Estuary-on-a-chip: unexpected results for the fate and transport of nanoparticles

The aim of this work is to evaluate the influence of a spatial salinity gradient, as encountered in estuaries when fresh water meets salt water, on the aggregation features of fullerene nanoparticle aggregates (nC(60)). To model these environmental conditions, we design a specific microfluidic device. In the literature, physical phenomena occurring in estuarine areas, such as the salinity gradient and the flow conditions, were never considered. Our results suggest that even a short time exposure (a couple of seconds) to the salinity gradient, i.e. dynamical spatial conditions, profoundly affects the aggregation properties of nanoparticles and therefore their environmental behavior and fate. It appears that the salinity gradient could enhance the stability of nanoparticles, especially at high ionic strength (close to that of seawater). Contrary to the common approach of particle aggregation in the lab under environmental conditions, our study shows the need to reconsider the spatial and temporal variations of abiotic parameters (ionic strength, pH, organic matter concentration) in the understanding and evaluation of the environmental fate and transportation mechanisms of nanoparticles.