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Chemical elements that are either present naturally in the soil or introduced by pollution are more usefully estimated in terms of “availability” of the element, since it is this property that can be related to mobility and uptake by plants. A good estimate of the immediately available fraction can be achieved by measuring the concentration, or activity, of chemical species in soil pore water. Current analytical techniques enable the application of this approach to trace elements, such as plant and animal micronutrients and those defined as potentially toxic elements (PTEs) in environmental studies. A complete chemical analysis of soil pore water represents a powerful diagnostic tool for the interpretation of many soil chemical phenomena relating to soil fertility, mineralogy, and environmental fate. This chapter describes some of the current methodologies used to extract soil pore water. In particular, five laboratory-based methods are described and discussed in detail: (i) high speed centrifugation-filtration, (ii) low (negative-) pressure Rhizon samplers and passive diffusion samplers, (iii) high pressure soil squeezing, (iv) equilibration of dilute soil suspensions, and (v) diffusive gradients in thin-films (DGT). A number of operational factors are presented: pressure applicable (i.e., pore size accessed), moisture prerequisites of the soil, pore water yield, efficiency, duration of extraction, materials and possible sources of contamination for micronutrient and PTE studies. There is also consideration of the advantages and disadvantages of the methods, including costs and material availability.

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 1m. 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.

Systematic multi-media geochemical surveying by the British Geological Survey's Geochemical Baseline Survey of the Environment (G-BASE) project has revealed significant anomalous patterns of enrichment for a suite of elements – copper (Cu) and uranium (U) – with exceptionally high levels of molybdenum (Mo), in soils and stream sediments in central England. Enrichment of these elements is most often associated with organic-rich, sulphidic ‘black shale’ lithofacies, typical of oxygen-deficient, euxinic depositional environments. The main anomaly lies between Evesham and Rugby where the bedrock comprises the Blue Lias and Charmouth Mudstone formations. Concentrations of Mo are particularly high, reaching soil values of 50 mg/kg, where the regional background is

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.

Urban waste disposal occurred on fenland to the west of Manchester, England, between 1900 and 1964. The reclaimed fenland, Chat Moss, is now used for mixed arable farming. A total of 1.92 Mt of waste including privy midden, street sweepings, clinkers and slaughterhouse refuse was incorporated into the moss resulting in a modified topsoil with raised pH and reduced organic matter content compared with the subsoil. Elevated levels of potentially toxic elements (PTEs) are observed in the topsoil beyond the typical depth of atmospheric contamination; Cd and As concentrations exceed soil guideline values (SGVs) at 1.8 and 43 mg/kg, respectively. Sequential extraction indicates that waste-derived Pb, Zn and Ni remain predominantly in the residual fraction, whereas Cu was mainly organically bound. Arsenic was predominately found in oxide and organic matter fractions with Cd in carbonate, oxide, organic matter and residual fractions. Pot trials indicated limited uptake of PTEs by vegetables grown on the waste-amended soil, with the exception of Cd uptake by lettuce (0.22 mg/kg FW) and Pb uptake by radish (0.16 mg/kg FW), which exceeded current EU limits of 0.2 and 0.1 mg/kg FW, respectively. Hazard quotients (HQs) identified no risks to adults from consumption of vegetables grown in these soils with the exception of lettuce consumption with a HQ of 1.4. Risks to children were slightly greater with HQs >1 for Cd in lettuce, spinach, carrots and onion, As in lettuce, parsley and onion and for Zn in spinach.

An assessment of the natural radiation dose to wildlife in England and Wales was made to determine the contribution it may make to the total radiation dose estimated during environmental impact assessments. Significant use was made of systematic datasets for environmental media (stream sediments, stream waters and soils), in particular those produced by the Geochemical Baseline Survey of the Environment (G-BASE) project. This provided extensive, although variable, coverage for different elements and sample types after normalisation of data to account for changes in sampling and analysis over time. Almost complete coverage for K in stream sediments was achieved by merging G-BASE andWolfson Atlas data. This required normalisation of theWolfson data to the G-BASE results. Coverage was improved greatly for U and Th in sediments, and K, U and Th in soils, by using the strong relationship between soils and sediments and geology (both solid and superficial) to extrapolate the data. The total U, Th and K data were used to derive activity concentrations of 238U and 232Th series radionuclides and 40K. External dose rates to wildlife were then estimated from derived media concentrations; internal dose rates were estimated from measured activities in biota or activities predicted using recommended concentration ratios.

