Who to blame for groundwater fluoride anomaly in São Paulo, Brazil? Hydrogeochemistry and isotopic evidence

Accepted Manuscript Who to blame for groundwater fluoride anomaly in São Paulo, Brazil? Hydrogeochemistry and isotopic evidence Veridiana T.de S. Martins, Daphne Silva Pino, Reginaldo Bertolo, Ricardo Hirata, Marly Babinski, Diego Felipe Pacheco, Ana Paula Rios PII:

S0883-2927(17)30395-5

DOI:

10.1016/j.apgeochem.2017.12.020

Reference:

AG 4015

To appear in:

Applied Geochemistry

Received Date: 18 May 2017 Revised Date:

8 December 2017

Accepted Date: 18 December 2017

Please cite this article as: Martins, V.T.d.S., Pino, D.S., Bertolo, R., Hirata, R., Babinski, M., Pacheco, D.F., Rios, A.P., Who to blame for groundwater fluoride anomaly in São Paulo, Brazil? Hydrogeochemistry and isotopic evidence, Applied Geochemistry (2018), doi: 10.1016/ j.apgeochem.2017.12.020. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Who to blame for groundwater fluoride anomaly in São Paulo, Brazil? Hydrogeochemistry and isotopic evidence

Veridiana T. de S. Martins1*; Daphne Silva Pino2, Reginaldo Bertolo1, Ricardo Hirata1, Marly

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Babinski3, Diego Felipe Pacheco4, Ana Paula Rios2

1 Departamento de Geologia Sedimentar e Ambiental, Instituto de Geociências, Universidade de São Paulo;

2 Programa de Pós-Graduação em Recursos Minerais e Hidrogeologia, Instituto de Geociências, Universidade de São Paulo;

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3 Departamento de Mineralogia e Geotectônica, Instituto de Geociências, Universidade de São Paulo 4 PETROBRAS

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*corresponding author: [email protected]

ABSTRACT

Fluoride concentrations up to 10 mg.L-1 have been described in the groundwater of the biggest South American City, São Paulo, Brazil. Possible suspects were minerals in crystalline or

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sedimentary rocks, or industrial activities. Hydrochemistry tools pointed that the fluoride occurrence has positive correlation with Na and HCO3- concentrations and negative correlation with Ca2+. The saturation index are negative for fluorite in all samples, but samples with high fluoride

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content have calcite saturation index close to zero, indicating the precipitation of calcite maybe a

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mechanism that is taking out the Ca+2 and enhancing fluorite dissolution. Samples with fluoride concentrations >1.5 mg.L-1 are related to samples more depleted in H and O heavier isotopes and deeper groundwater flow with higher temperature. This anomaly is probably associated with fluorite dissolution, present in a fault system with an ancient hydrothermal activity, with deep circulation of groundwater flows in the crystalline basement rocks.

Keywords: fluoride, stable isotopes, crystalline rocks, deep groundwater systems, fractured aquifer 1 INTRODUCTION

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Fluoride can be ingested by humans through food and water, but its major source of human intake is groundwater (Jacks et al., 2005). Fluoride in groundwater can be considered both beneficial and harmful to health (Shand et al., 2007). Its absence in human dietary may limit the growth and impair fertility. However, if ingested in excess fluoride can cause some diseases

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(Edmunds and Smedley, 2005). Water with fluoride concentrations of up to 1.5 mg.L-1 promotes dental health, but dental fluorosis is generated above this value. Skeletal fluorosis may occur above 4 mg.L-1, and the disabling fluorosis happens above 10 mg.L-1 of F- (Edmunds and Smedley, 2005).

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However, these values are not norm as nutrition is considered to be an essential factor in the disease outcome, as well as diet (deficiencies in calcium and vitamin C are recognized as exacerbating

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factor) and age (Edmunds and Smedley, 2005). Besides dental and skeletal fluorosis, enzyme damages is another effect of fluoride in high concentrations, resulting in genetic damage, premature aging, mental retardation, cancer, bone pathology, etc. (Hurtado and Tiemann, 2000). Chae et al. (2007) mention several articles describing the occurrence of fluorosis in many countries, related to the consumption of water with high fluoride levels, showing that this is a global

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problem, particularly in water-stressed regions (Chen et al., 2012). Although the World Health Organization (WHO) guideline values for fluoride in water was

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set at 1.5 mg.L-1 in 1984 and reaffirmed in 1993 (WHO, 2011), it is not a global value. People that live in hot climates perspire and drink more water. On the other hand, the fluoride standard should

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be revised in some cases where the WHO guideline is adopted: in Brazil, endemic cases of dental fluorosis were reported in places where fluoride concentration reached only 1.18 mg.L-1 (Diniz, 2006).

In spite of having some cities with endemic fluorosis, Brazil did not appear in a compilation of studies presented by Unicef, where 27 countries are indicated suffering of endemic fluorosis (Qian et al., 1999) nor in other similar works (Ali et al., 2016; Vithanage and Bhattacharya, 2015). The same study presents a conservative estimation of tens of millions people affected. For instance, in Mexico, 5 million people (approximately 6% of the population) suffer from fluorosis due to

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consumption of water with high concentration of fluoride (Qian et al., 1999). In turn, in India, 62 million people are affected by the disease, of which 6 million are children (Bishnoi and Arora, 2007; Jacks et al., 2005). On the other hand, in some parts of central and western China, fluorosis is caused not only by drinking groundwater with high fluoride concentrations but also by breathing

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airborne fluoride released from the burning of fluoride-laden coal (Qian et al., 1999). Understanding the origin of fluoride in groundwater is an essential tool for the management of water resources, not only to minimize the negative impact of fluoride on human health but also to

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use this anomaly for improving the water quality exploited by public supply surveys.

The Environmental Agency of São Paulo State (CETESB), Brazil, identified fluoride above

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the Brazilian standards value of 1.5 mg.L-1 (equal to the WHO guideline) in some wells. These wells, used as an alternative supply system, were located in the Barra Funda District, west side of São Paulo city, and presented F concentrations up to 10 mg.L-1.

The occurrences of anomalous concentrations of fluoride in the Brazilian aquifers are usually overlooked in publications with international reach. From the sixteen studies reported,

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seven are in Portuguese. Regarding Sao Paulo State, the place where the current research took place, just two studies were reported but no one in the same city of this work.

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Fluorine is the 13th most abundant element in the continental crust, with a mean concentration of 300 mg/kg (Brindha and Elango, 2011). It occurs mainly in igneous and alkaline

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rocks, and in phosphatic and micaceous sedimentary deposits. Its most common mineral occurrence is fluorite, but fluorine may also be present in apatite, biotite, illite and amphibole group. The chemical composition of groundwater is a result of its interaction with the minerals existing on the aquifer’s rocks plus the possible anthropogenic inputs present at the recharge water. The primary sources of high concentrations of fluoride in the groundwater are: i) mixing between shallow aquifers and deep thermal waters, ii) dissolution of rock minerals containing fluoride and iii) anthropogenic inputs in aqueous systems (Leybourne et al., 2008).

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The natural concentration of fluoride in groundwater is commonly less than 1 mg.L-1 (Leybourne et al., 2008; Msonda et al., 2007). There are, however, occurrences of higher natural concentrations, such as those observed in the waters of the Guarani Aquifer System in the Pontal do Paranapanema (SP), which exceed 12 mg.L-1 (Silva, 1983; Perroni et al., 1985). The presence of

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this ion in the groundwater and sedimentary rocks of the Guarani Aquifer System is mainly attributed to the weathering processes of igneous rocks (Fraga, 1992).

The anthropogenic sources are related to F-bearing minerals exploration (Tirumalesh et al.,

and the use of phosphate in agriculture (Datta et al., 1996).

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2007), mineral ore processing using hydrofluoric acid (Senior and Sloto, 2006), pottery industry

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Ions (major, minor or trace) transported by water can be used as markers of the environment, since the presence and concentrations of these ions reflect the geochemical signature of sources, both recharge water or host rocks.

Stable isotopes such as H, and O have been used in studies to trace fluoride contamination in groundwater, as in Datta et al. (1996), Travi and Chernet, (1998), and Tirumalesh et al. (2007).

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Datta et al. (1996) observed that high-fluoride groundwaters are related to high δ18O signatures (isotopically enriched) indicating significant quantities of evaporated irrigation and surface-runoff

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waters that infiltrate and leaches the fluorite salts from soils. Tirumalesh et al. (2007) applied isotopes of oxygen and hydrogen (also including tritium dating) to a study in India and described a

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positive correlation between fluoride and δ18O, associated to the presence of high tritium indicating the contribution of surface waters contaminated by anthropogenic activities. Kim and Jeong (2005) associated high fluoride samples to higher deuterium-excess values, low nitrate levels and low δ18O that support the idea of higher fluoride levels being associated with older groundwater. O and H isotopes helped to describe two groups of high fluoride groundwater in Canada (Desbarats, 2009) indicating a group highly depleted

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O compositions indicative of recharge under much cooler

climatic conditions than present and another group less depleted associated with local recharge.

