Geochemical environments and the geographical distribution of some diseases in Sri Lanka

G E O C H E M I C A L E N V I R O N M E N T S AND T H E G E O G R A P H I C A L

D I S T R I B U T I O N OF S O M E D I S E A S E S IN SRI L A N K A

C. B. D I S S A N A Y A K E and A. S E N A R A T N E

Department of Geology, University of Peradeniya, Peradeniya, Sri Lanka

(Received April 2, 1981; Revised July 29, 1981)

Abstract. A survey of on the incidence of dental diseases and the distribution of fluoride in drinking water wells in Sri Lanka, confirms that a distinct causal relationship exists and is clearly geographically related. A similar study on the incidence of total cancer in Sri Lanka in relation to environmental factors such as rainfall, concentration of total dissolved ions, hardness of drinking well water, etc. showed an association resting entirely upon correlation.

1. Introduction

The importance of trace elements in human health and nutrition is well known and there appears to be geographical patterns in the incidence of certain diseases. Well established relationships with the geochemical environment include iodine deficiency with goitre, fluoride deficiency with dental caries and fluoride excess with fluorosis. Webb (1975) points out that there are numerous and controversial correlations with no proven causal relationship, and these include water hardness and cardio-vascular diseases, Pb and multiple sclerosis, Cd and hypertension and atherosclerosis, a range of trace elements with cancer, etc. The delineation of areas of different trace element concentrations thus

helps in the initial demarcation of geographical areas liable to be affected by the disease concerned. The production of national geochemical maps and the establishment of national geochemical data banks are therefore of prime importance to a country (Hamil- ton, 1976). This is more apparent in a developing country such as Sri Lanka where a

very high percent of the population lives close to the soil and depends on it and the natural environment for their food, shelter and all other necessary amenities. The geochemical status of trace elements in such environments, to a great extent, governs the general health of the community, and some recent research has been devoted to the study of the effect of trace elements on environmental health (Hemphill, 1967-71; Underwood, 1971; Cannon and Hopps, 1971; Shacklette et aI., 1971; Kubota and Allaway, 1972; Fortescue, 1972; 1973; 1974).

This paper considers further work carried out in a project designed to study the significance of natural environmental factors in the geographic distribution of health and disease, nutrition etc. (Dissanayake, 1979, 1980; Dissanayake and Jayatilaka, 1980; Dissanayake and Ariyaratne, 1980; Dissanayake and Hapugaskumbura, 1980). Even though there is no geochemical map of Sri Lanka, the available geochemical data can be used to good advantage to study the geographic distribution of some diseases. Since Sri Lanka is very densely populated with an average of 180 persons km -2 and since the majority of the people obtain their drinking water supply from dug wells, the study of

Water, Air, and Soil Pollution 17 (1982) 17-28. 0049-6979/82/0171-0017501.80. Copyright © 1982 by D. Reidel Publishing Co., Dordreeht, Holland, and Boston, U.S.A.

18 C. B. DISSANAYAKE AND A. SENARATNE

the geochemistry of well water provides an ideal opportunity to correlate the geographic al diseases with hydrogeochemistry and associated environmental factors.

This paper considers the geographical distribution of two diseases namely dental fluorosis and caries, and total cancer in relation to the hydrogeochemistry of well water in the rural community of Sri Lanka.

2. Geography and Geology of Sri Lanka

The island of Sri Lanka with an area of 69 450 km 2 is primarily a part of the shield area which comprises peninsular India. Geologically and physically, Sri Lanka is a southern continuation of India, only recently separated from the mainland by the shallow sea covering the Palk Strait and the Gulf of Mannar. On the basis of height and slope characteristics, the island can be divided into 3 main morphological regions (Vitanage, 1970) (Figure 1). Geologically the greater part (about 92~o) of the country consists of rocks of Precambrian age, the island having remained stable over a long period of time.

Colorr

Mal~rcl

Fig. 1. The main morphological regions and the climatic zones of Sri Lanka. I: Lowlands; II: Uplands; III: Highlands.