Urban geochemical maps of Wolverhampton and Nottingham, based on multielement analysis of surface soils, have shown distribution patterns of “total” metals concentrations relating to past and present industrial and domestic land use and transport systems. Several methods have been used to estimate the solubility and potential bioavailability of metals, their mineral forms and potential risks to urban population groups. These include sequential chemical extraction, soil pore water extraction and analysis, mineralogical analysis by scanning electron microscopy, source apportionment by lead isotope analysis and the development of models to predict metal uptake by homegrown vegetables to provide an estimate of risk from metal consumption and exposure. The results from these research strategies have been integrated with a geographical information system (GIS) to provide data for future land-use planning.

Synopsis The Southern Uplands (southern Scotland) and Lake District (northern England) terranes contain thick and extensive sequences of macroscopically homogeneous, Lower Palaeozoic wacke-type sandstone. There is a close spatial relationship between the outcrop of biostratigraphically defined rock units and distinctive patterns of element distribution in stream sediments derived from those units, with the stream sediment patterns indicating cryptic compositional variations that are not otherwise apparent. Analysis of the stream sediment composition relative to whole-rock values shows that it is not a direct surrogate for the underlying bedrock. Instead, elevation and depletion trends for any given element are controlled by the nature of its mineral host(s) and provide a previously unappreciated means of assessing the detrital mineralogy, and hence provenance of the bedrock sandstones. Stream sediment composition also provides a valuable alternative means of evaluating possible correlation between different stratigraphical sandstone units. Further, since the fine-grained matrix to the wacke sandstones makes a major contribution to the stream sediment, an assessment of the latter allows variations in matrix composition to be taken into account. Examples are given from the Silurian turbidite sequences of the central and southern Southern Uplands (Gala, Hawick and Riccarton groups; the affinity of the Ross Formation with the Hawick Group is demonstrated) and the southern Lake District (Windermere Supergroup).

The Geochemical Baseline Survey of the Environment is a long established high-resolution regional geochemical mapping project run by the British Geological Survey. A project initially stimulated for mineral exploration and to assist geological mapping has successfully evolved into a survey that has many environmental applications. Much of the current demand for surface geochemical data is driven by legislation. The geochemical mapping, originally based on the collection of drainage samples, has expanded to include soils and a further suite of determinands in stream waters. The methodology of the project and application of the baseline data are described and issues common to worldwide geochemical mapping programmes are discussed.

Stream-sediment geochemistry is commonly used to provide a regionally averaged, background composition against which may be judged the anomalies caused by unusual geology, mineralisation or pollution. Its interpretation may be based on assumptions of relative compositional uniformity within broad categories of bedrock lithology. This approach is undermined by the dramatic variations in stream-sediment chemistry that occur over some large areas of superficially homogeneous geology. In these cases, regional geochemistry may pickout subtle compositional variations in bedrock that are not otherwise apparent. Thick greywacke sequences present a particular problem of geological interpretation by virtue of their general uniformity, with a good example provided by the Southern Uplands terrane. There, some stratigraphical variations in greywacke composition, reflecting changes in sedimentary provenance, are known from petrographic and analytical work but are not visible macroscopically. However, contoured ...

