139 Fluodde Vol. 34 No. 2 13$149 2001 Research Report

WELLWATER FLUORIDE, DENTAL FLUOROSIS, AND BONEFRACTURES IN THE GUADIANA VALLEY OF MEXICO

M Tsresa Alarc6n-Herrera,' lgnacio R Martfn-Domlnguez,aRodoFo Trejo-v6zque4D sandra Rodriguez-Dozalc

Chihuahua, Aguascalientes, and Durango, M6xico

SUM ARY: In the Guadiana Valley (lhe city of Durango and its suBoundingsin nor0rweslern ftlexho), the drinking water supply comes ftom undergroundwells and is chalacnerized by a high content of f,uofile. ]n this study, a quanti-tative assessment of dental fluorcsis was made in the school age (5-12 years)and adult (1360 parc) population of Guadhna valley tfirough a multistagesampling by conglomerdes of the Population. The Dean index of dental fluo'rosis was colre|ad witt the fluoride concentration in drinking water. In thosepads of lhe valby with fluoride concentratiorc higher than 12 mg/L, all thechildren surveyed efi3biH dental fluorosis, ard 350/6 of them had sufferedserious damage to their teeth. A linear correhion beiureen the Dean index ofdental fluorosis and the frequency of bone fracttles was also observedamong both chiHr€n and adults.

Keywords: Bone tadures, Dental fluorosis, Dlinking water, Durango City, GuadianaValley, Me,dco, Water fluoride.

INTRODUCTIONDurango is the capital city of fte state of the same name in the northwest-

em part of Mexico. The valley where the city is located, together with 23small communities, is named Guadiana Valley. In this semi-arid region, wellwater is used to supply drinking water, after il'situ disinfection

In an epidemiological study, made in 1982, a Dean community index ofdental fluorosis of 1.42 was reported for the 6-12 year-old child populationin the city of Durango. r Later, Trejo'Vrizquez et aP mearured the fluoridecontent of the wells supplying drinking water and concluded thaq with fewo<ceptions, most ofthe fluoride concenfations were 200 to 300yo above the1.5 mg& limit permitted by Mexican regulations. Moreover, Diaz-Berriga etal3 found that endemic fluorosis is an environmenal health problem that af-fects around 5 million people in Mexico. They correlated endemic hydrofluorosis with mining activities of fluorspar deposits in the subsoil in severalstates in Mexico and showed that it results from natural contamination ofaquifen with fluoride. In their study they found areas of endemic fluorosisin the state ofDurango.

Recently, Ottiz et al reported that fluoride levels in Durango City rangedmainly from 1.54 tD 4.7 mg/L, with 5.67 mglL as the highest concentration.

"For conespondence: Dr. M. Tere€a Alarc6n-HerreG, Centro de Investigaci6n enMateriales Avanzados, S.C., Miguel de Cervantes 120 ComPlejo lndustial Chihuahua'31109 Chihuahua, Chih, M€xico. E-rnail alarcont@cimav.edu.mx; "lnstituto Tecnol6gicode Aguascalientes, Aguascalientes, Ags, M6xico; 'lnstituto Tecnol6gico de Ourango,Durango, Dgo, Mexico.

'140 Alarc6n-Herrera, Martin-Domlnguez, Tre.jo-Vezquez, Rodriguez-Dozal

They used a geographic information system to identifu four different rislareas, identi$ing a high-risk area in the northeast and southeast sectors o:the city. A low risk area was detected in the south sector of the city. The'reported that almost 959/o of the people living in Durango City are exposecto fluoride levels higher than 2.0 mg/L, but they did not measure hedtdamage in the people.

MATERIALS AND METHODS

Methodologt: The present investigation has two components: (l) samplingof water sources and (2) survey ofthe population. The former included fluaride analysis ofthe water in all the municipal and village wells, and the latte:involved a survey of the 1990 population of Guadiana Valley: 397,687 in-habitants in Durango City and 20,817 inhabitants in the other 23 smal.communities of the valley.

