Hydrochemical Assessment of Spring Waters from the Iron Quadrangle Region, Minas Gerais, Brazil

Cláudia A. Ferreira, Helena E. L. Palmieri, Maria Ângela de B. C. Menezes, Lúcia M. L. A. Auler

American Journal of Water Resources

Hydrochemical Assessment of Spring Waters from the Iron Quadrangle Region, Minas Gerais, Brazil

Cláudia A. Ferreira1,, Helena E. L. Palmieri2, Maria Ângela de B. C. Menezes2, Lúcia M. L. A. Auler2

1Pos Graduation in Science and Radiation Technology, Minerals and Materials, (CDTN/CNEN), Belo Horizonte, Minas Gerais, Brazil

2Nuclear Technology Development Centre/Brazilian Commission for Nuclear Energy (CDTN/CNEN), Belo Horizonte, Minas Gerais, Brazil

Abstract

This study deals with the hydrochemical characterization and water quality assessment of springs spread throughout the Iron Quadrangle (IQ) in the state of Minas Gerais, Brazil. In the past these spring waters played an essential and strategic role in supplying towns with potable water. Up to this day water is used by both the local population and tourists who thrust in its quality. A total of forty-four spring water and four artesian well water samples were collected at 26 points in different municipalities of the IQ in two different surveys, March and August 2015, wet and dry seasons, respectively. These water samples were studied for 38 physico-chemical parameters: turbidity (TB), electrical conductivity (EC), total dissolved solids (TDS), total hardness (TH), pH, Ca2+, Mg2+, Na+, K+, F-, Cl-, SO42-, HCO3-, NH4+, NO3-, NO2-, PO4-, SiO2, Fe, Li, V, Cr, Cr (VI), Co, Ni, Cu, As, Ba, Al, Mn, Zn, Sb, Cd, Mo, Se, Tl, Hg and U, as well as thermotolerant coliforms (TC). The pH value of groundwater in the study area ranges from 3.8 to 7.0, indicating the acid nature of most of the spring water samples. In these samples, Ca2+ and Na+ are the major cations and HCO3- and NO3- the dominant anions. As expected, the trace metals presented the following decreasing concentrations: Fe> Ba> Al> Mn> Zn> Ni, since the IQ region is abundant in iron, aluminum and manganese minerals. The chemical relationships in Piper diagram identified mixed-bicarbonate, magnesium-bicarbonate and sodium-bicarbonate as the most prevalent water types. The Gibbs plots of data from the study area indicated that the chemical composition of most spring water samples was controlled primarily by rainfall dominance. Except for some springs, groundwater in the study area are inappropriate for drinking and domestic purposes but good for animal consumption, irrigation and recreation.

Cite this article:

  • Cláudia A. Ferreira, Helena E. L. Palmieri, Maria Ângela de B. C. Menezes, Lúcia M. L. A. Auler. Hydrochemical Assessment of Spring Waters from the Iron Quadrangle Region, Minas Gerais, Brazil. American Journal of Water Resources. Vol. 5, No. 2, 2017, pp 29-40. http://pubs.sciepub.com/ajwr/5/2/2
  • Ferreira, Cláudia A., et al. "Hydrochemical Assessment of Spring Waters from the Iron Quadrangle Region, Minas Gerais, Brazil." American Journal of Water Resources 5.2 (2017): 29-40.
  • Ferreira, C. A. , Palmieri, H. E. L. , Menezes, M. Â. D. B. C. , & Auler, L. M. L. A. (2017). Hydrochemical Assessment of Spring Waters from the Iron Quadrangle Region, Minas Gerais, Brazil. American Journal of Water Resources, 5(2), 29-40.
  • Ferreira, Cláudia A., Helena E. L. Palmieri, Maria Ângela de B. C. Menezes, and Lúcia M. L. A. Auler. "Hydrochemical Assessment of Spring Waters from the Iron Quadrangle Region, Minas Gerais, Brazil." American Journal of Water Resources 5, no. 2 (2017): 29-40.