We performed a risk assessment of metal exposure to population subgroups living on, and growing food on, urban sites. We modeled uptake of cadmium, copper, nickel, lead, and zinc for a selection of commonly grown allotment and garden vegetables. Generalized linear cross-validation showed that final predictions of Cd, Cu, Ni, and Zn content of food crops were satisfactory, whereas the Pb uptake models were less robust. We used predicted concentrations of metals in the vegetables to assess the risk of exposure to human populations from homegrown food sources. Risks from other exposure pathways (consumption of commercially produced foodstuffs, dust inhalation, and soil ingestion) were also estimated. These models were applied to a geochemical database of an urban conurbation in the West Midlands, United Kingdom. Risk, defined as a "hazard index," was mapped for three population subgroups: average person, highly exposed person, and the highly exposed infant (assumed to be a 2-year-old child). The results showed that food grown on 92% of the urban area presented minimal risk to the average person subgroup. However, more vulnerable population subgroups (highly exposed person and the highly exposed infant) were subject to hazard index values greater than unity. This study highlights the importance of site-specific risk assessment and the "suitable for use" approach to urban redevelopment.

Areas showing anomalously high levels of heavy metals (eg. Cu, Pb, Sn, Zn) in both peri-urban and rural soils in parts of western Lancashire (UK) were indentified during a regional geochemical survey. The sites were identified as areas of former peat fenland that had been filled in with a variety of domestic and industrial wastes including furnace slag, as well as inert rubble. The very high levels of heavy metals present in the soil raises concerns about possible translocation into food crops, as this is an important market gardening area. There is no direct evidence of a health risk, and the high-pH soils will limit metal mobility and bioavailability, but these soils are worthy of further multidisciplinary scientific investigation.

Stream sediment geochemistry provides an innovative method of assessing the basinal history of the Caledonian slate belts. Despite glaciation, the stream sediment geochemical patterns spatially mimic the outcrop of underlying bedrock lithologies. However, erosion from rock to sediment by fluvial processes may either increase or reduce an element’s abundance depending on the nature of its mineral host. An element held in heavy, resistate minerals will be concentrated, whereas one residing in unstable ferromagnesian minerals, which readily break down to clays during weathering, may be preferentially removed. Examples are provided from the Cr-Ni-V-Mg, base metal and Rb-Sr element suites. Primary and secondary bedrock patterns are recognized in the stream sediments. Primary patterns follow the original composition of the source bedrock, with steep gradients in the element distribution coinciding with lithostratigraphical boundaries. Such patterns also reveal subtle divisions within the established geological units for which the main compositional control was the nature of the ancient sedimentary provenance. Secondary patterns reflect remobilization of elements within the bedrock and so may cut across lithostratigraphical boundaries. These patterns (or their absence) are influenced by the thermal histories of the Caledonian basins, and so are indicative of the geotectonic regime in which the sedimentary sequences were originally deposited.

International agreements (e.g. OSPAR) on the release of hazardous substances into the marine environment and environmental assessments of shelf seas require that concentrations and bioavailability of metals from anthropogenic sources can be distinguished from those originating as a result of natural geological processes. The development of a methodology for distinguishing between anthropogenic and natural sources of metals entering the Irish Sea through river inputs is described. The geochemistry of stream, river and estuarine sediments has been used to identify background geochemical signatures, related to geology, and modifications to these signatures by anthropogenic activities. The British Geological Survey (BGS) geochemical database, based on stream sediments from 1 to 2 km2 catchments, was used to derive the background signatures. Where mining activity was present, the impact on the signature was estimated by comparison with the geochemistry of sediments from a geologically similar, but mining free, area. River sediment samples taken upstream and downstream of major towns were used respectively to test the validity of using stream sediments to estimate the chemistry of the major river sediment and to provide an indication of the anthropogenic impact related to urban and industrial development. The geochemistry of estuarine sediments from surface samples and cores was then compared with river and offshore sediment chemistry to assess the importance of riverine inputs to the Irish Sea. Studies were undertaken in the Solway, Ribble, Wyre and Mersey estuaries. The results verify that catchment averages of stream sediments and major river samples have comparable chemistry where anthropogenic influences are small. Major urban and industrial (including mining) development causes easily recognised departures from the natural multi-element geochemical signature in river sediment samples downstream of the development and enhanced metal levels are observed in sediments from estuaries with industrial catchments. Stream sediment chemistry coupled with limited river and estuarine sampling provides a cost-effective means of identifying anthropogenic metal inputs to the marine environment. Investigations of field and laboratory protocols to characterise biological impact (bioaccumulation) of metals in sediments of the Irish Sea and its estuaries show that useful assessments can be made by a combination of surveys with bioindicator species such as clams Scrobicularia plana, selective sediment measurements that mimic the ‘biologically available’ fractions, and laboratory (mesocosm) studies.