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Petelet-Giraud et al. (2007) investigated the anthropogenic contamination of an aquifer in a heavily industrialized area in Germany, where isotopic data of hydrogen and oxygen were essential to distinguish different groups of water and mixtures. Regarding the source of fluoride contamination, few published studies are related to

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anthropogenic sources, e.g.: India (Datta et al., 1996; Kundu et al., 2009; Tirumalesh et al., 2007), China (Hu et al., 2013), Indonesia (Heikens et al., 2005), Palestine (Abu Jabal et al., 2014), Pakistan (Farooqi et al., 2007), Mexico (Birkle and Merkel, 2000), USA (Senior and Sloto, 2006) and Brazil

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(Mirlean and Roisenberg, 2007). Nonetheless, the majority of the researches are related to natural sources of fluoride, mainly derived from weathering of F-bearing minerals.

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The higher fluoride concentrations were reported in volcanic rocks assemblages, such as the African Rift Valley, at Ethiopia, where wells are found with up to 32 mg.L-1 of fluoride (Furi et al., 2011) and Kenya, whose springs present fluoride concentrations of up to 110 mg.L-1 (Gaciri and Davies, 1993) and lakes with 2,800 mg.L-1 (Murray, 1986).

In Brazil, most examples come from the Rio Grande do Sul State (six studies), in the south

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of the country (Costa et al., 2004; Marimon, 2006; Mirlean and Casartelli, 2002; Mirlean and Roisenberg, 2007; Nanni et al., 2008; Viero et al., 2009), where endemic fluorosis has been

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detected in several districts (e.g. Venâncio Aires, Santa Cruz do Sul, Vera Cruz, Pântano Grande, General Câmara, Cidade do Rio Grande). Viero et al. (2009) studied a fluoride anomaly that occurs

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in a granitic aquifer in the area of Porto Alegre city, Rio Grande do Sul state, with concentrations up to 6.13 mg.L-1. This concentration results from the dissolution of secondary fluorite filling fractures in the granitic and gneissic rocks. There is also an important occurrence at Minas Gerais State (southeast Brazil,), where endemic fluorosis is also reported in the districts of Verdelândia, Varzelândia and São Francisco (four studies). These occurrences are related to karstic aquifers and presented fluoride concentrations up to 11 mg.L-1 (Dias and Bragança, 2004; Diniz, 2006; Menegasse-Velásques et al., 2004; Silva et al., 2008). Two other studies related to endemic fluorosis occur in the northeast Brazil at the districts of São João do Rio do Peixe, and Catolé do

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Rocha, in the Paraíba State. These are related to magmatic and metamorphic aquifers with fluoride concentrations up to 9.3 mg.L-1 (CPRM, 2005; Martins et al., 2012; Souza et al., 2013). In São Paulo State (southeast Brazil), where this study took place, there are only five works published, which included studies in the innermost part of the state (Cities of Santa Albertina, Salto,

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Indaiatuba and many other localities), far away from the site where this study was conducted. One of these cases was related to the Guarani Aquifer System, where fluoride is associated with the black shale from Irati Formation, of the Paraná Sedimentary Basin (Kern et al., 2007). The

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remaining three articles related the fluoride contamination to hydrothermal fluids associated to the basaltic lava of the Paraná Basin (Ezaki et al., 2016; Giampá and Franco Filho, 1982; Hypolito et

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al., 2010) or to the sediments of the basin (Ezaki et al., 2016; Hypolito et al., 2010), originated from Neoproterozoic granitic rocks of the basement (Fraga, 1992). Hypolito et al. (2010) showed the occurrence of fluoride of up to 3.31 mg.L-1 in the crystalline aquifer at Salto and Indaiatuba region (São Paulo state), caused by weathering of minerals such as biotite, present in the granitic rocks. Some other studies (Valenzuela-Vásquez et al., 2006 - Mexico; Kim and Jeong, 2005 -

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Korea; Kundu et al., 2001 - India) indicated the relationships between deep regional flows, hydrothermal systems, and faults that cut granite bodies as a possible origin for fluoride in

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groundwater.

Both Banerjee (2015) and Vithanage and Bhattacharya (2015), in compilation studies of

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fluoride occurrences, and Ezaki et al. (2016) in São Paulo State occurrences study, describe common features for this anomaly, being a Na-HCO3- groundwater type, poor in Ca2+ and with long residence time.

The present study aims to investigate the origin of the fluoride anomaly at Barra Funda district (Sao Paulo city), using isotopic (H and O) and hydrochemistry tools. Helping the groundwater resource management in evaluating the possible risks of high concentrations of fluoride to human health, expanding and improving similar studies in Brazil and contextualizing this research among others, may be important contributions of this work.

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ACCEPTED MANUSCRIPT 2 STUDY AREA: A DISTRICT IN SAO PAULO, BRAZIL 2.1 Population, climate and relief This study focused on the Barra Funda district, São Paulo city, where fluoride

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concentrations higher than 1.5 mg.L-1 have been observed by environmental agencies. The study area is located within the Upper Tietê Watershed - UTW (Fig. 1), the most densely populated hydrologic unit in Brazil with 17.5 million people (Hirata and Ferreira, 2001). Particularly, São

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Paulo city is highly urbanized and has a complex urban infrastructure, not being self-sustained in water supply and therefore imports water from other watersheds (FABHAT, 2013). Barra Funda

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district has over 14,000 people living in 5.9 km2 (PMSP, 2010).

The UTW is under humid tropical climate, with a total mean annual precipitation of 1,400 mm (FUSP, 2009). The rain is irregularly distributed along the year, with periods of intense rainfalls (December to March) and droughts (May to August). In the sub-region of the UTW that comprises the study area, Pereira Filho et al. (2007) indicate, over a period of 70 years, an increase

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of 2.1ºC in the temperature and of 395 mm in annual precipitation, and a decrease of 7 % in relative humidity. The study suggests that the cause is mainly anthropic, given the reduction in green areas,

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the horizontal and vertical expansion of the urban area, and the increase of air pollution. Climate changes in urban areas affect the hydrologic cycle, favour the formation of heat islands, accelerate

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evapotranspiration and withdraw the local water table (FABHAT, 2013). Regarding topography, three regional relief units constitute the UTW: two plateau units and a fluvial plain (FABHAT, 2013). The former two have altitudes between 760 and 800 m, with a ridge of 800 and 850 m and slopes of 20-30%. The latter lies at elevation of 720 to 740 m.

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Fig. 1 – Localization and geology of the study area.

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2.2 Geology

The study area is comprised within the São Paulo Sedimentary Basin (BSP), consisted of Cenozoic (Paleogene to Neogene) sedimentary deposits, settled on Precambrian (Archean to Neoproterozoic) crystalline basement rocks (Fig. 2). The BSP has a maximum thickness of 290

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meters (Takiya, 1997). The basement rocks are composed of metamorphic and granitic rocks. According to Juliani (1993), the crystalline basement rocks and intrusive granitoids that crop out in the BSP region are separated by Taxaquara (Hennies et al., 1967) and Rio Jaguari

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(Cavalcante and Kaefer, 1974) fault zones (Fig. 2). The São Roque and the Serra do Itaberaba Groups are located north of these faults, where meta-volcanic rocks and metasediments

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predominate. The Embu Complex presents metamorphic rocks such as schists, gneisses, quartzites, granites and calcsilicate and is located south of these faults (Hasui and Oliveira, 1984; Juliani, 1993; Melo et al., 1989). Minor faults and shear zones affect the whole set of rocks. The presence of faults favours fluids percolation, including hydrothermal ones, allowing their filling with crystallized minerals from these fluids, including fluorite..

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The BSP is placed within the context of the Continental Rift of Southeastern Brazil (Riccomini, 1989) and is formed by Taubaté Group rocks, Itaquaquecetuba Formation and recent

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deposits. The Taubaté Group consists of: i) Resende Formation, comprising diamictites and conglomerates, and sandy mudstones, originated in a system of alluvial fans in a braided river

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floodplain, and represent 80% of the volume of sediments in the BSP; ii) Tremembé Formation, with a predominance of mudstones and shales, that are associated with lacustrine depositional system, iii) São Paulo Formation is comprised of sandstone to mudstone-siltstone deposits of a meandering fluvial system.

Tremembé Formation was recognized in excavations for the construction of the underground station of Barra Funda (Riccomini et al., 2004), located in the area of this study. Drill core data show that the formation exceeds 60 m thickness in this area. Based on pollen spectrum, this sediments were dated as Oligocene (Riccomini et al., 2004).

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By turn, the Itaquaquecetuba Formation, composed of rocks with various granulometry, from mudstones to sandstones, conglomerates and breccias, represents a system of braided river (Riccomini, 1989; Riccomini et al., 1992), deposited in disconformity over São Paulo Formation. Finally, as recent deposits of Holocene age, unconsolidated sediments and clayed sandstone occur

deposits outcrop around the study area (Fig. 1).

