Bottled water consumption has increased significantly in recent decades. Eighty percent of bottled water is sold in plastic containers usually made from polyethylene terephthalate (PET). Trace leaching of phthalate esters (PEs) from these bottles into the water and their effects on human health has become a serious concern. In this study, the effects of freezing on the release of PEs from PET bottles have been investigated. Four common PEs were determined in bottled water samples before and after freezing–remelting by a dispersive liquid–liquid micro-extraction method and gas chromatography–mass spectrometry (GC/MS) analysis. PE levels after freezing–remelting of samples were significantly lower than before (mean ± SD = 0.71 ± 0.28 and 0.33 ± 0.003 ppb, respectively). Electrical conductivity (EC) also decreased after freezing–remelting of the water (mean ± SD = 260.2 ± 80.6 and 130.6 ± 17.4 μs/cm, respectively). Significant correlation has been detected between reduction in water EC and elimination of PEs from water. Dissolved minerals and contaminants in water concentrate and conglomerate in the center of the ice during the freezing process and form white sediments mainly of calcium bicarbonate after remelting of the water. It seems that calcium bicarbonate effectively adsorbs PEs and traps them in its structures. These sediments do not have significant gastrointestinal absorption and cannot pose health consequences. The freezing–remelting process could be introduced as an effective procedure for water treatment.

INTRODUCTION

There has been a consistent rise in bottled water consumption over the last three decades worldwide due to rising concerns over tap water quality and safety (Al-Saleh et al. 2011). It is generally supposed that mineral water has better quality with greater convenience from a nutritional point of view than tap water. Lack of accessible safe sources for drinking water in many countries, the unpleasant taste of tap water (due to disinfection procedures and the release of materials from network pipelines) and efficient marketing and advertising strategies by producers of bottled water (Leivadara et al. 2008) have caused a growing demand for bottled water, and its consumption in some countries has reached 155 L per year per capita (Potera 2002; Thurman et al. 2002; Al-Saleh et al. 2011).

Glass and plastic are two common types of packaging materials for bottled water. Lower production costs in comparison with glass and chemical properties such as strength, transparency, light weight, and easy recycling have made plastic the preferred packaging material for this purpose (Amiridou & Voutsa 2011). Currently, 80% of mineral water is sold in plastic containers, normally polyethylene terephthalate (PET), while glass bottles are primarily destined for restaurants or biological feeding (Pinto & Reali 2009).

PET is a high molecular weight polymer and is synthesized by chemical reaction between ethylene glycol and either terephthalic acid or its esters under vacuum and high-temperature conditions (Montuori et al. 2008).

Moreover, there are growing concerns about different types of pollution in bottled water including possible migration of chemicals from the plastic matrix during long storage periods and under unsuitable conditions (vigorous shaking, high temperatures, freezing, solar radiation, etc.) (Ebrahimi et al. 2016).

The chemical bonds between phthalate esters (PEs) and polymer chains in the plastic are very weak. This causes significant leaching of PEs from the plastic matrix into the drinking water in PET bottles (Heudorf et al. 2007; Sathyanarayana et al. 2008; Thompson et al. 2009). Significant levels of different PEs have been detected in almost all brands of bottled waters in many countries and storage conditions show a significant effect on the concentrations of the examined compounds (Evandri et al. 2000; Dąrowska et al. 2003; Westerhoff et al. 2008).

Recently, increasing social concern has been aroused about adverse health effects caused by phthalates. These compounds are suspected to be endocrine-disrupting chemicals and to exhibit carcinogenic action (Latini et al. 2006; Heudorf et al. 2007). Due to their potential risks for human health and the environment, several phthalates have been listed as priority substances by many national and international regulatory organizations (Serôdio & Nogueira 2006).

