Urban soil geochemistry of Glasgow

This report presents the results of a geochemical survey carried out by the British Geological Survey (BGS) between 2001 and 2002. The survey collected 1381 urban soil samples at a density of 1 per 0.25 km2 and 241 rural samples at a density of 1 per 2 km2 on a systematic grid across the Glasgow conurbation. The study was carried out as part of the BGS Geochemical Baseline Survey of the Environment (G-BASE) project. Top (5 - 20 cm) and deeper (35 - 50 cm) soil samples underwent analysis for approximately 46 chemical elements including contaminants such as As, Al, Cd, Cu, Cr, Ni, Pb, Se, V and Zn according to standard G-BASE procedures. In addition, pH and loss on ignition (LOI) as an indicator of organic matter content were determined in the samples. The aim of the project was to provide an overview of the urban soil geochemistry of Glasgow and the immediate rural hinterland as an aid to planning and development. This report presents the initial findings of the Glasgow soil survey. The data have a wide range of applications and will be interpreted in more detail as part of a wider BGS Clyde Urban Super-Project (CUSP), to be reported elsewhere. This report documents the G-BASE soil survey and analytical methods and presents the distribution of soil parameters as a series of geographic information system (GIS)-generated graduated symbol geochemical maps. The Glasgow conurbation is the largest built-up area in Scotland and has a long history of urban and heavy industrial development including coal and other mineral mining; ship building; steel and iron making; railway engineering; car manufacture and - until the 1960s - was home to the world’s largest chromium ore processing plant based in Rutherglen in the south-east of the city. As with all cities, urban land quality in Glasgow is the result of complex interactions between these man-made inputs and the natural concentrations of substances in soil, which are influenced by the geology and soil forming processes. Therefore, comparisons with rural soils can help elucidate the level of anthropogenic input to soils in urban areas. As an indication of anthropogenic (man-made) pollution, the results of the present study reveal that on the basis of median values, Cd, Cr, Ni and Zn concentrations are 2-3 times and Cu and Pb 5-7 times higher in Glasgow than the national average in Scottish soils. However, these results should be treated with caution due to the difference in analytical methods between the current G-BASE project and the national data for Scotland. Nevertheless, Ag (x 3.5), As, Co, Ge, Mo and P2O5 (~ x2) are also enhanced in Glasgow urban soils relative to world averages. Similarly, Pb (x 7.5), Cu, Ni, Sb, Sn and Zn (~ x2) and Se (x3) are enriched in Glasgow urban soils relative to world averages and are higher than BGS regional geochemical median values for the Humber-Trent area of England. This may in part reflect anthropogenic pollution and in the case of As, Co, Mo, Ni, and Se the presence of coals and volcanic bedrock in the Glasgow area. Comparisons between median values in the Glasgow dataset and other urban areas surveyed by the G-BASE project in the UK show that Cr and Ni are higher in Glasgow soils than most other cities. This is attributed to the history of Cr-processing and heavy industry in Glasgow and the presence of coals underlying the city and volcanic bedrock on the outskirts of Glasgow. In contrast, As, Cd and Pb are lower in Glasgow soils than most other urban areas. The results of the present study demonstrate that regardless of parent material type, concentrations of As, Bi, Ba, CaO, Ce, Co, Cr, Cu, Ge, Mo, Ni, Pb, Sb, Se, Sn, Sr, Th, Y, Zn and pH are generally higher in urban than rural soils in the Glasgow area. Elements that are rare in nature in most environments but commonly associated with anthropogenic pollution such as Pb, Sb and Sn show greatest levels of enrichment (2.6 – 3.3 times, based on median values) in the urban soils. Calcium is also enhanced significantly (x2.1, based on median values) in deeper urban than rural soils probably as a result of buildings, coal and industrial waste in the urban environment, which tend to be calcareous in nature and commonly used as fill materials. Indeed, high Ba, CaO, Sr and pH soils are closely associated with made ground, industrial and derelict land in the city probably reflecting the presence of fill materials. The elements that show greatest enhancement in the Glasgow urban environment, namely CaO, Cu, Mo, Ni, Pb, Sb, Sn and Zn are a typical indicator ‘suite’ of urban anthropogenic pollution commonly identified in studies of urban areas under the G-BASE project. Conversely, levels of organic matter are lower in urban than rural soils and several elements that are closely associated with organic matter show the same relationship including Br, I, U and W. Concentrations of Hf, SiO2, TiO2 and Zr are also lower in urban than rural soils as these elements are more closely associated with the detrital mineral composition of natural soils. Despite the over-riding influence of urban anthropogenic pollution on the soil geochemistry of many elements, geology and geogenic processes still exert a fundamental control on soil composition. Results in rural and urban Glasgow soils demonstrate that, for example, many elements such as Al2O3, Co, Cr, Cu, Ga, Ni, Pb, Se, Sn, Th, TiO2, U, V and Zn are relatively lower in concentration over Devonian sandstones present in the Dumbarton area as a result of natural geological processes including the lower clay content of these rock types. Similarly, many elements associated with alkali basaltic lavas (for example, CaO, Fe2O3, MgO, Na2O, Nb, Ni, P2O5, Sr, TiO2 and V) are relatively higher in soils over the Clyde Plateau Volcanic Formation, to the north and south of the city than other rock types in the area. Superficial peat deposits also have an effect on the geochemistry of the soils due to the importance of organic matter on the distribution of many elements such as As, Br, Cd, Co, Cs, Ga, Ge, I, Mo, Pb, Sb, Se, Sn and U in the environment. As might be anticipated, pH is also lower in these soils due to the presence of humic acids.