I`ll present experimental work aiming to characterize the influence of macroscopic suspended particles on the transport and dispersion of solutes, such as contaminants, in confined flows at low Reynolds number. Initial experiments studying pressure-driven flow in a parallel-plates channel, showed that, for a range of flow rates and particle volumetric fractions, the presence of macroscopic particles decreased the dispersivity of a passive solute, allegedly due to particle migration to the centerline and consequent lattening of the flow velocity profile. This result contradicts the idea that the streamline distortion caused by the random diffusive motion of the particles increases the dispersion and mixing of the solute. Therefore, to estimate the influence of this motion on he dispersivity of the solute, and investigate the origin of the reported decrease, we performed complementary experiments to study the distribution of particle velocities, and spatio-temporal correlations, in identical experimental conditions. Our results show evidence of particle migration to the centerline, and also that the contribution of particle diffusive motion to the solute dispersivity is much smaller than the reported decrease, and thus negligible. In our configuration, solute dispersion is then much more ffected by how particles modify the flow velocity profile across the channel, than by their diffusive random motion.