Mapping metallic contamination of soils in the Lower Foyle catchment

Using the Tellus and Tellus Border geochemistry data, the distribution of metals in topsoils in and around Derry–Londonderry has been mapped and assessed. The concentrations of metals have been compared with the UK Environment Agency’s Soil Guideline Values (SGVs). Of 763 samples analysed, only 11 samples exceed the SGV for arsenic and two for that of cadmium. Of these 13 sites, only two were within an urban area. Concentrations of metal in the rural sub-catchments appear to be mainly determined by the underlying geology. Using a geographic information system (GIS) and multi-element plots (spidergrams) for analysis, the geological background was modelled at a sub-catchment scale in order to determine whether high soil metal concentrations were of natural origin or a consequence of anthropogenic activities. The level of enrichment due to contamination was calculated for 12 metals and metalloids. In the urban area of Derry–Londonderry, levels of arsenic, cadmium and seven other elements are slightly enhanced due to anthropogenic activities. However, as the enrichment factors do not exceed a factor of 3 these enhancements are classified as minor. Possible modern and historic sources of contamination are likely to be buildings, households and waste disposal, hospitals and medical facilities, surface run-off from road traffic, manufacturing industries, coal disposal and sewage works.