garcia et al 2012
TRANSCRIPT
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S P E C I A L I S S U E
Geochemistry and health aspects of F-rich mountainous streamsand groundwaters from sierras Pampeanas de Cordoba,
Argentina
M. G. Garcıa • K. L. Lecomte • Y. Stupar •
S. M. Formica • M. Barrionuevo • M. Vesco •
R. Gallara • R. Ponce
Received: 15 November 2010 / Accepted: 8 March 2011 / Published online: 18 March 2011 Springer-Verlag 2011
Abstract Symptoms of dental fluorosis have been
observed in rural communities located in the SierrasPampeanas de Cordoba, a mountainous area in Central
Argentina. The clinical assessment was performed in the
Charbonier Department, where the fluoride (F-) intake was
determined to be 3.90 ± 0.20 mg day-1 (n = 16). In this
community, mild and severe fluorosis reach an incidence of
86.7% (total teeth surface = 636 teeth) among the children
population. To determine the origin and distribution of
fluorine in natural waters from the Charbonier Department
and nearby regions, sampling was performed in the area
covering the San Marcos River basin. The obtained results
show that F- concentrations vary between *1 to
*2.5 mg l-1, with an outlier value of 8 mg l-1. The
spatial distribution of F- shows that the lowest concen-
trations are found at the basin’s catchments. Maximum
values are located in two sectors of the basin: the Char-
bonier depression in the eastern part and at the San Marcos
village, downstream the main collector, in the western part
of the basin. In these two regions, the F- contents in
ground- and surface waters are [2.0 mg l-1 and nearly
constant. Dissolved F- in natural waters from the study
area has its origin in the weathering of F-bearing minerals
present in the region’s dominant lithology. The extent of mineral weathering is mostly determined by the residence
time of water within the aquatic reservoir. Longer resi-
dence times and a major solid–water interaction lead to
enhanced release of F-. This explains the higher F- con-
centrations found in basin areas with lower run off. The
removal of F- from water appears to occur by neither
fluorite precipitation, nor by adsorption. Hence, variations
in F- concentrations seem to be more related to regional
hydrological conditions.
Keywords Dental fluorosis Geogenic F-biotites
Pampean ranges Weathering
Introduction
High levels of naturally occurring F- in Argentina have
been traditionally described in groundwaters from different
parts of the Chacopampean plain (i.e., Fiorentino et al.
2007; Gomez et al. 2009; Kruse and Ainsil 2003; Warren
et al. 2005), and the source was generally attributed to the
presence of volcanic shards spread within the loessic sed-
iments that are in contact with these water reservoirs. It is
estimated that about 1.2 million inhabitants in the Chaco
Pampean plain drink groundwaters with contents of fluo-
ride that exceed the Argentinean and the international
guideline value of 1.5 mg l-1 for drinking water (Codigo
Alimentario Argentino 1994; WHO World Health Orga-
nization 2004). In contrast, there are almost no references
in the scientific literature about the occurrence of F--rich
river waters in the mountainous region of Sierras Pampe-
anas (central and north Argentina), where the occurrence of
F-bearing minerals in crystalline rocks from the northern to
M. G. Garcıa K. L. Lecomte S. M. Formica
Centro de Investigaciones en Ciencias de la Tierra(CICTERRA/CIGeS) CONICET, Cordoba, Argentina
M. G. Garcıa (&) K. L. Lecomte Y. Stupar S. M. Formica M. Barrionuevo M. Vesco
FCEFyN, Universidad Nacional de Cordoba,
Av. Velez Sarsfield 1611, X5016CGA Cordoba, Argentina
e-mail: [email protected]
R. Gallara R. Ponce
Catedra ‘‘A’’ de Quımica y Fısica Biologicas,
Facultad de Odontologıa, Universidad Nacional de Cordoba,
Cordoba, Argentina
1 3
Environ Earth Sci (2012) 65:535–545
DOI 10.1007/s12665-011-1006-z
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the southernmost extreme have been extensively informed
(e.g. Colombo et al. 2010; Dahlquist et al. 2006, 2010).
Fluoride has very interesting properties related to human
health, particularly in preventing dental caries. However,
when its concentration in drinking water is higher than
1 mg l-1, a clinical condition called dental fluorosis may
appear. This consists of a dental enamel hypomineraliza-
tion that manifest through a greater surface and subsurfaceporosity than normal enamel, and which develops as a
result of an excessive fluoride intake during its formation
(Burt and Eklund 1992). Typical symptoms of dental
fluorosis are fine white stripes to dark stains in the teeth
surface.
