Sediment-borne Contaminants in Rivers Discharging into the Humber Estuary, UK

As part of a project to characterise and quantify the volume of sediments which comprise the Holocene (10,000 years to present) fill of the Humber Estuary, a study was undertaken to determine the geochemistry and heavy mineralogy of bed sediments in the river systems that discharge into the estuary. A total of 19 sediment samples in the Trent and Ouse river systems were taken for analysis. Contamination was evaluated by comparison of the sample geochemistry with that of the appropriate catchment (using existing data), and by evaluation of the proportion of anthropogenic heavy minerals (including natural minerals which have been mobilised by mining) in the sediment sample. Heavy metals fall into two groups with different patterns of distribution. Pb–Zn concentrations are greatest in catchments and rivers draining the Pennine orefields. Levels of these metals remain high between source areas and the Humber Estuary suggesting that large quantities are trapped in sediments stored within the fluvial systems. By way of contrast other heavy metals, associated with manufacturing industry, such as Cu and Co, have high concentrations near source cities, but decrease rapidly in amount down the river systems because of dilution by other sediments. The differing behaviour of mining and industrial related contaminants is generally reflected by the heavy minerals. Concentrations of gangue minerals, such as barytes and fluorite, are generally highest in rivers draining mining areas; ‘furnace’ materials, such as slags are highest in industrialised rivers such as the Aire and the Don. The anthropogenic origin of all the contaminants is illustrated by comparison of the catchment and river sediment geochemistry and heavy mineralogy with that of early Holocene fluvially-derived sediments cored in boreholes drilled in the present Humber Estuary. The findings of the study corroborate those of others focused on water chemistry and floodplain sediments ( Neal et al., 1996 , 1997; Macklin et al., 1997 ). However, the comparison of pre-existing data on catchment geochemistry with a limited number of river samples, as demonstrated here, provides a fast and cost effective tool for the determination of contamination characteristics in river systems.