Science of the Total Environment 681 (2019) 497–502

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Science of the Total Environment

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Total arsenic and inorganic arsenic speciation in groundwater intended for human consumption in : Correlation with fluoride, iron, manganese and sulfate

Ignacio Machado a,⁎, Valery Bühl a, Nelly Mañay b a Analytical Chemistry, DEC, Faculty of Chemistry, Universidad de la República, Gral. Flores 2124, , Uruguay b Toxicology, DEC, Faculty of Chemistry, Universidad de la República, Gral. Flores 2124, Montevideo, Uruguay

HIGHLIGHTS GRAPHICAL ABSTRACT

• Arsenic in groundwater is one of the main concerns of Medical Geology in Uruguay. • Analytical methodologies were devel- oped for arsenic and arsenic species as- sessment. • The validated methods were success- fully applied to the analysis of ground- water. • Arsenic levels were correlated with other relevant inorganic parameters. • These relationships should be deeply studied to prevent long-term health effects.

article info abstract

Article history: Medical Geology is a growing field in Uruguay and the groundwater quality has been the focus of multiple Received 22 December 2018 studies, being As levels one of its main concerns. The aim of this study was the application of analytical method- Received in revised form 7 May 2019 ologies for the assessment of total arsenic and inorganic arsenic species, fluoride, iron, manganese and sulfate in Accepted 8 May 2019 groundwater samples from private wells, used for human consumption, and to evaluate the possible correlations Available online 9 May 2019 among these parameters. The accuracy of the methods was ensured by using certified reference materials. A total Editor: Dr. Elena Paoletti of 48 groundwater samples from Uruguay were analyzed. The concentration ranges found were: tAs (1.72–120.48) μgL−1,F− (0.024–1.528) mg L−1,Fe(0.62–211.38) μgL−1 and Mn (0.11–8.705) μgL−1. Almost Keywords: half of the samples presented tAs concentration levels above those recommended by WHO for drinking water − Groundwater (10 μgL 1), with the corresponding risks for human health. Results showed higher As(V) levels in the samples, Arsenic speciation which is in agreement with the oxidant conditions of the wells. Pearson correlations were performed, resulting in Inorganic parameters − − 2− strong positive correlations for As/F , As(V)/F and As(V)/SO4 . As levels in groundwater and its relationship with other inorganic parameters, should be deeply studied to prevent long-term health effects. © 2019 Elsevier B.V. All rights reserved.

1. Introduction

⁎ Corresponding author. Uruguay is a South American country located between E-mail address: [email protected] (I. Machado). and . It is home to an estimated 3.3 million people, of whom 1.8

