Modelling Zn (II) sorption onto clayey sediments using a multi-site ion-exchange model

International audienceIn environmental studies, we need to be able to predict the behaviour of contaminants in more or less complex physico-chemical contexts. The improvement of this prediction partly depends on establishing thermodynamic models that can describe the behaviour of these contaminants and, in particular, the sorption reactions on mineral surfaces. In this way, based on the mass action law, it is possible to use surface complexation models and ion exchange models. Therefore, the aim of this study is i) to develop an ion-exchange model able to describe the sorption of transition metal onto pure clay minerals and ii) to test the ability of this approach to predict the sorption of these elements onto natural materials containing clay minerals (i.e. soils/sediments) under various chemical conditions. This study is focused on the behaviour of Zn(II) in the presence of clayey sediments. Considering that clay minerals are cation exchangers containing multiple sorption sites, it is possible to interpret the sorption of Zn(II), as well as competitor cations, by ion-exchange equilibria with the clay minerals. This approach is applied with success to interpret the experimental data obtained previously in the Zn(II)-H+-Na+-montmorillonite system [Baeyens, B., Bradbury, M.H., 1997. A mechanistic description of Ni and Zn sorption on Na-montmorillonite. Part I: Titration and sorption measurements. J. Contam. Hydrol. 27, 199–222]. Our research team has already studied the behaviour of Na+, K+, Ca2+ and Mg2+ versus pH in terms of ion exchange onto pure montmorillonite, leading us to develop a thermodynamic database including the exchange site concentrations associated with montmorillonite and the selectivity coefficients of Na+, K+, Ca2+, Mg2+, and Zn2+ versus H+. In the present study, we report experimental isotherms of Zn(II) on two different sediments in batch reactors at different pH and ionic strengths, using NaCl and CaSO4 as electrolytes. Assuming clay minerals are the main ion-exchanging phases, it is possible to predict Zn(II) sorption onto sediments under different experimental conditions, using the previously obtained data base on montmorillonite. Whatever the physico-chemical conditions tested, we observe a relatively good agreement between experimental results and the predicted sorption behaviour

Uptake of anionic radionuclides onto degraded cement pastes and competing effect of organic ligands

http://www.radiochimacta.deInternational audienceHardened cement pastes (HCP) present a high affinity with a lot of radionuclides (RN) and can be used as waste confining materials in radioactive waste repository. Indeed, in cementitious media, RN can be removed from solution via (co)precipitation reactions or via sorption/diffusion mechanisms. In this study, the affinity of anionic RN (Cl−, I−, SeO32− and CO32− chemical forms) with a CEM-I HCP has been studied vs. the degradation of the HCP particles. These RN are considered as mobile in repository media and it is important to have a set of distribution ratio (Rd) in cement environment. The Rd values have been measured in batch experiments as a function of the pH, used as the degraded state parameter of the HCP suspensions. The Rd values increase in all cases, from the unaltered state (pH 13.3) to the altered state of HCP, i.e. until all portlandite is dissolved, corresponding to pH 12.6. Then, Rd values decrease until degraded states (pH 12.0), corresponding to the decalcification of the calcium silicate hydrate (C-S-H) phases. The behaviour of anionic RN seems to be correlated to the evolution of calcium concentration and is opposed to the evolution of sulphate concentration in solution which could have a competing effect. Comparison is done with the behaviour of caesium and uranium(VI), which is a cationic RN but has a major negative hydrolysed species at high pH. As awaited, the uranium(VI) behaviour is very different from purely anionic RN one in accord with spectroscopic analyses from literature works. The Rd values have also been measured for the organic ligands isosaccharinate (ISA) and EDTA. The uptake of ISA can be important and competing effect with the sorption of SeO32− has been evidenced in HCP suspensions as a function of the ISA concentration

Decision Support Frameworks and Tools for Conservation

The practice of conservation occurs within complex socioecological systems fraught with challenges that require transparent, defensible, and often socially engaged project planning and management. Planning and decision support frameworks are designed to help conservation practitioners increase planning rigor, project accountability, stakeholder participation, transparency in decisions, and learning. We describe and contrast five common frameworks within the context of six fundamental questions (why, who, what, where, when, how) at each of three planning stages of adaptive management (project scoping, operational planning, learning). We demonstrate that decision support frameworks provide varied and extensive tools for conservation planning and management. However, using any framework in isolation risks diminishing potential benefits since no one framework covers the full spectrum of potential conservation planning and decision challenges. We describe two case studies that have effectively deployed tools from across conservation frameworks to improve conservation actions and outcomes. Attention to the critical questions for conservation project planning should allow practitioners to operate within any framework and adapt tools to suit their specific management context. We call on conservation researchers and practitioners to regularly use decision support tools as standard practice for framing both practice and research

