Bottled mineral water in Iranian Market
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Determination of Some Heavy Metals Contents in the bottled mineral water in Iranian Market
Abstract
Zn, Pb, Cd and Cu are four heavy metals which are commonly present in trace amounts in drinking waters. Many researches show a harmful effects by taking excess amounts of any of these metals. 17 commercial brands of bottled waters were investigated for these four ions contents using polarography method. The aim of this study was to assess the heavy metal concentration in the bottled drinking water. The levels of Pb, Cu, Cd and Zn were determined in the bottled drinking water sample. 17 different bands of bottled drinking water samples were collected from the city and were analysed using polaroghraphy. The concentration of Pb, Cu, Cd and Zn measured (in ppm) in the bottled drinking water samples ranged from 0.48 to 11.3, 0.36 to 2.56, 43.7 to 304.0, and 0.10 to 17.0, respectively. Zinc contents in the measured samples is much higher than the other elements but non of them were exceeded than the threshold limits set by the WHO health-based guideline for drinking water
Key words:
Pb, Cd, Zn, Cu, Polarography, mineral water, heavy metals
Measurements were made using linear scan anodic stripping voltammetry.
Zinc, copper, cadmium and lead concentrations were determined simultaneously with KCl–Na acetate as a supporting electrolyte by anodic stripping voltammetry (ASV).
Anodic stripping voltammogram recorded for the analysis of a synthetic sample solution containing similar mass fractions of Zn, Cd, Pb and Cu (nominally 250 ng g−1) in a pH 4.6 buffered solution with a deposition time of 60 s at −1.15V, prior to the stripping scan at 33mVs−1 from −1.15to 0.05 V.
Introduction
Water is essential for life and pure water is probably the most important resource on earth. Freshwater is scarce, and resources are unevenly distributed throughout the world, with much of the water located far from human populations. With growth, demand for water has increased dramatically, and its uses have become much more varied. Good-quality drinking water may be consumed in any desired amount without adverse effect on health. Such water is called “potable''. It is free from harmful levels of impurities such as bacteria, viruses, minerals, and organic substances. It is also aesthetically acceptable and is free of unpleasant impurities, such as objectionable taste, color, turbidity, and odor.
Nowadays, many people living in urban areas are increasingly consuming bottled water because it is associated with “naturalness” (Saad et al.,1998), because they object to unpleasant tastes and odors such as chlorine from municipal water supplies The most common problems in household water supplies may be attributed to hardness, iron, sulphides, sodium chloride, acidity, and disease-producing pathogens, such as bacteria and viruses (Tamagnini and Gonza´ lez, 1997), and because bottled water is often regarded as safer and healthier than tap water (Armas and Sutherland, 1999). In many parts of the world, there is also a common belief that natural (mineral) waters have beneficial medicinal and therapeutic effects (Warburton et al., 1992).
Bottled water consumption has been steadily growing in the world for the past 30 years. It is one of the fastest growing and the most dynamic sector of all the food and beverage industry; in spite of its excessively high price compared to tap water and the presumed access consumers have to cheap and good quality tap water. However, bottled water is not necessarily safer than tap water. Literature reveals that the levels of some water constituents in bottled waters are in violation of action levels for various parameters, especially for some toxic trace metals [1,2].
Minerals are required by human beings for nutrition, growth, sustaining body functions and well-being. Moreover, many metal ions play dual roles in the human physiology; some are essential for life, while most of them are toxic at elevated concentrations. Metal ions such as Na, K, Mg, and Ca are essential to sustain biological life. Additional metals ions such as Mn, Fe, Co, Cu, Zn, Cr, V, Se and Mo are also essential for optimal growth, development and reproduction. Drinking water is an important source for the daily intake of many of these elements ().
These metals function mostly as catalysts for enzymatic activity in human bodies but become toxic, when their concentration becomes excessive. In addition to the metals essential for human metabolism, water may contain toxic metals like Hg, Pb, Cd, Ag, Al, As and Ba sometimes called heavy metals. Epidemiological studies in recent years have indicated a strong association between the occurrence of several diseases in humans, particularly cardiovascular diseases, kidney-related disorders, neurocognitive effects and various forms of cancer and the presence of toxic trace metals [3]. These metals should be eliminated from drinking water, if possible (Edmunds and Smedley 1996).