https://doi.org/10.1016/j.scitotenv.2019.05.107 0048-9697/© 2019 Elsevier B.V. All rights reserved. 498 I. Machado et al. / Science of the Total Environment 681 (2019) 497–502 million live in the metropolitan area of its capital and largest city, As appears with different oxidation states (-III, 0, III, V) and can be Montevideo (INE, 2011). present in inorganic and organic chemical forms. As species mostly OSE is the Uruguayan state-run utility company in charge of drinking found in groundwater are As(III) and As(V), as previously reported water supply and sanitation throughout the country. The source of (Bundschuh et al., 2008; Litter et al., 2009). In reducing aquifers, As drinking water supply to Montevideo and Canelones (most densely (III) generally constitutes a high proportion of the total As (tAs). Its mo- populated cities) is from Santa Lucía River. Only 28% of the population bilization is usually originated by desorption of mineral oxides and the receive drinking water from groundwater sources (OSE, 2018). UNIT is reductive dissolution of Fe and Mn oxides. On the other hand, in pre- the institution that establishes the regulations for drinking water qual- dominantly oxidizing environments, As(V) generally constitutes the ity parameters in Uruguay (UNIT, 2010). However, rural homes and highest proportion. This can be related to high levels of dissolved oxy- − small towns do not have water supply from OSE. In these cases, people gen, high pH values, relatively high concentrations of nitrate (NO3 ) 2− − drink water from their own wells, which sometimes are not properly and sulfate (SO4 ), often high concentrations of fluoride (F ), along + controlled. with low concentrations of ammonium (NH4 ), Fe and Mn. Since inor- The geological profile of the main Uruguayan aquifers shows great ganic As (iAs) species present different degrees of toxicity among variability due to the rocky substratum of the country, which varies them, being As(III) more toxic than As(V), it is important to carry out from sedimentary basins with good porosity and permeability, to areas speciation analysis (Smedley et al., 2001; Smedley and Kinniburgh, of crystalline where the water is lodged in, along with a system 2013). of interconnected faults that give rise to fissured porous aquifers. The aim of this study was the application of analytical methodolo- The Uruguayan territory can be divided into three hydrogeological gies for the determination and assessment of tAs and iAs species, F−, 2− systems according to the hydrogeological chart: Paranaense, Meridional Fe, Mn and SO4 in private wells destined for human consumption in and Costero (Collazo and Montaño, 2012). The Paranaense system oc- Uruguay, of which no systematic control studies are carried out. Also, cupies the northeast and northcentral part of the country. The most im- to evaluate the possible correlations between tAs and iAs with the men- portant aquifer of this system is the Guaraní aquifer, which represents tioned inorganic parameters. The application of speciation techniques is one of the largest freshwater reservoirs in the world, also shared with of utmost importance in Uruguay, for geochemical and toxicological Argentina, Brazil and Paraguay. Mercedes and Salto aquifers also belong studies. to this system. The Meridional system occupies most of the country sur- To the best of our knowledge, this is the first study specifically fo- face and possesses extremely changing hydrogeological characteristics. cused on the evaluation of As species and its correlation with other inor- The Costero system is formed by the Raigón aquifer, which represents ganic parameters present in groundwater in Uruguay. Thus, novel the largest reserve of underground water in the south part of the coun- information is presented from different samples collected at different try, and Chuy aquifer, which is located discontinuously on the east coast geographic points of the country. of the country (Collazo and Montaño, 2012). This work is inspired by the research interest on As levels in ground- Arsenic (As) levels in natural waters have been reported in different water sources in Uruguay, that arose in the last decade owing to the fact environments, although the highest concentrations were found in that WHO lowered the maximum recommended levels for this element groundwaters, mainly linked to natural geochemical processes in drinking water for health reasons (WHO, 2018). Also, the fact that As (Smedley and Kinniburgh, 2002), including volcanic eruptions and the is a naturally occurring element in the Earth's crust that can be released of As containing minerals (Bundschuh et al., 2008). into drinking water supply sources throughout different hydrogeological As possess a high mobility and transformation capacity that makes it processes, and the high levels found in groundwaters in certain regions of easy to be slurped or desorbed from particles, and to change its oxida- the neighboring country Argentina, emerged as the research hypothesis tion state by the action of microorganisms or when reacting with oxy- for carrying out a deeper study in our country, focused on groundwater gen or other molecules present in the air, water or soil. For this samples intended for human consumption that are out of the scope of reason, it may be present in many environmental matrixes, specially the water state-run utility. The evaluation of correlations with other water (Litter et al., 2009). inorganic parameters will increase the knowledge of the geochemical dis- Medical Geology is a growing field in Uruguay and the groundwater tribution and behavior of As in groundwaters, contributing to more effi- quality has been recently the focus of multiple studies, being As risks ex- cient remediation actions. posure from drinking water, one of its main concerns. The presence of geogenic As in groundwater has been reported in publications since 2. Materials and methods 2007, showing levels above those recommended by WHO guidelines for drinking water (10 μgL−1) in several samples collected from differ- 2.1. Reagents ent aquifers (WHO, 2018). Manganelli et al. studied the main aquifers of the southwest part of the country. Elevated As concentrations were Standard solutions for calibration curves were prepared by serial di- found in Chuy (up to 41.9 μgL−1), Raigón (up to 18.9 μgL−1)and lution of commercial stock solutions (1000 mg L−1)ofAs(V),FeandMn −1 Mercedes (up to 58 μgL ) aquifers. Guérèquiz et al. and Bundschuh (Merck, Germany) in 0.1% v/v nitric acid (HNO3)preparedfromconcen- −1 et al. found As levels between 25 and 50 μgL in groundwaters from trated HNO3 (67% v/v, Merck, Germany). A commercial solution of Pd −1 San José department. Authors assumed that As occurrence in Raigón (NO3)2 (Merck, Germany) containing 10,000 mg L was used to pre- aquifer is related to continental sediments containing volcanic ashes, pare the chemical matrix modifier for As determinations by ETAAS. as in the nearby Puelche aquifer located in Buenos Aires, Argentina. A stock solution (1000 mg L−1) of As(III) was prepared by dissolu- −1 This assumption is supported by the positive correlations between As tion of sodium arsenite (NaAsO2 99.0%, Sigma-Aldrich) in 1 mol L so- contents with other trace elements, which are typical elements from dium hydroxide (NaOH 98.0%, Merck, Germany). The reductant was a volcanic sources (Bundschuh et al., 2012; Guérèquiz et al., 2006; 0.5% w/v solution of sodium tetrahydroborate (NaBH4 99.5%, Sigma- Manganelli et al., 2007). Aldrich, Germany) in 0.4% w/v potassium hydroxide (KOH 99.0%, Gastmans et al. studied the “Thermal Corridor” of Uruguay river, lo- Merck, Germany) filtered after preparation and stored frozen. cated in the triple border between Argentina, Brazil and Uruguay, For F− determinations, a 1000 mg L−1 stock solution was prepared mainly based on groundwaters from Guaraní Aquifer System (GAS). from sodium fluoride (NaF 99.5%, Merck). A total ionic strength adjust- They found As concentrations up to 10 μgL−1 in groundwaters from ment buffer (TISAB II, Orion Thermo Scientific) was used. 2− −1 this area. As occurrence was associated to the desorption from iron ox- For SO4 determinations, a 1000 mg L stock solution was pre- ides/hydroxides, as result of the higher pH values of these sodium bicar- pared from sodium sulfate anhydrous (Na2SO4 99.9%, Merck). The bonate type waters (Gastmans et al., 2010). buffer solution was prepared from magnesium chloride hexahydrate I. Machado et al. / Science of the Total Environment 681 (2019) 497–502 499

