Multivariate analysis of U.K. salt marsh sediment contaminant data with reference to the significance of PCB contamination

A data set acquired to establish an inventory of pollutants in salt marsh sediments has been evaluated using two numerical techniques, principal component analysis and discriminant analysis. Results indicate that sites proximate to the River Thames exhibit a greater degree of contamination, and numerical analysis supports the hypothesis that the river has been the major source of contaminants to the region. The presence of the contaminants within salt marsh sediments may be of concern due to changes in flood defense techniques. The use of managed realignment, where the line of flood defense is moved back to higher ground which requires only a low, minimal cost, sea-wall protected by newly created salt marsh from former farmland, is not free from problems of historical pollution. Mature salt marsh, laid down during previous decades, may be eroded and reworked within the new coastal geomorphology created by breaching existing seawalls and what were previously considered to be sinks of pollutants may have become sources. However, evaluation of the sediment burden of PCB within the salt marshes of the U.K. Essex coast indicates that they are not likely to be a major source of pollutants should sediments be remobilized during managed realignment programs.