Many cases of groundwater contamination by immobile pollutants have been described in the last years. These phenomena are hardly predictable if mechanisms inducing leaching of high amounts of contaminant within short periods are not taken into account. This is the case of particulate transport of pollutants, although only few experimental evidence is available to date. Especially, the effect of bacterial cells on the facilitated transport of heavy metals is not yet well characterised, although micro-organisms, as colloidal particles, can be found every where in soil and water and present very specific mobility and pollutant mobilization potential. The objective of the present work was to show the capability of two well known bacterial strains: Ralstonia metallidurans CH34 and Escherichia coli, to accelerate the transport of mercury, zinc and cadmium in a simple model soil: the Fontainebleau sand. The results showed that under certain conditions, bio-sorbed heavy metals were transported from 1.2 to 3.5 times faster than metals in solution and that this last transport mechanism becomes negligible (5 to 7 times lower). Furthermore, the main factors controlling accelerated pollutant transport by bacterial colloids were identified and quantified. Soil solution ionic strength and velocity control the mobility of the colloids, so do their own concentration. Hydrophobicity and cell surface charge control both adhesion to the matrix i.e. cell mobility, and heavy metal adsorption, i.e. cell carrier potential. These results demonstrate clearly that micro-organisms can mediate the transport of heavy metal pollutants in soil and that this important mechanism can become dominant under precise climatic conditions.