Distribution of mercury in the upper sediments from a polluted area (Ria de Aveiro, Portugal)

This work reports levels of Hg, Fe and Mn and sulphides in the upper sediments of the Laranjo Basin, and examines the influence of these elements on the distribution of mercury

Estudo termo-reológico e estrutural de peças obtidas por microinjeção

Mestrado em Engenharia MecânicaNas últimas décadas, a miniaturização dos equipamentos eletrónicos e apar- elhos mecânicos tem sido uma tendência em constante desenvolvimento. A micromoldação por injeção é uma das técnicas mais utilizadas para obtenção de microcomponentes plásticos para os mais variados propósitos. Através desta técnica é possível obter microcomponentes em grandes quantidades e a baixo custo, usufruindo ainda do alto nível da automação inerente ao processo. Contudo, durante o processo de moldação são originadas ten- sões residuais internas nas peças moldadas, devido ao escoamento do fun- dido e ao arrefecimento e solidicação do plástico. Neste trabalho propõe- se uma metodologia que contempla a simulação numérica do processo de obtenção de peças plásticas por injeção juntamente com uma análise es- trutural. Esta última visa levar em consideração o histórico do proces- samento bem como o comportamento típico de um material polimérico aquando em serviço. Desse modo, o trabalho inclui o estudo e de nição do comportamento viscoelástico do material. Para tal, são abordadas tam- bém metodologias de análise do comportamento viscoelástico dos materiais. O trabalho divide-se em duas partes principais: a primeira onde são feitos ensaios DMTA para caracterização do comportamento mecânico do material e propostas metodologicas de análise do mesmo através do uso do pricípio de sobreposição tempo-temperatura; a segunda parte incide na obtenção das tensões residuais através da simulação numérica do processo de injecção e da simulação numérica de um ensaio de relaxação de tensões no qual o modelo viscoelástico previamente criado é inserido. Os resultados obtidos permitem conluir a adequabilidade da metodologia desenvolvida, permitindo postular a sua viabilidade na simulação do comportamento de micropeças quando em serviço.In recent decades, the miniaturization of electronic and mechanical equip- ment is a tendency in constant development. Micro-injection is one of the most used techniques for obtaining plastics micro-components for various purposes. Through this technique it is possible to obtain micro-components in large quantities and at low costs, yet taking advantage of the high level of automation inherent to the process. However, during the moulding process, residual stresses start to develop on the part, due to the melt ow and due to the cooling and solidi cation of the plastic. In this study a methodology that addresses the numerical simulation of the injection moulding coupled with a structural analysis is proposed. The latter takes into a count the e ect of residual stresses on the part and the fact that polymers are viscoelastic materials. For this purpose, methodologies to analyse viscoelastic behaviour of polymers are also proposed. This work is composed by two main parts: the first, where DMTA tests are performed to characterize the mechanical behaviour of the material and where analysis methods to handle resultant data are proposed, namely by using the principle of time-temperature su- perposition; the second part relates to obtaining the part residual stresses through the numerical simulation of the injection process and the numerical simulation of a stress relaxation test, in which the previously developed viscoelastic model is a counted for. The obtained results provide an insight on the adequacy of the methodology here developed to assess the durability of the injected microparts when in a duty cycle

