Microplastic pollution and polymer-specific hazards in different water sources of Thimphu, Bhutan

Microplastics (MPs) are an emerging contaminant of concern due to their persistence, polymer-specific toxicity, and potential human exposure through drinking water. This study provides the first systematic assessment of MPs in diverse water sources in Thimphu, Bhutan (n=54), including streams, rivers, groundwaters, municipal taps, and bottled waters. Samples were analysed using pyrolysis–GC/MS and evaluated through Polymer Risk Index (PRI) and Estimated Daily Intake (EDI). MPs concentrations varied widely, with streams (5.12 ± 0.70 µg/L) and groundwaters (2.70 ± 0.32 µg/L) showing the highest levels, followed by rivers (2.69 ± 0.26 µg/L). Treated waters, including municipal taps (1.05 ± 0.18 µg/L) and bottled waters (0.78 ± 0.10 µg/L) had comparatively lower concentrations. PET (52.5%) was the dominant polymer, followed by PVC (14.6%) and SBR (14.3%), with upstream-to-downstream increases linked to urban pressures. While all sources showed overall moderate MPs concentrations, PRI classified every source as “high hazard” due to toxic polymers such as PVC and SBR. EDI values were highest in streams (0.17 ± 0.02 µg/kg/day) and lowest in bottled water (0.02 ± 0.00 µg/kg/day), comparable to intermediate global estimates. Although concentrations were moderate, the predominance of hazardous polymers and chronic low-dose exposure highlight potential ecological and health risks. The presence of MPs in municipal tap and bottled water shows treatment and packaging does not fully eliminate contamination, highlighting the need for strengthening catchment protection, management, and long-term monitoring. Polymer-specific toxicological studies are crucial for risk-based policy under rapidly urbanizing and climate-sensitive context. • Raw water (stream, river and groundwater) had slightly higher MPs than treated water. • PET, PVC, and SBR were dominant polymers with clear downstream accumulation. • Pollution Load Index showed low risk, but Polymer Risk Index indicated high hazard. • Estimated Daily Intake revealed variable human exposure from different sources. • Findings call for catchment protection, waste management, and improved treatment.