Due to a drought crisis in Iran, use of bottled water has been increasing significantly during the last decade, and in some areas of country, bottled water is the primary source for safe drinking water supply. Moreover, based on an old bad habit, the Iranian general population prefers to drink very cold water and therefore they put water bottles in the refrigerator or freezer for cooling or freezing of the water. Many shops and supermarkets sell bottled drinking water in frozen form to attract customers. Many people use PET bottles as drinking water containers for several months and freeze water in these containers several times. There are no documents about the effects of freezing on the amount and pattern of phthalate released from PET bottles into drinking water. Therefore, in the present study we investigated this issue and possible related health risks that it poses to the Iranian general population.

MATERIALS AND METHODS

Water sampling

The survey was conducted in the fall and winter of 2015 in Iran and a variety of commercial bottled water samples were collected. These samples included different water types, such as natural mineral water, light water (low mineralization water), carbonated water, and oxygenated water from miscellaneous commercial brands. The level of mineralization was available on bottle labels.

Three water bottles of each of 15 commercial brands (Brand ID#) were purchased randomly from different shops in the various regions of Isfahan, Iran, and finally a total of 45 water samples were collected. All bottles were made of PET, although some were colorless and others had a blue tint. All samples were labeled and stored under the same conditions (at 4 °C in darkness) until analysis.

Materials

Analytical standards of dimethyl phthalate (DMP), di n-butyl phthalate (DnBP), bis(2-ethylhexyl) phthalate (DEHP), and benzyl butyl phthalate (BBP) were purchased from Sigma Aldrich (Sigma, St Louis, USA, catalog numbers: 41320, 53008, 36735, 36927, respectively).

The GC grade acetonitrile, carbon tetrachloride, methanol, and ultrapure water were purchased from Merck (Darmstadt, Germany).

Sample preparation

Determinations of PEs in bottled waters were conducted in two phases. Initially, 5 ml of each water sample was subjected to analyses and the rest was placed in the freezer for 48 hours for freezing the samples. After that, the frozen water samples were remelted in room temperature and 5 ml of each (without sediments) was subjected to analyses in the second phase.

Stock and working standard preparation

A mixed stock standard solution of 1,000 ppm from all PEs was prepared in methanol. The working standard solutions of 50, 10, 5, 1 and 0.1 ppb were prepared in ultrapure water. The stock and working standard solutions were stored at 4 °C.

Extraction of PEs

PEs were extracted from the water samples by a dispersive liquid–liquid extraction (DLLME) method according to previous work (Farahani et al. 2007) with some modifications. For this purpose, an aliquot of 5 mL of each sample was placed in a 10 mL glass test tube with a conical bottom. A mixture of acetonitrile (0.75 mL) as dispersive solvent and carbon tetrachloride (50 μL) as extraction solvent was prepared and injected rapidly into the sample solution using a 1 mL Hamilton syringe. After that, a cloudy solution (sample + acetonitrile/CCl4) was formed and the analytes were extracted into the fine CCl4 droplets. After centrifugation for 5 min at 4,500 rpm, the extraction solvent was sedimented in the bottom of the conical test tube (about 50 μL). Two microlitres of sedimented phase was removed using a 10 μL gas chromatography–mass spectrometry (GC/MS) microsyringe and injected into the GC system for analysis.

Analytical methods

The extracts were analyzed by gas chromatography/mass spectrophotometry using a quadruple Agilent GC-MSD (Agilent Technologies, Palo Alto, CA, USA) model 7890A coupled to a mass selective detector model 5975C inert, operated in the electron-impact mode at 70 eV. Data recording and instrument control were performed by the MSD ChemStation software (G1701CA; Version C.00.00; Agilent Technologies). Helium (99.999%) was employed as carrier gas at the flow rate of 1 mL/min. The analytes were separated using a capillary column (HP-5, 30 m, 0.25 mm id, 0.25 μm coating thickness). The gas chromatographic conditions were as follows: injection volume 2 μL; split ratio 1/10; injector temperature 280 °C. The oven temperature was programmed from 100 °C (holding for 2 min), to 210 °C at 10 °C/min then to 250 °C at 5 °C/min and finally to 280 °C at 30 °C/min keeping the final temperature for 4 min. The MS transfer line and ion source were kept at 280 and 230 °C, respectively. The MS was tuned to selective ion monitoring (SIM) mode with m/z 69, 219, and 502 for the electron impact (EI) corresponding to perfluorotetra butyl amine (PFTBA). Data acquisition was carried out in the full-scan mode (m/z = 149) and results were qualified by comparison with the NIST and Wiley's library spectral data bank (G1035B; Rev D.02.00; Agilent Technologies).

