Lead in the Soils and Stream Sediments of an Urban Catchment in Tyneside,UK

This paper focuses on lead contamination in topsoils and stream sediments of public access areas in a largely urban UK catchment. It compares severity of contamination with accepted trigger thresholds, examines spatial patterns relative to urban and industrial development, and explores potential mobility of lead using ‘plant available’: total lead ratios. Total and ‘plant available’ lead concentrations, organic content and pH were determined on 298 topsoil and 54 stream sediment samples using standard laboratory procedures. At the lowest total lead trigger threshold, approximately two thirds of topsoil and one third of stream sediment samples were contaminated. For ‘plant available’ lead the proportions were somewhat lower. The spatial pattern was characterised by ‘hot spot’ contamination, with highest values occurring in central and southern parts of the catchment which have a long urban and industrial history. Potential lead mobility is greatest in rural western and northern parts of the catchment where the lead fractions are probably derived from pedological alteration and weathering of soil parent materials. Conversely, in the urban and industrial areas, much of the lead probably consists of less mobile particulate forms. The implications of these findings for assessment, monitoring and management of contaminated areas are discussed.