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At a glance: Figures

1. Introduction

Water is probably the only natural resource which is a primary requirement in all aspects of human civilization, from agricultural and industrial development to cultural and religious values embedded in society [1]. It is an essential element for life, a basic necessity and is the world’s most valuable asset in future resources. Therefore, potable water must be provided to all [2]. Although almost two thirds of our planet is covered with water, only a tiny fraction of less than 1% is available to the needs of mankind as pure and healthy freshwater. Almost all available resources are stored underground (about 99%) from where they must be tapped for drinking water supply as well as for agricultural, industrial and environmental purposes. Hosted in various types of aquifers, groundwater appears at the surface in the form of spring feeding streams and wetlands. While still underground, they provide an estimated 25% to 40% of all drinking water on the planet. They may interact with various minerals in the aquifer and become enriched in several elements, some of which are good for our health but others are less so and some can even be toxic if the critical concentrations are exceeded [3].

The increased and inadequate use of conventional fresh water sources like rivers, reservoirs, lakes, and wells have severely decreased the quality and availability of fresh water resources and have, therefore, intensified the search for alternate sources for meeting potable water requirements worldwide. Spring discharge, rain water harvesting, desalination of sea water, etc., are some of the alternate sources of fresh water in several tropical and subtropical regions [4].

Groundwater quality depends not only on natural factors such as aquifer lithology, groundwater velocity, quality of recharge waters and interaction with other types of water or aquifers, but also on anthropogenic activities, which can alter these fragile systems, either by polluting them or by modifying the hydrological cycle [5].

Toxic inorganic element concentrations are very important for the evaluation of groundwater quality. When these concentrations exceed the maximum permissible limits set by national and international regulations on the quality of water intended for human consumption, adverse health effects can be expected. Natural or anthropogenic origins may lead to elevated levels of trace elements in groundwaters. The large increase in groundwater consumption has required more rigorous quality controls and a better understanding of naturally occurring groundwater mineralization processes with respect to the trace elements [6].

Several studies have already been carried out on groundwater and spring water resources worldwide. The large number of papers found in the literature reflects the permanent concern for water quality assessment, hydrochemical and hydrogeochemical characterization in mining areas, as well as in legally protected tropical and subtropical areas [4, 7, 8, 9].

The Iron Quadrangle, located in the central-southeast of Minas Gerais state, stands out in the Brazilian scenario for the extraction of gold, iron and manganese. Since the discovery of gold in the late 17th century, the region of the IQ has been home to the largest urban concentration of Minas Gerais, with gold, iron and manganese mining, as its main economic activities. However, the intense exploitation of these mineral resources has had a great impact on nature, such as groundwater and soil pollution, biodiversity loss and erosion. Previous studies carried out in different regions of the IQ have shown high levels of arsenic and other toxic metals in soils, sediments, groundwater and stream waters [10, 11, 12, 13, 14].

The public supply of water in the IQ is done mainly by water impound of water sheds, but, as today, in some historic towns, like Ouro Preto, Mariana, Congonhas, Sabará, spring waters are still used to supply the fountains located in churches, stately homes, monuments and cobbled streets of these historic towns. These waters are used by the local population and visitors who trust its drinking water quality. Unfortunately, some of the springs have decreased their supply and others have already completely dried up. Springs are important elements in the environment and react to changes that occur in natural ecosystems. A decrease in the number of springs or a drop in their discharge as well as changes in their chemistry and quantity often indicate geological changes in the environment [4, 15, 16].

As yet there is no data available on the quality of several of the spring waters used by the population in urban and rural areas of the IQ. Therefore, this study was undertaken to document the hydrochemistry, assess the water quality in several spring waters and wells inside and outside the Iron Quadrangle.

2. Materials and Methods

2.1. General Features of the Area Studied

The Iron Quadrangle (Quadrilátero Ferrífero) covers an area of approximately 7000 km2 in the central-southeast of Minas Gerais state, Brazil, and is internationally recognized as an important Precambrian terrane with significant mineral resources, particularly gold and iron. The geology of the Iron Quadrangle comprises an Archean greenstone belt sequence, represented by the Rio das Velhas Supergroup, surrounded by Archean granite-gneiss terrains which are overlaid by a Paleoproterozoic sedimentary succession, i.e., the Minas Supergroup [17].

This region is rich in water resources, hosting the headwaters of the basins of the Rivers Velhas and Doce, two of the main Brazilian watersheds, with wide diversity of biomes, including remnants of the Atlantic Forest, Cerrado stretches and rupestrian fields [17]. The underground water potential in this region has been known since the early occupation of the area due to the abundance and quality of its spring waters. Data available [18] indicate the existence of large reserves of groundwater in various geological formations of the IQ: the hematites and itabirites of the Cauê Formation, the quartizites ferruginous of the Cercadinho Formation, the dolomites of the Gandarela Formation and the quartzites of Moeda Formation. The Cauê aquifer is the main groundwater reservoir in the IQ, with a high storage capacity.

