Microplastics in Urinary Calculi: Evidence from Human Urinary Stones

Microplastics and nanoplastics are ubiquitous environmental contaminants with documented presence in human tissues, including urine and renal tissue. Whether microplastics become incorporated into urolithiasis has not been previously explored. The aim of this study was to determine the presence and polymer composition of microplastics in human urinary stones.

Renal and bladder calculi from 13 patients were collected intraoperatively at the University of New Mexico Hospital. Stone debris, otherwise discarded, underwent potassium hydroxide digestion followed by ultracentrifugation for microplastics isolation under contamination-controlled conditions. Polymer identification was performed using pyrolysis gas chromatography-mass spectrometry targeting 12 polymer standards. Quality controls included blanks and procedural standards to exclude contamination.

Microplastics were identified in 100% (13/13) of specimens, with each specimen containing at least 1 polymer quantified above the limit of quantification (LOQ). Additional polymer detections between the limit of detection and limit of quantification further supported the presence of microplastics across all samples. Polyethylene, polyethylene terephthalate, polyvinyl chloride, nylon 6, and styrene-butadiene rubber were consistently detected across all samples. All stones contained multiple polymer types, suggesting heterogeneous incorporation. Detection rates exceeded those previously reported in urine and renal tissue studies, indicating a potential affinity of microplastics and nanoplastics for stone matrices.

This study provides the first evidence of microplastics within human urolithiasis. The consistent detection of common environmental polymers supports the hypothesis that microplastics and nanoplastics may act as nucleation substrates or become entrapped during stone crystallization. Given the rising global prevalence of urolithiasis, these findings implicate environmental plastic exposure as a novel contributor to stone pathogenesis and underscore the importance of investigating planetary health determinants of urologic disease.