Heavy metals in the rock oyster Crassostrea iridescens (Filibranchia : Ostreidae) from Mazatlan, Sinaloa, Mexico

Two populations of Crassostrea iridescens were sampled off Mazatlan and in a zone free of anthropogenic activity. The bivalves were collected from Feb ruary 1992 to February 1993. Concentrations of Cd, Co, Cr, Cu, Fe, Mn, Ni a nd Zn were determined by flame atomic absorption spectrophotometry. Annual mean values in the sampling zone off Mazatlan were higher in Co, Cu, Fe, Mn , Ni and Zn than in the sampling zone free of anthropogenic activity; howev er, differences were not statistically significant at 95% confidence level. Urban discharges in the coastal zone in front of Mazatlan city, have littl e or no heavy metal concentrations dissolved or particulated.