Health Effects of Microplastics in Municipal Drinking Water: Systematic Review of AnimalModels and Emerging Human Data

Abstract

Microplastics and nano plastics are now detected across drinking-water sources and distribution systems, making ingestion a likely and widespread exposure route. The small size,persistence, and varied polymer types of microplastics allow for contact with the gastrointestinal epithelium. Potential movement past the gut increases public health relevance, despite uncertainties surrounding dose-response relationships. This systematic review synthesized recent experimental and observational evidence to evaluate how microplastics in municipal drinking water may affect human health. A PRISMA-guided PubMed search finalized in May 2025 resulted in 3,797 records; 2,000 titles/abstracts were screened; 99 full texts were assessed; 16 studies met inclusion for narrative synthesis. Evidence was dominated by animal studies (15/16,primarily rodents) conducted in China, with one human observational study which was conducted in Canada. Most animal exposures used drinking-water dosing (12/15) rather than gavage (3/15). Polystyrene was the most frequently tested polymer, and particle sizes commonly fell within 0.1-5 µm. Across studies, ingestion irritated gut microbial communities and epithelial integrity, aligning with low-grade inflammation and metabolic changes in connective tissues.Immune signals included cytokine upregulation and NF-κB pathway activation; metabolic signals included hepatitis lipid accumulation and impaired glucose control. Limited neurological evidence in rodents showed blood-brain barrier interactions and brain oxidative stress under polystyrene exposure. Male reproductive endpoints showed dose-responsive declines in sperm quality and hormone alterations. The human study associated fecal microplastic burden withliver and lipid biomarkers, supporting biological plausibility but not causality. Limitations include narrow test materials (spherical polystyrene), doses that often exceed plausible daily intake, short exposure durations, and geographic concentration of studies in one country. Overall, the evidence supports a mechanistic pathway in which small, ingested particles disrupt gastrointestinal barriers and amplify immune and metabolic stress, with signals in neurological and reproductive domains under specific conditions. To complete a decision-grade risk assessment, future studies should consider standardization of particle reporting, realisticdrinking-water exposures at low doses and longer durations, life-stage and multigenerational designs, and integrated human studies linking stool microplastics with clinical biomarkers and specific health endpoints.