Current and emerging technologies for the remediation of difficult-to-measure radionuclides at nuclear sites

Difficult-to-measure radionuclides (DTMRs), defined by an absence of high energy gamma emissions during decay, are problematic in groundwaters at nuclear sites. DTMRs are common contaminants at many nuclear facilities, with (often) long half-lives and high radiotoxicities within the human body. Effective remediation is, therefore, essential if nuclear site end-state targets are to be met. However, due to a lack of techniques for in situ DTMR detection, technologies designed to remediate these nuclides are underdeveloped and tend to be environmentally invasive. With a growing agenda for sustainable remediation and reduction in nuclear decommissioning costs, there is renewed international focus on the development of less invasive technologies for DTMR clean-up. Here, we review recent developments for remediation of selected problem DTMRs (129I, 99Tc, 90Sr and 3H), with a focus on industrial and site-scale applications. We find that pump and treat (P&T) is the most used technique despite efficacy issues for 129I and 3H. Permeable reactive barriers (PRBs) are a less invasive alternative but have only been demonstrated for removal of 99Tc and 90Sr at scale. Phytoremediation shows promise for site-scale removal of 3H but is unsuitable for 129I and 99Tc due to biotoxicity and bioavailability hazards, respectively. No single technique can remediate all DTMRs of focus. Likewise, there has been no successful site-applied technology with high removal efficiencies for iodine species typically present in groundwaters (iodide/I-, iodate/IO3- and organoiodine). Further work is needed to adapt and improve current techniques to field scales, as well as further research into targeted application of emerging technologies.

The distribution and enrichment of trace elements in surface and core sediments from the Changjiang River Estuary, China: Evidence for anthropogenic inputs and enhanced availability of rare earth elements (REE)

Huge amount of trace metals emitted through manmade activities are carried by the Changjiang River into the East China Sea. Most of them deposit in the Changjiang River Estuary and threaten the regional aquatic environment. In this study, major and trace elements of 34 archive surface sediments and two cores are examined. Sequential extraction procedures were also performed on surface sediments from 12 sites. We found that Tl, Tm, Er show distinct accumulation in surface sediments in the order of Tm > Tl > Er. Particularly, abnormally elevated HREE are observed mainly in those sites near the mouth of the estuary. Most elements exhibit an obvious reduction in the upper 30 cm of core B8, reflecting a decrease of sediment discharge from Changjiang River runoff. The increase of some trace elements recorded in the upper 20 cm of core C3 demonstrates a distinct local anthropogenic input in recent years.

The Searsville Lake Site (California, USA) as a candidate Global boundary Stratotype Section and Point for the Anthropocene series

Cores from Searsville Lake within Stanford University's Jasper Ridge Biological Preserve, California, USA, are examined to identify a potential GSSP for the Anthropocene: core JRBP2018-VC01B (944.5 cm-long) and tightly correlated JRBP2018-VC01A (852.5 cm-long). Spanning from 1900 CE ± 3 years to 2018 CE, a secure chronology resolved to the sub-annual level allows detailed exploration of the Holocene-Anthropocene transition. We identify the primary GSSP marker as first appearance of 239,240Pu (372-374 cm) in JRBP2018-VC01B and designate the GSSP depth as the distinct boundary between wet and dry season at 366 cm (6 cm above the first sample containing 239,240Pu) and corresponding to October-December 1948 CE. This is consistent with a lag of 1-2 years between ejection of 239,240Pu into the atmosphere and deposition. Auxiliary markers include: first appearance of 137Cs in 1958; late 20th-century decreases in δ15N; late 20th-century elevation in SCPs, Hg, Pb, and other heavy metals; and changes in abundance and presence of ostracod, algae, rotifer and protozoan microfossils. Fossil pollen document anthropogenic landscape changes related to logging and agriculture. As part of a major university, the Searsville site has long been used for research and education, serves users locally to internationally, and is protected yet accessible for future studies and communication about the Anthropocene.

Plain Word Summary

The Global boundary Stratotype Section and Point (GSSP) for the proposed Anthropocene Series/Epoch is suggested to lie in sediments accumulated over the last ~120 years in Searsville Lake, Woodside, California, USA. The site fulfills all of the ideal criteria for defining and placing a GSSP. In addition, the Searsville site is particularly appropriate to mark the onset of the Anthropocene, because it was anthropogenic activities-the damming of a watershed-that created a geologic record that now preserves the very signals that can be used to recognize the Anthropocene worldwide.

Time-Integrated Bioavailability Proxy for Actinides in a Contaminated Estuary

Actinides accumulate within aquatic biota in concentrations several orders of magnitude higher than in the seawater [the concentration factor (CF)], presenting an elevated radiological and biotoxicological risk to human consumers. CFs currently vary widely for the same radionuclide and species, which limits the accuracy of the modeled radiation dose to the public through seafood consumption. We propose that CFs will show less dispersion if calculated using a time-integrated measure of the labile (bioavailable) fraction instead of a specific spot sample of bulk water. Herein, we assess recently developed configurations of the diffusive gradients in thin films (DGT) sampling technique to provide a more accurate predictor for the bioaccumulation of uranium, plutonium, and americium within the biota of the Sellafield-impacted Esk Estuary (UK). We complement DGT data with the cross-flow ultrafiltration of bulk seawater to assess the DGT-labile fraction versus the bulk concentration. Sequential elution of Fucus vesiculosis reveals preferential internalization and strong intracellular binding of less particle-reactive uranium. We find significant variations between CF values in biota calculated using a spot sample versus using DGT, which suggest an underestimation of the CF by spot sampling in some cases. We therefore recommend a revision of CF values using time-integrated bioavailability proxies.

Bioavailable actinide fluxes to the Irish Sea from Sellafield-labelled sediments

Nuclear discharges to the oceans have given rise to significant accumulations of radionuclides in sediments which can later remobilise back into the water column. A continuing supply of radionuclides to aquatic organisms and the human food chain can therefore exist, despite the absence of ongoing nuclear discharges. Radionuclide remobilisation from sediment is consequently a critical component of the modelled radiation dose to the public. However, radionuclide remobilisation fluxes from contaminated marine sediments have never been quantitatively determined in-situ to provide a valid assessment of the issue. Here, we combine recent advances in the Diffusive Gradients in Thin Films (DGT) sampling technique with ultrasensitive measurement by accelerator mass spectrometry (AMS) to calculate the remobilisation fluxes of plutonium, americium and uranium isotopes from the Esk Estuary sediments (UK), which have accumulated historic discharges from the Sellafield nuclear reprocessing facility. Isotopic evidence indicates the local biota are accumulating remobilised plutonium and demonstrates the DGT technique as a valid bioavailability proxy, which more accurately reflects the elemental fractionation of the actinides in the biota than traditional bulk water sampling. These results provide a fundamental evaluation of the re-incorporation of bioavailable actinides into the biosphere from sediment reservoirs. We therefore anticipate this work will provide a tool and point of reference to improve radiation dose modelling and contribute insight for other environmental projects, such as the near-surface and deep disposal of nuclear waste.

