Terrigenous debris and mussel pollution — a differentiation based on trace element concentration by means of multivariate analysis

The total content of nine trace elements (Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg and Pb) of the soft edible part of mussels (Mytilus galloprovincialis Lamarck) sampled in two different sites was considered. The first sampling site was located at the extremity of a pier near the sewage of Trieste in a polluted area of the Muggia Bay (Gulf of Trieste in the Northern Adriatic Sea), whereas unpolluted mussels were simultaneously sampled in the second one, i.e. a hatchery just off the southern extremity of the bay. The sampling was extended over a year and occurred with a frequency of nearly ten days. Both mussel groups had an equal sample numerosity (n1=n2=43) and standard atomic absorption methods were used for all the trace elements. Linear discriminant analysis (LDA) was applied to this two-group sampling in order to test a possible differentiation between the polluted and unpolluted mussels. LDA gave in this two-group sampling a nearly complete separation of scores, whereas the bidimensional and tridimensional score plots, obtained by means of linear principal component analysis (LPCA), gave a certain degree of entanglement. The detrital origin of pollutants is also discussed.