Selected European studies have illustrated the impacts of elevated CO2 concentrations in shallow soils on pasture. For the first time, general unified conclusions can be made, providing CO2 thresholds where effects on plants and soil microbiology are observed and making recommendations on how this information can be used when planning projects for CO2 storage. The sites include those where CO2 is being naturally released to the atmosphere from deep geological formations; and a non-adapted site, with no previous history of CO2 seepage, where CO2 has been injected into the unsaturated soil horizon. Whilst soil gas concentrations will be influenced by flux rates and other factors, the results suggest that a concentration of between 10% and 15% CO2 soil gas at 20 cm depth, which is within the root zone, is an important threshold level for observing changes in plant coverage. Site-specific plant ‘indicators’ are also observed for CO2 concentrations at ≥35%. Microbiological changes are seen where CO2 soil gas concentrations are between 15% and 40%. As part of site characterisation, an evaluation of the risks of leakage and their potential environmental impacts should be undertaken.

As part of a project to characterise and quantify the volume of sediments which comprise the Holocene (10,000 years to present) fill of the Humber Estuary, a study was undertaken to determine the geochemistry and heavy mineralogy of bed sediments in the river systems that discharge into the estuary. A total of 19 sediment samples in the Trent and Ouse river systems were taken for analysis. Contamination was evaluated by comparison of the sample geochemistry with that of the appropriate catchment (using existing data), and by evaluation of the proportion of anthropogenic heavy minerals (including natural minerals which have been mobilised by mining) in the sediment sample. Heavy metals fall into two groups with different patterns of distribution. Pb–Zn concentrations are greatest in catchments and rivers draining the Pennine orefields. Levels of these metals remain high between source areas and the Humber Estuary suggesting that large quantities are trapped in sediments stored within the fluvial systems. By way of contrast other heavy metals, associated with manufacturing industry, such as Cu and Co, have high concentrations near source cities, but decrease rapidly in amount down the river systems because of dilution by other sediments. The differing behaviour of mining and industrial related contaminants is generally reflected by the heavy minerals. Concentrations of gangue minerals, such as barytes and fluorite, are generally highest in rivers draining mining areas; ‘furnace’ materials, such as slags are highest in industrialised rivers such as the Aire and the Don. The anthropogenic origin of all the contaminants is illustrated by comparison of the catchment and river sediment geochemistry and heavy mineralogy with that of early Holocene fluvially-derived sediments cored in boreholes drilled in the present Humber Estuary. The findings of the study corroborate those of others focused on water chemistry and floodplain sediments (Neal et al., 1996, 1997; Macklin et al., 1997). However, the comparison of pre-existing data on catchment geochemistry with a limited number of river samples, as demonstrated here, provides a fast and cost effective tool for the determination of contamination characteristics in river systems.

The model of Begum et al. (2010) that predicts alkalinity and Ca and Mg concentrations in river water from available sediment composition data has been critically re-evaluated using an independent validation data set. The results support the hypothesis that readily available stream water sediment elemental composition data are useful for prediction of mean and minimum concentrations of alkalinity and Ca and Mg in river water throughout the River Derwent catchment in North Yorkshire without requiring land-use data inputs as stream water sediment composition reflects all aspects of the riparian zone soil system, including land-use. However, it was shown for alkalinity prediction that rainfall exerts a significant dilution effect and should be incorporated into the model in addition to flow path-weighted sediments Ca% and Mg%. The results also strongly suggest that in catchments with substantial rough moorland land-use neutralization of organic acids consumes alkalinity and this fact should be considered in any future development of the model.

