Andrew B. Cundy

Use of iron-based technologies in contaminated land and groundwater remediation: A review

Reactions involving iron play a major role in the environmental cycling of a wide range of important organic, inorganic and radioactive contaminants. Consequently, a range of environmental clean-up technologies have been proposed or developed which utilise iron chemistry to remediate contaminated land and surface and subsurface waters, e.g. the use of injected zero zero-valent iron nanoparticles to remediate organic contaminant plumes; the generation of iron oxyhydroxide-based substrates for arsenic removal from contaminated waters; etc. This paper reviews some of the latest iron-based technologies in contaminated land and groundwater remediation, their current state of development, and their potential applications and limitations.

Reconstructing historical trends in metal input in heavily-disturbed, contaminated estuaries: studies from Bilbao, Southampton Water and Sicily

Estuaries may be important reservoirs for contaminants as they tend to act as sinks for fine, contaminant-reactive sediments, and, historically, they have acted as centres for industrial and urban development. Analysis of dated sediment cores from these areas may allow historical trends in heavy metal input to be reconstructed, and recent and historical inputs of metal contaminants to be compared. Undisturbed saltmarsh settings have been used widely in the reconstruction of historical trends in metal input as saltmarshes provide a stable, vegetated substrate of dominantly fine sediments, and are less prone to erosion and reworking than adjacent mudflat areas. In comparison, much less research on historical pollution trends has been undertaken at estuarine sites which are prone to severe local disturbance, such as intertidal areas which are routinely dredged or where sedimentary processes have been modified by human activities such as shipping, salt working, port activities, land claim etc. This paper assesses the usefulness of 210Pb and 137Cs dating, combined with geochemical studies, in reconstructing historical trends in heavy metal input and sediment accretion in 3 heavily-modified, industrialised estuarine areas in Europe: the Bilbao estuary (Spain), Southampton Water (UK), and the Mulinello estuary (Sicily). Of these sites, only a salt marsh core from the Mulinello estuary provides a high-resolution record of recent heavy metal inputs. In Southampton Water only a partial record of changing metal inputs over time is retained due to land-claim and possible early-diagenetic remobilisation, while at Bilbao the vertical distribution of heavy metals in intertidal flats is mainly controlled by input on reworked sediment particles and variations in sediment composition. Where 137Cs and 210Pb distributions with depth allow a chronology of sediment deposition to be established, and early-diagenetic remobilisation has been minimal, mudflat and saltmarsh cores from even the most heavily-disturbed estuarine sites can provide useful information on variations in historical contaminant input. When the sediments have been vigorously mixed or reworked, large-scale compositional variations are present, or significant early-diagenetic remobilisation has occurred, however, only general information on the scale of contamination can be obtained.

Heavy metal distribution and early-diagenesis in salt marsh sediments from the Medway Estuary, Kent, UK

Salt marsh cores are increasingly being used to study metal pollution chronologies. Salt marshes in macro-tidal estuaries, however, tend to retain a time-integrated or ‘smoothed’ signal rather than a record of discrete pollutant inputs, due to extensive sediment reworking. More generally, an accurate chronology of metal input to salt marsh sediments can be difficult to assess because of the potential early-diagenetic mobility of both the radionuclides used for dating and the contaminants of interest. A dated salt marsh core from the macro-tidal Medway Estuary, southeast England, was assessed using both total sediment metal data and partitioning data. These data indicate that both Mn and Fe have been significantly remobilised and that these diagenetic processes have slightly modified the vertical distributions of Cu, Pb and Zn. Zinc is the most diagenetically reactive followed by Cu and then Pb. However, general trends in pollutant loading can still be identified with maximum inputs occurring between ca. 1900 and 1950, decreasing towards the present day.

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.

Sedimentary and geochemical variations in a salt marsh/mud flat environment from the mesotidal Hamble estuary, southern England

