# Assessment of Heavy Metals Concentration in Arsenic Contaminated Groundwater of the Chaco Plain, Argentina

Authors: M. Cecilia Giménez; Patricia S. Blanes; Edgar E. Buchhamer; Rosa M. Osicka; Yamila Morisio; Silvia S. Farías
Journal: ISRN Environmental Chemistry
 (2013)

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## Abstract

The occurrence and distribution of arsenic and 23 other trace elements have been investigated in groundwater from Comandante Fernández Department in the Central region of Chaco Province, Northern Argentine. The arsenic concentrations samples ranged between 0.7 to 1990 µg L−1; 91% (n=45) exceeds the 10 µg L−1 World Health Organization (WHO) provisional standard limits for drinking water. Fluorine was detected in 31% of groundwater samples. Furthermore, there was found a significant correlation between As and F (r2=0.50), indicating an association in the prevalence of both elements. In addition, about 78%, 31%, 16%, 13%, and 4.5% of groundwater samples had, respectively, B, Fe, Al, Mn, and Sb exceeding Código Alimentario Argentino (CAA) guideline values. In contrast of the previously values descript, the corresponding to Cr, Be, Ni, Pb, Ag, Se, and Zn were found below the quantification limit. The presence of As and trace elements in groundwater represents an important issue because it can cause a public health problem.


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## Body

## 1. Introduction

Among known pollutants, trace elements are widely recognized as being potentially toxic to living organisms. Water contamination with heavy metal (HM) are mainly determined by natural (i.e., weathering, erosion of bed rocks, and ore deposits) [1] and anthropogenic (i.e., mining, industries, and agriculture) processes [2].Soils and water containing high levels of arsenic and other toxic trace elements can easily contaminate plants, animals, and human beings in contact with them, as they either produce toxic effects or accumulate in plants and thereby enter animal and human food chains [3].Certain elements like sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), copper (Cu), cobalt (Co), and zinc (Zn) are essentially required by living organisms in specific concentrations but may produce toxic effects in high concentrations [2]. The main threats to human health from HM are associated with exposure to lead (Pb), mercury (Hg), cadmium (Cd) and arsenic (As), which are extremely prejudicial owing to their toxicity, long persistence, and bioaccumulative nature [4]. Their toxic effects include headache, hypertension, irritability, abdominal pain, nerve damages, liver and kidney problems, sideroblastic anemia, intellectual disabilities, fatal cardiac arrest, and carcinogenesis. These metals have been extensively studied and their effects on human health regularly reviewed by international bodies such as the WHO [5].Long-term drinking of arsenic contaminated water can cause severe skin diseases including skin cancer; lung, bladder, and kidney cancers, and perhaps other internal tumors; peripheral vascular disease; hypertension; and diabetes [6, 7]. It also seems to have a negative impact on reproductive processes (infant mortality and weight of newborn babies) and cardiovascular diseases [8].The occurrence of high concentrations of As and trace elements in drinking water has been recognized, over the past two or three decades, as a great public health concern in several parts of the world [6, 9]. The Chaco-Pampean plain is the largest one in Latin America and one of the largest geographic units in the world affected by As-contaminated groundwater [10]. In the Chaco plain (north of the Chaco-Pampean plain), the major source of arsenic in groundwater is chemical weathering of the rocks, and no anthropogenic sources of contamination have been reported [11].Particularly, it has been identified that there are elevated As concentrations in groundwater and reported in different regions of Argentina such as La Pampa [1], Buenos Aires [9], Chaco [11], Cordoba [12], Santiago del Estero [13], Santa Fe [14], and Tucumán [15] Provinces. Detailed information of the arsenic concentration in the groundwater of the Central-West region of Chaco is available in recent publications; high fluorine (F) and As contents in drinking waters have also been reported [11, 16]. In addition, a positive correlation between As and F has been found (r2=0.66).In the study area, it is necessary to carry out the research on the presence of the trace elements in groundwater which are present in concentrations higher than the WHO reference values assigned for health reasons. These elements were selected taking in view the geology of the study area and possible leaching of As and other trace metals previously reported in other areas in Chaco-Pampean plain [14, 15, 17], like vanadium, strontium, barium, chromium, uranium, molybdenum, manganese, and selenium. The residents who lives in As-contaminated areas and consume groundwater are not only exposed to As concentrations but also to high concentration of multiple metals that can cause adverse health effects.This paper presents an integrated study on the occurrence and the distribution of arsenic and heavy metals (HM) in groundwater in the area of Comandante Fernández in the Central region of Chaco Province, Northern Argentine. In addition, the relations between arsenic occurrence and these chemical components are discussed from a chemical point of view.


## 2. Materials and Methods

### 2.1. Location of the Study Area

The study area is located in the Department Comandante Fernández, Chaco Province, Northern Argentina (Figure1). It covers an area of 1500 km2, and approximately 0.10 million population [11]. Presidencia Roque Sáenz Peña (90000 inhabitants), located between 26°47′27′′ latitudes S and 60°26′29′′ longitudes W, is the most important town where we could find an economy based on agricultural and livestock exploitation.Figure 1
Geographical location of the study area and distribution of arsenic concentrations.This area is located within the geologic province known as the Chaco Pampean [11]. The aquifers are hosted in superposed sequences of aeolian and fluvial sediments of the tertiary and quaternary ages [18]. As there are no superficial sources of groundwater, recharge of the phreatic aquifer is produced from rainfalls, while deep aquifer recharge occurs from west to east and northwest-southeast, and it is supposed to be located in the higher parts of the sub-Andean outcrops [19, 20].The studied zone has a semiarid and subtropical continental type climate, characterized by sultry summers and cold winters, receiving an annual precipitation of 900 mm, between November and March [21].


### 2.2. Sampling and Analysis

Forty-five groundwater samples were collected during May–October 2010 (a dry season), in rural and suburbs areas of the Comandante Fernández Department (Chaco Province), (Figure1). Each sample has been collected from each tube well. Latitude and longitude of these tube wells were determined using a Garmin eTrex Legend, Global Positioning System (Garmin Ltd., UK). Specific well information, that is, the depth of the well was obtained from its owner. The sampling points were selected taking into account their spatial distribution in the area, in order to obtain an accurately representative hydrochemistry.For all analyses, cleaning and sampling procedure involved deionized distilled water (DDW) produced by MilliQ water (Millipore Elix 5) and high-purity solvents. All glassware and polyethylene bottles were kept in 10% (v/v) HNO3 (Merk 65%) for 24 hours, rinsed out with DDI, and dried in a stove. All tube-wells samples were collected after 3 min flushing, filtered through 0.45 μm membrane filters and transferred to three different polyethylene bottles to undertake different analysis. Samples for major cations analysis (Ca2+, Mg2+, Na+, and K+) and total As were acidified with 0.06 M HCl. For trace metals analysis, samples were acidified to pH < 2 by addition of ultrapure nitric acid (Fluka). No acidified fractions were collected without headspaces in the sample bottles for measurements of anions such as Cl−, SO42-, NO3-, F, and alkalinity. All the samples were kept at 4°C until analysis.


### 2.3. Groundwater Analyses

The physical parameters like water temperature (T), pH, and electrical conductivity (EC) were measured in situby using a HANNA HI991301 Portable PH/EC/TDS/Temperature Meter. Na+ and K+ were determined by emission flame spectrometry (JENWAY PFP7) and Ca2+ and Mg2+ concentrations were determined by complexometric titration using ethylenediaminetetraacetic acid (0.05N EDTA). Chloride, nitrate, and fluorine ionic activity were measured with ion-selective electrodes using OAKTON CE pH/ION Mod. 510. Alkalinity was analyzed by titration method with sulfuric acid, and sulfate was measured by turbidimetric method using Spectrophotometer UV-Visible Metrolab 1700. For a better detection limit, arsenic was analyzed by hydride generation atomic absorption spectroscopy method (HGAAS) using hollow cathode lamps at 193.7 nm wavelength. The instrument quantification limit for this system was 5 μg L−1; an intermediate precision of less than ±10% was achieved. All these analyses were performed at the Laboratories of Química Analítica, Universidad Nacional del Chaco Austral, Argentina.Total concentrations of 23 trace elements (Ag, Al, Ba, Be, B, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, P, Pb, S, Sb, Se, Si, Sr, Ti, V, and Zn) were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES), (PERKIN ELMER 5100 DV, axial, solid state detector, cross-flow nebulizer, associated with Scott Type chamber, and AS type auto sampler. The equipment was linearly calibrated from 1 to 100μg L−1 with custom certified standard solution (Merck ICP Multielement Standard Solution XIII). R2 values of calibration curves were >0.995, and no trend was observed in the residuals for all analyzed metals. Linearity was checked after every 10 samples using homemade control solution. If the recovery was greater than ±10%, the recalibration was performed for the concerned element. Accuracy of the procedure it has been tested by analyzing a certified reference material, NIST SRM 1643 c “Trace elements in water.” For the studied elements, bias ranged from 2 to 7%. Precision, expressed as intermediate precision was better than 9% for all analyzed elements.


### 2.4. Statistical Analysis

All statistical analysis of data, including maximum and minimums, means and medians, was performed using the program STATGRAPHICS 5.1 (Statistical Graphic Corporation. Manugistics Inc.; Rockville, USA). The software Rock Ware Aq.QA version 1.1.5.1 was used to construct the Piper diagrams that depicted the groundwater types.


