The European Water Framework Directive came into force in 2000, taking the 1976 Barcelona Convention into account and thus encouraging the contracting parties to evaluate pollution discharge to the Mediterranean Sea. Under the umbrella of the Rhone Sediment Observatory a monitoring station was set up upstream from Lyon in order to measure hydrophobic organic compounds and mercury contents of particles and to evaluate fluxes. To analyse those various contaminants several grams of dried suspended particulate matter (SPM) are required – which can be challenging considering low SPM levels in the Rhone river during base-flow regime. To face that problem several sampling techniques have been implemented: manual or automatic sampling, a continuous centrifuge running during several hours and an integrative sediment trap. For the sake of data homogeneity, we must assess and compare these different sampling techniques. The particle size distribution analysis of SPM sampled manually in the Rhone river showed two main peaks: one around 0.25 µm (10% volume) and another around 8 to 15 µm (90% volume). In contrast, the particle size distribution analysis of SPM collected with the continuous centrifuge and the sediment trap highlighted that finest particles were not successfully sampled. These results were confirmed by detectable SPM concentrations for water collected at the outlet of the continuous centrifuge and of the sediment trap. Thus, we investigated SPM contaminant contents according to the particle size classes. Particulate mercury analysis revealed that finest particles are the most contaminated ones. Therefore, all particulate contaminant contents should be normalized using particle size distribution data especially when comparisons are needed between contaminants content of particles sampled with different techniques, or sampled in bed deposits.