Microplastics in potable water of a coastal city of Bangladesh: Efficacy of boiling as a point-of-use mitigation strategy.

Microplastic (MP) contamination of potable water is an emerging concern, particularly in developing countries where treatment infrastructure is limited and plastic pollution is widespread. This study quantified MPs levels in Khulna City's major domestic water sources and assessed the effectiveness of boiling as a point-of-use mitigation strategy. Forty-five samples were collected from three distinct domestic water supply sources in Khulna city: i) supplied tap water, ii) ponds, and iii) submersible groundwater, and analyzed using microscopy and Fourier Transform Infrared (FTIR) spectroscopy. Total water hardness was measured to examine its association with MP reduction in nine composite samples. MPs were detected in all samples, with pond water exhibiting the highest concentration (71.2 ± 10.6 particles/L), followed by supplied tap water (45.5 ± 6.1 particles/L) and submersible groundwater (40.1 ± 3.1 particles/L). Most MPs were < 400 μm in size, predominantly fibers and fragments, with blue and transparent particles being most common. Six polymer types were identified, of which polyethylene terephthalate (PET), high-density polyethylene (HDPE), and polyvinyl chloride (PVC) were the most prevalent. Boiling significantly (p < 0.001) reduced MP concentrations by >70% across all water types, with reductions reflecting physical settling of MPs in very hard water, consistent with calcium carbonate scale formation and co-precipitation reported previously, rather than thermal degradation. MP reduction showed a strong positive association with water hardness (r = 0.76). Estimated daily and annual MP intake values were consistently higher for non-boiled than boiled water, indicating that boiling can effectively reduce exposure. However, because MPs accumulate at the bottom of the container rather than being eliminated, gentle decanting of the clear supernatant after cooling and settling is recommended to minimize ingestion.