Statistical design: Water samples of all wells were taken, 51 in the city anc23 more in the surrounding areas (Figure l). Five different areas were defined according to the F concentration levels (Table l),

Population surveys were conducted according to a descriptive transvers€correlated design. Through a polystage conglomerate random sampling, 38(families were selected and prorated into 77 to 80 families per concentratio:area zone. This division yielded a total of 1,437 individuals from the fir:different areas. Since the dental effects of fluoride are easily detected r:school-age children, only 6-12 year-old children were considered for thr.part ofthe study, and from them, only those who had established permzrner.:residence in the area (333 children).

Figure 1. Location of the Guadiana Valley.

Ftuoride 34 (2\ 2001

Table 1. Fluoride con'

Fluoride concentlranges mg,4-

Zone IZone llZone ll lzone tvZone V

Sludy Inslrumetus: The follormixed questionnaire form to ga

cal informalion; the Dean inde

tion; bone fracture data; and an

centration determmatlons

ReliabilitY and validation o.f s

vised according to the stated ob

formal apPlication. The staff Pecarefullv trained to conduct a

charge of evaluating the denta

ceming water F concentratlon

The analgical techntqueSPADNS method 4500-F- D

always analYzed before and z

measurements was 2.7o/o Wat

one year.

RESU

Fluo ride w ater concen lra ti o n I

wells and their water fluorrdewells situated in the south ar

below 1.5 mg/L About 94% t

1.5 to 4.9 mg/L and16%o of th

est fluoride concentration (5 4

in the northeast sector of the (

the two wells in the southem 1

Oriz et af rePorted fluoridwhich corresPonds roughlY tc

concentrations. Their highest

the 5.11 mg/L found here fc

them as a high-risk area The

Non-detectable1 .51 - 4 995.0 - 8 .498 . 5 - 1 1 . 9

> 1 2T

- l

DentalfluoroGis and bone ftac-tures '141

Tabb 1. Fluoride concentation areas in Guadiana Valley

Fluoride concentration Number of wellsranges mg/L City Rurat

Population(1990 c€nsus)

Zone IZone llZone lllZone lVZone V

9,428400,5913,8234,270392

418,504

Sndy Instrumen s: The following instruments were used in this study: amixed questionnaire form to gather relevant social, demographic, and olini-cal information; the Dean index of dental fluorosis;s stomatology informa-tion; bone fracture datq and analytical chemical techniques for fluoride con-centration determinations.Reliability and wlidation of sudy instruments: A questionnaire was de-vised according to the stated objectives, and a pilot test was made prior to itsformal application. The staffpersonnel who assisted with the fieldwork werecarefully trained to conduct a uniform interview procedure. The staff incharge of evaluating the dental information did not have information con-ceming water F concentration.

The analpical technique used for fluoride determination was theSPADNS method 4500-F- D.6 Primary standard reference solutions werealways analyzed before and after measurements, the relative error duringmeasurements wu 2.7"/o. Water sarnples were taken every three months forone year.

RESULTS AND DISCUSSION

Fluoride waar concentrarrozs: Figures 2 and 3 show the locations of thewells and their water fluoride concentsations. In the city of Durango only 2wells situated in the south and southeast sectors had a concenration levelbelow 1.5 mglL. About 94Vo of the wells had concentrations in the range of1.5 to 4.9 mgll and 76o% ofthese were betw€en 3.0 and 4.9 mg/L. The high-est fluoride concentation (5.4 and 5.11 mgll) was found in 2 wells situatedin the northeast sector ofthe city, and the lowest concentration was found inthe two wells in the southem part ofthe city already mentioned.

Oraz et af reported fluoride levels ranging mainly from 1.9 to 4.7 mgfL,wtrich corresponds roughly to the 94% of wells in our study that have dreseconcentrations. Their highest fluoride concentatioq 5.67 mglL, is close tothe 5.11 mg/L found here for a well in the northeast sector, identified byfiem as a high-risk area They considered a fluoride concentration range of