Dental fluorosis in primary dentition is often described
as less severe than that found in permanent teeth (Fejeskov
et al. 1988), but fluorosis in primary teeth usually predicts
the occurrence of the illness in the permanent dentition
(Mann et al. 1990; Warren et al. 2001). The primary
molars, especially the second molars, are usually the most
affected (Browne et al. 2005; Weeks et al. 1993).A number of studies have described the prevalence of
dental fluorosis worldwide, and in most cases, the illness is
closely associated with the consumption of F-rich waters
(i.e., Dean et al. 1950; Milsom et al. 1996; Oruc 2008;
Shitumbanuma et al. 2006; Yadav et al. 2009). The inci-
dence of this illness is also closely correlated with climatic
conditions, eating habits, and the social status of the
population.
Most of the fluoride found in natural waters is geo-
genic. Because fluorine is an incompatible lithophile
element (Faure 1991), it preferentially partitions into sili-
cate melts as magmatic crystallization proceeds (Xiaolin
and Zhenhua 1998). For that reason, F-bearing minerals are
generally associated with late-stage pegmatite granites,
hydrothermal vein deposits and rocks that crystallize from
highly evolved pristine magmas (Nagadu et al. 2003;
Scaillet and Macdonald 2004; Taylor and Fallick 1997).
Among primary minerals, biotite and muscovite may
contain about 1 wt% of F, while contents are higher in
accessory minerals, such as fluorapatite (*1.5 wt%),
apatite (*4 wt%), topaz (*11.5 wt%), and fluorite
(*48 wt%) (Bailey 1984).
In this paper, the geochemical and health aspects of the
occurrence of F-rich waters in a mountainous granitic
region in central Argentina are analyzed. Geochemical
assessment involves the identification of sources and the
proposal of some mechanisms that explain the variability
of F- concentrations within the basin. Health aspects
include the investigation of clinical evidence and fluoride
intake in a small community of the region. The achieved
conclusions may also be extrapolated to other sectors of the
Sierras Pampeanas region with similar lithology and
environmental conditions.
Study area
The study area is a mountainous region located in the
northern Sierras Pampeanas of Cordoba, Argentina,
between 30440 and 30550 S, and 64460 and 64280 W
(Fig. 1). Metamorphic rocks of middle to high amphibolite
facies are the most widespread component of the basement.
Medium-grade para- and ortho- gneisses and schists con-stitute the dominant lithology. Subordinate amounts of
marble, amphibolite and discontinuous strings of ultrabasic
rocks complete the association (Rapela et al. 1998).
Igneous rocks in the northern Sierras Pampeanas of
Cordoba are represented by a series of plutons emplaced
into medium grade polymetamorphic basement (Rapela
et al. 1998) along a prominent shear zone (Hockenreiner
et al. 2003). The intrusion of these granitoids with an
A-type signature (Dahlquist et al. 2006) followed several
periods of intense magmatic activity: Middle Cambrian,
Early Middle Ordovician, and Middle Devonian—Lower
Carboniferous. The Carboniferous granites were emplacedat shallow depth and are dominated by facies with K-fel-
spar megacrysts (Dahlquist et al. 2010).
Within the study area, two main granitic bodies are
emplaced: La Fronda, a trondhjemite–tonalite unit and the
Capilla del Monte monzogranite (Fig. 1). The first magmatic
unit was described by Caffe (1993), Lyons et al. (1997) and
Massabie (1982) and was geochemically characterized by
Rapelaetal.(1998). It is an ovoidal pluton that covers an area
of about 25 km2 and intrudes the gneisses, schists and
amphibolites of the Cruz del Eje-La Falda Metamorphic
Complex. La Fronda is a leucotonalite with granodioriticand
granitic facies, light gray colour, equigranular texture of
coarse grain (2–10 mm), made of 30–40% quartz, 35–50%
plagioclase, 2–4% K-feldspar, 5–16% muscovite (primary
and secondary), and 3–6% biotite. Accessory minerals are
apatite, zircon, monazite, and opaques. Secondary epidote
and chlorite are found as alteration assemblages. The Capilla
del Monte monzogranitealso intrudes the metamorphic Cruz
del Eje-La Falda Complex. The pluton consists of a biotitic
muscovitic monzogranite, made of quartz, plagioclase,
microcline and biotite. Main accessory minerals are fluorite,
apatite, zircon, magnetite, topaz, and magmatic andalucite
(Pastore and Methol 1953; Saavedra et al. 1998). The pluton
is associated with aplites and apatite-rich pegmatites. Fluo-
rite is also present in pegmatitic veins that intrude the
metamorphic basement.