Bottled and municipal water quality are subjected to intensive investigation in many countries world wide, in order to evaluate its suitability for human consumption. The quality of water may vary from one source to another based on several parameters such as water sources, type of water purification, storage tanks and many other factors.
The levels of heavy metals in the environment have been seriously increased during the last few decades due to human activities. Since the toxicity of the heavy metals is related to their existing species, the speciation of them is increasingly attracting more attentions [1]. There is an increasing need to determine concentration of contamination rapidly and precisely, in particular those of toxic heavy metals. Most available methods utilize expensive equipment or consist of time consuming laboratory analyses, resulting in the need for fast and in situ methods [2]. Around the world several studies have evaluated the heavy metal concentrations in bottled drinking water using polarographyia ().
In this context, the aim of this study was to survey the heavy metals content of some of the most widely distributed bottled mineral waters in the Iranian market. A total of 17 bottled mineral water samples collected from nine different Iranian provinces and were analyzed for heavy metal content in order to compare their ingredients with existing national and international standards.
Experimental
Sampling
Seventeen samples of commercial brands of bottled mineral waters were collected from those available in the major supermarkets and grocery stores (Tehran, Iran, June 2008). Six bottles of each brand, each with a different batch number and date of bottling were purchased. All samples were sold in polyethylene terephthalate (PET) bottles in two different volumes (500 and 1500 mL).
Reagents
Analytical reagent-grade (AR) or suprapure chemicals were used for the preparation of all the solutions. All aqueous solutions were prepared with deionized water that had been passed through a Milli-Q system (18 MΩ cm resistivity). Sodium hydroxide (30 %), Acetic acid 100 %, KCl and HNO3 were AR and purchased from E-Merck (Germany). Diluted solutions were prepared using HNO3 = 0.014 mol/L. Standard solutions of Zn, Cd, Pb, and Cu (1 g/l) were obtained from Acros Organics (N.V. USA). Working multi-standard solutions concentration were Zn+2=10 mg/L; Cd+2=0.1 mg/L; Pb+2=0.5 mg/L; Cu+2=2.5mg/L and prepared by diluting appropriate amounts of standard solutions with diluted HNO3 (0.014 mol/L) . KCl-Sodium acetate solution (KCl=1.5 mol/L and Sodium acetate =0.5 mol/L) was used as buffer for fixating pH at a constant value (pH 4.60) and also as a supporting electrolyte in electrochemical cell was prepared by mixing 55.9 g KCl + 25 mL NaOH + 14.2 mL CH3COOH filled up to 500 mL with high purity water adjusted to pH 4.6 ± 0.2 by diluted HNO3.
All solutions were prepared and stored in polypropylene vessels, which were cleaned prior to use by soaking in 10% HNO3 and then rinsing several times with ultra-pure water. Appropriate known volumes of the standard solutions were then introduced into the measurement cell using a solution-dispensing unit (Brand;).
Blank solutions for method testing were prepared as follows: 10 mL of diluting solution (HNO3; 0.014 mol/L) + 50 μL of 3M KCl and 1 ml of supporting buffer. The standard solutions for method ; testing were obtained by adding the adequate amounts of the above described standard solutions.
Apparatus
A Metrohm model 746 VA Trace Analyzer connected to a 747 VA Stand and a personal computer using Backup2 package was used for recording anodic stripping voltammograms in all experiments. A multi-mode mercury electrode (MME, Metrohm) comprising a hanging mercury drop electrode (HMDE) as a working electrode, an auxiliary platinum electrode and a reference electrode (double junction type (Ag/AgCl saturated with a 3.0M KCl solution)) completed the three-electrode cell. A PTFE stirring arm (comprising a cylinder with a bevelled end), in a low-volume inverted cone shaped glass cell were used. 10.0 ml of sample was placed in the measurement vessel together with 1.0 ml of a KCl-sodium acetate buffer mixture to maintain the pH at 4.6 to ensure good separation of the stripping peaks. The potential of the peak was measured to within ±0.01V. All measurements were carried out in an inert atmosphere in glass cell at room temperature about 25°C. The pH measurements were made with pH meter (692-pH/Ion meter, Metrohm, Herisau, Switzerland) with glass electrode and internal reference electrode. All measurements were carried out after the deoxygenating of the solutions with argon (analytically pure with 99.99%; Roham, Iran) for 5min and for 30s before each measurement.