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along extensive flood plains associated with major rivers in the area (Tietê and Pinheiros). All these

Riccomini (1989) identified smectite and illite as the main clay minerals in the BSP

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sediments, particularly in the Taubaté Group, which may carry adsorbed fluoride in their structure. This was also observed by Melo et al. (1989). Evidence of hydrothermal activity in the

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conglomeratic sediments of the BSP was also identified, which would be explained by the circulation of juvenile or meteoric heated acid solutions (250 ± 150 °C) through the intersection of Caucaia and Taxaquara faults under the BSP. The occurrence of hydrothermal events is significant because of the ability of such solutions to mobilize fluoride contained in the rocks. Sant’Anna and Riccomini (2001) also noted the occurrence of hydrothermal cementation in BSP sediments,

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specifically in the Resende Formation, consisting of kaolinite and opal-CT. The authors report that there were favourable conditions for the movement of hydrothermal solutions in the sediments

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during the development of the local process of continental rifting during the Eocene. Among such conditions, there is an extensional tectonic regime of ENE-NE direction, increasing regional heat

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flow and magmatism of ankaramitic lava extrusion. Common minerals possibly containing fluorine in the Precambrian basement rocks are biotite, apatite, tourmaline, amphibole and titanite, among other minerals (Coutinho, 1972). Therefore, both basement rocks minerals and sediments (illite and smectite) may be the primary natural source of fluoride observed in groundwater.

2.3 Regional Hydrogeology

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Two main aquifer systems occur in UTW (Hirata and Ferreira, 2001): i) the Crystalline Aquifer System (CAS), represented by granites and gneisses, schists and phyllites associated with the Precambrian basement rocks; and ii) Sedimentary Aquifer System (SAS), represented by Cenozoic sediments (claystones, sandstones and mudstones) of the BSP. The SAS occurs along the

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whole study area with thicknesses up to 100 m deposited on top of Precambrian basement rocks, most composed by granitoids and gneisses. The basement rocks may also comprise weathered rock. The geological contact between CAS and SAS in the study area is very irregular, since the top of

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the basement rocks may occur from 30 to 100 m depth.

The recharge of these aquifer units occurs both by rainwater in permeable areas and by

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leakages of public water supply and sewage systems (Hirata and Ferreira, 2001), in a proportion of 40% and 60%, respectively (Viviani-Lima et al 2007). Considering both water sources, the average recharge of UTW aquifers is 306 mm.y-¹ (from <150 to >450 mm.y-¹ with a modal value of 425 mm.y-¹) that exceeds 33 m³.s-¹ for the whole watershed. The discharge zones of both sedimentary and fractured aquifers are the creeks and rivers of the UTW, besides the supply wells exploiting

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both aquifers, which number is estimated in 12,000, extracting an outflow of about 10 m³.s-¹ in the UTW watershed (Hirata and Ferreira, 2001). Many areas of intensive pumping promote the

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decrease of hydraulic heads, especially in some areas of the SAS, which is the case of the area

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under study in the Barra Funda district.

3 MATERIALS AND METHODS

The sampling strategy was based on the available databases from Department of Water and Electric Power (DAEE), Municipal Sanitary Surveillance Coordination (COVISA) and State Environmental Agency (CETESB). All samples (n=22) were collected between May and July 2009. The Environmental Impact Report for the underground (subway) construction (METRO, 2011) also

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provided information about the geological profile and was used to make the conceptual model of the aquifer. The supply wells with fluoride anomalies were selected according to their access (private wells required authorization) and with the widest possible range of information: water chemistry,

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geology/aquifer system, well construction data (screening/filters depth and presence of coating) and static and dynamic water levels. Some wells without fluoride anomalies were also selected in the same area, to evaluate the conditions under which this contamination occurs.

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Eighteen water samples were collected from supply wells in operation and equipped with submersible electric pumps, and two from natural shallow springs. The dynamic water level in

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those wells ranged from 35 to 320 m deep. Physicochemical parameters, such as pH, redox potential (ORP), temperature and electrical conductivity, were measured in situ before sampling, using standard electrodes. Corrections were performed to the values obtained from ORP electrodes to estimate Eh values. Alkalinity was determined by titration with 0.01N H2SO4, in the same day of

membranes.

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sampling. All samples for cations were filtered in the field by inert 0.45 µm cellulose-acetate

Two effluent samples (EF-1 and EF-2) were collected in a potentially polluting company,

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according to the environmental agency identification and classification. This company is a glass manufacturing plant that uses fluorine-based raw materials and has been established for decades in

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the study area. The effluent samples were not filtered to obtain the total metal composition that could be available to be leached into water samples. As the aqueous samples were analyzed for major and trace cations, some samples were acidified to pH < 2 with ultrapure 50% HNO3, after filtration (except for the effluent), to avoid cation precipitation, and bottles were stored at 4o C to guarantee no chemical reactions. Cations (Al+3, Ba+2, Ca+2, Cr+3, Cu+4, Fe+3, K+1, Mg+2, Mn+2, Na+1, Ni+2, Sr+2 and Zn+2) in water samples were analyzed by ICP-AES, following SMEWW 21th ed 3210B, at IGc-USP labs. The anions (F-1, Cl-1, Br-1, NO3-1 and SO4-2) determination was performed by ion chromatography

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(model DX120, Dionex) at CEPAS-USP, according to the method established by EPA 300.1. The total analytical errors of the analyses were evaluated through ion balance and are lower than 8%. Groundwater samples for stable isotopes were collected in amber glass vials of 20 mL, which were rinsed with the water to be sampled and sealed without leaving air bubbles inside. The

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stable isotopes of H and O of water molecule were measured on raw water using an IRMS (Isotope Ratio Mass Spectrometer) Delta Plus MAT 252, with H/Device for H and a GasBench for O. Both results are presented relative to the VSMOW, with an uncertainty of 0.5 ‰ for H and of 0.2 ‰ for

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O.

Mineral saturation indices were calculated using the geochemical model PhreeqC (Parkhurst

4 RESULTS AND DISCUSSION

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and Appelo, 1999), with its thermodynamic database.

4.1 Databases Information and Aquifer Conceptual Model

The geological information obtained from the construction of the underground stations and

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tunnels (METRO, 2011), plus the recovered data from the various reports of supply wells located in the study area, enabled to build a schematic geological cross-section (Fig. 2). The top of the

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basement rocks occurs from 30 to 100 m bgs. The thickness of the sedimentary rocks above the basement varies from 4 to 100 meters (Table1). The recharge water infiltrates into the outcrop areas

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of the SAS and flows horizontally towards the main rivers and drains. A portion of this water infiltrates and recharges the CAS that is located below the SAS. This downward vertical flow between the two aquifers occurs naturally, due to the higher hydraulic head of the SAS concerning the CAS, but it can be increased by wells that extract water from the CAS. The water of both aquifers leads to the Tietê River, which drains all surface and groundwater from the study area (Fig. 2).

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Fig. 2 – Schematic geological cross-section (A-B), defined in Fig. 1

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In the study area the sedimentary rocks are composed mainly of claystones, coarse to fine sandstones and gravel, but less shale is also present. In turn, granites, gneisses and migmatites represent the crystalline rocks. Mylonitic texture and minerals like K-feldspars and biotite are

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commonly described in these rocks, whereas garnet is less frequent. During the evaluation of the reports for the wells selection for sampling, it was also noted

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that: (1) the majority of wells with high fluoride content extracts water only from the CAS, (2) the dynamic water level of most wells is considerably deep, greater than 100-150 m and below the top of the CAS (Table 1); (3) fluoride anomalies were not detected in the shallower wells that extract water only from the SAS. These observations are the first evidence that fluoride occurrence is related to the deep crystalline basement rocks aquifer, and not to SAS. This conclusion excludes the sedimentary minerals as possible natural sources of fluoride in the groundwater.

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Table 1 - Well information and physical-chemical parameters, measured in situ, for all water samples. 7.1 8.4 7.8 8.7 8.4 5.7 5.7 4.9 8.5 8.3 6.4 5.3 8.0 8.8 7.5 5.9 4.9 5.8 8.3 8.5

D.O. E.C. (mg.L -1 ) (μS.cm -2 ) 2.4 69 1.1 767 0.6 1121 1.3 534 1.0 884 1.5 179 1.0 183 1.3 253 0.9 568 1.0 947 2.3 166 2.2 203 1.5 294 0.8 582 1.3 608 1.3 71 1.4 128 2.9 208 1.2 205 0.7 610

Eh (mV)

D.L.

S.L.

