The Human Plastiphere: A Bioparticulate System Challenging Microplastic Risk Assessment and Governance

The infiltration of microplastics (MPs) into human tissues represents a paradigm shift in environmental health, transforming external pollution into internal biological integration. Drawing on 90 clinical studies (2016-2025), we define the human plastiphere as a bioparticulate system composed of nonendogenous plastic particles that accumulate, distribute, and interact with host tissues. This system displays key biological features: persistence (decade-scale tissue retention), organized distribution (organotropism across 63 human biological compartments), and active biological engagement (e.g., cardiovascular, reproductive, and metabolic interference). We identify eight unresolved paradoxes─ranging from size-defying barrier penetration to absent toxicity thresholds─that highlight critical gaps in synthetic particle biology. The plastiphere challenges conventional toxicology by showing that MPs: (1) follow selective biological rules (e.g., vascular trafficking) while violating others (e.g., phagocytic clearance), and (2) form a measurable, transgenerational burden with escalating health risks as plastic production continues to rise. To address this emerging bioparticulate phenomenon, we propose three urgent actions: harmonized detection protocols, polymer-specific safety thresholds, and source-targeted policy interventions. The plastiphere, both as a biological system and a conceptual framework, offers a roadmap for advancing science from descriptive detection to health-relevant, mechanistically grounded, and policy-actionable solutions.