Measurement of Radon-222 and Lead-210 in Bottled Spring Water Timothy A. DeVol, John P. Clements and Lara D. Hughes, Environmental Engineering & Science Department, Clemson University Radon-222 and 210 Pb concentrations were measured in bottled mountain spring water. Six bottled spring water samples, from three different companies in the southeast, were analyzed using standard and published methods to determine the 222 Rn and 210 Pb concentrations. Radon-222 was measured with a mineral-oil based liquid scintillation cocktail method, while the 210 Pb, a long lived decay product of 222 Rn, was concentrated with a lead-selective resin and quantified by liquid scintillation. The 222 Rn concentration measured and decay corrected to the time of bottling ranged from 130 to 3,140 pci/l (4,800 to 116,600 Bq/m 3 ). The measured 210 Pb concentration in the samples ranged from 0.5 to 3.0 pci/l (19 to 110 Bq/m 3 ). Assuming all the 210 Pb is attributed to the 222 Rn at the time of bottling, the 222 Rn concentration ranged from 1850 to 6,420 pci/l (68,450 to 237,540 Bq/m 3 ). The difference between the measured 222 Rn concentration and the concentration calculated from 210 Pb can be attributed to several factors. The 210 Pb concentration in several of these samples would result in a higher risk of cancer than would be acceptable for a municipal drinking water. Introduction Consumers drink bottled water either because they dislike the taste of tap water or because they believe that bottled water is of superior quality and therefore healthier (Opel, 1999; Pip, 2000). The image of bottled spring water has become increasingly associated with the picture of pristine clear springs originating from an untouched mountain range. This is the result of the advertising of a 4 billion dollar a year industry. Consumers are willing to pay between 240 to 10,000 times more for bottled water than for tap water (Opel, 1999; NRDC, 2003). However, many consumers are unaware how the quality of bottled water compares with their local tap water. Natural waters originating from springs or wells may contain natural radionuclides, mainly from the uranium decay series. Concentrations may vary over a wide range and depend on the bedrock in which the aquifer is located as well the water parameters (ph, Eh, alkalinity) (Hess et al., 1985; Kralik et al., 2003; McCurdy and Mellor, 1981; Skwarzec et al., 2003). There exists a number of spring water companies located in the Appalachian Mountain range near the state border between North and South Carolina, USA, claiming the superior purity of groundwater filtered by several hundred feet of granitic bedrock (Bottled Water Web, 2003; Opel 1999). The main uraniferous geologic formations consist of phosphates and granites (USEPA, 2000a; Skwarzec et al., 2003), which according to the U.S. EPA NIRS survey results in a mean concentration of 222 Rn in groundwater of 450 pci/l to 2000 pci/l, Figure 1.
Figure 1. Radon occurrences of groundwater in the United States (USEPA, 1985). Source: EPA web-site: http://www.epa.gov/safewater/radon/natmap.html Background Radon solubility is highly temperature and pressure dependent. Its solubility in water rapidly decreases as temperature increases in the 10-30ºC range. The volatility of radon is generally high compared to its water solubility, so when exposed to air, radon easily escapes and does not stay in the water (U.S. EPA, 1999a). This is one reason why there is generally more concern with radon in air, than in water. Naturally occurring radioactive material in groundwater mainly comes from the three natural decay chains. In groundwater the major members of the uranium series that are of concern for human health are 238 U and 234 U, 226 Ra, 222 Rn and 210 Pb (Milvy and Cothern, 1991; NCRP, 1996). Radium-228 is a member of the 232 Th natural decay chain and may be of concern as a drinking water contaminant, its short half-life (t 1/2 = 5.7 yr), however, limits its accumulation and unsupported transport in groundwater (Michel, 1991; Focazio et al., 2001). Natural uranium and its decay chain members are present in concentrated amounts within granite, metamorphic rocks, lignites, monazite sands and phosphate deposits, as well as within the uranium-rich materials such as uraninite, carnolite, and pitchblende (USEPA, 2000a). For radionuclide concentrations in groundwater, 222 Rn can be thousands of times greater than the values for either uranium or radium, because radon is a gas and does not reabsorb to the rock surfaces like other radionuclides (Hess et al., 1985). The highest concentrations of radon in water within the U.S. have been found to occur within the Appalachian Mountains, Rocky Mountains, and Basin and Range territories. A study in Maine produced a mean value of 22,000 pci/l for radon in water in granite zones. A maximum value over 1,000,000 pci/l was reported in one the sample (Hess et al., 1985). The overall US population-weighted average for domestic water equaled 249 pci/l. Smaller systems serving less than one thousand had a population weighted mean of 602 pci/l (Longtin, 1990). Numerous studies on the quality of bottled natural waters have been done, mainly in European countries (Duenas et al., 1999; Gans, 1985; Kralik et al., 2003, Marovic et al.,