Forty-four spring water samples were collected in the municipalities of Sabará, Caeté, Barão de Cocais, Santa Bárbara, Catas Altas, Mariana, Ouro Preto, Congonhas, Moeda, Nova Lima, Rio Acima, Raposos, Itabirito, Mário Campos and four artesian well water samples in the municipalities of Santa Bárbara and Belo Horizonte. Figure 1 shows the sample sites in the various municipalities as well as the main aquifers in the Iron Quadrangle region. The geoprocessing program used was the ArcGIS (ESRI), version 10.2.2, [19]. Six sampling sites (4, 5, 7, 8, 16 and 17) fell into the Cercadinho Formation (quartzitic ferruginous aquifer), one (14) in the Cauê Formation (aquifer in iron formations) and one (28) in the Moeda Formation (quartzitic aquifer).

Results of the hydrochemical data were subjected to graphical evaluation using Piper diagram [20] to classify and compare the different water types based on the ionic composition of the different spring water samples, and Gibbs plot [21] was used to evaluate the functional sources of the dissolved ions in the groundwaters.

Figure 1. Map of the study area with the sample sites in the various municipalities and the main aquifers in the Iron Quadrangle region
2.2. Sampling and Analysis

Natural spring waters and artesian well waters samples were collected in two different surveys, i.e., March 2015 (wet season) and August 2015 (dry season). The well samples were included in our study due to the fact that these waters were also used for human consumption.

Electric conductivity (EC) and total dissolved solids (TDS) were measured in the field using a multiparameter (Myron L Company Ultrameter) and water turbidity (TB) was measured using HACH 2100Q (HACH, USA). Bicarbonate was determined by acid-base titration and total hardness (TH) was estimated by EDTA titrimetric method using eriochrome black-T as indicator. Thermotolerant coliform (TC), also known as fecal coliforms due to their role as fecal indicators was evaluated according to the methodology established by (Standard Methods – SM-9222 D) [22]. Coliform density was computed in terms of the Most Probable Number (MPN)/100 mL. Total mercury was determined by cold vapor atomic absorption spectrometry (CVAAS) using a Perkin Elmer flow-injection mercury system, FIMS 400. Chromium (VI) was determined colorimetrically by reaction with diphenylcarbazide in acid solution (Standard Methods – 3500-Cr D) [22].

Samples for anions, cations and trace element analysis were collected into washed polyethylene narrow-mouth bottles with screw cap. Before sample collection, the bottles were rinsed with spring water filtered through 0.45 µm membrane (mixed cellulose esters-Merck Millipore). The samples for laboratory element trace analysis were immediately acidified to pH<2 with ultrapure nitric acid and then stored at 40C before analysis. The anions, fluoride, chloride, nitrite, nitrate, sulfate, and the cations, sodium, potassium and ammonium were determined by high performance ionic liquid chromatography (HPLC) using a Shimadzu chromatographic system with a CDD-6A conductivity detector. Concentrations of the trace elements, including Li, V, Cr, Co, Ni, Cu, As, Ba, Al, Mn, Zn, Ca, Mg, Si, P, Fe, Sb, Cd, Mo, Se, Tl and U were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) (Perkin-Elmer Elan DRCe). Ultra-pure water (18.2 MΩ.cm) obtained from a Milli Q Element System (Millipore, Belford, MA, USA) and ultrapure HNO3 69.5% (w/w) (Fluka) were used for the preparation of all standard solutions and for the preservation of the samples. Multi-element Standard 3 PerkinElmer N9301720 solution (STD 3) containing Ag, Al, As, Ba, Be, Bi, Ca, Cd, Co, Cr, Cs, Cu, Fe, Ga, In, K, Li, Mg, Mn, Na, Ni, Pb, Rb, Se, Sr, Tl, U, V, Zn (10.0 mg L-1) was used for preparing the calibration curves. All solutions and samples were prepared in 1% HNO3 for ICP-MS.