Metal ores are densely spread into the Sierras Pampe-
anas system. Mutti et al. (2005) proposed that successive
stages of deposition and mobilization of metallic elements
originated mineralized belts in Sierras Pampeanas rich in
Cr, W, Fe, Cu, Zn, Pb, Ti, Au, Bi, Be, Li, U, Mn, F and B,
with subordinated Sn, Mo, ETR, Ta, Nb, V, Cd, Ag, Sb,
Co, P, As, S, Te, Se and Ba.
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The sedimentary sequence overlies discordantly the
crystalline rocks. The oldest deposit correspond to the
Cretacic conglomerate Los Terrones, which is made of
granitic blocks spread in a conglomerate matrix and coarse
grained sand lenses (Massabie 1982). This formation con-
stitutes the nuclei of the ranges Pajarillo, Copacabana and
Maza (Pastore and Methol 1953). The sequence continues
with modern valley deposits, 35-m thick, consisting of
agglomerates, sands and carbonate lenses (Massabie 1982)that were accumulated in an erosive depression that
extends from the Calabalumba River to the Charbonier
stream (Beltramone 2004). Loess-like sediments (alloch-
tonous) are present in some parts of the region. Typical
forms of bare granitic outcrops are found in the southern
border of the study area.
The San Marcos River basin occupies an area of about
362 km2 and the main collector is a fourth-order stream
(Horton 1945; Strahler 1987) with a total length of 40 km
(Fig. 1). The San Marcos River runs with an SE–NW trend.
Its catchments are located in the western flanks of the
Pajarillo, Copacabana and Maza ranges and also in the
highest part of the Cuniputo ranges. The river discharges
into the Cruz del Eje reservoir lake, located in the North-
western part of the study area. The runoff reflects the
seasonal rainfall regimen of the mountain watersheds.
During the dry season (from March to September), base
flows mainly correspond to contributions from water storedin fractures and colluvium.
Climate in the study area is mountainous sub-humid to
semiarid. Mild temperatures, irregular rainfall concentrated
in one season (summer), and occasional snowfall in
autumn–winter are typical features. Annual average pre-
cipitation decreases from 700 mm on the eastern flanks of
the ranges to 400 mm on the northwestern border of the
study region. The mean annual temperature in the area is
16C, increasing to 19C towards the northwestern border.
Fig. 1 Geological map of the study area and location of water sampling stations. The inset shows the extension of the Sierras Pampeanas region
and the relative location of the study area. The sector corresponding to the Sierras Pampeanas de Co rdoba is indicated in blue pale
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The climatic and geomorphologic characteristics of the
area define the conditions for a denudation regime of the
weathering-limited kind (Stallard and Edmond 1983),
where the transport processes removing weathered material
are potentially more rapid than the processes generating
mineral debris. Furthermore, Kirschbaum et al. (2005)
examined weathering profiles in granites of the nearby
Sierra Norte of Cordoba and reported that mineralogical,petrographic and geochemical information indicate incipi-
ent weathering for the region. Concordantly, Lecomte et al.
(2009) concluded that the geochemistry of dissolved ele-
ments in mountainous rivers from Sierras Pampeanas de
Cordoba, besides being affected by climatic characteristics
and lithology, are also indirectly controlled by the domi-
nant geomorphology, which affect the water residence time
in the catchments and hence, the extension of rock–water
contact.
Methodology
Geochemical sampling and analysis
Streams and groundwaters located in the mountainous area
of Sierras Pampeanas de Cordoba, at elevations from 1,100
to 600 m a.s.l. were sampled during March and May 2008,
and June 2009. The rivers Calabalumba, Seco, and the
Charbonier stream were sampled twice in March and May
2008. The location of surface and groundwater sampling
stations is shown in Fig. 1.
Field determinations consisted of pH, electrical con-
ductivity, temperature, alkalinity, and dissolved oxygen.
Determinations were performed using standardized solu-
tions (Hach Co.). All samples were filtered through
0.22-lm cellulose acetate membrane filters (Millipore
Corp.) and divided into two aliquots. Aliquots used for
trace elements and major cations (50 ml) were acidified to
pH\ 2 with ultrapure HNO3 (C99.999%, redistilled,
Aldrich Chemical) and stored in pre-cleaned polyethylene
bottles. The remaining 100-ml aliquot was stored in
polyethylene bottles, without acidifying, at 4C for the
determination of anions. The filtration equipment was
thoroughly rinsed with acidified distilled water before uti-
lization. The filtration glass funnel was repeatedly rinsed
with sample water prior filtration.
