Geochemical Implication of Chemical Composition of Mineral Water (Bottled Water) Produced Near Mt. Baekdu (Changbai), Northeast China

: Two kinds of bottled mineral water from wells located in the northern (Baeksansu, BSS) and southern (Baekdusansu, BDS) areas near Mt. Baekdu (Changbai) were collected in order to monitor the chemical compositions of the groundwater near a potential volcanic area. The bottled water was produced between August 2014 and June 2017, and corresponds to the Na-HCO 3 water type. The trend in variation of each chemical component between the two bottled waters was different. The BDS bottled water from the southern area of Mt. Baekdu showed a dramatic change in chemical composition during the study period, whereas the BSS bottled water from the northern area did not show any signiﬁcant change in chemical composition. In particular, the BDS bottled water showed either systematic increases or decreases of chemical components relative to the Cl concentrations. However, the BSS bottled water did not show such trends. It was conﬁrmed that the chemical composition in the groundwater was constant, even though the monitoring period lasted for about two years. Our data indicate that it may be possible to use the chemical composition of the bottle water produced from the groundwater in the volcanic area as a proxy for monitoring the geochemical environmental change of the groundwater aquifer.


Introduction
Mt. Baekdu (Changbai) volcano, which is located at the border between China and the Korean Peninsula, is one of many potentially eruptive volcanos in the world. Recently, many researchers expected that Mt. Baekdu might erupt again in the near future [1][2][3][4]. Notably, Shangguan et al. [5] and Hahm et al. [6] have tried to exploit contemporary geothermal activity associated with recent volcanism at Mt. Baekdu using gas components, such as He and CO 2 , from the geothermal volatiles. These authors mentioned that a stable reservoir of geothermal water and deep-seated gases may exist under the Mt. Baekdu geothermal area. In addition, Han and Huh [7] reported that, using geothermometric calculations and δD-δ 18 O data, the hot spring waters of Mt. Baekdu emerge at the surface before attaining equilibrium with their host rock, even though meteoric water infiltrates the geothermal field in the Mt. Baekdu area. Recently, Yan et al. [8][9][10] reported that chemical compositions of the hot spring and mineral (spring) water in Mt. Baekdu were produced from water-rock interaction through the deep and long water cycle of the thermal water. However, there were no reports of systematic observations concerning the hydrogeochemistry of the groundwater in the Mt. Baekdu area. This is due to the fact that this area is a border area between China and North Korea and is a nature reserve, and so it is very difficult to systematicallly collect groundater and hot spring water around Mt. Baekdu.
Since 2009, a large amount of research results related to the geochemical characteristics of bottled water have been reported [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. The chemical composition of bottled water is a result of water-rock interactions in the bedrock aquifer (such as groundwater or surface water) [27,28], and therefore can provide us with information about the main hydrogeochemical processes and influences controlling the chemical content of the bottled water. Particularly, since bottled water produced from natural spring or groundwater wells have relatively constant chemical compositions, their chemical component monitoring may provide important information for tracing the variation of geochemical factors in groundwater reservoirs. For example, based on the survey of bottled waters produced near the epicenter of the 17 January 1995 Kobe Earthquake, Tsunogai and Wakita [29,30] reported that the chemical contents of the bottled water showed anomalous changes before and after the earthquake. This means that the chemical composition of mineral water might be altered due to crustal activity such as earthquakes or volcanic activity. It also indicates the possibility that monitoring of the chemical composition of mineral water (such as the bottled water which was produced from groundwater in accessible areas) could be used to detect chemical changes in the groundwater caused by geological fluctuations in the crust.
Therefore, in this study, we monitored the hydrogeochemical characteristics of the groundwater near the Mt. Baekdu area using bottled waters produced in the surrounding area. We also compared the hydrogeochemical characteristics of the bottle with those of hot spring water and cold spring water in the surrounding area of Mt. Baekdu using our collected waters and the data available in the literature [7]. This was undertaken due to the fact that the hydrogeochemistry of the bottled waters from volcanic areas may have, at least, a twofold importance: (1) they may contribute to the understanding of the role of the aquifers of bottled waters in the recharging of groundwaters, and (2) they provide an opportunity to conduct an assessment of possible volcanic activity near the volcanic area.
The objectives of this study were: (a) to monitor the chemical components of the mineral waters produced near to a volcanic area; (b) to ascertain the geochemical implications of the chemical components in the mineral water; and (c) to find a relatively effective geochemical proxy which can monitor geological activity such as volcanic activity or earthquakes.