Since the samples to be analyzed were primarily groundwaters, the elements of interest were calibrated at levels typical of the samples analyzed. Germanium (Aldrich 356247) and holmium (Perkin Elmer N9300123) were used as internal standards at a concentration of 100 µg L-1 (Ge) and 20 µg L-1 (Ho) in 2% (v/v) nitric acid. The internal standards were added on-line to standards and samples using a separate feeding tube on the peristaltic pump (Trident Internal Standard Kit - PerkinElmer). Standards and samples were aspirated into the ICP-MS using 1 mL min-1 carrier flow and the isotopes selected were measured using the experimental conditions established by [23].

The standard reference materials, SRM 1640a, trace elements in natural water from the National Institute of Standards and Technology (NIST) and the synthetic water SPS- SW1 Batch 116 from Spectra pure Standards (Oslo, Norway) were used for recovery and precision studies. The recovery obtained for the elements Mg, Ca, Li, V, Cr, Co, Ni, Cu, As, Ba, Al, Mn, Zn and Si, using the SRM 1640a, was 100%, 91%, 107%, 98%, 101%, 101%, 101%, 94%, 103%, 103%, 106%, 104%, 89% and 95%, respectively. Iron recovery, using the SRM SPS-SW1, was 106%. To obtain phosphorus recovery, a secondary standard produced by the Minas Gerais metrological network (RMMG) was used and the value obtained was 96%. The relative standard deviation (RSD, n=3) used to assess the precision of the selected elements were smaller than 10%.

3. Results and Discussion

3.1. Hydrochemical Characteristics and Spring Water Quality

The quality of the spring and well samples was monitored based on guidelines set by the World Health Organization (WHO), [24] and by the Brazilian Environment Council (CONAMA) 396/2008 [25]. The latter lists the maximum permitted values (MPV) for inorganic (Al, Sb, As, Ba, Be, B, Cd, Pb, CN, Cl-, Co, Cu, Cr, Cr (VI), Fe, F-, Li, Mn, Hg, Mo, Ni, NO3-, NO2-, Ag, Se, Na, TDS, SO42-, U, V, Zn), organic, pesticides and microorganisms parameters that might occur in groundwater, for use of human and animal consumption, irrigation and recreation. Table 1 and Table 2 summarize the measured parameters and their units, the minimum and maximum values found in each survey during the wet and dry seasons in March and August 2015, respectively, and the MPV established by [24] and [25]. The parameters Sb, Cd, F-, NO2-, NH4+, Cr (VI), Hg, Mo, Se, and U were not included in Table 1 and Table 2 because their concentrations were close to the detection limit. As can be seen in Table 1 and Table 2, parameters such as pH, turbidity, Fe, Mn, Al, As, NO3- and TC in some samples presented concentrations above MPV. A correlation matrix was carried out to find the relation among the parameters used for characterization and evaluation of the water quality. Table 3 presents the Pearson correlation coefficients matrix for a 95% confidence level.

Table 1. Water quality parameters of spring and well samples collected in March 2015

Table 2. Water quality parameters of spring and well samples collected in August 2015

Table 3. Pearson correlation coefficient matrix for water samples

The pH value of groundwater in the study area ranges from 3.8 to 7.0, indicating the acid nature of most of the spring water samples, which could enhance the dissolution of some elements present in the soils or bedrock. Only 11 samples showed pH values within the recommended standards (6.5 - 8.5) for drinking water (Table 1 and Table 2). Although pH usually has no direct impact on human health, it shows close relations with some chemical constituents of water [26]. Total hardness (TH) and pH show positive correlations with HCO3- (r = 0.946, r = 0.542, respectively), whereas pH and TH are also positively correlated (r = 0.450), Table 3. These positive correlation values are an indication of the interdependency and control of pH in the CO2 dissolution process in the groundwater system of the study area [27].

Turbidity (TB) was measured in nephelometric turbidity units (NTU). Of the four samples that showed turbidity above the VMP, three samples from Nova Lima (M19), Rio Acima (M23) and Congonhas (M29) (Figure 1) were collected in the rainy season and only one sample (AG 29 - Congonhas) in the dry season. Samples M29 and AG29 presented close values in March and August, whereas the same was not observed in M23 and AG23 (Table 1 and Table 2). Therefore, it may be concluded that the turbidity of M23 was influenced by mud and silt resulting from the rainy season. The turbidity of points 23 and 29 may also have been influenced by the high iron content found in these samples. This was confirmed by the high positive correlation between turbidity and iron (r = 0.826), (Table 3).

