Microplastics and nanoplastics as possible carriers and/or indirect modulators of microbial metagenomes: Any effect on human health?

Micro- and nanoplastic particles (MNPs) are ubiquitous environmental pollutants detected across diverse ecosystems and human tissues. While chemical toxicity is widely studied, emerging evidence suggests that MNPs act as dynamic biological vectors. Preliminary experimental studies suggest that MNPs colonized with microorganisms may enhance microbial pathogenicity or facilitate host–pathogen interactions, leading to increased mortality in small animal models. However, key questions remain unresolved, including whether MNP-associated microbial communities can be transferred to humans and contribute to chronic disease development. We first examine how the plastisphere can concentrate opportunistic pathogens, enrich antibiotic-resistance genes (ARGs) via biofilm dynamics, and display distinct ecological behaviors across biodegradable polymers and airborne environments. We then assess preclinical and emerging observational data exploring how ingested and inhaled MNPs may interact with mucosal interfaces, potentially influencing gut and respiratory microbiota composition and barrier integrity. While experimental models suggest that MNP-associated dysbiosis could indirectly fuel systemic inflammation and metabolic/cardiovascular risks, direct causal evidence in humans is currently lacking. Finally, we outline pragmatic preventive strategies, discuss methodological bottlenecks, and advocate for standardized longitudinal studies to clarify the true clinical relevance of the plastisphere.