[en] The process of labelling by precipitation has recently been extrapolated to the double-labelling of fine particles. The first, ''conservative'' radioisotope (scandium-46 or hafnium-175+181) is fixed on the sediment particles in order to keep track of them in the natural environment. A second ''reactive'' radioisotope selected from among the pollutant elements (zinc-65, chromium-51 or mercury-203) is deposited at the same time on the same particles. This new technique is aimed at clarifying the mechanisms by which certain pollutant metal elements are redissolved during their entrainment by suspended sediments in a tidal estuary. A laboratory investigation has shown that hafnium or scandium hydroxide remains bound to the particles, whereas zinc hydroxide may be solubilized by certain chemical agents, particularly those present in estuaries in variable quantities, such as sodium chloride