In this study, Fe and Mn concentrations ranged between <1 - 605 µg L-1 and <0.50 - 266 µg L-1, respectively.  Four samples  in the study  area presented iron concentrations above the VMP (0.3 mg L-1), being that the samples from Rio Acima (M23), Congonhas (M29) and Itabirito (M31) were collected in the rainy season and (AG29) in the dry season. Three samples collected in Barão de Cocais (M7/AG7) and Santa Bárbara (M9) presented manganese concentration above the VMP (0.1 mg L-1). It was observed that these samples as well as the other spring waters, points (14, 26, 32, 33), presented high Mn concentrations and low pH values, confirming the solubility of Mn in low pH waters (Table 1 and Table 2). The correlation between Mn and pH was (r = -0.377), Table 3. The strong correlation between Mn and Al (r = 0.935) showed that these ions could be derived from the same source.

Water with concentrations close to 0.3 mg L-1 Fe and 0.05 mg L-1 Mn has its color, odor and taste altered and usually causes aesthetic problems to water consumers. At these concentrations, however, the health risk of dissolved Fe and Mn in drinking water is insignificant. Although Mn is essential for human health, it may act as an environment contaminant when its concentration in groundwater exceeds the VMP. The most common sources of iron and manganese in groundwater are due to the weathering of iron and manganese bearing minerals and rocks. Industrial effluent, acid-mine drainage, sewage and landfill leachate may also contribute to the increased Fe and Mn levels in local groundwater [28].

High values of aluminum were detected in spring waters from Barão de Cocais (M7/AG7), Passagem de Mariana (M14/AG14), Santa Bárbara, Ouro Preto, Rio Acima, Congonhas, Itabirito and Lavras Novas, (M9, M17, M23, M29, M31, M32/M33, respectively), but the Al concentrations were relatively higher in the former, exceeding the VMP (0.2 mg L-1), since bauxite is one of the main minerals extracted in the Iron Quadrangle. These spring waters showed also low pH values. A negative correlation between Al and pH (r = -0.401) was found (Table 3), indicating the aggressiveness of the acidic media towards soil and host rocks, increasing de Al concentration at those points. According to [29] Al in groundwater is strongly pH dependent. Aluminum is not soluble in water under normal circumstances. In surface and groundwaters, at low pH, Al occurs as free Al3+ and at pH>6, it may form the highly insoluble Al(OH)3 solid (gibbsite). In acidic waters (pH<5) Al can be mobilized by dissolution of gibbsite and the accelerated weathering of both clay minerals (e.g. kaolinite) and rock-forming minerals. However, Al concentrations are still very low in natural waters due to the extreme low solubility of Al-bearing minerals. Elevated aluminum concentrations are also mostly linked to acidic conditions e.g. rainfall acidity, acid mines drainage. Health effects of Al have been linked to Alzheimer disease [30].

In only one points studied (M15/AG15 - Lajes - Ouro Preto) the level of arsenic was above the limit of 0.010 mg L-1 established by the legislations (Table 1 and Table 2). In this region of the Iron Quadrangle, As has been found closely associated with sulfide-rich gold-bearing rocks [31]. Previous studies have shown high levels of arsenic [32, 33] in aquatic and terrestrial environments in different regions of the IQ. According to [32], such high amounts of arsenic in water, soils, and sediments in the IQ is related to natural causes as well as to past and recent mining activities.

Silica (SiO2) and phosphous (PO4-) in the samples ranged from 2.38 - 46.5 mg L-1 and <1.6 - 227 µg L-1, respectively. High levels of SiO2 and PO4- were found in the well samples of Santa Bárbara and Belo Horizonte, points (10, 27), as well as in the spring waters, points (19, 20, 21, 22, 30), Table 1 and Table 2. There was a strong correlation between SiO2 and PO4- (r = 0.868), as well as between SiO2 - and Mg2+, Ca2+, HCO3-, Na+, Zn (r = 0.599, r = 0.654, r = 0.737, r = 0.476, r = 0.498, respectively), (Table 3) indicating that these ions could originate from the common source. The high Mg2+, Ca2+, HCO3- and SiO2 concentrations in these samples result from the reaction between carbonic acid (H2CO3) and reactive silicate in the aquifer matrix [34]. Sixty percent of the Earth’s crust is composed of silicate minerals, and therefore constitutes the bulk of common rocks, soils, clays and sands. Water that drains deposits high in silicate minerals, particularly feldspars, often contains high contents of silica [35]. There are several water soluble forms of silica referred collectively to as silicic acid (ortho, meta, di, and tri-silicates), which are present in surface and well waters in the range of 1 - 100 mg L-1. Silica is essential for human health and has myriad beneficial effects. Its deficiency induces deformities in skull and peripheral bones, poorly formed joints, reduced contents of cartilage, collagen and disruption of mineral balance in the femur and vertebrae [36].