766 371 30 241 328 410 319 495 45 90 389 424 375 20 260 387 487 451 372 331

61.0 295.7 210.1 110.0 59.9 64.9 1.0 190.6 224.5 208.0 320.1 151.2 50.0 40.0 65.4 130.4 35.0

12.0 112.3 60.0 153.3 60.0 17.0 24.3 186.5 205.0 180.0 240.2 99.1 20.0 20.0 26.2 26.4 15.0

flow rate F SAS CAS (m 3 /h) (mg.L -1) thickness thickness 4 0.32 100 3.7 9.10 52 338 5 5.80 96 154 3.03 7.80 82 323 4 10.00 30 120 11.28 0.05 97 68 3.6 0.06 90 60 5 0.01 4 6 6.60 69 191 7 5.30 84 246 0.01 0 0.01 0 1.56 4.20 102 128 25 9.30 92 268 1 0.84 60 167.5 2.5 0.32 66 2 0.01 72 2 0.02 52 48 2.48 0.41 77 103 3.5 3.00 30 70 0.35 0.27

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pH

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BF-01 BF-02 BF-03 BF-04 BF-05 BF-06 BF-07 BF-08 BF-09 BF-10 BF-11 BF-12 BF-13 BF-14 BF-16 BF-17 BF-18 BF-19 BF-20 BF-21 E2-SG E1-SG

Temp. Total Aquifer* depth (m) ( oC) 100 SAS 24.1 390 CAS 24.8 250 CAS 24.8 405 CAS 28.2 150 CAS 25.1 165 CAS 22.8 150 CAS 22.9 2 SAS 23.1 260 CAS 26.3 330 CAS 25.0 0 spring 20.2 0 spring 23.1 230 CAS 27.0 360 CAS + SAS 27.6 227.5 CAS 23.4 66 SAS 22.4 72 SAS 23.0 100 CAS 23.5 180 CAS 23.9 100 CAS 23.4 effluent effluent

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Sample

*CAS = Crystalline Aquifer System, SAS = Sedimentary Aquifer System.; D.O. = dissolved oxygen; E.C. = Electric Conductivity; D.L. = Dynamic water level (meters bgs); S.L. = static water level (meters bgs). SAS and CAS thickness unit is meter.

Among the 18 wells studied, historical data from the environmental agency reported that 9 of them presented acceptable concentrations of fluoride (<1.5 mg.L-1), while the other 9 show

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values above the limits for potable water (>1.5 mg.L-1). The values obtained in this work (Tables 1 and 2) are consistent with the values found in the environmental agency database, showing that

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even at different periods of time samples have similar fluoride concentrations. From the well construction profiles, the thickness of the sedimentary packages and the

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boundary between CAS and SAS were used to discuss the relationship between these features and the fluoride occurrence (discussed the section 4.3).

4.2 Hydrogeochemistry

Waters from CAS present an alkaline pH, mostly above 7 UpH, and the lowest dissolved oxygen (D.O.) values, as expected for deep waters and far from the interaction zones between the atmosphere and the saturated zone (Table 1). Their electric conductivity is much higher than that

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observed in the SAS samples, with mean values of 500 µS/cm². The Eh mean values, around 280 mV (from 30 to 451 mV) are lower than SAS samples (387-766 mV) and springs (389-424 mV). The lower DO values are related to the lower Eh values, except for BF-21. The SAS is characterized by the lowest values for all parameters evaluated (Table 1), except

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for the Eh parameter and temperature. Finally, the spring samples presented an acid pH, around 5.85 UpH, and the highest D.O. values, compatible with waters in contact with the atmosphere.

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The results of chemical analyses for the 20 water samples are presented in Table 2. The samples collected in CAS presented the highest concentrations of the bicarbonate and carbonate

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(Table 2; Fig. 3). The bicarbonate and carbonate ion concentrations are lower in springs samples than that from CAS and SAS samples. In general, CAS samples have higher concentrations of all ions anlysed except for nitrate, barium and iron (Fig. 3).

Chemical analyses of water for fluoride presented values between 0.02 and 10 mg.L-1 for CAS samples, 0.01 and 0.320 mg.L-1 for SAS, and 0.009 and 0.011 for the springs. Fluoride

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concentrations in SAS, when detected, were always lower than 0.5 mg.L-1 (Table 2), while fluoride anomalies (BF-2, 3, 4, 5, 9, 10, 13 and 21) were always detected at the CAS or a mixture of both

20).

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(BF-14), although not all CAS samples presented levels of anomalous fluoride (BF-6, 7, 16, 19 and

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Table 2 - Chemical Analyses of water samples

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17.6 357.1 268.1 229.7 390.6 14.6 34.5 4.1 220.1 393.5 14.3 10 134.9 240.4 367.2 30.6 1.4 31.9 88.3 314.4

0 15 0 9.3 14 0 0 0 6 19.8 0 0 0 16.9 0 0 0 0 1.8 4.8

5.2 26 13 19 29 15 17 23 21 33 14 17 7.9 10 13 1.6 5.8 18 6.5 18 117 152

NO 3 -

SO 4 -2

Al +3

Ba +2

Ca +2

Sr +2

0.32 9.1 5.8 7.8 10 0.05 0.055 0.013 6.6 5.3 0.011 0.009 4.2 9.3 0.84 0.32 0.01 0.02 0.41 3 0.27 0.35

0.39 <0.01 0.01 <0.01 <0.01 18 23 60 <0.01 <0.01 35.56 13.33 0.04 <0.01 <0.01 0.32 35 7.8 <0.01 <0.01 160 103

3.1 18 215 27 29 41 16 19 29 55 16 10 11 28 20 6.9 6.9 3.3 16 8.8 45 88

0.043 <0.001 <0.001 0.095 <0.001 <0.001 <0.001 0.04 <0.001 3.1 0.035 0.13 <0.001 0.011 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001

0.017 0.082 0.005 0.002 0.078 0.19 0.18 0.046 <0.002 <0.002 0.018 0.002 0.002 <0.002 0.21 0.053 0.64 0.49 0.011 0.002

6.3 2.8 16 2.2 5 5.7 7.1 8.1 5 4 7 5.4 8.9 1.6 23 1.2 2.3 6.6 15 2.7

0.044 0.19 0.45 0.055 0.17 0.1 0.1 0.037 0.06 0.071 0.018 0.034 0.21 0.054 0.65 0.024 0.13 0.26 0.38 0.068

-1

Fe +2

0.091

0.03

Mg+2

Mn +2

K+

Na + SiO 2

0.01 0.83 0.002 1.8 4 0.003 0.34 0.002 1.7 156 0.004 0.44 0.02 3.1 199 <0.001 0.11 <0.001 1.2 106 <0.001 2.1 0.001 1.3 156 <0.001 2.4 0.075 5.5 24 0.031 2.5 0.038 5.1 23 <0.001 1.5 0.033 3.7 32 <0.001 2 0.001 0.86 94 <0.001 0.1 <0.001 3.5 165 0.01 0.71 0.007 2.6 23 <0.001 1.1 0.014 4.9 15 <0.001 1.6 0.006 1.8 45 <0.001 0.025 <0.001 1.4 120 0.002 6 0.047 5.8 93 <0.001 0.53 0.002 2.4 11 0.1 1.8 0.022 11 7.1 0.06 3.3 0.027 12 11 <0.001 0.36 0.023 2 23 <0.001 0.053 <0.001 1.2 125

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SAS CAS CAS CAS CAS CAS CAS SAS CAS CAS spring spring CAS CAS + SAS CAS SAS SAS CAS CAS CAS effluent effluent

F-

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BF-01 BF-02 BF-03 BF-04 BF-05 BF-06 BF-07 BF-08 BF-09 BF-10 BF-11 BF-12 BF-13 BF-14 BF-16 BF-17 BF-18 BF-19 BF-20 BF-21 E1-SG E2-SG

Aquifer* HCO 3 -2 CO 3 -2 Cl -

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SAMPLE

37

0.16

0.21

5.1

0.19

20

173

10 14 11 17 1.8 59 57 4.9 22 8.7 4.7 5.3 30 17 25 76 21 28 35 16 10

all concentrations are reported in mg.L *CAS = Crystalline Aquifer System, SAS = Sedimentary Aquifer System.

Ion concentration increases with alkalinity, pH, E.C. and T; the inverse is observed with D.O. and Eh, suggesting alkaline groundwater in the study area (pH > 7.3 UpH; total alkalinity > 50

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mg.L-1 CaCO3), with electric conductivity > 200 µS.cm-2 and in situ temperature > 24.5 ºC, will have a tendency to present fluoride concentrations above 1.5 mg.L-1. Regarding D.O. and Eh values, the limit between samples with fluoride concentrations below and above potability limit is

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not clear; nevertheless D.O. < 1.7mg.L-1 and Eh < 420mV could be indicative of samples with

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higher fluoride content.

One SAS sample also presented nitrate concentration above the potability limit (45 mg.L-1) as illustrated in Fig. 3. For the other analyzed chemical parameters (table 2, fig. 3), concentrations are below the standard limits. Samples with higher nitrate concentrations do not have high fluoride concentrations and were collected in shallower wells (<10 m bgs), mainly in the southern area of the Barra Funda district. Sample BF-03 has relatively high sulphate concentration (215 mg.L-1) and sample BF-10 high aluminium concentration (3.1 mg.L-1), and are considered as isolated cases.

