Role of the Protein Corona in the Colloidal Behavior of Microplastics

Researchers showed that microplastics from our waste are dispersed in water by proteins adsorbed to their surface. This discovery opens the way to low-tech strategies for collecting them. 

Plastic waste scattered in nature breaks up into invisible particles of micrometric or nanometric size. Because scientists do not yet know their physical and chemical properties and their biological interactions, they cannot fully assess the environmental impact of this diffuse pollution. In nature, microplastics quickly become coated with molecules of biological origin. How do these biomolecules modify their behaviour?

To find out, research teams from CEA, IMMM, UPC, and Soleil Synchrotron in France, have studied microplastics in water to understand the role of the protein corona on their stability. The most persistent microplastics in the environment, polyethylene and polypropylene (5 and 10 µm in diameter), were chosen for this study. In the absence of proteins, buoyancy and capillary forces tend to gather the microplastics towards the surface ('creaming') and very few particles remain in solution. In the presence of proteins, hydrophobic microplastics become hydrophilic and can diffuse in water. In addition, this protein corona prevents agglomeration and stabilises microplastics suspensions in water. Taking advantage of this effect, size fractions of stabilized microplastics could be prepared for toxicological screening using a protein corona formed with a well-known protein, serum albumin.

Alternatively, it is also possible to destabilise the protein corona surrounding the microplastics, either by adding a salt, which induces protein precipitation, or by heating, which results in protein aggregation. In both cases, 95% of the microparticles were removed from water by creaming after 24 hours. Heat treatment could be used to purify water to make it drinkable, where industrial depollution facilities are lacking