Essential Trace Elements and Arsenic in Thermal Springs, Afghanistan

Thermal springs are natural hydrogeological features which are highly affected by local volcanism or tectonic activity. Thermal springs are the best source of hydrothermal energy to heat houses and aid in the recovery of skin diseases. However, they consist of some heavy and trace metals such as arsenic, lead, zinc, copper, iron, and so forth. Somehow, the thermal springs of central Bamyan have become contaminated with some essential trace elements. Thus, this study was conducted to assess and determine the number of these trace elements in the thermal springs. To achieve these objectives, a preliminary survey, water sampling, and in situ measurements of physicochemical parameters were conducted in research areas. All the collected water samples were analyzed chemically to determine the amount of trace elements, including arsenic, barium, copper, iron, manganese, and zinc. The study shows that temperature ranged from 16 to 32 °C, while the average pH value was 6.25. Almost all of the trace elements showed an extremely high value of electrical conductivity (average: 5713 µS/cm) and significantly high total dissolved solids (average: 3063 mg/L). The average value of chloride was 797 mg/L, which is dramatically higher than standard values. In regard to trace element concentration, almost all thermal springs were heavily contaminated with arsenic and it was recorded as 100 µg/L in the eastern part of central Bamyan. The average amounts of barium, copper, iron, manganese, and zinc were 4.14, 6.05, 1.90, 1.76, and 0.74 mg/L, respectively. In conclusion, the water of the thermal springs of central Bamyan are not suitable for human consumption because of the significant amount of trace elements as well as the high-water quality index value. Using these springs for drinking and irrigation purposes has been deemed inappropriate.


Introduction
Thermal springs are natural phenomena [1] and geological features which can be found in "active or semi active volcanic areas" [2] or observed in and around tectonic zones [1]. Generally, thermal springs have advantages and disadvantages for human and livestock use [3]. They act as the surface expression of underlying hydrothermal systems [2] and can be used for hydrothermal energy production. However, thermal water often presents anomalously high background values of different potentially toxic elements, which can present severe risks for human consumption. Due to lack of clean water resources, some consume it for drinking water [4,5], but most of the water is affected by high concentrations of arsenic [6] and other trace elements. Arsenic is also released through the thermal springs into the environment and surface/groundwater [4,7]. Contamination of groundwater through trace elements is a substantial concern for environmental health scientists since this water normally is required for human and animal consumption [8].

Location and Climate Condition
Bamyan is located in the center of Afghanistan (Figure 1) within latitude 33 • 48 N to 35 • 28 N and longitude 66 • 24 E to 68 • 14 E [32]. The specific study area is situated in the central highland of Bamyan province between two main mountainous ranges: the Hindu Kush Mountains in the north and the Baba Mountain range in the south. Geographically, it is placed within longitude 67 • 20 E to 68 • 10 E and latitude 34 • 30 S to 35 • 10 N (Figure 1), and topographic elevation is around 2520 m above sea level. Kahmard and Saighan districts are located in the northern part, the Baba Mountain range in the south, the Shaikh Ali and Surkh Pars districts of Parwan province in the east, and the Yakawlang district in the western part of study area (Figure 1).

Location and Climate Condition
Bamyan is located in the center of Afghanistan ( Figure 1) within latitude 33°48′ N to 35°28′ N and longitude 66°24′ E to 68°14′ E [32]. The specific study area is situated in the central highland of Bamyan province between two main mountainous ranges: the Hindu Kush Mountains in the north and the Baba Mountain range in the south. Geographically, it is placed within longitude 67°20′ E to 68°10′ E and latitude 34°30′ S to 35°10′ N (Figure 1), and topographic elevation is around 2520 m above sea level. Kahmard and Saighan districts are located in the northern part, the Baba Mountain range in the south, the Shaikh Ali and Surkh Pars districts of Parwan province in the east, and the Yakawlang district in the western part of study area (Figure 1).  The climate of Bamyan varies significantly throughout the region from arid to semiarid, with warm summers and cold winters. During cold winters, the average temperature is −5 • C, while sometimes it can decrease to −20 • C [33]. The average recorded precipitation is 165 mm, which mainly occurs as snow [34].