Determination of water electrical conductivity

Water conductivity was determined by a water conductivity meter (sensION5, HACK, USA) according its manufacturer's instructions and reported as μs/cm.

Method validation

The validation was done according to International Conference of Harmonization (ICH) recommendations for linearity, range, accuracy and precision, limit of detection (LOD), limit of quantification (LOQ) and relative recovery (Ermer & Miller 2006).

Statistical analysis

Experiments were repeated at least three times and the results are expressed as mean ± SD. Data were analyzed by Student t-test and analysis of variance (ANOVA) with significance level defined as p < 0.05 using GraphPad-Prism 5 software (GraphPad-Prism Software Inc., San Diego, USA).

RESULTS

Validation of the method

This is a highly sensitive, selective and accurate analytical method for phthalate detection and determination in aqueous solutions. A good resolution was achieved for phthalate separation in this method. The four PEs left the column at 11.4, 14.3, 15.4, and 20.6 min as shown in Figure 1.
Figure 1

A typical chromatogram of PEs obtained by DLLME-GC/MS under SIM data acquisition mode (m/z: 149).

Figure 1

A typical chromatogram of PEs obtained by DLLME-GC/MS under SIM data acquisition mode (m/z: 149).

Quantification was done using the external calibration method showing linear correlations with R2 > 0.98 for all the target analytes from the range of 1–1,000 ppb. Other method validation parameters are presented in Table 1.

Table 1

Method validation parameters for determination of PEs by DLLME extraction and GC/MS analysis

IndexR2LOD (ppb)LOQ (ppb)
PEs DMP DEHP DnBP BBP DMP DEHP DnBP BBP DMP DEHP DnBP BBP 
Value 0.99 0.99 0.99 0.98 0.03 0.02 0.04 0.05 0.11 0.09 0.13 0.17 
Index RSD% Recovery % 
Within days Between days     
PEs DMP DEHP DnBP BBP DMP DEHP DnBP BBP DMP DEHP DnBP BBP 
Value 6.3 6.8 4.5 7.2 7.6 6.6 6.5 9.7 96.1 88.7 91.2 87.6 
IndexR2LOD (ppb)LOQ (ppb)
PEs DMP DEHP DnBP BBP DMP DEHP DnBP BBP DMP DEHP DnBP BBP 
Value 0.99 0.99 0.99 0.98 0.03 0.02 0.04 0.05 0.11 0.09 0.13 0.17 
Index RSD% Recovery % 
Within days Between days     
PEs DMP DEHP DnBP BBP DMP DEHP DnBP BBP DMP DEHP DnBP BBP 
Value 6.3 6.8 4.5 7.2 7.6 6.6 6.5 9.7 96.1 88.7 91.2 87.6 

Determination of PE levels

DMP were not detected in any water sample but various amounts of other PEs were detected in almost all water samples. Type and concentration of PEs were different by water brands, indicated that producers use different chemical formulae for PET bottle production. Mean concentrations of DEHP, DnBP and BBP in water samples before freezing were 1.4 ± 0.45, 1.21 ± 0.32 and 0.43 ± 0.07 ppb, respectively. After the freezing–remelting process, mean PE concentrations decreased to 0.5 ± 0.1, 0.3± 0.03 and 0.11 ± 0.02 for DEHP, DnBP and BBP, respectively (full details are presented in Table 2).

