Mechanisms of goethite dissolution in the presence of desferrioxamine B and Suwannee River fulvic acid at pH 6.5

Siderophores are Fe3+ specific low MW chelating ligands secreted by microorganisms in response to Fe stress. Low MW organic acids such as oxalate have been shown to enhance siderophore mediated dissolution of Fe3+ oxides. However, the effect of fulvic acid presence on siderophore function remains unknown. We used batch dissolution experiments to investigate Fe release from goethite in the goethite-fulvic acid desferrioxamine B (goethite-SRFA-DFOB) ternary system. Experiments were conducted at pH 6.5 while varying reagent addition sequence. FTIR and UV-Vis spectroscopy were employed to characterise the Fe-DFOB, Fe-SRFA and DFOB–SRFA complexes. Iron released from goethite in the presence of SRFA alone was below detection limit. In the presence of both SRFA and DFOB, dissolved Fe increased with reaction time, presence of the DFOB-SRFA complex, and where SRFA was introduced prior to DFOB. FTIR data show that in the ternary system, Fe3+ is complexed primarily to oxygen of the DFOB hydroxamate group, whilst the carboxylate C=O of SRFA forms an electrostatic association with the terminal NH3+ of DFOB. We propose that SRFA sorbed to goethite lowers the net positive charge of the oxide surface, thus facilitating adsorption of cationic DFOB and subsequent Fe3+ chelation and release. Furthermore, the sorbed SRFA weakens Fe-O bonds at the goethite surface, increasing the population of kinetically labile Fe. This work demonstrates the positive, though indirect role of SRFA in increasing the bioavailability of Fe3+

Cations extraction of sandy-clay soils from Cavado valley, Portugal, using sodium salts solutions

Cases of contamination by metals in the water wells of the Cavado Valley in north-west Portugal can be attributed to the heavy leaching of clay soils due to an excess of nitrogen resulting from the intensive use of fertilisers in agricultural areas. This work focuses on the natural weathering characteristics of soils, particularly the clay material, through the study of samples collected near the River Cavado. Samples taken from various sites, after physico-chemical characterisation, were subjected to clay dissolution tests, using sodium salts of different ionic forces, to detect the relationship between certain physico-chemical parameters of water, such as pH, nitrate, chloride and sulphate content, in the dissolution of clay and the subsequent extraction of such cations as Al, Fe and K. In acidic sandy clay soils, the mineralogical composition of which was characterised by a predominance of quartz, micas, kaolinite and K-feldspars, decreases of the clay material/water pH ratio increases dissolution of the micaceous and K-feldspars phases. The presence of nitrates in the aqueous solution apparently advanced the extraction of all three cations Al, Fe and K. The specific surface area of the clay material showed a significant correlation with the main kinetic parameters of cation extraction.Têm ocorrido casos de contaminações de águas de poços, por metais, no vale do Rio Cávado, região noroeste de Portugal. A princípio, poderiam ser explicáveis pela elevada lixiviação dos solos arenoargilosos da região, quando da prática de adubações intensivas de nitrogênio em áreas agrícolas. Assim, estudaram-se as características do intemperismo natural dos solos, particularmente da fração argila, característica da margem norte do rio Cávado. Coletaram-se amostras de vários locais, que foram submetidas, após caracterização físico-química, a ensaios de dissolução a partir de soluções de sais de sódio com diferentes forças iônicas. O objetivo foi observar as relações de determinados parâmetros físico-químicos da água, tais como: pH, nitratos, cloretos e sulfatos na dissolução das argilas e a conseqüente extração de espécies químicas tais como Al, K e Fe. Para solos areno-argilosos, ácidos, cuja composição mineralógica se caracteriza por um predomínio de quartzo, micas, caulinita e feldspato-K, o abaixamento do pH da suspensão solo/água promove a solubilização das fases micáceas e feldspáticas. A presença do nitrato nas soluções aquosas promoveu aparentemente a extração de todos os três cátions: Al, K e Fe. O efeito da área superfícial específica das partículas dos solos condicionou fortemente vários dos parâmetros cinéticos estudados relativos à extração dos cátions.(undefined

