A new screening framework to support the identification of exogenous particles and suspect microplastics in situ in pathological tissue samples

BACKGROUND: Microplastics are ubiquitous environmental pollutants that have been detected in various human tissues. Often the particle sizes reported challenge established theory in toxicokinetics, and fundamental data on whether exogenous microparticles can enter tissues (and which tissues) is needed. This observational and method validation study aimed to develop a screening framework to determine whether particles including microplastics can access tissues using human ileal tissue sections and to investigate the presence of exogenous particles within the subepithelial mucosa. METHODS: As proof of concept that exogenous particles may translocate into tissues, a screening framework was established using polarised light microscopy (PLM), to identify birefringent particles in ileal tissue sections from 101 subjects. The population included adults who had undergone endoscopy and biopsy for the investigation of bowel symptoms at King's College Hospital. Exclusion criteria were applied to differentiate between true particles and procedural contaminants. The remaining particles were analysed for their morphology and size. To further illustrate the potential for plastic to access intestinal tissue, a bulk intestinal tissue sample underwent a basic digestion, filtration, and analysis using pyrolysis gas chromatography mass spectrometry. FINDINGS: Results revealed the presence of subepithelial birefringent particles in a small number of ileal tissue sections. However, of the 35 samples containing sub-epithelial particles, 31 (i.e., 91% of observations) were concluded to be due to procedural contamination. Of the 'true' observations, some of these particles, which include starch, likely entered the tissue via persorption. Additionally, a single viscose fibre was observed within the lumen of the small intestine. Supplemental chemical data finding signatures of polypropylene and polyvinylchloride demonstrate how the framework would fit in a wider analytical pipeline. INTERPRETATION: This study highlights the importance of a robust screening framework for the identification of particles and suspect microplastics in human tissues. While the frequency of particles like microplastics in the subepithelial mucosa was low, the findings suggest that microplastics could indeed penetrate the intestinal epithelium and this was supplemented with example chemical data. Further research is needed to investigate the distribution, accumulation, and potential health effects of microplastics in human tissues. FUNDING: Medical Research Council.