8b

Environ Geochem Health (2007) 29:155–162 DOI 10.1007/s10653-006-9070-0

ORIGINAL PAPER

Medical geology in tropical countries with special reference to Sri Lanka C. B. Dissanayake Æ Rohana Chandrajith

Published online: 26 January 2007 Ó Springer Science+Business Media B.V. 2007

Abstract Sri Lanka provides an ideal opportunity for the study of the effect of geology on human health. The vast majority of the people of Sri Lanka still live in rural areas within areas termed geochemical provinces. Very broadly, one could say that a geochemical province has characteristic chemical composition in soil, water stream sediments and rocks, enabling their delineation from others. The chemical composition is presumed to be have an impact on the health of the inhabitants of the particular geochemical province, particularly because of the fact that their food and water are obtained mostly from the terrain itself. This leads to the concept of ‘‘diseases of geochemical origin’’. Among these are dental fluorosis, iodine deficiency disorders (IDDs) and selenium-based diseases. The Dry Zone of Sri Lanka has several areas rich in groundwater fluoride, the ingestion of which leads to dental fluorosis. Iodine deficiency diseases are more common in the Wet Zone, though their aetiologies are more complicated. Interestingly, it has also been observed that significant proportions of the female population of Sri Lanka are C. B. Dissanayake (&)
R. Chandrajith Department of Geology, University of Peradeniya, Peradeniya 20400, Sri Lanka e-mail: [email protected] R. Chandrajith e-mail: [email protected]

selenium-deficient, which could well be related to the geological environment. Chronic renal failure (CRF) has been observed in some areas of the Dry Zone of Sri Lanka, where there is a relationship of CRF with the mineral content of drinking water. This subject matter falls under the auspices of Medical Geology, a scientific discipline still in its infancy, and much more concerted studies are needed to attract the attention of medical research. Keywords Geochemical provinces
Climatic zones
Dental fluorosis
Defluoridation
Iodine deficiency disorders (IDDs)
Selenium geochemistry


Introduction Sri Lanka is located within the confines of the tropical belt. Geochemically, tropical environments display unique characteristics. Of particular importance is the very strong fractionation of chemical elements caused by periodic heavy rainfall and droughts. This characteristic geochemical partitioning can result in either severe depletion of elements or accumulation to toxic levels. Some of the world’s most underdeveloped counties lie in the tropical belt, and the poor agricultural productivity is clearly a result of this extreme fractionation of the elements. The

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chemical weathering of rocks is often so intense that the weathered overburden reaches depths of over 150 m. The accompanying severe depletion of essential chemical nutrients, notably potassium, is a characteristic of tropical soils. Furthermore, the extensive clay formations found in tropical terrains aggravate the depletion of these essential elements. Kaolin and gibbsite are of particular significance in complexing these elements. Kronberg, Fyfe, Leonardos Jr, and Santos (1979) observed that, so long as smectite clays are present with abundant unweathered minerals, many trace elements (e.g. Zn, Cu, Pb, Cs) are concentrated in the weathering process. When the primary minerals are leached and their surface areas are reduced to the point where groundwater solution concentrations drop below their metastable solubilities, the smectite and other complex clays begin to degrade, with kaolin increasing in abundance in the soil. This type of process is most commonly seen in humid tropical environments. Among the elements that are geochemically fractionated are those classified as essential and toxic. Humans and animals very often suffer from diseases caused by either excess or deficiency of such elements, and their distribution in soil, plants and water are controlled to a great extent by geochemical parameters. What is of critical importance is the dosage of the element concerned. Even essential elements, if ingested in excessive quantities, cause ill health, as exemplified by debilitating diseases such as skeletal fluorosis caused by the ingestion of excess fluorides from drinking water. Depending on the abundance of chemical elements in rocks, soils, water and plants, terrains could be geochemically classified as ‘‘geochemical provinces’’. Some terrains, for example, may show very high levels of copper and zinc, while others may display severe paucity of these and other elements. Geochemical atlases are thus very useful in delineating areas that may be prone to diseases of geochemical origin, the arsenic distribution maps of Bangladesh and West Bengal being good examples (Bhattacharya, Chatterjee, & Jacks, 1997). The dependence of the aetiology of certain diseases on the geology of the terrain concerned is particularly well seen in under

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developed counties in the tropics, where large populations live in close contact with the physical environment.

