Geochemistry and mineralogy of arsenic in (natural) anaerobic groundwaters

Here new data from field bioremediation experiments and geochemical modeling are reported to illustrate the principal geochemical behavior of As in anaerobic groundwaters. In the field bioremediation experiments, groundwater in Holocene alluvial aquifers in Bangladesh was amended with labile water-soluble organic C (molasses) and MgSO₄ to stimulate metabolism of indigenous SO₄-reducing bacteria (SRB). In the USA, the groundwater was contaminated by Zn, Cd and SO₄, and contained <10 μg/L As under oxidized conditions, and a mixture of sucrose and methanol were injected to stimulate SRB metabolism. In Bangladesh, groundwater was under moderately reducing conditions and contained ∼10 mg/L Fe and ∼100 μg/L As. In the USA experiment, groundwater rapidly became anaerobic, and dissolved Fe and As increased dramatically (As > 1000 μg/L) under geochemical conditions consistent with bacterial Fe-reducing conditions. With time, groundwater became more reducing and biogenic SO₄ reduction began, and Cd and Zn were virtually completely removed due to precipitation of sphalerite (ZnS) and other metal sulfide mineral(s). Following precipitation of chalcophile elements Zn and Cd, the concentrations of Fe and As both began to decrease in groundwater, presumably due to formation of As-bearing FeS/FeS₂. By the end of the six-month experiment, dissolved As had returned to below background levels. In the initial Bangladesh experiment, As decreased to virtually zero once biogenic SO₄ reduction commenced but increased to pre-experiment level once SO₄ reduction ended. In the ongoing experiment, both SO₄ and Fe(II) were amended to groundwater to evaluate if FeS/FeS₂ formation causes longer-lived As removal. Because As-bearing pyrite is the common product of SRB metabolism in Holocene alluvial aquifers in both the USA and Southeast Asia, it was endeavored to derive thermodynamic data for arsenian pyrite to better predict geochemical processes in naturally reducing groundwaters. Including the new data for arsenian pyrite into Geochemist’s Workbench, its stability field completely dominates in reducing Eh–pH space and “displaces” other As-sulfides (orpiment, realgar) that have been implied to be important in previous modeling exercises and reported in rare field conditions.     

National-scale estimation of potentially harmful element ambient background concentrations in topsoil using parent material classified soil:stream–sediment relationships

Regulatory authorities require estimates of ambient background concentrations (ABCs) of potentially harmful elements (PHEs) in topsoil; such data are currently not available in many countries. High resolution soil geochemical data exist for only part of England and Wales, whilst stream sediment data cover the entire landscape. A novel methodology is presented for estimating soil equivalent ABCs for PHEs from high-resolution (HR) stream sediment geochemical data grouped by common parent materials (PM), using arsenic (As) as an example. Geometric mean (GM) values for local PM groups are used to investigate different approaches for transforming sediment to soil equivalent concentrations. Holdout validation is used to assess: (i) the optimum number of samples for calculating local GM values, and (ii) the optimum scale at which to group data when using linear regression analysis to estimate GM soil ABCs from local sediment geochemical values. Holdout validation showed that the smallest differences were generally observed when five observations were used to calculate the GM and that these should be grouped over the smallest possible area in order to encompass soils over PMs with elevated GM As concentrations. Geometric mean ABCs are estimated and mapped for As in mineral soil across all of England and Wales within delineations of PM polygons. Errors for the estimation of soil equivalent GM As ABCs based on sediment data for an independent validation set were of a similar magnitude to those from holdout validation applied to the original data suggesting the approach is robust. The estimates of soil equivalent ABCs suggest that As exceeds the regulatory threshold used in risk assessments for residential land use (20 mg kg⁻¹) across 16% of the landscape of England and Wales. The applicability of the method for cognate landscapes, and potential refinements is discussed.     

