Microplastic in Human Urine: Early Observations and potential Influencing factors

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Abstract
Background Microplastics (MPs) have been found in human tissues, indicating widespread exposure, but little is known about their excretion and influencing factors. We investigated MP-like particles in human urine and potential differences related to menstrual cycle status in women. Methods Urine samples from 30 healthy adults (15 women, 15 men) were collected twice, with female samples timed for menstruation and non-menstruation, and male samples at random. Samples were purified (hydrogen peroxide), stained (Nile-Red), filtered (3 mm gold coated membrane), scanned (FITC fluorescence) and examined for MP-like particles (manual counted and categorised). Participants completed a questionnaire, statistical analyses explored links between exposure factors and particle counts. Results 30 volunteers provided 2 urine samples; 59 samples could be collected, of which 53 were evaluable. MP-like particles were detected in 48 samples, counts varied across individuals and timepoints (up to 15 particles/mL). No significant difference was observed between sexes, though a trend toward lower counts during menstruation was noted (p = 0.076). In explanatory modelling, self-reported period pad use, composite-packaged drink consumption, coffee preparation method, intimate shaving habits, and sea-salt intake emerged as potential explanatory factors for particle concentrations. Conclusion MP-like particles were detectable in the majority of urine samples analysed using a Nile Red/DAPI fluorescence microscopy workflow. Considerable variability in particle concentrations was observed between individuals and across sampling timepoints. Several questionnaire-derived variables emerged in exploratory analyses; however, given the limited sample size, and the absence of polymer-specific particle identification, these findings should be viewed as exploratory signals needing further confirmation.

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