Unveiling Hidden Threats: Introduction of a Routine Workflow for Label-Free and Non- destructive Detection of Microplastics in Human FFPE Tissue Sections

Microplastic (MP) pollution has emerged as a significant environmental and health concern. This study aimed at developing a novel method for detecting MP particles in deparaffinized formalin-fixed paraffin-embedded (FFPE) routine tissue sections of human colon samples. By utilizing mid-infrared photothermal (MIP) microscopy, also known as optical photothermal infrared (OPTIR) spectroscopy, we here aimed to establish a work-flow representing a non-destructive infrared spectroscopic approach for distinct identification and localization of polymers in FFPE colon tissue sections by respecting standardized protocols well integrated into clinical routine. After OPTIR analysis, samples were processed to H&E staining for histopathological analysis at defined regions of interest. By using OPTIR spectroscopy, we succeeded in localizing polyethylene (PE), polystyrene (PS), and polyethylene terephthalate (PET) MPs in distinct regions of interest (21 PE particles, 1 PS particle, 1 PET fiber) and clearly identifying the embedded polymers in the respective colon tissue sections. Subsequent H&E analysis confirmed characteristic histopathological features of inflammation spatially associated with the respective MP polymers. We present here for the first time a diagnostic workflow that has the potential to enhance our understanding of MP accumulation in routine organ tissue slides and allows for exploration of its implications for human health. The observed morphological H&E features in proximity to the identified MPs could possibly indicate a link between MP exposure and colon inflammation.