Journal of Environmental Protection, 2011, 2, 744-749
doi:10.4236/jep.2011.26086 Published Online August 2011 (http://www.SciRP.org/journal/jep)
Fluorine in Water and Dental Fluorosis in a
Community of Queretaro State Mexico
Ma Lilia A. Juárez-López1, Rafael Huízar-Álvarez2, Nelly Molina-Frechero3,
Francisco Murrieta-Pruneda1, Yazmin Cortés-Aguilera2
1FES Zaragoza, Universidad Nacional Autónoma de México, Mexico City, México; 2Institute of Geology, Universidad Nacional
Autónoma de México, Mexico City, México; 3 Universidad Autónoma Metropolitana, Mexico City, México.
Received May 11th, 2011; revised June 18th, 2011; accepted July 23rd, 2011.
ABSTRACT
The community La Llave, Queretaro State, Mexico, has not been identified by the sanitary authorities as living in a
hazard area related to dental fluorosis. However; a high concentration of fluoride is found in their drinking water
causing them dental fluo rosis. Physical-chemical analysis was carried out in the groundwater sources to de termine the
prevalence of dental fluorosis risk and caries accordingly to criteria of The World Health Organization, and 154 school
children of ages 10 to 13 years were examined. As a result, 1.9 mg/L of fluorine concentration in drinking water was
obtained; dental fluorosis presence was detected in the school children with an incidence of about 98%, in 47% of cases
severe fluorosis with a dental caries index of 3.06 was traced. The groundwater sources in La Llave community con-
tains fluorine above th e limits dictated by Mexican regu lations , producing serious repercussions on the health of school
children, with an unnaturally high incidence of dental fluorosis.
Keywords: Fluorosis, DEAN Index, Groundwater, La Llave Querétaro, Mexico
1. Introduction
The Community of La Llave, Queretaro State, where this
work was carried out, is located at 1900 m above mean
see level (amsl) on the southern part of the plain that ex-
tends from El Zamorano volcano, north of Queretaro
City, to San Juan del Rio City, located in the central part
of Mexico (Figure 1). The plain contains some volcanic
reliefs hardly 100 m heights above the plain surface, such
as Cerro La Cruz and La Carbonera, at whose base La
Llave is located.
The geological framework of the region is constituted
by rocks of chemical composition ranging from interme-
diate to acid, represented by interstratified ignimbrites
with pumice tuffs, both expulsed through the Caldera of
Amealco. These materials are covered on the plain by
alluvial deposits. Alluvial deposits consist of sediments
of several sizes ranging from clay and sand to rounded
blocks of different composition derived from pre-existing
nearby rocks. These deposits form the most surface layer
of the plain and have a thickness from 5 to 30 m.
Comisión Estatal de Agua [1] shows the existence at
La Llave’s zone of an aquifer formed jointly by fractured
rocks and granular sediments that reaches a thickness of
200 m, settlements of the region obtain their water sup-
ply from this aquifer. The geological model shows the
existence of volcanic bodies of Olocene Age, suggesting
the presence of high temperature in the rocks beneath,
this feature is consider in determining the temperature
(26˚C) of tapped groundwater by wells.
The La Cruz, La Carbonera, and Viejo hills are con-
stituted by ignimbrites, rhyolites, and tuffs rocks. Con-
taining abundant fluorine where groundwater dissolves
accessory minerals contained in rocks such as, mica,
amphibole and apatite, the later releases fluorine to
groundwater.
On the other hand, groundwater rich in HCO3, during
the interaction between water and mineral (fluorite) the
following reaction takes place [2]
23 3
CaFNaCOCaCO2F 2Na

 (1)
233 2
CaFNaHCOCaCO2Na2FHOCO2

 (2)
According to this reaction high contents of NaHCO3 in
water increase the CaF2 dissolution in the rock releasing
fluoride in the groundwater. The dissociation of fluo-
rine-rich minerals, is also favored by the existence of rich
mineral calcite (CaCO3), as shown in the following reac-
tions [3].

Fluorine in Water and Dental Fluorosis in a Community of Queretaro State Mexico 745
Figure 1. Location of groundw ate r sample borehole.
32
CaCOH2FCaFHCO 3

(3)
2
CaF Ca2F (4)


 

3
KaHCO aH*aF (5)
where K is the equilibrium constant, a is the activity. If
pH is constant, the activity of fluorine is directly propor-
tional to HCO3. This relationship is independent of Ca2+
produced by the low solubility of CaF2.
Fluorine content in groundwater is positively corre-
lated with Na+ and pH, the presence of F−; is associated
with sodium bicarbonate type water with a high pH.
However, it has a negative correlation with Ca2+, this
indicates that the fluorine concentration is associated
with reactions where Na+ and pH increase, and Ca2+ de-
creases as a result of cation exchange, or precipitation of
calcite. This suggests that F- concentration is controlled
by the Fluorite (CaF2) equilibrium, i.e., the limits of fluo-
rine are determined by the calcium ion [4-8].
According to Edmunds [9], the upper limit on fluoride
activity in aqueous solutions is controlled by the solution
of the products, Kfluorite
2+
2
CaFCa+2F  (6)

