Micro/nanoplastics contamination of the terrestrial environment: exposure routes, dose, and co-contaminants complicate the risk calculus

Abstract As xenobiotics in the environment, microplastics and nanoplastics have become ever-present in the environment, especially in terrestrial environment. However, a critical issue is that these anthropogenic contaminants are toxic to some terrestrial microorganisms, and the results of that toxic interaction over time can significantly impact microbial community structure and function, with unknown ramifications for ecosystem health. This viewpoint highlights the fact that, considering the diverse array of MPs/NPs, the broad dose range, and the presence of co-contaminants (e.g., retained organic and elemental pollutants, polymer additives) associated with these materials, their risk calculus to microbiome in terrestrial environment is incredibly complex. Short- and long-term dose-response that spans environmentally relevant concentrations and includes appropriate levels of analyte complexity (additives, co-contaminants). This should include microcosm studies that enable assessment of 'omic' parameters over the long term, as well as detailed assessment of impacts on soil microbiome function. We also need to understand impacts on eukaryotic microbes. In conclusion, for both toxicity and benefit, we should focus more on the dynamics of impacts on the microbiome. As some populations are inhibited, others increase. It is not because the plastics are conveying benefit directly but because more sensitive species are decreasing, which frees up resources from less competition. Those changes then have additional consequences, such as shifts in predator species and nutrient cycling and redox conditions. Graphical Abstract