## 2.1. Location of the Study Area

The study area is located in the Department Comandante Fernández, Chaco Province, Northern Argentina (Figure1). It covers an area of 1500 km2, and approximately 0.10 million population [11]. Presidencia Roque Sáenz Peña (90000 inhabitants), located between 26°47′27′′ latitudes S and 60°26′29′′ longitudes W, is the most important town where we could find an economy based on agricultural and livestock exploitation.Figure 1
Geographical location of the study area and distribution of arsenic concentrations.This area is located within the geologic province known as the Chaco Pampean [11]. The aquifers are hosted in superposed sequences of aeolian and fluvial sediments of the tertiary and quaternary ages [18]. As there are no superficial sources of groundwater, recharge of the phreatic aquifer is produced from rainfalls, while deep aquifer recharge occurs from west to east and northwest-southeast, and it is supposed to be located in the higher parts of the sub-Andean outcrops [19, 20].The studied zone has a semiarid and subtropical continental type climate, characterized by sultry summers and cold winters, receiving an annual precipitation of 900 mm, between November and March [21].


## 2.2. Sampling and Analysis

Forty-five groundwater samples were collected during May–October 2010 (a dry season), in rural and suburbs areas of the Comandante Fernández Department (Chaco Province), (Figure1). Each sample has been collected from each tube well. Latitude and longitude of these tube wells were determined using a Garmin eTrex Legend, Global Positioning System (Garmin Ltd., UK). Specific well information, that is, the depth of the well was obtained from its owner. The sampling points were selected taking into account their spatial distribution in the area, in order to obtain an accurately representative hydrochemistry.For all analyses, cleaning and sampling procedure involved deionized distilled water (DDW) produced by MilliQ water (Millipore Elix 5) and high-purity solvents. All glassware and polyethylene bottles were kept in 10% (v/v) HNO3 (Merk 65%) for 24 hours, rinsed out with DDI, and dried in a stove. All tube-wells samples were collected after 3 min flushing, filtered through 0.45 μm membrane filters and transferred to three different polyethylene bottles to undertake different analysis. Samples for major cations analysis (Ca2+, Mg2+, Na+, and K+) and total As were acidified with 0.06 M HCl. For trace metals analysis, samples were acidified to pH < 2 by addition of ultrapure nitric acid (Fluka). No acidified fractions were collected without headspaces in the sample bottles for measurements of anions such as Cl−, SO42-, NO3-, F, and alkalinity. All the samples were kept at 4°C until analysis.


## 2.3. Groundwater Analyses

The physical parameters like water temperature (T), pH, and electrical conductivity (EC) were measured in situby using a HANNA HI991301 Portable PH/EC/TDS/Temperature Meter. Na+ and K+ were determined by emission flame spectrometry (JENWAY PFP7) and Ca2+ and Mg2+ concentrations were determined by complexometric titration using ethylenediaminetetraacetic acid (0.05N EDTA). Chloride, nitrate, and fluorine ionic activity were measured with ion-selective electrodes using OAKTON CE pH/ION Mod. 510. Alkalinity was analyzed by titration method with sulfuric acid, and sulfate was measured by turbidimetric method using Spectrophotometer UV-Visible Metrolab 1700. For a better detection limit, arsenic was analyzed by hydride generation atomic absorption spectroscopy method (HGAAS) using hollow cathode lamps at 193.7 nm wavelength. The instrument quantification limit for this system was 5 μg L−1; an intermediate precision of less than ±10% was achieved. All these analyses were performed at the Laboratories of Química Analítica, Universidad Nacional del Chaco Austral, Argentina.Total concentrations of 23 trace elements (Ag, Al, Ba, Be, B, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, P, Pb, S, Sb, Se, Si, Sr, Ti, V, and Zn) were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES), (PERKIN ELMER 5100 DV, axial, solid state detector, cross-flow nebulizer, associated with Scott Type chamber, and AS type auto sampler. The equipment was linearly calibrated from 1 to 100μg L−1 with custom certified standard solution (Merck ICP Multielement Standard Solution XIII). R2 values of calibration curves were >0.995, and no trend was observed in the residuals for all analyzed metals. Linearity was checked after every 10 samples using homemade control solution. If the recovery was greater than ±10%, the recalibration was performed for the concerned element. Accuracy of the procedure it has been tested by analyzing a certified reference material, NIST SRM 1643 c “Trace elements in water.” For the studied elements, bias ranged from 2 to 7%. Precision, expressed as intermediate precision was better than 9% for all analyzed elements.


## 2.4. Statistical Analysis

All statistical analysis of data, including maximum and minimums, means and medians, was performed using the program STATGRAPHICS 5.1 (Statistical Graphic Corporation. Manugistics Inc.; Rockville, USA). The software Rock Ware Aq.QA version 1.1.5.1 was used to construct the Piper diagrams that depicted the groundwater types.