Phosphorus retention by phlogopite-rich mine tailings

Sewage water rich in P poses a threat to natural water systems. In households that are not connected to a sewer network, an easily maintained purification technique is needed to remove P from domestic waste waters. In the present study, the P retention properties of phlogopite-rich mine tailings were studied to determine whether the untapped tailings can be utilised in wastewater treatment for this purpose. On the basis of its chemical and mineralogical properties, this material, produced in the enrichment process of apatite ore in Siilinjärvi, Finland, can be assumed to act as a P sorbent. The P retention capacity and the P sorption mechanisms of phlogopite-rich tailings were studied with desorption–sorption isotherms and various chemical extractions. The impact of the artificial weathering of the material as well as the reaction time and particle size on P retention were also investigated. The fluctuating shape of the isotherm determined for the untreated material suggests the operation of several sorption mechanisms. The results imply that phlogopite-rich tailings retain P efficiently through specific sorption by amorphous Al and Fe oxides and possibly also by calcite present as an accessory mineral. Acidification of the material, extended reaction time and decrease in particle-size markedly increased the P retention.     

First U–Pb SHRIMP age of the Hauterivian stage, Neuquén Basin, Argentina

A high-resolution ion-microprobe (SHRIMP) U–Pb zircon age from a tuff layer intercalated in the ammonoid bearing sedimentary succession of the Neuquén Basin in Argentina provides a robust geochronologic date to add to the absolute ages and to improve the relative chronology of the Early Cretaceous Hauterivian stage. The tuff layer appears interbedded between shales of the upper member (Agua de la Mula) of the Agrio Formation within the Spitidiscus riccardii ammonoid zone (base of the Late Hauterivian) yielding a date of 132.5 ± 1.3 Ma. This date confirms and supports an accurate correlation between the ammonoid biostratigraphy of the Neuquén Basin with the Western Mediterranean Province of the Tethys during the Early Cretaceous and matches with the most recently published time scale. It also casts doubts on the validity of K–Ar ages on glauconite-grains recently reported from the Lower Cretaceous of the Vocontian Basin of France.     

Feasibility of pre-earthquake strengthening of buildings based on cost-benefit and life-cycle cost analysis, with the aid of fragility curves

There are two fundamental questions this article aims to deal with. First, whether a pre-earthquake strengthening of a large and heterogeneous building stock (the emphasis here is on building types common in S. Europe), is economically feasible or not, and second what is the optimal retrofit level for mitigating the seismic risk. To this purpose contemporary decision making tools, namely cost-benefit and life-cycle cost analyses, are tailored to the needs of the present study, and implemented with the aid of an ad-hoc developed new software application (COBE06). A method for estimating the reduction in structural vulnerability due to retrofit is proposed, as well as a methodology to determine the optimum retrofit level using the fragility curve approach. Finally, the proposed methodology is used in a pilot application that concerns the city of Thessaloniki, and results are drawn for the feasibility of strengthening the reinforced concrete building stock in this city.     

An operational multiscale system for hazards prediction, mapping, and response

By definition, a crisis is a situation that requires assistance to be managed. Hence, response to a crisis involves the merging of local and non-local emergency response personnel. In this situation, it is critical that each participant: (1) know the roles and responsibilities of each of the other participants; (2) know the capabilities of each of the participants; and (3) have a common basis for action. For many types of natural disasters, this entails having a common operational picture of the unfolding events, including detailed information on the weather, both current and forecasted, that may impact on either the emergency itself or on response activities. The Consequences Assessment Tool Set (CATS) is a comprehensive package of hazard prediction models and casualty and damage assessment tools that provides a linkage between a modeled or observed effect and the attendant consequences for populations, infrastructure, and resources, and, hence, provides the common operational picture for emergency response. The Operational Multiscale Environment model with Grid Adaptivity (OMEGA) is an atmospheric simulation system that links the latest methods in computational fluid dynamics and high-resolution gridding technologies with numerical weather prediction to provide specific weather analysis and forecast capability that can be merged into the geographic information system framework of CATS. This paper documents the problem of emergency response as an end-to-end system and presents the integrated CATS–OMEGA system as a prototype of such a system that has been used successfully in a number of different situations.     

Modeling households’ decisions on reconstruction of houses damaged by earthquakes––Japanese case study

In this study, households’ decisions on reconstruction of damaged houses were modeled, using questionnaire data in Japan. Characteristics of households’ decisions were investigated using parameter estimation results. The effects of subsidizing policy were evaluated as follows. First, subsidy for rebuilding may be effective for the households whose houses were heavily damaged. Second, there is a possibility that subsidy accelerated rebuilding of houses by the households having children. Third, subsidy for rebuilding may not be effective for elderly people’s households and households in depopulated areas.