Combination of single and sequential chemical extractions to study the mobility and host phases of potentially toxic elements in airborne particulate matter     

《Chemie der Erde / Geochemistry》2016,76(4):481-489

Risk assessment of metals associated to airborne particulate matter (PM) has usually been based on the analysis of their total concentrations, which is a poor indicator of metal mobility. Chemical fractionation processes may provide an additional level of information, however, chemical complexity and small sample sizes do not allow to combine several extraction methods. Additionally, analysing the metal concentrations during the extractions exceptionally provides restricted information about metals’ speciation. To overcome these limitations we collected total suspended particulate matter (TSP) samples from the air filters placed in the air supply channel of methane-heated turbines of thermal power stations which allows collecting large amounts of TSP materials. Additionally, we combined single and sequential chemical extractions in which not only the concentrations of potentially toxic elements (PTE) (Cd, Cr, Cu, Ni, Pb, Zn) but also that of the major chemical components (Al, Ca, Fe, K, Mg, Mn, Na, P, S, Ti) were analysed. Our aims were to study these metals’ mobility and speciation through the study of their association to major chemical components.Accumulation of the studied PTEs in the TSP material suggests moderate contamination for Ni, Cd and Cr whereas a heavy one for Cu, Zn and Pb. Three groups of these PTEs could be distinguished based on their mobility. The highly mobile Zn and Cd (large ratios of water and weak acid soluble fractions) can be considered as especially harmful elements to environment. The moderately mobile Pb and Cu (large ratios of reducible and oxidizable fractions, respectively) may potentially have a negative effect on the environment, whereas the immobile Cr and Ni cannot be expected to pose a serious risk. Based on the statistical evaluation of extraction data, the potential phases for Zn and Cu are presented by metal-sulphates, -nitrates, -chlorides, -carbonates and -hydroxides, as well as sorbed forms. Lead primarily hosted by metal-carbonates and sorbed forms, as well as by -hydroxides, whereas Cu by organic matter. Finally, Cr and Ni are mostly incorporated into very resistant phases, most probably by magnetite or other resistant metal-oxides.Combination of single and sequential extractions, as well as that of the analysis of not only the target elements but also the major chemical components were found to be a very effective tool to study the host phases of PTEs in the TSP material. The necessity for relatively large sample amounts for such analyses could be fulfilled using special sampling methodology; however, obvious disadvantages of this kind of sampling must be taken into account when resulted data are evaluated.  相似文献   

An approach for estimating vaccination coverage for communities using school-level data and population mobility information     

《Applied geography (Sevenoaks, England)》2016

Childhood vaccination data are made available at a school level in some U.S. states. These data can be geocoded and may be considered as having a high spatial resolution. However, a school only represents the destination location for the set of students who actually reside and interact within some larger areal region, creating a spatial mismatch. Public school districts are often used to represent these regions, but fail to account for private schools and school of choice programs. We offer a new approach for estimating childhood vaccination coverage rates at a community level by integrating school level data with population commuting information. The resulting mobility-adjusted vaccine coverage estimates resolve the spatial mismatch problem and are more aligned with the geographic scale at which public health policies are implemented. We illustrate the utility of our approach using a case study on diphtheria, tetanus, and pertussis (DTP) vaccination coverage for kindergarten students in California. The modeled community-level DTP coverage estimates yield a statewide coverage of 92.37%, which is highly similar to the 92.44% coverage rate calculated from the original school-level data.  相似文献   

Town dwellers in their networks: urban-rural mobility and household strategies in Cameroon     

Hélène Mainet 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2017,117(2):117-129

Abstract

Urban-rural interactions are important features of spatial dynamics in Africa that have been affected by recent economic, social and cultural transformations. The attention of academics and policy-makers has concentrated on the impact of such mobility on rural actors and economies. Our objective is to consider the point of view of urban households and to analyse how they manage to develop and use their “rural connections”. The paper is based on in-depth qualitative fieldwork conducted in Cameroon, in Douala and Bafoussam. It presents an analysis of the configurations of urban resident mobility to rural regions. By mapping mobility we show the role of linkages with rural areas in urban household strategies. We also illustrate how a major city and a fast-growing secondary one differ in their connections with rural areas. The paper addresses what is one of the recurrent questions in the literature: will urban-rural linkages change in the long-term as the trend towards urbanization intensifies. Urban-rural mobility remains crucial, contributes to creating complex and dynamic networks. Collective connections are reaffirming the importance of the village and the region of origin. Mobility is a key element for many urban households in developing their urban position and strategies.  相似文献   

