Fluoride Concentrations in a Collection of Urinary Calculi

0022-534 7/87 /1383-0644$02.00/0 Vol. 138, September Printed in U.S.A.

THE JOURNAL OF UROLOGY

Copyright© 1987 by The Williams & Wilkins Co.

FLUORIDE CONCENTRATIONS IN A COLLECTION OF URINARY CALCULI M. A. E. W ANDT*

AND

A. L. RODGERS

From the Department of Physical Chemistry, University of Cape Town, and the Council for Scientific and Industrial Research, National Accelerator Centre, Van de Graaf/ Group, Faure, South Africa

ABSTRACT

Fluoride concentrations in 42 urinary calculi were determined using a microdiffusion procedure in conjunction with a fluoride sensitive electrode. Mean values of 56, 230 and 1112 ng./mg. fluoride were obtained for uric acid, calcium oxalate monohydrate and apatite/struvite stones, respectively. Fluoride concentration was found to be related to calcium oxalate dihydrate levels as well as to apatite content. It is suggested that the former has zeolithic properties which might trap fluoride while formation and growth of the latter appears to be enhanced by elevated urinary fluoride levels. (J. Ural., 138: 644-647, 1987) Since the advent of fluoridated drinking water in the 1950's there has been much controversy over the possible role of fluorine in the genesis of urolithiasis. For example, it has been shown that the marked differences between the fluoride content of ground water in the coastal region of southeast Finland (1.3 to 1.9 mg.fl.) and other parts of the country (0.06 to 0.13 mg./ 1.) closely matches the higher hospital admission rates for urolithiasis in the former. 1 Another study concerning fluoride concentration in urinary tract calculi from areas with and without drinking water fluoridation established a difference of 41.1 % between the two districts, matching the 40.5% difference between the fluoride concentration in the urines of both groups. 2 In yet another investigation, considerable amounts of (dental) calculus-like deposits were found on the upper and lower molars of rats in the presence of dietary sodium fluoride. 3 This is in accordance with Anasuya's findings that rats which had ingested high fluoride diets exhibited a higher incidence of crystalluria and bladder stones than those receiving low fluoride diets. 4 Furthermore, evidence has been presented which indicates a definite increase in the percentage of calcium oxalate stones in a community after receiving a fluoridated water supply. 5 - 7 However, contrary to these observations, Zipkin et al. have reported only non-significant differences when comparing the fluoride concentration of urinary tract calculi of individuals from a low fluoride area with that from an area where the drinking water contained 2.6 mg.fl. fluoride. 8 Studies of rats fed one mg.fl. and 10 to 500 mg.fl. F- drinking water also showed that the ingested fluoride did not produce calculi in any of the animals. 9 In fact, Hering et al. reported that fluoride inhibited artificially induced oxalate stone formation in rats receiving 10 mg.fl. fluoride in their drinking water. 10 Biochemical findings of other researchers have further suggested that prolonged ingestion of a high amount of fluoride does not alter plasma and urinary biochemistry to make it congenial for stone formation. 11 Despite these somewhat contradictory reports, it nevertheless seems likely that fluoride may play some role in the genesis of urinary calculi. If this is indeed so, the qualitative and quantitative determination of fluoride in uroliths might provide investigators with clues which will shed some light on such a relationship. Accepted for publication April 23, 1987. * Requests for reprints: Council for Scientific and Industrial Research, National Accelerator Centre, Van de Graaff Group, ZA-7131 Faure, South Africa. Supported by the Council for Scientific and Industrial Research, the Medical Research Council and the University of Cape Town. 644

