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Article Health Risk Assessment of Nitrate and Fluoride in the Groundwater of Central Saudi Arabia

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10 May 2023

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15 May 2023

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Abstract
High nitrate and fluoride contamination in groundwater cause a variety of disorders, including methemoglobinemia, teratogenesis, and dental and skeletal fluorosis. The present work assesses the non-carcinogenic health risks posed by nitrate and fluoride in infants, children, and adults using the USEPA method. Groundwater samples were collected from 36 wells and boreholes in three central Saudi Arabia study areas. Nitrate concentrations varied from 0.70 to 47.00 mg/L. None of the 36 studied boreholes had nitrate levels that exceeded WHO guidelines (50.00 mg/L). Fluoride ranged from 0.63 to 2.00 mg/L, and 30.55% of the fluoride samples (11 out of 36) exceeded the WHO recommendations for acceptable drinking water (1.5 mg/L). The average hazard index (HI) values for adults, children, and infants were 0.99, 2.59, and 2.77, respectively. Water samples surpassed the safety level of 1 for adults, children, and infants at 44.44, 97.22, and 100%, respectively. Accordingly, water samples from Jubailah and a few from Wadi Nisah may expose infants, children, and adults to non-cancer health concerns. Infants and children are more vulnerable to non-carcinogenic health risks than adults, possibly due to their lower body weight.
Keywords: 
Subject: 
Environmental and Earth Sciences  -   Pollution

1. Introduction

Groundwater is an important resource for drinking and irrigation, especially in dry and semi-arid regions [1,2]. However, shallow groundwater is vulnerable to contamination from various geogenic and anthropogenic sources, such as rock weathering, cation exchange during oxidation or reduction, rapid industrialization, urbanization, and excessive fertilizer use [3,4]. Recently, there has been a growing concern about groundwater quality and its influence on human health due to water consumption with high concentrations of nitrate and fluoride. Nitrate and fluoride concentrations in groundwater can negatively affect human health. These two toxic ions are listed as non-carcinogens by the US Environmental Protection Agency (USEPA) and have received worldwide attention for their devastating effects on human health [2].
Nitrate is an inorganic ion (NO3−) that naturally occurs in the nitrogen cycle and is widely found in nitrogen-containing fertilizers. Nitrate can enter groundwater through different natural and anthropogenic sources, e.g., rock-water interaction from the weathering of nitrite-bearing rocks, septic tanks, dairy lagoons, wastewater effluents, livestock waste, agricultural land, landfill leachate, fertilizers, pesticides, and manure application [5,6]. High levels of NO3 in water bodies and drinking water create eutrophication, toxic algal blooms, and various diseases, including blue infant disorder (methemoglobinemia), thyroid disorders, teratogenesis, and mutagenesis [2,7,8]. Pregnant women, infants, and young children are most susceptible to the harmful effects of NO3 [9].
The USEPA lists fluorine as a potentially harmful chemical pollutant [10,11]. Fluoride enters water bodies through natural and artificial sources, e.g., weathering of fluoride-bearing minerals, aluminum smelters, coal-based power stations, phosphatic fertilizer plants, brick manufacturing, steel production, coal combustion, sewerage, over-withdrawal of groundwater, and electroplating industries [12,13]. Drinking water with excessive fluoride can cause side effects including tooth decay (0.50 mg/L), fluorosis (1.50–5 mg/L), and skeletal fluorosis (5–40 mg/L) [14,15]. Arthritis, neurological problems, thyroid disease, cancer, infertility, hypertension, and a low fetus-to-sperm ratio are all linked to high fluoride concentrations (> 10 mg/L). Moreover, fluoride alters DNA structure, which impacts teeth and bones [14,16].
The groundwater in central Saudi Arabia has been subjected to intense study in the last two decades regarding water resources, groundwater quality for drinking and agricultural usage, and general hydrochemical evaluations ([e.g., 17–23]. Previous studies in the Northwest Riyadh area indicated that average concentrations of TDS, Ca2+, Na+, K+, Cl−, SO42−, and F− exceeded the WHO’s permissible limits for drinking water. The evaluation of groundwater quality from Wasia and Biyadh aquifers in Wasia Well Field (Northeast Riyadh) concluded the suitability of Wasia samples for drinking and agricultural purposes but not for industrial ones. Conversely, water samples from Biyadh are unsuitable for drinking, industrial, or agricultural purposes. Furthermore, the groundwater quality in Wadi Nisah, south of Riyadh, is unsuitable for drinking. Previous studies concluded that extensive and repeated irrigation could increase ion levels in general. They attributed the higher NO3− and F− values to the widespread application of fertilizers and pesticides in the study area. None of the studies on groundwater in central Saudi Arabia treated the impacts of nitrate and fluoride on human health. Therefore, we aimed to examine the distribution of NO3− and F− in the groundwater of three areas in central Saudi Arabia and document the role of geology, aquifer depths, and agriculture activity on NO3− and F− levels. Moreover, we sought to determine the impact of NO3− and F− contamination on adults, children, and infants’ health using a methodology suggested by the USEPA. The results of this investigation will benefit risk management, safeguarding groundwater quality, and health professionals’ decision-making.

