The Dispersal, Storage and Remobilisation of Heavy Metals in the River Aire Contaminated by Urban and Industrial Wastes

Industrial and urban activities in the Leeds catchment of the River Aire have caused the widespread dispersal and contamination by a variety of pollutants, including heavy metals. This contamination is reflected by enhanced metal concentrations in the sediments and soils of the river and floodplain. The cycling of sediment and associated metals in the fluvial environment is highly related to hydrological, geomorphological and chemical phenomena. The main research objective is to investigate quantitatively the dispersal, storage and remobilisation of heavy metals in the Leeds reach of the River Aire.

A wide variety of relevant processes are analysed. Metal pollution studies have often neglected urban and industrial catchments, where sources of pollutants to the river channel are diverse. In the past, heavy metals have entered the river from industrial activities, sewage disposal and coal combustion. The main present source of metals is the disposal of domestic and industrial effluent from sewage treatment works.

The fluvial dispersal of wastes has caused enhanced concentrations of heavy metals in aquatic sediment and floodplain soils. This results in long-term storage of metals in river corridors and poses problems as sediments act as a source of contaminants long after pollution of the fluvial system has been abated. The pollution problem is most severe immediately downstream of sewage treatment works, through the city centre, where traffic and industrial density is greatest and where floodplains are frequently inundated with floodwaters.

Heavy metals are not necessarily permanently fixed by the sediment and can be remobilised through mechanical, chemical and biological processes, affecting surface and groundwater quality and plant animal and human health. However, it is not the total amount of a metal stored in sediment, but how it is actually bound that is important in assessing its environmental impact. Results suggest that a significant proportion of each metal is held in a potentially mobile and bioavailable
form, particularly cadmium.

The data collected is used to compile mass budgets of sediments and associated metals for the alluvial area of the River Aire in Leeds.