Environmental risk of trace metals and metalloids in estuarine sediments: An example from Southampton Water, U.K

Industrial and commercial port activities are widely recognized worldwide as an important source of pollution to proximal estuaries. In this study, we analysed geochemical and sedimentological parameters including major and trace elements, organic matter and sediment texture in surface sediments from the estuarine environment of Southampton Water, U.K. Using these data, and multivariate statistical tools [correlation, factor and cluster analysis and pollution indices such as Enrichment Factor (EF), Pollution Load Index (PLI) and the Adverse Effect Index (AEI)], we examine sedimentary trace metal and metalloid contamination, contamination sources, and potential biological impacts of the contamination present. The geochemical data, multivariate statistical analysis and pollution indices indicate that the spatial distribution of trace metals and metalloids is influenced by both sediment composition (and mixing) and anthropogenic activities. Most trace metal and metalloid concentrations are close to local geological background levels, except for Cu, Zn and Pb. The spatial distribution of these elements indicates that the Exxon oil refinery, Southampton port, local marinas and runoff from domestic and industrial activities act effectively as point sources of these elements. Pollution indices calculations highlight a degraded environment as a result of these pollutants, and further work is needed to assess the current impact of trace metals and metalloids on local ecology.

Developing field-scale, gentle remediation options for nuclear sites contaminated with 137Cs and 90Sr: The role of Nature-Based Solutions

The remediation of contaminated land using plants, bacteria and fungi has been widely examined, especially in laboratory or greenhouse systems where conditions are precisely controlled. However, in real systems at the field scale conditions are much more variable and often produce different outcomes, which must be fully examined if 'gentle remediation options', or GROs, are to be more widely implemented, and their associated benefits (beyond risk-management) realized. These secondary benefits can be significant if GROs are applied correctly, and can include significant biodiversity enhancements. Here, we assess recent developments in the field-scale application of GROs for the remediation of two model contaminants for nuclear site remediation (⁹⁰Sr and ¹³⁷Cs), their risk management efficiency, directions for future application and research, and barriers to their further implementation at scale. We also discuss how wider benefits, such as biodiversity enhancements, water filtration etc. can be maximized at the field-scale by intelligent application of these approaches.

Battling the known unknowns: a synoptic review of aquatic plastics research from Australia, the United Kingdom and China

Plastic pollution is a global environmental and human health issue, with plastics now ubiquitous in the environment and biota. Despite extensive international research, key knowledge gaps ("known unknowns") remain around ecosystem-scale and human health impacts of plastics in the environment, particularly in limnetic, coastal and marine systems. Here we review aquatic plastics research in three contrasting geographic and cultural settings, selected to present a gradient of heavily urbanised (and high population density) to less urbanised (and low population density) areas: China, the United Kingdom (UK), and Australia. Research from each country has varying environmental focus (for example, biota-focussed studies in Australia target various bird, fish, turtle and seal species, while UK and China-based studies focus on commercially important organisms such as bivalves, fish and decapods), and uses varying methods and reporting units (e.g. mean, median or range). This has resulted in aquatic plastics datasets that are hard to compare directly, supporting the need to converge on standardised sampling methods, and bioindicator species. While all the study nations show plastics contamination, often at high levels, datasets are variable and do not clearly demonstrate pollution gradients.

Novel DGT Configurations for the Assessment of Bioavailable Plutonium, Americium, and Uranium in Marine and Freshwater Environments

Plutonium, americium, and uranium contribute to the radioactive contamination of the environment and are risk factors for elevated radiation exposure via ingestion through food or water. Due to the significant environmental inventory of these radioelements, a sampling method to accurately monitor their bioavailable concentrations in natural waters is necessary, especially since physicochemical factors can cause significant temporal fluctuations in their waterborne concentrations. To this end, we engineered novel diffusive gradients in thin-film (DGT) configurations using resin gels, which are selective for UO₂²⁺, Pu(IV + V), and Am(III) among an excess of extraneous cations. In this work, we also report an improved synthesis of our in-house ion-imprinted polymer resin, which we used to manufacture a resin gel to capture Am(III). The effective diffusion coefficients of Pu, Am, and U in agarose cross-linked polyacrylamide were determined in freshwater and seawater simulants and in natural seawater, to calibrate these configurations for environmental deployments.

Systematic and bibliographic review of sustainability indicators for contaminated site remediation: Comparison between China and western nations

Sustainable remediation, which promotes the use of more sustainable practices during environmental clean-up activities, is an area of intense international development. While numerous indicators related to sustainable remediation assessment have been utilized and published in related academic literature, they are difficult to unify and vary in emphasis between countries. Following literature retrieval from CNKI, Springer, ScienceDirect, and Wiley Online databases, we present a systematic and bibliometric analysis of relevant national and international literature to define the most frequently considered indicators of sustainability, which play important roles in selecting remediation technologies or site management methods from a sustainability perspective. Following the application of co-occurrence analysis and social network analysis, the results indicate that 1) environmental criteria are most commonly used in evaluating remediation technologies, with significantly less emphasis on social criteria in Chinese publications in particular; 2) with an increasing number of publications in the last 20 years, sustainable remediation has gone through an initial stage, rising stage, and burst or wider adoption stage, characterized by a transformation of the research theme from a predominantly risk-based management approach to a sustainability-based one, with risk management as an underpinning principle; 3) health, resource, cost, and time are the most widely used indicators in terms of social, environmental, economic, and technical criteria, respectively; 4) clear differences exist between China and other nations, particularly in the frequency of usage of each indicator, the application of social criteria, and preferred stakeholders. Nevertheless, China has made significant progress and now makes increasing contributions to sustainable remediation at an international level.

Towards the application of electrokinetic remediation for nuclear site decommissioning

Contamination encountered on nuclear sites includes radionuclides as well as a range of non-radioactive co-contaminants, often in low-permeability substrates such as concretes or clays. However, many commercial remediation techniques are ineffective in these substrates. By contrast, electrokinetic remediation (EKR), where an electric current is applied to remove contaminants from the treated media, retains high removal efficiencies in low permeability substrates. Here, we evaluate recent developments in EKR for the removal of radionuclides in contaminated substrates, including caesium, uranium and others, and the current benefits and limitations of this technology. Further, we assess the present state of EKR for nuclear site applications using real-world examples, and outline key areas for future application.