## 3. Results and Discussion

### 3.1. Physicochemical Parameters

The physicochemical parameters determined in selecting 45 groundwater samples are shown in Table1. Well depth ranged between 5 and 220 m, with average value of 23 m. The pH values of the assorted groundwater samples varied from 6.50 to 8.94 with average value of 7.54 indicating that the waters are generally neutral to slightly alkaline. The measured water temperatures vary from 22.6 to 27.5°C with an average of 23.8°C.Table 1
Major ions composition of groundwater from the Comandante Fernández Department, Chaco.
Sample ID
Depth (m)
pH
EC (mS cm−1)
HCO
3
-
Cl−
SO
4
2
-
NO
3
-
Na+
K+
Ca2+
Mg2+
Water type
M1
30
7.53
2.62
656
269
351
23.1
644
7.10
3.54
1.65
Na–HCO3
M2
18
7.46
0.94
509
14.4
18.0
10.4
326
31.3
11.6
7.50
Na–HCO3
M3
13
8.08
7.07
860
510
3108
nd
1595
29.8
31.9
8.30
Na–SO4
M4
8
6.50
1.78
584
99.1
335
111
669
110
8.96
5.03
Na–SO4
M5
5
7.82
1.55
681
99.2
209
2.50
338
20.0
10.9
16.6
Na–HCO3
M6
20
7.11
0.83
408
21.1
159
12.2
132
13.9
24.5
11.4
Na–HCO3
M7
18
6.90
1.27
490
57.1
226
21.2
221
11.0
9.10
5.50
Na–HCO3
M8
20
7.68
2.69
497
427
369
49.3
1034
16.5
77.4
44.3
Na–Cl
M9
13
8.25
1.34
895
45.4
45.0
nd
257
2.10
7.39
5.43
Na–HCO3
M10
220
7.98
21.5
936
8193
2070
12.2
5857
32.2
206
44.7
Na–Cl
M11
50
7.89
2.44
135
135
480
nd
522
19.2
101
47.9
Na–SO4
M12
15
6.96
0.95
679
111
165
4.35
213
15.2
20.4
6.45
Na–HCO3
M13
12
7.29
1.36
722
140
107
2.10
382
9.10
1.40
0.54
Na–HCO3
M14
12
7.93
1.49
654
129
83.1
14.4
806
10.0
2.30
0.52
Na–HCO3
M15
12
7.61
2.37
769
512
412
107
531
17.2
18.9
12.8
Na–Cl
M16
35
7.51
0.69
198
89.2
136
2.30
200
6.87
28.5
7.54
Na–HCO3
M17
15
6.84
4.48
760
1447
431
20.1
825
23.2
14.9
46.4
Na–Cl
M18
8
6.91
3.36
448
1661
182
14.5
1161
12.1
122
56.9
Na–Cl
M19
12
6.78
1.75
302
408
335
200
132
12.9
6.46
2.18
Na–Cl
M20
13
7.78
4.41
751
1425
421
20.3
775
18.4
22.7
59.8
Na–Cl
M21
15
8.28
8.56
1017
908
3485
27.3
1814
19.4
63.4
78.7
Na–SO4
M22
17
7.36
0.88
251
140
49.2
24.5
216
18.4
12.5
0.92
Na–Cl
M23
10
7.24
1.59
980
28.0
113
13.4
309
16.3
9.37
3.50
Na–HCO3
M24
8
7.16
1.06
806
104
35.0
19.3
661
19.0
32.4
20.3
Na–HCO3
M25
14
7.31
23.3
835
5536
1486
19.5
3158
22.4
109
152
Na–Cl
M26
12
7.95
1.33
356
112
117
nd
877
21.2
71.6
32.6
Na–HCO3
M27
50
7.25
4.18
651
571
190
nd
836
23.3
50.1
22.3
Na–HCO3
M28
14
7.88
9.76
321
1142
804
nd
1969
69.8
432
147
Na–Cl
M29
15
7.06
5.35
405
1099
707
45.2
1065
57.7
319
120
Na–Cl
M30
10
7.64
1.41
864
110
164
12.2
320
15.2
33.2
22.1
Na–HCO3
M31
50
7.76
3.05
964
244
519
6.50
563
7.59
4.57
2.24
Na–HCO3
M32
12
7.29
8.05
1868
1300
43.2
10.1
489
3.12
355
92.2
Na–HCO3
M33
10
7.26
5.29
679
762
582
2.30
747
19.5
123
88.4
Na–Cl
M34
12
7.53
1.15
500
85.1
91.2
21.3
268
9.71
19.1
11.3
Na–HCO3
M35
8
8.17
2.98
1652
165
116
25.4
549
6.16
3.74
3.90
Na–HCO3
M36
10
7.17
11.8
1868
742
1506
2.25
2100
2.71
90.4
150
Na–SO4
M37
8
7.55
1.74
920
73.2
108
13.5
823
8.54
15.6
9.30
Na–HCO3
M38
20
8.94
6.33
214
1012
1350
nd
994
10.8
18.3
55.8
Na–Cl
M39
15
7.26
10.0
463
2634
1258
72.1
1029
67.8
498
202
Na–Cl
M40
52
7.00
19.4
764
4636
1520
23.4
200
54.2
183
182
Mg–Cl
M41
65
8.51
24.9
817
5121
1537
39.4
2100
67.9
67.0
144
Na–Cl
M42
12
8.92
1.43
668
26.0
35.5
21.2
244
11.5
8.06
3.37
Na–HCO3
M43
8
7.28
1.81
618
234
74.2
4.50
765
32.4
57.6
16.3
Na–HCO3
M44
11
7.07
2.50
723
450
90.1
56.1
223
30.3
132
64.6
Ca–Cl
M45
12
6.81
14.4
298
5674
26.3
42.4
459
28.6
1100
400
Ca–Cl
Nd: non detected. All concentrations are expressed as mg L−1.Major ion compositions of the analyzed groundwater samples and the major water types are shown in Table1. High nitrate concentrations (max = 200 mg L−1) are present locally in some wells, probably due to anthropogenic influences, and a significant amount of NO3- is thought to be from evaporation. However, since the correlation between NO3- and Cl− is weak (r2=0.04), evaporation is unlikely to be the most important cause of the high NO3- concentrations.Considerable spatial variation is observed for the distributions of major cations with dominance of Na+ (132 to 5857 mg L−1); K+ (2.10 to 110 mg L−1); Ca2+ (1.40 to 1100 mg L−1), and Mg2+ (0.54 to 400 mg L−1). The same variation is observed for distribution of major anions, with dominance of HCO3- (median value 679 mg L−1), Cl− (median value 269 mg L−1), and SO42- (median value 209 mg L−1). Statistical parameters are shown in Table 2.Table 2
Statistical summary of the chemistry of groundwater (major ions and trace elements;n=45) from Comandante Fernández Department, Chaco, Northeast Argentina.
Parameter
Mean
Median
Range
10th percentil
90th percentil
Standard deviation
Depth (m)
22.0
13.0
5.00–220
8.00
50.0
33.1
pH
7.54
7.51
6.50–8.94
6.90
8.22
0.55
EC (mS/cm)
5.27
2.50
0.69–24.9
0.99
13.4
6.28
HCO
3
- (mg L−1)
699
679
135–1868
299
974
376
Cl− (mg L−1)
1082
269
14.4–8193
50.1
3835
1832
SO
4
2
- (mg L−1)
570
209
18.0–3485
43.9
1514
789
NO
3
- (mg L−1)
29.7
14
bdl–200
0.03
53.4
36.1
F (mg L−1)
1.29
1.00
0.10–4.20
0.30
3.08
1.10
Na+ (mg L−1)
875
644
132–5857
214
1907
989
K+ (mg L−1)
23.6
18.4
2.10–110
6.96
56.3
21.5
Ca2+ (mg L−1)
101
28.5
1.40–1100
5.33
274
191
Mg2+ (mg L−1)
53.7
20.3
0.52–400
2.20
149
76.2
S (mg L−1)
49.3
0.57
0.006–724
0.06
125
130
P (mg L−1)
2.70
0.8
0.17–22.9
0.30
8.26
4.41
As (µg L−1)
213
100
7–1990
17.0
500
347
Al (µg L−1)
561
99.0
60.0–17380
60.0
257
2601
Ba (µg L−1)
122
14.0
bdl–1400
2.00
135
211
B (µg L−1)
4020
1970
156–21910
283
7896
5599
Cd (µg L−1)
2.00
2.00
bdl–7.0
1.00
4.00
1.40
Cu (µg L−1)
23.0
6.00
bdl–280
0.10
65.8
48.7
Co (µg L−1)
27.2
3.00
bdl–280
1.40
82.6
6.20
Fe ( µg L−1)
276
81.0
bdl–2000
0.10
716
396
Mn (µg L−1)
152
5.00
bdl–3740
0.10
327
574
Mo (µg L−1)
23.9
21.0
bdl–160
3.00
42.0
30.8
Si (µg L−1)
1057
150
bdl–16570
0.40
2415
2803
Sr (µg L−1)
449
86
2.00–4871
15.0
873
873
Se (µg L−1)
1.9
1.00
bdl–10.0
0.1
6.60
2.70
Sb (µg L−1)
5.4
1.00
bdl–111
0.10
9.00
1.7
Ni (µg L−1)
0.9
0.10
bdl–10.0
0.10
3.00
1.90
V (µg L−1)
204
76.0
bdl–2646
11.4
416
431
Zn (µg L−1)
83.8
3.00
bdl–2813
0.10
67.0
487Major ion compositions plotted on a Piper diagram (Figure2) indicate that bicarbonate and chloride were the dominant anions followed by sulfate, and that sodium was the prevalent cation. The major water types in the samples are presented in Table 1.Figure 2
Piper diagram showing the chemical compositions of groundwater samples.EC values vary from 0.69 and 24.9 mS cm−1 with a median value of 2.50 mS cm−1 and mean value of 5.27 mS cm−1. This may be due to contribution of Na+, HCO3-, Cl−, and SO42-. In saline groundwater, chloride and sulfate are also important. The most saline groundwater samples are of Na–Cl type (maximum Cl− concentration 8193 mg L−1; Tables 1 and 2) although Na–SO42- types are also important (maximum SO42- concentration 3485 mg L−1). The most significant correlations are those of chloride versus EC and sodium (r2=0.91; r2=0.69) and sulfate versus EC and sodium (r2=0.62; r2=0.61), which is related to the predominance of sodium chloride types in groundwater with higher salinity. Sodium bicarbonate waters are related generally with low salinity samples; in analyzed groundwater samples the EC shows poor correlation with HCO3- (r2=0.21).Results of chemical analysis show large variations in chemical composition and also indicate the high salinity of many of the groundwater samples. According to Larroza and Fariña [19], the salinity of groundwater in the basin of the Chaco region is due to the previous existence of a shallow sea of restricted environment, which has left its salts; this geographical feature, called Paranaense Sea, has originated during the Middle and Upper Miocene. The extremely heterogeneous values of EC from groundwater could be explained by the local variation in sedimentary and hydrogeological characteristics [13]. Moreover, the evaporation in arid and semiarid zones favors the increase of salinity and alkalinity [15, 22].


### 3.2. Total Arsenic and Fluoride

Arsenic is classified as a human carcinogen (Type A) based on sufficient epidemiologic evidence linking increased mortality from liver, kidney, bladder, and lung cancers to drinking As-contaminated water [23]. The provisional guideline value recommended by the WHO [5] for this carcinogenic contaminant in drinking water is 10 μg L−1 and in Argentina this would be enforced in 2017 [24]. On the basis of this criterion, only 9% (4/45) of groundwater source is within levels recommended for consumption; whereas about 73% (33/45) of all analyzed samples showed As values above 50 μg L−1 (CAA) [25]. Mean concentration of total arsenic in groundwater was 213 μg L−1 and maximum was 1990 μg L−1 (Table 2). The highest As concentration was found in groundwater collected in sample M36. The presence of arsenic in the groundwater samples collected from this region of Argentina is natural; the local geology and rainfall have been shown to have major impact on the variations of As concentration in groundwater.Different positive correlation were observed in groundwater between As versusHCO3- and Na+ (r2=0.75; r2=0.45), and a negative correlation was found between As and Ca2+ (r2=-0.05). It could be assumed that As is associated with Na–HCO3- system, related to feldspar dissolution [26]. Based on values of pH found in groundwater of this region of Chaco, including data reported from other sites of the region [1, 13, 27], it can be presumed that pH controls As mobility.The study made by Smedley et al. [28] reveals that highly As(V)-contaminated groundwater in oxidizing environments throughout the world are characterized by high concentration of HCO3- (>500 mg L−1) and SO42- (>250 mg L−1) and pH > 7.50. Similar geochemical conditions occur in the Chaco-Pampean plain, like in the arid regions of Santiago del Estero, Córdoba y La Pampa [13, 14, 27]. High As concentrations are common and dominated by As(V), and the groundwater have correspondingly high F concentrations. These general characteristic are consistent with the analyzed groundwater. However, arsenic speciation is not performed in the present study.On the other hand, smaller quantities of fluoride ion in the order of 1 mg L−1 in ingested water are usually considered to have a beneficial effect by lowering the rate of occurrence of dental caries. Excessive intake (>1.5 mg L−1) would results in pathological changes in teeth and bones, such as mottling of teeth or dental fluorosis, along with metabolic changes reported on soft tissues such as thyroid, reproductive organs, brain, liver, and kidneys [29].The WHO guideline value for F concentration in drinking water is 1.5 mg L−1 [5], whereas the Código Alimentario Argentino (CCA) [25] establishes a limit that varies according to the average temperature of the place (1 mg L−1 for an average temperature of 21.5°C in the area under study). The distribution of F concentrations is heterogeneous and similar to As. A positive correlation was observed between As and F with r2=0.50. The analyzed groundwater, 31% (14/45) of the samples exceeded the WHO guideline value of 1.5 mg L−1 [5]. About 47% of all analyzed samples showed F values above 1 mg L−1 recommended by CAA (Table 4). Similar correlations between As and F were also observed in groundwater from neighboring Santiago del Estero [13], Santa Fe [14], and Salta Provinces [30].In the same way as arsenic, the F rich water is characterized by high concentration of Na+ and low concentration of Ca2+ and Mg2+ (r2=0.45; 0.09 and 0.16; resp.). Fluoride is a highly reactive element that combines with other elements in covalent and ionic bonds. It is mainly found in alkaline rocks and alkaline soils, fluorite being the principal component. Gomez et al. [27] explain that the processes that could control the low relationship between F and Ca2+ and the positive relationship between F and bicarbonate (r2=0.24) would be the balance equation relating calcite and fluorite when both are in contact with water.As and other trace elements such as V, Mo, U, and minor elements such as B and F are presumed to have their original source in volcanic ashes originated from the volcanism in the Andes (5–25% in the loess-type sediments of the Chaco-Pampean plain) [9]. The main components of these sediments are feldspars, quartz, volcanic glass shards, and minor amounts of muscovite and calcite. The composition of volcanic glass is typically rhyolitic, containing a high concentration of F, As, V, and B among other trace elements [28].


