Regional geochemical mapping and interpretation in Britain.

Regional geochemical atlases of Britain and the British North Sea prepared by the Institute of Geological Sciences are discussed with special reference to their environmental significance. Factors affecting the selection of sample types are considered, and sample preparation, analytical procedure and monitoring error discussed. Stream sediment is shown to be the optimum sample type for regional geochemistry in areas of upland Britain underlain by crystalline bedrock, although soils may provide the optimum sample medium in areas of intensive agriculture. Geochemical mapping of the continental shelf is based on superficial seabed material obtained by grab or cone dredge. Examples of geochemical maps of northern Scotland for several elements of environmental significance including Cu, Mo, Pb, and U are considered in relation to geology, topography, vegetation, land use and the chemistry of surface waters. Geochemical maps are shown to provide the best available source of information on chemical variations in bedrock, although there are many difficulties in relating geochemical or biological activity to the total trace element values. In any attempt to correlate trace element levels with disease, careful consideration must be given to factors affecting the availability and flux of the trace elements if meaningful associations are to be obtained. Geochemical maps of the North Sea indicate that the contents of Cu, Pb, Zn, Cd and Hg are uniformly low over most of the offshore area although higher concentrations occur in coastal samples. The highest concentrations of Cu, Pb and Zn occur off the Tyne estuary while the highest values for Cd and Hg occur further south.