Comparison of the 2000 and 2005 spatial distributions of heavy metals in wild mussels from the North-Atlantic Spanish coast

Spatial distributions of Cd, Cu, Hg, Pb and Zn in Mytilus galloprovincialis in 41 sampling sites in the North-Atlantic Spanish coast were monitored in 2000 and 2005 to assess the coastal environmental pollution. A pool of mussel soft tissue was prepared using 50 or more individuals representing the available size range. Samples were grounded, homogenised and quantified by atomic absorption spectrometry. Quality of the chemical analyses was assessed by participation in periodic interlaboratory exercises. Univariate and multivariate statistical studies, Principal Components Analysis and Procrustes rotation (a technique intended to compare several data spaces) were carried out. Some decreasing trends were observed for the concentrations throughout the 2000-2005 period, mainly for Hg and Pb. In general, the Northern area showed higher median concentrations (e.g., 3.79 and 4.28 mg Pb/kg dry weight, and 0.160 and 0.191 mg Hg/kg dry weight, for 2000 and 2005, respectively) than the Atlantic ones (e.g., 1.47 and 1.44 mg Pb/kg dry weight, and 0.097 and 0.084 mg Hg/kg dry weight, for 2000 and 2005, respectively). Nevertheless, some Atlantic sampling points, located far from human inputs (cities, industries, rivers, etc.) exhibited high concentrations of Cd, which was attributed to the influence of the natural upwelling processes which occur annually in that geographical region.