Carbon Capture and Storage is increasingly seen as a way of combating rising CO2 concentrations in the atmosphere. Although storage sites will be designed for zero leakage it is important to consider the possible environmental effects in the unlikely event that leakage does occur, for both risk and environmental impact assessments. The potential responses of ecosystems depend on CO2 concentrations, event duration, the sensitivities of different organisms and external environmental factors

High-density regional geochemical data for surface soils in central England and East Anglia reveal that much of their geochemical character is inherited from the tills that they are developed upon. Multivariate statistical analysis highlighted three significant element associations of Al–Fe–Ga–K–La–Mg–Rb, Ca–Sr and K–Fe accounting for almost 93% of the geochemical variability of soils derived from tills. Provenancing the geochemical signatures of the latter elements enabled the construction of ice flow paths associated with two different Middle Pleistocene ‘chalky’ till sheets. A lower till sheet relating to ‘Pennine’ ice flowing from west to east across the region, and an upper till sheet deposited by North Sea ice moving into northern East Anglia, and to the west of the Fen Basin, before fanning-out across central England. Overall, geochemical signatures of different till units are largely derived from local bedrock sources, with dilution and a new geochemical signature acquired as the ice flows over and incorporates new bedrock lithologies. The results show that high resolution soil geochemical data provides a further proxy with which the flow paths of former ice sheets can be delineated.

Many national and regional databases of soil properties and associated estimates of soil carbon stock consider organic, but not inorganic carbon (IC). Any future change in soil carbon stock resulting from the formation of pedogenic carbonates will be difficult to set in context because historical measurements or estimates of IC concentration and stock may not be available. In their article describing a database of soil carbon for the United Kingdom published in this journal, Bradley et al. [Soil Use and Management (2005) vol. 21, 363–369] only consider data for organic carbon (OC), despite the occurrence of IC-bearing calcareous soils across a substantial part of southern England. Robust techniques are required for establishing IC concentrations and stocks based on available data. We present linear regression models (R2 between 0.8 and 0.88) to estimate IC in topsoil based on total Ca and Al concentrations for soils over two groups of primary, carbonate-bearing parent materials across parts of southern and eastern England. By applying the regression models to geochemical survey data across the entire area (18 165 km2), we estimate IC concentrations on a regular 500-m grid by ordinary kriging. Using bulk density data from across the region, we estimate the total IC stock of soil (0–30 cm depth) in this area to be 186 MtC. This represents 15.5 and 5.5% of the estimated total soil carbon stock (OC plus IC) across England and the UK, respectively, based on the data presented by Bradley et al. [Soil Use and Management (2005) vol. 21, 363–369]. Soil geochemical data could be useful for estimating primary IC stocks in other parts of the world.

Synopsis Newly-acquired regional geochemical data for the Down-Armagh (Northern Ireland) sector of the Southern Uplands–Down-Longford terrane are assessed by comparison with the equivalent dataset for southern Scotland. Despite the much thicker glacigenic cover to the Down-Armagh bedrock, the principal geochemical lineaments identified in the Southern Uplands are still apparent. Patterns of element distribution emphasize the continuity of structure and stratigraphy between the two regions, with Cr, Zr, Sr, Rb, Ba and Ca (as CaO) proving particularly instructive. Much of the Down-Armagh outcrop consists of Llandovery strata from the Gala and Hawick Groups, so it is this part of the terrane that is most closely considered. Though continuity is clear, there is a suggestion of additional structural imbrication in Down-Armagh, whilst variability in the defining element ratios suggests along-strike compositional changes in the turbidite sandstones. These changes may be controlled by lithostratigraphical variation in sedimentary provenance, or may be influenced by the dominant palaeocurrent flow towards the SW, which has resulted in a broadly more distal and mature Llandovery turbidite lithofacies in Down-Armagh than in the Southern Uplands.

