Trace metal distribution between suspended matter and dissolved phase has been determined in an organic rich aquatic system: the Lena River estuary and the adjacent Laptev Sea. The partitioning between dissolved and particulate phases of Cs Cd, Co, Cs, Mn and Zn is determined through the so- called fast distribution coefficient (FDC). Application of a surface complexation model has been attempted so as to describe the FDC's variations in the estuarine system. The relative effects of inorganic dissolved species and colloidal and particulate reactivity on FDC are discussed. The particulate reactivity is related either to the composition of the particulate component (mineral and organic) or to the bulk particulate surface properties such as the ammonium saturation index or the heat of immersion in water. For Cd, the low FDC variation with the salinity can be explained by the variation of the chloro and sulphato dissolved species, by the complexation of some colloidal organic species and by a high particulate surface reactivity. The complexation constant of the particulate phase (log K(s(Cd))) has been calculated equal to 5.2. Zn exhibits a similar range of FDC variations but the scattered relationship with salinity does not allow an identification of the determining parameters. Co and Mn exhibit similar behaviours. The high changes in their FDC (compared to Cd) have been simulated by a surface complexation model in which the effect of the major cations (Ca2+ and Mg2+) is taken into account. The complexation constant of the particulate phase (log K(s(Mn))) and log K(s(Co)) calculated from the model is 7.2. For Cs, the competitive sorption with K+ chiefly controls the change in FDC. Using the number of sites given by the ammonium saturation index, a mean value of the particulate complexation constant (log K(s(Cs))) has been estimated to be 5.1. Implications of the low temperature of the water in the studied area on the trace metal sorption on the particulate phase are discussed.