Fluorine in Water and Dental Fluorosis in a Community of Queretaro State Mexico

doi:10.4236/jep.2011.26086

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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.

Email: [email protected]

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.

CaCOH2FCaFHCO 3



(3)

CaF Ca2F (4)





 



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

CaFCa+2F

 (6)



2+ 10.57

fluorita

K=CaF=10 at 2

 5˚C (7)

or,





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



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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