Assessing the role of the "estuarine filter" for emerging contaminants: pharmaceuticals, perfluoroalkyl compounds and plasticisers in sediment cores from two contrasting systems in the southern U.K

The environmental occurrence, fate and ecotoxicity of emerging contaminants (ECs) has been the subject of increasing research, policy and public concern over the past two decades. While a wide range of publications have examined the environmental persistence and sediment/soil interactions of ECs following their discharge into aquatic environments, the extent to which ECs are sequestered in estuarine sediments, and the impact of this on their environmental persistence and supply to the ocean, in comparison remains unclear. This Article examines the environmental concentrations of seven, relatively water-soluble and environmentally mobile, ECs (including pharmaceuticals, perfluoroalkyl compounds, and plasticisers) in dated intertidal saltmarsh cores from two contrasting estuarine sites in the southern U.K. (one heavily urbanised/industrial, the other non-urbanised). Mean sediment EC concentrations are similar in both estuarine systems (in the range 0.1 (acetaminophen) to 17 (4-hydroxyacetophenone) ng/g dry weight). Despite their variable reported Log K_ow values (from ca. 0.5 to > 7), the ECs are all apparently mobile in the marsh systems studied, and where subsurface concentration maxima are present these most likely relate to local flushing or diffusive processes and cannot be clearly linked to likely input trends or changes in sediment geochemistry (including sedimentary organic carbon content). The "estuarine filter" here, at least with respect to intertidal saltmarsh sediments, shows reduced potential to sequester the seven ECs examined and mediate their supply to coastal and shelf environments.

Validation of a method to quantify microfibres present in aquatic surface microlayers

Many of the methods for microplastics quantification in the environment are criticised creating problems with data validity. Quantification of microplastics in the surface microlayer of aquatic environments using glass plate dipping holds promise as a simple field method, but its efficiency has yet to be validated. We tested a standard glass plate dipping method to assess recovery of four common polymer microfibres and two common natural fibres, under three different salinities (freshwater, brackish water, saltwater). Overall recovery rates were low (26.8 ± 1.54%) but higher recoveries were observed under saltwater treatments (36.5 ± 3.01%) than brackish water (24.5 ± 1.92%) or freshwater (19.3 ± 1.92%). The fibre types showed different recovery rates, with acrylic yielding significantly higher recovery rates (37.0 ± 2.71%) than other fibres across treatments. No clear relationship between the density of the fibres and the recovery efficiency was seen. We suggest that, where this method is used for monitoring microplastics, the results will typically underestimate the total amount present, but that recovery is sufficiently consistent to allow comparison of differences between sampling locations. When comparing data across river-estuarine or similar transects salinity should be monitored to account for salinity-induced differences in sampling recovery.

Novel nanostructured iron oxide cryogels for arsenic (As(III)) removal

Novel macroporous iron oxide nanocomposite cryogels were synthesized and assessed as arsenite (As(III)) adsorbents. The two-step synthesis method, by which a porous nanonetwork of iron oxide is firstly formed, allowed a homogeneous dispersion of the iron oxide in the cryogel reaction mixture, regardless of the nature of the co-polymer forming the cryogel structure. The cryogels showed excellent mechanical properties, especially the acrylamide-based cryogel. This gel showed the highest As(III) adsorption capacity, with the maximum value estimated at 118 mg/g using the Langmuir model. The immobilization of the nanostructured iron oxide gel into the cryogel matrix resulted in slower adsorption kinetics, however the cryogels offer the advantage of a stable three-dimensional structure that impedes the release of the iron oxide nanoparticles into the treated effluent. A preliminary toxicity evaluation of the cryogels did not indicate any apparent inhibition of human hepatic cells activity, which together with their mechanical stability and high adsorption capacity for As(III) make them excellent materials for the development of nanoparticle based adsorption devices for drinking water treatment.

Driving forces and barriers in the removal of phosphorus from water using crop residue, wood and sewage sludge derived biochars

The removal of phosphorus (P) from sewage effluents is necessary to control eutrophication in receiving waters. Biochar has been proposed and is investigated for the capture and reuse of P, however the forces driving and limiting P adsorption are still largely unclear. To identify the forces governing P uptake by biochar, biochars with markedly different physicochemical characteristics derived from a variety of biomass (oilseed rape straw, wheat straw, miscanthus straw, rice husk, soft wood and sewage sludge residue), pyrolysed at various temperatures, were investigated. The biochar samples were characterised in terms of pH, electrical conductivity, total acidity, carbon chemistry, metal composition, surface area_, and porosity, and the uptake and release of P was compared to the biochar properties using multivariate analysis. Uptake of P by the biochars as such was low (< 0.71 mg P/g biochar with feed solutions of 50 mg P/l) and, among the variables studied, the biochars' Ca and Mg content was key in P removal and found to be pH dependant. Enhancement of biochar surface area and porosity was carried out by activation with CO₂ at 800 °C and the uptake significantly improved (p < 0.05) (i.e. an increased surface area from <20 m²/g up to 781 m²/g gave a limited improvement in P removal to <1.2 mg P/g biochar at feed level of 50 mg P/l). These results confirm that the potential to use these unmodified biochars derived from a variety of biomass for P sorption is low, but that the material provides properties that may be modified or enhanced to increase sorption capacity. This study indicates that biochar/biochar feedstock with greater content of Ca and Mg will be more advantageous for P capture.

A cryogel-based bioreactor for water treatment applications

The aim of this study was to develop and test a non-diffusion limited, high cell density bioreactor for biodegradation of various phenol derivatives. The bioreactor was obtained using a straightforward one-step preparation method using cryostructuration and direct cross-linking of bacteria into a 3D structured (sponge-like) macroporous cryogel composite material consisting of 11.6% (by mass) cells and 1.2-1.7% polymer, with approximately 87% water (in the material pores). The macroporous cryogel composite material, composed of live bacteria, has pore sizes in the range of 20-150 μm (confirmed by SEM and Laser Scanning Confocal Microscopy). The enzymatic activity of bacteria within the cryogel structure and the effect of freezing on the viability of the cross-linked cells was estimated by MTT assay. Cryogels based on Pseudomonas mendocina, Rhodococcus koreensis and Acinetobacter radioresistens were exploited for the effective bioremediation of phenol and m-cresol, and to a lesser extent 2-chlorophenol and 4-chlorophenol, utilising these phenolic contaminants in water as their only source of carbon. For evaluation of treatment scalability the bioreactors were prepared in plastic "Kaldnes" carriers to improve their mechanical properties and allow application in batch or fluidised bed water treatment modes.

Sediment structure and physicochemical changes following tidal inundation at a large open coast managed realignment site

Managed realignment (MR) schemes are being implemented to compensate for the loss of intertidal saltmarsh habitats by breaching flood defences and inundating the formerly defended coastal hinterland. However, studies have shown that MR sites have lower biodiversity than anticipated, which has been linked with anoxia and poor drainage resulting from compaction and the collapse of sediment pore space caused by the site's former terrestrial land use. Despite this proposed link between biodiversity and soil structure, the evolution of the sediment sub-surface following site inundation has rarely been examined, particularly over the early stages of the terrestrial to marine or estuarine transition. This paper presents a novel combination of broad- and intensive-scale analysis of the sub-surface evolution of the Medmerry Managed Realignment Site (West Sussex, UK) in the three years following site inundation. Repeated broad-scale sediment physiochemical datasets are analysed to assess the early changes in the sediment subsurface and the preservation of the former terrestrial surface, comparing four locations of different former land uses. Additionally, for two of these locations, high-intensity 3D-computed X-ray microtomography and Itrax micro-X-ray fluorescence spectrometry analyses are presented. Results provide new data on differences in sediment properties and structure related to the former land use, indicating that increased agricultural activity leads to increased compaction and reduced porosity. The presence of anoxic conditions, indicative of poor hydrological connectivity between the terrestrial and post-inundation intertidal sediment facies, was only detected at one site. This site has experienced the highest rate of accretion over the terrestrial surface (ca. 7 cm over 36 months), suggesting that poor drainage is caused by the interaction (or lack of) between sediment facies rather than the former land use. This has significant implications for the design of future MR sites in terms of preparing sites, their anticipated evolution, and the delivery of ecosystem services.