Barium was monitored because it is associated with a potential health concern. The short-term or acute problems include gastrointestinal disturbance and muscular weakness and the long-term impacts are associated with high blood pressure. It has also been suggested to cause kidney damage and problems with the nervous system [24]. In this study barium concentrations ranged from less than <1.1 µg L-1 to 241 µg L-1 and presented association to Na+, K+, Cl-, SO42-, NO3- (r = 0.934, r = 0.741, r = 0.786, r = 0.758, r = 0.717, respectively), Table 3. The highest levels of Ba were found in the samples (M2/AG2, M7/AG7, M9, M27/AG27, M30/AG30), but at levels below the VMP (0.7 mg L-1). At these points, pH was below 6.6, which may enhance Ba concentration, once the solubility of Ba compounds increases as the pH level decreases. Barium in water comes primarily from natural sources. Acetate, nitrate and halides are soluble in water, but the carbonate, chromate, fluoride, oxalate, phosphate and sulfate are quite insoluble [24].

Zinc is an essential element in all living organisms, but may be toxic at higher concentrations. In natural surface waters, the concentration of zinc is usually below 10 µg L-1, and in groundwaters, 10 - 40 µg L-1 [24]. In this work zinc concentrations ranged from less than <2.0 µg L-1 to 411 µg L-1 and presented association with SiO2 and PO4- (r = 0.498 and r = 0.636, respectively), Table 3. Zinc is known to occur in small amounts in almost all igneous rocks. The principal zinc ores are sulfides (ZnS), calamine (Zn4Si2 O7 (OH)2), smithsonite (ZnCO3), franklinite (Zn, Mn (Fe2O4)) [37].

Nitrate in samples under investigation ranged from 0.05 to 60.3 mg L-1. Nitrate occurred in many samples: Sabará (M2/AG2), Barão Cocais (M7/AG7), Santa Bárbara (M9), Passagem de Mariana (M14/AG14), Nova Lima (M20/AG20; M21/AG21), however at levels below the VMP (44.3 mg L-1) for drinking water. Only the Congonhas (M30/AG30) sample exceeded the VMP established by WHO and CONANA [24, 25] (Table 1 and Table 2). Nitrate is found naturally in the environment and is an important plant nutrient. It is present in all plants at varying concentrations and is part of the nitrogen cycle. Nitrite (NO2-) is not usually present in significant concentrations except in a reducing environment, as nitrate is the more stable oxidation state. Nitrate can reach both surface water and groundwater as a consequence of agricultural activity, from wastewater disposal and from oxidation of nitrogenous waste products in human and animal excreta, including septic tanks [24]. Other main potential sources of naturally occurring nitrate in groundwaters are bedrock nitrogen and nitrogen leached from natural soils [24]. The guideline values for nitrate and nitrite ions to protect against methaemoglobinaemia in bottle-fed infants (shot-term exposure) are 44.3 mg L-1 and 3 mg L-1, respectively [24].

Bacteriological analysis reveals the presence of thermotolerant coliforms in the spring waters from Caeté, Catas Altas, Moeda and Congonhas (M4/AG4, M11/AG11, M28/AG28; M29/AG29, respectively) in the samples collected in the two surveys with the highest values observed in the rainy season (March). Spring waters 4 and 28, located along the roads are generally used by by-passers and also animals. Therefore these spring waters sources are not well protected nor wisely used or managed and susceptible to contamination. The depth of ground water occurrence and the extent of anthropogenic activities in the spring catchment areas, as well as climatic conditions, soil and geologic characteristics may contribute to the presence and survival of coliform bacteria in spring discharges [4].

3.2. Mechanism Controlling Groundwater Chemistry

Total dissolved solids (TDS) indicate the salinity behavior of groundwater and, in the study area, varied from 2.68 - 170 mg L-1. The classification of the groundwaters on the basis of TDS, according to [38] establishes: up to 500 mg L-1 (desirable for drinking); 500 - 1000 mg L-1 (permissible for drinking) and up to 3000 mg L-1 (useful for agricultural purposes). Based on this classification, all the water samples studied are of the fresh water type.