Geological Setting
The geology of Bamyan valley, similar to many mountain chains around the world, consists of crystalline or metamorphic bedrock with different rock formations from the Paleoproterozoic to Quaternary periods [30]. Metamorphic and igneous rocks mainly exist in most parts of the southern hills and the Baba Mountain ridge. At higher elevations, granite to gabbro, schist, slate quartzite, and gneiss are major rock units in the southern ridges that are especially exposed [35].
Glacial and alluvial deposits of snow-glacier melting processes during the Quaternary period created hollows/cirques, huge moraines, and alluvial fans/plains that provide the major water reservoirs for Bamyan valley [30].
The northwestern Bamyan ridges ( Figure 1) primarily have sedimentary rock formations comprised mostly of limestone and carbonates with an intercalation of basic to intermediate volcanic. Their ages vary from Carboniferous, to Permian, and to Cretaceous. Granitic batholiths of the northern Hindu Kush (Triassic-Jurassic) intrude the strata several times [35].
A deep east-west regional fault through Bamyan valley cuts all rock formations and channels into deep hydrothermal brines. Related hot springs and brines are widespread alongside the fault, especially in the eastern (Paymory Area) and western (Azhdar Area) sides of the city of Kabul ( Figure 1).

Hydrological Setting
Bamyan is a mountainous region and the central part of this province is surrounded with two main mountains called the Baba Mountain, which is located at the southern part and prolongs from east to west, and the Hindu Kush Mountain, located at the northern part of central Bamyan and which prolongs almost parallel to the Baba Mountain. Central Bamyan is a wide valley located between the Hindu Kush Mountain range (north) and the Baba Mountain range (south). Many valleys and subvalleys connect these mountainous regions to the main Bamyan valley.
From a hydrological point of view, the main river of Bamyan flows from the main Bamyan valley ( Figure 2). Almost all the southern valleys are wet during the year because the water from the rivers that flow through these valleys originates from Baba Mountain's glaciers and snow at high elevations and natural lakes. The main rivers which originate from Baba Mountain include the Foladi River, which has several subrivers: the Dokani River, the Darra Sadat River, the Darra Ahangaran River, and the Kalu River ( Figure 2). Comparatively, the Hindu Kush Mountain provides less water than the Baba Mountain. Therefore, the majority of the valleys located in the northern part are dry except for some small flows which have water for a limited time during the year.
There are a variety of thermal hot and cold springs throughout central Bamyan, especially in the south, such as the Foladi, Dokani, Sadat, Agangaran, and Kalu valleys (Table 1). Further, some cold springs are situated in the Bamyan main valley, which supply the urban water systems. In some parts, these springs are used for irrigation and drinking. There are a variety of thermal hot and cold springs throughout central Bamyan, especially in the south, such as the Foladi, Dokani, Sadat, Agangaran, and Kalu valleys (Table 1). Further, some cold springs are situated in the Bamyan main valley, which supply the urban water systems. In some parts, these springs are used for irrigation and drinking.

Water Sampling and Field Parameter Measurements
The geographical location and elevation of every observation point (sampling point) were recorded by a handheld global positioning system (GPS) and the results were plotted in the maps (Figures 1 and 2) by the use of the WGS1984 geographic coordinate system. Further, in autumn (October-December 2018), water samples were collected from every study site into a 1000 mL sterile and dried glass bottles for the purpose of analyzing the essential trace elements and arsenic. A cool bag equipped with ice bags was used to keep the water samples stable, to prevent any possible chemical characteristic changes of the water samples, and to keep the water temperature at 4 • C until the laboratory analysis could be completed. During the sampling, some physicochemical parameters, including the pH, temperature ( • C), electrical conductivity (mS/cm), and total dissolved solids (TDS) (mg/L), were measured directly in situ using a portable multimeter DR 2800 Spectrophotometer (manufacturer Hatch, Colorado, USA) with two probes for pH and EC.

Water Analysis Methods
All targeted essential trace elements and arsenic were analyzed at Green Tech water laboratory in Kabul city. Arsenic was analyzed with an EZ Arsenic Test Laboratory Kit. These kits indicate the linear range of As analysis, which were previously immobilized with the detector as 10-250 µg/L of arsenic. The amount of barium was measured by HACH model 8014, copper with HACH 8026, iron with HACH 8008, manganese with HACH 8149, and zinc with HACH 8009 (Table 2). DR 3900 Laboratory Spectrophotometer for water analysis (manufacturer Hatch, Colorado, USA) was applied. All these methods of HACH for the purpose of water and wastewater analysis have been reviewed, approved, and accepted by the US Environmental Protection Agency (USEPA) to monitor regulatory requirements. For greater accuracy and to ensure the accuracy of the lab chemical analysis, a duplicate analysis was conducted and the physicochemical parameters were measured again in the lab and compared with the field values.