Anions (Cl-, NO3
-, NO2
-, SO4
2-, and F-) were
determined by chemically suppressed ion chromatography
with conductivity detection, and major, minor, and trace
elements by ICP-MS (Perkin Elmer Sciex Elan 6000—
quadrupole mass spectrometer). The validity of the results
for major, minor, and trace elements were checked with
NIST-1640 (Riverine Water Reference Materials for Trace
Metals certified by the National Research Council of
Canada) and SRLS-4, carried out along with sample
analysis. For most of the analyzed stream waters, the
charge imbalance between cations and anions was\5%.
Health sampling and analysis
Clinical studies were performed in 7–12-year-old children
from the Charbonier County, following the methodologyand ethical guidelines recommended by the WHO World
Health Organization (2004).
Dental fluorosis index was calculated using the tooth
surface index of fluorosis proposed by Horowitz et al.
(1984) that varies from 0 to 7, and classify dental surfaces
as: 0, without fluorosis; 1–3, mild forms of fluorosis (white
spots); 4–7, severe forms of this disease (yellow to brown
spots).
Total fluoride intake (mg/person per day) was deter-
mined through enquires and calculations proposed by
WHO World Health Organization (1985).
Results
Chemical composition of ground and surface water
and F- hydrochemistry
The major chemical composition of surface and ground-
waters from the study area is mostly controlled by litho-
logy, geomorphology, and rainfall distribution. Human
perturbations mostly affect shallow groundwaters through
the leakage of domiciliary wastes, while surface waters are
almost not affected.
Table 1 shows pH values, electrical conductivity, and
major ions concentrations measured in the sampled waters.
Saturation index (SI) calculated for calcite using the
PHREEQC 2.15 code (Parkhurst and Appelo 1999) is also
included in the table. The pH ranges between *7.2 and
*8.4, the groundwater samples being slightly more acidic
than river waters (mean groundwater pH: 7.45 ± 0.19;
mean surface water pH: 7.99 ± 0.28). Electrical conduc-
tivity (EC) varies between 160 and 860 lS/cm, and as
expected, it increases downflow in the basin. Oxidizing
conditions predominate in the basin, with dissolved oxygen
values[4.8 mg l-1. According to Piper (1944) classifica-
tion, ground- and stream waters are predominantly of the
Ca-HCO3 type.
Dissolved F- and other trace element concentrations are
compiled in Table 2. Dissolved F- concentration ranges
from 0.96 to 2.87 mg l-1 with one outlier value of
8.00 mg l-1. About 70% of the river water samples exceed
the 1.5 mg l-1 guideline value for F- in potable water set
by the WHO World Health Organization (2004) and the
Argentine standard requirements (Codigo Alimentario
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Argentino 1994), while the 100% of groundwater samples
exceed this value. Surface waters show a higher variability
of the F- concentrations (mean F- concentration 1.84 ±
0.62) than groundwaters, where concentrations remainalmost constant (mean F- concentration 2.23 ± 0.33).
The spatial distribution of the F- contents is shown in
Fig. 2. According to this figure, the higher F- concentra-
tions are located in two sectors of the basin, one encom-
passed between the Calabalumba and Charbonier streams,
in the Charbonier depression, and the other in the lower
San Marcos basin. In these parts of the basin, F- concen-
trations in both ground- and surface waters always exceed
2 mg l-1. Concentrations lower than 1.7 mg l-1 are typi-
cally found at the basin’s catchments.
Fluoride intake and dental fluorosis assessment
The fluoride intake in the study area is 3.90 ± 0.20 mg
day-1 (n = 16), which is almost twice the estimated
maximum fluoride dose for 7–11 years old children
(1.68 mg day-1) in fluoridated areas (Harrison 2005).
Dental fluorosis index varies from 0 to 7, and classify
dental surfaces as: 0 without fluorosis, 1–3 mild forms of
fluorosis (white spots), 4–7 severe forms of this disease
(yellow to brown spots) (Horowitz et al. 1984). From the
analysis of the dental fluorosis index, it was found that
mild and severe fluorosis (Fig. 3) reach an incidence of
86.7% (total teeth surface = 636 teeth) among the chil-
dren population. Most severe forms of dental fluorosiswere found in 11–12 years old children with an incidence
of 28.5%, while in younger children (7–10 years old) this
incidence only reaches 15%. These results could be
explained by structural defects of enamel, which become
more evident with time as a result of prolonged exposure
to high levels of fluoride during amelogenesis. About
20% of severe forms of dental fluorosis affect axillary
anterior teeth, with a consequently negative aesthetic
implication.
