CHARACTERIZATION OF MICROPLASTICS IN BOTTLED DRINKING WATER AND HEAVY METALS IN PLASTIC PACKAGING USING RAMAN SPECTROSCOPY, LASER INDUCED BREAKDOWN SPECTROSCOPY (LIBS) AND PRINCIPAL COMPONENT ANALYSIS.

Abstract

Microplastics have become a notable concern in the context of plastic bottled drinking water. As plastic bottles degrade over time, they can release microscopic plastic particles into the water. This raises concerns about potential human exposure to microplastics and their associated health effects, therefore it has prompted researchers and regulatory agencies to investigate and set guidelines for the acceptable levels of microplastics in bottled drinking water to ensure consumer safety. This work delved into the characterization of microplastic particles in plastic bottled drinking water and analyzed the presence of heavy metals in plastic packaging through the utilization of two spectroscopic techniques: Raman Spectroscopy and laser-induced breakdown spectroscopy (LIBS) along with Principal component analysis (PCA). The Raman experimental parameters were: Excitation wavelength 785 nm and 532 nm; exposure time, 10s; spectra accumulation, 5; microscope objective, x100; 0.9 numerical aperture and 600 lines grating. The LIBS experimental parameters were: Excitation wavelength 1064 nm; laser power 250 mW; spectra acquisition mode, continuous; Pulse repeat frequency (PRF) 1Hz. A total of 14 different popular marque of plastic jarred drinking water from various manufacturing companies from local vendors in Narok and Nairobi counties were examined. Heavy metals were analyzed by cutting the packaging into small pieces measuring 2000µm x2000 µm and used LIBS for analysis. The water samples were filtered using Whatmann 1442-0.70 quantitative filter paper with a retention rate of 2.5 microns. We then utilized a Raman Optical Microscope BX51 to scan the filter paper and identify any plastic particles. Raman Spectroscopy and LIBS were employed to rapidly classify and identify the types of microplastics present, providing molecular and atomic information through scattered signals and plasma spectra. The analysis uncovered the presence of five distinct polymer types in the samples: Polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS) and Polyethylene terephthalate (PET). Among these polymers, polyethylene (PE) emerged as the most prevalent, appearing in 5 out of the 14 samples (35.71%). Polyethylene terephthalate (PET) followed as the second most common polymer, detected in 4 out of the 14 samples (28.57%). Polystyrene (PS) and polypropylene (PP) were each identified in 2 out of the 14 samples, while polyvinyl chloride (PVC) was found in only 1 sample. Furthermore, we calculated the C/H ratios for each polymer: PVC (0.89), PET (1.11), PP (1.17), PS (1.40) and PE (1.56). The trend observed in the C/H ratios is as follows: PE > PS > PP > PET > PVC. Furthermore, the study successfully detected and identified several heavy metals, including lead (Pb), antimony (Sb), mercury (Hg), uranium (U), manganese (Mn), zirconium (Zr), palladium (Pd), praseodymium (Pr), and thorium (Th), in the plastic packaging of the bottled water. Uranium was the most prevalent, appearing in 12 out of the 14 samples (86% prevalence), followed by mercury, which was present in 10 out of the 14 samples. Lead (Pb) was the third most prevalent, detected in 5 out of the 14 samples. The molecular spectra for polystyrene showed distinctive peaks at 999 cm⁻¹, 1028 cm⁻¹, 1601 cm⁻¹, 2899 cm⁻¹, and 3050 cm⁻¹ and a C/H ratio of 1.18. The Raman spectra of the polystyrene standard sample exhibited no significant difference while being analyzed under 785 nm (250mW) and 785 nm (500 mW). The results are supported by a 3D scatter plot which clusters 250 mW and 500 mW together and segregates 785 nm and 532 nm respectively Key Words: Microplastics, Laser Induced breakdown spectroscopy, Raman spectroscopy, Drinking water.