Table 2

Concentration (ppb) of PEs found in bottled drinking water of different brands before and after freezing–melting

 DEHP
DnBP
BBP
Brand IDBeforeAfterBeforeAfterBeforeAfter
#1 2.18 ± 0.98 0.63 ± 0.12 0.91 ± 0.11 0.19 ± 0.02 0.23 ± 0.01 ND 
#2 2.49 ± 0.56 0.31 ± 0.09 1.04 ± 0.18 0.31 ± 0.06 0.57 ± 0.01 ND 
#3 2.50 ± 0.66 0.99 ± 0.12 2.08 ± 0.25 0.97 ± 0.09 2.12 ± 0.31 0.85 ± 0.11 
#4 1.56 ± 0.47 0.82 ± 0.13 1.59 ± 0.11 0.41 ± 0.02 0.93 ± 0.14 0.19 ± 0.05 
#5 1.89 ± 0.63 1.03 ± 0.22 1.40 ± 0.21 0.81 ± 0.06 0.31 ± 0.01 ND 
#6 0.65 ± 0.21 ND 0.70 ± 0.18 ND ND ND 
#7 1.65 ± 0.56 0.41 ± 0.08 1.22 ± 0.19 0.61 ± 0.04 0.24 ± 0.01 ND 
#8 1.24 ± 0.36 0.21 ± 0.19 1.30 ± 0.65 0.51 ± 0.09 ND ND 
#9 0.61 ± 0.25 ND 1.50 ± 0.32 0.41 ± 0.05 0.18 ± 0.01 ND 
#10 0.71 ± 0.22 ND 0.67 ± 0.15 ND 0.27 ± 0.02 ND 
#11 2.24 ± 1.02 1.61 ± 0.51 0.83 ± 0.12 ND 1.14 ± 0.32 0.617 ± 0.12 
#12 0.12 ± 0.01 ND 1.33 ± 0.93 0.79 ± 0.06 0.15 ± 0.06 ND 
#13 2.90 ± 0.91 1.51 ± 0.14 0.55 ± 0.12 ND ND ND 
#14 0.11 ± 0.01 ND 1.55 ± 0.35 0.31 ± 0.03 ND ND 
#15 0.21 ± 0.01 ND 1.59 ± 0.94 0.41 ± 0.01 0.35 ± 0.09 ND 
 DEHP
DnBP
BBP
Brand IDBeforeAfterBeforeAfterBeforeAfter
#1 2.18 ± 0.98 0.63 ± 0.12 0.91 ± 0.11 0.19 ± 0.02 0.23 ± 0.01 ND 
#2 2.49 ± 0.56 0.31 ± 0.09 1.04 ± 0.18 0.31 ± 0.06 0.57 ± 0.01 ND 
#3 2.50 ± 0.66 0.99 ± 0.12 2.08 ± 0.25 0.97 ± 0.09 2.12 ± 0.31 0.85 ± 0.11 
#4 1.56 ± 0.47 0.82 ± 0.13 1.59 ± 0.11 0.41 ± 0.02 0.93 ± 0.14 0.19 ± 0.05 
#5 1.89 ± 0.63 1.03 ± 0.22 1.40 ± 0.21 0.81 ± 0.06 0.31 ± 0.01 ND 
#6 0.65 ± 0.21 ND 0.70 ± 0.18 ND ND ND 
#7 1.65 ± 0.56 0.41 ± 0.08 1.22 ± 0.19 0.61 ± 0.04 0.24 ± 0.01 ND 
#8 1.24 ± 0.36 0.21 ± 0.19 1.30 ± 0.65 0.51 ± 0.09 ND ND 
#9 0.61 ± 0.25 ND 1.50 ± 0.32 0.41 ± 0.05 0.18 ± 0.01 ND 
#10 0.71 ± 0.22 ND 0.67 ± 0.15 ND 0.27 ± 0.02 ND 
#11 2.24 ± 1.02 1.61 ± 0.51 0.83 ± 0.12 ND 1.14 ± 0.32 0.617 ± 0.12 
#12 0.12 ± 0.01 ND 1.33 ± 0.93 0.79 ± 0.06 0.15 ± 0.06 ND 
#13 2.90 ± 0.91 1.51 ± 0.14 0.55 ± 0.12 ND ND ND 
#14 0.11 ± 0.01 ND 1.55 ± 0.35 0.31 ± 0.03 ND ND 
#15 0.21 ± 0.01 ND 1.59 ± 0.94 0.41 ± 0.01 0.35 ± 0.09 ND 

Data are presented as mean ± SD from three independent experiments.

