T.R. Lister

GSUE: urban geochemical mapping in Great Britain

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 (one sample per 0.25 km2). Samples are analysed for c. 46 total element concentrations by X-ray fluorescence spectrometry, pH and loss on ignition 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 assessment of point and diffuse metal pollution of soils from an urban geochemical survey of Sheffield, England

A model of soil variability as a continuous background process with superimposed point contamination was applied to 569 measurements of metal concentrations (Cr, Ni and Pb) in the topsoils of Sheffield, England. Robust estimators of the variogram were shown to be required to describe spatial variation of the metal concentrations at most sampled locations. This is diagnostic of the presence of a contaminant process. Values of the standardized kriging error from the cross-validation of each datum were used to identify spatial outliers for each metal. The ordinary kriged estimates of Cr, Ni and Pb were mapped after removing the outliers to estimate the background variation. Each of the 35 spatial outliers that occured in gardens have concentrations exceeding their Soil Guideline Value for residential land use with plant uptake, highlighting a potentially significant exposure pathway. The frequent observation of coal and furnace waste at these sites suggests that their dispersal, following domestic use and industrial processes, respectively, represents a significant point contaminant process. There was no evidence for spatial clustering of the point process. However, the spatial outliers of Cr and Ni showed a significant association with disturbed sites identified from historical land use maps, in part due to their prevalence in areas of historical steel manufacture. The magnitude of diffuse pollution for each metal in the urban soil was estimated by removing the spatial outliers and comparing robust measures of location with those from a survey of soils developed over the same parent materials in adjacent rural and peri-urban environments. The Winsorized mean Pb concentrations in urban topsoil (203 mg kg−1) were twice the value in the rural environment (101 mg kg−1), highlighting a very substantial diffuse Pb load to urban soils. The equivalent estimated diffuse components in urban soils for Cr and Ni were, respectively, 25% and 14% higher than the rural soils.

Temporal and spatial variability of stream waters in wales, the welsh borders and part of the West Midlands, UK-1. Major ion concentrations

Spatial and temporal controls on major ion stream water chemistry are assessed using hydrochemical survey data for Wales and the West Midlands, and time-series data from the intensively studied Plynlimon catchment (mid-Wales). Spatial variations in stream water chemical composition are interpreted in relation to the environmental chemistry of the major ions and controls such as bedrock geology, land-use, anthropogenic activities and atmospheric inputs. Piper diagrams are used to illustrate compositional variation, allowing comparison to be made between samples of widely varying Total Dissolved Solids (TDS). Spatial and temporal data sets are overlaid on Piper plots to determine the relative importance of these two factors in controlling major ion chemistry. Bedrock geology, atmospheric input and land-use can satisfactorily explain compositional variation in the spatial data set. Combined analysis of the spatial and temporal data sets indicated that the variation in cation composition at the Plynlimon site is considerably more constrained than that on the corresponding anion diagram. Time-series data sets for sites of different bedrock geology and at a range of distances from sources of marine derived solute inputs are necessary for further investigation of the relative importance of temporal and spatial controls on major ion stream water chemistry.

Mercury contamination in surface sediments and sediment cores of the Mersey Estuary, UK

Mercury (Hg) is one of the most important heavy metals in estuarine and coastal sediments. This is due to its toxic effect on marine invertebrates and tendency for the methyl-Hg to bio-accumulate up trophic levels, where it can enter humans via the has a highly industrialised and urbanised drainage basin of approximately 5000 km 2. Elevated Hg concentrations (>2 mg/kg) in sediments from the Mersey estuary can be attributed in part to the high density of chemical factories in the Widnes-Runcorn area (Fig. 1). In particular, the alkali, bleaching and detergents industries developed in this area in the mid-19 th century used the Castner-Kellner process for large-scale sodium hydroxide and bleach production. This process required a flowing liquid mercury cathode in an electrolytic reaction cell. Losses and discharges from such plants, plus releases from other industries and domestic coal-burning, will have released many tonnes of Hg to the estuary over several decades. In addition to their anthropogenic metal burden, Mersey estuary sediments are also contaminated with persistent organic pollutants (POPs) sourced from the dockyards, shipping, chemical works, oil refineries and

Geochemical mapping of stream water for environmental studies and mineral exploration in the UK

Abstract The stream water hydrogeochemical database, prepared by the British Geological Surveys 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.

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.

Temporal and spatial variability in stream waters of wales, the welsh borders and part of the West Midlands, UK-2. Alumino-silicate mineral stability, carbonate and gypsum solubility

Stream water chemical composition, which in many systems represents the integration of weathering throughout the catchment, has been used to predict the stability and degree of saturation with respect to a range of minerals, based on the assumption of a pure closed system, and in the case of alumino-silicates, the hydrolysis reaction of a primary mineral phase. The distributions of predicted mineral stability and saturation have been mapped for Wales, the Welsh borders and part of the West Midlands. The incorporation of monitoring data from a site-specific study (Plynlimon, mid-Wales) has been used to interpret the significance of factors such as seasonality and hydrological regime on mineral stability and solubility. The derived maps can be used to identify: (i) regions in which streams are most susceptible to freshwater acidification and (ii) local variations in bedrock geochemistry, such as calcite mineralisation, which cannot be identified by conventional field mapping.

Methods for the integration, modelling and presentation of high-resolution regional hydrochemical baseline survey data

The completion of the high-resolution (ca. 1 sample per 1.5 km2) geochemical survey of Wales and part of the West Midlands by the British Geological Survey has created a unique data set containing over 13,500 site-specific hydrochemical and stream-sediment analyses for a typical suite of over 21 major and trace components. The collection of such a wide range of data over an area with contrasting geology, soils, geomorphology and land use has enabled the delineation and study of hydrochemical processes on a regional basis. Methods are presented describing transformations performed from basic concentration-based data (pH, conductivity and 21 major and trace elements) into hydrochemically relevant trilinear and solubility diagrams predicting aqueous speciation and ionic domination. These data are then displayed and interpreted using a series of thematic composites. The utility of coupling speciation diagrams, based upon pure ideal systems, with Geographical Information Systems for describing processes controlling hydrogeochemical evolution at a regional scale is described. The validity of using solubility diagrams to describe large regional hydrochemical data sets is tested using geographically linked representations of aqueous saturation and chemical speciation generated from the individual modelling of each sample using PHREEQC. Comparison of the pure and real (PHREEQC) systems for calcite and gypsum indicated that there was a small over-prediction in the pure system; the greatest differences occurred in samples of the highest ionic strength.

Data Conditioning of Environmental Geochemical Data: Quality Control Procedures Used in the British Geological Survey's Regional Geochemical Mapping Project

Abstract Data conditioning procedures involve the verification, quality control and data levelling processes that are necessary to make data fit for the purpose for which it is to be used. It is something that has to be planned at the outset of any project generating geochemical data. Whether it is in the sampling phase, for example, determining how sites and samples should have a unique identity, or through to the data presentation phase in which disparate data sets may have to be joined to form a seamless map. This account describes the methods currently used by the British Geological Surveys regional geochemical mapping project that has been generating geochemical data for various sample media for nearly 40 years. It is important that users of the data are given information that will help them ascertain whether the provided environmental data is suitable for the purpose of its intended use.

The identification of mining related contamination in the UK using high resolution geochemical mapping: examples from Northeast England and North Wales.

The Geochemical Survey programme (GSP) of the BGS is currently undertaking the systematic multi-element regional geochemical mapping of the UK landmass.