GEOCHEMICAL ENVIRONMENTS AND THE GEOGRAPHICAL DISTRIBUTION 19

The Precambrian rocks have been divided into a Highland Group consisting mainly of

rocks belonging to granulite facies such as charnockites, a Vijayan Complex of granites,

granitic gneisses and migmatites of the amphibolite facies and a Southwestern Group,

a complex of cordierite gneisses and charnockites. For a detailed account of the geology

of Sri Lanka the reader is referred to Cooray (1967).

Sri Lanka has a humid tropical climate being in the monsoon region of Southeast Asia.

The island has clearly demarcated dry and wet zones. The average mean temperature

of the wet zone lies between 21 and 29 °C and in the dry zone it is approximately 32 °C.

3. Distribution of Fluorine in Well Water in Sri Lanka

Fluoride ions were measured with the Orion ion specific electrode and the details of the

method are described by Senewiratne et al. (1974).

TABLE I

The average fluoride concentrations in the well water of Sri Lanka and the DFM rates for the provices

Fluoride a DFM b content (ppm) rates

Northern Province 0.65 2.28 Sabaragamuwa Province 0.20 3.50 Western Province 0.20 3.90 Eastern Province 0.76 3.50 North-Central Province 1.40 1.37 North-Western Province 0.78 2.32 Southern Province 0.30 3.55 Central Province 0.50 3.15 Uva Province 0.40 1.70

a After Senewiratne and Senewiratne (1975). b After Tillekeratne (1966).

Table I shows the fluoride concentration of well water in Sri Lanka and Figure 2

illustrates the geographical distribution in relation to the population of the 9 provinces

of Sri Lanka. It can be seen from Figure 2 that the central hill country and the southwest

coastal region are relatively free of fluoride. The lowland dry zone contains a higher

amount of fluoride in water with areas around Eppawala in the North Central Province,

Maha Oya in the Eastern Province and Uda Walawe in the Southern Province showing

anomalously high fluoride concentrations: The effect of the fluoride concentrations in well water on the dental health of the people

in the areas can be seen in Table II where details for 3 areas are given. It is clearly seen

that the areas of high fluoride content have higher dental fluorosis whereas those in the

low fluoride regions suffer from dental caries. The marked difference in the fluoride

concentration in well water in the dry zone and the wet zone is put into proper perspective


, 7 Z °2 pm

V , 5 ......

Fig. 2. Distribution of fluoride containing water in relation to the provinces of Sri Lanka. NP: Northern Province; NCP: North Central Province; NWP: North Western Province; CP: Central Province; WP: Western Province; EP: Eastern Province; UP: Uva Province; Sab. P: S abaragamuwa Province; SP: Southern Province.

TABLE II

Fluoride concentrations and the incidence of the dental fluorosis and dental caries in 3 areas of Sri Eanka

Anuradhapura Polonnaruwa Kandy

Dental fluorosis 77.5 ~o 56.2 ~o 13.0 ~o Dental caries 26.2 ~o 26.5 ~o 95.9 ~o Fluoride concentration 0.34-3.75 ppm 0.26-4.25 ppm less than 0.2 ppm

Note: The maximum fluoride concentration in the Anuradhapura area was 9.0 ppm; 5.8 ppm in Maha Oya and 4.8 ppm in Uda Walawe (see Figure 2 for localities).


1.5

1,25

,£

o .75

,5

" 2 5 1 .

0

Fig. 3b.

l NC A

NU aA

C &

W Set# ~A . . . . . . . . #l

Mean annual yield per km 2 in meters Fig. 3a. Variation of fluoride concentration in well water with rainfall,

,.51

1.25 [ • <150 Meters

I > 1 5 0 Maters

E .75 l ff~'-~-~

,25 Sab

Provinces Variation of fluoride concentration in well water with respect to the height characteristics of the

9 provinces of Sri Lanka (the names of the provinces are as given in Figure 2).


in Figures 3a and 3b where the variation of the fluoride concentration with rainfall and with height characteristics is shown. The marked decrease in fluoride can be attributed to the continuous leaching of fluoride from fluoride-bearing rocks and minerals, the physiography of the region playing an important role in the process of leaching. While the intensity of rainfall is a major factor in the geographical distribution of fluoride in well water, the natural geological factors are also significant.