Electrical conductivity (EC) as an indicator for water hardness was measured before and after freezing–melting and the results are presented in Table 3. The hardness of the bottled waters varied from 124 to 402 μs/cm before freezing and 102 to 156 μs/cm after freezing–melting. On average, the freezing–melting process reduced water EC by 44.8%. Linear correlation showed a significant relation between reduction in water EC and elimination of PEs from water (Figure 2).
Table 3

Total PE levels (TPEsL) levels found in bottled drinking water of different brands and EC before and after freezing–melting

 TPEsL
EC
Brand IDBefore (ppb)After (ppb)Efficiency of elimination (%)Before (μS/cm)After (μS/cm)Efficiency of reduction (%)
#1 1.1 ± 0.36 0.2 ± 0.04 75.3 291 155 46.7 
#2 1.3 ± 0.25 0.2 ± 0.05 84.8 265 142 46.4 
#3 2.2 ± 0.40 0.9 ± 0.1 58.0 174 132 24.1 
#4 1.3 ± 0.24 0.4 ± 0.06 65.1 202 127 37.1 
#5 1.2 ± 0.28 0.6 ± 0.09 48.8 184 141 23.3 
#6 0.4 ± 0.13 0.0 ± 0.0 100 402 123 69.4 
#7 1.0 ± 0.25 0.3 ± 0.04 67.2 245 155 36.7 
#8 0.8 ± 0.50 0.2 ± 0.09 71.6 124 102 17.7 
#9 0.7 ± 0.19 0.1 ± 0.01 82.0 310 124 60 
#10 0.5 ± 0.13 0.0 ± 0.0 100 350 102 70.8 
#11 1.4 ± 0.48 0.7 ± 0.21 47.1 195 122 37.4 
#12 0.5 ± 0.33 0.2 ± 0.02 50.6 241 156 35.2 
#13 1.1 ± 0.34 0.5 ± 0.04 56.2 215 140 34.8 
#14 0.5 ± 0.12 0.1 ± 0.01 81.3 365 124 66 
#15 0.7 ± 0.34 0.1 ± 0.01 80.9 340 112 67 
 TPEsL
EC
Brand IDBefore (ppb)After (ppb)Efficiency of elimination (%)Before (μS/cm)After (μS/cm)Efficiency of reduction (%)
#1 1.1 ± 0.36 0.2 ± 0.04 75.3 291 155 46.7 
#2 1.3 ± 0.25 0.2 ± 0.05 84.8 265 142 46.4 
#3 2.2 ± 0.40 0.9 ± 0.1 58.0 174 132 24.1 
#4 1.3 ± 0.24 0.4 ± 0.06 65.1 202 127 37.1 
#5 1.2 ± 0.28 0.6 ± 0.09 48.8 184 141 23.3 
#6 0.4 ± 0.13 0.0 ± 0.0 100 402 123 69.4 
#7 1.0 ± 0.25 0.3 ± 0.04 67.2 245 155 36.7 
#8 0.8 ± 0.50 0.2 ± 0.09 71.6 124 102 17.7 
#9 0.7 ± 0.19 0.1 ± 0.01 82.0 310 124 60 
#10 0.5 ± 0.13 0.0 ± 0.0 100 350 102 70.8 
#11 1.4 ± 0.48 0.7 ± 0.21 47.1 195 122 37.4 
#12 0.5 ± 0.33 0.2 ± 0.02 50.6 241 156 35.2 
#13 1.1 ± 0.34 0.5 ± 0.04 56.2 215 140 34.8 
#14 0.5 ± 0.12 0.1 ± 0.01 81.3 365 124 66 
#15 0.7 ± 0.34 0.1 ± 0.01 80.9 340 112 67 

Data are presented as mean ± SD from three independent experiments.