Sources of dissolved fluoride
Devonian–carboniferous granitoids with a typical A-type
signature that were emplaced in the Eastern Sierras
Pampeanas region (Dahlquist et al. 2010) are considered
the most likely source of F- in natural waters from the
study area. A-type or anorogenic granites are characterized
by their relatively elevated F contents (0.05–1.7%) (Eby
1990). Experimental data show that A-type magmas con-
tain dissolved OH–F-bearing fluids (Bonin 2007).
Table 1 Major ionic composition and physico-chemical parameters of sampled waters
Sample pH Conductivity
(lS cm-1)
D.O.
(mg l-1)
NO3
-
(mg l-1)
Na?
(mg l-1)
Mg?2
(mg l-1)
K ?
(mg l-1)
Ca?2
(mg l-1)
Cl-
(mg l-1)
SO4
-2
(mg l-1)
HCO3
-
(mg l-1)
SI
calcite
March 2008
1CLB-1 8.24 240 10.0 n.d. 12.90 5.19 2.62 60.80 3.86 8.32 228.09 0.92
1ACH-2 7.60 660 9.5 n.d. 72.66 7.58 3.82 56.80 8.57 35.87 343.43 0.99
1CH-3 8.08 560 8.8 n.d. 41.57 5.42 4.86 71.20 7.22 38.57 292.80 0.511PSM-4 7.70 600 10.8 3.02 35.00 6.89 3.80 64.80 34.98 49.62 201.30 0.34
1RS-5 7.72 480 10.0 n.d. 35.00 6.45 4.34 63.20 4.96 21.13 282.20 0.51
May 2008
2LTRS-6 8.35 350 10.3 n.d. 11.60 5.04 2.53 65.60 2.46 3.87 246.56 1.09
2LTRN-7 8.38 320 10.1 n.d. 20.90 6.16 3.00 72.80 5.31 8.93 238.51 1.13
2PQL-8 7.61 650 8.4 1.5 n.d. 8.83 4.52 n.d. 9.20 86.00 270.84 0.11
2CLB-9 8.30 160 10.2 4.04 19.80 7.06 3.19 60.80 5.14 18.18 241.20 0.99
2PSI-10 7.18 860 8.5 32.47 268.92 14.20 5.71 64.00 275.72 92.40 387.96 n.d.
2ACH-11 7.80 690 7.5 n.d. 89.78 9.10 4.40 55.20 9.75 36.16 389.18 0.63
2RS-12 7.71 530 9.7 n.d. 41.18 7.42 4.25 66.40 19.99 27.46 279.38 n.d.
June 2009
3RD-13 8.10 613 8.4 2.30 70.00 10.60 4.50 51.40 16.10 9.00 365.30 0.88
3AET-14 7.77 640 8.3 \0.5 62.30 16.50 6.30 61.60 18.30 17.00 382.58 0.65
3PCT-15 7.31 510 4.8 3.60 48.70 9.40 4.80 45.20 18.00 40.00 232.23 -0.13
3PVS-16 7.47 570 6.7 3.80 54.30 10.70 5.10 48.50 21.90 54.00 239.17 0.06
3PVN-17 7.42 570 5.6 3.50 54.20 10.50 5.10 47.60 22.00 54.00 234.98 0.00
3RSM-18 7.80 550 10.9 3.70 55.50 10.00 4.50 49.10 23.20 59.00 232.07 1.25
n.d. not determined, DO dissolved oxygen, SI saturation index
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T a b l e 2
F -
a n d t r a c e e l e m e n t c o n
c e n t r a t i o n s m e a s u r e d i n s a m p l e d w a t e r s
S a m p l e
F -
( m g l -
1 )
S i
( m g l -
1 )
A l
( l g l -
1 )
V ( l g l -
1 )
C r
( l g l -
1 )
M n
( l g l -
1
)
F e
( l g l -
1 )
C o
( l g l -
1 )
N i
( l g l -
1 )
C u
( l g l -
1 )
Z n
( l g l -
1 )
A s
( l g l -
1 )
S e
( l g l -
1 )
L i
( l g l
- 1 )
M o
( l g l -
1 )
U ( l g l -
1 )
M a r c h 2 0 0 8
1 C L B - 1
1 . 3
2
9 . 2
0
1 6
. 0 0
2 . 7
0
0 . 9
0
1 0
. 9 0
1 0
. 0 0
0 . 0
8
1 . 8
0
2 . 9
0
1 5
. 1 0
0 . 8
9
b d l
6 . 0 0
0 . 9
0
2 . 7
9
1 A C H - 2
2 . 3
2
1 9
. 6 0
3 8
. 0 0
3 0
. 6 0
4 . 7
0
2 9
. 2 0
2 0
. 0 0
0 . 1
3
2 . 3
0
0 . 5
0
1 1
. 4 0
8 . 8
7
1 . 1
0
4 8 . 0 0
8 . 7
0
1 5
. 8 0
1 C H - 3
2 . 0
0
1 4
. 1 0
4 0
. 0 0
1 8
. 1 0
4 . 3
0
2 . 1
0
5 0
. 0 0
0 . 0
5
1 . 8
0
0 . 9
0
9 . 8
0
6 . 8
2
1 . 1
0
3 9 . 0 0
9 . 1
0
4 . 2
5
1 P S M - 4
2 . 1
5
1 4
. 8 0
5 . 0
0
1 7
. 6 0
4 . 3
0
1 . 4
0
3 0
. 0 0
0 . 0
5
1 . 4
0
5 . 8
0
1 5 6
. 0 0
4 . 9
4
1 . 8
0
3 0 . 0 0
4 . 6
0
8 7
. 6 0
1 R S - 5
2 . 6
3
1 6
. 4 0
1 6
. 0 0
1 5
. 7 0
3 . 5
0
5 . 4
0
4 0
. 0 0
0 . 0
7
1 . 3
0
2 . 6
0
1 9
. 1 0
2 . 7
0
1 . 0
0
2 2 . 0 0
5 . 0
0
3 8
. 7
M a y 2 0 0 8
2 L T R S - 6
1 . 4
4