### 3.3. Other Trace Elements

A series of various trace elements, including Ag, Al, B, Ba, Be, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, P, Pb, S, Sb, Se, Si, Sr, Ti, V, and Zn were also determined in the studied groundwater. The concentrations of target elements are summarized in Table3. Among all 23 target analytes, concentrations exceeding the WHO recommended drinking water limits (in parentheses) were found for B (2400 μg L−1), Ba (700 μg L−1), Cd (3 μg L−1), and Sb (20 μg L−1). Table 4 shows the percentage of groundwater samples exceeding these WHO and CAA elemental concentration guidelines. On the other hand, concentrations of Sn, Co, Cu, Ni, S, Se, Sr, V, and Zn were very low. Silver, beryllium, chrome, selenium, lead and titanium are not includ in Tables 2 and 3 because these elements were never found above respective quantification limits.Table 3
Trace element composition of groundwater samples from the Comandante Fernández Department, Chaco.
Sample ID
As(tot)
F
Al
Fe
Mn
B
Ba
Mo
Si
V
Cd
Sr
Co
Ni
Zn
Cu
S
P(tot)
Sb
QL
5.00
0.10
10.0
10.0
5.00
20.0
10.0
10.0
50.0
10.0
3.00
25.0
10.0
10.0
10.0
10.0
0.025
0.10
2.50
M1
500
1.90
110
60.0
5.00
1598
bql
126
bql
83.0
5.00
73.0
bql
bql
bql
bql
11.0
0.80
bql
M2
25.0
0.50
120
40.1
bql
310
156
bql
309
45.0
bql
420
bql
bql
bql
bql
2.00
0.30
bql
M3
100
1.80
90.0
160
3.00
875
bql
bql
bql
10.0
bql
691
bql
bql
30.0
bql
107
2.90
bql
M4
15.0
0.30
100
bql
bql
206
bql
bql
bql
22.0
bql
290
bql
bql
bql
bql
7.00
0.30
bql
M5
127
0.74
220
bql
9.00
811
79.1
42.0
227
119
bql
594
bql
bql
41.0
bql
0.20
0.90
bql
M6
58.0
0.80
110
bql
bql
297
10.0
bql
bql
44.0
bql
498
bql
bql
bql
bql
7.00
0.50
bql
M7
24.0
0.40
100
bql
bql
275
48.2
12.0
bql
43.0
bql
230
bql
bql
bql
bql
8.00
0.30
bql
M8
120
1.00
100
bql
6.00
2654
79.0
bql
2099
90.0
3.00
2012
bql
bql
bql
bql
11.0
0.80
bql
M9
178
1.98
130
550
7.00
1550
10.1
99.0
549
163
7.00
81.1
bql
bql
bql
63.0
7.00
0.80
9.00
M10
500
2.60
80.0
220
870
15070
bql
160
16570
39.0
4.00
4871
bql
bql
bql
bql
725
1.90
bql
M11
250
2.24
100
bql
6.00
1387
bql
14.0
480
23.0
bql
641
bql
bql
bql
bql
132
0.50
bql
M12
11.0
0.44
100
bql
19.4
500
62.0
bql
114
53.0
bql
334
bql
10.0
bql
bql
13.0
0.60
bql
M13
95.2
1.10
110
bql
5.00
500
26.9
42.0
bql
76.0
4.00
68.3
bql
bql
bql
bql
10.0
0.30
3.00
M14
116
1.50
110
bql
5.00
665
bql
43.1
bql
65.0
5.00
54.0
bql
bql
bql
bql
7.00
0.70
bql
M15
31.0
0.50
102
50.0
5.00
2449
40.2
30.3
680
57.0
bql
521
bql
bql
bql
bql
49.0
0.60
bql
M16
29.0
0.40
130
150
5.00
255
51.8
bql
490
11.0
bql
362
bql
bql
bql
bql
26.0
0.30
bql
M17
83.0
1.20
100
bql
bql
1782
40.3
bql
3940
94.0
3.00
1427
bql
bql
bql
bql
113
0.20
3.00
M18
62.0
0.80
70.0
bql
18.2
734
bql
bql
2550
28.0
bql
2510
bql
bql
bql
bql
281
0.60
bql
M19
10.0
0.20
110
bql
5.00
298
14.4
bql
bql
30.0
bql
157
bql
bql
bql
bql
8.00
0.50
bql
M20
112
1.45
100
bql
bql
2316
22.0
10.9
4750
112
3.00
1390
bql
bql
bql
bdl
147
0.40
bql
M21
700
1.90
100
bql
25.4
2470
bql
11.2
353
28.0
bql
1361
bql
bql
bql
bql
415
8.90
bql
M22
10.0
0.20
100
bql
29.2
156
16.9
bql
bql
bql
bql
86.0
bql
bql
bql
bql
6.00
1.50
bql
M23
36.0
0.30
110
bql
bql
630
109
bql
bql
30.0
bql
225
bql
bql
bql
bql
5.00
0.70
9.00
M24
86.0
0.75
17380
310
296
21560
111
bql
1380
12.0
3.00
32.4
bql
bql
321
bql
0.10
0.80
bql
M25
77.0
1.20
2980
bql
521
6308
bql
bql
1647
22.0
Bql
bql.
bql
10.0
2831
32.0
0.10
2.50
4.00
M26
100
3.40
60.0
110
bql
1800
150
21.0
150
198
3.00
15.0
bql
bql
bql
bql
0.06
1.80
bql
M27
214
4.20
60.0
855
bql
6890
bql
21.3
150
560
3.00
213
280
bql
67.0
280
0.06
1.10
bql
M28
100
3.40
60.0
428
bql
8450
bql
21.4
150
219
3.00
15.0
22.0
bql
bql
22.0
0.06
6.70
bql
M29
100
0.60
60.0
660
bql
6850
bql
20.8
150
100
3.00
15.0
bql
bql
67.0
bql
0.06
7.70
bql
M30
244
0.90
60.0
81.0
33.0
3050
185
21.0
150
547
3.00
15.0
bql
bql
24.0
bql
0.06
1.30
25.0
M31
770
3.40
280
1013
23.0
7290
bql
21.0
150
2646
3.00
32.2
bql
bql
bql
bql
0.30
0.30
bql
M32
7.00
0.10
210
286
3740
5080
63.2
20.9
150
bql
3.00
164
64.0
bql
110
64.0
0.20
2.30
3.00
M33
174
1.70
60.0
734
32.1
2790
69.0
21.0
7540
266
3.00
15.0
bql
bql
27.0
bql
Bql
2.20
bql
M34
317
0.30
360
575
24.0
1970
11.8
21.4
150
436
3.00
15.0
bql
bql
bql
bql
0.40
0.60
bql
M35
1073
0.30
60.0
194
bql
6340
30.1
20.5
150
1249
3.00
15.0
120
bql
49.0
120
0.06
0.30
30.0
M36
1990
4.25
60.0
510
13
5580
bql
21.0
150
251
3.00
288
24.0
bql
13.0
bql
0.06
5.30
3.00
M37
200
0.30
570
606
13
1290
113
21.0
150
387
3.00
20.3
240
10.0
16.0
67.0
0.60
0.50
bql
M38
150
1.90
60.0
2000
bql
3710
bql
21.0
150
38.0
3.00
20.0
95.0
bql
bql
bql
0.06
0.30
3.00
M39
20.0
0.50
60.0
300
bql
4830
14.0
21.0
150
104
3.00
20.0
bql
bql
bql
67.0
0.06
9.90
14.0
M40
20.0
0.50
60.0
689
bql
21910
bql
21.0
150
124
3.00
20.0
bql
bql
bql
24.0
0.06
1.30
3.00
M41
150
1.50
60.0
988
bql
21580
bql
21.0
150
176
3.00
30.2
bql
bql
bql
bql
0.06
1.10
3.00
M42
130
0.80
60.0
426
bql
1970
bql
21.0
150
345
3.00
369
180
bql
27.0
111
0.06
0.20
3.00
M43
150
1.40
60.0
70.0
431
1030
107
21.0
150
bql
3.00
bql
55.0
bql
22.0
27.0
0.06
0.80
bql
M44
100
1.20
60.0
80.0
bql
2600
289
21.0
150
191
3.00
bql
bql
bql
bql
bql
0.06
4.80
bql
M45
200
1.60
60.0
262
331
240
1400
21.0
150
35.0
3.00
bql
bql
bql
110
49.0
0.06
2.30
bql
QL: quantifiction limit; bql: bellow  quantification limit; all concentrations are expressed as µg L−1 excepted for F, S, and P expressed as mg L−1.Table 4
Risk-based drinking water criteria and the percentage of groundwater samples exceeding these criteria.
Element
Risk-based drinking water criteria
Percentage of groundwater samples exceeding these criteria
WHO*
CAA**
WHO
CAA
As (µg L−1)
10***
50
91
73
Al (µg L−1)
not established
200
NA
16
B (µg L−1)
2400
500
78
78
Ba (µg L−1)
700
None
2
NA
Cd (µg L−1)
3
5
13
2
Cr (µg L−1)
50***
50
0
0
Cu (µg L−1)
2000
1000
0
0
Fe total (µg L−1)
not established
300
NA
31
F (mg L−1)
1.50
1.00
31
47
Mn (µg L−1)
not established
100
NA
16
Ni (µg L−1)
70
20
0
0
Pb (µg L−1)
10***
50
0
0
Sb (µg L−1)
20
20
4.5
4.5
Se (µg L−1)
10***
10
0
0
Zn (µg L−1)
not established
5000
NA
0
NA: not applicable.
*WHO: World Health Organization, have not established risk-based drinking water criteria for  Al, Ag, Be, Bi, Co, Fe, Mn, Mo, Si, Sr, Ti, V, and Zn.
**CAA: Código Alimentario Argentino.
***Provisional guideline value.From the samples investigated, only one (M45) showed elevated value of barium (1400μg L−1) than in the WHO drinking water guideline (700 μg L−1) with an average value of 122 μg L−1 (Table 2).In small quantities, B is essential for healthy bones, joint function, and the metabolism of steroidal hormones. Boron deficiency seems to affect calcium and magnesium metabolism and affects the composition, structure, and strength of bone [31]. The concentrations of boron (B) ranged from 1560 to 21910 μg L−1 with an average of 4020 μg L−1 (Table 2). Boron concentration in the 44% (20/45) of the samples exceeds the WHO and 78% (35/45) of the samples exceeds the CAA standard limits for drinking water (Table 4). The highest concentration of boron was observed in sample M40 which is associated with the largest value of EC (19371 μS cm−1). In general, the presence of boron in groundwater depends on its salinity (represented as EC), such that it increases with increasing salinity [32]. In this study, a positive correlation between EC and boron (r2=0.64) suggests that boron might be associated with the salinity of these samples. Hence, the salinity mainly reflects the variation of Cl− concentration, with a strong linear correlation (r2=0.91) between EC and Cl−, suggesting that the increase of Cl− concentration contributes to increase in EC value. The hydraulic conductivity, salinity, type of clay sediments, pH and temperature are the crucial factors that determine boron mobility in the groundwater system [32]. Boron was strongly correlated with Na+, K+, Mg2+, Cl−, SO42-, HCO3-, and As, probably due to their common origin. The correlation between B and As is often observed in groundwater [1, 13].Our results indicate that approximately 31% of the groundwater samples tested exceeded the CAA criteria of 300μg L−1 for total Fe in drinking water. The highest total Fe concentration (2000 μg L−1) appeared in sample M38. In general, Fe concentration was low in the studied groundwater samples; only fourteen samples had higher Fe with a mean value of 276 μg L−1 and median value of 81 μg L−1. On the other hand, weaker correlation is observed between Fe and As in groundwater (r2=0.17). Moreover, almost all groundwater with high Fe concentration (>300 μg L−1) contained total As concentration over 10 μg L−1 (Table 3).The concentration of dissolved Al varied between 60.0 to 17380μg L−1 with a mean value of 561 μg L−1 (Table 2). A 16% (7/45) exceeded the 200 μg L−1 CAA drinking water guideline. However, the mean concentration of Al decreases significantly down to 178 μg L−1 (median 98.5 μg L−1), if the anomalous of sample M24 is excluded. Also Aluminum shows no correlation with As (r2=-0.06).Manganese exceeded the 100μg L−1 CAA drinking water guideline value in 13% (6/45) of the samples (Tables 3 and 4). The highest Mn concentration (3740 μg L−1) was found in sample M32. However, the mean concentration of Mn decreases significantly from 152 to 70.0 μg L−1 (median 5.00 μg L−1), if the anomalous value of this sample is excluded. Manganese shows no correlation with As (r2=-0.07). Mn is known as an essential element for human survival, serves as a catalyst and cofactor in many enzymatic processes involved in the synthesis of fatty acids and cholesterol. The chronic ingestion of Mn in drinking water is associated with neurologic damage [33]. Moreover, manganese is a known mutagen [34].Many samples have Fe, Al, and Mn concentrations below detection limits and most have below CAA guideline value. However, concentrations are higher in a few samples (Table2). Smedley et al. [1] suggest that at the pH of the groundwater, the high concentrations for these elements trace are most likely due to presence of colloidal particles. As the groundwater are oxidizing, solubility of Fe, Al, and Mn oxides is low and concentrations of dissolved Fe, Al, and Mn are, therefore, mostly low.The processes of dissolution and release from oxides and oxyhydroxides, mainly Al, Mn, and Fe, control the presence and mobility of As and F in groundwater [1]. Kim et al. [35] suggested that the cocontamination of As and F observed in oxidizing aquifers in many countries is associated with the desorption from the Fe-(hydr) oxides by the pH increases. The correlations between As and F are generally very high in those aquifers because the As released from Fe-(hydr) oxides does not readily precipitate again in the oxidizing alkaline condition. This is consistent with our observations, as many of the samples show high pH values and moderate coefficient correlation value between As and F (r2=0.50). Also, solubility of Al minerals may be enhanced by the complex of dissolved Al with F that is also released from volcanic glasses.Vanadium in groundwater ranged between <10.0 (QL) and 2646μg L−1. The highest V concentration was found in sample M31 (Table 2). Vanadium shows a moderated positive correlation with As (r2=0.42) and is likely to be derived from similar mineral sources (secondary Fe and Mn oxides) under the high pH conditions [1]. Our results also indicate that Mo in general appears in low concentrations (Table 3). Molybdenum is weakly correlated with As (r2=0.20).Gomez et al. [27] suggest that V, U, B, and Mo are enriched in volcanic materials and are mobilized as vanadate, molybdate, borate, and so forth, under oxidizing conditions. Alternatively, they are mobilized in alkaline solutions under conditions of high pH and high HCO3-, controlled by carbonate reactions, (e.g., the F may be forming anionic complexes with B, Fe, and Al).Antimony (Sb) is ubiquity a Group V of the periodic table and is similar to As in aspects as chemical behavior and toxicity to animals [5]. The Sb concentrations in studied samples exceeded 20 μg L−1, WHO and CAA drinking water guideline values in 4.5% (2/45) of the analyzed samples (Tables 3 and 4).Cadmium reaches a maximum of 7.0μg L−1 with most samples being less than 3.0 μg L−1. As this element forms cationic species in solution, its mobilization is not favored under the alkaline conditions of the groundwater [1].The presence of arsenic and heavy metals in the samples collected from this region of Chaco in Argentina may be due to local geochemical conditions that facilitate the transfer of naturally occurring arsenic from soil and sediment to the water. The people in the Comandante Fernández Department may be overexposed not only to As, but also to B, Cd, Mn, and F. Adverse health effects may appear in coming years. This problem is a serious concern for the local population.