MATERIALS AND METHODS

Forty-two urinary calculi from patients admitted to the urology clinic at Tygerberg Hospital, Cape Town, were first analyzed by x-ray powder diffraction to identify major and minor constituent phases and then by elemental ICP-AES (inductively coupled plasma atomic emission spectroscopy) 12 • 13 to determine their relative concentrations. Thereafter, different aliquots of each stone were analyzed for fluoride using a quantitative micro-diffusion procedure. The method has been described in detail elsewhere. 14 Essentially, weighed portions (ca. 150 mg.) of powdered stone were introduced into the outer compartment of a diffusion chamber and a mixture of nitric and perchloric acids, saturated with HMDS (hexamethyldisiloxane), was added. A two ml. aliquot of sodium hydroxide was pipetted into the inner cup and used as the trapping solution. Diffusion was carried out at 75C for at least three to four hours after which the fluoride concentration was determined using an Orion 94 series fluoride sensitive electrode together with a 90 series sleeve type Ag/AgCl reference electrode as previously described. 14 All experimental conditions were established in preliminary tests using artificial stone samples of known fluoride concentrations. In these tests recovery, accuracy and reproducibility were assessed as a function of diffusion time and temperature. RESULTS AND DISCUSSION

The composition and mean fluoride concentrations of the 42 calculi analyzed in the present study are given in table 1 while table 2 lists values reported by other workers. The mean concentration in the present study is 1237 ng./mg. (range 26 to 9740 ng./mg.). In another study in which we analyzed a collection of 20 uroliths from India, the mean fluoride concentration was found to be 267 ng./mg. (range 21 to 1152 ng./mg.). 15 At first glance these results suggest that the mean fluoride concentration in calculi from the Cape Town area is higher than that of their Indian counterparts. However, a completely different picture is obtained if the results are grouped and compared according to major stone components. The mean fluoride concentration in eight Indian stones containing uric acid as major component has a mean value of 91 ng./mg. (ranging from 27 to 254 ng./mg.) 15 which is significantly higher than the mean of 56 ng./mg. (range from 26 to 86 ng./mg.) in five South African stones of similar composition. The same trend occurs in 10 'pure' whewellite (mineralogical name for calcium oxalate monohydrate, COM) stones from India where a mean fluoride concentration of 454 ng./mg. (range 22 to 1152 ng./mg.) is set

PLUOR!DE CO?,JCENTRATI0!'78 TABLE

Stone Number 288 279 27 168 207 386 17 425 488 500 258 293 345 349 351 481 389 198 282 301 281 319 358 322 400 178 370 303 101 297 361 379 99 320 135 339 172 211 56

rr-:r

l. Fluoride concentration in South African stones

Composition [wt.-%]'

AAU

UA

UAD 100 100 90 85 75

15 40

COD

COM

APA

STR

Mass [mg.]

20 30 35 40 40 55 60 60 50 60 65 65 70 70 75 75 80 80 85 95

143.0 219.2 140.2 211.3 174.1 131.6 130.3 156.8 106.7 79.0 120.0 134.0 152.9 119.5 124.0 122.9 143.4 112.8 190.3 141.8 146.4 169.1 191.9 158.1 141.7 172.1 159.6 151.0 149.2 146.0 152.5 155.9 156.1 115.5 148.4 173.2 149.5 150.7 147.9 142.4 148.l 151.3

10

95

645

CALCULI

15 25 5 100 100 100 100 90 85 85 80 60 60

10 15 20 40

100 85 85 55

15

15

75 60

10

296 321 193

45 25 40 80 70 65 60 60 45 40 40 40 40 35 35 30 30 25 25 20 20 15 5

Fluoride Concentration [ng./mg.]*

C1 28 29 91 78 65 251 290 228 211

196 9848

2395 5563

2847 3571 2515 311 971 367 207 1019 281 1471

259 119

c,

Ca

24 24

82

151 253 172 279 182 191 152 860 918 179 9633 2131 2177 331 2688 5168 3566 2369 781 2876 3371 435 2711 347 388 211 1038 294 417 1883 985 824 264 941 121

75 64 153 242 306 233 188 875 1054

2448 2225 352 2744 5228 3313 2608 899 3104 392 2523 332 1125 372 1021 1096 249 409 1667 949 791 245 938 132

mean 26 26 86

77 64 152 249 172 292 205 212 170 867 986 187 9740 2290 2201 342 2609 5323 3439 2488 840 2942 3473 413 2583 330 1049 376 209 1030 1058 275 413 1674 967 807 256 940 124