2. Geological Setting

The exposed sedimentary succession in central Saudi Arabia is represented mainly by Triassic–Cretaceous rocks and subdivided into the following formations from older to younger: Minjur, Marrat, Dhruma, Tuwaiq Mountain Limestone, Hanifa, Jubaila, Arab, Hith, Wasia, and Aruma formations. The Jurassic and Cretaceous rocks in central Saudi Arabia have been described from many points of view, such as stratigraphy, paleontology, sedimentology, and depositional history ([e.g., 24–38].
The major aquifer systems identified in the Wasia Well Field are Wasia (Middle Cretaceous) and Biyadh (Lower Cretaceous). Both Biyadh and Wasia have a primarily continental origin. The Biyadh aquifer has mainly cross-bedded quartzite and sandstone with some thin shale, marl, dolomite, and ironstone. The Wasia aquifer comprises medium- to coarse-grained, well-sorted, non-cemented, and poorly cemented rock. The Wadi Nisah area consists of sedimentary formations ranging from the Upper Triassic to the Quaternary period, with outcrops decreasing in age from west to east. Hydrogeologically, the study area consists of a multi-layered aquifer system with the Manjur, Biyadh, and Jurassic Limestone Formations, Cretaceous Wasia, and Quaternary alluvial deposits forming the main water supply sources.

3. Material and Methods

Groundwater samples were collected from 36 groundwater wells, mainly used for agricultural water supply in central Saudi Arabia: 12 from Wadi Nisah, 14 from the Al Jubailah area, and 10 from the Wasia Well Field (Figure 1). The Al Jubailah area is located 40–55 km northwest of Riyadh, at 24°53′14.4″ to 24°54′59.4″ N and 46°20′41.5″ to 46°25′47.2″ E in Wadi Hanifa, which runs south through Riyadh. The Wasia Well Field is located some 110 km northeast of Riyadh between latitudes 25°09’ and 25°14’N and longitudes 47°28’–47°33’ E. The samples were collected in pre-rinsed plastic bottles and filtered through 0.45-mm pore-size filters. Nitric acid was added to the samples for preservation, and the bottles were stored in cooling boxes at temperatures below 5 °C. F− and NO3− levels were analyzed using standard analytical procedures in the laboratories of King Saud University.
In this study, we assessed the danger that NO3− and F− pose to human health for adults, children, and infants via the oral channel. The following equations calculate the daily water intake (CDI), hazard quotient (HQ), and non-carcinogenic hazard index (HI) associated with drinking water [39,40].
CDI = (C × DI × F × ED)/(BW × AT)
HQ = CDI/RfD
HI = Σ (HQfluoride + HQnitrate)
where C is the concentration of nitrate and fluoride in the water in milligrams per liter; DI is the amount of water consumed daily in liters; F is the number of days per year of exposure; ED is the number of years of exposure; BW is the weight of the age group under consideration in kilograms; AT is the average timing in days; and RfD is the reference dose (NO3− = 1.6 and F− = 0.06 mg/kg/day) [41]. Table 1 describes the parameter values applied to health exposure assessment.

