Principal component analysis and pollution by trace elements in a mussel survey

Abstract

The total content of nine trace elements (Mn, Fe, Co, Ni, Zn, Cd, Hg, Pb) in the soft part of mussels (Mytilus galloprovincialis Lamarck) sampled in two sites was considered. Wild, polluted molluses were sampled in Muggia Bay (Gulf of Trieste, Northern Adriatic Sea) in the proximity of an important sewer of the city. Edible, unpolluted mussels were simultaneously sampled in a hatchery just off the Bay. Principal component analysis has been applied to correlation matrices obtained from data matrices from the literature. The nine variables were reduced to three or two principal components, which explained 70–80% of the total variance. The unrotated and orthogonally rotated matrix of the correlations of variables with principal components showed that the clusters of elements are positively associated to the first two eigenvectors. The origin of some toxic elements in the soft part of mussels from Muggia Bay is discussed. The projection on the first two eigenvectors of all data as component scores allow a nearly complete separation of polluted from unpolluted molluscs.