1997; Skwarzec et al., 2003; Sparovec et al., 2001), probably because Europe is the world s leading bottled water consumer (Anon., 2001). Other countries that conducted comparable studies include Algeria (Amrani, 2002), Mexico (Rangel et al., 2002) Canada (Pip, 2000) and Argentina (Bomben et al., 1996). Even though most countries either regulate bottled water or use the recommendations by the World Health Organization as guideline, occasionally elevated levels of uranium decay chain nuclides are detected in these waters. Table 1 gives an overview on previously reported maximum levels for uranium chain nuclides from the studies mentioned above. The only published reference for the United States looking at radionuclide content in bottled water is by McCurdy and Mellor. The study from 1981 was done long before the dramatic increase in bottled water consumption in recent years. The short article focuses on Ra-226 and Ra-228 content in 11 different brands of (domestic and imported) bottled waters purchased in the region around Massachusetts and Rhode Island, where the highest Ra-226 concentration found in domestic water was only 2.19 pci/l. Table 1. Summary of previously reported NORM levels in bottled drinking water. Nuclide (unit ) Activity detected Location Reference (max.) Uranium (µg/l) 187.78 Germany Sparovec et al., 2001 0.12 Poland Skwarzec et al., 2003 226 Ra (pci/l) 1.14 Algeria Amrani, 2002 6.22 Austria Gans, 1985 3.51 Brazil Duenas et al., 1999 8.11 Croatia Kralik et al., 2003 25.95 France Gans, 1985 48.65 Germany Gans, 1985 18.92 Italy Gans, 1985 59.05 Portugal Duenas et al., 1999 16.22 Spain Duenas et al., 1999 2.19 USA McCurdy and Mellor, 1981 16.59 Yugoslavia Duenas et al., 1999 222 Rn (pci/l) 378 Algeria Amrani, 2002 22,000 Portugal Duenas et al., 1999 1,405 Spain Duenas et al., 1999 1,773 USA Duenas et al., 1999 1,703 Yugoslavia Duenas et al., 1999 210 Pb (pci/l) 8.7 Austria Katzlberger et al., 2001 1.43 Germany Gans, 1985 5.41 Italy Gans, 1985 10.59 Portugal Kralik et al. 2003 It is interesting to realize that the regulations governing the water quality of bottled water are less thorough and often less stringent than the one in place for tap water (NRDC, 2003). In the US bottled water and tap water are regulated by different agencies, bottled water by the Food and Drug Administration (FDA) and tap water by the Environmental
Protection Agency (EPA). Specific regulations for bottled water are published in Title 21 of the Code of Federal Regulations parts 101, 129 and 165 (21 CFR 101, 21 CFR 129, 21 CFR 165) (FDA, 2003). Whereas by looking at the FDA regulations it seems that there is an extensive regulatory network in place, the Natural Resources Defense Council (NRDC, 2003) has highlighted several regulatory gaps: First, all bottled water sold in the intrastate market in the United States has to be regulated by the respective state agency and is not regulated by FDA. Currently this applies to about 60-70 % of all bottled water on the market. Not all states have regulations for bottled water in place. Also, a violation of the regulatory standards for bottled water, does not necessary mean that the water cannot be sold, it can, provided it has a label specifying that the contents may exceed a particular contaminant. Whereas tap water testing has to be done by a certified laboratory, the testing facility for bottled water is not specified. Also, there is no mandatory reporting of violations for bottled water and records have to be kept only for two years (NRDC, 2003; FDA, 2003). This combined with the FDA statement that bottled water regulations are a low priority in the ranking of their tasks (NRDC, 2003), may lead to many undetected violations. The FDA regulation on radionuclides in bottled water are consistent with those established by the South Carolina Department of Health and Environmental Control, namely uranium 30 µg/l, 226 Ra/ 228 Ra 5 pci/l, gross alpha 15 pci/l, gross beta and photon 4 mrem/yr (SCDEHC, 2003). The North Carolina agency does not publish any regulations for intrastate bottled water (NCDAS, 2003). In the regulations of FDA, the gross alpha radiation limit