Bioavailability in soils

The consumption of locally-produced vegetables by humans may be an important exposure pathway for soil contaminants in many urban settings and for agricultural land use. Hence, prediction of metal and metalloid uptake by vegetables from contaminated soils is an important part of the Human Health Risk Assessment procedure. The behaviour of metals (cadmium, chromium, cobalt, copper, mercury, molybdenum, nickel, lead and zinc) and metalloids (arsenic, boron and selenium) in contaminated soils depends to a large extent on the intrinsic charge, valence and speciation of the contaminant ion, and soil properties such as pH, redox status and contents of clay and/or organic matter. However, chemistry and behaviour of the contaminant in soil alone cannot predict soil-to-plant transfer. Root uptake, root selectivity, ion interactions, rhizosphere processes, leaf uptake from the atmosphere, and plant partitioning are important processes that ultimately govern the accumulation ofmetals and metalloids in edible vegetable tissues. Mechanistic models to accurately describe all these processes have not yet been developed, let alone validated under field conditions. Hence, to estimate risks by vegetable consumption, empirical models have been used to correlate concentrations of metals and metalloids in contaminated soils, soil physico-chemical characteristics, and concentrations of elements in vegetable tissues. These models should only be used within the bounds of their calibration, and often need to be re-calibrated or validated using local soil and environmental conditions on a regional or site-specific basis.Mike J. McLaughlin, Erik Smolders, Fien Degryse, and Rene Rietr

A Comparison of Computerized Chemical Models for Equilibrium Calculations in Aqueous Systems

A survey of computer programs which are currently being used to calculate the distribution of species in aqueous solutions, especially natural waters, has been made in order to 1) provide an inventory of available programs with a short description of their uses, 2) compare the consistency of their output for two given test solutions and 3) identify major weaknesses or problems encountered from their use. More than a dozen active programs which can be used for distribution of species and activity calculations for homogeneos equilibria among the major anions and cations of natural waters have been inventoried. Half of these programs can also accept several trace elements including Fe, Al, Mn, Cu, Ni, Zn, Cd, Pb, Ag, Hg, As, Ba, Sr, and B. Consistency between programs was evaluated by comparing the log of the molal concentrations of free ions and complexes for two test solutions: a hypothetical seawater analysis and a hypothetical river water analysis. Comparison of the free major ion concentrations in the river water test case shows excellent agreement for the major species. In the seawater test case there is less agreement and for both test cases the minor species commonly show orders of magnitude differences in concentrations. These differences primarily reflect differences in the thermodynamic data base of each chemical model although other factors such as activity coefficient calculations, redox assumptions, temperature corrections, alkalinity corrections and the number of complexes used all have an affect on the output

Os Açores e os impérios : séculos XV a XX

[...]. Os Açores não constituem simplesmente um elo da correspondência transatlântica. Aliás, possuem uma identidade bem complexa. Com efeito, se a História evidencia muito a mundividência, apresentando as ilhas como o centro do Mundo, já a literatura ressalta muito o isolamento, resultante do afastamento dos continentes e da descontinuidade territorial, apresentando as ilhas como o fim do Mundo. Curiosamente, a política e os políticos, talvez com maior sentido do pragmatismo e da oportunidade, agem em função das circunstâncias. De facto, proclamam a projecção da universalidade, quando reivindicam mais capacidade de auto-governo, mas insistem na pobreza da ultraperifericidade, quando exigem mais contrapartidas financeiras. Apesar da divergência das perspectivas, atentemos mais na universalidade dos Açores, que historicamente influi na definição das dinâmicas do Atlântico, conferindo maior projecção à Europa

Which marketing condition makes organic products more accessible? A case study in Brazil.

Abstract: Concern over health and environmental and social problems generated by the production of conventional agricultural products, promotes expansion of the organic market. At the same time, it is necessary to understand how and under which conditions the market valorises local production, strengthening organic family farming. This study analyses the commercialisation of organic food production in Vitoria (Brazil), evaluating the diversity and prices of these products in different marketing channels, such as supermarkets, grocery stores and organic farmers markets. It also compares the price of organic products with conventional products in these establishments. The results demonstrated that organic farmers markets had the greatest product diversity, in addition tobetter prices. It concluded that this channel valorises organic family production, helping to empower producers and promoting access to healthy food for local consumers, meeting the goals of Organic 3.0

Agricultura orgânica do estado do Espírito Santo: diversidade e comercialização de seus produtos na região metropolitana de Vitória.

