Assessment of Major and Trace Elements in Drinking Groundwater in Bisha Area, Saudi Arabia

Department of Chemistry, College of Science, University of Bisha, Bisha, Saudi Arabia Department of Chemial Engineering, College of Engineering, King Khalid University, Abha, Saudi Arabia Department of Chemistry, College of Science, King Khalid University, P.O. Box 9004, Abha 61413, Saudi Arabia School of Allied Health Science, Faculty of Health Sciences, De Montfort University, -e Gateway, Leicester LE1 9BH, UK


Introduction
Groundwater is an important source of drinking water for many countries; high percentages come from groundwater in Saudi Arabia (40%), Denmark (98%), e Netherlands (67%), and Sweden (49%), as reported by UNDEP. Worldwide, there is an increasing trend of using groundwater as a source of drinking water. erefore, an increasing number of studies have investigated the contamination of groundwater, because groundwater is susceptible to impurities due to its contact with rocks, soil, and plants [1]. Consequently, heavy metals were shown to be the major impurities in groundwater due to the nature of the rocks and weathering phenomena or anthropogenic activities, including the use of fertilizers. All the mentioned parameters could result in serious pollution, which harms human health [2,3].
Essential and toxic elements are the paramount issues in the investigation of groundwater.
e existence of such elements depends on the nature of bedrock and the pH value [4,5]. e World Health Organization (WHO) [6,7] set a guideline value of 40 and 10 μg/L in drinking water for essential Se and toxic As, respectively.
Numerous studies have investigated trace elements and other contaminants in groundwater [8,9]. e presence of radioactive elements was also measured to determine the suitability of groundwater for drinking [10]. A previous study in Saudi Arabia investigated the presence of heavy metals in groundwater and concluded that some samples were not suitable for human consumption [11]. e driving forces behind the investigation of groundwater are the avoidance of ecosystem disturbance and the determination of the causes of contamination, either geogenic or anthropogenic, to allow strategies for remediation to be set.
is has raised awareness of the need to stop harmful human activities that had negative impacts on the environment. is has also led to comprehensive studies on the effects of toxic elements such as uranium, which has adverse health effects in humans, especially in the kidneys [12][13][14]. Most of the studies that investigated uranium in drinking water suggested that the safe range of uranium in drinking water is 2-30 μg/L. erefore, it is essential to determine the tolerable daily intake (TDI), which refers to the amount that can be consumed every day over a lifetime without significant health risk [15]. e hardness of drinking water has a long history of continuous debate. Different epidemiological studies have shown an inverse relationship between drinking hard water and cardiovascular disease. erefore, there is no stark evidence to associate the consumption of hard water with health adverse effects. Consequently, no health-based guidelines have been set by the WHO (2003). is leads us to recommend being cautious about the consumption of hard water. Few studies were focused on the evaluation of elements in drinking groundwater in the south area of Saudi Arabia. Previous studies [16][17][18] were in Najran, Jazan, and Asir (city of Khamis Mushait), respectively. However, no specific study was carried out in the Bisha area. Moreover, the groundwater from wells is the major source of drinking water in the Bisha area. Yet, no studies are available related to the evaluation of Bisha's drinking groundwater. erefore, the purpose of this study was to assess the major and trace elements in groundwater from the Bisha region.

Sample Collection and Preparation.
In total, 25 samples were collected from groundwater (wells) in the Bisha area, Asir province, Saudi Arabia ( Figure 1). Figure 1(a) shows the whole map of Saudi Arabia including Asir province. Figure 1(b) presents the locations of collected samples. e depth of all wells was between 60 and 70 meters. e samples were collected between July and August 2018. All samples were kept in polyethylene bottles before analysis.

Measurement of Some Parameters (EC, TDS, and TH)
Including Chloride. Electrical conductivity (EC) total dissolved solids (TDS) and pH were measured for all samples at room temperature upon arrival at King Khalid University using an Oakton PC 450 Waterproof Portable Meter. Total hardness (TH) was determined by complexometric titration method. Each water sample was titrated with 0.01 M EDTA disodium, including ammonia buffer (pH � 10) and using Eriochrome Black T as the indicator. 2 mL of the buffer followed by 3 drops of the indicator was added to 25 mL of a sample and then was titrated against the titrant (0.01 M EDTA) until the solution changed from wine red to blue [19]. Chloride concentration was measured by the precipitation titration method (Mohr's method). 25 mL of the water sample was used and a pH was adjusted between 7 and 10; 1 mL of 5% K 2 Cr 2 O 4 was added as an indicator and then titrated against 0.014 M AgNO 3 until the solution color was changed to brown-red.  [20].

