A critical evaluation of the use of cluster analysis to identify contaminated sediments in the Ria De Vigo (NW Spain)

The indiscriminate use of cluster analysis to distinguish contaminated and non-contaminated sediments has led us to make a comparative evaluation of d ifferent cluster analysis procedures as applied to heavy metal concentratio ns in subtidal sediments from the Ria de Vigo, NW Spain. The use of differe nt cluster algorithms and other transformations from the same departing set of data lead to the formation of different clusters with a clear inconclus ive result about the contamination status of the sediments. The results sho w that: this approach is better suited to identifying groups of samples dif fering in sedimentological characteristics, such as grain size, rather than in the degree of contamination. Our main aim is to call attention to these aspects in cluster analysis and to suggest that researchers should be rigo rous with this kind of analysis. Finally, the use of discriminant analysis allows us to find a discriminant Function that separates the samples into t wo clearly differentiated groups, which should not be treated jointly.