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Figure 3 – Boxplot graphics showing the range and median value for the anions and cations

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concentrations in the groundwater samples for SAS (left side) and CAS (right side). Black lines are (from top to bottom of each box) the maximum, 75%, median, 25%, and minimum concentrations values. The red line is the potability limit established by Ordinance 2914/2011 from the Ministry of Health and the Guiding Values for Soil and Groundwater (CETESB, 2014). On Piper diagram (fig. 4), all samples with high fluoride content (F>1.5 mg.L-1), which are CAS samples, were classified as sodium bicarbonate waters, without significant contribution of magnesium and calcium (Fig. 4). The other samples are classified as sodium-chloride and sodium-

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sulphate waters. This second group includes the shallow wells, the springs, the effluent samples and

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also SAS and some CAS samples with low fluoride concentration.

Figure 4 – Piper Diagram showing the different groundwater types groups

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The comparison of fluoride with other parameters indicates a positive correlation of fluoride with sodium and alkalinity (as HCO3-; fig 5a and 5b), and a negative correlation with nitrate (Fig

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5c). Potassium and calcium have similar behaviour compared to fluoride and are not associated with the enriched fluoride samples (fig. 5d). High fluoride contents also occur on samples under high pH conditions and in warmer waters (Fig. 5e), an observation also made by Rafique et al. (2009) and Valenzuela-Vásquez et al. (2006). The negative correlation with nitrate might indicate that fluoride is not associated with the sampled effluents.

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Table 2 also exhibits the analytical results of the two effluent samples sampled from the effluent collection system in a glass manufacturing plant (E-1 and E-2). In both analyses, all elements are in relatively low concentrations, even below the potability limit, except for nitrate which is more than two times the potability limit of 45 mg.L-1, indicating the influence of domestic

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effluents in this system. With direct contact with SAS, this effluent system could leak into the aquifer and contaminate it.

Although the well (BF-05) with the highest fluoride concentration (10 mg.L-1) is fairly close to the manufacturing plant where the effluent samples were collected, their fluoride content is 27

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times smaller (0.27 mg.L-1 for E-1 and 0.35 mg.L-1 for E-2). Is also important to consider the

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dilution effect during this contaminant transport through the aquifer, and also the fact there is no evidence of high fluoride content in SAS water. The effluent would have to be directly injected on the CAS instead of simply stored or discarded inappropriately to leak into SAS, be transported through it into CAS and then be detected in higher concentrations in CAS groundwater samples. Thus, fluoride concentration in effluent samples would not be enough for relating this

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anthropogenic source, with the anomaly of fluoride in groundwater.

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Figure 5 – Correlation for chemical and phyicochemical parameters. (pH, Temperature, alkalinity, nitrate, sodium, potassium and saturation index).. 21

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The negative values of saturation index for fluorite (Table 3 and fig 5f) suggest that this mineral is unsaturated in all samples, which means that any existing fluoride crystal tends to dissolve, releasing fluoride into the groundwater. It can also be observed that the high fluoride content only occurs in samples with values of saturation index for calcite close to zero or positive.

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This observation shows that calcite is near its chemical equilibrium with the groundwater. Ionic ratios (Table 3) comparing silica to non halite sodium (SiO2/Na+K-Cl) and non halite sodium to calcium (Na+K-Cl/Na+K-Cl+Ca) indicated that cation exchange is probably the source

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of most of the excess sodium (SiO2/Na+K-Cl<1) and plagioclase weathering is unlikely (Na+KCl/Na+K-Cl+Ca >0.8) (Housnlow, 1995) for all CAS samples with fluoride concentrations above

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1.5 mg.L-1. Values of ionic ratios of HCO3/SiO2 higher than 10 for this same samples also indicate the presence of calcium carbonate in the system.

All SAS wells present (table 3) the ratio HCO3/SiO2 lower than 5, indicating that the hydrochemistry is being controlled by the weathering of silicate minerals (Hounslow, 1995). The positive correlation of fluoride with sodium and the lower concentration of calcium

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relative to sodium were already observed by other works (Abu Jabal et al., 2014; Apambire et al., 1997; Gomez et al., 2009; Leybourne et al., 2008; Meenakshi et al., 2004; Rafique et al., 2009;

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Sreedevi et al., 2006; Tirumalesh et al., 2007; Valenzuela-Vásquez et al., 2006), and indicate that the adsorption of calcium enables the release of sodium from rocks, maybe enhancing fluoride

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solubility due to calcium depletion.

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Table 3 - Ionic Ratios and Saturation Index for groundwater samples F-

pH

BF-01 BF-02 BF-03 BF-04 BF-05 BF-06 BF-07 BF-08 BF-09 BF-10 BF-11 BF-12 BF-13 BF-14 BF-16 BF-17 BF-18 BF-19 BF-20 BF-21

SAS CAS CAS CAS CAS CAS CAS SAS CAS CAS spring spring CAS CAS + SAS CAS SAS SAS CAS CAS CAS

100 390 250 405 150 165 150 2 260 330 0 0 230 360 227.5 66 72 100 180 100

0.32 9.1 5.8 7.8 10 0.05 0.055 0.013 6.6 5.3 0.011 0.009 4.2 9.3 0.84 0.32 0.01 0.02 0.41 3

7.1 8.4 7.8 8.7 8.4 5.7 5.7 4.9 8.5 8.3 6.4 5.3 8 8.8 7.5 5.9 4.9 5.8 8.3 8.5

SiO2/(Na+K-Cl) >2 2.269 <1 0.038 <1 0.020 <1 0.069 <1 0.005 >1; <2 1.289 >1; <2 1.456 <1 0.097 <1 0.104 <1 0.023 <1 0.116 <1 0.296 <1 0.280 <1 0.057 <1 0.109 >2 2.557 <1 0.819 >1; <2 1.678 <1 0.671 <1 0.054

Na+K-Cl/ Na+k-Cl+Ca <0.8 0.189 >0.8 0.978 >0.8 0.913 >0.8 0.974 >0.8 0.960 <0.8 0.648 <0.8 0.457 <0.8 0.675 >0.8 0.934 >0.8 0.969 <0.8 0.658 <0.8 0.525 ~0.8 0.800 >0.8 0.984 <0.8 0.769 >0.8 0.892 <0.8 0.788 <0.8 0.537 <0.8 0.728 >0.8 0.974

HCO3/SiO2 <5 >5 >5 >5 >5 <5 <5 <5 >5 >5 <5 <5 ~5 >5 >5 <5 <5 <5 <5 >5

1.73 25.12 26.40 14.41 213.69 0.60 1.12 0.82 9.85 44.54 3.00 1.86 4.43 15.93 14.46 0.40 0.07 2.59 0.24 19.97

S.I.

S.I.

fluorite calcite

-5.57 -5.25 -1.61 -6.30 -1.42 -4.55 -4.35 -0.75 -3.53 -0.75 -0.21 -2.83 -0.57 -2.31 -5.71 -0.50 -0.49 -0.18 -0.83 -6.02

-4.87 -3.26 -0.02 -5.76 -0.10 -3.83 -3.27 -0.04 -3.90 -0.08 -0.15 -2.21 -0.34 0.04 -2.98 0.11 -0.08 0.21 0.01 -4.35

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depth (m)

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Aquifer*

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samples

4.3 Delimitation of the Fluoride Anomaly

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A surface map of the basement was generated and was identified a depression in the basement rocks surface aligned approximately in WNW-ESE direction. Fig. 6 shows the fluoride iso-concentration lines overlaying the surface topography of the basement rocks. The area where

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the anomaly is concentrated (F> 1 mg.L-1) coincides with the WNE-ESE structure, the deepest zone

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in the basement rock surface, which is also slightly oblique to the river direction. This could indicate the existence of some graben structure delimited by normal faults generated in a shear zone, typical in the BSP basement (Riccomini et al., 1992), where the occurrence of fluorite is related to hydrothermal processes (Sant’Anna and Riccomini, 2001). The basement rocks are affected by different shear zones reactivated during the SAS sedimentation (Campanha, 2002), which had contributed to the percolation of hydrothermal fluids that could contain fluorine, especially during Eocene. The sedimentary cover at the study area is described as oligocene sediments from Tremembé Formation.

23

7.400.000

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750

7.399.000

70 0

A

70 0

BF-09 BF-04 BF-14 650

BF-16

BF-1

BF-10

700

Fluorine (mgL )

9 - 11 7-9

A 650

330.000

B Schematic geological - cross section (Fig.3)

5-7 3-5

B

Basement rocks - Topographic surface (m)

BF-20

BF-19

500 m

331.000

332.000

333.000

BF

Wells used to make this map

BF

Wells not used to make this map

1-3

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-1

329.000

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7.396.000

BF-11

328.000

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BF-13

700

BF-12

Tam rive andu ate r í

PC-1454

0 5 6

BF-06 BF-07 BF-17

BF-8

327.000

BF-21

BF-03 650

7.397.000

BF-18

Tietê riv er

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BF-02 7.398.000

700

BF-05

Fig. 6 – Fluorine iso-concentration lines overlaying the basement rocks topographic surface

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4.4 Hydrogen and oxygen Isotopes

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Water samples from wells that exploited SAS provided values of δ18O between -6.1 and -6.9 and δD values between -36.9 and -44.3, slightly enriched in heavier isotopes of oxygen and hydrogen compared to the water wells that exploit the CAS, whose δ18O values are between -6.3 and -7.9 and δD between -38.8 and -51.1 (Table 4 and Fig. 7a).