The highest TDS values were found in the spring waters in Nova Lima and Congonhas, points (20, 21, and 30), Table 1 and Table 2. The values of TDS, EC and hardness of these samples suggest that these points are the most mineralized groundwater systems in this study area. Strong correlations exist among the major cations, Mg2+, Ca2+, Na+, and TDS (r = 0.935, r = 0.897, r = 0.675, respectively), Table 3, which is a clear indication of the contribution of these ionic components to the overall mineralization [39].

In this study the natural or anthropogenic presence of nitrate, sulfate and chloride in the spring waters was also evaluated. The variation of EC and TDS in the groundwater is dependent on the geochemical processes, but may also be related to anthropogenic activities. Ions such as Cl-, SO42-, NO3-, and Na+ may also originate from agricultural fertilizers, animal waste and industrial and municipal sewage. The correlation of these ions with TDS can be used to indicate the influence of human activities on the water chemistry [40]. In this work the chemical variables (Mg2+, Ca2+, Na+, K+, Cl-, SO42-) and nitrate show a strong correlation (r = 0.675, r = 0.538, r = 0.823, r = 0.536, r = 0.953, r = 0.766, respectively). The major anions, (Cl-, SO42-, HCO3-, NO3-), also have positive correlations with TDS (r = 0.793, r = 0.531, r = 0.832, r = 0.809, respectively), Table 3, suggesting that these ions present in the groundwater system of the study area mostly derived from geogenic sources. A low correlation between TDS and (NO3- + Cl-)/Na+ as well as between TDS and (NO3- + Cl-)/ HCO3- (Figure 2 a, b) molar ratios, also confirm geogenic input of Cl-, SO42-, NO3- into QF spring waters [40].

Figure 2. Plots showing variations of (a) TDS versus (NO3- + Cl-)/Na+ and (b) (NO3- + Cl-)/HCO3- for waters from the study area

The plots of the spring water ionic parameters in the study area, (Figure 3 a-d) show a distinct group of samples with very low TDS (2.68 -10.0 mg L-1). The very low TDS in the groundwater system of these samples was a reflection of the general characteristics of groundwater in basement terrain. It is assumed that some of these springs may have been originated from aquifers located beneath outcrops of ferruginous rocks (cangas) and iron formation, common in the Iron Quadrangle, such as the well-known outcrop of the Serra do Rola Moça State Park, located at 1400 m altitude. The cangas act as important areas of water recharge and due to the huge amount of pores, cracks, channels and cavities in these soils, function as real sponges, effectively transferring rainwater into the mountains [41]. Low ion values in the spring waters are a reflection of meteoric source water with limited migratory history [39]. The chemical character of groundwater is influenced by the minerals and gases reacting with the water in its relatively slow passage through the rocks and sediments of the Earth’s crust. Many variables cause extensive variation in the quality of groundwater, even in local areas. In general, groundwater increases in mineral content as it moves along through the pores and fracture openings in rocks. This is why deeper, older waters can be highly mineralized. At some point, the water reaches an equilibrium, which prevents it from dissolving additional substances [37].

Figure 3. Relationship among TDS and anions/cations in spring waters from the study area

A plot of TDS versus (Na+/Na+ + Ca2+) for cations and TDS versus (Cl-/Cl- + HCO3-) for anions, referred to as Gibbs plot [21], illustrate the natural mechanism controlling groundwater chemistry, including rainfall, rock weathering, and evaporation-precipitation dominance. The Gibbs plot of data from the study area (Figure 4 a, b) indicate that the chemical composition of most spring water samples was controlled primarily by rainfall dominance. Only three points (20, 21 and 30) may have been influenced by rock weathering reaction. The interaction between rocks and water results in ion leaching into the groundwater system, thereby influencing the water chemistry [34].

Figure 4. Gibb’s Plot Controlling mechanisms for spring waters quality in the study area. 1- Evaporation dominance; 2 - Rainfall dominance
3.3. Geochemical Classification and Relationships

The chemical composition of groundwater is primaly dependent on the geology as well as on the geochemical processes and antrophogenic activities which take place within the aquifer system [34]. Normally the classification of groundwater is based on the concentration of various predominant cations and anions and on the interrelationships of ions. Results of the hydrochemical data of the spring water samples were graphically evaluated through the Piper diagram using the AquaChem program 2011.1 of Schlumberger Water Services. Based on this diagram (Figure 5), the spring waters were classified into eight types: mixed-bicarbonate (29.2%), magnesium-bicarbonate (27.1%), sodium-bicarbonate (18.8%), mixed-chloride (8.3%), sodium-chloride (6.3%), mixed-water (6.3%), calcium-bicarbonate (2%) and sodium-mixed (2%), Table 4.