2
2+ 10.57
fluorita
K=CaF=10 at 2
 5˚C (7)
or,


2+
fluorita
log K=Ca+2logF=10.57
 (8)
Those equations show that in the presence of fluoride,
the fluorine contents are inversely proportional to Ca2+.
The silicates dissolution in alkaline rocks, where oligo-
clase is plagioclase dominant, rich in sodium and calcium
deficient, provides sodium and fluorine enrichment in
groundwater [6,10,11]. Based on the foregoing, F− can be
removed by precipitation when there is a high concentra-
tion of Ca2+ [7].
Fluorosis is a disturbance caused by excessive inges-
tion of fluorine during the odontogenic stage [12]. In
Mexico, the prevalence and incidence of fluorosis have
increased during the past years, as a result of ingestion of
fluorine during dental formation by means of water, food
prepared with fluorated salt, and inadvertent ingestion of
this element during dental brushing with fluorated tooth-
paste, as well as hidden fluorine in beverages [13,14].
In light of dental spots observed to children of this

Fluorine in Water and Dental Fluorosis in a Community of Queretaro State Mexico 746
community and the lack of reports related to the fluorine
concentration in water in this area, it was considered to
be important to carry out the present study. The goal of
this study is to determine the fluorine concentration in
drinkable water, as well as to analyze the effects of
fluorosis and dental caries in school children residents in
La Llave town.
2. Methodology
2.1. Water Sample
Samples of water were taken for physical chemical
analysis in polyethylene bottles prewashing in lab with
hydrochloric acid (5%) and distilled water solution. Air
bubbles were avoided to limit any potential change in the
original chemical water composition. A 100 ml bottle
was taken without adding any preservation agent or fil-
tered, this sample was used in anions determination. The
sample for cations and trace elements was taken in a bot-
tle of 125 ml; it was filtered using a cellulose acetate
membrane of 0.45m and was then acidified (to a pH ≈ 2)
by means of nitric acid of high purity (in order to avoid
precipitation and absorption of elements on the walls of
the bottle). Analyses were carried out by a mass spec-
trometer with inductive plasma coupling (ICP-MS). The
detection limits obtained with this equipment is very low
(less than 0.001 mg/l). The analyses were performed by
Actlabs of Canada.
2.2. Clinical Examination
For convenience, the 154 subjects, between 10 to 13
years old, were checked; all of them are residents of the
community La Llave, Municipality of San Juan del Rio,
Queretaro. Only children with explicit permission from
their parents participated in this study, their residence
greater than 10 years in the zone was also demonstrated.
Children with background of metabolic disease or those
under orthodontic treatment were excluded from the
study.
The clinical examinaton was carried out with natural
light without desiccation, using dental plain mirrors, #5,
without amplification. Results were recorded in indivi-
dual files. The exam was performed by two qualified and
standardized observers accordingly to the WHO criteria
[15]. Among the Dean Fluorosis Index (ID) and dental
caries index (DMF-T and DMF-S), when the Kappa test
was applied, congruence was observed in the diagnosis
criteria of 87% and 95% for fluorosis caries index re-
spectively.
3. Results and Discussion
3.1. Water Quality
According with the prevailing geological framework, the
chemical quality of the water that the population drinks
depends of the type of rock material it circulates through.
Consequently, fluorine concentration in the aquifer is
associated to rock-water interaction and is determined on
the one hand by the abundance in the minerals forming
the rocks [16,17], as well as by the solubility of the mi-
nerals, and the water subsaturation as related to calcite.
In as much as the calcium limits the solute or dissolved
fluorine concentration[18], Table 1 contains the chemi-
cal analytical results for this paper, where it can observed
that the greater calcium content the lower content of
fluorine, and vice-versa. Based on the solubility control
of fluoride it may be removed by precipitating it by
maintaining a high concentration of Ca2+ [7], these re-
searchers propose that fluorine dispersion and transport
are determined by pH and water temperature.
In a laboratory experiment, the quantity of solute or
dissolved fluorine in acidic rocks was found to be almost
double the quantity to that in basic rocks; this also
showed the close relationship between fluorine content in
groundwater and the nature of strata it flows through
[19].
In most of the towns of Mexico, the water supply is
derived from groundwater sources, whose natural minera-
lization has increased in some elements such as fluorine
[20], In many cases, the result depended on the way the
water is extracted. i.e., an intense extraction of ground
Table 1. Groundwater chemical composition of the wells
analyzed in this study (Lourdes, La Valla, and La Llave),
values in mg/L.
Parameter Lourdes Llave Valla WHO (g/v)
pH 8.05 8.10 8.07 n-h
Water temp 31.0˚C 30.0˚C 25.9˚C n-h
Alcalinity 140.00 107.00 150.00 n-h
Ca2+ 22.00 12.10 21.00 n-h
Mg2+ 5.61 3.16 7.92 n-h
K+ 10.50 10.10 13.70 n-h
Na+ 40.00 45.00 42.00 n-h
Cl− 3.79 4.84 3.95 n-h
2
4
SO

6.91 7.35 10.40 n-h
Si 37.00 43.50 39.20 n-h
Mn 0.05 0.01 0.01 0.4
Fe 0.10 0.10 0.10 N-H
F− 0.52 1.94 0.51 1.5
WHO (g/v), Guideline value; n-h = Not of health concern at levels found; in
drinking-water.