Geochemical provinces of Sri Lanka The concept of geochemical provinces becomes very useful in the study of the distribution of diseases linked to geology and geochemistry. It has been recognized that imbalances resulting from deficiencies or excesses of elements from dietary sources are linked to anomalies in the inorganic element composition of various food chains. This, in turn, arises from the compositional nature of the geochemical environment closely associated with the food chains. Very broadly, one could define a geochemical province as a geological terrain consisting of a characteristic chemical composition in soil, rocks, water and stream sediments. Each such geochemical province could be delineated from the other. Each population living in these delineated provinces could, therefore, be susceptible to diseases caused by the chemical imbalances characteristic of that geochemical province. In Sri Lanka, four major geochemical provinces can be delineated, based on the geochemical maps of the country (Dissanayake & Weerasooriya, 1986). What is apparent is the heavy influence of climate on the nature of the chemical composition of the geochemical provinces. Even though the primary rocks basically influence the chemical composition of the geological materials in the terrain, the climate markedly changes the final composition of the soils and water on account of the intense effects of either leaching or evaporation. The Dry Zone in Sri Lanka is therefore chemically markedly different from the Wet Zone in terms of general geochemistry, and this is reflected in the incidence of some diseases.

Fluoride geochemistry and dental health Fluorine is classified as an essential element, though health problems could arise from either a deficiency or excess (Fig 1). Unlike most other

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Fig. 1 Mechanism for fluoride ingestion in arid and semi-arid areas (modified after Ramesam and Rajagopalan, 1985)

trace elements, much of the fluorine entering the human body is obtained from water. This is of particular importance to Sri Lanka, because the majority of the population uses ground and surface water for their domestic needs. Pipeborne water is still a rarity in most parts of Sri Lanka (Dissanayake, 1991). Table 1 shows the concentrations of fluorides that have an impact on the health of people. The mechanism for fluoride ingestion in arid and semi-arid areas (Ramesam & Rajagopalan, 1985) is applicable to the Dry Zone of Sri Lanka, where dental fluorosis is prevalent (Fig. 2). The degree of weathering and the leachable F- in a terrain is of greater significance in the fluoride concentration of water than the mere presence of fluorinebearing minerals in the soils and rocks. Christensen and Dharmagunawardena (1986) considered

Table 1 Impact of fluoride on health (source: WHO, 1971) Concentration of Impact on health fluoride in groundwater Nil 0.0–0.5 mg/l 0.5–1.5 mg/l

1.5–4.0 mg/l 4.0–10.0 mg/l

>10.0 mg/l

Limited growth and fertility Dental caries Promotes dental health resulting in healthy teeth. Prevents tooth decay Dental fluorosis (mottling of teeth) Dental fluorosis, skeletal fluorosis (pain in back and neck bones) Crippling fluorosis

Fig. 2 A case of dental fluorosis showing the marked brown staining of the teeth. This photograph was taken in the Dambulla area in the Dry Zone of Sri Lanka, where dental fluorosis is prevalent

the Ca–Mg carbonate-bearing rocks in the Matale and Polonnaruwa districts as good sinks for the fluoride ion. The easy leachability of the fluoride ion causes the soils in the Wet Zone to be depleted of the ion and, hence, lower concentrations in the groundwater. The Dry Zone soils and water, on the other hand, are particularly rich in fluorides, with a resulting fluoride-rich water. Fig. 3 illustrates the distribution of fluoride in the deep wells of Sri Lanka, and it is quite apparent that there is a marked enrichment of fluoride in the deep groundwater of the Dry Zone. The fact that a majority of the population of Sri Lanka lives in a rural environment without central water-treatment plants supplying domestic water clearly highlights the need for simple, village level defluoridation techniques using locally available, cheap raw materials.

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length and an elbow bend. In order for there to br a longer retention time of water to pass through the defluoridating material, i.e. burnt bricks, upward flow technology was used. The use of this filter should retain the high-fluoride water for a minimum period of 12 h in the defluoridator. Then, the high fluoride water is fed into the column and the defluoridated water comes out from the outlet. This simple technique has been quite successfully used in the remote areas of Sri Lanka affected by dental fluorosis resulting from the intake of high-fluoride water.

