Selected trace metals in oysters (Crassostrea iridescens) and sediments from the discharge zone of the submarine sewage outfall in Mazatlán Bay (southeast Gulf of California): chemical fractions and bioaccumulation factors.

Concentrations of Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn in the soft tissue of Crassostrea iridescens and the associated surface sediments (bulk and bioavailable metal concentrations) from an area influenced by a sewage outfall in Mazatlán Bay (southeast Gulf of California), were determined by atomic absorption spectrophotometry. Significant spatial differences in metal concentrations in both the bulk and bioavailable forms in the sediments were identified. An enrichment of Cu, Ni, Pb and Zn in sites located on a south-north transect was detected indicating a dominant influence of the sewage outfall toward the north. C. iridescens accumulated more Zn, Cu, Ni, Fe, Cd; and less Mn, Cr and Pb than were bioavailable in the sediments, as measured using conventional extraction analysis. The degree of enrichment and the bioavailable metal concentrations in the sediments of the south portion of Mazatlán Bay is discussed. The potential ability of C. iridescens as a biomonitor of metallic pollutants is postulated.