‘Pour votre tranquillité’: Ambiance,atmosphere, and surveillance     

《Geoforum》2013

This is a paper concerned with security, surveillance and notions of atmosphere and ambience. Whilst surveillance and security research has been excellent at examining socio-spatial relations drawn into the production and consumption of surveillance technologies, systems and practices, it has been far less well attuned to the material–affective relations, presences and absences it comes to constitute as the fabric of public space. Research within human geography and a broader ‘new materialism’ within the humanities and social sciences has become increasingly interested in exploring affective atmospheres, yet largely ignorant of a well established school of thought within French urban and social theory of ‘ambiance’. This paper explores the providence of considering atmospheres and ambiances for the examination of surveillance through the case study of two major railway stations in Britain and France. The paper proffers some methods and techniques for the further exploration of atmospheres/ambiances of security.  相似文献   

Mobility endowment and entitlements mediate resilience in rural livelihood systems     

《Global Environmental Change》2019

In economically marginal rural areas, choice in livelihood strategy such as decisions to move location mediates levels of individual and household resilience under conditions of environmental change. It is widely recognised that endowments associated with mobility and the entitlement to mobility are unevenly distributed across populations. This paper integrates these insights and conceptualises location choice as a set of mobility endowments and mobility entitlements. Through focussing on endowments and entitlements, the paper explores how choice affects the ability to be mobile and its role in mediating levels of resilience to livelihood shocks associated with changing environmental conditions. The research design involves measuring the impact of different climatic perturbations in rural locations in Anhui Province, China. Mixed methods of rural appraisal, life history interviews, and a household survey generate objective and perceived elements of individual and household responses to risks. These data are augmented by biophysical observations on the nature of the climatic perturbations. The results show that mobility endowments and mobility entitlements are important in determining the impact of mobility on resilience. The life history interview data highlight significant individual agency within the structures that impact on individual choices. Further, individuals and households who possess the ability to decide and to subsequently enact decisions about mobility, are shown to be more resilient compared to other individuals and households that lack such ability. Moreover, households practicing short-term, circular mobility are more resilient than those households that practice long-term mobility. The study confirms that, in these instances, choice and the ability to enact those choices mediates resilience and highlights the implications of location decisions but also the conditions in which those decisions are made.  相似文献   

Moving young lives: Mobility, immobility and inter-generational tensions in urban Africa     

Gina Porter  Kate Hampshire 《Geoforum》2010,41(5):796-331

This paper explores young people’s experiences and perceptions of mobility and mobility constraints in poorer urban areas of Ghana, Malawi and South Africa within the specific context of inter-generational relations. Drawing principally on qualitative research findings from a study involving both adult and child researchers, our aim is to chart the diversities and commonalities of urban young people’s mobility experiences in the everyday - how they use and experience the city - developing a comparative perspective across three urban study sites which links young people’s mobility with the power relations that operate to shape their movements in individual locations. In particular, we consider how positive and negative images of young people’s mobility play out in terms of the inter-generational frictions and negotiations generated by their mobility performances. We also reflect on the developmental implications, in terms of young people’s access to services and income and their participation in the social networks and peer culture which may shape their life trajectories. Three themes are explored in detail: mobility as challenge, mobility as temptation and mobility control.  相似文献   

向海湿地沉积剖面化学元素相对迁移特征分析   总被引：4，自引：0，他引：4  

王国平  刘景双  汤洁 《海洋与湖沼》2006,37(4):377-384

旨于探索沉积剖面元素迁移强度的描述方法,讨论向海沼泽湿地沉积物化学元素的迁移积聚等基本地球化学特征,以深化对沼泽湿地沉积化学行为的某些认识。冬季在向海两处沼泽采集了代表一定范围汇水区与人类活动影响的沉积芯。利用Tessier等(1979)提出的连续提取法对沉积物中多种常量与微量元素地球化学相进行分离。可迁移系数、潜在迁移系数、非迁移系数的计算结果表明,在向海沼泽沉积剖面中,化学元素相对迁移强度为:Ca、Sr、Mn、Pb潜在活性最大,Ti、Al、K、Rb潜在活性最小,以此为依据,Ti、Al、K、Rb等元素适宜作为示踪元素。为消除沉积物构成组织的影响,以Al为参考元素对重金属元素形态两种分量进行归一化后,重金属环境非迁移分量与相对迁移分量均表现出在表层的富集,尤其表现在上游霍林河煤矿开发后20余年这一时期,人类活动的介入加速了重金属元素通过河流搬运向下游湿地的输入。  相似文献   