Partition, accumulation and speciation of mercury in salt marshes

Doutoramento em QuímicaCom o trabalho desenvolvido nesta tese pretende-se contribuir para um melhor conhecimento do ciclo do mercúrio em sapais; como tal diversos aspectos relacionados com o ciclo biogeoquímico do mercúrio neste tipo de ecossistemas foram abordados, nomeadamente: o impacto que as descargas de mercúrio tiveram nos sapais da baía do Largo do Laranjo bem como o processo de recuperação do sapal (temporal e espacial) pela análise da diversidade do numero de espécies das plantas de sapal e das concentrações de mercúrio no sedimento ao longo do anos; a mobilidade do mercúrio em sedimentos de sapal colonizados pela espécie Halimione portulacoides, a sua distribuição nas camadas de sedimento e a sua incorporação na biomassa subterrânea da planta bem como a potencial exportação de mercúrio do sapal para as áreas adjacentes; o papel das plantas de sapal na conversão de espécies inorgânicas de mercúrio em espécies orgânicas; os processos bioquímicos por detrás do mecanismo de tolerância ao mercúrio da H. portulacoides; avaliação do potencial de uma planta de sapal muito difundida ao longo da costa Portuguesa como biomonitor da contaminação de mercúrio em sedimentos de sapal. A análise dos resultados revelou que as descargas de mercúrio nos sapais da baía do Largo do Laranjo ocorridas no passado induziram uma diminuição na diversidade florística, conduzindo-o a um estado alternativo com a predominância de apenas uma espécie, nos anos de maiores descargas. Após o fim das descargas podemos concluir com base na diversidade do sapal que o sistema demonstra histerese na sua recuperação vindo a recuperar lentamente a sua diversidade florística ao longo dos anos. Em ralação à mobilidade o mercúrio em sedimentos de sapal verificou-se que as taxas de turnover da biomassa subterrânea eram mais elevadas do que as que da biomassa aérea indicando uma maior mobilidade do mercúrio na rizosfera. Tendo em conta o pool de mercúrio encontrado na biomassa aéra verificou-se que a exportação de macro detritos da planta não é significativa para o balanço de mercúrio. Os estudos de especiação de mercúrio realizados nos sedimentos e na biomassa demonstraram que nenhuma outra espécie de mercúrio orgânico foi encontrada para além do MeHg. As concentrações de MeHg nos sedimentos colonizados revelaram-se mais elevadas no entanto as percentagens relativamente aos valores de mercúrio total são baixas. Os resultados sugerem que as plantas de sapal contribuem para a metilação de mercúrio. Os mecanismos de tolerância da H. portulacoides ao mercúrio envolvem essencialmente a sua imobilização nas paredes celulares, contudo o sequestro de mercúrio intracelularmente por fitoquelatinas foi demonstrado neste trabalho. Finalmente demonstrou-se que para além da H. portulacoides ser um bom bioindicador pode também ser usada com um biomonitor da contaminação de mercúrio em sedimentos de sapal.This thesis intends to contribute to the better understand of mercury cycling in salt marsh ecosystems and thus several aspects regarding mercury biogeochemical cycle in salt marshes are discussed, namely the impact of mercury discharges and the recovery processes (temporally and spatially) by the examination of the richness of the species of salt marsh plants and mercury concentrations in sediments over the years; the mobility of mercury in a salt marsh colonised by the species H. and its redistribution in the sediment layers containing plants and subsequently incorporation into below ground biomass, as well the potential export of mercury from the salt marsh to the adjacent areas; the potential role of salt marsh plants on the conversion of inorganic mercury into organic mercury species; the biochemical processes behind mercury tolerance in a salt marsh plant species; the evaluation of the potential role of a well wide distribute salt marsh plant (H. portulacoides) along the Portuguese coast as biomonitor of mercury contamination. The results showed that salt marshes of Laranjo bay shows how a considerable loading of mercury into a salt marsh for four decades has affected its resistance, inducing a change from salt marsh plants species richness into an alternative state dominated by one species. Ten years after the cessation of the loading of mercury and based on the salt marsh plants species richness, the system still shows an incomplete resilience due to the lag in recovery, named hysteresis. With respect to the mercury mobility in the salt marsh sediments, the results shows that the turnover rates for below ground biomass were higher than those observed for above ground biomass, corresponding to higher mercury mobility within H. portulacoides rhizosphere. Taking into account the pool of mercury in above ground biomass, the export of mercury by macro-detritus is not significant for the mercury balance in the studied system. Regarding the mercury speciation studies, no other organic mercury species rather than MeHg were found. MeHg concentrations in the vegetated sediments were higher than in non-vegetated sediments and although the percentages in the sediments were low, comparatively to the total mercury the results suggest that salt marsh plants contribute to methylation in sediments. Mercury tolerance strategies of H. portulacoides seem to involve root cell wall immobilization as a major mechanism of metal resistance, rather than metal chelation in the cytosolic fraction. Intracellular mercury sequestration by PCs in the environment was also demonstrated in this work;however mercury chelation in environmental exposures seems to be a complexed, involving the formation of different types of complexes Finally it was demonstrated that that besides H. portulacoides can be a suitable bioindicator, can also be used as a biomonitor for mercury pollution. Leaves responded following a positive linear model for a contamination range, while roots responded within the sigmoidal model. H. portulacoides may be considered an appealing tool for mercury pollution assessment in salt marshes

