Spatial distribution of trace metals in urban soils and road dusts : an example from Manchester, UK

Urban soil quality is of concern under current UK contaminated land legislation in terms of potential impacts on human health, due to the legacy of industrial, mining and waste disposal activities and the fact that soils can act as a sink for potentially harmful substances (PHS) in the urban environment. As part of the the Geochemical Baseline Survey of the Environment (G-BASE) project of the British Geological Survey (BGS), 27 UK cities have been surveyed to establish baselines and assess the quality of urban soils. The G-BASE soil geochemical dataset for Manchester forms the basis of this project. Another medium that is a likely sink for PHS in urban environments is road dust sediment (RDS). RDS forms as an accumulation of particles on pavements and road surfaces, and has been shown to be both spatially and temporally highly variable in composition, as it is more susceptible to remobilisation and transport. RDS has been documented as carrying a high loading of contaminant species, including significant amounts of trace metals. Geochemical data from both soils and RDS, despite having different properties, are essential for environmental assessment in urban areas. Although studies of PHS in RDS and soils have been published, little is known about the spatial, geochemical and mineralogical linkages between these two media. The aim of this research is to define and establish these linkages, and produce novel mineralogical data on the PHS–particulate relationships within soils and RDS

Biofortification of UK food crops with selenium

Se is an essential element for animals. In man low dietary Se intakes are associated with health disorders including oxidative stress-related conditions, reduced fertility and immune functions and an increased risk of cancers. Although the reference nutrient intakes for adult females and males in the UK are 60 and 75 μg Se/d respectively, dietary Se intakes in the UK have declined from >60 μg Se/d in the 1970s to 35 μg Se/d in the 1990s, with a concomitant decline in human Se status. This decline in Se intake and status has been attributed primarily to the replacement of milling wheat having high levels of grain Se and grown on high-Se soils in North America with UK-sourced wheat having low levels of grain Se and grown on low-Se soils. An immediate solution to low dietary Se intake and status is to enrich UK-grown food crops using Se fertilisers (agronomic biofortification). Such a strategy has been adopted with success in Finland. It may also be possible to enrich food crops in the longer term by selecting or breeding crop varieties with enhanced Se-accumulation characteristics (genetic biofortification). The present paper will review the potential for biofortification of UK food crops with Se

The collection of drainage samples for environmental analyses from active stream channels

The collection of drainage samples from active stream channels for geochemical mapping is now a well-established procedure that has readily been adapted for environmental studies. This account details the sampling methods used by the British Geological Survey in order to establish a geochemical baseline for the land area of Great Britain. This involves the collection of stream sediments, waters and panned heavy mineral concentrates for inorganic chemical analysis. The methods have been adapted and used in many different environments around the world. Detailed sampling protocols are given and sampling strategy, equipment and quality control are discussed

Geochemistry and related studies of Clyde Estuary sediments

Geochemical and related studies have been made of near-surface sediments from the River Clyde estuary and adjoining areas, extending from Glasgow to the N, and W as far as the Holy Loch on the W coast of Scotland, UK. Multibeam echosounder, sidescan sonar and shallow seismic data, taken with core information, indicate that a shallow layer of modern sediment, often less than a metre thick, rests on earlier glacial and post-glacial sediments. The offshore Quaternary history can be aligned with onshore sequences, with the recognition of buried drumlins, settlement of muds from quieter water, probably behind an ice dam, and later tidal delta deposits. The geochemistry of contaminants within the cores also indicates shallow contaminated sediments, often resting on pristine pre-industrial deposits at depths less than 1 m. The distribution of different contaminants with depth in the sediment, such as Pb (and Pb isotopes), organics and radionuclides, allow chronologies of contamination from different sources to be suggested. Dating was also attempted using microfossils, radiocarbon and 210Pb, but with limited success. Some of the spatial distribution of contaminants in the surface sediments can be related to grain-size variations. Contaminants are highest, both in absolute terms and in enrichment relative to the natural background, in the urban and inner estuary and in the Holy Loch, reflecting the concentration of industrial activity

Evidence for repository-relevant element dispersion from the geosphere into the biosphere