Using a conceptual site model for assessing the sustainability of brownfield regeneration for a soft reuse: A case study of Port Sunlight River Park (U.K.)

Brownfield regeneration to soft reuse such as recreation and amenity has become increasingly common due to the demand for the potential environmental, social and economic benefits that it can deliver. This has led in turn to an increased demand for improved tools to support decision-making for this style of regeneration: tools which are simple to use, based on robust scientific principles and preferably which can ultimately link to quantitative or semi-quantitative cost-benefit analyses. This work presents an approach to assessing and comparing different scenarios for brownfield regeneration to soft reuse and other end-points. A "sustainability linkages" approach, based on sustainability assessment criteria produced by the UK Sustainable Remediation Forum (SuRF-UK), is developed and used in a refined qualitative sustainability assessment, and applied to develop a conceptual site model of sustainability, for a specific case study site (Port Sunlight River Park, U.K., a public leisure park established and maintained on a capped and managed former landfill site). Ranking, on an ex post basis, highlighted the clear sustainability advantages that the establishment of the Port Sunlight River Park has compared with a hypothetical non-development scenario. The conceptual site model provides a clearer basis for understanding cause and effect for benefits and disbenefits and a rationale for grouping individual effects based on their ease of valuation, providing a road map for cost-benefit assessments by (1) being able to match specific linkages to the most appropriate means of valuation, and (2) transparently connecting the sustainability assessment and cost benefit assessment processes.

Agricultural wastes from wheat, barley, flax and grape for the efficient removal of Cd from contaminated water

Agricultural production results in wastes that can be re-used to improve the quality of the environment. This work has investigated for the first time the use of abundant, un-modified agricultural wastes and by-products (AWBs) from grape, wheat, barley and flax production, to reduce the concentration of Cd, a highly toxic and mobile heavy metal, in contaminated water. At concentrations of 1.1 mg Cd per L, flax and grape waste were found superior in removing Cd compared with a granular activated carbon used in water treatment, which is both more expensive and entails greater CO₂ emissions in its production. At a pH representative of mine effluents, where Cd presents its greatest mobility and risk as a pollutant, grape and flax waste showed capacity for effective bulk water treatment due to rapid removal kinetics and moderate adsorption properties: reaching equilibrium within 183 and 8 min - adsorption capacities were determined as 3.99 and 3.36 mg Cd per g, respectively. The capacity to clean contaminated effluents was not correlated with the surface area of the biosorbents. Surface chemistry analysis indicated that Cd removal is associated with exchange with Ca, and chemisorption involving CdCO₃, CdS and CdO groups. This work indicates that some AWBs can be directly (i.e. without pre-treatment or modification) used in bulk to remediate effluents contaminated with heavy metals, without requiring further cost or energy input, making them potentially suitable for low-cost treatment of persistent (e.g. via mine drainage) or acute (e.g. spillages) discharges in rural and other areas.

Historical trace element accumulation in marine sediments from the Tamaulipas shelf, Gulf of Mexico: An assessment of natural vs anthropogenic inputs

The Gulf of Mexico is considered one of the world's major marine ecosystems, supporting important fisheries and habitats such as barrier islands, mangrove forests, seagrass beds, coral reefs etc. It also hosts a range of complex offshore petroleum exploration, extraction, and refining industries, which may have chronic or acute impacts on ecosystem functioning. Previous work on the marine effects of this activity is geographically incomplete, and has tended to focus on direct hydrocarbon impacts, while impacts from other related contaminants (e.g. heavy metals, salt-rich drilling muds) which may be discharged from oil facilities have not been widely assessed. Here, we examine historical trace element accumulation in marine sediments collected from four sites in the Tamaulipas shelf, Gulf of Mexico, in the area of the Arenque oil field. Dated sediment cores were used to examine the sources, and historical and contemporary inputs, of trace metals (including those typically present in oil industry discharges) and their potential biological impact in the Tamaulipas aquatic environment over the last 100years. CaO (i.e. biogenic component) normalized data showed increasing V, Cr, Zn, Cu, Pb, Zr and Ba towards the sediment surface in three of the four cores, with Ba and V (based on an adverse effect index) possibly associated with adverse effects on organisms. Dated Ba/CaO profiles show an increase of 30-137% after opening of oil installations in the study area, and can be broadly correlated with increasing oil industry activities across the wider Gulf of Mexico. Data do not record however a clear enhancement of Ba concentration in sediment cores collected near to oil platforms over more distal cores, indicating that any Ba released from drilling platforms is incorporated quickly into the sediments around the drilling sites, and once this element has been deposited its rate of resuspension and mobility is low.

CAPSULE ABSTRACT

Sediment core data from the Tamaulipas shelf show the influence of oil industry activities on selected trace element concentrations, with Ba/CaO broadly correlating with increasing oil industry activities across the wider Gulf of Mexico.

Analysis of influencing factors on public perception in contaminated site management: Simulation by structural equation modeling at four sites in China

Public perception towards contaminated site management, a not readily quantifiable latent parameter, was linked through structural equation modeling in this paper to 22 measurable/observable manifest variables associated with the extent of information dissemination and public knowledge of soil pollution, attitude towards remediation policies, and participation in risk mitigation processes. Data obtained through a survey of 412 community residents at four remediation sites in China were employed in the model validation. The outcomes showed that public perception towards contaminated site management might be explained through selected measurable parameters in five categories, namely information disclosure, knowledge of soil pollution, expectations of remediation and redevelopment outcomes, public participation, and site policy, along with their interactions. Among these, information dissemination and attitude towards management policies exhibited significant influence in promoting positive public perception. Based on these examples, responsible agencies therefore should focus on public accessibility to reliable information, and encourage public inputs into policies for contaminated site management, in order to gain public confidence during remediation and regeneration projects.

