259 individual bottles of 11 brands of bottled water purchased at 19 locations in nine countries were examined [77]. The samples were stained with Nile red (a fluorescent dye used to stain the particles) and processed through a filter with a 1.5 μm pore size. Particles larger than 100 µm were removed and analyzed by FTIR spectroscopy. The smaller fluorescent particles were counted using a software system. Blank samples were treated with the same procedure. It was found that the number of particles larger than 100 μm in bottled water ranged from 0 to 66 particles/L, the average was 10.4 particles/liter. In terms of occurrence, fragments were the most common (66%), followed by fibers (13%) and films (12%). The most abundant polymer (54%) was PP, the plastic most often used for bottles; 4% of the particles contained industrial lubricants. According to the authors, the contamination at least partly came from the packaging and/or the bottling process. Smaller particles between 6.5 and 100 µm were identified only by fluorescence without spectroscopic confirmation. Their average number was a very high 315 particles/L of bottled water (in the range of 0-10,000 particles/L). The authors believe that the smaller particles are microplastics of anthropogenic origin, although this was not confirmed by spectroscopic analyses.

Micro-Raman spectroscopy was used to identify small microplastic contamination in bottled water [78]. The authors tested water samples taken from 22 different reusable and disposable plastic bottles, 3 beverage cartons, and 9 bottles, all purchased in Germany. The samples were filtered through a filter with a pore size of 3 μm. Larger (50-500 µm) and very small (1-50 µm) microplastic fragments were found in all water samples, most of them (80%) were between 5 and 20 µm. The average number of particles was 118 ± 88 pieces/L (in the range of 28–241 particles/L) in reusable bottles, 14 ± 14 pieces/L (in the range of 2–44 particles/L) in disposable plastic bottles, 11 ± 8 pieces/L (in the range of 5–20 particles/L) in beverage cartons and surprisingly 50 ± 52 pieces/L (in the range of 4-156 particles/L) in glass bottles. Only the reusable bottles showed a statistically significant difference compared to the blank value (14 ± 13 particles/L). Most of the particles in water in reusable plastic bottles were identified as PET (84%) and PP (7%), consistent with the material used to make the bottles (PET) and caps (PP). Microplastic particles other than PET, such as PE or other polyolefins, were found in other types of bottles. The authors pointed out that plastic contamination may also come from the packaging of the bottles (e.g. foiling).

32 samples of bottled mineral waters purchased in Germany were analyzed for the microplastic particle concentration using 0.4 μm membrane filters and micro-Raman spectroscopy [79]. The average number of microplastic particles in mineral water samples was 2649 pieces/L in single-use PET bottles, 4889 particles/L in reusable PET bottles and in glass bottles, it was between 3074 particles/L and 6292 particles/L. An average of 384 microplastic particles/L (in the range of 0-1175) were found in blank samples, mainly from PP, some from PS, PE and PET. While the predominant polymer type in plastic bottles was PET, various polymers such as PE or styrene-butadiene copolymer were found in glass bottles. The authors concluded that other sources of contamination should be considered in addition to the material of the bottles. More than 95% of the microplastic particles found in plastic bottles were smaller than 5 μm, and more than 75% of the particles found in glass were smaller than 5 μm.

A debate arose in the literature regarding the article [80] published by Zuccarello et al. in Water Research, one of the most prestigious journals in the field in 2019. The authors claimed that their study was the first to investigate the reasons for microplastics entering mineral waters and to estimate the number and mass concentration of particles smaller than 10 μm. The authors extracted and analyzed the microplastic contamination of mineral water bottled in 500 ml bottles, according to a patent registered in Italy (a patent for industrial invention to the Italian Ministry of Economic Development number no. 102018000003337 of March 7 of 2018 entitled “Method for the extraction and determination of MPs in organic and inorganic matrix samples”). In addition to the fact that microplastic particles were found in all samples, their concentration, especially the number of particles (656.8 ± 632.9 μg/L or 5.42×10+7 ± 1.95×10+7 pieces/L), was very high. From this, the Estimated Daily Intake (EDI) of children and adults was also very high (1.5 and 3.3 million particles/kg body weight/day, i.e. 40.1 or 87.8 μg/kg body weight/day). It was pointed out that a larger amount of microplastic particles from poor quality bottles enters the water; moreover, that the establishment of a reference-method of analysis is essential for risk analysis of human intake. According to authors who are experienced in this field and had previously published an article [79], questionable analytical methods were used in some parts of the study [81]. Namely, the SEM-EDX analytical method used for the identification and quantification of microplastic particles is neither established nor validated, so its results [80] are highly questionable. They mention that unfortunately, the media often use such results to attract the reader’s attention. In their response [82], Zuccarello et al. presented their method for counting all extractable plastic particles and tried to defend their analytical and evaluation methods, as well as their results.

Contaminants of emerging concern (CEC) have recently been discovered in bottled waters and discussions have begun about their potential hazards to human health [35]. Akhbarizadeh et al. reviews the literature on six major groups of new contaminants found in bottled water from different countries, including microplastics (MPs), pharmaceuticals and personal care products, bisphenol-A (BPA), phthalates, alkylphenols (APs) and substances containing perfluoroalkyl and polyfluoroalkyl groups (PFAS). The data collected show that potentially toxic microplastics in the size range of 1–5 μm are the most abundant in bottled water (see Table 1 for data in pieces/L for both size ranges). In addition, PFASs, APs and BPA occur at ng/L concentration levels, while phthalates are present at μg/L levels in bottled water. The type of bottle plays an important role in the level of contamination. As expected, water in plastic bottles with plastic caps is more polluted than in glass bottles. Other contamination sources, such as materials that come into contact during cleaning, bottling and storage, are also not negligible. The authors concluded that, based on the collected data, the CEC levels – except for the MPs found in the bottled water of most countries (without any threshold) – do not pose a threat to humans. However, more accurate data on the occurrence and association of some CECs in bottled water are needed to understand their individual and synergistic effects on human health.