Browsing by Author "Duarte, Armando"
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- Effect of organic matter on determination of reactive mercury in contaminated watersPublication . Ramalhosa, Elsa; Río-Segade, Susana; Pereira, Eduarda; Vale, Carlos; Duarte, ArmandoDissolved reactive mercury was determined in water samples from Ria da Aveiro, a coastal lagoon contaminated by mercury. Concentrations increased with acid dilution to a maximum of 193% in samples containing organic matter with high aromaticity, as inferred from absorbances at 250, 280 and 365 nm. Laboratory experiments with potassium hydrogenoftalate and humic acids solutions proved the influence of aromaticity in complexing mercury, how acid dilution protonates the aromatic Hg-complexes and consequent release of labile forms of mercury to solution. On the basis of these results it is proposed that natural waters from mercury contaminated ecosystems should be analysed without dilutions, otherwise additional studies should be performed to access the protonation of mercury organic complexes.
- Mercury behaviour in the water column of an impacted coastal lagoon: Ria de Aveiro (Portugal) as a case studyPublication . Ramalhosa, Elsa; Pereira, Eduarda; Duarte, ArmandoAs mercury presents high toxicity and is of great concern when dealing with protection of human health, mercury pollution related issues are the main subject of this work. At first, two general themes are discussed, namely: I) Mercury: highlights of physicochemical and biogeochemical properties of interest and of the main natural and anthropogenic metal sources; and II) Biogeochemical cycling of mercury in the water column of natural waters. Secondly, a case study performed in Ria de Aveiro (Portugal) during the last 10 years will be presented, focusing on water column processes. Ria de Aveiro is a coastal lagoon, located along the Atlantic Ocean on the north-western coast of Portugal, which was subjected to a discharge of an effluent rich in mercury from a chlor-alkali industry, during more than five decades. In the last seventeen years, the industry changed its technology and the discharge of anthropogenic mercury diminished considerably. However, the dissolved total and reactive mercury concentrations, as well as the total mercury contents determined in the suspended particulate matter, obtained in a particular area of Ria de Aveiro, namely Largo do Laranjo, during the years of 1997 to 2000, are still high in comparison to other locals located world wide. In Largo do Laranjo water column, mercury does not show a conservative behavior, due to the inexistence of a linear relationship between the dissolved total mercury concentrations and salinity. Owing to this, mercury behavior is variable and seems to result from a mixture of different phenomena. One of the most important factors that affect the dissolved mercury behavior is the dissolved organic matter, as a significant correlation is found between both parameters (r=0.788). The mercury partition evaluation performed in Largo do Laranjo water column shows that in both tide conditions, the dissolved and particulate fractions are important for mercury transport and distribution in Largo do Laranjo. However, mercury is more closely associated with the particulate phase (58 to 77%) than with the dissolved fraction. Moreover, this case study also allows verifying that Largo do Laranjo still is a mercury source to the rest of Ria de Aveiro, as the estimated annual mean quantities of mercury that are transported in the dissolved and particulate fractions from the end of Largo do Laranjo, namely Cais do Chegado, to seaward are of 38 and 60 kg, respectively.
- Mercury cycling between the water column and surface sediments in a contaminated areaPublication . Ramalhosa, Elsa; Río-Segade, Susana; Pereira, Eduarda; Vale, Carlos; Duarte, ArmandoMercury cycling in the water column and upper sediments of a contaminated area, the Largo do Laranjo, Aveiro (Portugal), was evaluated after determination of reactive and non-reactive mercury concentrations in the water column and pore waters of sediments, collected in several places of this bay. In the water column, reactive mercury concentrations varied between 10 and 37 pmol dm−3, the highest values being observed near the mercury anthropogenic source. However, reactive mercury was a narrowly constrained fraction of the total mercury, making up only 4–16% of the total, showing evidence of the importance of dissolved organic matter on mercury transport. In sediments, higher concentrations of mercury were also determined near industrial discharges. Results indicate the existence of an equilibrium between solid and liquid phases, determined by solid sediment/pore water distribution coefficients. Much of the mercury present in the solid fraction is associated with organic matter (r=0.837) and iron oxyhydroxides (r=0.919), but as oxides begin to dissolve in reduced sediments and organic matter decays, the adsorbed mercury is released. In fact, the mercury concentrations in pore waters of those contaminated sediments largely exceeded the values determined in the water column. As molecular diffusion may contribute to the dissolved mercury distribution in the overlying water column, this phenomenon was evaluated. However, the pore waters of Largo do Laranjo do not enrich the water column substantially in terms of reactive and non-reactive mercury. In fact, pore waters can contribute only to 0.2% and 0.5% of the reactive and non-reactive mercury present in the water column, respectively, showing that as long as mercury is being incorporated in sediments, it stays in stable forms.