For example, the high fluoride bearing zone around Anuradhapura coincides with the location of a large economically exploitable deposit of apatite (fluoro-hydroxy phosphate) (Jayawardena, 1976) containing a fluoride concentration of 1.5 to 2.470. The free availability of large concentrations of fluoride ions due to natural geochemical factors as mentioned above and the leaching and upward movement of ions due to the rainfall conditions results in a geographical pattern being established.

Figure 4 illustrates the geographical variation of the DFM (Decay, Filling and Missing) by provinces with the respective fluoride ion concentration in well water. Figure 5 shows the relationship of the hardness of water with the fluoride concentrations. It can be seen

Fig. 4.

4 -

"2-

NC I

Fluoride in ppm

Relationships of the DFM rates with the fluoride concentration for the 9 provinces of Sri Lanka (the names of the provinces are as given in Figure 2).


E

3

,sJ 1.0-

NW E

I

$ab n

16o 26o sbo 4o0- Fatal hardness t n ppm

Fig. 5. Relationship of the total hardness of water with the fluoride concentrations.

that there is a proportional increase of fluoride with hardness reflecting the geochemical status of ions in the rocks and minerals of the area. It is known that the fluoride ion can

proxy for the hydroxyl ion and that an equilibrium could be maintained. The substitution of fluoride for hydroxyl is expected due to the similarity of ionic radii and charges and

indeed F - ~ OH - interchange between minerals and the aqueous medium has been the subject of extensive research as shown by the work of Nada and Ushio (1964), Gillberg

(1964), Stormer and Carmichael (1972), Ekstrom (1972), and Munoz and Ludington (1974).

It can thus be seen that a direct causal relationship between the geochemical status of F - ions in the natural environment can be established with the geographical distri-

bution of dental diseases in Sri Lanka. This clearly illustrates the need for the establishment of multielement geochemical maps of the country. Potential areas for health and

disease could thus be delineated and precautionary measures such as defluoridation or fluoridation of well water can be undertaken.

4. Geographical Distribution of Cancer in Sri Lanka

Whereas the relationships between I and goitre and fluorine and dental diseases demonstrate very clearly the relationship between geochemical environment and human

health and disease, other links are less convincing. Underwood (1971) points out that

24 c . B . D I S S A N A Y A K E A N D A. S E N A R A T N E

most of the associations of trace elements with diseases rest heavily upon correlation

rather than causation, as in the case of Cd and human hypertension, Pb andmultiple

sclerosis, etc. The problem of cancer in human beings certainly belongs to this category.

Cancer is known to be caused by a wide variety of factors often acting in combination

with one another, over periods of many years. Even though research into the causes of

cancer is now based on the hypothesis that all cancers are environmentally caused until

the contrary is proved (Epstein, 1974), a proper causative relationship - particularly a

geochemical one, is yet to be established. Most of the factors isolated are in one way or

another environmental and relate to the air breathed, water consumed or to the environ-

ment of work, etc.

It is the aim of this study to investigate into a possible association of the geographical

variation of total cancer in Sri Lanka with the geochemical status of the potable waters.

Total c a n c e r i n c i d e n c e / 100,000 populalion

1 - 1 . 5

a~ic zon'e boundaries

1 ---4

~ k m v i i I

Fig. 6. Map showing the incidence of total cancer in Sri Lanka (the names of the provinces are as given in Figure 2).


The fact that more than 300 compounds are known to be carcinogenic, as compiled by the International Agency for Research on Cancer (IARC), further complicates the isolation of natural environmental and geochemical factors as being associated with the incidence of cancer.

