The xenobiotic impact of sedimentary metals in an urban river

The Brent catchment is a heavily urbanized area with a long history of pollution. Consequently, a restoration enhancement project was carried out between 1999 and 2003 at Tokyngton Park to improve/restore the river’s general quality and natural channel features whilst also incorporating flood-attenuating features. Like most urban rivers in the UK, sediment quality is not routinely monitored and hence little is known of the nature and levels of pollutants accumulating within them. In this study, surface sediment samples have been collected three adjacent restored and unrestored reaches of the river and analysed for selected heavy metals [Cadmium (Cd), Chromium (Cr), Lead (Pb), Nickel (Ni), Copper (Cu) and Zinc (Zn)], microbial parameters and sediment ecotoxicity using the Microtox® Solid Phase Test. Results show considerable spatial and temporal variation in sediment metal and faecal indicator organism (FIO) concentrations within the same and in different river reaches. With the exception of Ni and Cr, mean sediment metal concentrations exceeded existing sediment quality criteria at all sites. However a measured sediment ecotoxicity data range of 10 to 991g/L indicated negligible toxicity (EC50 ≥10g/L). The chemical and microbiological analyses results obtained potentially highlights the key role sediments play in the persistence of pollutants in urban watercourses and the long-term implications for river ecology and human health and safety, particularly with restored rivers granting open access to recreational users.