Chemicals, Reagents, and Analytical Method.
A singlestock solution was prepared from a mixture of 29 elements at a concentration of 10.0 ± 0.05 μg/mL from ULTRA Scientific (North Kingstown, RI, USA). A stock solution (1000 μg/mL) of an internal standard (Sc) was also obtained from ULTRA Scientific (North Kingstown, RI, USA). A stock solution (1 g/L) of an internal standard (Rhodium, Rh) was obtained from AppliChem (Panreac, Germany). Also, a stock solution (1 g/L) of an internal standard (germanium, Ge) was obtained from AppliChem (Panreac, Germany).
Fresh standards for the analysis were prepared daily from stock solutions in 1% HNO 3 . A concentration of 100 μg/L of Sc was used as an internal standard for the analysis. Also, concentrations of 20 μg/L of Rh and Ge were used as internal standards for the analysis. e calibration standards for trace elements (including all fourteen elements) were 5, 10, 20, 50, and 100 μg/L, and for major elements (including all four elements), they were 5, 10, 20, 40, and 80 mg/L.

Quality Control.
e daily performance of ICP-MS in terms of sensitivity and background signals was checked by using a tune solution (B iCAP) containing U, In, Li, and Co, which contained 1 μg/L for each element in 2.0% HNO 3 and 0.5% HCl. Kinetic energy discrimination (KED) mode including helium gas was used.
Limits of detection (LODs) and limit of quantification (LOQ) for all eighteen elements were calculated by measuring the blank (1% HNO 3 ) ten times, and the standard deviation (SD) was used for calculations as follows: A continuing calibration verification (CCV) was also used for a quality control (QC) test for each run. It was performed by measuring 50 μg/L of a mixed standard of all measured elements after each set of ten samples. In the QC, each element was measured three times (n � 3). roughout the whole session, the QC analysis was repeated three times; thus, each element was measured nine times (n � 9). e recoveries in one session were as follows: V (97.3%), Cr (96.8%), Mn (99.7%), Co (98.4%), Ni (94.4%), Cu (94.7%), Zn (117.5%), As (99.2%), Se (106.2%), Cd (98.2%), and Pb (98.5%). For the major elements, 40 mg/L of a mixed standard of all four elements was used for CCV, and the recoveries were as follows: Na (112.4%), K (112.1%), Mg (114.9%), and Ca (109%).

Statistical Analysis.
One-way analysis of variance (ANOVA) SPSS version 20 was used to evaluate and to 39   identify significant differences (p < 0.05) for values presented for all elements and parameters, measured for all collected water samples from different locations in the Bisha region, with the influence of 95% confidence level. e ANOVA was used to decide whether there were any statistically significant differences between the means of concentrations/values of all measured elements and parameters of all samples from different locations in the Bisha region. e mean difference is significant at the 0.05 level. A correlation analysis was also performed for all 15 measured elements (Na, K, Mg, and Ca, V, Cr, Mn, Co, Ni, Cu, Zn, As, Se, Cd, and Pb), by using SPSS.
is was to establish if there were correlations between every two elements and to explore the strength of such correlations.

