Spatial distribution of potentially bioavailable metals in surface soils of a contaminated sports ground in Galway, Ireland

Assessing the environmental risk of metal contamination in soils requires the determination of both total (TCs) and bioavailable (BCs) element concentrations. A total of 200 surface (0–10 cm) soil samples were collected from an urban sports ground (South Park) in Galway, Ireland, a former landfill and dumping site, which is currently under remediation. The potential BCs of metals were measured using ethylene-diamine-tetra-acetic acid (EDTA) extraction followed by inductively coupled plasma-optical emission spectrometry analysis, while the TCs were determined using portable X-ray fluorescence spectrometry. It was found that Zn was primarily present in the insoluble residue (EDTA un-extractable) fraction in soils, with the median ratio of BCs/TCs 0.27. However, Pb and Cu had higher ratios of BCs/TCs (median values of 0.60 and 0.39, respectively) suggesting that they are potentially more bioavailable in the soils. The spatial distribution maps showed that both TCs and BCs for Cu, Pb and Zn in the study area were spatially heterogeneous. It was found that the BCs exhibited generally similar spatial patterns as their TCs of Cu, Pb and Zn: high values were mainly located in the west, north-east and south-east portions of the study area, where only a thin layer of topsoil existed. It was recommended that the current remediation action for this site needs to be carried out on an urgent basis.     

Nanoscale zero-valent iron (nZVI): aspects of the core-shell structure and reactions with inorganic species in water

Aspects of the core-shell model of nanoscale zero-valent iron (nZVI) and their environmental implications were examined in this work. The structure and elemental distribution of nZVI were characterized by X-ray energy-dispersive spectroscopy (XEDS) with nanometer-scale spatial resolution in an aberration-corrected scanning transmission electron microscope (STEM). The analysis provides unequivocal evidence of a layered structure of nZVI consisting of a metallic iron core encapsulated by a thin amorphous oxide shell. Three aqueous environmental contaminants, namely Hg(II), Zn(II) and hydrogen sulfide, were studied to probe the reactive properties and the surface chemistry of nZVI. High-resolution X-ray photoelectron spectroscopy (HR-XPS) analysis of the reacted particles indicated that Hg(II) was sequestrated via chemical reduction to elemental mercury. On the other hand, Zn(II) removal was achieved via sorption to the iron oxide shell followed by zinc hydroxide precipitation. Hydrogen sulfide was immobilized on the nZVI surface as disulfide (S(2)(2-)) and monosulfide (S(2-)) species. Their relative abundance in the final products suggests that the retention of hydrogen sulfide occurs via reactions with the oxide shell to form iron sulfide (FeS) and subsequent conversion to iron disulfide (FeS(2)). The results presented herein highlight the multiple reactive pathways permissible with nZVI owing to its two functional constituents. The core-shell structure imparts nZVI with manifold functional properties previously unexamined and grants the material with potentially new applications.     

Carbon trading across sources and periods constrained by the Marrakesh Accords

We examine the potential effects on permit prices and abatement costs of four compliance rules governing emissions trade across sources and periods in the Kyoto Protocol: The banking rule that allows excess permits to be used later; the restoration rate rule that penalizes borrowing; the commitment period reserve rule that limits sales; and finally, the suspension rule that restricts borrowing and sales. Our framework is a two-period model where parties may be out of compliance in the Kyoto period, but are assumed to comply at a later time. Under varying assumptions about market power and US participation, we find that the rules may have pronounced effects on individual costs, but overall efficiency is not severely affected.     

Removing nitric oxide from flue gas using iron(II) citrate chelate absorption with microbial regeneration

The addition of metal chelates such as Fe(II)EDTA or Fe(II)Cit to wet flue gas desulfurization systems has been shown to increase the amount of NO(x) absorption from gas streams containing SO(2). This paper attempts to demonstrate the advantage of not only using Fe(II)Cit chelate to absorb nitrogen oxides from flue gas but also the advantage gained from adding microorganisms to the system. Two distinct classes of microorganisms are needed: denitrifying and iron-reducing bacteria. The presence of oxygen in flue gas will affect the absorption efficiency of NO by Fe(II)Cit chelate. The oxidation of Fe(II) can be slowed with the help of bacteria in two ways: bacteria can serve to directly reduce Fe(III) to Fe(II) or they can serve to keep levels of dissolved oxygen in the solution low. As a result, after NO absorption, Fe(II)(Cit)NO will be reduced by denitrifying bacteria to Fe(II)Cit while Fe(III) is reduced by anaerobic bacteria back to Fe(II). Our experiments have shown that the implementation of our protocol allowed for an NO reduction rate constant increase from standard levels of 0.0222-0.100 m Mh(-1) with inlet NO changed from 250 to 1000 ppm. We have also found that total Fe concentration tends to decrease after prolonged periods of operation due to the loss of some Fe to the formation of Fe(OH)(3) that settles together with the sludge at the bottom of bioreactor tank.