The stream water hydrogeochemical database, prepared by the British Geological Survey's Geochemical Survey Programme, in conjunction with databases for stream sediments, soil samples and mineral concentrates, has recently been enhanced for a range of economic and environmental objectives. The density of systematic stream water sampling and analysis has been increased to one sample per km 2 and a broader spectrum of determinands introduced. An orientation suite of hydrogeochemical maps has been produced from water samples collected at 1279 sample sites in North Wales to test the methodology. Preliminary results indicate that bedrock geology and mineralisation are the most important variables which influence the surface water chemistry. The primary control by geological parameters is variously modified by secondary influences which include geomorphological factors (especially altitude) atmospheric (climatic and coastal effects), and anthropogenic (agriculture, urban and industrial developments). Regional hydrogeochemical stream water maps have a wide range of economic and environmental applications, especially when interpreted in conjunction with geological data. Results obtained so far indicate that interpretation is likely to be further enhanced in the future by intercomparison with regional stream sediment, hydrogeological, geomorphological, pedological, agricultural, landuse, climatic and remotely sensed datasets in a GIS environment. Hydrogeochemical sampling and analysis represents a cost-effective addition to the Regional Geochemical Survey of the UK.

Regional geochemical data from the classic mining districts of Southwest England, the Pennine orefields of Central England, and the Dalradian belt of Scotland, with its important occurrences of gold, are considered as a basis for understanding metallogenic provinces. The deposit types are granite-associated Sn-U, Mississippi Valley Type Pb-Zn-Ba-F and vein Au. It is suggested that crustal reservoirs, enriched in ore-forming elements, were important in the genesis of the examples of Sn-U and Au mineralisation studied. The reservoirs comprise evolved subalkaline granites and carbonaceous sulphur-enriched turbidities in listric faulted orogenic basins, respectively. In the case of the Pennine base-metal deposits, the reservoirs from which the ore-forming fluids were derived, comprise sedimentary basins approximating in composition to average shale and ore deposition mainly reflects the nature of basin evolution. The regional geochemical data used in the study were derived from geochemical atlases produced for different purposes and to different standards. Nevertheless, simple trace-element plots normalised, for example, to average crustal abundances can be used together with geological and geophysical criteria to summarise key characteristics of the crustal reservoirs identified and to develop methods suitable for screening spatially related data sets using Image Analysis or Geographical Information Systems.

It has been suggested that, when assessing radiation impacts on non-human biota, estimated dose rates due to anthropogenically released radionuclides should be put in context by comparison to dose rates from natural background radiation. In order to make these comparisons, we need data on the activity concentrations of naturally occurring radionuclides in environmental media and organisms of interest. This paper presents the results of a study to determine the exposure of terrestrial organisms in England and Wales to naturally occurring radionuclides, specifically (40)K, (238)U series and (232)Th series radionuclides. Whole-body activity concentrations for the reference animals and plants (RAPs) as proposed by the ICRP have been collated from literature review, data archives and a targeted sampling campaign. Data specifically for the proposed RAP are sparse. Soil activity concentrations have been derived from an extensive geochemical survey of the UK. Unweighted and weighted absorbed dose rates were estimated using the ERICA Tool. Mean total weighted whole-body absorbed dose rates estimated for the selected terrestrial organisms was in the range 6.9 x 10(-2) to 6.1 x 10(-1) microGy h(-1).

A regional geochemical survey using soils, stream sediment and stream water sampling revealed multi-element geochemical anomalies, though of low environmental mobility, associated with Mesozoic sedimentary ironstones in Lincolnshire, UK. The most prominent of these anomalies were of As and V in soils and sediments, but elevated levels of elements such as Cr, La, Ce and Th were also observed. These were initially thought to be part of a residual resistate element or heavy-mineral suite, but careful examination suggests that these too may be primarily associated with the process of Fe oxide precipitation during the initial formation of the ironstones.

The British Geological Survey is responsible for the national strategic geochemical survey of Great Britain. As part of this programme, the Geochemical Surveys of Urban Environments (GSUE) project was initiated in 1992 and to date, 21 cities have been mapped. Urban sampling is based upon the collection of top (0.05 to 0.20 m) and deeper (0.35 to 0.50 m) soil samples on a 500 m grid across the built environment (1 sample per 0.25 km2). Samples are analysed for c. 46 total element concentrations by X-ray Fluorescence Spectrometry (XRFS), pH and loss on ignition (LOI) as an indicator of organic matter content. The data provide an overview of the urban geochemical signature and because they are collected as part of a national baseline programme, can be readily compared with soils in the rural hinterland to assess the extent of urban contamination. The data are of direct relevance to current UK land use planning, urban regeneration and contaminated land legislative regimes. An overview of the project and applications of the data to human health risk assessment, water quality protection and contaminant source identification are presented.

