Not all microplastic particles are created equal - physical properties matter for their interactions with cell

Microplastics are everywhere in our environment. The oceans, rivers, soil, air – wherever researchers look for these microscopically small plastic particles, they usually find them. Therefore, microplastics have been described as contaminants of emerging concern since their ubiquity might pose a risk to organisms, ecosystems, and to human health.

Consequently, numerous studies on the potential effects of microplastics for cells, organisms, and ecosystems have been published. Often, these studies use commercially available spherical microparticles made from polystyrene as a model for microplastics. However, these studies often show contradictory results, some of them showing adverse effects whereas others do not. This discrepancy in detected effects makes it hard to assess the risks associated with microplastic particles.

An interdisciplinary research team from the Collaborative Research Centre 1357 – “Microplastics” at the University of Bayreuth and the Leibniz Institute of Polymer Research Dresden discovered that seemingly identical polystyrene microplastic particles from different manufacturers tremendously differ in their physicochemical properties. These differences are an important factor for the interactions of the microplastic particles with cells.

One important factor that was identified by the researchers was the particles’ zeta potential, which is related to the charge of a particle in a solution. Particles with a larger magnitude of the zeta potential interacted stronger with the cells. Particles that interacted stronger with cells were then internalized more efficiently into the cells.

“The interactions of microplastic particles with cells are a basis for potentially hazardous effects on organisms”, stresses Prof. Dr. Holger Kress, one of the initiators of the study. He continues: “These interactions may also determine how microplastic particles can cross biological barriers, infiltrate tissues, and distribute in the organism”.

The results of this study, which was published in the journal Nature Communications provide a possible explanation for the seemingly contradictory results of previous studies that relied on polystyrene microplastic model particles. By highlighting the strong differences between nominally identical polystyrene particles from different manufacturers, the researchers show the necessity to thoroughly characterize the physicochemical properties of the microplastic model particles in effect studies.

Prof. Dr. Christian Laforsch, spokesperson of the CRC 1357 – “Microplastics” and one of the initiators of the study emphasizes: “Microplastics are not just microplastics. Our study underlines this complexity of the microplastic problem and highlights that physicochemical properties of microplastic particles are important to understand their interactions in the environment”.

With their study, the researchers want to raise awareness about this problem in the scientific community. It’s only when the comparability of studies about the potential negative effects of microplastics is guaranteed that a reliable assessment of the risks associated with microplastic particles as well as the development of new environmentally friendly plastics becomes feasible.