Water Type Determination
The water quality index (WQI) is an index reflecting the composite impacts of parameters to determine the water type and assess the health risk rate of the thermal springs.
WHO guidelines were used for the WQI calculations. The number of parameters were selected, then the relative weight (Wi) of the selected parameters was calculated by this equation [36]: where W i means the relative weight, w i shows the weight of every parameter, and i is equal to the number of parameters. After that, the quality rating scale (q i ) was determined for every parameter [36]: where q i shows the quality rating according of ith parameter concentration, and n is a chemical parameter number, C i is the concentration of every parameter of each water sample (mg/L), and S i is the WHO standard value of the parameter. Afterward, the sub index (SI i ) of each parameter and WQI was calculated as by applying these equations [36]: Based on WQI, water has an excellent quality if the WQI ranges from 0 to 25. Water is considered good quality if the WQI range is from 25 to 50. Water of poor quality has a WQI range from 50 to 75. Water is very poor quality if the WQI ranges from 75 to 100. Water that is unsuitable for human consumption has a WQI number greater than 100 [36].

Physical Parameters of Thermal Springs
The physical parameters of thermal springs are shown in Table 3. The temperature values ranged from 16 • C in Azhdar spring (wp 7 ) to 32 • C in the Paymory (Figure 1 Table 3).

Major Ions
The results of the hydrochemistry analysis of the thermal springs are given in Table 4. The chloride (Cl − ) amount in these thermal springs changed from 49 mg/L in wp 6 (Table 4).

Trace Element Concentrations
Five trace elements, including arsenic, were assessed in the thermal springs and the results are given in Table 4. Just over half of the thermal springs contained arsenic. The amount of arsenic in the first group, located in the northwestern part of the study area, was 10 µg/L,

Trace Element Concentrations
Five trace elements, including arsenic, were assessed in the thermal springs and the results are given in Table 4. Just over half of the thermal springs contained arsenic. The amount of arsenic in the first group, located in the northwestern part of the study area, was 10 µg/L, which is equal to the maximum value of arsenic suggested by the WHO (Table 4); this included the wp 3 , wp 4 , and wp 5 (Figure 3c) study points (Figure 1). However, the value of arsenic in the second group of thermal springs, situated in the eastern part of the study area ( Figure 1) and included wp 8 , wp 9 , and wp 10, were recorded at 100 µg/L. This amount is high compared with the accepted WHO standard amount. The high amount of arsenic in the second part of the thermal springs is potentially related to the geological singularities of the spring locations. The thermal spring range in the Kalu valley (including wp 8 -wp 11 ) flows through Paleoproterozoic-geological-age gneisses bedrock, which are the oldest rocks in Bamyan valley and partly covered by sandstone. This is the reason why the thermal spring contains arsenic and trace elements. The second range of thermal springs with a concentration of 10 µg/L of arsenic (including wp 3 , wp 4 , and wp 5 ) flows through Pliocene-geological-age conglomerate and sandstone-based rocks, which cover the older bedrock. The high arsenic concentration in the thermal spring originates from these bedrocks.
The amount of barium fluctuated significantly and ranged from 1 to 7 mg/L, with an average of 4.14 mg/L (Figures 4 and 5), which is significantly higher than 0.7 mg/L, which is suggested in the WHO standard ( Figure 6). Copper and total iron are present in the range of 0.11-9.02 mg/L (average: 6.05 mg/L) and 0.08-3.89 mg/L (average: 1.90 mg/L), respectively (Figures 4 and 5).
Water 2021, 13, x FOR PEER REVIEW 11 of 18 which is equal to the maximum value of arsenic suggested by the WHO (Table 4); this included the wp3, wp4, and wp5 ( Figure 3c) study points (Figure 1). However, the value of arsenic in the second group of thermal springs, situated in the eastern part of the study area ( Figure 1) and included wp8, wp9, and wp10, were recorded at 100 µg/L. This amount is high compared with the accepted WHO standard amount. The high amount of arsenic in the second part of the thermal springs is potentially related to the geological singularities of the spring locations. The thermal spring range in the Kalu valley (including wp8-wp11) flows through Paleoproterozoic-geological-age gneisses bedrock, which are the oldest rocks in Bamyan valley and partly covered by sandstone. This is the reason why the thermal spring contains arsenic and trace elements. The second range of thermal springs with a concentration of 10 µg/L of arsenic (including wp3, wp4, and wp5) flows through Pliocene-geological-age conglomerate and sandstone-based rocks, which cover the older bedrock. The high arsenic concentration in the thermal spring originates from these bedrocks. The amount of barium fluctuated significantly and ranged from 1 to 7 mg/L, with an average of 4.14 mg/L (Figures 4 and 5), which is significantly higher than 0.7 mg/L, which is suggested in the WHO standard ( Figure 6). Copper and total iron are present in the range of 0.11-9.02 mg/L (average: 6.05 mg/L) and 0.08-3.89 mg/L (average: 1.90 mg/L), respectively (Figures 4 and 5).
The concentration of manganese varied from 0.017 to 3.01 mg/L, with an average value of 1.76 mg/L, whereas zinc ranged from 0.23 to 1.18 mg/L (average: 0.74 mg/L) (see Figure 4).

