Systematic mapping of the chemical environment of urban areas from around the world has demonstrated the strong impact of urbanisation on topsoil geochemical distributions originally controlled by the underlying parent material (PM). The variance of some elements including As, Ba, Ca, Cr, Cu, Mo, P, Pb, Sb, Se, Sn and Zn in urban domains appears to be impacted by a mixture of geogenic and anthropogenic controls. This study evaluates how soil chemistry has been influenced by different eras of urbanisation within London and other UK urban areas using (a) the pre-1940 Dudley Stamp First Land Utilisation Survey data and (b) the modern urban domain principally defined by the aggregate classes of the 2007 Land Cover Map. In the London area, calcium, and possibly a substantial proportion of Cu, Pb, Sn and Zn enrichment observed in soils impacted by pre-1940 urbanisation relative to soils impacted only by post-1940 urbanisation, may be partly related to the destruction of buildings during the period 1940–۱۹۴۱ rather than from the disposal or aerial dispersion of coal ash from domestic fires. Some Pb, Cu, Sb, Sb, Sn and Zn contamination appears to be caused by road traffic (leaded petrol and brake dust). The relationships between pre- and post-1940 urbanised areas in London also characterise most of 20 other urban centres in England and Wales for which BGS holds soil chemistry data.

Introduction

Whilst parent material (PM) is the primary geogenic control for some chemical elements in urban areas (Appleton and Adlam, 2012; Appleton et al., 2013), the variance of many elements including As, Ba, Ca, Cr, Cu, Mo, P, Pb, Sb, Se, Sn and Zn in urban domains appears to be impacted by a mixture of geogenic and anthropogenic controls which have developed over different eras of urbanisation. Sources of anthropogenic contamination in urban areas include industrial manufacturing and processing, power and waste incineration plants, domestic coal burning including the historic disposal of ash, emissions from vehicles (especially from the use of leaded petrol), fertilizer use, dispersion of Pb and other metals together with cement, concrete and bricks from demolition and construction including the use of building and demolition waste material for land reclamation and the creation of artificial ground (Albanese and Breward, 2011). The highest levels of contamination are to be expected in areas with the longest history of urbanisation. Preliminary assessments of the topsoil chemistry of the predominantly urban Greater London Authority (GLA) area are available in BGS (2011), Knights and Scheib (2011), Scheib et al. (2011), Ferreira et al. (2017). Lark and Scheib (2013) used model-based analysis, cokriging and Wald statistics to examine how land use recorded at soil sample sites within the Great London Authority (GLA) area accounts for variations in soil Pb concentrations. McIlwaine et al. (2017) reporting on the relationship between potentially toxic element (PTE) concentrations and historical urban development in the soils of Belfast and Sheffield concluded that different PTEs are associated with different periods of development and that soil pollution can be linked to diffuse contamination from road traffic, domestic fuel combustion and industrial processes. The study reported here focusses on processes causing widespread dispersion of contaminants rather than local sources such as industrial manufacturing or waste incineration plants. In particular, we assess whether the different eras of urbanisation in the UK have resulted in significantly different concentrations of elements in surface soils once the confounding influence of parent material (geology) has been eliminated.