Spatial distribution and accumulation of heavy metals in tidal flat sediments of Shanghai coastal zone

Surface and core sediments from the high, middle and low tidal flats of Sha nghai coastal zone were analyzed for heavy metal (e.g. Cu, Pb, Zn, Cr, Cd, Fe, Mn) concentrations. Besides Cd, the concentrations of Cu, Zn, Cr and Pb are 2-5 times higher than their background values and show serious polluti on trend due to the direct discharge of industrial and municipal sewage alo ng the Shanghai tidal flat, as well as the wet and dry depositions of indus trial dusts, It seems that heavy metals prefer to accumulate and be enriche d in the sediments near large sewage outlets, high flats, and the subsurfac e layer at the depth of 10-30 cm. Several main factors, which include the d irect sewage discharge along the tidal flat, tidal hydrodynamic action, lar ge engineering activity, early diagenesis and windstorm tide, are considere d to be responsible for influencing spatial distribution patterns of heavy metals in the Shanghai tidal flat.