The use of sediment cores from stable and developing salt marshes to reconstruct historical contamination profiles in the Mersey Estuary, UK

Depth-profiled sediment cores from two marshes in the Mersey Estuary were analysed for concentrations of 137Cs, 238Pu, 239,240Pu, 241Am, As, Cr, Cu, Pb, Hg and Zn. Mersey sediments contain three diagnostic and persistent chemical species arising from either a unique, or a dominant, source – 137Cs, Hg and DDT. Dating of features in these cores has been completed using up to four benchmark events identifiable from these chemical species – the initial expansion of the chemical industry, commencement of DDT manufacture, initial appearance of radionuclides from a reprocessing site in NW England, and the introduction of new technology to reduce mercury discharges. The sediment pollutant profiles depend on the rate of sediment accumulation but clearly record the historical increase in discharges of metals to the environment between the mid-19th and 20th centuries. They also reflect recent regulatory and technological efforts to minimise estuarine contamination and the discontinuation of specific manufacturing and refining processes