Microplastics and Nanoplastics in human tissues: Systematic review of evidence, analytical protocols, and methodological challenges

Microplastics and NanoPlastics (MNP) have emerged as ubiquitous environmental contaminants with potential implications for human health. This systematic review synthesizes current evidence on the occurrence of MNP in human solid tissues and critically evaluates the analytical protocols employed for their detection and quantification. A comprehensive literature search conducted in September 2025 across MEDLINE, EMBASE, and the Cochrane Library, in accordance with PRISMA guidelines, identified 26 eligible studies encompassing 564 human samples from diverse biological matrices, including placenta, lung, liver, blood, and bone. Polyethylene, polypropylene, and polyvinyl chloride were the most frequently detected polymers, while particle sizes predominantly ranged between 20 and 100 µm. Analytical techniques varied substantially across studies, with Raman and Fourier-transform infrared (FTIR) spectroscopy representing the most widely applied methods, often complemented by microscopy or pyrolysis–GC/MS for polymer confirmation. Reported MNPs abundances ranged from less than one to several thousand particles per gram of tissue, reflecting the lack of standardized procedures for extraction, quantification, and contamination control. Recent investigations have increasingly implemented plastic-free workflows and procedural blanks, leading to improved reliability and reduced overestimation of MNP burden. Nevertheless, persistent methodological heterogeneity continues to hinder cross-study comparability and the establishment of true human tissue loads. Preliminary correlations between MNP accumulation and clinical or pathological parameters have been observed, but causal links remain unconfirmed. This review highlights the urgent need for internationally harmonized protocols, rigorous contamination prevention, and standardized reporting to ensure reliable biomonitoring and clarify the potential health implications of microplastic exposure in humans.