Although this has only been a brief and limited study, it has covered a wide range of elements in a variety of natural and anthropogenically modified anomalous systems. For the most part, element behaviour has followed established norms of theoretical resistate or mobile character, though there are important exceptions. The concept of an ‘insoluble’ element may no longer be entirely justifiable, thanks to improvements in analytical methods, but elements such as Nb (and, to a lesser extent, Zr) must still be regarded as essentially immobile under normal surface conditions. In contrast, chloride (irrespective of isotope) is highly mobile and essentially conservative, i.e. non-interacting. Variables such as Eh, pH, organic matter and counter-ions are the dominant controls on element solubility, complexation and mobility. A few elements, such as Sr, are much more mobile than their published thermodynamic Eh-pH diagrams might suggest, whereas others, such as Rb and Cs, are less so. Copper can be mobile in alkali solution if levels of Cl- and organic matter are high, as in coal waste effluents, whereas it is normally immobilised by near-neutral pH levels in natural anomalies. The mobility of molybdenum is likely to be higher in alkaline waters than in acid ones, and radiogenic technetium will probably behave in a similar manner. Regional data for some elements such as Se, Br and I have only recently become available and further improvements in analytical techniques are awaited to confirm the mobility of these elements at low natural concentration levels in solution. It is important to note that there are limitations to this report. The main limitation is the use of available data with a sampling regime which was not designed with the study of element dispersion as its main aim. If new studies were undertaken to investigate element dispersion specifically, these would require a specialised sampling system which would aim to follow the dispersion of an element from a well-defined bedrock source into soils, groundwater, and surface drainage, following streams at a suitably high sampling rate and analysing sediments and waters to establish the rate of concentration tail-off, and changes in substrate host and element speciation over an area sufficiently large for background conditions to be re-established at its boundaries. This may be an idealised situation, and may not be easily attainable, but should be a ‘gold standard’ to be aimed for. The transfer of elements from the geosphere to the biosphere is clearly dependent primrily on their mobility, and this has been examined and assessed carefully in this study. The actual mechanisms of bioavailability and element uptake into biota are highly complex. Many academic studies have compared element concentrations in plants and soil organisms and in their host soils, and some empirical data exists on this topic in BGS, but on a very local, not a regional, scale. However, a thorough examination of these processes would require a much more focused and multidisciplinary project than was possible within this desk-study

Regional geochemical soil data as aid to the reconstruction of Mid-Pleistocene ice flows across Central and Eastern England

Principal component analysis of high-density, regional soil geochemical data was used to reveal element associations within Mid-Pleistocene glacigenic till deposits across Central and Eastern England. Results have helped to characterise tills by their geochemical composition at a regional scale, leading to a better understanding of, (i) which parent materials tills have been derived from, (ii) sediment transportation paths and flow trajectories of the British Ice Sheet, and (iii) the evolution of the British Ice Sheet during the Mid-Pleistocene

Pb reactivity in soils using 204Pb stable isotope dilution

Stable isotope dilution has been used to quantify the ‘reactivity’ of lead in a variety of contaminated soils. ‘Reactivity’ or ‘lability’ of lead is difficult to measure using traditional methods. This study used isotopic exchangeability, as a proxy for Pb reactivity, by determining the extent to which an added 204Pb spike mixed with the native soil Pb pool. After spike equilibration, the 204Pb/208Pb atom ratio in the solution phase of equilibrated soil suspensions was measured by ICP-MS to determine the isotopically exchangeable Pb or ‘E-value’ for the soil: Method development involved testing post-spike equilibration times and electrolyte composition to determine the most robust method. This method was then tested on five soils with different contamination histories to demonstrate the range of application of the method. The soils tested were historically contaminated from a range of sources, including petrogenic Pb, Pb/Zn minespoil, sewage sludge application and C19th urban waste disposal. 0.05 M EDTA is a commonly used extractant to estimate the reactive pool of metal in soils. Our results however suggest that the use of this extractant is not viable for Pb. Increasing EDTA concentrations appear to convert non-labile Pb to isotopically-exchangeable forms. Nevertheless, the reactive pool of soil Pb may be larger than intuitively expected. For example, in soils contaminated with Pb/Zn minespoil ~38% Pb was isotopically exchangeable

The use of 204Pb stable isotope dilution to measure lead lability in soils

Isotopic dilution was used to quantify the mobility or ‘reactivity’ of lead in a range of contaminated soils. Lead is a common contaminant in soils and the mobility of lead is not easily measured, but is an important factor in the prediction of toxicity and risk assessment. The technique developed here uses 204Pb to spike soils and thereby alter the ratio of abundance in the reactive or ‘labile’ pool of soil Pb. The atom ratio 204Pb/208Pb in the solution phase of equilibrated soil suspensions is then measured by ICPMS to resolve the total amount of isotopically exchangeable (Labile) Pb present. The method development involved testing several pre- and post-spike equilibration times, and electrolyte concentrations to provide the most robust method. The final method was then tested on five soils with different contamination histories to demonstrate the range of application of this method. The soils tested had been historically contaminated from a range of sources, including petrogenic Pb, Pb/Zn minespoil, sewage sludge, C19th urban waste and artificial contamination as Pb(NO3)2 salt