Mapping the chemical environment of London, UK : an important contribution to understanding national levels of normal background contaminant concentrations

In May 2011 the British Geological Survey (BGS) released the results from the largest systematic urban geochemical mapping survey ever undertaken - ‘London Earth’. Soils were sampled at a density of four samples per kilometre square from the Greater London Authority Area and nearly 7000 topsoil samples were analysed for more than 50 elements by X-ray fluorescence spectrometry (XRFS) and other soil parameters such as pH and loss on ignition. Smaller subareas have been studied for mercury, persistent organic pollutants, element bioaccessibility , and profile lines mapping the occurrence of platinum group elements (PGEs) across the capital have been investigated. Results demonstrate a strong geological control on element distributions with significant anthropogenic modifications in many areas for some elements. The urban baseline information generated has been invaluable, used alongside national and c ontinental scale geochemical mapping results, to determine normal background concentrations of contaminants in soil. The revised contaminated land Statutory Guidance (SG) for England and Wales refers to “normal” levels of contaminants in soil and BGS, with its substantial database of both rural and urban geochemical data, has been able to make an important contribution in support of the SG revision. In the SG “normal” levels of contaminants are considered to consist of contributions from both natural and diffuse anthropogenic sources.