Materials
Currently, two bottled waters (i.e., Baeksansu (BSS) and Baekdusansu (BDS)) produced near Mt. Baekdu (see Figure 1 for location) can be obtained relatively easily in the supermarkets of Korea. The BSS is a bottled water produced from artesian groundwater at Eedaobai, Jilin Province, China, at an altitude of 670 m, 50 km from the northern gateway of Mt. Baekdu. The BDS is a groundwater produced by pumping in Changbai Country, Jilin Province, China, at an altitude of 800 m, 35 km from the southern gateway of Mt. Baekdu. These two bottled waters are sold in the Korean market within one to two weeks of production.
Two commercial bottled water samples (BSS and BDS) produced near Mt. Baekdu, China were purchased at a retail mart in Korea, based on the label information regarding the production date on the bottle. We collected a total of 75 bottled waters of the two commercial mineral water samples with different dates ranging from August 2014 to June 2017. Of them, sample BSS140801 was purchased at the Eedaobai (Jilin Province, China) when we visited there on August, 2014, which is located area of the product company of BSS (Baeksansu). We also collected hot spring and cold spring water samples near the Mt. Baekdu area when we visited this area to collect rock samples in August 2014 (see Table 1). The sample BSS140801 was the motivation for the study of chemical composition change in groundwater around volcanic area using bottled water. The others had been purchased at the supermarket at Korea almost every two or three weeks. All samples including BSS140801 were purchased within one month since they were produced by the product company. This means that all of the measurements for chemical components had been performed within two months since production at the respective sites.

Methods
The analysis for the samples was conducted within one week after purchase, most of which are within one month after being produced in the China, locally.
The collected samples were filtered through 0.2 µm Millipore filters before pretreatment for instrumental analysis, and subsequently analyzed for major and minor constituents and hydrogen, oxygen, and Sr isotope compositions.
Cation concentrations (Ca 2+ , Mg 2+ , Na + , K + , Li + , and Sr 2+ , as well as SiO 2 ) were analyzed using an inductively coupled plasma-optical emission spectrometer (ICP-OES, 8300DV, Perkin Elmer, Waltham, MA, USA) at the Korea Institute of Geoscience and Mineral Resources (KIGAM). The bicarbonate content was determined by titration of 50 mL of the sample after the bottles had been opened in the laboratory. Then, anion concentrations, such as Cl − , SO 4 2− , and F − , were measured using ion chromatography (ICS-3000, Dionex, Sunnyvale, CA, USA) at KIGAM. The analytical precision for cations and anions was determined using calculations of the ionic balance error, most of which were generally within 10%. δ 18 O and δD values were analyzed by wavelength-scanned cavity ring-down spectroscopy (L2120-i, Picarro, Santa Clara, CA, USA) which is one type of isotopic ratio infrared spectroscopy [31] available at KIGAM. Water samples were injected eight times per sample, and the last three or four measurements were used for determination of isotopic compositions to eliminate memory effects. The typical analytical uncertainties are better than 0.1 ‰ and 1 ‰ for δ 18 O and δD, respectively [32].
The 87 Sr/ 86 Sr ratio was measured on a TRITON TIMS at KIGAM. The average value for NBS 987 during the analyses was 0.710254 ± 0.000002 (2σ m ) for 30 measurements. The analytical uncertainties were approximately 0.002% for 87 Sr/ 86 Sr. The total procedural blanks during the Sr isotopic measurements were less than 30 pg.

