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FACTOR ANALYSIS OF SEDIMENT MERCURY FROM THE TAGUS ESTUARY

The multivariate statistical technique of Principal Component Analysis (PCA) was applied in this ... more The multivariate statistical technique of Principal Component Analysis (PCA) was applied in this work to study interrelationships of sediment parameters and metal speciation data (Hg and MeHg), as well as spatial variations in different sites from Tagus estuary (CN, BRR, ALC and VF). Data pre-treatment and descriptive statistics allowed the interpretation of factors accounting for different patterns of distribution. Screeplots and cumulative percentage of variance as well as factor and score loadings are presented using different data pre-treatment techniques. Analysis were carried out for solid fraction, pore-water and a combination of both. Based on overall results, approximately 80% of data variance is explained in general by three factors in the Tagus estuary. The prominent factor accounted in average for more than 45% of the total variation, generally accompanied with other two factors. Methylmercury, both in dissolved and solid fractions, is one of the factors accounting in da...

Mercury is currently considered one of the most hazardous metals to the environment. Among mercur... more Mercury is currently considered one of the most hazardous metals to the environment. Among mercury compounds, methylmercury (MeHg) presents a serious risk to wildlife due to their known toxicity. Biogeochemistry and fate of MeHg in sediments is still not completely understood due to the complexity of factors influencing methylation, partitioning, and transport. In order to contribute to better knowledge of MeHg biogeochemistry and fate in sediments four sites in the Tagus estuary were selected. Two highly contaminated (CN and BRR: HgT up to 125 μg g-1) and two with moderate contamination (ALCX and PE: HgT<1 μg g-1). Sediment cores were collected (2010) and pore waters were separated by centrifugation. Concentrations of total mercury (Hg) and methylmercury (MeHg) in solid sediments and dissolved Hg (HgR and HgT) and MeHg were quantified in pore waters and overlying water. Other interpretative parameters such as total Al, Si, Fe, Mn, Corg, DOC, Cl-, SO42- and HS- concentrations wer...

METHYLMERCURY SEASONAL AND SPATIAL VARIATIONS IN SEDIMENTS FROM THE TAGUS ESTUARY

Biogeochemistry of methylmercury (MeHg) in sediments is not completely understood, regarding seas... more Biogeochemistry of methylmercury (MeHg) in sediments is not completely understood, regarding seasonal and spatial variations within estuaries. Historical mercury (Hg) contamination in Tagus estuary is known but MeHg variability is poorly documented. Here, seasonality of MeHg is assessed in pore waters for the first time and in solid sediments from two highly contaminated sites (CN and BRR) and two with low to moderate Hg contamination (ALC and VF), contextualized with other relevant environmental parameters. Seasonally retrieved cores indicate that MeHg concentrations generally increase in pore waters with the exception of VF site. Respectively, winter and summer periods account to a maximum amount MeHg/HgT of 20% and 43% in CN, 15% and 86% in BRR, 18% and 95% in ALC and 60% to 25% in VF. On the other hand, few significant correlations (p<0.05) were found for MeHg in the dissolved phase during summer contrarily to the winter period. Despite MeHg/HgT being always less than 1% in s...

Papers by Carlos Monteiro

Improved voltammetric method for simultaneous determination of Pt and Rh using second derivative signal transformation – application to environmental samples

