Potential impacts of water injection dredging on water quality and ecotoxicity in Limehouse Basin, River Thames, SE England, UK K.L. Spencer a, * , R.E. Dewhurst b , P. Penna c a Geography Department, Queen Mary, University of London, Mile End Road, London E1 4NS, United Kingdom b MWH UK Ltd., Terriers House, 201 Amersham Road, High Wycombe, Buckinghamshire, HP13 5AJ, United Kingdom c URS Italia SpA, Via Bertieri, 4-20146 Milano, Italy Received 18 January 2005; received in revised form 25 July 2005; accepted 5 August 2005 Available online 3 November 2005 Abstract The use of water injection dredging (WID) is increasing in the UKÕs inland waterways and marinas. Jets of water are injected under low pressure directly into bottom sediment creating a turbulent water-sediment mixture that flows under the influence of gravity. Many of these sediments are highly contaminated and little is known of the effects of conta- minant release on water quality or the risk to biota living in both the sediment and the water column. Sediment cores were collected from Limehouse Basin, a proposed WID site in SE England and current sediment toxicity was assessed using a number of techniques. Comparison of metal data to US sediment quality guidelines indi- cated intermediate levels of toxicity while, calculation of acid volatile sulphide to simultaneously extracted metal ratios underestimated the potential toxicity to sediment dwelling organisms. In contrast, porewater ammonia concentrations were in excess of all published ecotoxicological guidelines and indicate serious risk to biota. Re-suspension experiments were used to mimic the effects of WID on overlying water quality and ecotoxicity tests were carried out on elutriates using Daphnia magna to examine the impacts on biota. Concentrations of a range of met- als in the elutriates predict that adverse biological effects would be observed during WID, however only 10% of the elu- triate samples caused an adverse effect on Daphnia. Limehouse Basin is a complex aquatic environment receiving predominantly fresh waters while the sediments have high porewater chloride concentrations reminiscent of previous tidal inputs to the basin, making the choice of test organism problematic. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Sediment quality; Ammonia; Ecotoxicity; Acid volatile sulphides 1. Introduction Over 100 000 m 3 of fine sediment are dredged from the UKÕs estuaries annually in order to maintain naviga- tion routes and allow boat access to commercial and recreational ports, docks and harbours. Numerous envi- ronmental studies have demonstrated that the bottom 0045-6535/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2005.08.009 * Corresponding author. Tel.: +44 (0) 207 7882 5400; fax: +44 (0) 208 981 6276. E-mail address: k.spencer@qmul.ac.uk (K.L. Spencer). Chemosphere 63 (2006) 509–521 www.elsevier.com/locate/chemosphere