Study of microplastic release during the use phase of products from the plastics processing industry

The widespread use of plastics has led to an overconsumption of low-cost products considered as disposable or single-use while they keep their durability property. Several studies have highlighted the ubiquity of microplastics (MP) in all ecosystems, but also in our food. It is now established that plastic particle ingestion through food consumption is a widespread phenomenon, raising significant concerns regarding its potential impacts on human health. At the same time, to address pollution issues linked to the increasingly intensive production of plastics, the plastics industry is currently transitioning toward a logic of object reuse, particularly in the agri-food sector. The work carried out in this thesis aims to propose methodologies that improve our understanding of the behavior of food-contact objects reused many times, focusing on their potential to release MPs.To this end, a protocol was developed to simulate the repeated use of an object, followed by the extraction and quantification of MPs generated during this simulation. This protocol was implemented using a plastic salt shaker as a case study. Although its use is occasional, it involves a significant number of mechanical solicitations.The extraction, but more importantly the quantification, of MPs from the samples was further developed, relying on studies published before or during the thesis, with the aim of producing reliable results and eventually applying the protocol to other types of products that may expose consumers to MPs. Measurement by microscopy coupled with infrared spectroscopy was used for its ability to identify, differentiate, and quantify MPs. This technique creates a chemical map of the sample, where each analysed point on the surface is associated with an infrared spectrum that enables identification of the material at that location. An in-depth development of this already widely used method in the MP field was carried out at the data processing level, which involves comparing the large number of infrared spectra obtained to a database to identify the plastic particles.This development highlighted that the quantities of MPs measured were highly sensitive not only to operational conditions but also to the methodologies applied in chemical image processing. MP quantification by this method provides an estimate of the number of particles within the targeted size range and, above all, enables comparison between different samples provided if the experimental procedure remains strictly identical throughout the analysis. This highlights the importance of continuing efforts towards harmonization and standardization of methods, not only for the sample preparation stages, which have already seen significant progress, but also at the data processing level.Flow cytometry was also the subject of an in-depth bibliographic study and several tests. This study revealed that significant challenges remain, particularly due to the indispensable yet problematic use of the Nile Red fluorochrome, which generates a significant number of false positives.The results obtained on MP release from salt shakers showed that the amount generated through their use was largely negligible compared to that originating from the preparation and analysis steps, despite improvements made to limit biases. This highlights how challenging MP analysis remains, even under controlled experimental conditions.