Tire-Derived Microplastics as Chemically Complex Environmental Contaminants: Mechanistic Pathways, Exposure Gradients, and Implications for Environmental Health.

Tire-derived microplastics (TWPs) are now recognized as one of the largest and most persistent sources of environmental micro- and nanoplastic pollution, yet their implications for human health remain incompletely characterized. TWPs contain complex mixtures of synthetic polymers, metals, polycyclic aromatic hydrocarbons, plasticizers, antioxidants, and transformation products such as 6PPD-quinone. These constituents exhibit chemical reactivity and biological activity relevant to oxidative stress, endothelial injury, inflammation, immune perturbation, and metabolic disruption-processes increasingly linked to chronic disease and components of the inflammothrombotic immunologic response (ITIR). Despite widespread environmental distribution across air, water, soil, and food systems, TWPs remain underexamined within the broader environmental exposome framework. This review synthesizes environmental, toxicologic, and mechanistic evidence on TWPs, integrating data from atmospheric studies, stormwater and sediment analyses, chemical characterization, in vitro and in vivo models, and emerging microplastic health research. Particular emphasis is placed on oxidative and redox-active constituents, endothelial and vascular responses, immune activation, metabolic effects, and the toxicologic relevance of 6PPD-quinone. Environmental gradients in TWP exposure-especially in high-traffic urban settings-are examined in relation to environmental justice and cumulative risk. Collectively, the evidence indicates that TWPs function as biologically active environmental contaminants capable of engaging multiple mechanistic pathways associated with inflammation, vascular dysfunction, and systemic stress responses. Their ubiquity, persistence, and mechanistic plausibility underscore the need for expanded monitoring, improved analytical methods, and targeted toxicologic and epidemiologic research. TWPs are presented as contributors to sustained ITIR activation, which may increase susceptibility to cardiometabolic and vascular disease. ITIR is increasingly recognized as an established mechanistic framework supported by multiple experimental, clinical, and environmental studies. While definitive causal relationships between TWPs and human disease remain under investigation, the mechanistic plausibility is strong.