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 o f public access areas in a largely urban UK catchment. It compares severity of contamination with accepted trigger thresholds, examines spatial patter ns relative to urban and industrial development, and explores potential mob ility of lead using `plant available': total lead ratios. Total and `plant available' lead concentrations, organic content and pH were determined on 2 98 topsoil and 54 stream sediment samples using standard laboratory procedu res. At the lowest total lead trigger threshold, approximately two thirds o f topsoil and one third of stream sediment samples were contaminated. For ` plant available' lead the proportions were somewhat lower. The spatial patt ern was characterised by `hot spot' contamination, with highest values occu rring in central and southern parts of the catchment which have a long urba n and industrial history. Potential lead mobility is greatest in rural west ern and northern parts of the catchment where the lead fractions are probab ly derived from pedological alteration and weathering of soil parent materi als. Conversely, in the urban and industrial areas, much of the lead probab ly consists of less mobile particulate forms. The implications of these fin dings for assessment, monitoring and management of contaminated areas are d iscussed.