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ACCEPTED MANUSCRIPT d-excess 12.1 9.8 9.5 9.6 8.5 11.1 12.7 11.4 7.4 7.4 9.6 10.6 7.8 9.4 7.4 10.9 10.6 8.6 9.6 7.5

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-36.9 -44.5 -47.2 -46.3 -45.1 -41.5 -38.8 -37.3 -46.8 -45.2 -38.6 -36.5 -51.1 -49.0 -44.8 -44.3 -39.8 -36.6 -43.6 -43.2

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δ2 H

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BF-01 BF-02 BF-03 BF-04 BF-05 BF-06 BF-07 BF-08 BF-09 BF-10 BF-11 BF-12 BF-13 BF-14 BF-16 BF-17 BF-18 BF-19 BF-20 BF-21

Total depth Aquifer* F (mg/L) δ 18O (m) 100 SAS 0.320 -6.1 390 CAS 9.100 -6.8 250 CAS 5.800 -7.1 405 CAS 7.800 -7.0 150 CAS 10.000 -6.7 165 CAS 0.050 -6.6 150 CAS 0.055 -6.4 2 SAS 0.013 -6.1 260 CAS 6.600 -6.8 330 CAS 5.300 -6.6 0 spring 0.011 -6.0 0 spring 0.009 -5.9 230 CAS 4.200 -7.4 360 SAC + SAS 9.300 -7.3 227.5 CAS 0.840 -6.5 66 SAS 0.320 -6.9 72 SAS 0.010 -6.3 100 CAS 0.020 -5.6 180 CAS 0.410 -6.6 100 CAS 3.000 -6.3

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Sample

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Table 4 - Isotope data of water samples

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Figure 7 – Graphics of isotopicpParameters and chemical (F) and physico chemical parameters (pH)

Water samples from the springs and wells that exploit SAS have, in general, higher values of delta oxygen and hydrogen than the wells that exploit the CAS (Fig. 7a). The more negative values of delta hydrogen and oxygen, observed in samples from deeper waters (wells exploiting the CAS), are assigned to older waters than the present-day ones. This statement is supported by the inverse correlation between the delta values from stable isotopes with well depths, -0.71 and -0.74 for oxygen and hydrogen delta values, respectively (Table 5).

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Table 5 – Linear correlations (Pearson) between isotopes and some groundwater parameters 2

2

δ H

δ H δ 18 O

[F-¹]

Depth

1.00

0.93

-0.71

-0.74

-0.71 -0.74 -0.76 -0.59

1.00

-0.65

-0.71

-0.66 -0.61 -0.62 -0.44

1.00

0.77

0.76

δ 18 O -

Depth

1.00

SL

0.68

pH

0.79

EC

0.77

0.93

0.81

0.76

0.63

1.00

0.89

0.70

0.60

1.00

0.64

0.46

pH

1.00

0.68

EC

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[F ¹]

DL

DL SL

1.00

DL = dynamic level; SL = static level; EC = electric conductivity

There are three outliers samples (Fig. 7a): i) BF-21, which is related to the CAS with

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fluoride concentrations greater than 1.5 mg.L-1, but with stable isotopes behavior (δ18O = -6.3 and δD = -35.3) more similar to the samples of CAS with minor fluoride content and richer in heavy

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isotopes (less negative), ii) BF-17, is referred to the SAS, with fluoride concentration of less than 1.5 mg.L-1, but with isotopic signatures (δ18O = -7.5 and δD = -42.7) similar to the CAS samples and iii) BF-19 which is associated to CAS, but with F <1.5 mg.L-1 and signature similar to the shallower waters.

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The BF-21 sample presents shallowest dynamic water level (35m) among CAS samples, which may explain its similar behavior to SAS samples (Table 1). Furthermore, the BF-21 sample has the lowest concentration of fluoride (3.0 mg.L-1) among samples from the group with fluoride

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anomaly ([F]> 1.5 mg.L-1). This may indicate that there is mixing of waters from the two aquifers in this well, diluting the fluoride concentration and printing an isotopic signature of shallower waters.

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The BF-17 sample belongs to a 66 m deep well, described as SAS, with dynamic water level of 50 m (Table 1). However, the basement topographic surface from figure 7, indicates that this well, which is located at elevation 740m, should intercept CAS between 720-730m elevation contour, indicating that within 10-20 meters it would be at CAS not SAS. These observations and the isotopic results probably denote that the well description is wrong. The BF-19 sample, similarly to the BF-21 sample, is related to CAS and has an isotopic signature consistent with the shallower samples, but shows no fluoride anomaly. Likewise, this

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isotopic behavior can also indicate an important contribution from surface waters, revealing a water mixture. The deuterium excess (d-excess) reported in Table 4 and Fig. 7b indicate also that the CAS samples have preferentially values lower than 10-11 (present-day’s value), whereas SAS samples

different climatic condition than the current one.

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present d-excess values higher than 10. This also may indicate that the CAS was recharged in a

This relationship between the more negative values of δ18O and the deeper samples can also

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be seen in the scatter plots of pH and δ18O (Fig. 7c). The higher pH values are associated with deeper samples and more negative values of δ18O. The exception is the BF-19 sample, which is

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associated to the CAS with high pH, but somewhat less negative δ18O, which can also indicate a mixing with surface waters.

The fact that the less negative values of both δD as δ18O are associated with levels of fluoride concentrations lower than 1.5 mg.L-1 is possibly a consequence of the correlation between

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fluoride and depth, as well as between stable isotopes delta values and depth. This is supported by the significant correlations observed for these parameters (Table 5): 0.77 for depth and fluorine; between -0.71 and -0.74 respectively for δ18O and δD against depth, and -0.65 and -0.71

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respectively for δ18O and δD against fluoride. The dynamic water level (ND) shows excellent correlation with depth (0.93) and good correlation with fluoride (0.76) (Table 5), besides showing

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good correlation with δ18O and δD (-0.66 and -0.71). The depression observed on the basement surface in the centre of the study area (Fig. 6) presents wells with higher fluoride concentrations, H and O isotopic signatures more negative, higher temperature and higher pH.

Conclusions Within the Brazilian scenario, fluoride anomalies in groundwater are frequently related to sedimentary basins and/or presence of basalts, like the basaltic lava from the Paraná Basin (Ezaki et 28

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al., 2016; Giampá and Franco Filho, 1982; Hypolito et al., 2010). Some authors also indicated the influence of brittle structures, or tectonic lineaments in the fluoride mobilization (Dias and Bragança, 2004; Marimon, 2006; Menegasse-Velásques et al., 2004; Nanni et al., 2009). Granites and gneisses as source rocks for fluoride anomaly in Brazil were pointed out by Hypolito et al.

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(2010), Ezaki et al. (2016) and Viero et al. (2009). The fluoride anomaly discussed in this work is the first one related to the basement rocks of the São Paulo Sedimentary Basin, formed by gneisses and other metamorphic rocks.

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From the data compilation conducted, it was concluded that the anomalies of fluoride were exclusively linked to the wells extracting water from CAS. The data presented showed that there is

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a good correlation between the stable isotopes, the depth of the well, temperature, its dynamic water level and fluoride anomalies. There is also a positive correlation of fluoride with sodium and alkalinity.

Fluorine above 1,5 mg/L happens in alkaline water with electric conductivity higher than 200 µS.cm-2 and temperature aver 24.5 ºC.

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Ionic ratios comparing silica to non halite sodium and non halite sodium to calcium indicate that cation exchange is probably the source of most of the excess sodium for all CAS samples with

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higher fluoride concnetrations. Ionic ratios comparing alkalinty and silica suggest that there is calcium carbonate in the system of CAS. These observations may indicate that the adsorption of

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calcium enables the release of sodium from rocks, maybe enhancing fluoride solubility due to calcium depletion.

A depression in the basement rocks surface was identified aligned to the regional tectonic structures of the continental rifting from Eocene. The fluorine anomaly is concetrated in this depression. The H and O isotopes indicate the fluoride anomalies are related to samples with more depleted H and O signatures and higher pH values, which in turn are related to deeper environments.

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The H and O isotopes were able to relate this anomaly with depth, allowing correlating this anomaly with the depression WNW-ESE found on the surface of the basement, which was probably originated by a faulting system. The presence of faults contributed to percolation of hydrothermal fluids in Eocene, which may precipitate fluorite. This mineral was then weathered by more recent

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waters, which remobilized the fluorine. All data corroborates the hypothesis of this anomaly being associated with a fault system and ancient hydrothermal fluids, with deep circulation of

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groundwater flows.

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Acknowledgements

This work was only possible because of the investigation started by the Coordination of Health Surveillance of the Municipal Health Service (SMS / COVISA - SUVIS Lapa / Pinheiros), and the Company of Environmental Sanitation Technology (CETESB), which led to a partnership

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between them and researchers from the Groundwater Research Center (CEPAS/USP) and the Geochronological Research Center (CPGeo/USP). The authors thank all these institutions and all persons involved in the various stages of this work, and to CNPq (Process No. 482702/2007-9) and

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FAPESP (Process No 2010/20876-0) for financial support and FAPESP (Process No. 2008/086015) for scientific initiation scholarship. We also want to thanks the anonymous reviewer for the

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observations made, which helped the improvement of this manuscript.