Results and Discussion
Different parameters were measured in the 25 groundwater samples. EC values range was 124-3140 μS/cm, pH was 6.98-8.06, TDS was 107-5270, and TH range was 124-3140 mg/L, as presented in Table 1. Based on our results reported for the TDS, 28% of samples (n � 7) were not suitable for drinking water, because they exceeded the guideline value (1000 mg/L) for TDS set by WHO in drinking water [6]. Moreover, 92% of the samples contained very hard water, because they exceeded the value (180 mg/L), which characterize the hard water. Table 1 shows that 31.8% of the measured samples exceeded the guideline value (250 mg/L) for chloride in drinking water set by WHO [6]. Contamination of drinking groundwater by chloride is due to some anthropogenic sources of chloride in groundwater which are road salt, animal and human waste, and agricultural activities such as fertilizers [22].
In total, eight samples showed high levels of major elements Na, Mg, and Ca ( Concentration levels (μg/L) of all measured trace elements are shown in Table 3 for the 25 collected groundwater samples. e mean concentrations (μg/L) of the trace elements in increasing order were as follows: is is presented in Table 4. Ten trace elements (V, Cr, Mn, Co, Ni, Cu, Zn, As, Cd, and Pb) did not exceed the guideline levels set by the WHO [6]. Seven elements (Co, Cd, Cu, Cr, Ni, Pb, and As) had a mean concentration of less than 1 μg/L. However, one trace element (Se) was reported to have a higher level in some samples. In total, nine samples for Se were reported to exceed the guideline levels related to Se (10 μg/L) as shown in Table 3.
SPSS was used as shown in Table 4, to perform a correlation of 15 major and trace elements in 23 samples. 25 significant (p < 0.05) correlations were reported. irteen and twelve correlations were significant at the 0.01 and at the 0.05 levels, respectively. ree and twenty-two correlations were negative and positive, respectively. All the three negative correlations were related to Vanadium as follows: V/ Mn, V/Cu, and V/Zn. e twenty-two positive correlations were thirteen at the 0.01 level (Na/Mg, Na/Ca, Na/Co, Na/Se, Mg/K, Mg/Ca, Mg/Se, Ca/Se, Mn/Cu, Co/Ni, Ni/Pb, and Cd/ Pb). e twelve at the 0.05 level were Na/Mg, Mg/Co, K/Cd, Ca/Co, Cr/Cd, Cr/Pb, Co/As, Co/Cd, Ni/As, and negative correlations were V/Mn, V/Cu, and V/Zn. All major elements (Ca, Mg, and Na) had positive correlations with each other and also with Co and Se, except K. Only Mg showed a correlation with K (Mg/K). Remarkably, the two toxic elements Cd and Pb had a significant correlation (Cd/Pb, 0.85 * * ).
ANOVA was performed, by using SPSS (version 20) at a 95% confidence interval to determine the differences among the samples. e differences were related to the levels of variances such as parameters (EC, pH, TDS, and TH) anion (Cl − ), major elements (Na, Mg, Ca, and K), and trace elements (V, Cr, Mn, Co, Ni, Cu, Zn, As, Se, Cd, and Pb). All samples were divided into three groups: Bisha South, Bisha North, and the rest of the samples. pH showed a significant difference (p < 0.05) between Bisha samples (North and South) and the rest of the group. Among Bisha samples, there was no significant difference (p > 0.05). EC and TDS showed a significant difference (p < 0.05) between Bisha samples (North) and the rest of the samples. TH showed no significant difference (p > 0.05) between all groups. e Cl − only showed significant differences between Bisha North sample and the rest of the samples. For major elements, only Na showed significant differences (p < 0.05) between Bisha North sample and the rest of the samples. However, Ca, Mg, and K showed no significant difference (p > 0.05) between all groups. For trace elements, only V showed significant differences. V showed significant differences (p < 0.05) between Bisha samples (North and South) and the rest of the samples. For other trace elements (Cr, Mn, Co, Ni, Cu, Zn, As, Se, Cd, and Pb), no significant difference (p > 0.05) was reported.
Elements in drinking water are divided into major and trace elements. Trace elements are divided into four ranges based on their availability/concentrations (μg/L): 0.1-1 (V, Se, As, Cd, Co, Ni, Cr, Pb, and Al), 1-10 (Li, Ba, Cu, Mn, and U), 10-100 (P, B, Fe, and Zn), and 100-1000 (Sr). e major elements (mg/L) are divided into three ranges based on their concentrations: 1-10 (Mg, K, and Si), 10-100 (Na and Ca), and >100. Further, these elements are divided into essential (Se, Mn, Fe, Cu, Ni, Co, Cr, V, Li, P, Sr, Mg, K, Na, and Ca) and toxic elements (As, Cd, Pb, Al, U, and B) [23].    Journal of Chemistry Overall, a mean of 78.95% of the measured trace and major elements was within the expected ranges (as mentioned above). is is a promising result that shows that the majority of the measured elements are within the acceptable range in drinking water. e investigated groundwater samples in this study were shown to be sources of major and trace elements. Se was reported to have the highest concentrations among the trace elements in the five groundwater samples. erefore, 20% of the collected samples were not suitable for drinking because of the high level of Se. Four samples had high levels of Se and contained Na, Mg, and Ca: Aboy, Hassan, Bisha unia-1, and Damakh. is means that besides naturally occurring elements, these samples were shown to have high water hardness as well.