(MgCl2.6H2O 99%, Merck), sodium acetate trihydrate (CH3COONa.3H2O comparison of the reading with a standard curve (APHA-AWWA-WEF, 99%, Merck), potassium nitrate (KNO3 99%, Merck) and acetic acid 2017). (CH3COOH 99%, Merck). Barium chloride crystals (BaCl2 99.0%, Merck), were sieved to obtain a particle size of 20–30 mesh. All other re- agents were of analytical grade unless otherwise specified. 2.3. Samples Ultrapure water of 18.2 MΩcm resistivity (ASTM Type I) was ob- tained from a Millipore Simplicity 185 purifier (São Paulo, Brazil). All A total of 48 groundwater samples from private wells were collected glassware was soaked overnight in 10% v/v nitric acid and then rinsed from different points of Uruguay, as shown in Fig. 1, at depths between exhaustively with ultrapure water. 30 and 50 m. The specific depths of the wells were obtained from its owners. Samples were collected in the autumn season between March and June 2018. The sampling points were randomly selected consider- 2.2. Analytical determinations ing their spatial distribution in the area, in order to obtain an accurately representative hydrochemistry. The fractions destined to speciation Analytical determinations of tAs, Fe and Mn were performed by elec- analysis were collected without headspaces in the sample bottles and trothermal atomic absorption spectrometry (ETAAS), using a Thermo pH was adjusted to 2.0 with HCl, in order to minimize interchanges be- Scientific iCE 3500 spectrometer (Cambridge, United Kingdom) tween As species, following the recommendations of McCleskey et al. equipped with a graphite furnace atomizer and employing Zeeman- According to these authors, the acidification with HCl and storage in based correction. Argon (Ar 99.99%, Linde, Uruguay) was used as the dark at low temperatures, successfully preserves arsenic redox spe- purge and protective gas. The analytical lines used were: 193.7 nm cies in natural waters for periods longer than 5 months. The possible (As), 302.1 nm (Fe) and 279.5 nm (Mn) and the signal used for quanti- photocatalyzed As(III) oxidation caused by Fe(III), that may occur in fication was integrated absorbance (peak-area). Hollow cathode lamps acidified groundwater samples, is inhibited in the dark (McCleskey (Thermo Scientific) were operated as recommended by the manufac- et al., 2004). Not acidified fractions were also collected without head- − 2− turer. For all the determinations, pyrolytically coated graphite tubes spaces in the sample bottles for F ,SO4 and pH measurements. All (Thermo Scientific) were used. For tAs determination palladium matrix samples were stored in polypropylene bottles and kept at 4 °C in the modifier (Merck) was used (5 μg). The graphite furnace heating pro- dark until analysis. Pneumatic submersible pumps were used for sample grams used for the analytical determinations are showed in Table 1 for collection. Samples were preserved for a period of 15 days before speci- each element. ation analysis. For iAs speciation analysis, a continuous flow hydride generation Certified reference materials (NIST 1643f - Trace elements in water system made in-house was employed. Ar 99.99% (Linde, Uruguay) and ERM CA408-Ions in simulated rainwater) were used for trueness was used as carrier gas, with a flow rate of 75 mL min−1, controlled and precision evaluation. by means of a rotameter (Cole Parmer, USA). Two T-pieces (0.8 mm inner bore) were used to merge sample flow with reductant flow and, downstream, to merge the reaction mixture flow with Ar flow. The out- 2.4. Statistical analysis let from a second T-piece was connected to a 3-mL internal volume gas– liquid separator with a forced outlet. Sample and reductant solutions Pearson correlation analysis was carried out using MS Excel®. Differ- were delivered by a peristaltic pump (RP-1 Dynamax, USA). Sample ences at a 5% significance level (p b 0.05) were considered statistically and reductant flow rates were 4.0 mL min−1 and 1.5 mL min−1 respec- significant (Miller and Miller, 1993). tively. The system was coupled to flame atomic absorption atomic The differences between the analytes concentrations in the samples spectrometry (FAAS) using a Perkin Elmer AAnalyst 200 spectrometer were tested by a one-way analysis of variance (ANOVA) followed by t- (Norwalk, CT, USA). An EDL lamp (Perkin Elmer) operated at test to evaluate the relationship between them. The analysis was per- 193.7 nm was used. The quartz T-tube cell with a path-length of formed using MS Excel®. Differences among mean concentrations at a 165 mm and a diameter of 12 mm, was heated to 980 °C by an acetylene 5% significance level (p b 0.05) were considered statistically significant. (2.5 L min−1)-air(10.0Lmin−1) flame (Lindberg et al., 2007). The previous separation of the species was achieved by a liquid chro- matograph (LC-20AT Prominence Shimadzu) working in isocratic 3. Results and discussion mode, equipped with a PRP-X100 (4,1 × 250 mm) column, using −1 20 mmol L NH4H2PO4 solution adjusted to pH 5.6 as mobile phase 3.1. Main figures of merit obtained at 2.0 mL min−1. Injection volume was 500 μL. F− concentrations were measured using a combined fluoride elec- The accuracy of the methods described in 2.2 was checked for As, Fe − 2− trode connected to a pH/ion meter (Orion VersaStar Thermo Scientific). and Mn determinations using SRM NIST 1643f and for F and SO4 For each measurement, 5 mL of sample were mixed with 1 mL of TISAB using ERM CA408, according to the parameters certified in each II solution. material. The recommendations of Eurachem Guide were followed 2− SO4 was precipitated in an acetic acid medium with barium chlo- (Magnusson and Örnemark, 2014). ride (BaCl) to form barium sulfate (BaSO4) crystals of uniform size. For trueness evaluation, a comparative study using a Student's t-test Light absorbance of the BaSO4 suspension was measured by means of was performed to establish whether there was a difference between the 2− a spectrophotometer and SO4 concentration was determined by obtained values and the certified values. All the experimental t values were below the theoretical t (0.05, 5) 2.57. Thus, it may be concluded that at the 95% confidence level, the concentrations do not differ signif- Table 1 icantly from the certified or informed value. Analytical precision Temperature programs used for the determination of tAs, Fe, Mn by ETAAS. expressed as RSD (%) for the analysis of the CRM (n =6)wasb10% Stage Temperature (°C) Ramp rate (°C s−1) Hold time (s) for all the studied elements. So, the accuracy of the methods was

