Smaller-sized micro-plastics (MPs) contamination in single-use PET-bottled water in Thailand

Abstract

Micro-plastic (MP) contamination of drinking water is an emerging global concern. Findings on the cytotoxic effects of MPs in human cells are an incentive to investigate the MP concentration in drinking water. The present study quantitatively and qualitatively analyzes the MPs in 10 brands of single-use PET-bottled water, sourced from Thailand. A set of glass-bottled water was similarly analyzed to compare the MP concentrations between the two packaging. Two sorting techniques were used: 1) fluorescent tagging with Nile Red (≥6.5 μm) and 2) optical microscopy (≥50 μm). ATR-FT-IR (≥50 μm) and confocal Raman spectroscopy (1–50 μm) were also used. The MP concentration was found to be 140 ± 19 p/L in single-use plastic-bottled water and 52 ± 4 p/L in glass-bottled water. Plastic bottles had a significantly higher MP quantity than the latter. Both 6.5–20 μm and 20–50 μm MPs showed significant dominance over the ≥50 μm fraction. Fibers accounted for 62.8% of the total particle content, followed by fragments. Under optical microscopy, ≥50 μm particles were 10 ± 1 p/L (on average), which did not differ largely from that of fluorescent-tagged particles in the same size range (12 ± 1 p/L), implying the suitability of both techniques to sort ≥50 μm MPs. However, fluorescent-tagging was more reliable for MP identification in drinking water, particularly in the 6.5–50 μm range. Among the particles that were confirmed to be polymeric, PET, PE, PP, and PA were dominant. Accordingly, the contamination mainly emanates from the packaging, but could also occur during the manufacturing process. Given the direct human exposure to MPs through bottled water and their cellular toxicity, further studies are encouraged on smaller-sized MPs in drinking water.