Fhrcride 34 (2)2001

Nondetectable - 1.51.51 - 4.995.0 - 8.498 . 5 - 1 t . 9

> 1 2Totals

2 1 04 7 52 4- 2

51 23

142 Nat6n+1e.rera, Martin-Domtngueq Trejo-V6zqu€2, Rodriguez-Dozal

3.6 to 5.6 mg/L as high-risk areas.a Since in the southeast sector of the cifthere are 8 wells, 7 ofwhich have fluoride concentations in the rangea 4.9 mglL, we conclude that there is a general agreement with their resuhHowwer, w€ carmot establish a direct comparison because they definedrisk areas with a geographic informdion systerl which includedping concentration ranges. We also need to take into account that theytheir samples ftom homes, whereas we took ours from supply wells.fte municipal water distribution system combines water from wells withferent fluoride levels, it is not unusual to find different fluoridetions in the tap water. For the dental analysis, we took care to selectdwellings that were supplied by a well of lnown fluoride concentation.

i l , " o o A

I A A A l - l A

^ o AA n ^ l A -a ^o o o o

^ i ^ ^ 1 A

' Zone I^ Zone lla^ bE llb* zone lll

Flucide mgrl No. drvdb< 1.5 2

l.$eg 113.G,t g 365.0€.1 2

E

ozo 24.05

E

atooE8zs.ss

24.07

104.69 104.65 1M.61 104.59

Degrees Longitude West

Figurc 2. Fluoride concentations in Durango City.

Ouside the city the situation is different, since these are small commuities and have only one well supply for each village. Here l0 of the 23 vr*had fluoride concentrdions below 1.5 mglL, 9 wells had concentrdidranging from 3.0 to 8.4 mg/L, and 4 had values between 9.88 and 16 mgll.

To determine if there was a seasonal variation in fluoride conc€ntrdiqresults from all the sampling periods were analyzed through an ANOVAprocedure for 2 sources ofvariation, considering sampling periods as blocls.

Hfoilde u (212001

104'7DeglaE

ozo

lt

!f 24.03)oooooo

Fbure 3. Fludib c

Results showed a highlY sryb = 2.13E-166'), and a siPiftfot. n" dri-squared ft) awell for the different sarylia= 0.05, and the hYPoth*ical v=0.21.

Results showed that frm Isented a significant varire'-'fation range for each Zoc iseasonal variation, the latE tl

Dental sumeYs: the disrihlected for ihe studY bel4ilshown in Table 2. The mrrrzone because the samPle inddifferent numbers of childra

Dennl domage bY zoru: Ifrfluorosis classifi cations amthe five zones are Presented i

24.25

€ozo 24.05

(!J

@

Bze.as

23.75

Dentalfluorcsis and bone fractures 143

No. d Zone FluoddeFlb mgtL

10 'Zonel < 1.5

- ^ Zone lla I .12.9

5 ^ Zone llb 3.04.94 t zone lll 5.03.42 " Zone lV 8.t'l1.92

. Zc,.]tsV 12.G16.0

1M.9Oegrees Longitude West

Filure 3. Fluo de concentations in tlle Guadiana Valley.

1U.7 104.5 104,3

Results showed a highly sigrrificant variation between well concentrafions(p = 2.138-166), and a significant variation for simpling neriods 1p = 4.438-ZO1. fne chi-squared (12) test was used to determine the variance in everywell for the different sampling periods. The level ofsignificance used was c2= 0.05, and the hypothetical variance (mean of all sample variances) was oJ= 0.21.

Results showed that from the 74 wells, only 4 located in the valley pre'sented a significant variance. However, since the 3.4 mglL fluoride concen-lration range for each Zone is quite wide compared with the much smallerseasonal variation, the latter does not affect the analysis.

Dental surveys: The distribution of school-age children (6-12 years old) se-lected for the study belonging to the five fluoride concentration zones rsshown in Table 2. The number of children surveyed was different for eachzone because the sample included the wlrole population and therefore haddifferent numbers of children identified by zones.

Dental damage by zone: Absolute and percentage frequencies for the fivefluorosis classificafions according to the range of fluoride concentrations inthe five zones are presented in Table 3. As the fluoride concentations in the

Huoride 34 (212001

144 AIarc6n-Herrera, Martin-Dominguez, Trejo-V6zquez, Rodriguez-Dozal

home water supplies increased, both the prevalence and severity of dentalfluorosis increased.