The Agusan River basin of eastern Mindanao, the Philippines, hosts several centres of artisanal gold mining, the most important of which, Diwalwal, is a significant gold producer in global terms. An investigation of the environmental impacts of artisanal mining in the Agusan system, with particular reference to mercury contamination, was initiated in 1995 following reports of several incidents of human Hg poisoning in the province of Davao del Norte. Results show drainage downstream of Diwalwal is characterised by extremely high levels of Hg both in solution (maximum 2906 micrograms/l) and in bottom sediments (> 20 mg/kg). Filtered surface water Hg levels exceed the WHO Drinking Water guideline and the US-EPA Water Quality Criteria for the Protection of Aquatic Life for a downstream distance of more than 14 km, including channel sections utilised for fishing and potable water supply. The Environment Canada sediment quality Hg Toxic Effect Threshold for the Protection of Aquatic Life is exceeded for a downstream distance of 20 km. Hair Hg data indicate that ballmill and CIP plant operators processing Hg contaminated tailings at eastern Mindanao's principal gold beneficiation centre, Apokon, may be subject to enhanced occupational Hg exposure. It appears that the wider population of this area has not been affected.

Environmental contextThe chemical reactivity of lead in soil is difficult to assess and depends on both soil conditions and the origins of the lead. This paper tests the combined application of lead isotopic techniques and chemical extraction against our understanding of lead fractionation in soils. Possibly against expectation, it appears that the ‘reactivity’ of lead can be high and yet there is tentative evidence that the original source of the metal affects its fractionation in soil, even after long contact times. Abstract‘Reactivity’ or ‘lability’ of lead is difficult to measure using traditional methods. We investigated the use of isotopic dilution with 204Pb to determine metal reactivity in four soils historically contaminated with contrasting sources of Pb, including (i) petrol-derived Pb, (ii) Pb/Zn minespoil, (iii) long-term sewage sludge application and (iv) 19th century urban waste disposal; total soil Pb concentrations ranged from 217 to 13 600 mg kg–1. A post-spike equilibration period of 3 days and suspension in 5.0 × 10–4 M ethylenediaminetetraacetic acid provided reasonably robust conditions for measuring isotopically exchangeable Pb. However, in acidic organic soils a dilute Ca(NO3)2 electrolyte may be preferable to avoid mobilisation of ‘non-labile’ Pb. Results showed that the reactive pool of soil Pb can be a large proportion of the total soil lead content but varies with the original Pb source. A comparison of isotopic exchangeability with the results of a sequential extraction procedure showed that (isotopically) ‘non-labile’ Pb may be broadly equated with ‘residual’ Pb in organic soils. However, in mineral soils the ‘carbonate’ and ‘oxide-bound’ Pb fractions included non-labile forms of Pb. The individual isotopic signatures of labile and non-labile Pb pools suggested that, despite prolonged contact with soil, differences between the lability of the original contaminant and the native soil Pb may remain.