## 3.1. Physicochemical Parameters

The physicochemical parameters determined in selecting 45 groundwater samples are shown in Table1. Well depth ranged between 5 and 220 m, with average value of 23 m. The pH values of the assorted groundwater samples varied from 6.50 to 8.94 with average value of 7.54 indicating that the waters are generally neutral to slightly alkaline. The measured water temperatures vary from 22.6 to 27.5°C with an average of 23.8°C.Table 1
Major ions composition of groundwater from the Comandante Fernández Department, Chaco.
Sample ID
Depth (m)
pH
EC (mS cm−1)
HCO
3
-
Cl−
SO
4
2
-
NO
3
-
Na+
K+
Ca2+
Mg2+
Water type
M1
30
7.53
2.62
656
269
351
23.1
644
7.10
3.54
1.65
Na–HCO3
M2
18
7.46
0.94
509
14.4
18.0
10.4
326
31.3
11.6
7.50
Na–HCO3
M3
13
8.08
7.07
860
510
3108
nd
1595
29.8
31.9
8.30
Na–SO4
M4
8
6.50
1.78
584
99.1
335
111
669
110
8.96
5.03
Na–SO4
M5
5
7.82
1.55
681
99.2
209
2.50
338
20.0
10.9
16.6
Na–HCO3
M6
20
7.11
0.83
408
21.1
159
12.2
132
13.9
24.5
11.4
Na–HCO3
M7
18
6.90
1.27
490
57.1
226
21.2
221
11.0
9.10
5.50
Na–HCO3
M8
20
7.68
2.69
497
427
369
49.3
1034
16.5
77.4
44.3
Na–Cl
M9
13
8.25
1.34
895
45.4
45.0
nd
257
2.10
7.39
5.43
Na–HCO3
M10
220
7.98
21.5
936
8193
2070
12.2
5857
32.2
206
44.7
Na–Cl
M11
50
7.89
2.44
135
135
480
nd
522
19.2
101
47.9
Na–SO4
M12
15
6.96
0.95
679
111
165
4.35
213
15.2
20.4
6.45
Na–HCO3
M13
12
7.29
1.36
722
140
107
2.10
382
9.10
1.40
0.54
Na–HCO3
M14
12
7.93
1.49
654
129
83.1
14.4
806
10.0
2.30
0.52
Na–HCO3
M15
12
7.61
2.37
769
512
412
107
531
17.2
18.9
12.8
Na–Cl
M16
35
7.51
0.69
198
89.2
136
2.30
200
6.87
28.5
7.54
Na–HCO3
M17
15
6.84
4.48
760
1447
431
20.1
825
23.2
14.9
46.4
Na–Cl
M18
8
6.91
3.36
448
1661
182
14.5
1161
12.1
122
56.9
Na–Cl
M19
12
6.78
1.75
302
408
335
200
132
12.9
6.46
2.18
Na–Cl
M20
13
7.78
4.41
751
1425
421
20.3
775
18.4
22.7
59.8
Na–Cl
M21
15
8.28
8.56
1017
908
3485
27.3
1814
19.4
63.4
78.7
Na–SO4
M22
17
7.36
0.88
251
140
49.2
24.5
216
18.4
12.5
0.92
Na–Cl
M23
10
7.24
1.59
980
28.0
113
13.4
309
16.3
9.37
3.50
Na–HCO3
M24
8
7.16
1.06
806
104
35.0
19.3
661
19.0
32.4
20.3
Na–HCO3
M25
14
7.31
23.3
835
5536
1486
19.5
3158
22.4
109
152
Na–Cl
M26
12
7.95
1.33
356
112
117
nd
877
21.2
71.6
32.6
Na–HCO3
M27
50
7.25
4.18
651
571
190
nd
836
23.3
50.1
22.3
Na–HCO3
M28
14
7.88
9.76
321
1142
804
nd
1969
69.8
432
147
Na–Cl
M29
15
7.06
5.35
405
1099
707
45.2
1065
57.7
319
120
Na–Cl
M30
10
7.64
1.41
864
110
164
12.2
320
15.2
33.2
22.1
Na–HCO3
M31
50
7.76
3.05
964
244
519
6.50
563
7.59
4.57
2.24
Na–HCO3
M32
12
7.29
8.05
1868
1300
43.2
10.1
489
3.12
355
92.2
Na–HCO3
M33
10
7.26
5.29
679
762
582
2.30
747
19.5
123
88.4
Na–Cl
M34
12
7.53
1.15
500
85.1
91.2
21.3
268
9.71
19.1
11.3
Na–HCO3
M35
8
8.17
2.98
1652
165
116
25.4
549
6.16
3.74
3.90
Na–HCO3
M36
10
7.17
11.8
1868
742
1506
2.25
2100
2.71
90.4
150
Na–SO4
M37
8
7.55
1.74
920
73.2
108
13.5
823
8.54
15.6
9.30
Na–HCO3
M38
20
8.94
6.33
214
1012
1350
nd
994
10.8
18.3
55.8
Na–Cl
M39
15
7.26
10.0
463
2634
1258
72.1
1029
67.8
498
202
Na–Cl
M40
52
7.00
19.4
764
4636
1520
23.4
200
54.2
183
182
Mg–Cl
M41
65
8.51
24.9
817
5121
1537
39.4
2100
67.9
67.0
144
Na–Cl
M42
12
8.92
1.43
668
26.0
35.5
21.2
244
11.5
8.06
3.37
Na–HCO3
M43
8
7.28
1.81
618
234
74.2
4.50
765
32.4
57.6
16.3
Na–HCO3
M44
11
7.07
2.50
723
450
90.1
56.1
223
30.3
132
64.6
Ca–Cl
M45
12
6.81
14.4
298
5674
26.3
42.4
459
28.6
1100
400
Ca–Cl
Nd: non detected. All concentrations are expressed as mg L−1.Major ion compositions of the analyzed groundwater samples and the major water types are shown in Table1. High nitrate concentrations (max = 200 mg L−1) are present locally in some wells, probably due to anthropogenic influences, and a significant amount of NO3- is thought to be from evaporation. However, since the correlation between NO3- and Cl− is weak (r2=0.04), evaporation is unlikely to be the most important cause of the high NO3- concentrations.Considerable spatial variation is observed for the distributions of major cations with dominance of Na+ (132 to 5857 mg L−1); K+ (2.10 to 110 mg L−1); Ca2+ (1.40 to 1100 mg L−1), and Mg2+ (0.54 to 400 mg L−1). The same variation is observed for distribution of major anions, with dominance of HCO3- (median value 679 mg L−1), Cl− (median value 269 mg L−1), and SO42- (median value 209 mg L−1). Statistical parameters are shown in Table 2.Table 2
Statistical summary of the chemistry of groundwater (major ions and trace elements;n=45) from Comandante Fernández Department, Chaco, Northeast Argentina.
Parameter
Mean
Median
Range
10th percentil
90th percentil
Standard deviation
Depth (m)
22.0
13.0
5.00–220
8.00
50.0
33.1
pH
7.54
7.51
6.50–8.94
6.90
8.22
0.55
EC (mS/cm)
5.27
2.50
0.69–24.9
0.99
13.4
6.28
HCO
3
- (mg L−1)
699
679
135–1868
299
974
376
Cl− (mg L−1)
1082
269
14.4–8193
50.1
3835
1832
SO
4
2
- (mg L−1)
570
209
18.0–3485
43.9
1514
789
NO
3
- (mg L−1)
29.7
14
bdl–200
0.03
53.4
36.1
F (mg L−1)
1.29
1.00
0.10–4.20
0.30
3.08
1.10
Na+ (mg L−1)
875
644
132–5857
214
1907
989
K+ (mg L−1)
23.6
18.4
2.10–110
6.96
56.3
21.5
Ca2+ (mg L−1)
101
28.5
1.40–1100
5.33
274
191
Mg2+ (mg L−1)
53.7
20.3
0.52–400
2.20
149
76.2
S (mg L−1)
49.3
0.57
0.006–724
0.06
125
130
P (mg L−1)
2.70
0.8
0.17–22.9
0.30
8.26
4.41
As (µg L−1)
213
100
7–1990
17.0
500
347
Al (µg L−1)
561
99.0
60.0–17380
60.0
257
2601
Ba (µg L−1)
122
14.0
bdl–1400
2.00
135
211
B (µg L−1)
4020
1970
156–21910
283
7896
5599
Cd (µg L−1)
2.00
2.00
bdl–7.0
1.00
4.00
1.40
Cu (µg L−1)
23.0
6.00
bdl–280
0.10
65.8
48.7
Co (µg L−1)
27.2
3.00
bdl–280
1.40
82.6
6.20
Fe ( µg L−1)
276
81.0
bdl–2000
0.10
716
396
Mn (µg L−1)
152
5.00
bdl–3740
0.10
327
574
Mo (µg L−1)
23.9
21.0
bdl–160
3.00
42.0
30.8
Si (µg L−1)
1057
150
bdl–16570
0.40
2415
2803
Sr (µg L−1)
449
86
2.00–4871
15.0
873
873
Se (µg L−1)
1.9
1.00
bdl–10.0
0.1
6.60
2.70
Sb (µg L−1)
5.4
1.00
bdl–111
0.10
9.00
1.7
Ni (µg L−1)
0.9
0.10
bdl–10.0
0.10
3.00
1.90
V (µg L−1)
204
76.0
bdl–2646
11.4
416
431
Zn (µg L−1)
83.8
3.00
bdl–2813
0.10
67.0
487Major ion compositions plotted on a Piper diagram (Figure2) indicate that bicarbonate and chloride were the dominant anions followed by sulfate, and that sodium was the prevalent cation. The major water types in the samples are presented in Table 1.Figure 2
Piper diagram showing the chemical compositions of groundwater samples.EC values vary from 0.69 and 24.9 mS cm−1 with a median value of 2.50 mS cm−1 and mean value of 5.27 mS cm−1. This may be due to contribution of Na+, HCO3-, Cl−, and SO42-. In saline groundwater, chloride and sulfate are also important. The most saline groundwater samples are of Na–Cl type (maximum Cl− concentration 8193 mg L−1; Tables 1 and 2) although Na–SO42- types are also important (maximum SO42- concentration 3485 mg L−1). The most significant correlations are those of chloride versus EC and sodium (r2=0.91; r2=0.69) and sulfate versus EC and sodium (r2=0.62; r2=0.61), which is related to the predominance of sodium chloride types in groundwater with higher salinity. Sodium bicarbonate waters are related generally with low salinity samples; in analyzed groundwater samples the EC shows poor correlation with HCO3- (r2=0.21).Results of chemical analysis show large variations in chemical composition and also indicate the high salinity of many of the groundwater samples. According to Larroza and Fariña [19], the salinity of groundwater in the basin of the Chaco region is due to the previous existence of a shallow sea of restricted environment, which has left its salts; this geographical feature, called Paranaense Sea, has originated during the Middle and Upper Miocene. The extremely heterogeneous values of EC from groundwater could be explained by the local variation in sedimentary and hydrogeological characteristics [13]. Moreover, the evaporation in arid and semiarid zones favors the increase of salinity and alkalinity [15, 22].