Correlations
The study of the correlation coefficient between two variables is a way to determine the sufficiency of the first variable for the prediction of the second one [37]. This coefficient is utilized for the assessment of the correlation between the variables if the dependent variable is just influenced through the independent variable and vice versa [37].
The selection of variables was based on the physicochemical properties and the measured trace elements' importance with related correlation and determination of the variables' dependency for the trace elements (see Table 5). The results show a strong correlation (r > 0.9) and a good correlation (r = <0.9 to >0.5). The strongest correlations are recognized between electrical conductivity and total dissolved solids (r = 0.999), barium (r = 0.978) (see Figure 6), manganese (r = 0932), and zinc (r = 0.916), as well as between TDS and manganese (r = 0.930) and zinc (r = 0.913). Further, barium is strongly correlated with manganese (r = 0.892) and zinc (r = 0.871) and between manganese and zinc (r = 0.807) (see Table 5 and Figure 7). The constituents originate from the same source, and the thermal springs have near equal origins. The trace elements were from the same geological settings, which are located at the thermal The concentration of manganese varied from 0.017 to 3.01 mg/L, with an average value of 1.76 mg/L, whereas zinc ranged from 0.23 to 1.18 mg/L (average: 0.74 mg/L) (see Figure 4).

Correlations
The study of the correlation coefficient between two variables is a way to determine the sufficiency of the first variable for the prediction of the second one [37]. This coefficient is utilized for the assessment of the correlation between the variables if the dependent variable is just influenced through the independent variable and vice versa [37].
The selection of variables was based on the physicochemical properties and the measured trace elements' importance with related correlation and determination of the variables' dependency for the trace elements (see Table 5). The results show a strong correlation (r > 0.9) and a good correlation (r = <0.9 to >0.5). The strongest correlations are recognized between electrical conductivity and total dissolved solids (r = 0.999), barium (r = 0.978) (see Figure 6), manganese (r = 0932), and zinc (r = 0.916), as well as between TDS and manganese (r = 0.930) and zinc (r = 0.913). Further, barium is strongly correlated with manganese (r = 0.892) and zinc (r = 0.871) and between manganese and zinc (r = 0.807) (see Table 5 and Figure 7). The constituents originate from the same source, and the thermal springs have near equal origins. The trace elements were from the same geological settings, which are located at the thermal springs' pathway. These strong correlations between parameters represent the variables' dependency. Investigations of the geological setting and mineral composition of the bedrock are planned for future studies.

Water Type and Health Risk Assessment
In many parts of the study area, the thermal springs flow into the surface water, including rivers, and this water is directly used for drinking or irrigation purposes. The result outputs based on WQI were compiled in Figure 8. All the thermal springs water samples have high numbers, compared to the WQI = 100, maximum standard value for potable water. Only the Khaja Ali thermal spring (wp6 with WQI = 17) is suitable for drinking purpose.

Water Type and Health Risk Assessment
In many parts of the study area, the thermal springs flow into the surface water, including rivers, and this water is directly used for drinking or irrigation purposes. The result outputs based on WQI were compiled in Figure 8. All the thermal springs water samples have high numbers, compared to the WQI = 100, maximum standard value for potable water. Only the Khaja Ali thermal spring (wp6 with WQI = 17) is suitable for drinking purpose.