The contaminant legacy from historic coastal landfills and their potential as sources of diffuse pollution

Prior to modern environmental regulation landfills in low-lying coastal environments were frequently constructed without leachate control, relying on natural attenuation within inter-tidal sediments to dilute and disperse contaminants reducing environmental impact. With sea level rise and coastal erosion these sites may now pose a pollution risk, yet have received little investigation. This work examines the extent of metal contamination in saltmarsh sediments surrounding a historic landfill in the UK. Patterns of sediment metal data suggest typical anthropogenic pollution chronologies for saltmarsh sediments in industrialised nations. However, many metals were also enriched at depth in close proximity to the landfill boundary and are indicative of a historical leachate plume. Though this total metal load is low, e.g., c. 1200 and 1650kg Pb and Zn respectively, with >1000 historic landfills on flood risk or eroding coastlines in the UK this could represent a significant, yet under-investigated, source of diffuse pollution.

One-step formation of three-dimensional macroporous bacterial sponges as a novel approach for the preparation of bioreactors for bioremediation and green treatment of water

A novel method of crosslinking live bacteria into a stable 3D porous structure and its subsequent use in phenol degradation is reported.

Assessing phytotoxicity of trace element-contaminated soils phytomanaged with gentle remediation options at ten European field trials

Gentle remediation options (GRO), i.e. in situ stabilisation, (aided) phytoextraction and (aided) phytostabilisation, were implemented at ten European sites contaminated with trace elements (TE) from various anthropogenic sources: mining, atmospheric fallout, landfill leachates, wood preservatives, dredged-sediments, and dumped wastes. To assess the performance of the GRO options, topsoil was collected from each field trial, potted, and cultivated with lettuce (Lactuca sativa L.) for 48days. Shoot dry weight (DW) yield, photosynthesis efficiency and major element and TE concentrations in the soil pore water and lettuce shoots were measured. GRO implementation had a limited effect on TE concentrations in the soil pore water, although use of multivariate Co-inertia Analysis revealed a clear amelioration effect in phytomanaged soils. Phytomanagement increased shoot DW yield at all industrial and mine sites, whereas in agricultural soils improvements were produced in one out of five sites. Photosynthesis efficiency was less sensitive than changes in shoot biomass and did not discriminate changes in soil conditions. Based on lettuce shoot DW yield, compost amendment followed by phytoextraction yielded better results than phytostabilisation; moreover shoot ionome data proved that, depending on initial soil conditions, recurrent compost application may be required to maintain crop production with common shoot nutrient concentrations.

Trends in the recovery of phosphorus in bioavailable forms from wastewater

Addressing food security issues arising from phosphorus (P) scarcity is described as one of the greatest global challenges of the 21st Century. Dependence on inorganic phosphate fertilisers derived from limited geological sources of P creates an urgent need to recover P from wastes and treated waters, in safe forms that are also effective agriculturally - the established process of P removal by chemical precipitation using Fe or Al salts, is effective for P removal but leads to residues with limited bioavailability and contamination concerns. One of the greatest opportunities for P recovery is at wastewater treatment plants (WWTPs) where the crystallisation of struvite and Ca-P from enhanced biological P removal (EBPR) sludge is well developed and already shown to be economically and operationally feasible in some WWTPs. However, recovery through this approach can be limited to <25% efficiency unless chemical extraction is applied. Thermochemical treatment of sludge ash produces detoxified residues that are currently utilised by the fertiliser industry; wet chemical extraction can be economically feasible in recovering P and other by-products. The bioavailability of recovered P depends on soil pH as well as the P-rich material in question. Struvite is a superior recovered P product in terms of plant availability, while use of Ca-P and thermochemically treated sewage sludge ash is limited to acidic soils. These technologies, in addition to others less developed, will be commercially pushed forward by revised fertiliser legislation and foreseeable legislative limits for WWTPs to achieve discharges of <1 mg P/L.

The Fate of Contaminants and Stable Pb Isotopes in a Changing Estuarine Environment: 20 Years On

Estuarine sediments provide an important sink for contaminants discharged into fluvial, estuarine, and nearshore settings, and numerous authors have utilized this trapping function to assess historical contaminant loadings and contaminant breakdown/transformation processes. This Article examines the retention of elemental and isotopic sedimentary signatures in an industrialized estuarine system subject to a strongly upward sea-level trend, over a 20 year period. Two contrasting saltmarsh sites (at Hythe and Hamble, part of the wider Southampton Water estuarine system, UK) were examined, which had been previously cored and analyzed in the early 1990s. Much of the geochemical record of recent anthropogenic activity has been eroded and lost at the Hamble site. In contrast, radiometric, isotopic and elemental records of anthropogenic activity have been retained in the Hythe marsh, with ¹³⁷Cs and Cu depth profiles showing retention of input maxima related to fallout and local industrial discharges, respectively. Stable Pb isotope data show a broad degree of correspondence in cores analyzed in 1994 and 2014 when plotted against sediment (radiometric) age, indicating the usefulness of isotopic data in retaining information on Pb sources and in disentangling Pb input histories. New ultrahigh precision, double-spike mass spectrometry stable Pb isotope data allow clearer discrimination of historical Pb input phases, and highlight within-estuary mixing and supply of reworked, secondary contamination from erosion of anthropogenically labeled sediments elsewhere in the estuary.

Sedimentary heavy metal(loid) contamination in the Veracruz shelf, Gulf of Mexico: A baseline survey from a rapidly developing tropical coast

This study examines sediment texture, geochemistry and sediment accumulation in cores from four sites in the Veracruz shelf area of the Gulf of Mexico, to assess the inputs of heavy metal(loid)s (and their potential biological impacts) in this carbonate-dominated shelf system, and to examine the rate of sedimentation near to the mouths of the La Antigua and Jamapa Rivers. The use of different pollution indices showed enrichment with Pb in all cores studied, although based on sediment quality guidelines As was the only element that has potential to occasionally cause damage to the benthic organisms present in the area. Heavy metal(loid) and sediment input from terrestrial and coastal sources is limited compared to more proximal, near-shore areas. The sediment core data presented however give a baseline dataset for heavy metal(loid) concentrations in the Veracruz shelf, against which future anthropogenic inputs can be assessed.

Remediation of hexavalent chromium contamination in chromite ore processing residue by sodium dithionite and sodium phosphate addition and its mechanism

Large amounts of chromite ore processing residue (COPR) wastes have been deposited in many countries worldwide, generating significant contamination issues from the highly mobile and toxic hexavalent chromium species (Cr(VI)). In this study, sodium dithionite (Na₂S₂O₄) was used to reduce Cr(VI) to Cr(III) in COPR containing high available Fe, and then sodium phosphate (Na₃PO₄) was utilized to further immobilize Cr(III), via a two-step procedure (TSP). Remediation and immobilization processes and mechanisms were systematically investigated using batch experiments, sequential extraction studies, X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). Results showed that Na₂S₂O₄ effectively reduced Cr(VI) to Cr(III), catalyzed by Fe(III). The subsequent addition of Na₃PO₄ further immobilized Cr(III) by the formation of crystalline CrPO₄·6H₂O. However, addition of Na₃PO₄ simultaneously with Na₂S₂O₄ (via a one-step procedure, OSP) impeded Cr(VI) reduction due to the competitive reaction of Na₃PO₄ and Na₂S₂O₄ with Fe(III). Thus, the remediation efficiency of the TSP was much higher than the corresponding OSP. Using an optimal dosage in the two-step procedure (Na₂S₂O₄ at a dosage of 12× the stoichiometric requirement for 15 days, and then Na₃PO₄ in a molar ratio (i.e. Na₃PO₄: initial Cr(VI)) of 4:1 for another 15 days), the total dissolved Cr in the leachate determined via Toxicity Characteristic Leaching Procedure (TCLP Cr) testing of our samples was reduced to 3.8 mg/L (from an initial TCLP Cr of 112.2 mg/L, i.e. at >96% efficiency).

