Background heavy metal levels in estuarine sediments and organisms in Galicia (northwest Spain) as determined by modal analysis

We investigated metal (Al, Fe, Mn, Co, Cr, Cu, Ni, Zn and Pb) concentrations in surface sediments (107 samples) and intertidal organisms (424 samples of macroalgae, phanerogams, molluscs and polychaetes) from 44 estuarine areas in Galicia (northwest Spain). Three acid extraction procedures (HCl, HNO3 and HNO3 + HF) were used. Following analysis of the effect of sediment particle size distribution on metal contents, Al content was selected as a normalization element. For most species and most metals, there was only minor contamination of the organism samples by particulate matter, confirming the efficiency of the washing and depuration procedures used and thus obviating the need to correct for such contamination on the basis of Fe contents. Background metal levels in the sediments and organisms were estimated by modal analysis. To the best of our knowledge, this is the first time that this method has been used for this purpose.