Do microplastics affect human immune defenses?

Microplastic pollution has recently raised serious concerns on a global scale, yet their toxic effects are still underexplored. Microplastics, unlike most pollutants, consist of a wide variety of polymers, combined with additives that exhibit varying behaviors when dispersed in the environment. Microplastics can be coated by microbial biofilms and adsorb other pollutants. When microplastics age or aggregate to form larger particles, accurate detection and quantification is limited using current analytical methods. As a consequence, the occurrence of false positives introduces large uncertainties in the analysis of microplastics in the atmosphere, water, and soil. In short, microplastics in the environment are hard to investigate, thus making immunotoxicity experiments calibrated on environmental observations challenging to carry out. Here, we show that the toxicity of microplastics on the human immune system is higher for small microplastics and nanoplastics, based on evidence from toxicological experiments. By contrast, some plastics such as polyethylene probably display a low toxicity due to their structural similarity with natural polymers such as plant cuticular waxes.