Probing Microplastic Interactions in Undigested Human Semen: Lack of Sperm Adhesion and Clues to Organismal Translocation

Microplastics (MPs) are ubiquitous environmental contaminants that have recently been detected in human semen, raising concerns about potential implications for male reproductive health. However, how MPs are retained, distributed, and interact within seminal fluid remains poorly understood. In this study we investigated the presence, localization, and behaviour of environmental MPs in undigested human semen from five normozoospermic donors, adopting an analytical workflow designed to preserve the native architecture of the ejaculate and maintain biological context. Semen samples (whole semen and spermatozoa-enriched fractions) were analysed by fluorescence microscopy followed by chemical identification using µRaman microspectroscopy. MPs were consistently detected in all donors, with particles predominantly in the microscale range (on average <10 μm). Polymer composition reflected materials commonly reported in environmental and biological matrices, including polypropylene (PP), polyethylene (PE), and polystyrene (PS). Crucially, despite systematic examination of both whole semen and spermatozoa fractions, no evidence of MP adhesion to, or internalisation within, spermatozoa was observed within the particle size range accessible to the adopted µRaman-based analytical workflow. These findings indicate that, under native conditions, MPs are dispersed within seminal plasma and can co-sediment with sperm cells during processing without establishing detectable direct particle–membrane interactions. To explore a plausible source pathway within the male reproductive tract, prostate tissue from one donor was also analysed. In contrast to semen, prostate specimens contained larger MPs, up to ∼60 μm. Although preliminary and observational, this preliminary finding is consistent with the possibility that the prostate may contribute to the differential retention of particles, with smaller MPs potentially reaching the ejaculate more readily. Overall, our findings refine the biological interpretation of MPs in semen as a downstream signature of tissue-level exposure and transport, and support future studies, particularly addressing nanoscale plastics and clinical correlates, to clarify reproductive risk.