9 . 7
0
2 1
. 0 0
5 . 9
0
3 . 3
0
3 0
. 4 0
4 0
. 0 0
0 . 1
0
1 . 0
0
5 . 9
0
1 8
. 8 0
1 . 3
5
0 . 7
0
8 . 0 0
0 . 7
0
2 . 2
4
2 L T R N - 7
1 . 5
3
1 0
. 1 0
6 . 0
0
6 . 4
0
2 . 6
0
4 . 8
0
4 0
. 0 0
0 . 0
3
0 . 6
0
0 . 7
0
8 . 7
0
1 . 3
5
0 . 9
0
2 1 . 0 0
0 . 8
0
3 . 2
6
2 P Q L - 8
2 . 8
7
2 0
. 4 0
2 0
. 0 0
2 2
. 8 0
2 . 9
0
1 . 1
0
3 0
. 0 0
0 . 0
3
0 . 9
0
1 . 5
0
1 7
. 8 0
5 . 8
3
1 . 6
0
4 3 . 0 0
9 . 5
0
9 7
. 1 0
2 C L B - 9
1 . 6
1
9 . 8
0
1 0
. 0 0
6 . 6
0
2 . 2
0
1 0
. 8 0
3 0
. 0 0
0 . 0
6
0 . 7
0
1 . 6
0
1 1
. 4 0
1 . 9
4
1 . 2
0
9 . 0 0
1 . 7
0
5 . 6
5
2 P S I - 1 0
2 . 2
7
2 2
. 3 0
1 1
. 0 0
2 1
. 7 0
2 . 8
0
1 . 2
0
4 0
. 0 0
0 . 1
3
0 . 8
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0
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3
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0
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0
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1
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5
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7 . 9
0
3 0
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8
1 . 1
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2 R S - 1
2
8 . 0
0
1 7
. 0 0
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2 . 3
0
2 . 6
0
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8
0 . 8
0
1 . 4
0
1 9
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3
0 . 9
0
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0
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3 R D - 1
3
1 . 2
6
1 1
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0
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7
b d l
1 2 . 0 0
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0
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3
3 P C T - 1
5
2 . 0
0
1 2
. 1 0
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0
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0
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0
b d l
0 . 0
5
b d l
3 . 5
0
1 1
. 2 0
2 . 5
0
0 . 5
0
3 6 . 0 0
3 . 2
0
1 3
. 0 0
3 P V S - 1
6
2 . 1
0
1 0
. 3 0
1 0
. 0 0
1 0
. 1 0
0 . 9
0
1 . 5
0
b d l
0 . 0
4
b d l
2 . 0
0
1 0
. 5 0
4 . 7
5
b d l
4 3 . 0 0
4 . 1
0
1 6
. 8 0
3 P V N - 1
7
1 . 9
9
9 . 9
0
7 . 0
0
1 0
. 9 0
0 . 8
0
0 . 9
0
b d l
0 . 0
4
0 . 4
0
1 . 4
0
6 . 8
0
5 . 3
6
b d l
4 6 . 0 0
4 . 9
0
1 7
. 7 0
3 R S M - 1
8
2 . 6
7
1 0
. 4 0
8 1
. 0 0
1 0
. 4 0
0 . 7
0
2 . 9
0
6 0
. 0 0
0 . 0
6
1 . 1
0
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0
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8
b d l
6 4 . 0 0
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0
2 2
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b l d
b e l o w d e t e c t i o n l i m i t
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One important geochemical characteristic of the Devo-
nian–Carboniferous granites and their enclaves in the
Sierras Pampeanas region is the F-rich nature of the apatites
and biotites (Dorais et al. 1997). Although fluorite is a rare
accessory mineral in the granite, veins of economic interests
are often located close to the contacts with the metamorphic
host rock. In a recent study, Dahlquist et al. (2010) con-
cluded that biotites found in the granites near the study area
have distinctive compositions with variable contents of F,Cl and high FeO/MgO ratios. Concordantly, Colombo et al.