## 3.2. Total Arsenic and Fluoride

Arsenic is classified as a human carcinogen (Type A) based on sufficient epidemiologic evidence linking increased mortality from liver, kidney, bladder, and lung cancers to drinking As-contaminated water [23]. The provisional guideline value recommended by the WHO [5] for this carcinogenic contaminant in drinking water is 10 μg L−1 and in Argentina this would be enforced in 2017 [24]. On the basis of this criterion, only 9% (4/45) of groundwater source is within levels recommended for consumption; whereas about 73% (33/45) of all analyzed samples showed As values above 50 μg L−1 (CAA) [25]. Mean concentration of total arsenic in groundwater was 213 μg L−1 and maximum was 1990 μg L−1 (Table 2). The highest As concentration was found in groundwater collected in sample M36. The presence of arsenic in the groundwater samples collected from this region of Argentina is natural; the local geology and rainfall have been shown to have major impact on the variations of As concentration in groundwater.Different positive correlation were observed in groundwater between As versusHCO3- and Na+ (r2=0.75; r2=0.45), and a negative correlation was found between As and Ca2+ (r2=-0.05). It could be assumed that As is associated with Na–HCO3- system, related to feldspar dissolution [26]. Based on values of pH found in groundwater of this region of Chaco, including data reported from other sites of the region [1, 13, 27], it can be presumed that pH controls As mobility.The study made by Smedley et al. [28] reveals that highly As(V)-contaminated groundwater in oxidizing environments throughout the world are characterized by high concentration of HCO3- (>500 mg L−1) and SO42- (>250 mg L−1) and pH > 7.50. Similar geochemical conditions occur in the Chaco-Pampean plain, like in the arid regions of Santiago del Estero, Córdoba y La Pampa [13, 14, 27]. High As concentrations are common and dominated by As(V), and the groundwater have correspondingly high F concentrations. These general characteristic are consistent with the analyzed groundwater. However, arsenic speciation is not performed in the present study.On the other hand, smaller quantities of fluoride ion in the order of 1 mg L−1 in ingested water are usually considered to have a beneficial effect by lowering the rate of occurrence of dental caries. Excessive intake (>1.5 mg L−1) would results in pathological changes in teeth and bones, such as mottling of teeth or dental fluorosis, along with metabolic changes reported on soft tissues such as thyroid, reproductive organs, brain, liver, and kidneys [29].The WHO guideline value for F concentration in drinking water is 1.5 mg L−1 [5], whereas the Código Alimentario Argentino (CCA) [25] establishes a limit that varies according to the average temperature of the place (1 mg L−1 for an average temperature of 21.5°C in the area under study). The distribution of F concentrations is heterogeneous and similar to As. A positive correlation was observed between As and F with r2=0.50. The analyzed groundwater, 31% (14/45) of the samples exceeded the WHO guideline value of 1.5 mg L−1 [5]. About 47% of all analyzed samples showed F values above 1 mg L−1 recommended by CAA (Table 4). Similar correlations between As and F were also observed in groundwater from neighboring Santiago del Estero [13], Santa Fe [14], and Salta Provinces [30].In the same way as arsenic, the F rich water is characterized by high concentration of Na+ and low concentration of Ca2+ and Mg2+ (r2=0.45; 0.09 and 0.16; resp.). Fluoride is a highly reactive element that combines with other elements in covalent and ionic bonds. It is mainly found in alkaline rocks and alkaline soils, fluorite being the principal component. Gomez et al. [27] explain that the processes that could control the low relationship between F and Ca2+ and the positive relationship between F and bicarbonate (r2=0.24) would be the balance equation relating calcite and fluorite when both are in contact with water.As and other trace elements such as V, Mo, U, and minor elements such as B and F are presumed to have their original source in volcanic ashes originated from the volcanism in the Andes (5–25% in the loess-type sediments of the Chaco-Pampean plain) [9]. The main components of these sediments are feldspars, quartz, volcanic glass shards, and minor amounts of muscovite and calcite. The composition of volcanic glass is typically rhyolitic, containing a high concentration of F, As, V, and B among other trace elements [28].