Drying 100 10 50(As)/30(Fe, Mn) ensured. Pyrolysis 1200(As)/1100(Fe)/900(Mn) 150 20 Detection and quantification limits (LOD and LOQ) as well as linear- Atomization 2200(As)/2100(Fe)/1800(Mn) 03ity results for each element are summarized in Table 2. Cleaning 2600 0 3 After the evaluation of the main figures of merit, 48 groundwater Ar gas flow rate was 0.2 (L min−1) in all stages (except for atomization). samples were analyzed. Results are shown in Table 3. 500 I. Machado et al. / Science of the Total Environment 681 (2019) 497–502

Fig. 1. Main aquifers of Uruguay and 48 groundwater sampling points.

3.2. Determination of tAs and iAs species 10.28 and 17.85 μgL−1, being As(V) the predominant species in all cases. The tAs concentration values found in groundwater samples, ranged The samples form Salto department (S41 to S44 and S47 to S48) cor- from 1.7 to 120.4 μgL−1 as shown in Table 3. Almost half of the samples responds to a zone of thermal waters that emanates at 45 °C from a (23 samples) were above those levels recommended by WHO (10 depth of 1295 m (Salto aquifer). This relatively high natural concentra- μgL−1) for drinking water. Besides, 10 samples were above the limit tions (20.7–58.9 μgL−1) may be associated only to mineral components of 20 μgL−1 established by the national regulation (UNIT, 2010). of the geological framework, since there is no mining activity in this The highest concentrated samples in terms of tAs were S7 (120.4 area. These findings are in accordance with those reported by Gastmans μgL−1) and S23 (63.24 μgL−1). Both were taken from Santa Rosa city et al. in a previous study in which the occurrence of high As levels in located in Canelones department, being As(v) the predominant species groundwater in this thermal area was pointed out, mainly based on (110.5 and 61.40 μgL−1 respectively) in each case. This area corre- samples from Guaraní aquifer. The authors found levels up to 116 sponds to Cretácicos Sur aquifer, which is described as a porous aquifer μgL−1 in water samples from the “Thermal Corridor” of Uruguay river, composed of fine , with clay cement and low dissolved Fe with pH values N7(Gastmans et al., 2010). levels. These results are in accordance with the characteristics of the Moreover, 28 out of the 48 samples showed higher As(V) levels, geological environment, considering the high pH value, the relatively which is in agreement with the oxidizing conditions of the wells. 2− high SO4 concentration and the low Fe concentration obtained for Since the pH values of the wells were between 6.5 and 8.7, the higher these samples. Samples S1, S2, S10, S11, S17, S24, S26 and S27, also ex- As(V) levels found were in accordance with Smedley et al. who postu- tracted from this area, presented relatively high tAs values between lates that under the aerobic and near-neutral conditions typical of

Table 2 Main analytical figures of merit obtained for the applied methodologies.