Results
The chemical parameters such as major ions, stable isotopes, and 87 Sr/ 86 Sr ratios of the hot spring and cold spring waters at the Mt. Baekdu area as well as two bottled waters (BDS and BSS) were summarized in Supplementary Tables S1-S3. The chemical composition of the hot spring and cold spring waters at the Mt. Baekdu area and two bottled waters (BDS and BSS) were summarized in the piper diagram of Figure 2a. The hydrogen and oxygen isotopic data (δD and δ 18 O) of the two bottled waters were also drawn in Figure 2b.  [33] and the regional meteoric water line [34], respectively. The data of hot spring water and cold spring waters were used from this study (Table S1) and Han and Huh [7]. Figure 2a shows that most of the samples except one spring water plotted on the far left of the central diamond, which corresponds to the Na-Mg-HCO 3 type. However, the BDS bottled water also shows changes of water type including Na-HCO 3, Na-Mg-HCO 3 , and Na-HCO 3 during the two-year study period.
δD and δ 18 O values of the BDS bottled waters range from −94‰ to −100 ‰ and from −13.0‰ to −13.7 ‰. δD and δ 18 O values of the BSS bottled water range from −97‰ to −101.9 ‰ and from −13.3‰ to −14.2 ‰, respectively. In the plot of δD and δ 18 O (Figure 2b), samples from the BDS bottled waters are clustered along the Global Meteoric Water Line (GMWL, δD = 8 × δ 18 O + 10) by Craig [33], whereas the samples of the BSS bottled waters were plotted in a tight cluster on the lower section of GMWL. The Regional Meteoric Water Line (RMWL) by Chen et al. [34] also does not deviate significantly from the GMWL. The relationship between δD and δ 18 O values of the BSS bottled waters seems to suggest that δ 18 O values may be influenced by a CO 2 exchange reaction due to water-rock interactions [35]. Slight differences of δD and δ 18 O values between the BDS and BSS bottled waters can be interpreted as corresponding well with the altitude effect [36,37].
The 87 Sr/ 86 Sr ratios for BSS bottled waters were nearly constant (0.70719 ± 0.00002, 2σ m ) whereas those for BDS bottled waters are divided into two groups; one is 0.70677-0.70686, while the other is 0.70721-0.70733 (Tables S2 and S3). The 87 Sr/ 86 Sr ratios from the hot spring waters are 0.70510-0.71589, whereas those from the stream waters are 0.70541-0.709 (Table S1).

Variation of Chemical Composition in the Bottled Waters
Geochemical monitoring of the chemical constituents of mineral waters is a useful method for understanding the changes of geochemical environment in the Earth's crust. Recently, Takahashi et al. [38] reported a temporal change in thermal waters related to volcanic activity of Tokachidake Volcano, Japan. They observed an increase of Cl − and SO 4 2− concentrations at the Fujiage spa, and interpreted that such fluctuations were related to volcanic activity. Many such reports for the fluctuations of chemical constituents in groundwater or well waters related to geological activity, such as earthquakes, can also be found in the literature [29,[39][40][41][42].
Numerous factors such as lithology, groundwater residence time, and atmospheric and anthropogenic inputs can become a cause for change in the chemical composition of the groundwater. Therefore, relatively stable concentrations of constituent elements in groundwater may indicate that they are under a relatively equilibrium state due to long-term crustal residence time. Cl − is a useful ion as a conservative reference element to study water-rock interactions since it doesn't readily react with other chemicals and is not chemically altered as it travels along its underground flow path. Cl also is an ion which is difficult to dissolve via water-rock interaction. Therefore, recycling of Cl − within the aquifer system can be neglected. In addition, if the source of Cl − is rainfall, Na + and Cl − will fall on a line known as the Seawater Dilution Line (SWDL). Nevertheless, in bedrock aquifers, chloride concentrations tend to increase according to well depth [43]. In this case, systematic increases in chloride ion concentrations in the groundwater may be interpreted as a result of chloride ion accumulation in the aquifer due to precipitation [44].   Most of the cold spring waters around Mt. Baekdu were originated from the Cheonji (Tianchi) Lake of Mt. Baekdu. To determine the effect of hot spring waters on the BSS and BDS bottled waters, we compared the correlation between Cl − and other cations and anions (Figures 5 and 6). Cations and anions from the BSS and BDS bottled waters were plotted against Cl − in Figures 5 and 6, respectively. Figures 5 and 6 also include the data for hot and cold spring water around Mt. Baekdu (Supplementary Table S1). In Figure 5, Na + ion concentrations in the bottled waters, cold and hot spring waters all plot above the sea water dilution line (SWDL) indicating Na + ion excess and water-rock interactions. Figures 5 and 6 also show that cation and anions from the hot spring and cold springs have a positive relationship with Cl − concentrations, which clearly indicates that they were released by water-rock interactions. However, Na + and Ca 2+ of the BDS bottled waters seems to indicate that they are different from evolution trend of those of cold and hot spring waters. In the case of the BSS bottled waters, except for Mg 2+ and SO 4 2− , most cation and anions show a good relationship with those of the cold and hot spring waters. Such different features between the two bottled waters seem to suggest that the two bottled waters in this article have different evolution trends from one other.
In Figure 3, we mentioned that chemical components of the BDS bottled waters displayed dramatic changes during the specific period from 30 August 2015 to 18 March 2016. However, Figures 5 and 6 did not show such dramatic changes due to the large difference between the chemical components of between hot spring waters and the BDS bottled waters. Therefore, we redetermined the relationship between Cl − and other ions in the BDS bottle waters, excluding the data of hot and cold spring water around Mt. Baekdu (Figure 7). Figure 7 clearly reveals that the concentration variation of cations divided into two areas compared to Cl − ion concentration, such as low Cl − and high Cl − . Particularly, the BDS bottled waters produced during low Cl − ion concentration period has a geochemical characteristic that, except K + and Ca 2+ , the dissolved ions have positive (Na + , Li + , alkalinity) and negative (Mg 2+ , Sr 2+ and SO 4 2− ) correlation with Cl-ion concentration. Furthermore, it may be possible to interpret that a strong correlation between Na + and Cl − ions in the BDS bottled waters indicates that sodium is derived from the bedrock due to water-rock interactions over a long period. The decrease in Mg 2+ and Sr 2+ ion concentrations may be due to precipitation of carbonate minerals [45].  Therefore, in Figure 7, the relationship between cations and Cl − may be interpreted to the extent that the systematic variation in Li + , Na + , and Mg 2+ ion concentrations against Cl − concentrations in the BDS bottled waters does not necessarily relate to volcanic activity in the Mt. Baekdu area.