• Calculated from elemental (ICP-AES analysis) and phase data (XRD film technique), normalized to 100; figures written on column divisions represent mixtures of adjoining components. * c1 Calculated from diffused standards calibration curve parameters (without TIS AB). c2 Calculated from diffused standards calibration curve parameters (with TISAB III). ca Mean of three standard additions.

against a mean value of 230 ng./mg. (range 172 to 292 ng./mg.) in four 'pure' COM South African stones. The higher fluoride concentration in these two groups of Indian stones could be due to the fact that certain areas in India have an average fluoride concentration of 16 mg./1. in the drinking water 16 which far exceeds the level of one to two mg./1. recommended by the World Health Organization. 17 No comparison of a large group of 10 ammonium acid urate calculi in the Indian collection (mean 183 ng./mg., range 21 to 366 ng./mg.) with an equivalent South African group is one stone (152 ng./mg.) having this possible, as there is compound as major component in the present study. On the other hand 20 stones from the South African collection have struvite/apatite composition while none of this type occurs in the Indian group. These stones have a mean concentration of 1112 ng./mg. (range 124 to 3473 ng./mg.) and it is this group in the South African collection which strongly influences the overall mean value. In the present study, calcium oxalate calculi have higher fluoride concentrations than uric acid and urate stones. This was also observed in the Indian collection 15 as well as in other studies. 2 • 18 From table 1 it can be seen that the calcium oxalate calculi containing the monohydrate as the major constituent have lower fluoride content than those stones containing a mixture of both hydrates (COM and COD). Furthermore, when the dihydrate (COD) is the only calcium oxalate phase present,

the fluoride concentration is even higher (stones 281 and 319). (The most prevalent additional constituent in these calculi is apatite). This effect is also observed in table 2. 2 · 19 Thus, in general, it appears that the fluoride concentration increases with increasing COD content. The correlation between high fluoride content and high COD content might be explained by crystal structural considerations. It is well known that weddellite (mineralogical name for COD) is stabilized by foreign ions in urine, especially magnesium. 20 · 21 Due to the special arrangement of the hydrate water molecules, COD offers zeolithic binding sites not only for extra water molecules, but also for extraneous ions which are either embedded in or adsorbed on the surface. Thus fluoride might also be trapped in the COD lattice. It is of some interest to note that the presence of apatite and fluoride in urinary calculi might be related. Evidence in support of this speculation is presented in table 1. The 'pure' COM stones (nos. 17, 425, 488 and 500) contain no apatite and have a mean fluoride concentration of 229 ng./mg. On the other hand, the COM stones 258, 293, 349 and 481 contain variable amounts of apatite and have a mean fluoride concentration of 2777 ng./mg. Comparison of stones 198 and 282 yields the same conclusion. Further evidence is provided by the relatively high fluoride concentrations in struvite/apatite calculi. Apatite is the most abundant of the phosphatic minerals and is contained in almost all calculi where it is commonly present