Medical geochemistry of selenium

Fig. 3 Distribution of fluoride in the deep wells of Sri Lanka (after Dissanayake, 1991)

Phantumvanit, Songpaisan, and Moller (1988), who developed a defluoridator for individual households in Northern Thailand, noted that the shortcomings of most defluoridation methods are (a) high cost of plant, (b) high operational and maintenance costs, (c) low capacity for removing fluoride, (d) lack of selectivity for fluoride, (e) undesirable effects on water quality, (f) generation of sludge that is difficult to handle, (g) complicated procedures. In Sri Lanka some attempts have been made to defluoridate household drinking water, even though techniques for the defluoridation of fluoride-rich waters in remote parts of developing countries, where dental fluorosis is most common, has inherent problems. Padmasiri and Dissanayake (1995) discussed the use of burnt bricks as the defluoridating agent. The filter constructed is simple in design and is fabricated from a 225 mm diameter, 1 m PVC pipe length, 20 mm diameter, 1 m PVC pipe

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Selenium is considered necessary for several metabolic functions and is an essential component of the biologically important glutathione peroxidase enzymes (GSH-Px) known to act as anti-oxidants preventing the degeneration of biological membranes. An intake of selenium of less than 0.04 lg per day is considered deficient, while a dose in excess of 900 lg per day is considered toxic to human health (Yang & Xia, 1995). Keshan disease, a degenerative heart disease and Kashin–Beck disease, a disease causing deformity of joints, are known to be related to imbalances of selenium in the body. As noted by Fordyce, Johnson, Navaratne, Appleton and Dissanayake (1998), Se has been implicated in the aetiology of cancer, muscular sclerosis and muscular dystrophy. In recent years, it has been suggested that selenium deficiency may be an important factor in the onset of goitre and other iodine deficiency disorders (IDDs). Fordyce, Johnson, Navaratne, Appleton and Dissanayake (2000) studied the selenium geochemistry in relation to IDD for the first time in Sri Lanka. In their study they determined the chemical differences in the environment (measured in soil, rice and drinking water) and the selenium status of the human population (demonstrated by hair samples from women) from 15 villages. The villages were characterized by low (<10%), moderate (10–25 %) and high (>25%) goitre incidence (NIDD, MIDD and HIDD, respectively). Their results from analysis of 75 soil samples showed that concentrations of total Se and iodine

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(d) clay organic interactions (e) greater fractionation of elements in the physical environment

were highest in the HIDD villages. The soil clay and organic matter content, however, appeared to inhibit the bioavailability of these elements. Interestingly, the study by Fordyce et al. (2000) also showed that significant proportions of the Sri Lankan female population may be selenium deficient (24%, 24% and 40% in the NIDD, MIDD and HIDD villages, respectively). Table 2 shows the summary of selenium abundance. Fordyce et al. (2000) were of the opinion that, although Se-deficiency is not restricted to areas where goitre is prevalent, a combination of iodine and selenium deficiency could be involved in the pathogenesis of goitre in Sri Lanka.

Poverty and poor dietary habits are the main non-geological factors that influence IDD. The surface soils in tropical terrains receive more iodine from the atmosphere via rainwater than from the rocks. Rainfall, therefore, plays a critical role in the iodine cycle of tropical environments. It brings down more iodine to the terrestrial environment than does the dry deposition. The intensity of the leaching, however, impoverishes the soil of iodine, and, in tropical soils such as those in the Wet Zone of Sri Lanka, iodine content is particularly low. Figure 5 illustrates the endemic goitre belt of Sri Lanka. The climate, and also, perhaps, the heavily leached soils such as the lateritic soils are related to the incidence of goitre in Sri Lanka. Groundwater in the tropical environment rapidly removes the iodine from the already leached soils, thereby severely impoverishing the soils of iodine. Areas subjected to periodic water logging and areas in which there is a strong downward movement of the groundwater, particularly through highly porous media, are especially depleted in iodine. Figure 6 illustrates the geochemical cycle of iodine, and it is worthy of special note that the central mountain belt may have a major influence in the geochemical cycling of iodine in Sri Lanka.

