New universal approach for microplastics detection in tissues retains histology and reveals unprecedented quantities in placental samples

Summary Background Micro- and nanoplastics (MNPs) contamination may pose a significant risk to human health. However, their true impact remains underexplored due to substantial limitations of current analytical methods. Traditional techniques like Raman and FTIR microscopy, coupled with filtration, fail to detect smaller MNPs and are prone to external contamination. Likewise, pyrolysis-GC/MS lacks the ability to pinpoint MNP size or location. Methods This study presents a universal approach for MNPs detection in tissues, validated to mitigate external contamination risks and enable the identification of significantly smaller MNPs. The method preserves histological information, allowing for comprehensive spatial analysis, including assesment of local DNA damage using the γ-H2AX histone. Findings Applying this method to human placenta samples revealed orders of magnitude higher MNP loads than previously reported, with quantities ranging from thousands to millions per cm³, far exceeding current reports of fewer than 1 MNP per gram or cm 3 of tissue. Importantly, within the observed concentration range, we found a positive association between MNP load and placental DNA damage. Interpretation Our findings show that that the prevalence of MNPs in biological tissues has been substantially underestimated, as the smallest and potentially most harmful MNPs go undetected with traditional methods. Furthermore, we found that the concentations were linked with genotoxic effects in the placenta. This novel analytical workflow represents a significant advancement in MNPs research and provides crucial insights into their impact on human health. Research in context Evidence before this study Prior to our study, MNPs have been detected in human tissues, including the placenta, but in very low quantities, often fewer than 1 MNP per gram or cm 3 (Amereh et al., 2022; Ragusa et al., 2021). Current detection methods, such as Raman and FTIR microscopy, have significant challenges, particularly in detecting MNPs in the lower size range, which are considered more hazardous (Dzierżyński et al., 2024). These methods also involve lengthy sample preparation processes, including chemical dissolution and filtration, which inherently lead to the loss of histological information. Additionally, they carry a high risk of external sample contamination, as well as MNP degradation and alteration, compromising the accuracy and reliability of the results (Renner et al., 2018). Added value of this study This study introduces a universal analytical workflow for MNPs detection in tissues that addresses critical limitations of existing methods. By eliminating external contamination risks and enabling the detection of significantly smaller MNPs, this method revealed orders of magnitude higher MNPs loads in human placenta samples compared to previous reports. The preservation of histological information allows for detailed spatial mapping of MNPs, contributing to a more comprehensive understanding of their distribution and potential biological impacts. A key finding of this study is the positive association between MNP load and placental DNA damage, as quantified by γ-H2AX labeling. This direct correlation between MNP exposure and genotoxic effects strongly suggests that the observed DNA damage is not an artifact of external contamination but rather a consequence of internalized MNPs within the tissue. This first finding of the presence of γ-H2AX foci, a well-established biomarker of DNA double-strand breaks, underscores the potential genotoxic risk posed by MNPs and highlights their ability to induce cellular harm at the molecular level. Implications of all the available evidence Our research indicates that the true MNPs load in human tissues may be significantly higher than previously recognized. The analytical workflow presented here has the potential to transform the field of MNPs research by enabling more accurate assessments of MNP prevalence in human and other biological tissues. Designed with methods and techniques widely available to researchers across disciplines, this workflow can be readily applied to diverse biological and environmental studies. This, in turn, could inform future studies on their biological interactions, long-term health effects, and dose-response relationships. Given the widespread presence of MNPs in the environment, our findings underscore the urgent need for longitudinal studies to evaluate the chronic effects of exposure, particularly in vulnerable populations such as pregnant individuals and their developing fetuses. Additionally, our findings and methodology are a stepping stone towards true direct toxicological research on MNPs. Addressing MNP contamination at the source and improving public and regulatory awareness are critical steps toward developing effective mitigation strategies.