An integrative research framework for enabling transformative adaptation

Transformative adaptation will be increasingly important to effectively address the impacts of climate change and other global drivers on social-ecological systems. Enabling transformative adaptation requires new ways to evaluate and adaptively manage trade-offs between maintaining desirable aspects of current social-ecological systems and adapting to major biophysical changes to those systems. We outline such an approach, based on three elements developed by the Transformative Adaptation Research Alliance (TARA): (1) the benefits of adaptation services; that sub-set of ecosystem services that help people adapt to environmental change; (2) The values-rules-knowledge perspective (vrk) for identifying those aspects of societal decision-making contexts that enable or constrain adaptation and (3) the adaptation pathways approach for implementing adaptation, that builds on and integrates adaptation services and the vrk perspective. Together, these elements provide a future-oriented approach to evaluation and use of ecosystem services, a dynamic, grounded understanding of governance and decision-making and a logical, sequential approach that connects decisions over time. The TARA approach represents a means for achieving changes in institutions and governance needed to support transformative adaptationThe research was supported by CSIRO Land and Water. We thank the Embassy of France in Australia and the Australian Academy of Sciences for funding the first Transformative Adaptation Research Alliance workshop in Canberra, October 27-31, 2014. We thank Craig Beatty, Mirjam Kuzee (IUCN) and Alistair Hobday (CSIRO Oceans and Atmosphere) for reviewing the manuscript and providing constructive comments. The funding partners that have supported this research include the International Climate Initiative (IKI) of the German Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (BMUB) and the CGIAR Research Program on Forests, Trees and Agroforestry (CRP-FTA) with financial support from the CGIAR Fun

Exposição a radiações eletromagnéticas não ionizantes da telefonia celular e sintomas psiquiátricos

Resumo O objetivo desse estudo foi investigar a associação entre exposição a radiações eletromagnéticas não ionizantes da estação radiobase de telefonia celular e sintomas à saúde. Em um estudo transversal realizado em Salvador, Bahia, Brasil, entrevistaram-se 440 indivíduos. Queixas e diagnósticos psiquiátricos constituíram as variáveis dependentes e a distância do domicílio para estação radiobase foi considerada a variável independente principal. Realizou-se análise de regressão logística hierarquizada para avaliação de confundimento e efeito. Observou-se associação entre sintomas psiquiátricos e residir próximo à estação radiobase e formas de uso do telefone celular (sinal de cobertura fraco, perto do corpo, dois ou mais chips e nunca desligar o celular quando dorme) e com uso de outros eletroeletrônicos. Concluiu-se que a exposição à radiação eletromagnética não ionizante de telefonia celular e a outros eletroeletrônicos foi associada aos sintomas psiquiátricos independente do sexo, escolaridade e tabagismo. Recomenda-se a adoção de medidas precaucionárias no sentido de se reduzir este tipo de exposição

BioPIQuE 2013 : 25 questions émergentes pour les politiques publiques de biodiversité.

L’élaboration, la mise en oeuvre et l’évaluation des politiques publiques de biodiversité nécessitent d’anticiper les conséquences des décisions qui sont prises maintenant. Pour cela, des études sont lancées sur de nouveaux sujets mais elles sont souvent peu mobilisées et arrivent parfois trop tard par rapport à la définition des orientations des politiques. L’anticipation est encore compliquée par l’existence de nombreuses informations sur les évolutions possibles de la biodiversité et des politiques publiques associées, parmi lesquelles il s’agit de faire le tri : quelles sont les évolutions dont les impacts sont potentiellement les plus importants, sur la biodiversité elle-même ou sur d’autres sujets ? Quelles sont celles pour lesquelles l’anticipation permettrait de limiter les impacts négatifs et d’accroître les impacts positifs ? Quelle est leur plausibilité à court, moyen et long terme ? Il s’agit alors de dépasser les travers des anticipations spontanées grâce à une méthode rigoureuse de prospective.La Direction de l’eau et de la biodiversité du MEDDE a souhaité donc mettre en place un nouveau processus associant des scientifiques et des praticiens de l’action publique. BioPIQuE 2013 a pour objectif d’identifier des questions émergentes pour les politiques publiques de biodiversité, en France métropolitaine, à l’horizon 2020. Le présent document présente de manière synthétique les résultats de ce travail