Towards the characterisation of heavy metals in dredged canal sediments and an appreciation of 'availability': two examples from the UK

Canal sediments can act as sinks for a wide range of contaminants including heavy metals from various sources (e.g. industrial and waste water dischar ges). Dredging of canals is required to maintain navigational depth and pre vent flooding. The sediments removed from canals are often disposed of to l and, being deposited either straight on to the banks of the canal or, in re cent years, in licensed disposal sites. The aim of this work was to investi gate the nature of dredged sediment-derived soils and the heavy metals pres ent in them. Two disposal sites in the United Kingdom (UK) were investigate d and soil samples taken. A variety of analytical techniques were used, inc luding Aqua regia digestion and sequential extraction, in order to assess t he concentrations and associations of metals present. Diethylene triaminepe nta-acetic acid extracts, performed to illustrate plant-available metal con centrations, reveal that up to 40% of the total extracted metals were in an 'available' form. Variations in metal concentrations with depth in the soi l cores show a significant correlation with total organic carbon content. ( C) 2001 Elsevier Science Ltd. All rights reserved.