(2010) described F-rich micas in pegmatites and host
A-type carboniferous granites from the northern Sierras
Pampeanas region. Table 3 shows the mean major oxide
composition and F content found in micas from A-type
granites and pegmatites emplaced in the region (i.e.
Colombo 2001; Colombo et al. 2010; Dahlquist et al. 2010).
Fluoride and chloride may substitute OH- ions in the
biotite lattice (Bailey 1984), and therefore, these ions are
Fig. 2 Map showing the spatial
variation of F-
concentrations
in natural waters from the study
area. The circle diameter is
proportional to F- concentration
in water
Fig. 3 Examples of severe and
mild cases of dental fluorosis in
school children from
Charbonier Department
Table 3 Mean major oxide composition and F contents of micas
from A-type granites and pegmatites
Major composition Mean (n = 19)a (%)
SiO2 36.55
Al2O3 18.06
TiO2 2.10
FeO 24.83
MnO 0.52MgO 3.02
Li2Ocalc 1.24
CaO 0.04
Na2O 0.13
K 2O 9.47
F 2.40
Cl 0.20
H2Ocalc 2.15
a Dahlquist et al. (2010), Colombo et al. (2010), and Colombo (2001)
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released during weathering, along with K ?, Mg2?, Fe2?,
and H4SiO4 as indicated in Eq. 1.
2KMg2:5Fe2þ0:5AlSi3O10 OHð Þ1:75F0:25
þ 13:5 Hþ þ 1:5H2O ¼ Al2Si2O5 OHð Þ4þ 2K þ
þ 5Mg2þ þ 4Si OHð Þ4þ 0:5F þ Fe2þ ð1Þ
The dissolution of biotite is pH dependent, as it dissolvesmore rapidly under acidic conditions (Malmstrom and
Banwart 1997). In natural pristine waters, acidity mainly
originates from the dissolution of atmospheric CO2 or is
generated by the decay of organic matter or by root
respiration. The last two processes are responsible for the
high levels of CO2 often found in groundwater reservoirs
(Appelo and Postma 1999).
Regarding Eq. 1, a positive linear correlation between
the product solutes and the F- content should be observed in
the studied waters. The dispersion diagram between F- and
H4SiO4 concentrations is shown in Fig. 4a. In general,
points follow a clear positive trend that runs almost parallelto the estoichiometric line corresponding to the biotite
dissolution, but all points are displaced towards the right,
indicating that there is likely another source of F- in the
region. When considering this fact, the estoichiometric line
corresponding to the dissolution of phlogopite (KMg3Al-
Si3O10F(OH)) has also been included in the graph. This
mica has also been identified in the region and contains
higher concentrations of F in its composition (4.53% against
1.10% in biotite). As seen in the figure, sample points plot
between these two lines, suggesting that micas in the study
area have intermediate contents of F. Points corresponding
to stream water samples running through A-type granitesthat outcrop in central and southern border of the Sierras
Pampeanas de Cordoba (Garcıa et al. 2006; Lecomte 2006)
also follow the same trend, but F- concentrations in these
cases are much lower. The slope of the third dashed line in
the figure corresponds to the average molar ratio between Si
and F contents measured in micas from different outcrops in
the Sierras Pampeanas ranges (Table 3). A similar trend is
observed in the dispersion diagram showing the relation
between F- and (Mg2?? Fe2? ? K ?) (Fig. 4b), which
reinforces the hypothesis of F-rich micas as the main source
of dissolved F- in the study area.
Good correlations between F- and other trace elementssuch as Li (r
2: 0.97), As (r 2: 0.97), and V (r
2: 0.98) are also
found, but only in ground and stream waters collected in
the Charbonier depression reservoirs.