Figure 5. Water type classification using the Piper trilinear diagram

Table 4. Type of water samples in the study area

4. Conclusion

A total of forty-four spring water and four artesian well water samples were collected at 26 points in different municipalities of the IQ in two different surveys, March and August 2015. These samples have been assessed for water quality and hydrochemical characterization. The average of the values obtained from the analyzed water samples revealed Ca2+ and Na+ as the major cations followed by Mg2+ and K+, with concentrations ranging from 0.05 - 24.0, 0.15 - 24.7, 0.01 - 18.7 and <0.05 - 2.80 mg L-1, respectively. The dominant anions are HCO3- and NO3- followed by Cl- and SO42-, with concentrations ranging from 3.10 - 120, 0.05 - 60.3, 0.06 - 43.7, <0.05 - 7.20 mg L-1, respectively. As expected, the trace metals present the following decreasing concentrations: Fe> Ba> Al> Mn> Zn> Ni, since the IQ region is abundant in iron, aluminum and manganese minerals. The presence of iron in the samples also influenced the turbidity of the samples. The pH value of groundwater ranges from 3.8 to 7.0, indicating the acid nature of most of the spring water samples. It was observed that the acid nature in some springs enhanced the dissolution of mainly Al, Mn and Ba present in the soils or bedrock.

Based on Piper Trilinear diagram method, the spring waters were classified into eight types: mixed-bicarbonate (29.2%), magnesium-bicarbonate (27.1%), sodium-bicarbonate (18.8%), mixed-chloride (8.3%), sodium-chloride (6.3%), mixed-water (6.3%), calcium-bicarbonate (2%) and sodium-mixed (2%). These different kinds of waters are a reflection of the diversity of minerals and lithological types present in the Iron Quadrangle.

A distint group of samples with very low TDS (2.68 -10.0 mg L-1) was observed in this region. It is assumed that these springs may have been originated from aquifers located beneath outcrops of ferruginous rocks (cangas) and iron formation, common in the Iron Quadrangle. The cangas act as important areas of water recharge and due to the huge amount of pores, cracks, channels and cavities in these soils, function as real sponges, effectively transferring rainwater into the mountains. Low ion values in the spring waters are a reflection of meteoric source water with limited migratory history. The Gibbs plot of data confirm that the chemical composition of most spring water samples was controlled primarily by rainfall dominance. Only three points (20, 21 and 30) may have been influenced by rock weathering reaction.

In this study the natural or anthropogenic presence of nitrate, sulfate and chloride in the spring waters was also evaluated. The high positive correlations obtained between the major anions, (Cl-, SO42-, HCO3-, NO3-) and TDS and the low correlation between TDS and (NO3- + Cl-)/Na+ as well as between TDS and (NO3- + Cl-)/HCO3- induces geogenic input of Cl-, SO42-, NO3- into QF spring waters.

A comparison of spring water quality in relation to drinking water quality standards [24, 25] revealed that the parameters: turbidity at points (19, 23, 29), iron at points (29, 31), manganese at points (7, 9), aluminum at point 7, arsenic at point 15, nitrate at point 30, and the presence of thermotolerant coliforms at points (4, 11, 28, 29) exceeded the VMP. Therefore these waters are not suitable for human consumption, but can be used for animal watering, irrigation and recreation [25]. Although the following spring waters (2, 4, 5, 10, 11, 14, 16, 17, 20, 22, 25, 26, 27, 28, 32, and 33) showed pH and TC values outside the permissible limits, these waters can be used for drinking purpose, provided pH correction and proper disinfection are carried out prior to its end use.

One important lesson can be drawn from this study: if society does not protect and preserve all spring waters sources, future generations run the risk of not enjoying these natures gifts.

Acknowledgements

The authors thank Nuclear Technology Development Center (CDTN), Brazilian Nuclear Energy Commission (CNEN) and Research Support Foundation of the State of Minas Gerais (FAPEMIG) for their financial support (APQ-02575-13) and PhD scholarship. The authors also thank Dr. Paulo Rodrigues for the map elaboration.

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