Element LOD LOQ Linearity Precision Trueness (mg L−1)(3s; n = 10) (mg L−1) (10s; n = 10) (mg L−1) (RSD %; n = 6) (recovery %; n = 6)

tAsa 0.00051 0.0017 Up to 0.020 b10 97–105 iAs(III)b 0.00057 0.0019 Up to 0.020 b10 94–103 iAs(v)b 0.00096 0.0032 Up to 0.050 b10 96–104 Fea 0.0006 0.0020 Up to 0.100 b597–101 Mna 0.00003 0.00011 Up to 0.003 b597–103 F−c 0.006 0.020 Up to 2.0 b598–101 2−c SO4 0.018 0.060 Up to 40.0 b10 99–102 a NIST 1643f. b Fortified samples. c ERM CA408. I. Machado et al. / Science of the Total Environment 681 (2019) 497–502 501

Table 3 In general terms, As presence in water bodies is a function of space − 2− Concentrations of tAs, As(III), As(V), F , Fe, SO4 and Mn and pH values obtained after the and time. It depends on the As sources, the sample characteristics (pH, analysis of 48 groundwater samples intended for human consumption in Uruguay. redox potential, other ions presence, organic matter content) and the − 2− Sample tAs F Fe SO4 Mn pH As(III) As(V) interfacial processes that occur between the sample and the solid sup- (ug (mg (μg (mg (μg (μg (μg port. These interactions comprise chemical and physicochemical pro- −1 −1 −1 −1 −1 −1 −1 L ) L ) L ) L ) L ) L ) L ) cesses and microbiological transformations. The mobilization will be S1 14.33 0.668 51.04 10.9 4.51 8.351 5.81 9.19 determined by the As source and the hydrogeochemical conditions of S2 10.28 0.723 26.26 12.73 0.65 7.622 3.59 7.35 the sampling area (Bundschuh et al., 2012). S3 3.64 0.898 10.21 1.59 0.11 7.887 ND 3.60 S4 9.69 0.614 14.88 29.2 0.12 7.950 3.21 5.81 High As concentrations were found in groundwaters from 10 Latin S5 9.88 0.387 18.05 13.06 0.55 7.271 5.98 3.74 American countries, showing that many localities were affected by S6 6.33 0.726 9.93 11.41 0.47 8.048 3.59 3.45 high As levels in a significant manner (Bundschuh et al., 2012). The in- S7 120.38 1.0286 18.14 134.45 5.09 8.532 9.80 110.50 creased number of sites also suggests that other zones with similar geo- S8 1.72 0.207 9.61 11.11 1.16 7.428 1.91 ND logical characteristics may suffer the same problem. S9 20.92 0.522 12.35 25.05 0.11 8.526 4.82 15.00 S10 13.98 0.530 7.42 103.16 ND 8.477 ND 13.50 Chronic exposure to As concentrations in drinking water above 10 −1 S11 16.32 0.279 13.51 36.44 2.61 8.431 3.36 12.75 μgL is a major cause of concern, since substantial epidemiological ev- S12 1.93 0.037 3.94 0.63 0.13 6.684 1.95 ND idence is available to support its association with several detrimental ef- S13 12.97 0.8149 33.26 45.01 1.81 8.678 ND 12.25 fects on human health including skin lesions and different types of S14 1.89 0.1825 19.63 8.69 0.12 7.800 1.95 ND S15 1.72 0.6482 23.94 9.81 0.11 7.516 1.99 ND cancer, as well as neurological, respiratory, cardiovascular, immunolog- S16 1.79 0.444 17.99 13.47 0.15 7.644 1.97 ND ical and endocrine effects. However, effects of chronic exposure to low S17 16.89 0.5111 12.42 102.72 0.82 8.705 ND 16.32 concentrations, as occurs in many developed countries, are unclear S18 3.65 0.174 23.68 52.82 0.14 6.533 3.69 ND (Ahmad and Bhattacharya, 2019). For this reason, water utilities should S19 11.42 0.612 13.73 70.67 0.11 7.848 ND 11.22 make the effort to keep As levels in drinking water as low as reasonably S20 7.21 0.389 13.60 16.71 0.12 8.465 ND 7.72 S21 8.89 0.389 37.18 16.53 1.25 7.368 ND 8.73 possible by investing in research to better understand the fate and be- S22 19.15 0.586 5.67 11.07 0.18 7.510 4.51 14.75 havior of As in natural systems. One remarkable example is The S23 63.24 0.479 20.42 84.74 0.17 7.917 ND 61.40 Netherlands, where water companies are making efforts to establish a S24 17.85 0.145 13.27 468.45 0.99 7.266 ND 17.81 maximum limit for As in drinking water of 1 μgL−1 (Ahmad and S25 53.58 0.659 2.06 23.64 0.12 7.635 25.14 27.71 S26 16.34 0.300 8.52 13.44 0.11 8.057 ND 16.03 Bhattacharya, 2019). S27 10.50 0.417 11.66 63.57 0.14 8.115 3.02 7.67 S28 1.80 0.087 47.52 0.63 9.37 8.366 2.01 ND 2− S29 1.90 0.026 189.87 4.96 0.42 7.531 1.93 ND 3.3. Determination of F-, Fe, Mn and SO4 S30 1.95 0.024 242.69 10.26 0.90 7.112 1.98 ND − 2− S31 11.90 0.552 55.39 223.33 5.01 6.563 ND 11.22 Levels of F , Fe, Mn and SO4 in the analyzed samples ranged from S32 1.76 0.453 53.06 37.49 0.12 7.497 1.98 ND 0.024to1.53mgL−1, 2.0 to 242.7 μgL−1, 0.11 to 115.9 μgL−1 and 0.62 S33 1.86 0.224 52.33 4.91 0.38 7.397 1.95 ND − to 468.5 mg L 1 respectively (Table 3). These results revealed a signifi- S34 1.81 0.028 5.02 5.23 115.60 6.815 1.93 ND S35 2.20 0.306 5.74 16.4 28.00 7.313 2.15 ND cant variability among samples. This could be related to the geochemical S36 1.78 0.051 16.45 0.62 115.90 7.737 1.93 ND characteristics of the sampling area, as stated by various authors, includ- S37 2.39 0.183 14.23 2.22 59.32 7.030 2.41 ND ing Chenini et al. The type and concentration of minerals in groundwa- S38 2.48 0.152 211.38 16.0 6.75 7.849 2.35 ND ter samples depend on several factors such as soluble products of rock S39 18.33 0.535 6.65 45.9 2.00 7.801 ND 17.47 S40 7.41 0.632 2.37 76.65 2.93 7.232 ND 6.52 weathering and decomposition, in addition to water-rock interactions S41 32.66 0.844 30.52 13.73 0.95 8.686 ND 34.2 by dissolution and dilution processes (Chenini et al., 2010). The accu- S42 20.66 0.949 30.01 44.37 0.83 8.678 ND 21.9 mulation of ions in groundwaters may vary according to the geological S43 32.91 0.892 22.00 68.81 0.56 8.590 8.90 24.1 frame of the geographic location. In this case, an important factor could S44 29.62 0.926 22.19 43.68 0.55 8.659 2.02 27.4 be the different types of aquifers encountered at the south and north- S45 1.82 0.607 39.84 7.46 0.74 6.879 1.93 ND S46 1.87 0.102 2.00 13.22 1.54 7.257 1.91 ND west regions of Uruguay countryside (Collazo and Montaño, 2012). S47 42.00 1.525 61.50 45.2 0.50 8.325 4.75 37.10 The samples S47 and S48 from Salto department (Salto aquifer) pre- S48 58.9 1.528 95.50 51.8 0.45 8.514 6.30 50.30 sented the highest F− values, exceeding the limit of 1.5 mg L−1 recom- ND: not detected. mended by WHO. This could be related to natural geochemical processes such as the ion exchange with the increase of the precipita-