Figure 6 illustrates the incidence of total cancer in Sri Lanka in the provinces and Table 1II shows the types of cancer prevalent in Sri Lanka. Bearing in mind that only a very small percentage of the population of Sri Lanka uses pipe-borne water the rest using well water for drinking and domestic purposes, the dissolved ions in the water have an obvious effect on their general health. Figure 7 illustrates the variation of the total

k \ ~ 1 / N \ \ \ I / ~ / / / I

1{~0 200 3100 400 - - 5100 5=00

I. Total solids

2. Hardness

Fig. 7. Variation of total cancer rates with the dissolved solids in water and the nardness of water.

cancer rates with the total dissolved solids in water and the hardness for the water in the 9 provinces of Sri Lanka. It is apparent from Figure 7 that even though the curves for total solids and hardness against cancer incidence appear to be complimentary, the relationship is not a simple one and there is an optimum level of hardness and total solids that corresponds to a minimum incidence of cancer. Even though it cannot by any means be considered a causal relationship an optimum amount of ions in the water appears to be conducive for a low incidence of both dental diseases and cancer. In Figure 8 where

5

4

~3

1

Sab P

Wp ® NP

IUV A CP

o'.2, o!42 o',G3 Fluoride (pprn)

IEP INWP

01.84 1!05

INC P

Fig. 8. Relationship of the incidence of total cancer with the fluoride concentration of the well water of Sri Lanka.

26 C. B. D I S S A N A Y A K E A N D A. S E N A R A T N E

<

~}.~$

~ = . ~

~.~.~

~ o °

< <


the fluoride concent ra t ion of the well water of Sri L a n k a is plot ted against the incidence

of total cancer for all provinces a similar curve is seen. Even though this correlat ion does

not in itself const i tute a causal relat ionship, the compl imenta ry associa t ion of the

environmental factors (i.e., rainfall, d issolved ions and hardness of water, etc.) with the

incidence of cancer, points to the use of geochemical correlat ive factors as a guide in the

del ineat ion of disease areas.

5. Conclusions

The s tudy of the geochemical environments pertaining to the geographic dis t r ibut ion of

dental d iseases and total cancer in Sri L a n k a reveals that whereas there is a dist inct

causal re la t ionship between fluoride ions and dental diseases, only a geochemical

associa t ion can be l inked to the incidence of cancer. The well marked climatic and

physiographic zones of Sri L a n k a play a major role in the migrat ion of t race elements

in the aqueous medium and could be a contr ibutory factor in the geographic local izat ion

of diseases.

Acknowledgments

Grateful thanks are due to Miss S. J. Wi jesekera and K. D u n u h a p p a w a for their

assistance.

References

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Hemphill, D. D. (ed.), Trace Substances in EnvironmentalHealth -VI, Univ. of Missouri, Symp. 1973, p. 333. Fortescue, J. A. C.: 1973, Relationship between landscape Geochemistry and Exploration Geochemistry, Report

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28 C.B. DISSANAYAKE AND A. SENARATNE

Senewiratne, B. and Senewiratne, K.: 1975, Ind. J. Med. Res. 63, 302. Senewiratne, B., Thambipillai, S., Hettiarachchi, J., and Senewiratne, K.: 1974, Trans. Roy. Soc. Trop. Med.

Hyg. 68, 105. Shacklette, H. T., Boerngen, J. G., and Turner, R. L.: 1971, U.S. Geol. Surv., Circular 644, 5 p. Stormr, J. S. and Carmichael, I. S. E.: 1972, Contrib. Mineral. Petrol. 34, 201. Tillekeratne, L.: 1966, Cey. J. Med. Sci. 15, 7. Underwood, E. J.: 1971, Trace Elements in Human and Animal Nutrition, 3rd ed. New York and London,

Academic Press, 543 pp. Vitanage, P. W.: 1970, 'A Study of the Geomorphology and the Morphotectonics of Ceylon', Proc. 2nd Seminar

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Geochemical environments and the geographical distribution of some diseases in Sri Lanka