Abstract

Mercury (Hg) is one of the most important heavy metals in estuarine and coastal sediments. This is due to its toxic effect on marine invertebrates and tendency for the methyl-Hg to bio-accumulate up trophic levels, where it can enter humans via the ingestion of fish and shellfish (Boening, 2000; Bryan and Langston, 1992; Haitzer et al., 2003; Long et al., 1995). The Mersey Estuary (NW England, UK) has a highly industrialised and urbanised drainage basin of approximately 5000 km². Elevated Hg concentrations (>2 mg/kg) in sediments from the Mersey Estuary can be attributed in part to the high density of chemical factories in the Widnes-Runcorn area (Fig. 1). In particular, the alkali, bleaching and detergents industries developed in this area in the mid-19th century used the Castner-Kellner process for large-scale sodium hydroxide and bleach production. This process required a flowing liquid mercury cathode in an electrolytic reaction cell. Losses and discharges from such plants, plus releases from other industries and domestic coal-burning, will have released many tonnes of Hg to the estuary over several decades. In addition to their anthropogenic metal burden, Mersey Estuary sediments are also contaminated with persistent organic pollutants (POPs) sourced from the dockyards, shipping, chemical works, oil refineries and sewage works situated in close proximity to the Mersey, its tributaries and Manchester Ship Canal (Harino et al., 2003; Leah et al., 1997; Osborne et al., 1997; Thomas et al., 2002; Vane et al., 2007).