Resumo: O presente estudo apresenta a análise da diversidade das formas de comercialização de produtos orgânicos em Vitória (ES), além da discussão sobre essa temática da pesquisa. O objetivo é entender como e em que condições o mercado valoriza a produção local, fortalece a produção familiar ecológica e a soberania alimentar. A metodologia da pesquisa levou em consideração dados quantitativos e qualitativos, utilizando informações públicas disponíveis e dados adquiridos na pesquisa de campo. A avaliação mostra que os produtos orgânicos são comercializados por vendas diretas, em feiras livres de orgânicos e feiras de exposição, e por vendas indiretas em supermercados, lojas especializadas e restaurantes. Dentre os canais de comercialização avaliados, foram as feiras livres de produtos orgânicos que apresentaram a maior diversidade de produtos, além do melhor preço, que foi até cinco vezes menor do que nos supermercados. Ainda, os preços dos produtos orgânicos, quando comparado com os convencionais equivalentes, apresentaram-se sempre com valores maiores em canais de comercialização indiretos. Porém, entre feiras livres convencionais e orgânicas encontraram-se preços de produtos orgânicos maiores, iguais ou menores que seus equivalentes convencionais. Portanto, conclui-se que esse canal de comercialização valoriza a produção familiar orgânica, promovendo o empoderamento dos produtores familiares e o acesso à alimentação saudável para o consumidor local.Dissertação (Mestrado em Agroecologia e Desenvolvimento Rural) - Programa de Pós-graduação em Agroecologia e Desenvolvimento Rural, UFSCar, Araras. Orientadora: Lucimar Santiago de Abreu (CNPMA)

Consideration of the bioavailability of metal/metalloid species in freshwaters: experiences regarding the implementation of biotic ligand model-based approaches in risk assessment frameworks

After the scientific development of Biotic Ligand Models (BLMs) in recent decades these models are now considered suitable for implementation in regulatory risk assessment of metals in freshwater bodies. The approach has been developed over several years and has been described in many peer-reviewed publications. The original complex BLMs have been applied in prospective risk assessment reports for metals and metal compounds and are also recommended as suitable concepts for the evaluation of monitoring data in the context of the European Water Framework Directive. Currently, several user-friendly BLM-based bioavailability software tools are available for assessing the aquatic toxicity of a limited number of metals (mainly copper, nickel, and zinc). These tools need only a basic set of water parameters as input (e.g., pH, hardness, dissolved organic matter and dissolved metal concentration). Such tools seem appropriate to foster the implementation in routine water quality assessments. This work aims to review the existing bioavailability-based regulatory approaches and the application of available BLM-based bioavailability tools for this purpose. Advantages and possible drawbacks of these tools (e.g., feasibility, boundaries of validity) are discussed, and recommendations for further implementation are given

Low-frequency dilatational wave propagation through unsaturated porous media containing two immiscible fluids

An analytical theory is presented for the low-frequency behavior of dilatational waves propagating through a homogeneous elastic porous medium containing two immiscible fluids. The theory is based on the Berryman-Thigpen-Chin (BTC) model, in which capillary pressure effects are neglected. We show that the BTC model equations in the frequency domain can be transformed, at sufficiently low frequencies, into a dissipative wave equation (telegraph equation) and a propagating wave equation in the time domain. These partial differential equations describe two independent modes of dilatational wave motion that are analogous to the Biot fast and slow compressional waves in a single-fluid system. The equations can be solved analytically under a variety of initial and boundary conditions. The stipulation of 'low frequency' underlying the derivation of our equations in the time domain is shown to require that the excitation frequency of wave motions be much smaller than a critical frequency. This frequency is shown to be the inverse of an intrinsic time scale that depends on an effective kinematic shear viscosity of the interstitial fluids and the intrinsic permeability of the porous medium. Numerical calculations indicate that the critical frequency in both unconsolidated and consolidated materials containing water and a nonaqueous phase liquid ranges typically from kHz to MHz. Thus engineering problems involving the dynamic response of an unsaturated porous medium to low excitation frequencies (e.g. seismic wave stimulation) should be accurately modeled by our equations after suitable initial and boundary conditions are imposed