excludes the contribution of uranium and 222 Rn. The EPA guideline for municipal water analysis, which has been adapted by FDA, is somewhat problematic considering the analyses methods for decay chain radionuclides. An example is the combined 226 Ra and 228 Ra level issue. Initially a water sample to be tested is analyzed for gross alpha radioactivity. Only if the gross alpha level exceeds 5 pci/l, the same or equivalent sample has to be analyzed for 226 Ra. Then only if the sample exceeds 3.0 pci/l 226 Ra it also has to be analyzed for 228 Ra (McCurdy and Mellor, 1981; Focazio et al., 2001). Michel and Moore pointed out in 1980 that the geochemical and solubility properties of the two parent compounds of 226 Ra and 228 Ra are completely different, there should be no reason to expect a correlation between the aqueous concentrations of these two Ra isotopes (Michel and Moore, 1980). As shown by McCurdy and Mellor (1981), it is possible for (bottled or tap) water to exceed the total Ra limit, even though the water was analyzed as recommended in the regulation. They found that two of their water samples contained 226 Ra less than 3 pci/l, but a total Ra concentration well above 5 pci/l (in one case 226 Ra was 1.5pCi/L and 228 Ra was 12.8 pci/l). The next problematic regulation issue is 210 Pb, which is not specifically regulated at all, but can be captured under the gross beta and photon emitting nuclides limit of 4 mrem/yr effective dose rate. However, since 210 Pb is a weak beta emitter (E ave =16.1 kev at 19.8 % abundance and E ave =4.14 kev at 80.2 % abundance) (Shleien, 1992), its analysis requires 1) preconcentration and 2) the ingrowth of the higher energy beta emitter 210 Bi (E ave = 389 kev at 99.999 % abundance), which may take up to 35 days after sampling. Routine monitoring for gross beta emitters might easily miss any 210 Pb present in the water unless the sample is specifically analyzed for it. Radon-222 is a radioactive noble gas and has a half-life of 3.8 days. Bottled water will generally be stored for more than seven half lives of 222 Rn (t 1/2 = 3.8235 d) prior to consumption, so that most of the 222 Rn present at bottling can be assumed to be decayed away leaving 210 Pb, which has half-life of 22.26 years. The National Council on Radiation
Protection and Measurements Report 123 (1996) recommends an effective dose factor (EDF) for the ingestion of 210 Pb of 8.02x10-7 Sv/Bq. Given this and the commonly assumed water consumption rate of 2.2 L per day for reference man (ICRP, 1975), the concentration of 210 Pb needed to result in a dose rate higher than the recommended 4 mrem/year is only 1.85 pci/l. This is not considering any of the other nuclides that might be regulated under the beta emitter rule (ubiquitous 40 K as well as 228 Ra are thought to be the major contributors to the gross beta activity). To yield the amount of 210 Pb necessary to result in a violation of the 4 mrem/year gross beta limit, a water sample has to contain 3,950 pci/l of 222 Rn, assuming that any atom 222 Rn present at bottling will end up as 210 Pb after an appropriate amount of time. The Safe Drinking Water Act (which is applicable to municipal water) does not put any restrictions on radon in water. A 1999 report by the National Research Council indicates that there have been some recent studies on the matter of radon in water. In 1991 the EPA recommended the maximum contaminant level (MCL) of 300 pci/l for radon in water, and 4000 pci/l as the Alternative Maximum Contaminant Level (AMCL) for any water supplier providing water to more than 25 people (U.S. EPA, 1999b). This 300 to 4000 pci/l level is not a regulation, but they are levels that can use for comparison when looking at the bottled water results. There were not many studies found that specifically quantified 210 Pb. Lead-210 has a very low aqueous solubility, but is commonly present in natural waters in form of surface active species, either adsorbed on small particles of the host rock, organic colloids or the sample vessel walls (Katzlberger et al., 2001). One study which did reference 210 Pb was a 1998 U.S Geological Survey (USGS) of selected radionuclides in public ground water supplies throughout the United States (Focazio et al., 2001). This survey targeted areas already known to have radium in ground water, in order to determine the presence of 224 Ra and the relationship among the occurrences of the 3 radium isotopes ( 224 Ra, 226 Ra, and 228 Ra). The report noted that the presence of high concentrations of 210 Po and 210 Pb in ground waters is possible even in the absence of 224 Ra, and that it is known that lead is more difficult to extract from sediment material than radium, and