The sediment record in a salt marsh contains valuable information on anthropogenic and natural inputs. The reliability of this record for a single core depends on how representative the sample is for the whole marsh and whether the various indicator elements are immobile. A detailed radiometric and geochemical study has been carried out on a series of salt marsh cores from the Hamble estuary, southern England, a temperate mesotidal estuary. Cores have been taken in two transects to assess cross-marsh variations in sediment accretion, trace element deposition and early diagenesis. From this, conclusions are drawn about variations in sedimentary processes and marsh stability, trace element focusing and the effect of early diagenetic movement on historical pollution records. Sediment accumulation rates across the salt marsh vary between 4 and 8 mm yr?1 (137Cs and 210Pb dating) and are apparently independent of elevation in the marsh. 210Pb, 137Cs and anthropogenic Cu data show that the fronting mud flat is eroding, which may lead to increased wave attack and erosion at the marsh edge. The salt marsh itself, however, is accumulating at a rate significantly higher than the local rate of mean sea-level rise. The atmospheric deposition record of 210Pbxs is not well-preserved in the more organic-rich sediment at the rear of the salt marsh. 210Pb and Pb are apparently mobilised in highly reduced sediments beneath the permanent water table and precipitate in overlying partially reduced sediment with hydrous Mn and Fe oxides. Such diagenetic movement of 210Pb and Pb is localised and is not laterally continuous. At sites showing possible early diagenetic remobilisation of 210Pb the accuracy of 210Pb dating is reduced. Remobilisation of 210Pb does not preclude 210Pb dating, however, if peaks arising from redox mobility are identified and eliminated by comparison with other geochemical data (Fe, Pb, S, etc.). Of the trace elements examined, Cu shows a clear pollution spike. Anthropogenic Cu introduced into the Hamble estuary from the Esso refinery at Fawley, Southampton Water peaked around 1970 and has significantly reduced since 1971. Cu, 210Pbxs and 137Cs are focused to some degree at the front of the marsh due to input of material labelled with these elements which has been eroded from surrounding mud flat areas.

Heavy Metal and Hydrocarbon Pollution in Recent Sediments from Southampton Water, Southern England: A Geochemical and Isotopic Study

A sediment core from Southampton Water, a coastal plain estuary, has been investigated and is shown to provide a record of pollution following the expansion of the Fawley oil refinery in 1949-1951. A combination of heavy metal analyses, the first appearance of hydrocarbon contamination, radiometric dating, and stable Pb isotope ratios have been used to interpret the pollution history in the core. Indications are that following dredging activities, accompanying the refinery expansion, there was a relatively rapid sedimentation rate of ca. 20 mm p.a., which decreased with time to approximately 5 mm p.a. The higher accumulation rate is attributed to the response of the estuary following the major capital dredging works that occurred in 1950-1951. The accumulation rates are used to recalculate concentration profiles to reveal the heavy metal flux to the sediments. Lead isotope data indicate a significant post-1950 use of lead derived from ancient, non-U.K. (Precambrian) ores in local industry.

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.

pH-driven physicochemical conformational changes of single-layer graphene oxide

Single-layer graphene oxides (SLGOs) undergo morphological changes depending on the pH of the system and may account for restricted chemical reactivity. Herein, SLGO may also capture nanoparticles through layering and enveloping when the pH is changed, demonstrating potential usefulness in drug delivery or waste material capture.

Physical and chemical associations of radionuclides and trace metals in estuarine sediments: an example from Poole Harbour, Southern England

The physical (grain size) and chemical (mineral, oxyhydroxide coatings and organic matter) associations of 60Co, 137Cs, 210Pbxs, Pb, Zn and Cu have been examined in two intertidal sediments (from low and medium energy environments). 60Co, 210Pbxs, Pb, Zn and Cu show a distribution with particle size controlled by Fe- and Mn-oxyhydroxides and total organic carbon. Activity/concentration maxima for these isotopes and elements occur in the 2–8 ?m size fraction. A proportion of the 60Co present appears to have been diagenetically mobilised. In contrast 137Cs is strongly sorbed by clay particles and is virtually non-exchangeable.

Heavy metals in sediment cores from a tropical estuary affected by anthropogenic discharges: Coatzacoalcos estuary, Mexico

Large scale industrial development has taken place in the Coatzacoalcos river estuary, SE Mexico, over the last 32 years, and the area is now regarded as the most polluted coastal area of Mexico. A series of sediment cores were taken from the lower Coatzacoalcos river and the estuary, and the concentrations of trace elements (Zn, Co, Cu, Cr, Ni, Pb, V), major elements (Al, Si, Mn, Fe, Ti, Ca, Mg, Na, K, P) and organic matter determined. Heavy metal concentration seems to be largely dependant on proximity to industrial areas, with highest metal concentrations (particularly for Zn, Ni and Cu) found at Teapa, the most heavily industrialized site, and lowest values found at Jicaro, upstream of the main industrial areas. At all of the sites examined, heavy metals either show a relatively uniform distribution with depth, or subsurface maxima, which reflect changes in sediment composition. There is little evidence for significant early-diagenetic remobilization at any of the sites studied. 210Pb and 137Cs data at Teapa indicate that the sediments have accreted rapidly and may be vigorously mixed, and so these sediment cores cannot be used to reliably reconstruct temporal changes in pollutant input.