Before each experiment a new hanging mercury drop electrode was prepared and a cleaning potential of +0.2V were applied for 10 s before each experiment. Measurements were then made using a deposition potential of −1.15V that was applied to the solution for 90 s with rapid stirring, before sweeping the potential from−1.15 to 0.05V with stirring discontinued, using a scan rate of 33mVs−1.
Anodic striping voltamograms (AVS) at the hanging mercury drop electrode (HMDE) were scanned using the following experimental conditions which were kept constant across all experiments using proprietary Metrohm software: Working electrode HMDE, Drop Size 4, Stirrer 2000 rpm, Measurement mode DP, Purge time 300 s, Pulse amplitude 0.05 V, Deposition potential - 1.15 V, Deposition time 90 s, Equilibration time 10 s, Start potential - 1.15 V, End potential 0.05 V, Voltage step 0.006 V, Voltage step time 0.1 s, Sweep rate 0.06 V/s, Peak potential (Zn+2) - 0.98 V, Peak potential (Cd+2) - 0.56 V, Peak potential (Pb+2) - 0.38 V, Peak potential (Cu+2) - 0.10 V. Analyte peak was determined by the proprietary software.
The comparative study for the determination of Pb2+ was done by a PerkinElmer Model 700 (Norwalk, CT, USA) atomic absorption spectrometer, equipped with a graphite furnace HGA-400, pyrocoated graphite tube with integrated platform, an autosampler AS-800, were used for the analysis; the results show no significant difference between two methods.
Heavy metals Standard and analysis
Different concentration of multi-standard solutions containing zinc, cadmium, lead, and copper were prepared by diluting the stock standard solution and analyzed to ensure that the instrument was properly calibrated for the quantitative determination of ions in bottled mineral water samples.
Calibration graph for voltammetric determination
The repeatability, accuracy and precision were all checked. Each solution was transferred into the voltammetric cell and deoxygenated with argon (analytically pure with 99.99%) for 5min and for 30s before each measurement. To study the accuracy and repeatability of the applied ASV technique, recovery experiments were carried out using the standard addition method. In order to know whether the excipients show any interference with the analysis, known amounts of the Multi-standard solutions were added to the pre-analyzed standard solution and mixtures were analyzed by the proposed HMDE method. The recovery results were calculated using the related calibration equations after five repeated experiments.
Standard addition method
A fixed volume of sample solution (10.0 ml) is spiked with known amount of the analyte. The volumes of the additions are very small (10-50 μL) if compared with the volume present in the voltammetric cell (11 mL); for this reason the volume dilution may be considered negligible, i.e. it is correct to assume that all additions are diluted to the same volume. The peak current value, relevant to each addition, is plotted on the y-axis, while the x-axis is graduated in terms of the amount of analyte added. The regression line is calculated and extrapolated back to the point on the x-axis at which y = 0. It is clear that this negative intercept on the x-axis corresponds to the amount of the analyte in the test sample. It is important to highlight that such a method shows a particular advantage: the regression analytical calibration function does not present matrix effects.
Procedure for the analysis of BMW
Once the procedures for the voltammetric determination of Zn(II), Cd (II), Pb(II), and Cu(II) had been set up, the method was transferred to commercial BMW samples. Representive polarogram for Zn, Cd, Pb and Cu The experimental results are reported in Table I.
Results and Discussion
The typical stripping voltammograms obtained from the analysis of a synthetic solution containing similar mass fractions of Zn, Cd, Pb and Cu (nominally 250 ng g−1) and commercial samples of BMW are shown in Fig. 1. The linear calibration curves were obtained by plotting mAmp vs. concentration of standard solutions for polarography. The standard deviations of metal concentrations were calculated in accordance with the pooled standard deviations. Results revealed that the concentration of heavy metals are in allowed ranges (according to ).
Concentration of Cd (II), Cu (II), Pb (II), and Zn (II) in commercial BMW
A multi-element ASV at a scan range between −1 and 0V for the determination of 100 μgL−1 Zn, Cd, Pb and Cu ions deposited at the HMDE and using KCl-sodium acetate as supporting electrode. As it can be seen, good peak shapes, at −0.9, −0.55, −0.4 and −0.2V for Zn, Cd, Pb and Cu, respectively were obtained without overlapping. The obtained ASV curve indicated the possibility of using the ASV for the simultaneous determination of these metals in a single ASV run. As expected, the stripping currents of Zn, Cd, Pb, and Cu increased following the addition of increasing volumes of the standards (Fig. 1a). Moreover, in these figures it can be observed that the peak current variations between standards (metal concentrations ranging from 10 to 90 μgL−1) are proportional, showing its feasibility for the calibration.
