Thesis presented November 13, 2024

Abstract:
Plastics, made from synthetic polymers and chemical additives, have become indispensable materials in our society due to their very interesting properties (low cost, strength, versatility). However, their increasing production leads to serious environmental pollution due to inappropriate waste management. When dispersed in the environment, plastics undergo degradation processes caused by physical, chemical and biological constraints, resulting in their fractionation into smaller particles, known as micro- and nanoplastics (MNPs). Due to their large specific surface area, they can adsorb and transport chemical pollutants such as heavy metals and persistent chemical pollutants. Humans are exposed to MNPs through inhalation of polluted air and ingestion of contaminated food and drink. Little is known about the toxic effects of these particles on human health, either alone or in the presence of the pollutants they carry, particularly under realistic exposure conditions. Indeed, to date, studies have focused on pristine commercial particles, whose physical, chemical and toxicological characteristics differ from those that have remained in the environment. In this thesis project, the physico-chemical transformations caused by artificial weathering in environmental conditions on two types of plastic particles, i.e., polystyrene (PS) and polycaprolactone (PCL) were characterized, as well as their toxic effects, in the pristine and weathered state. To this end, 100-1000 nm PS and PCL particles were submitted to conditions simulating UV irradiation and the temperature of a sunny day at noon in the equator region, in a Q-SUN test chamber. Their transformation was characterized by dynamic light scattering, zeta potential characterization, FTIR and Raman spectroscopy, transmission and scanning electron microscopy and HPLC-MS/MS. Their toxicity to human intestinal cells was examined using co-cultures of Caco-2 enterocytes and mucus-secreting HT29-MTX cells. The used Caco-2 cells were either representative of healthy individuals or of individuals with susceptibility to Crohn's disease, as they had been genetically engineered to stably express either wild-type NOD2 or NOD2 carrying the 1007fs mutation. On these cell models were assessed the cytotoxic, genotoxic, oxidative and inflammatory potential of these particles, either pristine or aged, and alone or co-exposed with metals, as well as their impact on the intestinal barrier function. Thus, this project aims to provide data for a more accurate assessment of the risks associated with human exposure to MNPs waste.​

Keywords:
Micro- and nanoplastics, environment, physicochemical characterization, toxicity, intestine, Crohn's disease​