## 3.3. Other Trace Elements

A series of various trace elements, including Ag, Al, B, Ba, Be, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, P, Pb, S, Sb, Se, Si, Sr, Ti, V, and Zn were also determined in the studied groundwater. The concentrations of target elements are summarized in Table3. Among all 23 target analytes, concentrations exceeding the WHO recommended drinking water limits (in parentheses) were found for B (2400 μg L−1), Ba (700 μg L−1), Cd (3 μg L−1), and Sb (20 μg L−1). Table 4 shows the percentage of groundwater samples exceeding these WHO and CAA elemental concentration guidelines. On the other hand, concentrations of Sn, Co, Cu, Ni, S, Se, Sr, V, and Zn were very low. Silver, beryllium, chrome, selenium, lead and titanium are not includ in Tables 2 and 3 because these elements were never found above respective quantification limits.Table 3
Trace element composition of groundwater samples from the Comandante Fernández Department, Chaco.
Sample ID
As(tot)
F
Al
Fe
Mn
B
Ba
Mo
Si
V
Cd
Sr
Co
Ni
Zn
Cu
S
P(tot)
Sb
QL
5.00
0.10
10.0
10.0
5.00
20.0
10.0
10.0
50.0
10.0
3.00
25.0
10.0
10.0
10.0
10.0
0.025
0.10
2.50
M1
500
1.90
110
60.0
5.00
1598
bql
126
bql
83.0
5.00
73.0
bql
bql
bql
bql
11.0
0.80
bql
M2
25.0
0.50
120
40.1
bql
310
156
bql
309
45.0
bql
420
bql
bql
bql
bql
2.00
0.30
bql
M3
100
1.80
90.0
160
3.00
875
bql
bql
bql
10.0
bql
691
bql
bql
30.0
bql
107
2.90
bql
M4
15.0
0.30
100
bql
bql
206
bql
bql
bql
22.0
bql
290
bql
bql
bql
bql
7.00
0.30
bql
M5
127
0.74
220
bql
9.00
811
79.1
42.0
227
119
bql
594
bql
bql
41.0
bql
0.20
0.90
bql
M6
58.0
0.80
110
bql
bql
297
10.0
bql
bql
44.0
bql
498
bql
bql
bql
bql
7.00
0.50
bql
M7
24.0
0.40
100
bql
bql
275
48.2
12.0
bql
43.0
bql
230
bql
bql
bql
bql
8.00
0.30
bql
M8
120
1.00
100
bql
6.00
2654
79.0
bql
2099
90.0
3.00
2012
bql
bql
bql
bql
11.0
0.80
bql
M9
178
1.98
130
550
7.00
1550
10.1
99.0
549
163
7.00
81.1
bql
bql
bql
63.0
7.00
0.80
9.00
M10
500
2.60
80.0
220
870
15070
bql
160
16570
39.0
4.00
4871
bql
bql
bql
bql
725
1.90
bql
M11
250
2.24
100
bql
6.00
1387
bql
14.0
480
23.0
bql
641
bql
bql
bql
bql
132
0.50
bql
M12
11.0
0.44
100
bql
19.4
500
62.0
bql
114
53.0
bql
334
bql
10.0
bql
bql
13.0
0.60
bql
M13
95.2
1.10
110
bql
5.00
500
26.9
42.0
bql
76.0
4.00
68.3
bql
bql
bql
bql
10.0
0.30
3.00
M14
116
1.50
110
bql
5.00
665
bql
43.1
bql
65.0
5.00
54.0
bql
bql
bql
bql
7.00
0.70
bql
M15
31.0
0.50
102
50.0
5.00
2449
40.2
30.3
680
57.0
bql
521
bql
bql
bql
bql
49.0
0.60
bql
M16
29.0
0.40
130
150
5.00
255
51.8
bql
490
11.0
bql
362
bql
bql
bql
bql
26.0
0.30
bql
M17
83.0
1.20
100
bql
bql
1782
40.3
bql
3940
94.0
3.00
1427
bql
bql
bql
bql
113
0.20
3.00
M18
62.0
0.80
70.0
bql
18.2
734
bql
bql
2550
28.0
bql
2510
bql
bql
bql
bql
281
0.60
bql
M19
10.0
0.20
110
bql
5.00
298
14.4
bql
bql
30.0
bql
157
bql
bql
bql
bql
8.00
0.50
bql
M20
112
1.45
100
bql
bql
2316
22.0
10.9
4750
112
3.00
1390
bql
bql
bql
bdl
147
0.40
bql
M21
700
1.90
100
bql
25.4
2470
bql
11.2
353
28.0
bql
1361
bql
bql
bql
bql
415
8.90
bql
M22
10.0
0.20
100
bql
29.2
156
16.9
bql
bql
bql
bql
86.0
bql
bql
bql
bql
6.00
1.50
bql
M23
36.0
0.30
110
bql
bql
630
109
bql
bql
30.0
bql
225
bql
bql
bql
bql
5.00
0.70
9.00
M24
86.0
0.75
17380
310
296
21560
111
bql
1380
12.0
3.00
32.4
bql
bql
321
bql
0.10
0.80
bql
M25
77.0
1.20
2980
bql
521
6308
bql
bql
1647
22.0
Bql
bql.
bql
10.0
2831
32.0
0.10
2.50
4.00
M26
100
3.40
60.0
110
bql
1800
150
21.0
150
198
3.00
15.0
bql
bql
bql
bql
0.06
1.80
bql
M27
214
4.20
60.0
855
bql
6890
bql
21.3
150
560
3.00
213
280
bql
67.0
280
0.06
1.10
bql
M28
100
3.40
60.0
428
bql
8450
bql
21.4
150
219
3.00
15.0
22.0
bql
bql
22.0
0.06
6.70
bql
M29
100
0.60
60.0
660
bql
6850
bql
20.8
150
100
3.00
15.0
bql
bql
67.0
bql
0.06
7.70
bql
M30
244
0.90
60.0
81.0
33.0
3050
185
21.0
150
547
3.00
15.0
bql
bql
24.0
bql
0.06
1.30
25.0
M31
770
3.40
280
1013
23.0
7290
bql
21.0
150
2646
3.00
32.2
bql
bql
bql
bql
0.30
0.30
bql
M32
7.00
0.10
210
286
3740
5080
63.2
20.9
150
bql
3.00
164
64.0
bql
110
64.0
0.20
2.30
3.00
M33
174
1.70
60.0
734
32.1
2790
69.0
21.0
7540
266
3.00
15.0
bql
bql
27.0
bql
Bql
2.20
bql
M34
317
0.30
360
575
24.0
1970
11.8
21.4
150
436
3.00
15.0
bql
bql
bql
bql
0.40
0.60
bql
M35
1073
0.30
60.0
194
bql
6340
30.1
20.5
150
1249
3.00
15.0
120
bql
49.0
120
0.06
0.30
30.0
M36
1990
4.25
60.0
510
13
5580
bql
21.0
150
251
3.00
288
24.0
bql
13.0
bql
0.06
5.30
3.00
M37
200
0.30
570
606
13
1290
113
21.0
150
387
3.00
20.3
240
10.0
16.0
67.0
0.60
0.50
bql
M38
150
1.90
60.0
2000
bql
3710
bql
21.0
150
38.0
3.00
20.0
95.0
bql
bql
bql
0.06
0.30
3.00
M39
20.0
0.50
60.0
300
bql
4830
14.0
21.0
150
104
3.00
20.0
bql
bql
bql
67.0
0.06
9.90
14.0
M40
20.0
0.50
60.0
689
bql
21910
bql
21.0
150
124
3.00
20.0
bql
bql
bql
24.0
0.06
1.30
3.00
M41
150
1.50
60.0
988
bql
21580
bql
21.0
150
176
3.00
30.2
bql
bql
bql
bql
0.06
1.10
3.00
M42
130
0.80
60.0
426
bql
1970
bql
21.0
150
345
3.00
369
180
bql
27.0
111
0.06
0.20
3.00
M43
150
1.40
60.0
70.0
431
1030
107
21.0
150
bql
3.00
bql
55.0
bql
22.0
27.0
0.06
0.80
bql
M44
100
1.20
60.0
80.0
bql
2600
289
21.0
150
191
3.00
bql
bql
bql
bql
bql
0.06
4.80
bql
M45
200
1.60
60.0
262
331
240
1400
21.0
150
35.0
3.00
bql
bql
bql
110
49.0
0.06
2.30
bql
QL: quantifiction limit; bql: bellow  quantification limit; all concentrations are expressed as µg L−1 excepted for F, S, and P expressed as mg L−1.Table 4
Risk-based drinking water criteria and the percentage of groundwater samples exceeding these criteria.
Element
Risk-based drinking water criteria
Percentage of groundwater samples exceeding these criteria
WHO*
CAA**
WHO
CAA
As (µg L−1)
10***
50
91
73
Al (µg L−1)
not established
200
NA
16
B (µg L−1)
2400
500
78
78
Ba (µg L−1)
700
None
2
NA
Cd (µg L−1)
3
5
13
2
Cr (µg L−1)
50***
50
0
0
Cu (µg L−1)
2000
1000
0
0
Fe total (µg L−1)
not established
300
NA
31
F (mg L−1)
1.50
1.00
31
47
Mn (µg L−1)
not established
100
NA
16
Ni (µg L−1)
70
20
0
0
Pb (µg L−1)
10***
50
0
0
Sb (µg L−1)
20
20
4.5
4.5
Se (µg L−1)
10***
10
0
0
Zn (µg L−1)
not established
5000
NA
0
NA: not applicable.
*WHO: World Health Organization, have not established risk-based drinking water criteria for  Al, Ag, Be, Bi, Co, Fe, Mn, Mo, Si, Sr, Ti, V, and Zn.
**CAA: Código Alimentario Argentino.
***Provisional guideline value.From the samples investigated, only one (M45) showed elevated value of barium (1400μg L−1) than in the WHO drinking water guideline (700 μg L−1) with an average value of 122 μg L−1 (Table 2).In small quantities, B is essential for healthy bones, joint function, and the metabolism of steroidal hormones. Boron deficiency seems to affect calcium and magnesium metabolism and affects the composition, structure, and strength of bone [31]. The concentrations of boron (B) ranged from 1560 to 21910 μg L−1 with an average of 4020 μg L−1 (Table 2). Boron concentration in the 44% (20/45) of the samples exceeds the WHO and 78% (35/45) of the samples exceeds the CAA standard limits for drinking water (Table 4). The highest concentration of boron was observed in sample M40 which is associated with the largest value of EC (19371 μS cm−1). In general, the presence of boron in groundwater depends on its salinity (represented as EC), such that it increases with increasing salinity [32]. In this study, a positive correlation between EC and boron (r2=0.64) suggests that boron might be associated with the salinity of these samples. Hence, the salinity mainly reflects the variation of Cl− concentration, with a strong