Microplastics and Human Health: A Comprehensive Review of Exposure Pathways, Biological Mechanisms, and Clinical Implications

Microplastics (MPs) and nanoplastics (NPs), defined as plastic particles smaller than 5 mm and 1 μm respectively, have emerged as ubiquitous environmental contaminants with significant implications for human health. This comprehensive review synthesizes current evidence on human exposure pathways, biological mechanisms of toxicity, and clinical health outcomes associated with microplastic exposure. Human tissues contain quantifiable microplastic burdens ranging from approximately 1 to 61 particles per gram, with particle sizes spanning from sub-micrometer nanoplastics to several hundred micrometers. Exposure occurs primarily through ingestion of contaminated food and water, inhalation of airborne particles, and dermal contact. Once in the body, these particles can cross biological barriers, accumulate in multiple organ systems, and trigger adverse biological responses including oxidative stress, inflammation, endocrine disruption, and genotoxicity. Emerging epidemiological evidence links microplastic tissue burden to cardiovascular disease, respiratory disorders, gastrointestinal dysfunction, reproductive toxicity, and neurodegenerative conditions. Despite growing concern, standardized detection methods, comprehensive risk assessments, harmonized regulations, and proven treatment strategies remain limited. This review highlights the urgent need for further research to establish exposure thresholds, elucidate long-term health effects, develop effective mitigation strategies, and implement coordinated monitoring and regulatory frameworks to protect public health.