Trace element storage capacity of sediments in dead Posidonia oceanica mat from a chronically contaminated marine ecosystem

Posidonia oceanica mat is considered a long-term bioindicator of contamination. Storage and sequestration of trace elements and organic carbon (C_org ) were assessed in dead P. oceanica mat and bare sediments from a highly polluted coastal marine area (Augusta Bay, central Mediterranean). Sediment elemental composition and sources of organic matter have been altered since the 1950s. Dead P. oceanica mat displayed a greater ability to bury and store trace elements and C_org than nearby bare sediments, acting as a long-term contaminant sink over the past 120 yr. Trace elements, probably associated with the mineral fraction, were stabilized and trapped despite die-off of the overlying P. oceanica meadow. Mat deposits registered historic contamination phases well, confirming their role as natural archives for recording trace element trends in marine coastal environments. This sediment typology is enriched with seagrass-derived refractory organic matter, which acts mainly as a diluent of trace elements. Bare sediments showed evidence of inwash of contaminated sediments via reworking; more rapid and irregular sediment accumulation; and, because of the high proportions of labile organic matter, a greater capacity to store trace elements. Through different processes, both sediment typologies represent a repository for chemicals and may pose a risk to the marine ecosystem as a secondary source of contaminants in the case of sediment dredging or erosion. Environ Toxicol Chem 2017;36:49-58. © 2016 SETAC.

Brownfields to green fields: Realising wider benefits from practical contaminant phytomanagement strategies

Gentle remediation options (GROs) are risk management strategies or technologies involving plant (phyto-), fungi (myco-), and/or bacteria-based methods that result in a net gain (or at least no gross reduction) in soil function as well as effective risk management. GRO strategies can be customised along contaminant linkages, and can generate a range of wider economic, environmental and societal benefits in contaminated land management (and in brownfields management more widely). The application of GROs as practical on-site remedial solutions is still limited however, particularly in Europe and at trace element (typically metal and metalloid) contaminated sites. This paper discusses challenges to the practical adoption of GROs in contaminated land management, and outlines the decision support tools and best practice guidance developed in the European Commission FP7-funded GREENLAND project aimed at overcoming these challenges. The GREENLAND guidance promotes a refocus from phytoremediation to wider GROs- or phyto-management based approaches which place realisation of wider benefits at the core of site design, and where gentle remediation technologies can be applied as part of integrated, mixed, site risk management solutions or as part of "holding strategies" for vacant sites. The combination of GROs with renewables, both in terms of biomass generation but also with green technologies such as wind and solar power, can provide a range of economic and other benefits and can potentially support the return of low-level contaminated sites to productive usage, while combining GROs with urban design and landscape architecture, and integrating GRO strategies with sustainable urban drainage systems and community gardens/parkland (particularly for health and leisure benefits), has large potential for triggering GRO application and in realising wider benefits in urban and suburban systems. Quantifying these wider benefits and value (above standard economic returns) will be important in leveraging funding for GRO application and soft site end-use more widely at vacant or underutilized sites.

Carbon-cryogel hierarchical composites as effective and scalable filters for removal of trace organic pollutants from water

Effective technologies are required to remove organic micropollutants from large fluid volumes to overcome present and future challenges in water and effluent treatment. A novel hierarchical composite filter material for rapid and effective removal of polar organic contaminants from water was developed. The composite is fabricated from phenolic resin-derived carbon microbeads with controllable porous structure and specific surface area embedded in a monolithic, flow permeable, poly(vinyl alcohol) cryogel. The bead-embedded monolithic composite filter retains the bulk of the high adsorptive capacity of the carbon microbeads while improving pore diffusion rates of organic pollutants. Water spiked with organic contaminants, both at environmentally relevant concentrations and at high levels of contamination, was used to determine the purification limits of the filter. Flow through tests using water spiked with the pesticides atrazine (32 mg/L) and malathion (16 mg/L) indicated maximum adsorptive capacities of 641 and 591 mg pollutant/g carbon, respectively. Over 400 bed volumes of water contaminated with 32 mg atrazine/L, and over 27,400 bed volumes of water contaminated with 2 μg atrazine/L, were treated before pesticide guideline values of 0.1 μg/L were exceeded. High adsorptive capacity was maintained when using water with high total organic carbon (TOC) levels and high salinity. The toxicity of water filtrates was tested in vitro with human epithelial cells with no evidence of cytotoxicity after initial washing.

A simple method for the production of large volume 3D macroporous hydrogels for advanced biotechnological, medical and environmental applications

The development of bulk, three-dimensional (3D), macroporous polymers with high permeability, large surface area and large volume is highly desirable for a range of applications in the biomedical, biotechnological and environmental areas. The experimental techniques currently used are limited to the production of small size and volume cryogel material. In this work we propose a novel, versatile, simple and reproducible method for the synthesis of large volume porous polymer hydrogels by cryogelation. By controlling the freezing process of the reagent/polymer solution, large-scale 3D macroporous gels with wide interconnected pores (up to 200 μm in diameter) and large accessible surface area have been synthesized. For the first time, macroporous gels (of up to 400 ml bulk volume) with controlled porous structure were manufactured, with potential for scale up to much larger gel dimensions. This method can be used for production of novel 3D multi-component macroporous composite materials with a uniform distribution of embedded particles. The proposed method provides better control of freezing conditions and thus overcomes existing drawbacks limiting production of large gel-based devices and matrices. The proposed method could serve as a new design concept for functional 3D macroporous gels and composites preparation for biomedical, biotechnological and environmental applications.

Developing and validating a practical decision support tool (DST) for biomass selection on marginal land

Marginal, often contaminated, sites exist in large areas across the world as a result of historic activities such as industry, transportation and mineral extraction. Remediation, or other improvements, of these sites is typically only considered for sites with high exploitation pressure and those posing the highest risks to human health or the environment. At the same time there is increasing competition for land resources for different needs such as biofuel production. Potentially some of this land requirement could be met by production of biomass on brownfield or other marginal land, thereby improving the land while applying the crop cultivation as part of an integrated management strategy. The design and decision making for such a strategy will be site specific. A decision support framework, the Rejuvenate DST (decision support tool) has been developed with the aim of supporting such site specific decision making. This tool is presented here, and has been tested by applying it to a number of case study sites. The consequent SWOT (strength, weakness, opportunities and threats) analysis is discussed and evaluated. The DST was found to be systematic, transparent, and applicable for diverse sites in France, Romania and Sweden, in addition to the sites to which it was applied through its development. The DST is regarded as especially useful if applied as a checklist in an iterative way throughout the decision process, from identifying potential crops to identifying knowledge gaps, working/non-working management strategies and potential risks. The DST also provides a structure promoting effective stakeholder engagement.

