Catsiki V.A - Hellenic Centre ofMarine Research, P. ۰. Box ۷۱۲, Mavro Lithari, Anavyssos, Attiki, Greece,

Saronikos gulf -the gulf in front of Athens- suffers from an important water quality decline due to anthropogenic activities (mlmicipal and industrial wastes as well as naval activities). The Athens' wastes are treated since 1996. The aim of the present paper is to investigate the changes of metal concentrations in coastal marine environment due to the wastes treatment and the description of metallic temporal trends in Saronikos gulf by the means of metal accumulation in bioindicators (natural populations of mussels Mytilus galloprovincialis) . The knowledge of changes is useful in order to reveal the effectiveness of the measures taken for the protection of the marine environment. are used as bioindicators. Mussels were collected from four stations along the coasts of Saronikos Gulf, seasonally during the period 1986-2006 and scarcely till 201 1. Samples were analysed for Cu, Cr, Cr, Ni, Zn, Fe, Mn and occasionally for Pb and Hg by atomic abs01ption spectrophotometry. Results showed a decreasing metal gradient towards the open sea. A similar pattem in temporal evolution of metal bioaccumulation in mussels from the different stations was recorded for most metals. The pattem comprises several temporal variations. It was found that the operation of the wastes n·eatment unit caused a temporal reduction in metal bioavailability, followed by increase as the quantity of wastes increased too