Sources, mobility and bioaccessibility of potentially harmful elements in UK soils

Potentially harmful elements (PHE) occur both naturally from geogenic sources and from anthropogenic derived pollution. Anthropogenic sources can be further categorised into those derived from point sources. A point source is a single identifiable source which is confined to a very small area such as that arising from disposal of waste material or from an industrial plant. Diffuse pollution arises where substances are widely used and dispersed over an area as a result of land use activities, often associated with urban development. Examples of diffuse pollution include atmospheric deposition of contaminants arising from industry, domestic coal fires and traffic exhaust, and disposal of domestic coal ash. The total concentration and the chemical form and hence the mobility of the PHE in a soil is highly dependent on the source.