Model polyethylene particles for the study of micro/nano-plastics in the oceans – POEM
Thanks to their many advantages plastics have become ubiquitous in our society. Their low recyclability and poor end-of-life management lead to 10 to 20 million tons released into the environment each year. Because plastics degrade slowly, they persist in the environment where they are fragmented into smaller particle notably through UV-degradation. Over the last decades, micro/nano-plastics (MP/NP) have contaminated the Ocean and marine species at all levels of the food chain, from one pole to another down to the deep sea. Polyethylene (PE) is the most widely used plastic which accounts for 90% of plastic waste accumulated in the environment, yet most research on MP/NP uses commercially available polystyrene particles. The lack of environmentally realistic NP/MP models is a major and under-studied technical obstacle in this research field. Currently no method can easily produce PE particles because of the gaseous nature of the monomer and the poor solubility of the polymer. Three strategies are proposed for the production of PE MP/NP: 1) by cryo-grinding 2) by micro-emulsification and 3) by radical polymerization of the ethylene in aqueous emulsion. The first method will produce micro-sized MP, formulated with a known additive in order to identify its toxicity. However, grinding particles down to 10 µm from pristine polymers remain challenging and will be improved through a preliminary UV-irradiation of the pellets which will also help to reproduce weathering of the polymer. In the second method, the PE is solubilized in hot toluene followed by emulsification in water under vigorous stirring in the presence of biosurfactant (i.e. polysaccharides secreted by microalgae). This process allows producing particles ranging from 0.8 to a few µm which will be optimized by varying the molar masses (reduction of dispersed phase viscosity) and the oxidation state of the PE (less hydrophobic). The latter method makes it possible to produce particles below 500 nm and narrow size dispersity to precisely study the effect of size on toxicity. In this case, the use of a biosurfactant is incompatible with the polymerization conditions (degradation of the polysaccharide at high temperature). Therefore, a non-ionic polar surfactant will be used and later exchanged with the biosurfactant by dialysis. In addition, a small amount of polar comonomer will be introduced in order to simulate aging, thanks to their greater UV sensitivity. The expertise of polymer chemists and physical chemists will enable to develop a wide range of realistic PE MP/NP by reproducing the alteration of the properties of the polymer (photodegradation induced by UV) as well as the formation of a biofilm. The presence of a biofilm on the surface of MP/NP can have a significant impact on their buoyancy and aggregation. Thus, the study of the colloidal stability of PE particles coated with a biofilm will be carried out in order to better understand their behavior in the marine environment and their bioaccumulation. The production of stable aggregates of NP is a great asset to study their toxicity below the range 2-200 µm ingested by the filtering model organism chosen here for toxicity studies: the oyster. The assessment of the ecotoxicological effects of NP/MP will greatly benefit from the synthesis of such tailor-made PE particles by focusing on the two main mechanisms of toxicity known to date: i) identifying the most toxic additives (e.g. endocrine disruptor) in order to consider their substitution and ii) the nanotoxicity as NP increases physical interaction notably damages to biological membranes induced by their large specific surface.
Monsieur Fabrice Brunel (Catalyse, Polymérisation, Procédés et Matériaux)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
IPC Innovation Plasturgie Composites
CP2M Catalyse, Polymérisation, Procédés et Matériaux
LEMAR LABORATOIRE DES SCIENCES DE L'ENVIRONNEMENT MARIN
IMMM INSTITUT DES MOLÉCULES ET MATÉRIAUX DU MANS
Help of the ANR 541,949 euros
Beginning and duration of the scientific project: - 48 Months