Sodium.
e guideline for sodium in drinking water is 200 mg/L by WHO [6]. However, there is no health effect associated with a specific high level of ingested sodium for humans. Previous cases reported health effects related to the overdose of sodium chloride, which included vomiting, nausea, convulsions, cerebral effects, pulmonary oedema, and muscular twitching [24]. In addition, it was also reported that the ingestion of a high level of sodium in drinking water and the intake of excessive salt could seriously worsen chronic congestive heart failure. A study by [25] investigated the presence of a high level of sodium in drinking water and its relationship with high blood pressure. e study investigated two communities with similar socioeconomic parameters and exposed them to sodium in drinking water-one group was exposed to 405 mg/L and the other group was exposed to 5 mg/L. e study concluded that there was no significant difference in systolic blood pressure between groups, but there was a significant difference in diastolic blood pressure. e sodium adsorption ratio (SAR) was calculated as shown in (1) [26] to determine the suitability of the groundwater in this study either for drinking or for irrigation. e range of SAR was between 2.31 and 65.77 large. Many samples (26.1%) had SAR values of >26, which is not suitable for irrigation because SAR values of up to 18 are safe for irrigation [27,28]. (1)

Water Hardness: Magnesium and Calcium.
Water hardness is defined as the capacity of water to react with soap to produce lather. Further, water hardness can be temporary (carbonate) or permanent (noncarbonate). e water hardness is expressed as mg/L calcium carbonate. Water hardness is mainly defined by the presence of Ca and Mg salts. Nevertheless, other cations contribute to water hardness, such as Al, Mn, Zn, Br, Sr, and Fe. e water hardness is classified into four classes based on CaCO 3 concentration (mg/L): below 60 (soft), 60-120 (moderately hard), 120-180 (hard), and higher than 180 (very hard) [29].
ere is no clear evidence that water hardness can cause a diverse health effect on humans. Previous studies appeared to show an opposite casual association between water hardness and human health, specifically cardiovascular disease [30,31,32]. In contrast, other studies showed adverse health effects related to water softness (less than 75 mg/L), which affects the mineral balance [33]. erefore, there is an ongoing debate about the protective effect of water hardness and/or magnesium related to cardiovascular mortality. Numerous epidemiological studies have demonstrated a relationship between water hardness and reproductive failure, cardiovascular disease, and growth retardation. Absorption of magnesium and calcium in the renal tubules is caused by acidic water [34]. Accordingly, people must be cautious when drinking hard water due to the ambiguity surrounding the relationship between some diseases and drinking hard water. e effect of water softness and hardness on human health seems to be connected with the well-known ecological law of optimum according to which both extremely high and unusually low levels of these or that parameter are harmful to living beings.

Journal of Chemistry
Regarding magnesium, four samples (Aboy, Sahl, Bisha unia-1, and Alalyani) had higher concentrations than 150 mg/L (30-150 mg/L), the value that was set by Saudi Arabian Standards Organization [29]. e values were in the range of 155.75 to 309.25 mg/L. Regarding calcium, seven samples (Aboy, Sahl, Hassan, Bisha unia, Damakh, Alalyani, and Bisha unia-1) had higher concentrations than 200 mg/L; this value was set by WHO [35]. e values for the abovementioned seven samples were in the range from 220 to 3140 mg/L, which exceeds the permissible value.
Total permanent hardness is the sum of calcium hardness plus magnesium hardness, which is the concentration of calcium and magnesium ions and is equivalent to mg/L CaCO 3 . We found that 92% of our samples contained very hard water-higher than 180 mg/L. e water hardness was determined by titration, as detailed in Section 2.1.