Fluoride dynamics
Several factors may control the mobility of F- in natural
waters. Many authors described the dissolution of fluorite
enhanced by calcite precipitation, as one important mech-
anism of F- release to waters in equilibrium with calcite
(i.e. Desbarats 2009; Genxu and Guodong 2001; Handa
1975; Nordstrom and Jenne 1977; Pickering 1985). The
dissolution of fluorite may also be enhanced by other
mechanisms that result in Ca2? scavenging, such as cationexchange or apatite precipitation. Owing to the scarce
occurrence of fluorite in the bedrocks of the study area, its
dissolution likely constitutes a minor source of F- in
waters. Although most water samples are saturated with
respect to calcite (Table 1), the dissolution of fluorite
enhanced by calcite precipitation is not likely to be a key
process in controlling the dynamics of F- in the study area.
It is well known that calcite precipitation occurs under
alkaline conditions; therefore, it should be expected
Fig. 4 Bivariate plots showing the variation of F-
against a Si and
b Mg2?? K ? ? Fe concentrations measured in natural waters from
the study area and from other streams located in the southern parts of
the Sierras de Cordoba. Lines represent the corresponding molar
ratios in biotite and phlogopite and in regional micas
542 Environ Earth Sci (2012) 65:535–545
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increasing F- concentrations at increasing pH. However,
data show just the opposite trend: the lowest F- concen-
trations were measured in the more alkaline pH waters, as
shown in Fig. 5a.
The described trend with pH does not either explain the
removal/release of F- by adsorption/desorption, as F- is
preferentially attached to mineral surfaces (mainly Fe or Al
(hydr)oxides) under neutral to acidic conditions (i.e.,
Arnesen and Krogstad 1998; Hiemstra and Van Riemsdijk
2000; Omueti and Jones 1977; Sparks 1995; Sposito 1989;
Tang et al. 2009). Therefore, the lower concentrations
should be observed in more acidic waters, which are not
seen in the studied waters.
Concentrations of F- tend to increase downflow in the
studied basin, and as indicated above, the removal of F-
from water appears to occur by neither fluorite precipi-
tation, nor by adsorption. In a simple way, F- in the study
watershed behaves as a conservative element that typi-
cally shows a positive trend with conductivity (Fig. 5b).
Besides, concentrations decrease at increasing water dis-
charges as observed in the Calabalumba and Seco Rivers
and in the Charbonier stream stations, where samples
were collected at two different water discharge stages
(arrows in Fig. 5b).
Conclusions
Mild and severe forms of dental fluorosis were detected
among the population of some small villages located in
the Sierras Pampeanas region, Argentina. The daily
fluoride intake determined in the community of Char-
bonier (Cordoba province) has been estimated in
3.90 mg ± 0.20, which is almost twice the recommended
maximum fluoride dose for 7–11 years old children. This
disease is mainly caused by the consumption of F-rich
water.
Dissolved F- in natural waters from the study area is
mostly geogenic, as it originates in the weathering of F-bearing minerals that compose the dominant lithology in
the region. A great number of minerals containing F in
their compositions have been identified, fluorapatite, apa-
tite, fluorite, topaz, and micas being the most conspicuous
phases. The weathering of F-rich biotites has been con-
sidered the most important and representative source of
dissolved F- in waters from the study area, based on the
high F contents determined in micas collected from dif-
ferent granitic and metamorphic outcrops in the region and
in their abundance in the bedrocks.
The extent of mineral weathering in the study area is
mostly determined by the residence time of water within
the aquatic reservoir. Longer residence times and a major
solid–water interaction lead to enhanced release of F-.
This explains the high concentrations found in all
groundwater samples and in surface waters from the
Charbonier depression and from the lower San Marcos
basin. In these parts of the basin base flow mainly corre-
sponds to water stored in fractures and colluvium for long
periods of time. The removal of F- from water does not
likely occur by either fluorite precipitation, nor by
adsorption, thus is its concentration’s variability mostly
controlled by water residence time and alternating periods
of maximum and minimum discharges.
Owing to the occurrence of similar lithology and
hydrological conditions all along the Sierras Pampeanas
region, it is expected that F-rich waters are present
anywhere in the region, and in consequence, a number
of people living in these rural and isolated zones could
be also suffering from dental fluorosis. Future studies
should be carried out to characterize this environmental
disease and the fluorine geochemistry in the whole
region.
Fig. 5 a Bivariate plots showing the variation of F- concentrations
against pH and b conductivity in the study area. The arrows representthe chemical evolution from base flow to more humid conditions
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Acknowledgments This research was supported by Argentina’s
FONCYT, SECYT-UNC, and CONICET. M. Gabriela Garcıa, and
Karina L. Lecomte are members of CICyT in Argentina 0s CONICET.
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