Table 2, Children surveyed by Zone

Table 3. Frequency distribution of dental fluorosis classifications for schoolchildren grouped by fluoride content of their home water supplies

2934't1

81 8100

t 9 7| 112 t 38tv 27v 5 9

Total 333

Dental fluorosis classification (Dean Index)Normal Very mild Mild Moderate Severe

0 1 2 3 4No. (%) No. (%) No. (%) No. (%) No. (0/6)

reaching Dean indexes of 4, a

the fact that, in this zone, mz

water instead oftap waler'

Results from the highest fl

the entire PoPulation surveYalarsest percentage in the Deaoniv have badlY stained teeth

their teeth at early ages becauple, 100% exhibited fluorosis'

As noted above, a dental flr

at fluoride levels lower thanfluoride in the range of 1 51

877o rePorted bY Grimaldo e

1.2 mglL in San Luis Potosr

the USA, at least in the Parabove 3.7 mg/L. Summanztlin Durango, the Prevalence <

the values rePorted in the US

The communitY index . of

fluoride exPosure groups ls P

As seen in both Table 3 ar

fluorosis exhibited a Postttdrinkine water. Since the Chealth f,urposes, the values fr

The weighted mean CIDFthan the 1.42 weighted figurr

UnfortunatelY, there are t

from 1982. During the lastfrom the National Water Clevels became deplete{ ancgiving lower quality water'

Table tl. CommLgrouped bY fruori

Fluoride range Avera(mo/L) centrab

< 1 .50 01 .51 - 4 .99 35.00 - 8.49 68 .50 - 11 .99 10

12.00 - 16 .00 14Total

Fluoride range(mS/L)

No. ofchildren

< 1.501.51 - 4 .995.00 - 8.498.50 - 1 .99

12.00 - 16.00Total

97

J.J

59J55

23 (24) 57 (5s)16 (14) 63 (56)2 (5) 25 (66)4 (15) 13 (48)0 (0) 10 (17t

45 (14J 168 (50)

10 (10) 5 (5)19 (17) 12 (1't)10 (26) 1 (3)5 (18) 4 (1s)

't4 (24) 't4 (24r�s8 (17) 36 (11)

2 (2)2 (2)0 (0)1 (4)

21 (35)26 (8)

In the lowest fluoride group (Zone I), in which the average fluoride con-centration was 0.75 mgll-, 24% of the group did not exhibit dental damageThe remaining 76o/ohad, varying degrees of dental fluorosis, with the highestincidence of I on the Dean scale, or very mild damage.

Results obtained from Zone tr show that the percent of children withourdental fluorosis decreased to 14%, while the percentage with Dean indexesof 2 and 3 rose. In Zone nI, where the average fluoride concentration was6.7 mg/L, only 5%o of the children were free from dental fluorosis and 950,0had Dean index values of 1, 2, or 3.

Results from Zone IV differ from those of the previous zones. In Zone N.an increase in the percentage of non-affected children was seen; however, anincreased percentage of children with higher degrees of dental damage.

Fluoride 34 (2\ 2001

Denlalfluorosis and bone fractures 145

reaching Dean indexes of 4, also occurred. This finding can be attributed to

the fact that, in this zone, many of the habitants reported drinking bottled

water instead of tap water.

Results from the highest fluoride concentration areq Zone Y ' show that

the entire population surveyed had some degree of dental damage, with thelargest percentage in the Dean index level of 4. Inhabitants of Zone V not

oniy hutr" badly stained teeth, but at least 35% of them are at risk of losing

their teeth at early ages because of severe dental fluorosis. Of the total sam-

ple, 100% exhibited fluorosis, 4l% mild and 5970 moderate to severe.