Phenolic carbon tailored for the removal of polar organic contaminants from water: a solution to the metaldehyde problem?

Current water treatment technologies are inefficient at treating water contaminated with metaldehyde, an 8-member cyclic tetramer of acetaldehyde widely used as a molluscicide in large-scale agriculture and in gardens, and which has been frequently observed to breach European regulatory limits in the UK due to its high solubility and frequent use. Here, we examine the controls on metaldehyde adsorption onto activated phenolic carbon, namely the influence of activation degree, pore size distribution, particle size, point of zero charge and surface functionalisation, by synthesising "tailored" carbons from phenolic resin. Metaldehyde adsorption has been found to be independent of specific surface area (SBET), which is highly unusual for an adsorption process, and is favoured in carbons with (a) high microporosity with narrow pore size distribution, (b) presence of mesopores which allow efficient diffusive transport, and (c) an absence of negatively charged functional groups. The maximum adsorption capacity of the phenolic resin-derived carbons, tested at an elevated (i.e. exceeding environmental levels) water concentration of 64 mg metaldehyde/L, was 76 mg metaldehyde/g carbon compared with 13 mg metaldehyde/g carbon in industrial granular activated carbon (GAC). The phenolic resin-derived carbons and GAC showed similar adsorption kinetics with maximum metaldehyde uptake occurring within 30 min under batch adsorption conditions, although adsorption isotherms indicate much stronger adsorption of metaldehyde on the phenolic resin-derived carbons. Adsorption efficiency for metaldehyde was maintained even in the presence of high background concentrations of organic matter and inorganic salts, indicating the potential utility of these "designer" carbons in waste and/or drinking water treatment.

Three-dimensional geological modelling of anthropogenic deposits at small urban sites: a case study from Sheepcote Valley, Brighton, UK

Improvements in computing speed and capacity and the increasing collection and digitisation of geological data now allow geoscientists to produce meaningful 3D spatial models of the shallow subsurface in many large urban areas, to predict ground conditions and reduce risk and uncertainty in urban planning. It is not yet clear how useful this 3D modelling approach is at smaller urban scales, where poorly characterised anthropogenic deposits (artificial/made ground and fill) form the dominant subsurface material and where the availability of borehole and other geological data is less comprehensive. This is important as it is these smaller urban sites, with complex site history, which frequently form the focus of urban regeneration and redevelopment schemes. This paper examines the extent to which the 3D modelling approach previously utilised at large urban scales can be extended to smaller less well-characterised urban sites, using a historic landfill site in Sheepcote Valley, Brighton, UK as a case study. Two 3D models were generated and compared using GSI3D™ software, one using borehole data only, one combining borehole data with local geological maps and results from a desk study (involving collation of available site data, including ground contour plans). These models clearly delimit the overall subsurface geology at the site, and allow visualisation and modelling of the anthropogenic deposits present. Shallow geophysical data collected from the site partially validate the 3D modelled data, and can improve GSI3D™ outputs where boundaries of anthropogenic deposits may not be clearly defined by surface, contour or borehole data. Attribution of geotechnical and geochemical properties to the 3D model is problematic without intrusive investigations and sampling. However, combining available borehole data, shallow geophysical methods and site histories may allow attribution of generic fill properties, and consequent reduction of urban development risk and uncertainty.

Developing principles of sustainability and stakeholder engagement for "gentle" remediation approaches: the European context

Gentle Remediation Options (GRO) are risk management strategies or techniques for contaminated sites that result in no gross reduction in soil functionality (or a net gain) as well as risk management. Intelligently applied GROs can provide: (a) rapid risk management via pathway control, through containment and stabilisation, coupled with a longer term removal or immobilisation/isolation of the contaminant source term; and (b) a range of additional economic (e.g. biomass generation), social (e.g. leisure and recreation) and environmental (e.g. CO2 sequestration) benefits. In order for these benefits to be optimised or indeed realised, effective stakeholder engagement is required. This paper reviews current sector practice in stakeholder engagement and its importance when implementing GRO and other remediation options. From this, knowledge gaps are identified, and strategies to promote more effective stakeholder engagement during GRO application are outlined. Further work is required on integrating stakeholder engagement strategies into decision support systems and tools for GRO (to raise the profile of the benefits of effective stakeholder engagement and participation, particularly with sector professionals), and developing criteria for the identification of different stakeholder profiles/categories. Demonstrator sites can make a significant contribution to stakeholder engagement via providing evidence on the effectiveness of GRO under varying site contexts and conditions. Effective and sustained engagement strategies however will be required to ensure that site risk is effectively managed over the longer-term, and that full potential benefits of GRO (e.g. CO2 sequestration, economic returns from biomass generation and "leverage" of marginal land, amenity and educational value, ecosystem services) are realised and communicated to stakeholders.

Ionizing radiation-induced DNA damage response identified in marine mussels, Mytilus sp

There is growing concern over the potential detrimental impact of ionizing radiation on natural biota. The mechanistic cause-and-effect impact of ionizing radiation has yet to be characterized in any aquatic species. Adopting an integrated approach, including radiochemical analysis of environmental samples, we evaluate molecular responses to ionizing radiation in the marine mussel, Mytilus edulis. These responses included analyses of RAD51 mRNA expression, a gene involved in the repair of DNA double strand breaks, and induction of DNA strand breaks using the comet assay, in samples collected from a site impacted by low level ionizing radiation discharges. Based on activities of the radionuclides measured in sediment and mussel tissue at the discharge site, external and internal dose rates were low, at ca. 0.61 μGyh(-1) and significantly lower than the generic (all species) "no effect" dose rate of 10 uGyh(-1), yet DNA strand breakage and RAD51 mRNA expression were both altered.

Driving forces of conformational changes in single-layer graphene oxide

The extensive oxygen-group functionality of single-layer graphene oxide proffers useful anchor sites for chemical functionalization in the controlled formation of graphene architecture and composites. However, the physicochemical environment of graphene oxide and its single-atom thickness facilitate its ability to undergo conformational changes due to responses to its environment, whether pH, salinity, or temperature. Here, we report experimental and molecular simulations confirming the conformational changes of single-layer graphene oxide sheets from the wet or dry state. MD, PM6, and ab initio simulations of dry SLG and dry and wetted SLGO and electron microscopy imaging show marked differences in the properties of the materials that can explain variations in previously observed results for the pH dependent behavior of SLGO and electrical conductivity of chemically modified graphene-polymer composites. Understanding the physicochemical responses of graphene and graphene oxide architecture and performing selected chemistry will ultimately facilitate greater tunability of their performance.