Fluorine in Water and Dental Fluorosis in a Community of Queretaro State Mexico 747
water causes the drawdown of the water-table in wells
and induces water flow from the deeper levels [21],
where their mineral content might contribute with fluo-
rine in higher concentration than those considered, as
optimal for fluorosis prevention. However, in wells,
where water is extracted from low depth obtaining local
or intermediate flows with traces of fluoride can reduce
significantly the levels of fluoride in the obtained water.
The water extracted from the well in La Llave con-
tained more fluorine than those in neighboring towns as
Lourdes and La Valla (Table 1). However, that content is
low related to those reported in other regions in the
country also of volcanic origin, such as San Luis Potosí
(4 - 7 mg/L), [22], Tesistan Jal. (4.7 mg/L), [23], and Du-
rango (5.7 mg/L) [24]. In agree to groundwater flow sys-
tems model [25], the records of fluorine content and
temperature in the first three wells, led to assumption that
the obtained water is related to a groundwater flow sys-
tem of local type; whereas, for the other regions, it is
more related to an intermediate flow.
3.2. Dental Fluorosis
The prevalence of students affected by dental fluorosis
was 98%, this dental defect is regarded as a biomarker of
chronic toxicity caused by continuous exposure to fluo-
rine. The Community Dean Index (CDI) was 3.06 ± 1.
Moreover, approximately 48% of those children showed
severe fluorosis (Table 2) with loss of dental enamel
structure requiring prosthetic and anti-aesthetic actions.
The Ta ble 3 shows the mean of the different index by
gender, and the percentage of children with dental caries
was 70% with a DMFT of 2.7 ± 2.7 and a DMFS of 3.6 ±
3.7.
The prevalence of caries was greater in those children
with high severe fluorosis (Figure 1). There is informa-
tion about low levels of fluorosis preventing caries, but
severe levels constitute a risk factor for diseases since the
structural defects due to fluorosis alterations cause spots
where the bacterial plaque can remain [26].
Present study coincides in the general objective re-
garding the communities of La Fuente, Santillan, and San
José, all located close to San Juan del Rio Queretaro,
where a prevalence of 87% of fluorosis in children from
11 to 13 years of age, has been reported [27].
In the village of La Llave, the dental fluorosis could be
related not only with the fluoridated drinking water
above optimal limit level, but also by preparing meals
and milk formula, in addition fluoride is also ingested
through foods prepared with fluoridated salt.
Some authors report that the more fluorosis affected
populations are those located at high altitude [28]. At
1500 m high amsl renal filtration and filtration of some
substances are modified to favor an increase of fluorine
Table 2. Severity of fluorosis according to the DEAN index
affecting scholars of 10 - 13 years old at the Community La
Llave.
Severity of Fluorosis* F %
None Fluorosis 3 2.0
Very slight 13 8.0
Slight 29 19.0
Moderate 36 23.5
Severe 73 47.5
Total 154 100.0
*Criteria of Dean.
Table 3. Dental fluorosis and caries index by gender in
scholars of 10 to 13 years old at the Community La Llave.
IDC DFMT DMFS
X DEX DE X DE
Men 3.05 - 3.041.022.75 2.8 3.7 3.8
Women3.11 - 3.081.062.82 2.6 3.553.5
X = Mean. DE = Standard deviation. IDC = Community Dean Index.
DFM-T = Decayed Filled Missed Teeth. DMFS = Decayed Filled Missed
Teeth by Surface
in the blood, which eventually will be concentrated in
teeth and bones [29]
4. Conclusions
Fluorine concentration in water supplied to La Llave
village had a 1.9 mg/L concentration. Continuous che-
mical monitoring of water quality is considered relevant;
it has to be performed in the wells and water supply
plants of nearby zones to geographically determine an
acceptable and required fluorine characterization.
The results obtained in this paper highlights differ-
ences of dental fluorosis showing that the maternal and
offspring population are exposed to various sources of
fluoride that cause floruosis; these sources are:
 Boil drinking water
 Food prepared with water having high fluoride con-
tent
 Cooking with fluoridated salt
Boiling water consumption rises from 60% to 70% the
original concentration of fluoride, which puts at risk for
developing fluorosis in permanent teeth [14,30,31].
A high fluorosis prevalence was observed, the IDC
points a severe public health problem, so it is important
to consider that well-water purification systems will be
installed in La Llave village or that other sources for
supplying potable water will be needed. It appears a valid

Fluorine in Water and Dental Fluorosis in a Community of Queretaro State Mexico 748
proposal that the inhabitants receive information related
to the fluoride sources related to dental fluorosis risks.
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