Metabolites and biological activities of Thymus zygis, Thymus pulegioides, and Thymus fragrantissimus grown under organic cultivation

Thymus plants are marketed for diverse usages because of their pleasant odor, as well as high nutritional value and wealth of health-promoting phytochemicals. In this study, Thymuszygis, Thymuspulegioides, and Thymusfragrantissimus grown under organic cultivation regime were characterized regarding nutrients and phenolic compounds. In addition, the antioxidant and antibacterial properties of these species were screened. The plants were particularly notable for their high K/Na ratio, polyunsaturated fatty acids content and low omega-6/omega-3 fatty acids ratios, which are valuable features of a healthy diet. Caffeic acid and/or its derivatives, mainly rosmarinic acid and caffeoyl rosmarinic acid, represented the majority of the phenolic constituents of these plants, although they were less representative in T. pulegioides, which in turn was the richest in flavones. The latter species also exhibited the highest antioxidant capacity (DPPH● EC50 of 9.50 ± 1.98 μg/mL and reducing power EC50 of 30.73 ± 1.48 μg/mL), while T. zygis was the most active towards Gram-positive and Gram-negative bacteria. Overall, the results suggest that the three thyme plants grown in organic farming are endowed with valuable metabolites that give them high commercial value for applications in different industries.The authors wish to acknowledge the Foundation for Science and Technology (FCT), the European Union, the National Strategic Reference Framework (QREN), the European Regional Development Fund (FEDER), and Operational Programme Competitiveness Factors (COMPETE), for funding the Organic Chemistry Research Unit (QOPNA) (FCT UID/QUI/00062/2013) and Mountain Research Center (CIMO) (UID/AGR/00690/2013), through national funds and where applicable co-financed by FEDER, within the PT2020 Partnership Agreement. Susana Cardoso wishes to thank the research contract under the project AgroForWealth: Biorefining of agricultural and forest by-products and wastes: integrated strategic for valorisation of resources towards society wealth and sustainability (CENTRO-01-0145-FEDER-000001), funded by Centro2020, through FEDER and PT2020.info:eu-repo/semantics/publishedVersio

Mercury distribution in key tissues of fish (Liza aurata) inhabiting a contaminated estuary-implications for human and ecosystem health risk assessment

This study brings a new viewpoint based on multiple-tissue analyses to form the basis for a predictive mode of mercury accumulation dynamics in fish body under field conditions. Total mercury (T–Hg) was determined in key tissues of Liza aurata captured along an estuarine contamination gradient, displaying the following hierarchy: kidney > liver > muscle > brain > gills > blood. Brain was the tissue that better reflected the mercury contamination extent, closely followed by liver and muscle. Organic mercury (O–Hg) measured in muscle and liver represented more than 85% and less than 30% of the T–Hg, respectively. The lowest O–Hg percentage was found in the most contaminated area, for both muscle and liver. Mercury distribution and accumulation patterns showed dependence on the specific tissue. The high mercury levels found in organs involved in vital physiological processes point out the risk to autochthonous fish fauna. Human risk associated to the ingestion of fish living in the surveyed areas cannot be excluded

Mercury in salt marshes ecosystems: Halimione portulacoides as biomonitor

http://www.sciencedirect.com/science/article/B6V74-4TFV904-1/2/e4e4acaa50b773a40436188282a1f9e

Mercury distribution in Douro estuary (Portugal)

Determinations ofdissolved 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 ofriver Douro, in northern Portugal. The estuary was stratified by salinity along most ofits length, it had low concentrations of SPM, typically <20 mg dm-3, and concentrations of DOC in the range <1.0–1.8 mg dm-3. The surface waters had a maximum dissolved concentration of reactive mercury of about 10 ng dm-3, whereas for the more saline bottom waters it was about 65 ng dm-3. The surface waters had maximum concentrations oftotal suspended particulate mercury of ~7 ug g-1 and the bottom waters were always < l ug g-1. Concentrations of mercury in sediments was low and in the range from 0.06 to 0.18 ug g-1. The transport of mercury in surface waters was mainly associated with organic-rich particulate matter, while in bottom waters the dissolved phase transport ofmercury is more important. Lower particulate organic matter, formation ofchlorocomplexes in more saline waters and eventually the presence of colloids appear to explain the difference of mercury partitioning in Douro estuarine waters

