Legacy sources of mercury in an urbanised watershed

Abstract

Environmental context. Mercury is a neurotoxin that bioaccumulates and is associated with global contamination and often with regional atmospheric sources. However, in Connecticut, USA, in watersheds characterised by a gradient of forested to urban land uses we found that the predominant source of elevated Hg is local. This study uses a novel nested sampling method to pinpoint hot spots of mercury and presents inorganic mercury concentrations in water, sediment, soil, and aquatic organisms. The results indicate that mercury contamination is an environmental legacy associated with the silver plating industry and that local sources are critical to the biogeochemical mercury cycle here. Abstract. Mercury levels were measured in various environmental compartments of the Quinnipiac River system (CT, USA). In streams, dissolved mercury reached a maximum of 6.3 ng L–1 during baseflow and 30 ng L–1 during stormflow, whereas surficial impoundment sediments had a maximum mercury concentration of 420 μg kg–1. A sediment core collected from the Quinnipiac River indicates that peak loading of mercury occurred before 1940. Wharton Brook tributary of the Quinnipiac River represents 30% of the mercury loading to the river and the likely source of mercury to the sediment is a past silver manufacturing plant. Analysis of soil samples from the riparian zone of Wharton Brook, a tributary of concern because it empties into a popular fishing location, revealed mercury concentrations as high as 20 000 μg kg–1. It appears that the soil surrounding the former factory is acting as the current source of mercury to the water column and aquatic communities. Removal of contaminated soil will probably be necessary to reduce mercury levels and the threat to humans in downstream environments.