Various samples of commercial brand of BMW were analyzed; Table 1 shows the range of Zn, Cd, Pb, and Cu, concentrations determined by ASV in the studied samples. Fig. 1b provides evidence that cadmium is present in very low amounts, Abali mineral water presented the highest mean concentration of Cd (0.14 ), Parsi the lowest (0.03 ). Lead was also present in low concentrations, Dalahoo showed the highest mean value (5.35 ), Dasani the lowest (0.70 ). Sinsinat also presented the highest average amounts of zinc (989.87 ) and Nava the lowest (294.2). Dalahoo had also the highest mean content of copper (14.61 ); whereas Damash showed the lowest levels of this element (4.83 ).
These data evidenced that heavy metals amount; particularly cadmium and lead, in different brands of BMW are low and close to ones found in literature for BMW. Moreover lead content is lower than the legal limit (100 lg kg−1) in the entire studied sample. Copper concentrations found in this work were higher to those published for BMW or leagal limits (), whereas the levels of zinc are similar to those determined in BMW. Particularly the obtained results provide evidence that BMW especially Dalahoo is a good source of copper (>14.61 μg kg −1), whereas Sinsinat BMW are a good source of zinc (989.87 μg kg −1).
The proposed method based on anodic stripping voltammetric analysis provides a rapid, sensitive and reliable procedure to detect simultaneously trace levels of Zn, Cd, Pb, and Cu, in BMW. Moreover this technique do not request a sample preparation based on a pre-concentration step or the complete destruction of the organic matrix that often cause a severe loss of trace metals. Nevertheless the applied method represent an attractive alternative to different spectroscopic techniques for trace metal analysis in beverage matrices.
The obtained results compare well with those reported for the determination of heavy metals using SPEs [22,29]. Considering that the limit values recommended by WHO and EPA are 50 μgL−1 for Pb and 10 μgL−1 for Cd [2] in seawater, the ASV can be seen as a good choice to take into account for metal monitoring in BMW.
Wide working ranges as well as multi-element determination would allow the use of this technique for all types of BMW. This is an advantage compared to the conventional GFAAS. On the other hand, ICP-MS showing also wide linear ranges is not appropriated when dealing with waters of high salinity.
It has been demonstrated that polarography or graphite furnace atomic absorption spectrometry provide a reliable method for trace determination of heavy metals in several categories of natural waters. The main benefits of the polarography method were: simplicity, low cost, enhancement of sensitivity, and rapid analysis time in bottled mineral waters. Although it has been revealed that flame atomic absorption is not sensitive enough to measure the trace elements in such samples.
Different techniques and methods have been developed for heavy metals determination. Using electrothermal atomic absorption spectrometry (ETAAS), Neutron activation techniques, atomic emission spectrometry and X-ray fluorescence (XRF) (Stosnach, 2006) are very expensive and do not offer sufficient sensitivity for accurate determination of trace elements. Electrochemical stripping analysis has long been recognized as a powerful technique for trace metals owing to its remarkable sensitivity, relatively inexpensive instrumentation, and ability for multi-element determination and capable of determining elements accurately at trace and ultra trace levels ().
Great attention must be addressed to everything directly concerning the human healthy, especially diet and nutrition. Consumption of mineral waters has been increased enormously through few decades. One of likely pollutions of drinking waters are heavy metals depending on concentration have pharmacological and toxicological effects in human body. As many researches revealed, excessive intake of heavy metals may lead to a number of adverse effects, e.g. neurological damage or even cancer ().
Robles et al. (1999) indicated a slight variation in physicochemical parameters among different bottled water brands in Mexico City. Abdulrahman et al. (1997) investigated the chemical composition of bottled water in Saudi Arabia such as TDS, Ca, Na, K, NO3, Cl, and SO4 , and were within the standards set by the Saudi Arabia and WHO. In Jordan, no direct investigations reported concerning the bottled water quality, however, several studies on bacteriological and chemical composition of municipal and groundwater quality were carried out in Jordan (Jiries, 1998; Tarawneh et al., 2000; Salameh et al., 2002; Jiries et al., 2004; Ziadat, 2005).