Isotope Geochemistry of the Bottled Waters
The groundwater with isotopic data of δ 18 O and δD falling on the meteoric water line can be assumed to have originated form condensation of water vapor and to be unaffected by other isotopic processes. Therefore, it can be concluded that concentrations of chloride ions from both bottled waters are essentially meteoric in origin.
In Figure 2b, BDS derived from the bedrock aquifer showed that they are meteoric in origin. However, BSS produced from the artesian well showed a geochemical characteristic that may be a result of CO 2 exchange via water-rock interaction. The relationship between Cl − , δ 18 O, and δD also reveals that BSS and BDS bottled waters have different water-rock interactions ( Figure 8). in solution gradually increase during water-rock interaction experiments of one year, suggesting that the chemical composition of groundwater does not equilibrate during short periods. Therefore, it could be interpreted that the abrupt change in concentrations of chemical constituents in the BDS bottled waters may be derived from different aquifers during the monitoring period, suggesting that the different geochemical characteristics of the BDS bottled waters seem to be related to changes in the pumping wells (i.e., possible change of aquifer and lithology).  (Table S1) and Han and Huh [7]. At present, due to a lack of information on the two bottled waters, it may be difficult to define a water-rock interaction in the aquifer which could produce the two bottled waters. Nevertheless, the geochemical characteristics seem to indicate that the BSS bottled waters might be produced by simple water-rock interactions from one aquifer whereas the BDS bottled waters seems to be produced by pumping from mixed aquifers.

Summary and Conclusions
Two commercial bottled waters (BSS and BDS) from the Mt. Baekdu area were collected from April 2015 to September 2016 in order to investigate the possible usefulness of chemical composition variation of the bottled waters in monitoring nearby volcanic activity.
The BSS bottled waters produced from the northern part of Mt. Baekdu reveal a linear variation in chemical composition against Cl − , whereas the BDS bottled waters produced from the southern part of Mt. Baekdu show abrupt changes in its chemical composition. The change in chemical composition of the BDS bottled waters seems to be due to pumping the aquifer at different depths, whereas the variation in chemical components against Cl from the BSS bottle water seems to be due to water-rock interactions in the aquifer with bedrock of various kinds of mineral composition.
Our results suggest that monitoring of bottle water sourced near the volcanic area may be useful in understanding the cause of the variation in chemical compositions of the groundwater due to water-rock interactions.
Supplementary Materials: The following are available online at https://www.mdpi.com/article/ 10.3390/w13162191/s1. Table S1: Chemical composition of the hot and cold spring water at the Mt. Baekdu area; Table S2: Chemical composition of the BDS bottled waters; Table S3: Chemical composition of the BSS bottled waters.