The iodine cycle and iodine deficiency disorders In a large number of tropical countries, iodine deficiency disorders are rated as a major health problem (Fig 4). The geochemistry of iodine and its bioavailability influence the prevalence of IDDs, and geological and mineralogical factors play a key role in this process. Among these factors are: (a) intense rainfall (b) high temperatures and their marked diurnal variations (c) very high rates of weathering and leaching of rocks and soils Table 2 Summary of iodine and Se determinations in soil, rice, water and hair in the incidence of goitre in village groups (Fordyce et al., 2000) (NIDD no/low goitre

incidence, MIDD moderate goitre incidence, HIDD high goitre incidence, nd no data)

Group Sample type

Minimum Se

Maximum Se

Geomean Se

Number Minimum iodine

Maximum Iodine

Geomean iodine

Number

NIDD Soil(ng/g) Rice(ng/g) Water(lg/l) Hair (ng/g) MIDD Soil(ng/g) Rice(ng/g) Water(lg/l) Hair (ng/g) HIDD Soil(ng/g) Rice(ng/g) Water(lg/l) Hair (ng/g)

113 6.8 0.06 104 310 0.1 0.06 118 276 0.1 0.06 111

663 150 0.24 765 5238 776 0.09 2652 3947 127 0.09 984

226 42 0.11 294 875 55 0.07 389 1124 25 0.07 302

25 25 5 25 24 25 5 25 25 25 5 25

10000 58 84 nd 2008 <38 23.5 nd 9600 <38 7.02 nd

2260 51 66.5 nd 2008 <38 5.5 nd 3914 <38 7.02 nd

25 5 5

130 45 53 nd 130 <38 3 nd 1000 <38 3.3 nd

25 5 5 25 5 5

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Fig. 4 Typical case of endemic goitre in Sri Lanka. This photograph was taken in the Angunawala area near Kandy, where endemic goitre is prevalent

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roid enlargement by influencing the synthesis of thyroid hormone. The pituitary responds by increasing its output of thyroid-stimulating hormone (TSH), and this indicates hypertrophy in the gland in an effort to increase thyroid hormone production (Underwood, 1977). Goitrogens can be biological or mineralogical, and the latter is of particular interest to geochemists. In Sri Lanka, the prevalence of iodine deficiency disorders displaying geographical distribution and as isolated pockets, notably in the Kalutara and Kandy regions, point to the possible existence of geological and geochemical goitrogens. Kalutara has a goitre incidence of nearly 40% (Fernando, Balasuriya, Herath, & Katugampola, 1987), although it lies close to the sea—the major source of iodine. This enigma clearly points to the presence of geochemical goitrogens in the region. In the tropical soils, clay minerals and humic substances are two of the most important iodine fixers. As the vast majority of the population of Sri Lanka, as in the case of other developing counties, lives in close association with the geological environment, the iodine-fixing potential of the soil is of great importance from the point of view of the occurrence of iodine deficiency disorders. More research is needed, therefore to identify clearly the causes that lead to the poor bioavailability of iodine in the geological environment.

Chronic renal failure—geochemical basis

Fig. 5 The endemic goitre belt of Sri Lanka (after Dissanayake and Chandrajith 1996)

Another factor that could influence the bioavailability of iodine is the presence of goitrogens. These are substances capable of producing thy-

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Chronic renal failure (CRF) is an irreversible deterioration in renal function. It is known to affect (a) regulation of water content of the body and the nature of the body fluids, (b) regulation of the electrolyte content of the body, (c) maintenance of the normal acid–base balance of the body fluids, (d) retention of substances vital to body economy (glucose, amino-acids, phosphates, proteins) and (e) hormonal and metabolic functions. The quality of the drinking water in relation to CRF is now a subject of increasing interest to medical geologists. A study undertaken by ‘‘Action contre la Faim’’ (Lapegue, 2001) in the Trincomalee district, where CRF among the people is significantly high, shows a relationship

