The Invisible Burden: A Meta-Analysis of Methodological Evolutions and the Reassessment of Microplastic Concentrations in Human Tissues

Reports of microplastics (MPs) in human internal organs have surged since 2019, yet results remain characterized by extreme heterogeneity. While such inconsistencies are often attributed to environmental or biological factors, these results are consistent with the hypothesis that methodological limitations may result in a significant gap in our understanding of the systemic body burden and associated toxicological risks. This study presents a systematic review and meta-analysis of 11 high-quality benchmark datasets, totaling 190 observations, to explore the extent to which the transition from the "conventional era" (manual μRaman and μFTIR) to the "modern era" (automated LDIR and Py-GC/MS) may influence reported MP concentrations. Using a hierarchical mixed-effects meta-regression, we identified an overall pooled mean of 3.09 particles/g ( = 96.7%). However, the inclusion of an interaction term between the analytical era and matrix complexity significantly enhanced the model's explanatory power, accounting for 59.48% of the total literature variance (p = 0.0012). A significant interaction effect (p = 0.0231) revealed that while detection increased globally, modern automated platforms effectively "rescued" sequestered particles within solid parenchymal tissues, such as the placenta, lung, and endometrium, yielding concentrations nearly 70 times higher than those obtained via previous manual protocols. This "Scanning Power Paradox" infers that scanning efficiency, rather than mere optical resolution, may have been a primary historical bottleneck in human MP research. Our findings indicate that the human body burden may have been systematically underestimated, suggesting that current toxicological risk assessments may rely on "ghost data" that severely masks true human exposure. Consequently, the transition to automated, census-based standards is not merely a technical upgrade but a toxicological necessity for defining the true internal dose-response relationships in microplastic-linked chronic diseases.