Characterisation of suspended particulate matter in the Rhone River: insights into analogue selection

Environmental contextThe fate and behaviour of pollutants such as pesticides, metals and nanoparticles in natural waters will influence their effects on the environment and human health. Owing to the complexity of natural waters and suspended particulate matter (SPM) that can interact with pollutants, as well as low pollutant concentrations, determination of pollutant fate and transport is non-trivial. Herein, we report a characterisation of the Rhone River chemistry to provide insight into selecting SPM analogues for experimental and modelling approaches. AbstractSelection of realistic suspended particulate matter (SPM) analogues remains vital for realising representative experimental and modelling approaches in predicting the environmental fate of pollutants. Here, we present the characterisation of dissolved-ion and SPM compositions for nine sampling sites over the length of the Rhone River. Dissolved-ion concentrations remained stable, but SPM concentrations varied among sampling sites. Size fractionation and mineralogical characterisation of the SPM revealed that the same minerals (e.g. quartz, calcite, muscovite) constituted every size class from 0.5 to >50µm, as is usually found with allochthonous and large-scale systems. To gain insight into SPM analogue selection, aggregation kinetics of silica, calcite, muscovite, feldspars and clays were monitored in the native filtrate and related to the respective zeta potentials (ζ). An SPM mixture of calcite (49%), muscovite (14%), feldspar (23%) and chlorite (14%) proved the best match for the Rhone SPM, demonstrating that mineral surface chemistry, structure and size are all important in selecting a realistic SPM analogue for a riverine system.