linear correlation (r2=0.91) between EC and Cl−, suggesting that the increase of Cl− concentration contributes to increase in EC value. The hydraulic conductivity, salinity, type of clay sediments, pH and temperature are the crucial factors that determine boron mobility in the groundwater system [32]. Boron was strongly correlated with Na+, K+, Mg2+, Cl−, SO42-, HCO3-, and As, probably due to their common origin. The correlation between B and As is often observed in groundwater [1, 13].Our results indicate that approximately 31% of the groundwater samples tested exceeded the CAA criteria of 300μg L−1 for total Fe in drinking water. The highest total Fe concentration (2000 μg L−1) appeared in sample M38. In general, Fe concentration was low in the studied groundwater samples; only fourteen samples had higher Fe with a mean value of 276 μg L−1 and median value of 81 μg L−1. On the other hand, weaker correlation is observed between Fe and As in groundwater (r2=0.17). Moreover, almost all groundwater with high Fe concentration (>300 μg L−1) contained total As concentration over 10 μg L−1 (Table 3).The concentration of dissolved Al varied between 60.0 to 17380μg L−1 with a mean value of 561 μg L−1 (Table 2). A 16% (7/45) exceeded the 200 μg L−1 CAA drinking water guideline. However, the mean concentration of Al decreases significantly down to 178 μg L−1 (median 98.5 μg L−1), if the anomalous of sample M24 is excluded. Also Aluminum shows no correlation with As (r2=-0.06).Manganese exceeded the 100μg L−1 CAA drinking water guideline value in 13% (6/45) of the samples (Tables 3 and 4). The highest Mn concentration (3740 μg L−1) was found in sample M32. However, the mean concentration of Mn decreases significantly from 152 to 70.0 μg L−1 (median 5.00 μg L−1), if the anomalous value of this sample is excluded. Manganese shows no correlation with As (r2=-0.07). Mn is known as an essential element for human survival, serves as a catalyst and cofactor in many enzymatic processes involved in the synthesis of fatty acids and cholesterol. The chronic ingestion of Mn in drinking water is associated with neurologic damage [33]. Moreover, manganese is a known mutagen [34].Many samples have Fe, Al, and Mn concentrations below detection limits and most have below CAA guideline value. However, concentrations are higher in a few samples (Table2). Smedley et al. [1] suggest that at the pH of the groundwater, the high concentrations for these elements trace are most likely due to presence of colloidal particles. As the groundwater are oxidizing, solubility of Fe, Al, and Mn oxides is low and concentrations of dissolved Fe, Al, and Mn are, therefore, mostly low.The processes of dissolution and release from oxides and oxyhydroxides, mainly Al, Mn, and Fe, control the presence and mobility of As and F in groundwater [1]. Kim et al. [35] suggested that the cocontamination of As and F observed in oxidizing aquifers in many countries is associated with the desorption from the Fe-(hydr) oxides by the pH increases. The correlations between As and F are generally very high in those aquifers because the As released from Fe-(hydr) oxides does not readily precipitate again in the oxidizing alkaline condition. This is consistent with our observations, as many of the samples show high pH values and moderate coefficient correlation value between As and F (r2=0.50). Also, solubility of Al minerals may be enhanced by the complex of dissolved Al with F that is also released from volcanic glasses.Vanadium in groundwater ranged between <10.0 (QL) and 2646μg L−1. The highest V concentration was found in sample M31 (Table 2). Vanadium shows a moderated positive correlation with As (r2=0.42) and is likely to be derived from similar mineral sources (secondary Fe and Mn oxides) under the high pH conditions [1]. Our results also indicate that Mo in general appears in low concentrations (Table 3). Molybdenum is weakly correlated with As (r2=0.20).Gomez et al. [27] suggest that V, U, B, and Mo are enriched in volcanic materials and are mobilized as vanadate, molybdate, borate, and so forth, under oxidizing conditions. Alternatively, they are mobilized in alkaline solutions under conditions of high pH and high HCO3-, controlled by carbonate reactions, (e.g., the F may be forming anionic complexes with B, Fe, and Al).Antimony (Sb) is ubiquity a Group V of the periodic table and is similar to As in aspects as chemical behavior and toxicity to animals [5]. The Sb concentrations in studied samples exceeded 20 μg L−1, WHO and CAA drinking water guideline values in 4.5% (2/45) of the analyzed samples (Tables 3 and 4).Cadmium reaches a maximum of 7.0μg L−1 with most samples being less than 3.0 μg L−1. As this element forms cationic species in solution, its mobilization is not favored under the alkaline conditions of the groundwater [1].The presence of arsenic and heavy metals in the samples collected from this region of Chaco in Argentina may be due to local geochemical conditions that facilitate the transfer of naturally occurring arsenic from soil and sediment to the water. The people in the Comandante Fernández Department may be overexposed not only to As, but also to B, Cd, Mn, and F. Adverse health effects may appear in coming years. This problem is a serious concern for the local population.


## 4. Conclusions

The results of the current study indicate that approximately 91% of the groundwater samples used for consumption by human and livestock, from the Comandante Fernández Department (Chaco province, Argentina), exceed the WHO provisional guideline value of 10μg L−1 As, recommended as a maximum allowable level in potable water.Evaporation, potentiated in arid, and semiarid zone, favors the increase of salinity and alkalinity, the results is a low quality of the resource but is not conditioning the concentration of As and F. Hence, factors other than evaporation, such as desorption from metal oxides and possibly silicate reaction, could be likely controlling As and F mobilization. Furthermore arsenic, associated trace elements may be absorbed on the surface of iron and aluminum oxides and oxyhydroxides (hematite, goethite, Fe(OH)3, and gibbsite), limiting the mobility of trace elements. Groundwater with high pH values and high concentration of bicarbonate would facilitate the dissolution of volcanic glass; thus, trace elements may enter groundwater cycles, forming anionic complexes in alkaline solutions and acquiring great mobility.The hydrochemical trace in the region is characterized by high salinity and high As and F concentrations, which is related to volcanism and hydrothermal activity from the Andes. This association is often linked to presence of B, Cd, Mo, Mn, and V, indicating their common origin in the volcanic glasses.Due to high As concentrations found in groundwater, serious health risk must be considered. The population in the area may be exposed to the chronic toxicological effects of hydro arsenicism and fluorosis, increasing the risks of contracting other diseases derived from them. Since the groundwater studied here constitutes the principal source of drinking water in the zone, mitigation efforts should not be limited to As health risks from other toxic elements present in drinking water must also be addressed in this region.



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*Source: 930207-2013-09-17.xml*