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Abu Jabal, M.S., Abustan, I., Rozaimy, M.R., Al-Najar, H., 2014. Fluoride enrichment in groundwater of semi-arid urban area: Khan Younis City, southern Gaza Strip (Palestine). J. African Earth Sci. 100, 259–266. doi:10.1016/j.jafrearsci.2014.07.002 Ali, S., Thakur, S.K., Sarkar, A., Shekhar, S., 2016. Worldwide contamination of water by fluoride. Environ. Chem. Lett. 14, 291–315. doi:10.1007/s10311-016-0563-5 Apambire, W.B., Boyle, D.R., Michel, F.A., 1997. Geochemistry, genesis, and health implications of fluoriferous groundwaters in the upper regions of Ghana. Environ. Geol. 33, 13–24. doi:10.1007/s002540050221 Banerjee, A., 2015. Groundwater fluoride contamination: A reappraisal. Geosci. Front. 6, 277– 30

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4289 Valenzuela-Vásquez, L., Ramírez-Hernández, J., Reyes-López, J., Sol-Uribe, A., Lázaro-Mancilla, O., 2006. The origin of fluoride in groundwater supply to Hermosillo City, Sonora, México. Environ. Geol. 51, 17–27. doi:10.1007/s00254-006-0300-7 Viero, A.P., Roisenberg, C., Roisenberg, A., Vigo, A., 2009. The origin of fluoride in the granitic aquifer of Porto Alegre, Southern Brazil. Environ. Geol. 56, 1707–1719. doi:10.1007/s00254-008-1273-5 Vithanage, M., Bhattacharya, P., 2015. Fluoride in the environment: sources, distribution and defluoridation. Environ. Chem. Lett. 13, 131–147. doi:10.1007/s10311-015-0496-4 Viviani-Lima, J; Hirata, R; Aravena, R. 2007. Estimation of groundwater recharge in the Metropolitan Area of São Paulo, Brazil. IAH International Congress. Lisbon. WHO, (World Health Organization), 2011. Guidelines for drinking-water quality., 4th editio. ed. World Health Organization, Geneva.

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Tables for mansucript entitled: Who to blame for groundwater fluoride anomaly in São Paulo, Brazil? Hydrogeochemistry and isotopic evidence

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Table 1 - Well information and Physical-chemical parameters, measured in situ, for all water samples. Total D.O. flow Temp. E.C. Eh Sample depth Aquifer* rate pH (mg.LD.L. S.L. o -2 ( C) (μS.cm ) (mV) 1 (m) (m3/h) ) BF-01 100 SAS 24.1 7.1 2.4 69 766 61.0 12.0 4 BF-02 390 CAS 24.8 8.4 1.1 767 371 295.7 112.3 3.7 BF-03 250 CAS 24.8 7.8 0.6 1121 30 60.0 5 BF-04 405 CAS 28.2 8.7 1.3 534 241 210.1 153.3 3.03 BF-05 150 CAS 25.1 8.4 1.0 884 328 110.0 60.0 4 BF-06 165 CAS 22.8 5.7 1.5 179 410 59.9 17.0 11.28 BF-07 150 CAS 22.9 5.7 1.0 183 319 64.9 24.3 3.6 BF-08 2 SAS 23.1 4.9 1.3 253 495 1.0 5 BF-09 260 CAS 26.3 8.5 0.9 568 45 190.6 186.5 6 BF-10 330 CAS 25.0 8.3 1.0 947 90 224.5 205.0 7 BF-11 0 spring 20.2 6.4 2.3 166 389 BF-12 0 spring 23.1 5.3 2.2 203 424 BF-13 230 CAS 27.0 8.0 1.5 294 375 208.0 180.0 1.56 BF-14 360 CAS + SAS 27.6 8.8 0.8 582 20 320.1 240.2 25 BF-16 227.5 CAS 23.4 7.5 1.3 608 260 151.2 99.1 1 BF-17 66 SAS 22.4 5.9 1.3 71 387 50.0 20.0 2.5 BF-18 72 SAS 23.0 4.9 1.4 128 487 40.0 20.0 2 BF-19 100 CAS 23.5 5.8 2.9 208 451 65.4 26.2 2 BF-20 180 CAS 23.9 8.3 1.2 205 372 130.4 26.4 2.48 BF-21 100 CAS 23.4 8.5 0.7 610 331 35.0 15.0 3.5 effluent E2-SG E1-SG effluent

F (mg.L-1) 0.32 9.10 5.80 7.80 10.00 0.05 0.06 0.01 6.60 5.30 0.01 0.01 4.20 9.30 0.84 0.32 0.01 0.02 0.41 3.00 0.35 0.27

SAS CAS thickness thickness 100 52 96 82 30 97 90 4 69 84 0 0 102 92 60 66 72 52 77 30

338 154 323 120 68 60 191 246 128 268 167.5 48 103 70

*CAS = Crystalline Aquifer System, SAS = Sedimentary Aquifer System.; D.O. = dissolved oxygen; E.C. = Electric Conductivity; D.L. = Dynamic water level (meters bgs); S.L. = static water level (meters bgs). SAS and CAS thickness unit is meter.

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all concentrations are reported in mg.L

-1

0.32 9.1 5.8 7.8 10 0.05 0.055 0.013 6.6 5.3 0.011 0.009 4.2 9.3 0.84 0.32 0.01 0.02 0.41 3 0.27 0.35

0.39 <0.01 0.01 <0.01 <0.01 18 23 60 <0.01 <0.01 35.56 13.33 0.04 <0.01 <0.01 0.32 35 7.8 <0.01 <0.01 160 103

3.1 18 215 27 29 41 16 19 29 55 16 10 11 28 20 6.9 6.9 3.3 16 8.8 45 88

*CAS = Crystalline Aquifer System, SAS = Sedimentary Aquifer System.

Ba+2

0.043 0.017 <0.001 0.082 <0.001 0.005 0.095 0.002 <0.001 0.078 <0.001 0.19 <0.001 0.18 0.04 0.046 <0.001 <0.002 3.1 <0.002 0.035 0.018 0.13 0.002 <0.001 0.002 0.011 <0.002 <0.001 0.21 <0.001 0.053 <0.001 0.64 <0.001 0.49 <0.001 0.011 <0.001 0.002

Ca+2 6.3 2.8 16 2.2 5 5.7 7.1 8.1 5 4 7 5.4 8.9 1.6 23 1.2 2.3 6.6 15 2.7

Sr+2

0.091

0.03

37

Fe+2

Mg+2

RI PT

5.2 26 13 19 29 15 17 23 21 33 14 17 7.9 10 13 1.6 5.8 18 6.5 18 117 152

Al+3

0.044 0.19 0.45 0.055 0.17 0.1 0.1 0.037 0.06 0.071 0.018 0.034 0.21 0.054 0.65 0.024 0.13 0.26 0.38 0.068

0.01 0.003 0.004 <0.001 <0.001 <0.001 0.031 <0.001 <0.001 <0.001 0.01 <0.001 <0.001 <0.001 0.002 <0.001 0.1 0.06 <0.001 <0.001

0.83 0.34 0.44 0.11 2.1 2.4 2.5 1.5 2 0.1 0.71 1.1 1.6 0.025 6 0.53 1.8 3.3 0.36 0.053

0.16

0.21

5.1

SC

0 15 0 9.3 14 0 0 0 6 19.8 0 0 0 16.9 0 0 0 0 1.8 4.8

SO4-2

M AN U

17.6 357.1 268.1 229.7 390.6 14.6 34.5 4.1 220.1 393.5 14.3 10 134.9 240.4 367.2 30.6 1.4 31.9 88.3 314.4

NO3-

TE D

SAS CAS CAS CAS CAS CAS CAS SAS CAS CAS spring spring CAS CAS + SAS CAS SAS SAS CAS CAS CAS effluent effluent

F-

EP

BF-01 BF-02 BF-03 BF-04 BF-05 BF-06 BF-07 BF-08 BF-09 BF-10 BF-11 BF-12 BF-13 BF-14 BF-16 BF-17 BF-18 BF-19 BF-20 BF-21 E1-SG E2-SG

Cl-

AC C

Table 2 - Chemical Analyses of water samples HCO3 - CO3SAMPLE Aquifer* 2 2

Mn+2

K+

0.002 1.8 0.002 1.7 0.02 3.1 <0.001 1.2 0.001 1.3 0.075 5.5 0.038 5.1 0.033 3.7 0.001 0.86 <0.001 3.5 0.007 2.6 0.014 4.9 0.006 1.8 <0.001 1.4 0.047 5.8 0.002 2.4 0.022 11 0.027 12 0.023 2 <0.001 1.2 0.19