absorbs more quickly into aquifer solids. Levels higher than 1 pci/l of 210 Pb were frequently found in the Appalachian region of the U.S., and one explanation given was that there were most likely high levels of 222 Ra in the ground water of those areas. Another observation in the U.S. Geological Survey was that as the radon in solution decays through a series of very short half-lived products to 210 Pb, a small fraction of the 210 Pb may not be immediately sorbed onto the aquifer matrix, or may be only weakly sorbed, or may be re-ejected to the water through alpha recoil after weak absorption of the radioactive parent product, 214 Po. This observation would indicate that the likelihood of finding 210 Pb in water increases with a higher initial concentration of 222 Rn. Methods During the time period of September 2002 to December 2002, a number of tests for radon ( 222 Rn) were performed on 8 different brands of natural mountain spring waters in plastic bottles. The samples were gathered from local grocery and convenience stores in a variety of sizes. The goal was to obtain water as recently after it was bottled as possible, but also to obtain it off the store shelf, so as to simulate the same situation of the average customer purchasing and drinking such water. Samples were analyzed for uranium, 222 Rn and
210 Pb using the procedures outlined below. In cases where the production date was not labeled on the bottle, the production date was assumed to be 2 years prior to the expiration date. A few samples with both production and expiration dates listed on the bottle, confirmed this 2 year hypothesis, and every bottle sampled seemed to fit in this 2 year time frame. Samples will be analyzed for total uranium using Kinetic Phosphorescence Analysis (KPA), which is a mass analysis method for uranium in solution. KPA is based on the phosphorimetric determination of dissolved uranyl ion (UO 2+ ). A phosphoric acid compound agent added to a small amount of sample causes the UO 2+ to create a luminescent complex species with a relatively long lifetime. A laser exits the complex and the temporal resolution of the light pulse recorded as a signal (Brina and Miller, 1992, CTC, 1993). The amount of sample needed is extremely small, only 100-1000 µl are needed per measurement in addition to about 1.0 ml of complexing agent. The lower limit of detection of this method is 0.01 µg/l. Radon content in water will be determined using liquid scintillation counting of the alpha activity emitted by the 222 Rn progeny. A 10.0-mL sample was obtained from the closed bottle by insertion of a hypodermic needle into the bottle below the surface of the water and filling a glass syringe. The non-aerated water sample was subsequently injected underneath 10 ml of mineral oil based cocktail (NEF957A, New England Nuclear Research Products, Westwood, MA) contained in a 20 ml glass scintillation vial following the American Water Works Association procedure (AWWA 1998). It is important to avoid any contact of the sample with air to prevent losses of 222 Rn into the gas phase. To reduce error, the vial is weighed before and after addition of water sample, to obtain exact data on the amount of water sample. After the vial is capped, it is shaken to thoroughly mix the oil phase with the water phase. During this process, the 222 Rn partitions into the oil phase, whereas the 222 Rn progeny remain in the aqueous phase. After a four-hour delay, which allows for the phases to separate and the 222 Rn in the oil phase to come into equilibrium with its progeny, the sample is counted by LSC for the alpha activity in the oil phase. For 210 Pb analyses, the method published by Eichrom Technologies (2001) was used. An 800 ml water sample was acidified to a ph of 2 or lower then spiked with a stable lead tracer and an iron carrier. Ammonium hydroxide was added to form an iron hydroxide precipitate. The precipitate was centrifuged and then dissolved. The dissolved solution was run through an Eichrom lead-resin column (Eichrom Technologies Inc., Darien, IL) with the final eluent containing the 210 Pb. The lead tracer recovery was quantified using flame atomic absorption spectrometry (Perkin-Elmer 5100; Perkin Elmer Life and Analytical Sciences Inc., Wellesley, MA). The 210 Pb eluent from the Pb-resin column was acidified to a ph of at 2 or lower, to prevent lead from sorbing to the container walls of the vial in which it was collected. After secular equilibrium was established with the 210 Pb progeny, 210 Bi (t 1/2 = 5.013 d), 5.0 ml of the eluent were added to 10 ml of Hi-Safe 3 liquid scintillation cocktail and counted for 3 hours on a Wallac 1415 Liquid Scintillation Counter for beta radioactivity.