The stream water hydrogeochemical database, produced by the Geochemical Baseline Survey (GBASE) of the British Geological Survey, has recently been enhanced in the light of experimental pilot studies in North Wales, to meet a wider range of economic and environmental objectives which require modern, integrated and strategic geochemical surveys for their implementation. Hydrogeochemical data are therefore now collected, in conjunction with geochemical data for stream sediments, soil samples and mineral concentrates. The density of sampling, based on the collection of stream water at near-baseflow conditions during the late summer period each year, has been increased to one site per 1.75 km 2 and a broader spectrum of geochemical determinants introduced. Provisional regional datasets are being prepared for an extensive region covering Wales, the Welsh Borders, and part of the West Midlands representing over 17 000 sample sites. Bedrock geology and base metal sulphide mineralisation are particularly well reflected in the stream water chemistry at the regional scale. The influence of secondary factors, such as geomorphology, atmospheric controls, and anthropogenic contamination due to agriculture, urban, industrial and military developments, can also be readily distinguished. The data obtained by systematic high resolution sampling of first and second order streams, vary in concentration over three or four orders of magnitude for many of the analytes studied here. This compares with a range of only one or two orders of magnitude for many of the analytes in stream sediment samples. The extended range in values for stream water is an important factor in the gridding, plotting and production of relatively stable maps. They are relatively unaffected either by short temporal changes in stream water flow, which are attributable either to storm events noted during the sampling campaign, or by annual differences between wet and dry summers in different years. This has enabled a series of robust surface hydrogeochemical maps to be prepared for analytical data collected during the summer sampling campaigns conducted annually from 1989 to 1994. These maps provide a unique source of synoptic baseline information for a wide range of economic and environmental applications especially, when combined with other geoscience datasets in a GIS environment.

s 91 Orientation studies of stream water hydrogeochemistry for environmental and economic applications in North Wales P.R. Simpson 1, W.M. Edmunds 2, N. Breward 1, J.M.Cook 3, D. Flight 1 G.E.M. Hall4and T.R. Lister 1 1Geochemistry Group, British Geological Survey Nottingham NG12 5GG. UK 2Hydrogeology Group, British Geological Survey, Wallingford, OXlO 8BB, UK 3Analytical Geochemistry Group, British Geological Survey, Nottingham, NG 12 5GG, UK 4Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, KIA OE8, Canada The stream water hydrogeochemical database, prepared by the BGS's Geochemical Survey Programme in conjunction with databases for stream sediments , soil samples and mineral concentrates, has recently 'been enhanced for a range of economic and environmental objectives. The density of systematic stream water sampling and analysis has been increased to one sample per km 2 and a much broader spectrum of additional determinands introduced. An orientation suite of coregistered hydrogeochemical maps has been produced from water samples collected at 1,279 sample sites in North Wales. The preliminary results obtained indicate that bedrock geology and mineralisation are the most important variables which influence the surface water chemistry. These primary geological parameters are variously modified by secondary influences which include a tmospher ic (c l imat ic and coastal effects) , a n t h r o p o g e n i c ( ag r i cu l tu re and urban developments) and geomorphological factors. Such regional hydrogeochemical stream water maps have a wide range of economic and environmental appl icat ions, especial ly when interpreted in conjunction with geological data. Results obtained so far indicate that interpretation is likely to be further enhanced in the future by comparison with regional stream sediment , hydrogeolog ica l , geomorphologica l , pedological , agricultural, landuse, climatic and remotely sensed datasets in a GIS environment. Hydrogeochemical sampling and analysis therefore represents a costeffective addition to the Regional Geochemical Survey of the UK. The identification of mining related contamination in the UK using high resolution geochemical mapping: examples from Northeast England and North Wales D.M.A. Flight, T.R. Lister and F.M. Fordyce Geochemistry Group, British Geological Survey, Nottingham NG 12 5GG, UK The Geochemical Survey programme (GSP) of the BGS is currently undertaking the systematic multi-element regional geochemical mapping of the UK landmass° The GSP database presently holds information on the concentration of up to 35 elements determined in stream sediment, stream water, heavy mineral concentrate and soil samples collected at an average aensity of one sample per 1.25 km 2 in an area of northern Britain extending f rom S h e t l a n d to Nor th Wales. R e g i o n a l geochemical maps based on analysis of high density stream sediment samples from Northeast England and North Wales, both of which contain historically important mining fields are considered here. The Northern Pennine Orefield has been worked from Roman times until the early parts of this century primarily for galena but also for associated Zn, Ba and Cu bearing ores. The many historical mining centres of North Wales include Halkyn-Minera (Pb-Zn), Llanlwst (Pb-Zn), Llansannan (Cu-Pb-Zn), Beddgeler t (Cu-Pb-Zn) and Parys Mountain, Anglesey (Cu).

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.