Figure 2

Significant correlation between water hardness reduction efficiency and TPEsL elimination from drinking water due to freezing–remelting of water (p < 0.001).

Figure 2

Significant correlation between water hardness reduction efficiency and TPEsL elimination from drinking water due to freezing–remelting of water (p < 0.001).

DISCUSSION

PEs are mainly used as plasticizers in the production of plastic products including water bottles. These esters do not covalently bond to polymer chains in the structure of the plastics and are released under various physical and chemical conditions (Heudorf et al. 2007; Sathyanarayana et al. 2008; Thompson et al. 2009).

Previous studies have shown that time of storage, exposure to sunlight, temperature and type of packed media have direct and significant influences on phthalate release levels (Cirillo et al. 2013; Bach et al. 2014). Freezing of water in PET bottles is an emerging condition in Iran and the influence of freezing on phthalate release has not been the subject of any study. The results of the present study surprisingly showed that PE levels decreased in bottled water after freezing and remelting. Several reasons are proposed for this strange phenomenon, including surface interactions of the plastic matrix. Repeating of the experiments in glass bottles showed similar results (data are not shown) and indicated that reactions in the water during freezing lead to elimination of PEs. A major change in the water before and after freezing is the formation of white particles in the water after freezing and remelting. The freezing process starts from the outside of the bottle, so the center of the bottle is the last part to freeze. As the water in the bottle freezes, the dissolved minerals and pollutants are pushed to the center of the bottle and trapped there. Near the end of the freezing, when not much water remains in the center of bottle, the minerals become very concentrated and finally conglomerate to form white particles. These particles are precipitated after the ice melts (Symons 2011).

Dissolved minerals in drinking water, which is generally referred as water hardness, include several anions and cations added to the water when the water percolates through deposits of limestone and chalk, which are largely made up of calcium and magnesium carbonates (Rubenowitz-Lundin & Hiscock 2013), so it is very probable that the white precipitates in the melted frozen water contain significant levels of calcium and magnesium carbonates.

Several studies have shown that carbonate particles are a suitable absorbent for organic compounds in water. Bob & Walker (2001) used calcium carbonate particles for elimination of natural organic matter from the water and the results showed that calcium carbonate enhances natural organic matter removal during drinking water treatment. A study by Walker et al. (2005) showed that dolomitic sorbents effectively adsorb reactive dyes in aqueous solution. External mass transfer and intra-particle diffusion are two main mechanisms for this effective removal. The efficiency of calcium carbonate for the removal of some other organic compounds such as levothyroxine (Singh et al. 2000) and polyoxyethylated nonylphenol have been demonstrated in other studies (Kuno & Abe 1961).

PE plasticizers that release from PET bottles into drinking water are water-dissolving compounds. During the freezing process, they are concentrated in the center of the bottle where conglomeration of calcium carbonate is ongoing. It seems that calcium carbonate effectively adsorbs PEs and traps them in its forming structures. The result of this process is the significant elimination of plasticizers from water. As has been pointed out in the Results section, elimination has a direct relation to water hardness, and its efficacy reaches about 100% for lower concentrations of PEs in drinking water. These conglomerated calcium carbonates, after precipitation in bottles and human consumption, show no significant gastrointestinal absorption (Hanzlik et al. 2005) and consumption of bottled waters containing conglomerated calcium carbonates do not pose health effects related to PE toxicity. In other words, the freezing–melting process could be introduced as an effective procedure for the removal of PEs from bottled water.

CONCLUSION

This is the first report about water treatment by the freezing–melting process. Our findings reveal that this process could efficiently eliminate PEs from bottled drinking water. The consumer can simply put the water bottle in the freezer before consumption and after remelting drink safer water. The exact calculation of elimination recovery and optimization needs further studies. It is suggested that this process could effectively eliminate other organic and inorganic contaminants from drinking water.

ACKNOWLEDGEMENTS

This study was supported by a grant from the Environment Research Center, Research Institute for Primordial Prevention of Non-communicable Disease, Isfahan University of Medical Sciences, Isfahan, Iran (grant ID:294053).

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