particulate and sedimentary mercury, dissolved organic carbon (DOC), particulate organic carbon (POC) and suspended particulate matter (SPM) have been made in the estuary of river Douro, in northern Portugal. The estuary was stratified by salinity along most of its length, it had low concentrations of SPM, typically <20mgdm−3, and concentrations of DOC in the range <1.0–1.8mgdm−3. The surface waters had a maximum dissolved concentration of reactive mercury of about 10ngdm−3, whereas for the more saline bottom waters it was about 65ngdm−3. The surface waters had maximum concentrations of total suspended particulate mercury of ∼7μgg−1 and the bottom waters were always <1μgg−1. Concentrations of mercury in sediments was low and in the range from 0.06 to 0.18μgg−1. The transport of mercury in surface waters was mainly associated with organic-rich particulate matter, while in bottom waters the dissolved phase transport of mercury is more important. Lower particulate organic matter, formation of chlorocomplexes in more saline waters and eventually the presence of colloids appear to explain the difference of mercury partitioning in Douro estuarine waters. [Copyright &y& Elsevier]

The influence of the colonization of salt marsh sediments with Halimione portulacoides was evaluated by analysing the fluorescent dissolved organic matter (FDOM) in sediment pore waters from a salt marsh at different depths. Cores of sediments at colonized and non-colonized sites were collected from a coastal lagoon (Ria de Aveiro, Portugal). The DOC content of extracted pore waters was determined and characterized by synchronous molecular fluorescence (Δλ =60nm) and UV–visible spectroscopies. The common practice of freezing sediment cores for further and later chemical investigation was shown not to be an appropriate methodology of sample preservation. On the contrary, freezing of extracted and filtered pore water seemed not to affect either the DOC content or the fluorescence properties of pore waters. Two types of fluorescent substances were found in the pore waters spectra; one corresponding to humic-like substances and another one resembling proteins. However, major differences were found in the spectra of pore waters depending on both depth and the presence/absence of vegetation colonization. [Copyright &y& Elsevier]

Abstract: The influence of the colonization of salt marsh sediments with Sarcocornia perennis on the DOM quantity and its nature in the water column was evaluated by way of UV–visible and molecular fluorescence spectroscopy. Different light conditions occur along the night and the day periods, while, in parallel, flooding conditions vary along consecutive tidal cycles. Thus, a 24hour field assessment was carried out in order to encompass the daily (day/night) and intertidal (high/low tide) variations. The E 2:E 3 ratio and spectral slope (S) from UV–visible spectra pointed to an export of compounds of high molecular weight (MW) to surface waters during the tidal ebbing at the colonized site. Furthermore, three main types of fluorescent compounds were found in the water synchronous fluorescence spectra: one corresponding to protein-like compounds and two to humic-like compounds. Fluorescence intensity increased during tidal ebbing, both during the day and during the night and especially for water from the colonized site. However, major increases occurred for the protein-like fluorescence band at the S. perennis colonized site during the nocturnal tide ebbing, which may be related to the activity of plants at the rhizosphere. [Copyright &y& Elsevier]

Abstract: A proficiency-testing scheme concerning total mercury determination in soils and sediments (with different levels of contamination) and fish tissue involved 25 European laboratories as participants, who used their regular in-house analytical methods, and reference values were determined from the results obtained. The most precise results were obtained for the fish matrix. The majority of participants obtained satisfactory Z-scores, and laboratories that need to revise their procedures were singled out. When compared with performances in other previous interlaboratory exercises for total mercury, the overall performance of participants may be considered satisfactory, and the ability to produce results of acceptable quality for mercury appears to be improving. [Copyright &y& Elsevier]