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A new method for counting and sizing microplastic particles in water: investigating the presence of microplastics in Iranian bottled water

2024
Paria Moshtaghizadeh, Seyed Shahram Shekarforoush, Mohammad Hadi Eskandari

Summary

Researchers developed a novel method for counting and sizing microplastic particles in bottled water using Nile Red fluorescent staining combined with direct microscopic counting. Testing Iranian bottled water brands revealed widespread microplastic contamination, with the new method providing a faster and more accessible alternative to spectroscopic identification for routine bottled water monitoring.

Abstract The ubiquity of microplastics (MPs) in various foodstuffs and beverages has raised substantial public health concerns. This study aimed to develop a novel method for counting and sizing MP particles in bottled water using Nile Red staining combined with Direct Microscopic Count (DMC). A filtration process with a 0.25 µm mixed cellulose ester (MCE) membrane filter was employed, followed by dissolving the filter with acetone to avoid background interference, and staining MPs with Nile Red. MPs were counted and measured using a fluorescent microscope, and their polymer nature was confirmed via Raman Confocal Spectroscopy. This study tested 60 plastic bottled water samples from 20 brands produced in Iran for MP contamination. The concentration of MPs varied between 0 and 608 particles per mL, with an average of 109.5 particles per mL. The number of MP particles with size < 10, 11–100, 101–200 and > 200 µm was 74.3, 34.6, 1.5 and 0.9 per mL, respectively. Afterward, by exposing particles stained with Nile Red to laser using Raman Confocal spectroscopy it was found that 94% of the particles were PET, 5.7% were PE, and only 0.3% were PP.

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