The determination of Platinum-group elements (PGE) in relevant environmental matrices is a challe... more The determination of Platinum-group elements (PGE) in relevant environmental matrices is a challenging task. Sensitive and accurate analytical procedures for simultaneous determination of Pt and Rh are still needed. In this study, we report for the first time on the use of second derivative signal transformation to the ultra-trace simultaneous determination of Pt and Rh by Adsorptive Cathodic Stripping Voltammetry (AdCSV). With that step, the ill-defined peaks typically observed in the original voltammograms are transformed into well-shaped peaks, resulting in accurate detection. The experimental conditions were investigated and optimised: a suitable electrolyte for both elements, with less reagents consumption, (0.25 M H2SO4, 0.05 M HCl, 0.01 M FA and 0.5 mM HZ), deposition time (td) and deposition potential (Ed). For td = 120 s and Ed = −0.75 V, linear relationships r > 0.999 were obtained in the concentration range up to 5.8 ng L−1 (27 pM) for Pt and up to 3.4 ng L−1 (34 pM) for Rh. Limits of detection were 0.2 ng L−1 for Pt and 0.08 ng L−1 for Rh. Lower values can be achieved by increasing the deposition time. Limits of quantification, LOQ, calculated as 3 times LOD, were 0.5 ng L−1 for Pt and 0.2 ng L−1 for Rh. The sensitivity of Pt was affected by elevated Zn concentrations, whereas a minor effect was observed for Rh. However, Pt and Rh determinations were not influenced using the standard addition method. Precision as intermediate precision and expressed as relative standard deviation, based on Pt and Rh spiked solutions and digested road dust CRM BCR-723 was 17% and 20% for Pt and Rh, respectively. Recoveries of CRM were around 90% for both elements. The method was successfully applied in the simultaneous determination of Pt and Rh in sediments from Tagus estuary and, for the first time, dissolved Rh was determined in water samples of a waste water treatment plant. Application of this technique in a multidisciplinary approach will be a relevant contribution to the current understanding of PGE cycle and fate in the environment.

Mercury and Methylmercury Dynamics in Sediments on a Protected Area of Tagus Estuary (Portugal)

Science of The Total Environment, 2014

nZnO with 3 different surfaces were examined: bare, polyacrylic acid and hexametaphosphate. • Par... more nZnO with 3 different surfaces were examined: bare, polyacrylic acid and hexametaphosphate. • Particle agglomeration and particle dissolution were quantified with multiple techniques.

Abstract Seasonal and spatial variations of dissolved and particulate methylmercury were evaluate... more Abstract Seasonal and spatial variations of dissolved and particulate methylmercury were evaluated for the first time in sediment cores from the Tagus Estuary. Results showed the highest MeHg concentrations in summer months indicating that the “seasonally” methylation process occurs not only at the topmost layers of the sediments but also in the deeper layers of the sediment column. The proportion of MeHg (up to 92%) in some of our pore water samples was higher than values reported in the literature for other estuaries suggesting that the sedimentary environment in the Tagus tends to favour Hg methylation. This work points to the importance of seasonal variation of the MeHg production in sediment cores. In physically dominated estuaries this enhances seasonal MeHg production in deeper sediments that can have serious ecological impacts due to resuspension or advection processes under extreme events by the increase of MeHg transported to the water column.

Mercury is one of the major contaminants due to its toxicity and easy bioaccumulates in aquatic s... more Mercury is one of the major contaminants due to its toxicity and easy bioaccumulates in aquatic systems. The Tagus estuary has been contaminated by mercury from an inoperative industrial plant in Barreiro and an operative chloralkali industry in Cala Norte. To better understand Hg distribution in intertidal sediments, sampling campaigns were done covering these contaminated areas and two uncontaminated areas (Alcochete and Vale Frades), during 2010/2011. HgT was analyzed in solid fraction. Pore-waters were separated from sediments cores and analyzed for total and reactive mercury (HgT and HgR). The averaged [HgT] in sediments showed that Barreiro is the most contaminated site (24,2 µg g-1), due to historical industrial activity. Sediments in Cala Norte presented higher average HgT values (7,2 µg g-1) in the first 10-cm depth than in Barreiro (3,8 µg g-1), which may be related to the permanent operational chloroalkaly plant. The uncontaminated sites showed similar average [HgT] (0,50...

$Research paper thumbnail of Influence of an upwelling filament on the distribution of labile fraction of dissolved Zn, Cd and Pb off Cape São Vicente, SW Iberia$