646

WANDT AND RODGERS TABLE

2. Reported values of fluoride concentration in urinary calculi

Fluoride Concentration [ng./mg.- 1 ] n

Remarks Mean

Reference

Range

1 10 9 100

2000 449 624

4 16

663 2500

17

3700

28 11 13

1130 960 200

210-10650 270-1400 70-430

200

1400

0-3000

10 10

48 88

70 70 20 20 20 20 10 10 10 10 10 10 10 25

1100 644 808 2005 959 2103 405 457 358 406 345 529 362 22000

8400-41500

25

6200

30-9100

4-1560 0-1790 0-1800 150-1100

at the surface and at the walls of pores within the stone. 22 Biological apatites are modified by an exchange of anions and cations, analogous to the process of alteration and regeneration of phosphate minerals. This process influences the concentration of many trace elements that become trapped in apatite, such as fluorine. Because of similarities between the structures of hydroxyapatite and octacalcium phosphate (OCP, CasH 2 (P0 4 )G. 5H2 0), the latter has been proposed as either a suitable substrate which provides seeds for deposition of HAP through an epitaxial mechanism, or as a metastable precursor. 23 • 24 The effects of fluoride ion on the stability relationships of these calcium phosphates are, however, only poorly understood. 25 It is nevertheless known that fluorine fits readily into the lattice of the apatite molecule and that fluoroapatite is markedly less soluble than hydroxyapatite. 26 ' 27 For the formation of apatite structures under biological conditions, the presence of small quantities of fluoride ions has been found to be necessary. 28 This is thought to occur as a result of the elimination of the relatively unstable salt, OCP, in the presence of fluoride, by converting it to the more stable hydroxyapatite. Evidence in support of this has been reported in in vitro systems where OCP becomes transformed immediately into HAP when in contact with fluoridated solvents. 29 Even mere traces of fluoride (10- 6 M-about 1/50 of the concentration recommended for drinking water), alters the nature of the precipitate completely. 30• 31 Small quantities of fluoroapatite are likely to be formed and may aid in the deposition of further quantities of apatitic material. The effect of fluoride ion on the crystal growth of apatite is again complicated. It appears to inhibit the orderly deposition of calcium salt at small concentrations, 32 but enhances growth at greater concentrations. 33 However, it has been shown that during remineralization of partly demineralized tooth enamel,

Urinary calculus Urinary (analyst 1) Calculi (analyst 2) 38 renal, 28 ureteral, 34 vesical calculi Urinary calculi, 1 g samples Urinary calculi, 0.0 to 0.6 mg./1. F- in drinking water Urinary calculi, 2.6 mg./1. F- in drinking water Calcium oxalate Oxalate/phosphate Uric acid No drinking water fluoridation (ash basis) Calcium containing urinary Calculi (total mass basis) Calcium oxalate monohydrate Calcium oxalate dihydrate (ash basis) 1 mg./1. F- in drinking water 0.25 mg./1. F- in drinking water COM (0.25 mg./1. F-) COM (1 mg./1. F-) COD (0.25 mg.fl. F-) COD (1 mg./1. F-) Apatite (0.25 mg./1. F-) Apatite (1 mg./1. F-) Struvite (0.25 mg./1. F-) Struvite (1 mg./1. F-) Uric acid (0.25 mg./1. F-) Uric acid (1 mg.fl. F-) Cystine Endemic fluorotic area (16 mg./1. F- in drinking water) Nonendemic area Urinary calculi (ash basis)

37 38 39 40 8

18, 29

41 19

2, 7

16

there exists a maximum value of the fluoride concentration gradient above which lesions cannot be successfully repaired. 34 As apatite is one of the most frequently found major phases in kidney stones and OCP has also been reported as a constituent, the above data suggest that elevated urinary fluoride levels enhance the formation and growth of apatitic concrements. In addition, it has also been shown that dissolution of apatite is inhibited by fluoride ions (present in the dissolution medium) and that the inhibitory effect increases with a) the length of time that the crystals are exposed to fluoride ions and b) decreasing pH. 35 The fluoride content of an apatite calculus will therefore vary in relation to the amount of fluorine in the urine, the length of time exposure to fluoride, the percentage of apatite in the calculus and the surface area exposed. It is therefore not surprising that for the apatite stones no relationship between the calcium to phosphate ratio and fluorine concentration could be established in this or other studies. 8 • 16 Likewise, no relationship between calcium and fluoride concentration in the calculi was found in this study while no correlation between sex, age, race and location in the urinary tract on the one hand and fluoride content on the other, has been reported. However, in general, the crystallinity of bone apatite 36 and carbonate apatite 2 in urinary stones increases significantly with increasing fluoride content. The amount of struvite, coprecipitated with apatite in all infection stones, failed to correlate with fluoride concentration. The results of the present study thus suggest that fluoride may be of some importance in urinary stone disease. Although the exact mechanism by means of which it influences calculogenesis remains unclear, consideration of table 2 clearly shows the direct relationship between fluorine concentrations in drinking water and in calculi. This, no doubt, will be of some concern in an age of fluoridated water supplies.

l<'LUORmE CONCENTrtATIONS IN CALCULI

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