As noted above, a dental fluorosis prevalence of '16%o wx found in Zone I

at fluoride levels lower than 1.5 mg/L, and 86%o was found in Zone II with

fluoride in the range of 1.51 to 4.99 mgll-. These values are lower than the

87% reported by Grimaldo et af fot water fluoride levels between 0 7 and

t.2 m{L in San Luis Potosi (SLP) Mexico. The same authors state that in

the USe, at least in the past, a prevalence of 837o conesponds to levels

above 3.7 mg/L. Summarizing, although fluoride concentrations are higherin Durango, the prevalence of fluorosis is lower than in SLP, and closer to

the values reported in the USA.The community index of dental fluorosis (CIDFf for each of the five

fluoride exposure groups is presented in table 4.

As seen in both Table 3 and Table 4, the prevalence and severity of dental

fluorosis exhibited a positive conelation with levels of fluoride in the

drinking water. Since the CIDF is not supposed to exceed 0.6 for public

health purposes, the values found in this study are therefore too high.

The weighted mean CIDF for the total sample was 1.49' somewhat higherthan the 1.42 weighted figure found in 1982-'

Unfortunately, there are no data on fluoride concentrations in the water

from 1982. During the last two decades, according to verbal informationfrom the National Water Commission, many existing underground waterlevels became depleted, and, to sustain demand, deeper wells were drilled,giving lower quality water.

Table 4. Community index of dentalfluorosis for childrengrouped by fluoride content of their home water supplies

Fluoride range Average con-centration dentalfluorosis (cl

1 . 0 31.291.261.442.78

Weighted mean = 'l.49

< 1.501.51 - 4 .995.00 - 8.498.50 - ' t1 .9912.00 - 16.00

Total

0.753.256.74

10.2414.00

Community index ofNo. ofchildren

s7'112

382759

Huoride 34 (2\ 2001

'146 Alarc6n-Herrera, Martln-Dominguez, Trejo-Vazquez, Rodriguez-Dozal

Epidemiological interprelation: From the results presented, a clear trend oiincreased dental damage with higher fluoride concentration in the drinkingwater can be observed. Based on Dean's indexes, the most epidemiologi-cally favourable conditions exist for people living in Zone I areas, wherewater fluoride concentrations are below 1.5 mglL. The most unfavourableconditions exist for people living in Zone Y areas. However, this does notnecessarily imply that a direct cause-effect relationship exists. What can beinfened is that inhabitants of areas with higher fluoride concentrations are athigher risk.Bone Jracture susceptibility: The clinical information gathered in the suwelalso permitted an analysis of bone fracture frequency in the population andits conelation with the individual Dean dental fluorosis indexes independ-ently of the fluoride zone. Data selection for this analysis was done takinginto account only individuals who had permanent residence in the zone, andselecting only bone fractures that had ever occurred without apparent cause.where a bone fracture would not normally be expected to occur. This indi-cates that the fractures were not the result ofa clear major or minor traumaValidation ofsuch an event was a diffrcult task because we depended on thesubjectivity of both the interviewer and the interviewed.

Tables 5 and 6 show the number of fractures found in both children (6-12years: mean: 8.89, median = 9) and adults (13-60 years: mean = 30.28, me-dian : 30) in relation to their Dean index classifications of dental fluorosisand their corresponding fluoride concentration zone. Plotting normalizedbone fracture incidence versus corresponding Dean index revealed a linearassociation with a conelation of R3:0.94 for children and R3= 0.98 foradults (Figure 4). As is shown in these tables, the highest fracture incidencefor both groups was found in the fluoride concentration levels of 1.51 to4.99 mglL, which is one of lower concentration zones rather than one of thehigher ones, as we expected. Plotting the incidence of fractures versus theaverage corresponding fluoride concentration in each zone for the adults in-dicated a third order polynomial correlation with R3 = 0.9995 (Figure 5).

Table 5. Number of fractures (fr) identified in children age 6 to 12years associated with different degrees of dental fluorosis

Dental fl uorosis classifi cationNormal Very mild Mild Moderate Severe

0 1 2 3 4ftlno. frlno. f no. frlno. frlno.