Results and Discussion Uranium in Water Analyses The three companies that indicated elevated concentrations of 222 Rn were analyzed for uranium. In all cases, no uranium was detected in any of the samples above the detection limit of 0.01 µg/l. Radon-222 in Water Analysis The 222 Rn measurements were reported on five samples from three bottled water companies where the concentration ranged from 130 to 3,140 pci/l. For samples that were more than 30 days since bottling, these analyses were problematic. In these cases, the decay correction resulted in a significant uncertainty in the concentration. For this reason, analyses were restricted to samples (n=6) that were bottled less than 30 days ago. Table 2 summarizes the measured 222 Rn concentration as well as the decay corrected 222 Rn concentration on the day the sample was bottled. From the liquid-scintillation results there were potentially harmful radon levels in these water samples at the time of bottling. Table 2: Summary of 222 Rn analyses indicating the measured and projected concentration on the bottling date. The uncertainties are listed as 1-σ, based on counting statistics Lead-210 in Water Analysis (Bottle Date - Test Date) 222 Rn Measured Conc. 222 Rn Conc. at Bottling Sample ID* days pci/l pci/l A-1 26 15.4 ± 8.6 1690 ± 950 A-2 20 34.0 ± 8.7 1270 ± 320 A-3 26 28.5 ± 8.6 3140 ± 940 A-4 17 36.2 ± 8.7 780 ± 190 B-1 18 18.6 ± 8.6 480 ± 220 C-1 5 51.5 ± 8.9 130 ± 20 *sample ID is comprised of a letter (company) followed by a number (which corresponds to a bottling date) The samples that had elevated concentrations of 222 Rn were also analyzed for 210 Pb. The 210 Pb concentration of these samples ranged from 0.45 to 3.0 pci/l, Table 3. Two calculations were done after the 210 Pb analyses. First, since 210 Pb is a daughter product of 222 Rn, an estimate of the 222 Rn concentration at the time the water was bottled was calculated. Second, the 210 Pb concentration was compared against the gross beta regulatory limit of 4 mrem/yr based on typical risk assessment assumptions. Table 3 shows the measured 210 Pb concentrations along with the estimated 222 Rn concentrations assuming that all the 210 Pb in the sample can be attributed to the 222 Rn
concentration initially in the bottled sample. The back calculated 222 Rn concentrations from the 210 Pb analyses are consistently an order of magnitude above the initial radon results from the liquid-scintillation radon analysis in Table 2. There are several possible explanations for this discrepancy: 222 Rn off-gassed during the bottling process, 222 Rn diffusion through the bottle (Vesterbacka and Mäkeläinen, 2002), 226 Ra is present in the water (which was not analyzed for), or 210 Pb was already present in the water before it was bottled. As indicated earlier, a gross beta photon dose limit of 4 mrem/yr is equivalent to a 210 Pb concentration of 1.85 pc/l if the water is consumed at a rate of 2.2 L/d and there are no other radionuclides in the water. Although additional analyses are warranted, the concentration of 210 Pb in company A bottled water could present an undue risk to the consumer. Table 3: Results from 210 Pb analysis and the projected 222 Rn concentration at the time of bottling assuming all the 222 Rn decaying to 210 Pb in the bottle. The uncertainties are listed as 1-σ, based on counting statistics. Sample ID 210 Pb Conc. 222 Rn Conc. at bottling pci/l pci/l A-2 2.2 ± 1.1 4640 ± 2410 A-3 3.0 ± 1.1 6340 ± 2320 A-4 3.0 ± 1.1 6420 ± 2420 B-1 0.47 ± 1.1 1010 ± 2380 C-1 1.4 ± 1.1 3150 ± 2390 C-2 0.87 ± 1.1 1860 ± 2290 Conclusions In this paper it has been shown that there is the potential for 222 Rn and its decay products to be present in bottled spring water at the time of consumption. Unless water treatment is performed 222 Rn and decay products could be present, particularly if source of the spring water is in the Appalachian Mountains. Radon-222 and 210 Pb was measured at elevated concentrations in several companies bottled water. These results are consistent with findings of researchers analyses of spring waters in other countries. Given the limited sample size additional testing is necessary to draw firmer conclusions.
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