Discussion
Determination of the natural situation of the groundwater chemistry and water-rock interactions is one the of main aims of physicochemical studies [38][39][40]. Here, physical parameters such as temperature, pH, color, conductivity, resistivity, salinity, turbidity, and TDS were measured in the study area. Almost all of the water of the thermal springs was from a yellowish to brownish color. The values of almost all the water at the study points were higher than the WHO value (15 CoPt). However, the pH levels of all the thermal springs were in the standard range (6.5-8.5) and varied from 6.39 to 7.24. The amount of total dissolved solids (TDS) was extremely high (Max. = 4960 mg/L, Min. = 351 mg/L, Average = 3063 mg/L) compared with the WHO standard (1000 mg/L).
Arsenic concentrations in thermal water present values of one to three orders of magnitude higher compared with the cold groundwater [38]. Arsenic is introduced into the water via an accumulation of related deposits such as iron, sulfates, oxides, and hydroxides [41,42]. It can originate naturally and artificially: natural arsenic contamination can occur in different geological and climatic conditions [6]. The maximum amount of arsenic in the thermal springs of this study area was 100 µg/L, which is significantly higher than the maximum value of WHO (10 µg/L). In addition to arsenic, some other trace elements such as barium, copper, iron, manganese, and zinc were assessed in the thermal springs. The average amount of barium was 4.14 mg/L, which is much higher than the 0.7 mg/L maximum value of WHO. Concentrations of copper, iron, manganese, and zinc averaged at 6.05, 1.90, 1.76, and 0.74 mg/L respectively. Thus, the thermal water sources of central Bamyan are significantly contaminated with trace elements.
According to other research [37,43], water is considered to be of excellent quality if the WQI ranges from 0 to25, water is considered to be good quality if the WQI has a range from 25 to 50, water has poor quality if the WQI is from 50 to 75, water has very poor

Discussion
Determination of the natural situation of the groundwater chemistry and water-rock interactions is one the of main aims of physicochemical studies [38][39][40]. Here, physical parameters such as temperature, pH, color, conductivity, resistivity, salinity, turbidity, and TDS were measured in the study area. Almost all of the water of the thermal springs was from a yellowish to brownish color. The values of almost all the water at the study points were higher than the WHO value (15 CoPt). However, the pH levels of all the thermal springs were in the standard range (6.5-8.5) and varied from 6.39 to 7.24. The amount of total dissolved solids (TDS) was extremely high (Max. = 4960 mg/L, Min. = 351 mg/L, Average = 3063 mg/L) compared with the WHO standard (1000 mg/L).
Arsenic concentrations in thermal water present values of one to three orders of magnitude higher compared with the cold groundwater [38]. Arsenic is introduced into the water via an accumulation of related deposits such as iron, sulfates, oxides, and hydroxides [41,42]. It can originate naturally and artificially: natural arsenic contamination can occur in different geological and climatic conditions [6]. The maximum amount of arsenic in the thermal springs of this study area was 100 µg/L, which is significantly higher than the maximum value of WHO (10 µg/L). In addition to arsenic, some other trace elements such as barium, copper, iron, manganese, and zinc were assessed in the thermal springs. The average amount of barium was 4.14 mg/L, which is much higher than the 0.7 mg/L maximum value of WHO. Concentrations of copper, iron, manganese, and zinc averaged at 6.05, 1.90, 1.76, and 0.74 mg/L respectively. Thus, the thermal water sources of central Bamyan are significantly contaminated with trace elements.
According to other research [37,43], water is considered to be of excellent quality if the WQI ranges from 0 to25, water is considered to be good quality if the WQI has a range from 25 to 50, water has poor quality if the WQI is from 50 to 75, water has very poor quality if WQI ranges from 75 to 100, and water is unsuitable for drinking with a WQI greater than 100. As mentioned above, all the thermal springs in this study, except (wp 6 ), are in very bad condition because the WQI values are much higher than 100.
Overall, the thermal springs of central Bamyan that were studied are heavily contaminated with arsenic and some trace elements. Thus, this water poses a significant health risk if it is used for drinking and irrigation.

Conclusions
Thermal springs are natural phenomena with high concentrations of metals, including arsenic, as essential trace elements. Hence, it is imperative to determine the amount of these trace elements in thermal springs in order to protect public health. Originally, the majority of the thermal springs in central Bamyan were formed due to national and local tectonic activities except for the Khaja Ali thermal spring, which mainly originated from volcanic activities. This study found that some thermal springs located northeast of Bamyan City (in Kalu valley) have anomalously high concentrations of arsenic, copper, and barium. The amount of zinc in the thermal springs is significantly higher than acceptable standards. Electrical conductivity has a strong correlation with total dissolved solids, barium, manganese, and zinc, as well as barium with manganese. Based on the calculated values of the water quality index, water from all of these thermal springs are unsuitable for drinking except for the Khaja Ali thermal spring, which is of excellent quality. Thus, these sources of water should not be used for the purpose of drinking and irrigation.