4. Results and Discussion

4.1. Concentration and Distribution of Nitrate and Flouride

The nitrate concentration in the study areas varied from 0.70 mg/L in borehole 33 (Wasia Well Field) to 47.0 mg/L in borehole 22 (Jubailah), with an average of 22.59 mg/L (Table 2). None of the 36 boreholes studied had nitrate levels exceeding WHO guidelines (50.0 mg/L). However, by comparing these three study areas, we noticed that the lowest nitrate levels were recorded in Wasia Well Field, averaging 2.79 mg/L. By contrast, the highest concentrations were recorded in Jubailah, averaging 37.93 mg/L. The Wadi Nisah levels fell in between, averaging 21 mg/L (Figure 2). Similarly, fluoride ranged from 0.63 mg/L in borehole 31 from Wasia Well Field to 2.00 mg/L in borehole 25 from Jubailah, averaging 1.23 mg/L. Eleven out of thirty-six fluoride samples (30.55%) exceeded the WHO’s acceptable limit for drinking water (1.5 mg/L). The lowest nitrate levels were recorded in Wasia Well Field, averaging 0.82 mg/L, whereas the highest concentrations were recorded in Jubailah, averaging 1.70 mg/L. Wadi Nisah fell in between, averaging 1.00 mg/L (Figure 3).
The Al Jubailah area is a valley that consists primarily of palm farms alongside vegetables and fruits. The region’s irrigation source is shallow groundwater (25–100 m) resulting from flood waters. This region’s increased nitrate and fluoride concentrations may be due to intensive farming conditions and pollutants from heavy fertilizer use and sanitation. Some of these pollutants may also be due to the region’s rocky origin. On the contrary, the Wasia Well Field region is quite far from agricultural areas, and the groundwater is deeper (180–300 m), which is fossil water to some extent. The rocks in the aquifer are fine sandstones. Therefore, nitrate and fluoride concentrations are the lowest in these study areas. The Wadi Nisah area is a valley that collects water from other valleys. The valley has many palm farms and renewable groundwater, which decreases nitrate and fluoride levels. Compared to the Wadi Al Jubailah area, the farming area in the Wasia Well Field is significantly lower.

4.2. Human Health Risk

Fluoride and nitrate are two of the most frequent and pervasive contaminants in many groundwater supplies, making water contamination a major environmental problem. Excessive nitrate levels in drinking water have been linked to various human health issues, including gastrointestinal cancers, methemoglobinemia, Alzheimer’s disease, vascular dementia, and multiple sclerosis [42]. Furthermore, high and low fluoride doses in water can be dangerous [43]. Nitrate’s chronic daily intake (CDI) values (mg/kg/d) for adults, children, and infants ranged from 0.020 to 1.343 (average of 0.646), 0.053 to 3.525 (average of 1.695), and 0.056 to 3.76 (average of 1.808), respectively. The CDI values for fluoride in adults, children, and infants varied from 0.018 to 0.057 (average of 0.035), 0.047 to 0.150 (average of 0.092), and 0.050 to 0.160 (average of 0.098), respectively (Table 3). The average HQ values of nitrate and fluoride for adults, children, and infants were 0.40 and 0.58; 1.06 and 1.53; and 1.13 and 1.64, respectively (Table 4).
The hazard index (HI) ranged from 0.37 to 1.74 (average of 0.99) for adults, 0.98 to 4.56 (average of 2.59) for children, and 1.05 to 4.87 (average of 2.77) for infants (Table 4, Figure 4). Groundwater samples surpassed the safety level of 1 by 44.44 (16 out of 36), 97.22 (35 out of 36), and 100% for adults, children, and infants, respectively (Figure 4). According to the study’s findings, drinking water in most of the study areas, particularly in water samples from Jubailah (boreholes 13–26) and a few from Wadi Nisah (boreholes 5 and 10), could expose infants, children, and adults to non-cancer health concerns. Additionally, our findings show that infants and children are more vulnerable to non-carcinogenic health risks than adults, possibly due to their lower body weights. Many researchers worldwide obtained similar results assessing health risks caused by nitrate and fluoride in groundwater, e.g., in Northwest China [44] (Chen et al., 2016); Western Khorasan Razavi, Iran [45] (Qasemi et al., 2019); Medchal area, South India [11] (Duvva et al., 2022); and Noyyal basin, India [2] (Kom et al., 2022).

