The influence of chromium minerals (chromite and chromospinel), associated with ultrabasic rocks of Ortegal Complex (SW Europe), on the levels of Cr in water, particles and organisms from Ria Ortegal was studied. The sampling comprised 24 water samples in the tributary rivers Mera, Landoi and Lourido, 42 surface sediments in Ria and Ortegal shelf, and 8 samples of the mussel Mytilus edulis and Fucus spp. Total Cr was determined in all samples and the labile fraction determined in selective sediment samples using ICPMS and GFAAS. Levels of Cr in surface sediments (<2 mm) ranged within the intervals: 200-930, 230-1340 and 290-1660 mg·kg-1 in inner, outer Ortegal ria and shelf, respectively. Labile Cr was only up to 0.3% of total Cr. Results point to 5-10 times higher levels than the background concentration of other Galician rias. Chromium in sediments correlates with Mg, which is assumed to be a tracer of particles derived from the Ortegal complex. The levels of Cr in rivers corroborate the origin of Cr: Landoi and Lourido tributaries that cross the Ortegal complex showed 7-48 and 5-81 nM of dissolved Cr exceeding largely values registered in Mera River out of this geological complex (<0.2nM). Differences on SPM were less pronounced 0.2-0.8 and 0.2-1.3 g·kg-1 against <0.3 g·kg-1). Accordingly, increased concentrations of Cr were found in Fucus spp. (7-16 mg·kg-1) and similar levels in mussels (2.0-3.5 mg·kg-1) when compared to values found in other Galician Rias

15th ICHMET, International conference on heavy metals in the environment, 19 - 23 Septembre 2010, Gdansk, Pologne

This work is integrated in projects CTM2007-62546-C03-01/MAR (CICYT), 2007PT0021 and FCT/CSIC9/CSIC/08

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