Applicability of Single and Sequential Extractions for Assessing the Potential Mobility of Heavy Metals in Contaminated Soils     

J. Thming  W. Calmano 《洁净——土壤、空气、水》1998,26(6):338-343

Heavy metal polluted sites are bearing an acute hazardous risk for the groundwater, but also a potential one. While the acute risk can be assessed directly via seepage water measurements, determination of the potential risk is much more complex. It results from the sum of all reactions that are capable to mobilize heavy metals under worst case environ-mental conditions. Using a fourfold sequential extraction (SE₄) such a worst case was simulated for four soils highly contaminated with Pb, Zn, and Cu. The resulting potential mobilizable amounts ϕ_pm have been compared with those derived from 6 single extractions. By means of variance analyses, it is shown that ϕ_pm of lead can be represented by a single extraction with NH₂OH. In contrary, ϕ_pm of zinc can be represented using the pH_stat test or an extraction with aqua regia, while ϕ_pm of copper can be represented only by aqua regia extraction. The water-soluble amounts deriving from the DEV-S4 test do not correlate with the potential mobilizable amounts of any metal. Therefore, an assessment of contaminated sites should include an aqua regia extraction additionally to the seepage water analysis.  相似文献   

A GIS-based methodology for hazard mapping of small volume pyroclastic density currents     

G. P. Toyos  P. D. Cole  A. Felpeto  J. Martí 《Natural Hazards》2007,41(1):99-112

We present here a methodology implemented within a geographical information system (GIS) for hazard mapping of small volume pyroclastic density currents (PDCs). This technique is implemented as a set of macros written in Visual Basic for Applications (VBA) that run within GIS-software (i.e. ArcGIS). Based on the energy line concept, we calibrated an equation that relates the volume (V) and the mobility (ΔH/L) of single PDCs using data from Soufrière Hills volcano (Montserrat) and Arenal volcano (Costa Rica). Maximum potential run-outs can be predicted with an associated uncertainty of about 30%. Also based on the energy line concept and with data from Soufrière Hills volcano and Mt. St. Helens (USA), we were able to calibrate an equation that predicts the flow velocity as a function of the vertical distance between the energy line and the ground surface (Δh). Velocities derived in this way have an associated uncertainty of 3 m s⁻¹. We wrote code to implement these equations and allow the automatic mapping of run-out and velocity with the inputs being (i) the height and location of the vent (ii) the flow volume and (iii) a digital elevation model (DEM) of the volcano. Dynamic pressure can also be estimated and mapped by incorporating the density of the pyroclastic density current (PDC). This computer application allows the incorporation of uncertainties in the location of the vent and of statistical uncertainties expressed by the 95% confidence limits of the regression model. We were able to verify predictions by the proposed methodology with data from Unzen volcano (Japan) and Mayon volcano (The Philippines). The consistencies observed highlight the applicability of this approach for hazard mitigation and real-time emergency management.  相似文献   

Fractured space: a geographical reflection on the digital divide     

Patrick Poncet  Blandine Ripert 《GeoJournal》2007,68(1):19-29

What does it mean to reflect upon space in connection to telecommunications? If we start with a conception of urban space as being fully integrated, including on an equal footing both information and communication technologies (ICT) and mobility techniques, as well as the founding notion of copresence that we find at the heart of all urban organization, we might then be able to examine the notion of the ‘digital divide’ in a new light. This clearly experimental approach is conducted by a research group called ‘Urbatic’, which is composed of geographers who, for the last three years, have been conducting theoretical research whose objective is to take into account two fields of social science: the theory of urbanity and the theory of telecommunication. Surveys conducted in this perspective focus on the analysis of the choices people make between the different means they can use to cope with distances (copresence, mobility and telecommunication) with a view to constructing their own space. The analysis of these choices leads us to propose a new theorized interpretation of the ‘digital divide’.  相似文献