Selenium.
Nine samples (36%) exceeded the guideline value (40 μg/L) set by the WHO [7]. e levels (μg/L) of selenium in the samples were presented in Table 4 for the following samples: Aboy, Sahl, Hajes, Hassan, Bish unaia-1, Damakh, Alain Elharah, Alalyani, and Shahrani (Table 4). e rest of the samples were in the range of 2.12 to 7.79 μg/L, and the mean value for the 25 samples was 23.85 μg/L.
Se is abundant in clay-rich sedimentary rocks (shales and mudstone) due to its affinity for clay minerals [36,37]. e existence of Se in groundwater is due to the mobilization of selenium by irrigation or rainwater from selenium-rich soils and bedrock [38,39]. Exposure to a high level of selenium causes a decrease in sperm count, an increase in abnormal sperm, and disturbance of the menstrual cycle in monkeys. However, there is no evidence that it causes any changes in other mammals or the human reproductive system. Redundant selenium that enters the human body will be excreted in feces and urine. Nevertheless, exposure to a high level will cause the chemical form of selenium to build up in the human body. Mainly, selenium builds up in the lungs, liver, kidneys, testes, heart, and blood [40]. A recent study [41] was performed on groundwater from Makkah, Saudi Arabia, in 168 wells. eir results showed a selenium range of 3.12-22.22 μg/L, with a mean of 11.08 μg/L. ey reported that 61% of their samples exceeded the WHO guideline value. erefore, their results showed a higher percentage of samples exceeding the guideline value compared with our results. A previous study [42] investigated the concentrations of arsenic, antimony, and selenium in 49 samples of groundwater from the western region of Poland. ey reported less than 0.15 μg/L for selenium and concluded that the presence of selenium is due to geogenic factors. Table 4 presented 25 significant correlations for measured elements among all investigated samples. Major elements (Na, Ca, and Mg) were correlated together except K. e three major elements showed a correlation with only Co and Se, which means that they have a similar distribution in the investigated samples. pH and V showed a significant difference (p < 0.05) between Bisha samples (North and South) and the rest of the samples. e Bisha (North) samples were significantly different (p < 0.05) from the rest of the samples for EC, pH, TDS, and TH and Cl − . Fourteen elements Na, K, Mg, Ca, Cr, Mn, Co, Ni, Cu, Zn, As, Se, Cd, and Pb showed no significant differences (p > 0.05) among the investigated samples.
is indicates that their mean concentrations had no significant difference (p < 0.05) between the investigated samples.

Conclusions
Regarding trace elements, 36% of the samples exceeded the guideline value set by the WHO for Se. For the major elements, there were eight, six, and seven samples that exceeded the guideline values for Na, Mg, and Ca, respectively. A high percentage (92%) of samples showed very hard water, and one sample was moderately hard. erefore, the groundwater in this study is not suitable to be used for drinking due to water hardness. In addition, based on SAR values, 26.1% of all samples are not even suitable for irrigation. Moreover, high percentages (32%) of the measured samples are not potable due to high levels of chloride. A 25 significant (p < 0.05) correlations were reported among both major and trace elements. Major elements (Ca, Mg, and Na) had positive correlations among each other and two trace elements (Co and Se), except K, which had only one correlation with Mg. We conclude that these three major elements had a similar distribution in investigated samples. Noticeably, both toxic elements Cd and Pb had high significant correlation at the 0.01 level. A significant (p < 0.05) negative correlation was reported for V/Mn, V/Cu, and V/Zn, which means that these elements were inversely distributed in the studied samples. From ANOVA analysis, Na, Cl − , EC, and TDS showed a significant difference (p < 0.05) between Bisha samples (North) and the remaining samples. Only V and pH showed a significant difference (p < 0.05) between Bisha samples (North and South) and the remaining samples. No significant differences (p > 0.05) were reported for Na, K, Mg, Ca, Cr, Mn, Co, Ni, Cu, Zn, As, Se, Cd, and Pb between all samples. We conclude that there were no significant differences between the means of concentrations of these fourteen measured elements of all samples from different locations in Bisha region. Large numbers of samples are needed to endorse our outcomes in the study region.

Data Availability
e data used to support the findings of this study will be provided upon request.

Conflicts of Interest
e authors declare no conflicts of interest.