5. Conclusions

We evaluated the health effects of nitrate and fluoride in central Saudi Arabia. Our findings indicated that none of the 36 studied boreholes had nitrate levels above WHO guidelines (50.00 mg/L). By contrast, 11 out of 36 areas had fluoride levels exceeding the acceptable limit for drinking water (1.5 mg/L). The lowest nitrate and fluoride levels were recorded in the Wasia Well Field area, whereas the highest concentrations were recorded in the Jubailah area. The increased nitrate and fluoride concentrations in Jubailah may be attributed to intensive palm farms and the region’s heavy use of fertilizers and sanitation. The water samples had HI values exceeding the safety level for adults, children, and infants at 44.44, 97.22, and 100%, respectively. Infants and children are more vulnerable to non-carcinogenic health risks than adults due to their lower body weight.

Author Contributions

Conceptualization, T.A. and A.S.E.-S.; methodology, T.A. and A.S.E.-S.; software, T.A. and A.S.E.-S.; writing—original draft preparation, T.A. and A.S.E.-S.; writing—review and editing, T.A. and A.S.E.-S. All authors have read and agreed to the published version of the manuscript.

Funding

Researchers Supporting Project number (RSP2023R791), King Saud University, Riyadh, Saudi Arabia.

Informed Consent Statement

Not applicable.

Data Availability Statement

All data generated or analyzed during this study are included in this published article.