tion of fluorite (CaF2)(Navarro et al., 2017). Samples S7, S9, S13, S17 (Cretácicos Sur aquifer) and samples S41, many natural environments, As is very strongly adsorbed by oxide min- S42, S43, S44, S48 (Salto aquifer) exceed the pH limit of 8,5 recom- erals as the arsenate ion. As pH increases, especially above pH 8.5, As de- mended by WHO and UNIT (WHO, 2018; UNIT, 2010). Also, sample sorbs from the oxide surfaces, thereby increasing the concentration of S24 (Cretácicos Sur aquifer) exceeds the recommended SO2− value of As in solution (Smedley and Kinniburgh, 2002). 4 400 mg L−1. Samples S34 and S36 exceed the recommended Mn limit On the other hand, 20 out of 48 samples presented higher As(III) −1 − of 0.1 mg L . All these results show the needing of being aware of levels. The highest concentrated sample was S25 with 25.14 μgL 1.It the health risks associated with drinking water from private wells corresponds to the Mercedes aquifer area which is located in the which are not properly controlled. Mercedes Formation (Upper Cretassic), composed by continental sedi- ments based on conglomerates, sandstones and pelites (Bundschuh et al., 2012). Regarding tAs concentration, S25 was in fourth position 3.4. Correlation analysis (53.58 μgL−1), being this high level in accordance with previous results of Manganelli et al. (Manganelli et al., 2007). Pearson correlation analysis between As, As(III) and As(V) with the Samples S28–S30, S35 and S37, that corresponds to Guarani aquifer studied inorganic parameters were carried out, using MS Excel®. Re- − area, presented low tAs levels (1.80–2.39 μgL 1), being As(III) the pre- sults showed highly significant positive correlation coefficients (p b dominant species in all cases. Moreover, samples S45 and S46 that cor- 0.05) for some combinations as shown in Table 4. Highly significant pos- respond to Cebollati and Chuy aquifers respectively, presented low tAs itive correlation coefficients (p b 0.05) for tAs/F− (r = 0.5904), tAs/pH – μ −1 − 2− levels (1.82 1.87 gL ), being As(III) the predominant species as well. (r = 0.4385), As(V)/F (r = 0.5901), As(V)/SO4 (r = 0.3002) and As 502 I. Machado et al. / Science of the Total Environment 681 (2019) 497–502