Long-term fate of polycyclic aromatic hydrocarbons (PAH) in sediments from Loch Leven after closure of an aluminium smelter

An aluminium smelter discharged polycyclic aromatic hydrocarbons (PAHs) into Loch Leven on the west of Scotland from 1907 until it closed in 2000, resulting in elevated PAH concentrations in the sediment. A temporal monitoring programme to investigate any recovery in sediment concentrations began in 2004, with sampling each year until 2008 and again in 2010. Cores were also collected to investigate temporal trends over a longer time scale and to estimate the sedimentation rate in the loch. The loch is divided into two basins, and PAH concentrations were significantly higher in the upper basin, closer to the smelter, than in the lower basin. The PAH distribution and concentration ratios were consistent with a pyrolytic source of PAHs, with a high proportion of heavier parent PAHs. There was no evidence of any recovery in PAH concentrations, perhaps due to the mixing and disturbances of the sediment, and the persistence of PAHs. Concentrations of all PAHs were above the Background Assessment Concentrations (BACs) in both basins. In the lower basin only the 5- and 6-ring PAHs were above the Effects Range Low (ERL) values, but in the upper basin all but naphthalene were above the ERLs. There is therefore still an unacceptable risk of chronic effects in marine species. Concentrations decreased down the cores, falling below BACs in the deepest sections. However, ERLs were exceeded as far down the core as 30 cm for some PAHs.

High efficiency removal of dissolved As(III) using iron nanoparticle-embedded macroporous polymer composites

Novel nanocomposite materials where iron nanoparticles are embedded into the walls of a macroporous polymer were produced and their efficiency for the removal of As(III) from aqueous media was studied. Nanocomposite gels containing α-Fe(2)O(3) and Fe(3)O(4) nanoparticles were prepared by cryopolymerisation resulting in a monolithic structure with large interconnected pores up to 100 μm in diameter and possessing a high permeability (ca. 3 × 10(-3) ms(-1)). The nanocomposite devices showed excellent capability for the removal of trace concentrations of As(III) from solution, with a total capacity of up to 3mg As/g of nanoparticles. The leaching of iron was minimal and the device could operate in a pH range 3-9 without diminishing removal efficiency. The effect of competing ions such as SO(4)(2-) and PO(4)(3-) was negligible. The macroporous composites can be easily configured into a variety of shapes and structures and the polymer matrix can be selected from a variety of monomers, offering high potential as flexible metal cation remediation devices.

Morphological and chemical features of nano and macroscale carbons affecting hydrogen peroxide decomposition in aqueous media

Chemical and structural factors of carbon materials affect their activity in adsorption and surface reactions in aqueous media. Decomposition of hydrogen peroxide studied is a probe reaction for exploring parameters of carbons that might be involved, such as specific surface area, nitrogen and oxygen doping and conformational changes. To date, a detailed comparison of the behavior of carbon nanoscale (Carbon Nanotubes, CNT, Single Layer Graphene Oxide, SLGO) with macroscale (Activated carbons, AC) materials in this reaction has not been forthcoming. Herein, we demonstrate that on their first cycle, ACs in doped and undoped forms outperform all nanoscale carbons tested in the H(2)O(2) decomposition. Among the nanocarbons, nitrogen-doped CNT exhibited the highest activity in this reaction. However, subsequent recycling of each carbon, without chemical regeneration between uses, reveals SLGO exhibits greater reaction rate stability over an extended number of cycles (n>8) than other carbons including nitrogen-doped CNT and ACs. The effects of pH, temperature and concentration on the reaction were analyzed. Quantum-chemical modeling and reaction kinetics analysis reveal key processes likely involved in hydrogen peroxide decomposition and show evidence that the reaction rate is linked to active sites with N-and O-containing functionalities.

Electrokinetic remediation of plutonium-contaminated nuclear site wastes: results from a pilot-scale on-site trial

This paper examines the field-scale application of a novel low-energy electrokinetic technique for the remediation of plutonium-contaminated nuclear site soils, using soil wastes from the Atomic Weapons Establishment (AWE) Aldermaston site, Berkshire, UK as a test medium. Soils and sediments with varying composition, contaminated with Pu through historical site operations, were electrokinetically treated at laboratory-scale with and without various soil pre-conditioning agents. Results from these bench-scale trials were used to inform a larger on-site remediation trial, using an adapted containment pack with battery power supply. 2.4 m(3) (ca. 4t onnes) of Pu-contaminated soil was treated for 60 days at a power consumption of 33 kWh/m(3), and then destructively sampled. Radiochemical data indicate mobilisation of Pu in the treated soil, and migration (probably as a negatively charged Pu-citrate complex) towards the anodic compartment of the treatment cell. Soil in the cathodic zone of the treatment unit was remediated to a level below free-release disposal thresholds (1.7 Bq/g, or <0.4 Bq/g above background activities). The data show the potential of this method as a low-cost, on-site tool for remediation of radioactively contaminated soils and wastes which can be operated remotely on working sites, with minimal disruption to site infrastructure or operations.

Storage and behavior of As, Sb, Pb, and Cu in ombrotrophic peat bogs under contrasting water table conditions

Concentration depth profiles and inventories of solid-phase As, Sb, Pb, and Cu were determined in ²¹⁰Pb-dated cores from an ombrotrophic peat bog in northwest England. Cores were collected from the peat dome and adjacent to an eroding gully. Down-core distributions of As, Sb, Pb, and Cu in the dome core are almost identical. The water table is close to the dome surface with only short-term draw-down. Under these conditions, As, Sb, Pb, and Cu are immobile, allowing the reconstruction of trends in historical contaminant deposition. The peak in atmospheric deposition of As, Sb, Pb, and Cu (4.59, 2.78, 147, and 26.7 mg m⁻² y⁻¹, respectively) occurred during the late 19th century. Stable Pb isotope ratios reveal that Pb deposition during this period was from indigenous and foreign sources. The mean water table is much lower at the gully edge, and there are pronounced interannual fluctuations. These conditions have not affected the integrity of the Pb and Cu records but have caused postdepositional mobilization and redistribution of As and Sb. Cumulative inventories show significant loss of As and Sb at the gully edge site. Long-term water table draw-down in ombrotrophic peat bogs has the potential to alter the geochemistry and fate of previously deposited As and Sb.

Real-time imaging of complex nanoscale mechanical responses of carbon nanotubes in highly compressible porous monoliths

A facile and rapid assembly of powdered carbon nanotubes (CNTs) into compressible, porous, macroscale monoliths is reported. Despite a Poisson's ratio just above zero, we found that the sample under compression inside a scanning electron microscope (SEM) revealed CNT regions behaving in auxetic and vortex-like rotational modes as well as standard collapse responses. This method is crucial in understanding the macroscale behaviour based on the accumulation of nanoscale responses to an applied force.