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Fig. 6 A schematic diagram showing the iodine geochemical cycle in the tropical environment (after Dissanayake, Chandrajith, & Tobschall, 1998)

with the mineral content of the drinking water. The areas chosen for study were Gomarankadawela, Kebitigollewa and Padaviya-Siripura. Among the suspected causes linked to the geochemistry of the groundwater were (a) sulphides and pH (deep and shallow groundwater), (b) Pb (deep and shallow water), (c) Cd (only in deep water). Even though no direct cause for the CRF could be identified, the combination of high rates of sulphide and acidic conditions needs to be more thoroughly investigated. Table 3 shows the incidence of CRF in the study areas of the Trincomalee district. The alarming increase, notably in the Padaviya-Siripura area, is thought to be caused by the unsuitable quality of the drinking water. Pesticide toxicity is another factor that merits further consideration in these studies, particularly in the Padaviya-Siripura area. Interestingly, all patients from the Kebitigollewa area obtained their drinking water supplies from tube wells, while Table 3 The incidence of CRF in the Trincomalee district (Lapegue, 2001)

this was not the case in Gomarankadawela. In Padaviya-Siripura, open wells were used.

Conclusions Medical geology as a research field is still in its infancy. The effect of geology on the geographical distribution of some diseases has been observed in many parts of the world, notably in the tropical countries. Some diseases, such as dental and skeletal fluorosis and cancer of the oesophagus and bowels, are caused by excessive nitrate intake. Endemic goitre, and other iodine deficiency disorders, and chronic renal failure appear to be related to the geochemistry of the immediate physical environment. The excessive abundance of some diseases is related to chemical elements in the groundwater, and, hence, the drinking water, soils and vegetation are linked to anomalous incidence of these diseases.

Reference hospital

Trincomalee hospital

Anuradapura Padaviya– hospital Siripura hospital

Programme reference area CRF cases/1,000 in 1999 Change in rate of CRF cases/1,000/ year in the past 5 years

Gomarankadawela Kebitigollewa – 1.6 17 21.1 –0.025 +0.86 +4.22

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In Sri Lanka, in view of the fact that it is a tropical country with markedly defined geochemical provinces, such geochemistry–disease correlations are more visible. With better health data and other medical statistics, coupled with proper site investigations for geological and geochemical parameters, geochemists would be in a better position to contribute towards the study of the origin of diseases.

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Environ Geochem Health (2007) 29:155–162 Fernando, M. A., Balasuriya, S., Herath, K. B., & Katugampola, S. L. (1987). Endemic goitre in Sri Lanka’’ In: C. B. Dissanayake & L. Gunatilake (Eds.), Some Aspects of the Chemistry of the Environment of Sri Lanka (pp. 46–64). Colombo, Sri Lanka: Sri Lanka Association for the Advancement of Science. Fordyce, F. M., Johnson, C. C., Navaratne, U. R. B., Appleton, J. D., & Dissanayake, C. B., (1998). Studies of selenium geochemistry and distribution in relation to iodine deficiency disorders in Sri Lanka. Tech. Report. WC/98/28. Overseas Geology Series, BGS-UK. Fordyce, F. M., Johnson, C. C., Navaratne, U. R. B., Appleton, J. D., & Dissanayake, C. B. (2000). Selenium and iodine in soil, rice and drinking water in relation to endemic goitre in Sri Lanka. The Science of the Total Environment, 236, 127–141. Kronberg, B. I., Fyfe, W. S., Leonardos, Jr. O. H., & Santos, A. M. (1979). The chemistry of some Brazilian soils: element mobility during intense weathering. Chemical Geology, 24, 211–229. Lapegue, J., (2001). Chemical risks associated to the consumption of groundwater: The specificity of chronic renal failure in eastern areas of Sri Lanka. Technical report of Action Contre la Faim. Padmasiri, J. P., & Dissanayake, C. B. (1995). Simple defluoridater for removing excess fluorides from fluoride-rich drinking water. International Journal of Environmental Health Research, 5, 153–160. Phantumvanit, P., Songpaisan, Y., & Moller, I. J. (1988). A defluoridator for individual households. World Health Forum, 9, 555–558. Ramesam, V., & Rajagopalan, K. (1985). Fluoride ingestion into the natural waters of hard-rock areas, Peninsular India. Journal of the Geological Society of India, 26, 125–132. Underwood, E. J. (1977). Trace Elements in Human and Animal Nutrition. New York: Academic Press, 533. WHO (World Health Organization) (1971). International Standards for Drinking Water. Geneva: WHO. Yang, G., & Xia, M. (1995). Studies on human dietary requirements and safe range of dietary intakes of selenium in China and their application to the prevention of related endemic diseases. Biomedical and Environmental Sciences, 8, 187–201.