The mineral water industry has been very successful in marketing mineral waters as ‘better drinking water.' Up to now, there has been much debate about the health-giving effects of mineral water. Apart from the obvious function of providing liquid to the body, there are no scientific studies that actually show a significant beneficial effect of mineral water on the health. While mineral water clearly contains minerals that are, in principle, beneficial for the body, the ability of the body to absorb them from mineral water is not exactly proven. But since natural water is free of any calories, sugar or artificial ingredients, it is certainly better than a sweetened, flavored soft drink.
All these factors resulted in public distrust of tap water. As a result, in Turkey (population about 70 million) bottled water has become a lucrative market with a US$500 million retail value (C- elik, 2003). This is a proof that the bottled water industry has done an outstanding job in marketing its product as a safe alternative to tap water, even though the price of bottled water is 250–600 times higher than that of tap water.
CONCLUSIONS
Voltammetry is certainly a valid analytical technique, very simple and suitable for metal determinations in multi-component complex matrices. In fact, it shows good precision, accuracy and selectivity, and allows the simultaneous determination of metals. In addition, it shows a satisfactory high sensitivity, thus allowing very low limits of detection. Moreover, such a technique may be a good alternative to spectroscopy, which, in the case of determination of metals in complex matrices, needs expensive equipment or time consuming sample preparation. Finally, although legislative and environmental aspects are beyond the aim of this study, a comment may be made relevant to the metal content determined in beverage present on the market (Table 5). Even if a comparison with the present legal limits is impossible, because European Union legislation concerns only cereals and legumes,8 without considering the relevant meals, the metal concentrations seem too high,1,4,8 especially in the case of Cr(VI), Pb(II), Sn(II) and Sb(III).
Acknowlegments
References
(1) He Xu, Liping Zeng, Dekun Huang, Yuezhong Xian, Litong Jin, A Nafion-coated bismuth film electrode for the determination of heavy metals in vegetable using differential pulse anodic stripping voltammetry: An alternative to mercury-based electrodes, Food Chemistry 109 (2008) 834–839.
(2) Serife Tokalioˇglu, ¸Senol Kartal_, Latif Elçi, Determination of heavy metals and their speciation in lake sediments by flame atomic absorption spectrometry after a four-stage sequential extraction procedure, Department of Chemistry, Faculty of Arts and Sciences, Erciyes University, TR-38039, Kayseri, TurkeyAnalytica Chimica Acta 413 (2000) 33–40.
(3) Francis, W. et. Al. Determination of lead mean residence time in the atmosphere, J. Envir. Sci. teach, 4,1970, pp: 586-590 .
(4) Ellenhorn, M. J. and Barceloux, G. Medical toxicology diagnosis and treatment of human poisoning, 1988: 1036-1041.
(5) Nowak A, Nowak MV.Flouride concentration of bottled and processed water. Lowa Dent. 1989; 74(4): 280-282.
(6) Dadfarnia, Sh., Salmanzadeh A. M., Haji Shabani, A. M., A novel separation/preconcentration system based on solidification of floating organic drop microextraction for determination of lead by graphite furnace atomic absorption spectrometry, Analytica Chimica Acta 623(2008) 163–167.
Table 1. Concentration of Zn, Cu, Cd and Pb in 17 different bottled waters in ppm.
Pb
Cd
Cu
Zn
Brand Name
1.16
0.14
8.1
520.1
Abali
2.38
0.017
6.01
501.88
Anahita
1.19
0.07
9.87
389.02
Bisheh
5.35
0.04
14.61
462.9
Dalahoo
1.47
0.06
8
416.16
Damash
0.8
0.1
5.63
406.21
Damavand
0.701
0.04
5
500.12
Dasani
1.72
0.13
5.41
479.11
Exir
1.08
0.031
7.41
322.78
Jerino
0.725
0.04
5.67
664.24
Koohrang
0.93
0.12
6.18
294.2
Nava
0.91
0.03
4.99
316.12
Parsi
1.33
0.047
5.17
567.88
polor
1.77
0.085
11.85
989.87
Sinsinat
1.23
0.057
7.61
698.32
Solar
1.18
0.043
10.15
490.02
Tulip
1.05
0.077
5.72
313.76
Vata