Continental Shelf Research, 2015

Under northerly winds upwelling is recurrent at the Cape São Vicente, SW Iberia, and plays a majo... more Under northerly winds upwelling is recurrent at the Cape São Vicente, SW Iberia, and plays a major role on the distribution of dissolved nutrients and metals. The aim of this work was to characterize the dissolved metals distribution of zinc (Zn), cadmium (Cd) and lead (Pb), associated with a filament of upwelled water that stretches seaward from the Cape. Additionally, the relationships between labile metals and other oceanographic parameters, such as current velocity and wind field patterns, temperature and salinity, nutrients, chlorophyll a and suspended solids were evaluated. The mass transport of the dissolved metals exported offshore was estimated, after a period of relatively strong and persistent upwelling. At the end of October 2004 a total of 42 CTD Rosette casts up to 400 dbar were sampled, distributed on an almost regular grid, together with along-track Acoustic Doppler Current Profile (ADCP) velocities. Seawater samples from two transects across the filament were analysed: one closest to the shore, where upwelling was intense and phytoplankton noticeably grew; and another further offshore where the filament was still well defined, but narrower and less marked despite with the maximum velocity currents. Labile dissolved metals were determined using anodic stripping voltammetry (ASV). The range of the metals recorded at the transect closest to the coast recorded was 0.26-3.8 nM (mean: 0.8 nM) for Zn, 2-11 pM (mean: 3 pM) for Cd and 8-60 pM (mean: 13 pM) while for the offshore transect was: 0.26-5.1 nM (mean: 1.2 nM) for Zn, 2-26 pM (mean 4 pM) for Cd and 8-74 pM (mean: 15 pM). Zinc recorded the highest concentrations, similar at both transects, and like Cd the lowest concentrations were found at near-surface depths. In opposition, the highest Pb concentrations were found at the nearsurface depths at the northern stations in both transects. The filament exported more material in the offshore transect than in the transect closest to the coast, corresponding to a maximum export of $ 135 kmol d À 1 of Zn, 276 mol d À 1 of Cd and $ 1365 mol d À 1 of Pb. The quantification of the cross-shelf fluxes imposed by the filament did show that metals fluxes are strong enough to play a key role in the oceanographic behaviour of the transition zone between the coastal and offshore waters in the region. Considering the periods of strong upwelling events and the extent of their duration along the year, the amounts of exported water mass which include nutrients, metals and particles must be hugely increased and responsible for the high productivity of the waters.

OCEANS 2014 - TAIPEI, 2014

Upwelling filaments are mesoscale structures of cold water that stretch seaward in a tongue-like ... more Upwelling filaments are mesoscale structures of cold water that stretch seaward in a tongue-like shape with origin in the coastal upwelling zone. Filaments represent preferred pathways for the exchange of water, dissolved and particulate matter from the productive shelf region towards the oligotrophic offshore regions. Upwelling filaments are a common feature of the western margin of the Iberian Peninsula. The culminating point of SW Iberia, the Cape São Vicente, is the root of a recurrent well developed filament observed in the satellite imagery during the upwelling season.

Mercury (Hg) in the environment constitutes a threat to aquatic life and human health. Hg mobilit... more Mercury (Hg) in the environment constitutes a threat to aquatic life and human health. Hg mobility and bioavailability can be controlled by organic matter, which plays a complex role in Hg aquatic chemistry. The intertidal sediments surface layer, which is favorably subjected to deposition/erosion changes, is the most reactive layer and plays an important role regarding transport mechanisms such as molecular diffusion, as well as photoreduction of Hg. In order to understand Hg spatial and seasonal distribution on surface layers of intertidal sediments and the influence of organic matter on Hg distribution, sediment cores were collected in summer of 2010 and winter of 2010/2011 in two highly (BR and CN) and two low (AL and VF) Hg contaminated sites. Solid sediments (pore waters previously separated) were analyzed for Hg and organic carbon (OC). Dissolved reactive, non-reactive, and total mercury (HgR, HgNR and HgT), as well as dissolved organic carbon (DOC) in pore waters were quanti...

Mercury (Hg) in the environment constitutes a threat to aquatic life and human health, especially... more Mercury (Hg) in the environment constitutes a threat to aquatic life and human health, especially in its methylated form (MeHg). Among other transport mechanisms molecular diffusion play an important role being responsible for the increase of mercury concentrations in the water column due to the Hg concentrations gradient in pore- and over-lying waters. In this work we hypothesize that mercury and methylmercury diffusive fluxes may very seasonally due to the well know seasonal variation of methylmercury concentrations in surface sediments of the Tagus Estuary. In order to confirm this hypothesis sediment cores and overlaying waters were collected in summer of 2010 and winter of 2010/2011. Sediments were sliced in 1-2 cm and pore-waters were separated. Solid sediments were analyzed for Hg, MeHg. Dissolved reactive and total mercury (HgR and HgT) as well as MeHg were quantified in pore- and overlying waters. No significant differences were observed for total mercury concentrations in ...