Salinity increases the mobility of Cd, Cu, Mn, and Pb in the sediments of Yangtze Estuary: relative role of sediments' properties and metal speciation.

Batch leaching experiments, Freudlich isotherm, correlation analysis (CA) and principal component analysis (PCA) were undertaken to explore the mechanisms that govern the release of sediment-associated metals (i.e. Cd, Cu, Mn and Pb) under the salinity stress in the Yangtze River Estuary. Special attention has been paid to the role of sediments' physico-chemical properties and metal chemical speciation. The increase of salinity promoted the metal mobility which followed the order: Cd>Mn>Cu>Pb. Sediments properties (e.g., particle component and organic carbon) governed the mobility of Cd; metal chemical speciation controlled the release of Mn, while the mobility of Cu and Pb were simultaneously affected by the two factors. Different metal release mechanisms caused by salinity changes might be explained by: the chloro-complexation for Cd, the encouragement of acidity changes for Mn, and the high affinity to Fe-Mn oxides, organic substances and specific sorption sites in the sediments for Cu and Pb. Under salinity effect, Cd and Mn exhibited higher ecological risk and mobility, while Cu and Pb seemed to be more conservative.