Efeito das plantas na acumulação de mercúrio em sedimentos de sapais

Mestrado em Métodos Instrumentais e Controlo de Qualidade AnalíticaCom o objectivo de estudar o efeito das raízes na distribuição de mercúrio em sedimentos de sapais, foram recolhidos cores de sedimentos, com 60 cm de profundidade, em dois sapais da Ria de Aveiro com diferentes graus de contaminação. Os cores foram recolhidos em áreas não colonizadas e em áreas colonizadas pelo Halimione portulacoides e pelo Arthrocnemum fruticosum. Os cores foram seccionados em camadas de 5 cm de espessura e as raízes de cada camada foram separadas dos sedimentos. Para além dos sedimentos, foram também recolhidas folhas e caules das plantas colonizadoras nos dois sapais. Em cada camada de sedimento procedeu-se à determinação da temperatura, pH, matéria orgânica (LOI e Carbono orgânico), humidade, granulometria, biomassa subterrânea, alumínio, ferro e manganês (total e extraído com uma solução de hidroxilamina). As águas intersticiais foram extraídas de cada camada de sedimentos e procedeu-se à determinação de carbono orgânico dissolvido, ferro e manganês, nas mesmas. O mercúrio total foi analisado na fracção sólida do sedimentos e na biomassa subterrânea; nas águas intersticiais foi determinado mercúrio total e reactivo. Na biomassa subterrânea procedeu-se ainda à determinação de ferro e manganês totais. Todas as determinações químicas efectuadas nos sedimentos e nas águas intersticiais dos sedimentos colonizados do sapal contaminado, evidenciam um padrão de distribuição vertical semelhante, caracterizado pela existência de um incremento nas camadas sub-superficiais que contêm maior biomassa subterrânea (entre 10-25 cm de profundidade). Estes perfis contrastam com a uniformidade observada nos perfis verticais dos cores de sedimentos não colonizados. As concentrações máximas de ferro extraído indicam a existência de um zona com natureza óxica favorecendo a precipitação de óxidos e hidróxidos de ferro nas camadas de sedimentos sub-superficiais. As concentrações de mercúrio na fracção sólida e nas águas intersticiais apresentam também incrementos nessas mesmas camadas (max. 39,3 ?g g-1 e 29,3 ng L-1, respectivamente). Estas camadas por sua vez, são enriquecidas em carbono orgânico dissolvido e particulado. As concentrações máximas de mercúrio e ferro ocorrem acima das camadas de sedimentos com maior quantidade de biomassa subterrânea. As concentrações de mercúrio na biomassa subterrânea ocorreram nas mesmas camadas dos sedimentos (max. 120 ? g g-1 para o Halimione portulacoides e 49 ?g g-1 para o Arthrocnemum fruticosum) As concentrações de mercúrio nos sedimentos do sapal menos contaminado, apresentam um perfil semelhante, no entanto as concentrações de mercúrio são mais baixas (max. 1,7 ?g g-1). A biomassa subterrânea nestas camadas apresenta também maiores concentrações de mercúrio (3,2 ?g g-1 para o Halimione portulacoides e 1,5 ? g g-1para o Arthrocnemum fruticosum). Os resultados obtidos apontam para uma intensa mobilização do mercúrio em sedimentos colonizados. O mercúrio é transportado para a zona dos sedimentos com raízes à medida que a planta toma água e é incorporado em óxidos e hidróxidos de ferro formados na rizosfera. Os perfis paralelos de mercúrio dissolvido e carbono orgânico dissolvido observados nas águas intersticiais sugerem um mecanismo de competição entre o carbono orgânico dissolvido e os óxidos e hidróxidos de ferro para a retenção de mercúrio em sedimentos de sapais colonizados. As baixas concentrações de mercúrio registadas na biomassa aérea apontam para o facto da mobilização do mercúrio se processar fundamentalmente entre os sedimentos e as raízes, sendo apenas uma pequena fracção do metal translocada para os órgãos superiores das plantas.In order to examine the effect of roots on mercury distribution in salt-marsh sediments, 60-cm sediment cores were collected in two salt marshes of Ria de Aveiro with different degrees of contamination. Sediment cores were taken in non-vegetated areas and in sediments colonised by Halimione portulacoides and Arthrocnemum fruticosum. Cores were sliced in 5-cm layers. Roots were separated from each sediment layer of the core. Leaves and stems of the two plants from the two marshes were also collected. Temperature, pH, loss on ignition, total organic carbon, pore water content, particle size, belowground biomass, aluminium, total and extracted (hydroxylamine solution) iron and manganese were measured in each sediment layer. Pore waters were extracted from the several sediment layers and organic carbon, iron, manganese determined. Total mercury was analysed in sediment solids and biomass, and reactive and total mercury in pore waters. Total iron and manganese were also analysed in belowground biomass. All chemical determinations in colonised sediments and pore waters from the contaminated site showed a common vertical distribution pattern: sharp increase in the sub-surface layers containing high belowground biomass (between 10 and 25-cm depth). These profiles contrast with the uniformity observed in non-colonised sediment cores. The peak concentration of extractable iron indicates the existence of oxic/suboxic conditions favouring the precipitation of Fe-oxides at sub-surface sediments. Mercury concentrations in solids and pore waters display also sharp increments at the same sub-surface layers (max. 39.3 ? g g-1 and 29.3 ng L-1, respectively). These layers are also enriched in particulate and dissolved organic carbon. Mercury and iron peaks occurred above the higher root biomass. Concentration peaks were registered in sediments colonised by the two plants. Similarly, mercury in roots was higher at the same sediment layers (max 120 ? g g-1 for Halimione portulacoides and 49 ? g g-1 for Arthrocnemum fruticosum). The mercury concentration in the less contaminated site presented a similar profile in the solids, although levels being much lower (max. 1.7 ?g g-1). Roots from these layers showed also higher mercury concentrations: 3.2 for Halimione portulacoides and 1.5 ?g g-1 for Arthrocnemum fruticosum. Our results point to an intense mobilization of mercury in colonised sediments. Mercury is transported to the rooting sediments as plant uptakes water and then incorporated on Fe-oxides formed in the rhizosphere. Parallel concentrations of dissolved mercury and dissolved organic carbon in the sediment pore waters suggest a competition mechanism between organic carbon and Fe-oxides for mercury. Lower mercury concentrations in the aerial biomass point that mercury is mainly cycled between sediment and roots and only a small fraction is translocated to the upper parts

