Thesis defense of Alice Pradel

Environmental fate and behavior of nanoplastics :
Implication of physico-chemical processes


Plastics are the third most-produced material on Earth and a significant proportion (>25%) ends up in the environment. To elucidate the risks that this contamination can cause, it is necessary to track the sources, transport pathways, and sinks of plastic debris in the environment. This has proven difficult since plastic degrades into particles that are too small to sample and quantify. In particular, nanoplastics (<1μm), which are colloidal particles, could form a substantial fraction of the global budget of plastic debris.
Therefore, the goal of this work was to investigate where nanoplastics may accumulate, by studying physicochemical processes in lab experiments. Throughout this work, special attention has been devoted to the environmental relevance of the nanoplastic models used. First, nanoplastics’ aggregation dynamics was investigated since it impacts downstream transport processes. Then, this work studied nanoplastics' transfer through two environmental interfaces. These have physicochemical gradients suspected to control nanoplastics’ fate: porous media (as a proxy for soils, sediments and aquifers) and the interface between saltwater and ice (as a proxy for seawater/sea ice interfaces). This study shows that the different behaviors of the nanoplastic model are attributable to their sizes, shapes and surface properties that modify their hydrodynamic behaviors and interaction energies.

Keywords: Contamination,  Colloid, Transport, Transfer, Organic Matter

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