Table 6. Number of fracturassociated with d

Fluoriderange (mgr'L)

No. of NormaAduits 0

frlno< 1,50

'1.51- 4.995.00 - 8.4e8.50 - ' l 1.9912.00 - 16.00

I OIal

19233014613896902

0t675/96'1110

ot402t3

8t216

=

TL

s

20.0

1 5 . 0

1 0 . 0

5.0

0.0

Fluoride range No. of(mdl) Children

Figure 4. Bone frathe

In Figure 5, the incidence r

of adults, with the excePtlonof fractures Presented in Zoyears for the children (meal

adults (mean age 30 28 Yeardren. The overall similant'two groups (children = r -

orevalence of such fracture-'

< 1 . 5 01.51 - 4 .995.00 - 8.498.50 - 1 1.9912.00 - 16.00

Total

97112382759333

1t230/160t20t40101t45

3t574t631t251t13ot109/168

1t103/190/101t5

ot145/58

U52t120t10t4

2J144t36

0t21t2UO1t1

3t215t26

Fluoride 34 (2\ 2001

rll

DentalfluoroBis ard bone fractutes 147

Table 5. Number of fact$es (fr) identified in adults age 13 to 60 yearsassociated with differeEt degfeQs of defltal iuorosis

Dsnlal fl tlorosis da$mcationFluoride No. of Nomal Very mild Mitd Modsrate Severe

rangs (mg/L) Adults 'l

fr/no.3

frlno.< 1.50

1.51- 4.995.00 - 8.498.50 - 11.99't2.00 - 16.00

Total

't92' 33014013896s02

oi675/961t100t40z3

8f2'�t6

4n97t122157a471m

16ia,ae

1n13/t63tuu181t17

1tl't36

1t1S51464t35411S2D5

16t'�t44

0/66no3t101t14om10t72

E

Etl-

;

15.0

10.0

. Dean indo(

Figurc 4, Bone fracfures vs Dean dental fluolosis index forthe adults and the cfiildten.

In Figure 5, the incidence offractures arnong the children is similar to thatof addG, with the o<ception of the third point, corresponding to the numberof ftactures presernted n Zcrlre 3. However, the total lengih of ogosur-o inyears for the children (mean age 8.99 yeus) is only one-third thd of the"dultt 1to"* "ge 30.28 yers), rxrho hare lived 3.4 times as long as the chil-dren. The olnerafl si-iiarity of percentages of nontrauma ftactues in thetwo groups (children = 7.T/o:, adult = 6.37o) zuggests that the reldiveprevalence of such fractures among the children in relation to years ofexpo-

Ffrrdtule 34 (2)N1

/

148 Alarc6n-Henera, Martin-Domtngue.,'f]€.,!o'Vezqu€z, Rodriguez-Dozal

sule to fluoride is greater than in the adults. It is also possible that most ofthe adult fractures occurred during childhoo4 but unfornrnarcly we did notobtain this information during the population suwey. Results from fracturesversus fluoride concentations in children $able 5) could not be analysedstatistically. i.

a Adults r Children -Poly. (Adults)

We have no e:<Planation for lhserved, and this must be ansl"a

I

Our findings show that ncul!to inhabitants of the Guadimrcentration limits established blA hieher risk of increased dedin arias with higher fluoride le

lation between the Dean indexfractures also exisB. A Paradclcurrence of fractures md flumi

AC

This research was srPPorted

Council ofScience and Tech

I Secretaria de Salubridad Ysobre Caries Dental Y FbDirecci6n General & NcrD.F.:1982.Trej o Vrirzquez R' AlaciNiveles de fluoruros en cInsenieria Hi&tfu ica €n MDlaz-Birrriea F, NwaroJnodriguez JP, dd Ortiz M233-9.Ortiz D, Casto L, Turdio(posure to fluori& fiacraohic information gnrb"in fn. Chssificdh d2l:1421-6.APHA, AwwAwFcF-!Wastewater. 17th Etrb'Grimaldo M, BajaAhF. Endemic lluorcb iril-6.Schatz A. Schalschr E, Imat€rial, PaIt 2: Thc d€ffects in biologictt tt-Krook L, Minc RX- Er77-82.

12.O%

10.0%

o 8.0%o

E 6.0%l!

I 4.0%

2.O%

0.0%

0 3 6 9 ' � 1 2Fluoride concentration mg/L

Figure 5. Fractrres in adults and children vsaverage fluoride'concentration in each zone.