Mercury mobility in a salt marsh colonised by Halimione portulacoides

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 943 mg m-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 103 ng m-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 (0.06-0.16 mg m-2 and 29-102 mg m-2, respectively). The annual bioaccumulation of mercury in above ground tissues was estimated in 0.11 mg m-2 y-1, while in below ground biomass the values were higher (72 mg m-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.http://www.sciencedirect.com/science/article/B6V74-4SRM83C-1/1/afd89d1885b88e6149c4ae0e1e4adb5

Evidence for concentration of anthropogenic mercury in salt marsh sediments

Sediment cores from two salt marshes, Rosário (Tagus estuary) and Laranjo (Ria de Aveiro), were analyzed for total Hg and Al, and for Fe and Mn extracted with a hydroxylamine-acetic acid solution. Both areas have been contaminated by industrial discharges during the last decades. Vertical distributions of Hg in sediments colonized by Arthrocnemum fruticosum and Halimione portulacoides were compared to profiles in non-vegetated sediments. The same vertical distribution pattern was observed in all situations: Hg enriched in sediment layers with high root density. Mercury concentrations reached 9.3 and 29.1 nmol g–1 in Rosário, and 149.0 and 196.0 nmol g–1 in Laranjo. At both marshes, higher concentrations were found in sediments colonized by H. portulacoides. These values are one order of magnitude above the levels found in nonvegetated sediments. Mercury was enriched in sediment layers containing high concentrations of Fe extracted with a hydroxylamine-acetic acid solution, indicating the importance of Fe (and Mn) oxides formed in the rooting sediments for the retention of anthropogenic Hg