With the laboratory control, the aim of this study is to realize the effect of salinity on the distribution of heavy metal between dissolved and five heavy-metal binding fractions in river sediment as well as on the remobilization of metals from different size of particles.
Heavy metals could be adsorbed onto suspended particulate and sediments with different particle sizes when they were discharged into the river. When sediment flowed through estuary and mixed with overlying water containing different salinity, the remobilized metals (Cd, Co, Cr, Cu, Ni, Pb, and Zn) concentration from different size of particles increased with the increase of salinity. The smaller the particle size was, the lower concentration of metals remobilized.
Cd was remobilized from fractions of exchangeable and carbonates with the action of salinity. Similarly, Co and Cu was remobilized from carbonates fractions; Cr from Fe and Mn oxides fractions; Ni and Pb from Fe and Mn oxides and organic matters fractions; Zn from carbonates and Fe and Mn oxides fractions. The partitioning coefficients (KF1DSP, KF2DSP, KF3DSP, KF4DSP, and KF5DSP) of heavy metals between dissolved phase and five heavy-metal binding fractions were affected by salinity in sediment particles. The increase of salinity induced the decrease of KDSP, when the equilibrium of metals existed between particle and dissolved phases. The significant variation of one KDSP value with salinity means the easier release of heavy metals from one binding fraction to the dissolved phase. From the results the more significant variations of KDSP value were from KF1DSP and KF2DSP for Cd; from KF2DSP, KF3DSP, and KF4DSP for Co and Pb; from KF3DSP for Cr; from KF2DSP, and KF4DSP for Cu; from KF3DSP, and KF4DSP for Ni; and from KF2DSP,and KF3DSP for Zn.
The amounts of heavy metals remobilized from sediment with larger particle sizes and higher salinity were larger than these from sediment with smaller particle sizes and lower salinity environment.