Acknowledgments

The authors extend their appreciation to Researchers Supporting Project number (RSP2023R791), King Saud University, Riyadh, Saudi Arabia. Moreover, the authors thank the anonymous reviewers for their valuable suggestions and constructive comments.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Locations of the groundwater samples in central Saudi Arabia. a. Wadi Nisah, b. Al Jubaillah, C. Location of study in Saudi Arabia, d. Wasia Well Field.
Figure 1. Locations of the groundwater samples in central Saudi Arabia. a. Wadi Nisah, b. Al Jubaillah, C. Location of study in Saudi Arabia, d. Wasia Well Field.
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Figure 2. Distribution of nitrate concentrations (mg/L) in the groundwater of the study areas.
Figure 2. Distribution of nitrate concentrations (mg/L) in the groundwater of the study areas.
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Figure 3. Distribution of fluoride concentrations (mg/L) in groundwater of the study areas.
Figure 3. Distribution of fluoride concentrations (mg/L) in groundwater of the study areas.
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Figure 4. Non-carcinogenic risks induced by fluoride and nitrate in drinking water.
Figure 4. Non-carcinogenic risks induced by fluoride and nitrate in drinking water.
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Table 1. Parameters applied for health exposure assessment through drinking water and hazard index classification of in this work.
Table 1. Parameters applied for health exposure assessment through drinking water and hazard index classification of in this work.
Risk Exposure Factors Unit Adults Children Infants
DI L/d 2 1.5 0.8
F d/year 365 365 365
ED years 40 10 1
BW kg 70 20 10
AT d 14,600 3650 365
HI ≤1 no health risk to humans
HI >1 higher level of hazard
Table 2. Concentrations of nitrate and fluorite in the study areas.
Table 2. Concentrations of nitrate and fluorite in the study areas.
S.N. Lat. Long. Nitrates Fluoride S.N. Lat. Long. Nitrates Fluoride
1 24.16958 46.10469 18 0.92 21 24.90678 46.39139 36 1.3
2 24.16344 46.21425 16 0.86 22 24.89717 46.39886 47 1.8
3 24.40542 46.22508 26 0.86 23 24.90225 46.40614 40 1.5
4 24.17483 46.43194 16 1.1 24 24.90211 46.41181 43 1.7
5 24.36869 46.44094 32 1.32 25 24.899 46.41792 44 2
6 24.35672 46.57375 24 0.87 26 24.89272 46.42953 42 1.8
7 24.28703 46.75603 20 0.91 27 25.16055 47.5633 5.1 1.12
8 24.26814 46.80336 18 0.95 28 25.17417 47.56645 2.1 1.05
9 24.21053 46.97817 19 1.05 29 25.17642 47.55445 3.2 0.7
10 24.19528 47.08814 28 1.11 30 25.18752 47.55073 4.7 0.65
11 24.1885 47.19881 22 1.12 31 25.19228 47.54542 4.8 0.63
12 24.18442 47.25731 13 0.88 32 25.19123 47.51897 1.3 0.87
13 24.89375 46.34486 33 1.5 33 25.21192 47.50437 0.7 0.76
14 24.89539 46.3575 28 2 34 25.2234 47.50117 2.1 0.88
15 24.89628 46.36517 46 1.7 35 25.2195 47.487 1.1 0.78
16 24.90889 46.37775 18 2 36 25.23465 47.49712 2.8 0.79
17 24.9165 46.37911 44 1.3 Min. 0.7 0.63
18 24.89706 46.38039 44 1.9 Max. 47 2
19 24.88733 46.38731 26 1.8 Aver. 22.59 1.23
20 24.90019 46.39144 40 1.5
1–12 (Wadi Nisah); 13–26 (Jubailah); 27–36 (Wasia Well Field).
Table 3. Chronic daily intake (CDI) (mg/kg/d) of nitrate and fluoride for adults, children, and infants.
Table 3. Chronic daily intake (CDI) (mg/kg/d) of nitrate and fluoride for adults, children, and infants.
S.N. NO3− CDI F− CDI
Infants Children Adults Infants Children Adults
1 18 1.44 1.35 0.514 0.92 0.074 0.069 0.026
2 16 1.28 1.2 0.457 0.86 0.069 0.065 0.025
3 26 2.08 1.95 0.743 0.86 0.069 0.065 0.025
4 16 1.28 1.2 0.457 1.1 0.088 0.083 0.031