20

Na+

SiO2

4 156 199 106 156 24 23 32 94 165 23 15 45 120 93 11 7.1 11 23 125

10 14 11 17 1.8 59 57 4.9 22 8.7 4.7 5.3 30 17 25 76 21 28 35 16

173

10

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Table 3 - Ionic Ratios and Saturation Index for groundwater samples depth SiO2/(Na+Ksamples Aquifer* FpH (m) Cl)

BF-06 BF-07 BF-08 BF-09 BF-10 BF-11 BF-12 BF-13 BF-14 BF-16 BF-17 BF-18

CAS CAS CAS SAS CAS CAS spring spring CAS CAS + SAS CAS SAS SAS

2.269

<0.8

0.189

<5

1.73

-5.57

390

9.1

8.4

<1

0.038

>0.8

0.978

>5

25.12

-5.25

250

5.8

7.8

<1

0.020

>0.8

0.913

>5

26.40

-1.61

405

7.8

8.7

<1

0.069

>0.8

0.974

>5

14.41

-6.30

150

10

8.4

0.005

>0.8

0.960

>5

213.69

-1.42

165

0.05

5.7

1.289

<0.8

0.648

<5

0.60

-4.55

150

0.055

5.7

<1 >1; <2 >1; <2

1.456

<0.8

0.457

<5

1.12

-4.35

2

0.013

4.9

<1

0.097

<0.8

0.675

<5

0.82

-0.75

260

6.6

8.5

<1

0.104

>0.8

0.934

>5

9.85

-3.53

330

5.3

8.3

<1

0.023

>0.8

0.969

>5

44.54

-0.75

0

0.011

6.4

<1

0.116

<0.8

0.658

<5

3.00

-0.21

0

0.009

5.3

<1

0.296

<0.8

0.525

<5

1.86

-2.83

230 360

4.2 9.3

8 8.8

<1 <1

0.280 0.057

~0.8 >0.8

0.800 0.984

~5 >5

4.43 15.93

-0.57 -2.31

227.5 66

0.84 0.32

7.5 5.9

<1 >2

0.109 2.557

<0.8 >0.8

0.769 0.892

>5 <5

14.46 0.40

-5.71 -0.50

72

0.01

4.9

<1

0.819

<0.8

0.788

<5

0.07

-0.49

4.87 3.26 0.02 5.76 0.10 3.83 3.27 0.04 3.90 0.08 0.15 2.21 0.34 0.04 2.98 0.11 0.08

RI PT

>2

SC

BF-05

CAS

S.I. calcite

7.1

M AN U

BF-04

CAS

S.I. fluorite

0.32

TE D

BF-03

CAS

HCO3/SiO2

100

EP

BF-02

SAS

AC C

BF-01

Na+K-Cl/ Na+k-Cl+Ca

ACCEPTED MANUSCRIPT

BF-21

CAS CAS

100 180

0.02 0.41

5.8 8.3

>1; <2 <1

100

3

8.5

<1

0.054

dexcess 12.1 9.8 9.5 9.6 8.5 11.1 12.7 11.4 7.4 7.4 9.6 10.6 7.8 9.4 7.4 10.9 10.6 8.6 9.6 7.5

1.678 0.671

<0.8 <0.8

0.537 0.728

<5 <5

2.59 0.24

-0.18 -0.83

>0.8

0.974

>5

19.97

-6.02

δD

SAS CAS CAS CAS CAS CAS CAS SAS CAS CAS spring spring CAS SAC + SAS CAS SAS SAS CAS CAS CAS

0.320 9.100 5.800 7.800 10.000 0.050 0.055 0.013 6.600 5.300 0.011 0.009 4.200 9.300 0.840 0.320 0.010 0.020 0.410 3.000

-6.1 -6.8 -7.1 -7.0 -6.7 -6.6 -6.4 -6.1 -6.8 -6.6 -6.0 -5.9 -7.4 -7.3 -6.5 -6.9 -6.3 -5.6 -6.6 -6.3

-36.9 -44.5 -47.2 -46.3 -45.1 -41.5 -38.8 -37.3 -46.8 -45.2 -38.6 -36.5 -51.1 -49.0 -44.8 -44.3 -39.8 -36.6 -43.6 -43.2

M AN U

δ18O

TE D

F (mg/L)

EP

BF-01 BF-02 BF-03 BF-04 BF-05 BF-06 BF-07 BF-08 BF-09 BF-10 BF-11 BF-12 BF-13 BF-14 BF-16 BF-17 BF-18 BF-19 BF-20 BF-21

Aquifer*

AC C

Sample

Total depth (m) 100 390 250 405 150 165 150 2 260 330 0 0 230 360 227.5 66 72 100 180 100

SC

Table 4 - Isotope data of water samples

0.21 0.01 4.35

RI PT

BF-19 BF-20

CAS

ACCEPTED MANUSCRIPT

DL SL pH EC

1.00

SL

pH

EC

0.71 0.66

0.74 0.61

0.76 0.62

0.59 0.44

0.77

0.76

0.68

0.79

0.77

1.00

0.93

0.81

0.76

0.63

1.00

0.89

0.70

0.60

1.00

0.64

0.46

1.00

0.68

-0.74 -0.71

SC

Depth

1.00

0.71 0.65

DL

1.00

M AN U

[F ¹]

0.93

Depth

TE D

-

1.00

[F-¹]

EP

δ18O

δ18O

AC C

δ2H

δ2H

RI PT

Table 5 – Linear correlations (Pearson) between isotopes and some groundwater parameters

ACCEPTED MANUSCRIPT -47°

Jun

diu

-46°

N

lt Fau vira

study area

ault ia F

RI PT

ca Ca u

Quaternary deposits

Brazil

Neogene and Paleogene sediments

-24°

Intrusive Granitoids

Cu

SC

t

aul oF

“Serra de Itaberaba” and “São Roque” Groups

ã

bat

“Costeiro” Complex

A

BF-09

BF-01

BF-26

BF-21 BF-20

BF-19

B

AC C

EP

BF-10 BF-04 BF-18 BF-07 BF-14 BF-30 BF-03 BF-06 BF-12 BF-27 BF-08 BF-17 BF-13 BF-11 BF-29 BF-24

BF-25

7398000

BF-02

EF

7397000

BF-16

333000

BF-05 BF-22

TE D

BF-31

331000

7400000

329000

7399000

327000

7396000

325000

M AN U

“Embu” Complex

1 km F<1.5 mg/L

Quaternary

F>1.5 mg/L

Alluvial deposits

Neogene and Paleogene

Sediments

Resende Formation

Effluent

Gravel, sand and silt clay deposits Sandy clayed mudstones

Pre-Cambrian rocks Non foliated - Granitic rock Foliated - Granitic rock São Roque and Serra de Itaberaba Group Micaschists with subordinated quartzites and metassiltite

A

B Geological Cross Section (fig.3)

RI PT

ACCEPTED MANUSCRIPT

Discharge Area Recharge Area

Recharge Area

BF-05

SC

A

BF-06 BF-07

BF-02

+

+ +

+

+ +

670

+

+ +

+ +

+ +

+ +

+ +

+ +

+

+ +

+ +

+ +

+

?

+ +

+ +

+ +

+

+

+

+ +

+ +

+

+ +

Landfill

?

TE D

620

M AN U

720

Quaternary alluvium

Organic Clay and silty sand

Tertiary Sediments - Resende Formation

~

~

~

~

+ ~

+

+

~

~

+

+

~

+

~ ~

+

~

+

~

+ ~

~

+

Studied wells

~ ~

~

Crystalline bedrock (granitoids and gneisses)

Yellow and grey silty sand

+

+

Basement saprolith

Water Table

~ ~

~

+

+

+

Pre-Cambrian Basement Rocks

Groundwater Flow

EP

~

+

Grey silty clay

AC C

BF-17

BF-08

+

B

+

~

7.400.000

ACCEPTED MANUSCRIPT

750

7.399.000

70 0

RI PT

A

BF-05

SC

70

Tietê riv er

0

BF-04 BF-14 650

BF-06 BF-07 BF-17

BF-8

PC-1454

BF-03

BF-12

70

BF-20

BF-13

70

0

teí

650

7.397.000

BF-18

BF-10

Tam rive andu a r

BF-21

0

BF-16

BF-1

M AN U

BF-09

650

7.398.000

BF-02

700

BF-19

9 - 11 7-9

A

5-7 3-5

650

TE D

328.000

1-3

329.000

B

500 m 330.000

B Schematic geological - cross section (Fig.3) Basement rocks - Topographic surface (m)

AC C

-1

Fluorine (mgL )

327.000

EP

7.396.000

BF-11

331.000

332.000

333.000

BF

Wells used to make this map

BF

Wells not used to make this map

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT Highlights For Manuscript entitled: Who to blame for groundwater fluoride anomaly in São Paulo, Brazil? Hydrogeochemistry and isotopic evidence

RI PT

Fluoride up to 10 mg.L-1 is found in groundwater from São Paulo, Brazil; This fluoride is from natural origin; There is no fluorine related to the upper sedimentary aquifer; Fluoride is related to deep groundwater flow in the fractured aquifer.

AC C

EP

TE D

M AN U

SC

• • • •