The difference between the cases ofbone fractures among adults in Zone Iand 2, and Zone I and 3 are statistically significant by chi-squared analysis(f' *ith the Yates correction factor = 3.97 [p = 0.0461] and 4.188 [p =

0.040fl , respectively).It is lnown that fluoride has negative effects on bone cell metabolisrne A

may increase bone quantity, but it can also decrease bone quality andstrength. In other specific studies, fluoride has shown paradoxical effects'like the inhibition of human prostatic acid phosphatase at higher concenfr&tions.s The fact that the incidence of fractures was found to decrease dhigher fluoride concentatiors may reflect a paradoxical effect. The correlation of bone fractures and dental fluorosis se€ms to be linear, but bone frac-tures and fluoride water concentations show a third order pplynomial curve.

Todde 34 (2)2oo1

f

6

'f

I

g

y = 0.0001x3 - 0.0041)A + 0.0333x + 0.0088R2 = 0.9995

Dentalfluorosis and bone fractures 149

We have no explanation for this finding, although a clear tendency was ob-

served. and this must be analyzed in future studies

coNcLUSIONS

Our findings show that nearly 84% of the wells drat supply drinking water

," iJJi,-G of the Guadiana Valley exceed the.maximum fluoride con-

.""it"*i ff-iJ established by both Mexican and intemational regulations'

e fri"fr", rirt "i increased denial damage is directly related to persons living

i" "ti.t *tf, ftigfter fluoride levels in their drinking water' A positive cone-

i"i"rL*"." ti" Dean index of dental fluorosis and the occurrence of bone

F;;;;;r;.-ists. A paradoxical behaviour was observed between the oc-

currence of fractures and fluoride concentration in water'

ACKNOWLEDGMENTS

This research was supported by a project grant from the Mexican National

co*"ii oii"i.nce and technology -Conacyt - Sivilla Project 9502160'

REFERENCES

1 Secretaria de Salubridad y Asistencia (SSA) lnvestigaci6n Epidemiol6gica' ;;; Cil; Dental y Fluor6sis en Escolares Subsecretaria de Asistencra'

iitru""Ln Gn"t"l de Normas de Unidades de Atenci6n M6dica' M6xico'

D.F. ;1982.

z trlJlo-Varqr.z \ Alarc6n-Herrera MT, Martinez Y'- Ro^mcro P' Salvador J'-

Nit"te. de fluoruros en el agua de los pozos de la Ciudad de Durango'

Ineenieria Hidriulica en M6xico 197:12(3)51-7 . -- ^ .3 ;ff;;;; {-1.ip1a6-quezada e, -ctilutyu. MI'. Gnmaldo M' Lo1ol9--

ilA;;iP, "ita oJ, vro. Endemic fluoiosis in Mexico' Fluoride 1997;30:

233-9.q Ortt O,Casho L, Tumrbiartes F, Milan J, Di3'Barriga F Lssel-ry!-oi-lle

r*poaro" to fluoride fiom drinlung water rn Durango' Menco' uslng a geo-

e.riohic information system Fluoride 1998:31 : 183-7

5 ilfi;;-cil;ii'i"uti'"" J -.ttt"a enamei diagnosis' J Am Dent Assoc 1934;

2l:1421'6.e epffe, eWWe, WPCF. Standard Methods for the Examination of Water and-

Wuti"*ut t. tTth Edition. Washingtoq DC 1989;4-'102-4'z d.i."ia" Vf, Borja-Aburto V, Ra;rcz AL, Ponce M' Rosas M' Diaz-Barri'ga'

i. gJ"-i" ift"t6sis in San Luis Potosi' M6xico Environmental Res 1995;68:

1-6.t i"iutt A, Schalscha E, Schatz V' Soil organic matter as a. natural chelating-

."i"lJ,'prtt Z, The occorrence and impoiance-of.paradoxical concentration

"ff""i. i" Uiofogi"al systems' Compost Sci 1964;5(1):26-30 -9 il;t i, fui, nr- flootiae and alkaline phosphatase Fluoride 1998;31:

t77 -82.

Fluoride 34 (2\ 2OO1