5 32 2.56 2.4 0.914 1.32 0.106 0.099 0.038
6 24 1.92 1.8 0.686 0.87 0.07 0.065 0.025
7 20 1.6 1.5 0.571 0.91 0.073 0.068 0.026
8 18 1.44 1.35 0.514 0.95 0.076 0.071 0.027
9 19 1.52 1.43 0.543 1.05 0.084 0.079 0.03
10 28 2.24 2.1 0.8 1.11 0.089 0.083 0.032
11 22 1.76 1.65 0.629 1.12 0.09 0.084 0.032
12 13 1.04 0.98 0.371 0.88 0.07 0.066 0.025
13 33 2.64 2.48 0.943 1.5 0.12 0.113 0.043
14 28 2.24 2.1 0.8 2 0.16 0.15 0.057
15 46 3.68 3.45 1.314 1.7 0.136 0.128 0.049
16 18 1.44 1.35 0.514 2 0.16 0.15 0.057
17 44 3.52 3.3 1.257 1.3 0.104 0.098 0.037
18 44 3.52 3.3 1.257 1.9 0.152 0.143 0.054
19 26 2.08 1.95 0.743 1.8 0.144 0.135 0.051
20 40 3.2 3 1.143 1.5 0.12 0.113 0.043
21 36 2.88 2.7 1.029 1.3 0.104 0.098 0.037
22 47 3.76 3.53 1.343 1.8 0.144 0.135 0.051
23 40 3.2 3 1.143 1.5 0.12 0.113 0.043
24 43 3.44 3.23 1.229 1.7 0.136 0.128 0.049
25 44 3.52 3.3 1.257 2 0.16 0.15 0.057
26 42 3.36 3.15 1.2 1.8 0.144 0.135 0.051
27 5.1 0.408 0.38 0.146 1.12 0.09 0.084 0.032
28 2.1 0.168 0.16 0.06 1.05 0.084 0.079 0.03
29 3.2 0.256 0.24 0.091 0.7 0.056 0.053 0.02
30 4.7 0.376 0.35 0.134 0.65 0.052 0.049 0.019
31 4.8 0.384 0.36 0.137 0.63 0.05 0.047 0.018
32 1.3 0.104 0.1 0.037 0.87 0.07 0.065 0.025
33 0.7 0.056 0.05 0.02 0.76 0.061 0.057 0.022
34 2.1 0.168 0.16 0.06 0.88 0.07 0.066 0.025
35 1.1 0.088 0.08 0.031 0.78 0.062 0.059 0.022
36 2.8 0.224 0.21 0.08 0.79 0.063 0.059 0.023
Table 4. The Hazard Quotient (HQ) and Hazard Index (HI) for fluoride and nitrate in adults, children, and infants.
Table 4. The Hazard Quotient (HQ) and Hazard Index (HI) for fluoride and nitrate in adults, children, and infants.
S.N. HQ Nitrates HQ Fluoride HI
Infants Children Adults Infants Children Adults Infants Children Adults
1 0.9 0.844 0.321 1.227 1.15 0.438 2.127 1.994 0.76
2 0.8 0.75 0.286 1.147 1.075 0.41 1.947 1.825 0.695
3 1.3 1.219 0.464 1.147 1.075 0.41 2.447 2.294 0.874
4 0.8 0.75 0.286 1.467 1.375 0.524 2.267 2.125 0.81
5 1.6 1.5 0.571 1.76 1.65 0.629 3.36 3.15 1.2
6 1.2 1.125 0.429 1.16 1.088 0.414 2.36 2.213 0.843
7 1 0.938 0.357 1.213 1.138 0.433 2.213 2.075 0.79
8 0.9 0.844 0.321 1.267 1.188 0.452 2.167 2.031 0.774
9 0.95 0.891 0.339 1.4 1.313 0.5 2.35 2.203 0.839
10 1.4 1.313 0.5 1.48 1.388 0.529 2.88 2.7 1.029
11 1.1 1.031 0.393 1.493 1.4 0.533 2.593 2.431 0.926
12 0.65 0.609 0.232 1.173 1.1 0.419 1.823 1.709 0.651
13 1.65 1.547 0.589 2 1.875 0.714 3.65 3.422 1.304
14 1.4 1.313 0.5 2.667 2.5 0.952 4.067 3.813 1.452
15 2.3 2.156 0.821 2.267 2.125 0.81 4.567 4.281 1.631
16 0.9 0.844 0.321 2.667 2.5 0.952 3.567 3.344 1.274
17 2.2 2.063 0.786 1.733 1.625 0.619 3.933 3.688 1.405
18 2.2 2.063 0.786 2.533 2.375 0.905 4.733 4.438 1.69
19 1.3 1.219 0.464 2.4 2.25 0.857 3.7 3.469 1.321
20 2 1.875 0.714 2 1.875 0.714 4 3.75 1.429
21 1.8 1.688 0.643 1.733 1.625 0.619 3.533 3.313 1.262
22 2.35 2.203 0.839 2.4 2.25 0.857 4.75 4.453 1.696
23 2 1.875 0.714 2 1.875 0.714 4 3.75 1.429
24 2.15 2.016 0.768 2.267 2.125 0.81 4.417 4.141 1.577
25 2.2 2.063 0.786 2.667 2.5 0.952 4.867 4.563 1.738
26 2.1 1.969 0.75 2.4 2.25 0.857 4.5 4.219 1.607
27 0.255 0.239 0.091 1.493 1.4 0.533 1.748 1.639 0.624
28 0.105 0.098 0.038 1.4 1.313 0.5 1.505 1.411 0.538
29 0.16 0.15 0.057 0.933 0.875 0.333 1.093 1.025 0.39
30 0.235 0.22 0.084 0.867 0.813 0.31 1.102 1.033 0.393
31 0.24 0.225 0.086 0.84 0.788 0.3 1.08 1.013 0.386
32 0.065 0.061 0.023 1.16 1.088 0.414 1.225 1.148 0.438
33 0.035 0.033 0.013 1.013 0.95 0.362 1.048 0.983 0.374
34 0.105 0.098 0.038 1.173 1.1 0.419 1.278 1.198 0.457
35 0.055 0.052 0.02 1.04 0.975 0.371 1.095 1.027 0.391
36 0.14 0.131 0.05 1.053 0.988 0.376 1.193 1.119 0.426
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