Table 4 Declaration of competing interest Pearson correlation coefficients between tAs – As(III) – As(V) with the studied inorganic parameters F− – Fe – SO2− – Mn – pH, obtained after the analysis of 48 groundwater 4 The authors declare that there is no conflict of interest regarding the samples. publication of this article. 2− FFeSO4 Mn pH ⁎ ⁎ As 0.5904 −0.0893 0.2627 −0.1657 0.4385 References As(III) 0.2387 −0.0442 −0.0979 −0.0497 0.0637 ⁎ ⁎ ⁎ As(V) 0.5901 −0.0892 0.3002 −0.1679 0.4651 Ahmad, A., Bhattacharya, P., 2019. Arsenic in drinking water: is 10 μg/L a safe limit? Curr. Pollut.Rep.5(1),1–3. https://doi.org/10.1007/s40726-019-0102-7. ⁎ Significate correlations (level of significance: p b 0.05) are highlighted in bold. American Public Health Association (APHA), American Water Works Association (AWWA), Water Environment Federation (WEF), 2017. Standard Methods for the 2− fi Examination of Water and Wastewater. 23rd edition. Method 4500-SO4 E. (V)/pH (r = 0.4651) were found. However, non-signi cant correlation Bundschuh, J., Pérez Carrera, A., Litter, M. (Eds.), 2008. IBEROARSEN. Distribución del coefficients were found for the other pairs. arsénico en las regiones ibérica e iberoamericana. CYTED, Argentina. The strong correlation between tAs and F− may be due to the disso- Bundschuh, J., Litter, M., Faruque, P., Román-Ross, G., Nicolli, H.B., Jean, J., Liu, C., López, D., lution of As-containing minerals facilitated by the alluvial Armienta, M.A., Guilherme, L.R.G., Gomez Cuevas, A., Cornejo, L., Cumbal, L., Toujaguez, R., 2012. One century of arsenic exposure in Latin America: a review of fl basin, as well as the ion-exchange with uorite (CaF2)(Navarro et al., history and occurrence from 14 countries. Sci. Total Environ. 429, 2–35. https://doi. − 2017). F is a highly reactive element that combines with other ele- org/10.1016/j.scitotenv.2011.06.024. fi ments in covalent and ionic bonds. It is found mainly in alkaline rocks Chenini, I., Farhat, B., Ben Mammou, A., 2010. Identi cation of major sources controlling groundwater chemistry from a multilayered aquifer system. Chem. Speciat. and soils, being CaF2 the principal component (Giménez et al., 2013). Bioavailab. 22 (3), 183–189. https://doi.org/10.3184/095422910X12829228276711. − This high correlation between tAs and F supports the hypothesis of a Collazo, M.P., Montaño, J., 2012. Manual de agua subterránea. Ministerio de Ganadería common source for these analytes, which could be related to the disso- Agricultura y Pesca, Montevideo, Uruguayhttp://www.aquabook.agua.gob.ar/files/ upload/contenidos/10_2/Manual-de-agua-subterranea-Uruguay.pdf, Accessed date: lution of volcanic glass, especially in the western part of the country, as October 2018. stated by Guérèquiz et al. (2006). Moreover, the high correlation be- Gastmans, D., Veroslavsky, G., Chang, H.K., Marmisolle, J., Oleaga, A., 2010. Influence of tween tAs and F− with pH contributes to this hypothesis. hydrostratigraphic framework in aresenic occurence in groundwater along the 2− Uruguay River thermal corridor (Argentine-Brazil-Uruguay). Geociencias 29, The strong correlations between As(V) with pH and SO4 are in ac- 105–120 https://www.revistageociencias.com.br/geociencias-arquivos/29_1/Art% cordance with the oxidizing environment, since As(V) generally consti- 2008_Gastmans.pdf (Accessed: October 2018). tutes a high proportion of tAs in such conditions, given by high pH Giménez, M.C., Blanes, P.S., Buchhamer, E.E., Osicka, R.M., Morisio, Y., Farías, S., 2013. As- 2− sessment of heavy metals concentration in arsenic contaminated groundwater of the values and relatively high concentrations of SO4 . Chaco Plain, Argentina. ISRN Environ. Chem., 1–12 https://doi.org/10.1155/2013/ Despite of the very homogeneous geomorphologic features at a 930207. small scale, the distribution of As and the other inorganic parameters Guérèquiz, A.R., Mañay, N., Goso Aguilar, C., Bundschuh, J., 2006. Evaluación del riesgo concentrations in groundwater is heterogeneous. This is probably due ambiental por presencia de arsénico en el sector oeste del acuífero Raigón, Depto. de San José, Uruguay. Presentación del proyecto. En: M. Litter (ed): Libro de to differences in the materials that constitute each type of aquifer, that Resúmenes del Taller de Distribución del As en Iberoamérica. Buenos Aires, may induce the resulting changes in the geochemical conditions re- Argentina, 103–104. quired for the mobilization of these parameters. INE, 2011. Results of 2011 Uruguayan Population Census: population, growth and struc- ture by sex and age. http://www.ine.gub.uy/documents/10181/35289/analisispais. pdf, Accessed date: October 2018. 