- Microwave treatment of biological samples for methylmercury determination by high performance liquid chromatography-cold vapour atomic fluorescence spectrometryPublication . Ramalhosa, Elsa; Río-Segade, Susana; Pereira, Eduarda; Vale, Carlos; Duarte, ArmandoA simple and rapid microwave-assisted alkaline digestion procedure was developed in combination with high performance liquid chromatography-ultraviolet post-column oxidation-cold vapour atomic fluorescence spectrometric detection for methylmercury determination in biological tissues. Since the stability of methylmercury in methanolic potassium hydroxide solution under microwave irradiation was verified, the microwave-assisted extraction procedure was optimized in terms of quantitative recovery of methylmercury and minimum time required. The alkaline extracts were subjected to clean-up steps with dichloromethane and hydrochloric acid in order to reduce matrix interferences in methylmercury determination. The effects of matrix interferences were checked by comparison of the slopes corresponding to calibration and standard addition curves. The accuracy of the method was evaluated by the analysis of two biological certified reference materials, NRC TORT-2 and BCR 463. The results obtained by the proposed method were in good agreement with the certified values of methylmercury concentration in both materials. The detection limit was 10 mug kg(-1) and the relative standard deviation was < 8% for methylmercury concentrations ranging from 0.15 to 3.0 mg kg(-1).
- Microwave-assisted extraction for methylmercury determination in sediments by high performance liquid chromatography-cold vapour-atomic fluorescence spectrometryPublication . Ramalhosa, Elsa; Río-Segade, Susana; Pereira, Eduarda; Vale, Carlos; Duarte, ArmandoA simple and rapid procedure for methylmercury extraction from sediments based on microwave-assisted alkaline digestion with methanolic potassium hydroxide was optimized on parameters such as microwave power, extraction time and sample size. Organomercury species were extracted with dichloromethane in hydrochloric acid medium and back-extracted into ultra-pure water. The sediment extracts were injected into an analytical system composed of high-performance liquid chromatography-ultraviolet-post-column oxidation-cold vapour-atomic fluorescence spectrometry (HPLC-UV-PCO-CV-AFS) for methylmercury determination. Quantitative methylmercury recoveries were obtained when 0.15 g of sediment were suspended into 6 mi of 25% m/v methanolic potassium hydroxide and the slurry was exposed to microwave irradiation at 84 W for 2 min. The detection limit of proposed method was 12 ng g(-1) while the relative standard deviation was less than 5%. The method was validated by the analysis of two sediment certified reference materials and the methylmercury concentrations found were in good agreement (95% confidence level) with the certified values.
- Monomethylmercury behaviour in sediments collected from a mercury-contaminated lagoonPublication . Ramalhosa, Elsa; Río-Segade, Susana; Pereira, Eduarda; Vale, Carlos; Duarte, ArmandoSurface sediments and sediment cores were collected in a mercury (Hg)- contaminated lagoon, namely Largo do Laranjo – Ria de Aveiro, Portugal and analysed in order to establish the monomethylmercury (MeHg) behaviour in this kind of environment. In surface sediments, this compound was only detected in one place (13.2 ng g-1 (dry weight)). In this site, it was determined one of the lowest redox potentials (22 mV), indicative of oxic/anoxic conditions, which favours Hg methylation by enhancing the sulphate-reducing bacteria activity. However, the MeHg percentage obtained was low, namely less than 0.1% of the total Hg. This is probably due to Hg deposition with organic matter and iron oxyhydroxides, decreasing Hg availability to methylation. At the deeper layers, MeHg was also determined, reaching 46.4 ng g-1 (dry weight) and representing less than 0.1% of the total Hg. The higher MeHg percentages were observed near the surface, where Hg seems to be faster methylated as a result of the lower sulphide concencentrations that render bioavailable the inorganic Hg. At depth the low MeHg percentages obtained are due to the formation of HgS and to the adsorption of Hg to iron monosulphides.
- Storage and export of mercury from a contaminated bay (Ria de Aveiro, Portugal)Publication . Ramalhosa, Elsa; Monterroso, Paulo; Abreu, Sizenando; Pereira, Eduarda; Vale, Carlos; Duarte, ArmandoMercury has been determined in water, suspended particulate matter (SPM) and sediments (solid fraction and pore water) collected in a heavily contaminated confined area (Largo do Laranjo) of the Ria de Aveiro. Mercury has been analysed in seabass (Dicentrarchus labrax) captured in several locations of the lagoon. The levels of mercury in water and SPM in the contaminated sampled places fluctuated daily with the tide (from 10 to 53 ng.dm-3 and 3.5 to 26 ug.g-1, respectively), indicating the export at the tidal rhythm. Bottom sediments exhibited higher concentrations, the maximum (48 ug.g-1) occurring near the anthropogenic source at depths corresponding to the periods of higher industrial discharges. Mercury concentrations in pore waters (max. 80 ng.dm-3) exceed the values found in the water column and were higher at depths where Acid Volatile Sulphides (AVS) presented broad maximums. This implies a remobilization at anoxic conditions. However, the export across the sediment-water interface predicted through molecular diffusion is low (between 1 to 4 x 10-3 ng.cm-2.h-1) in comparison to the industrial input. The anthropogenic mercury appears to be rapidly accumulated in seabass, a predator fish that enter seasonally in Largo do Laranjo.