4. Conclusions Lindberg, A.L., Goessler, W., Grandér, M., Nermell, B., Vahter, M., 2007. Evaluation of the three most commonly used analytical methods for determination of inorganic arsenic and its metabolites in urine. Toxicol. Lett. 168, 310–318. Groundwater analysis showed that in some sampled points As levels Litter, M., Armienta, M., Farías, S. (Eds.), 2009. IBEROARSEN. Metodologías analíticas para were above those recommended by WHO guidelines for drinking water, la determinación y especiación de arsénico en aguas y suelos. CYTED, Argentina. being the highest values found in samples from the “Thermal Corridor” Magnusson, B., Örnemark, U., 2014. Eurachem Guide: The Fitness for Purpose of Analytical − 2− Methods – A Laboratory Guide to Method Validation and Related Topics. second ed. and the Cretácicos Sur aquifer. Parameters such as F ,MnandSO4 also 978-91-87461-59-0 Available from. http://www.eurachem.org. presented higher concentration values than those recommended by Manganelli, A., Goso, C., Guerequiz, R., Fernández Turiel, J., García Vallés, M., Gimeno, D., WHO in some of the samples. Besides, strong positive Pearson correla- Pérez, C., 2007. Groundwater arsenic distribution in South-Western Uruguay. Envi- − − 2− ron. Geol. 53, 827–834. tions were found for the pairs tAs/F , As(V)/F and As(V)/SO4 ,inac- McCleskeya, R.B., Nordstrom, D.K., Maest, A.S., 2004. Preservation of water samples for ar- cordance with the characteristics of the geological environments. senic (III/V) determinations: an evaluation of the literature and new analytical re- The lack of knowledge of As in groundwater issues as a drinking sults. Appl. Geochem. 19, 995–1009. water source for human consumption in Uruguay is a major area of in- Miller, J.N., Miller, J.C., 1993. Estadística para Química Analítica. second ed. Addison- Wesley Iberoamerican S.A, Wilmington, Del, USA. terest in Medical Geology research, as there is also a lack of epidemio- Navarro, O., González, J., Júnez-Ferreira, H.E., Bautista, C., Cardona, A., 2017. Correlation of logical studies on As exposure health risks. As levels in groundwater arsenic and fluoride in the groundwater for human consumption in a semiarid region – and its relationship with other elements, should be deeply studied to of Mexico. Procedia Eng. 186, 333 340. https://doi.org/10.1016/j.proeng.2017.03.259. OSE, 2018. Water supply. http://www.ose.com.uy/agua, Accessed date: September 2018. prevent long-term health effects. The results of this ongoing study will Smedley, P., Kinniburgh, D., 2002. A review of the source, behavior and distribution of ar- contribute not only to the understanding of the As situation of ground- senic in natural waters. Appl. Geochem. 17, 517–568. water in Uruguay but also to expand the existing information on the dis- Smedley, P., Kinniburgh, D., 2013. Arsenic in groundwater and the environment. In: Selinus, O. (Ed.), Essentials of Medical Geology. Springer, Dordrecht, pp. 279–310. tribution of As species in the regions of the world. Smedley, P.L., Zhang, M., Zhang, G., Luo, Z., 2001. Arsenic and other redox-sensitive ele- ments in groundwater from the Huhhot Basin, Inner Mongolia. In: Cidu, R. (Ed.), Acknowledgements Water-Rock Interaction. Lisse A.A. Balkerna, pp. 581–584. UNIT, 2010. Norma 833:2008. Agua Potable – Requisitos. http://www.ose.com.uy/ descargas/Clientes/Reglamentos/unit_833_2008_.pdf, Accessed date: October 2018. The authors would like to thank Agencia Nacional de Investigación e WHO, 2018. Arsenic. Key Facts. World Health Organization, Geneve, Switzerland http:// Innovación (ANII) and PEDECIBA-Química. www.who.int/news-room/fact-sheets/detail/arsenic (Accessed: September 2018).