An Introduction to Futuristic Science of “Medical Geology”....
To most people, geology is a subject concerning rocks and minerals and their distributions on Earth. But if we think “Earth” as a closed system it has a unique interdependence on each of the different living and nonliving components that make up the Earth including atmosphere, hydrosphere, lithosphere, and biosphere. Since the chemical elements on our planet flow through all of the different planetary compartments, humans and animals have become a part of complex biogeochemical cycles in which chemical elements pass into and out of them.
Obviously, then, the chemistry of any local geological environment should have a marked degree of influence on the chemical make-up of those living there. This is most readily seen in places where humans live in particularly intimate contact with the local physical environment, as is the case with rural people living in tropical countries. This has been linked with the emergence of a “New Science dealing with the influence of ordinary environmental factors on the geographical distribution of health problems in man and animals” It has now developed into a truly fascinating science called “Medical Geology” with potentially enormous consequences for the well-being of people around the world.
Professor C.B. Dissanayake from University of Peradeniya is a pioneering scientist in Sri Lanka to explore the little- known field of medical geology through comprehensive research work continued from early 80’s. In 2009 Professor Dissanayake in partnership with Professor Rohana Chandrajith from Geology Department of University of Peradeniya launched a new book “Introduction to Medical Geology” which emphasizes the origin and impacts of geogenic diseases particularly in tropical latitudes where millions of people are significantly affected by the unique geochemistry of these tropical environments. Being one of the first of its kind, this book serves as an excellent introduction to the emerging discipline of Medical Geology. The aim of the book is to introduce the subject to students and researchers who are engaged in both fields of Medicine and Geology to acquire comprehensive knowledge on geosphere-human interactions.
We met Prof. Dissanayake to explore the emerging trends of the futuristic science of medical geology. Here are some excerptions of the interview.
Q What are the prominent diseases that can be categorized as geogenic diseases?
Dental fluorosis, skeletal fluorosis, Iodine Difficiency Disorders such as endemic goitre, cretinism, foetal abnormalities, etc., Arsenic toxicity, Podoconosis, etc. can be considered as diseases of geologic origin.
Q Dental fluorosis which is caused by the excess fluoride in drinking water is a major medical concern of many parts of the world. What is the geochemical basis of dental fluorosis?
The link between fluoride geochemistry in water in an area and the incidence of dental as well as skeletal fluorosis is a well established relationship in medical geolo- gy. While the essentiality of fluoride for human health is still being debated, its toxicity has now caused considerable concern in many lands where fluoride is found in excessive quantities in the drinking water. As in the case of some essential trace elements, the optimum range of fluoride varies within a narrow range and this causes fluoride imbalances, very often in large populations, mostly in developing countries of the tropical belt. Deviation from the optimal levels therefore results in dental health effects such as caries and fluorosis. The beneficial and detrimental effects of fluoride are mainly on the tooth enamel and bone. While the prevalence of dental caries is inversely related to the concentration of fluoride in drinking water, the prevalence of dental fluorosis is strongly associated with the concentration of fluoride, with a positive dose-response relationship.
Q There is an upward trend in reported CKDu patients from around the world including Sri Lanka as well. Although agrochemicals such as the ‘Glyphosate’ are blamed as a causative factor of the disease, the real aetiology is yet to be identified. Also, the disease apparently has a localized distribution. What is the role of medical geology in solving CKDu issue?
Much research has been done on this subject. One has to give a precise answer to the fact that the wet zone of Sri Lanka is almost free of CKDu. Are there no glyphosates, Cd, As, in these areas? It is very clear that the disease is “geo- specific” which means it is the geogenic factors in a particular area which must play the major role in the etiology of CKDu. Fluoride is the major geochemical carrier since it is highly reactive and carries with it many of the so called disease causing ions. A combination of hard water with fluoride with a critical dose or an elemental ratio appears to play a major role in the disease. The geochemistry of the groundwater in the area where the disease is prevalent is of utmost importance.
Q Cancer is becoming a leading killer in many industrialized societies. But its link to environmental factors as causative factors is yet to be proved. How does medical geology apply in finding the aetiology of cancer?
Geogenic nitrates, in particular could lead to cancer visa reactions with nitrsamines in the human body. Excessive use of nitrogeneous fertilizers, for example, can cause nitrates to enter the human body via the food chain. Many other carcinogenic compounds from the geogenic environment could also enter the biogeochemical cycle resulting in some form of cancer.
Q The link between cardiovascular diseases (CVD) and water hardness may be an interesting field of study within medical geology. Some geographical areas with hard water shows a positive correlation with death rate due to cardiovascular diseases while some other areas with hard water have no reports of such a relationship. How could this be explained in medical geology?
This is a very interesting correlation. In many areas, where the water is hard, the prevalence of CVD is low. This is due to the “magnesium factor”. Hard water which has a high concentration of Mg has been proved to be beneficial to the humans as regards the cardiovascular health. Mg is known to be cadioprotective. Therefore people living in an area where the ground water is Mg rich, there will be a correlation with low CVD. It is only a correlation but one which needs to be studied in greater detail.
Q What is ‘Geophagy’? How does it affect human health?
Geophagy is referred to as regular consumption of some of the earthy materials such as soils, clays and related mineral substances by humans and animals. Kaolinite clay, smectitic minerals and aluminous minerals are some of the geophagic materials of interest. Seemingly it is a practice that is found in all continents, but it is common among tropical countries, notably in tropical Africa. Soil-eating is not only seen among humans but animals such as monkeys, chimpanzees, gorillas, birds, reptiles and horses. Why do humans and animals consume soil? This intriguing question will probably be answered by a number of recent investigations. It could well be that these geophagic materials have many useful medicinal properties such as ability to desorb dietary toxins, ability to alleviate gastrointestinal malfunctions, as well as it can be used as a mineral nutrient supplementation.
Q Although geophagy has some beneficial aspects, ingestion of earth materials may have medical concerns. Could you explain the geochemical background of the disease ‘Podoconosis’?
Podoconiosis is a disease characterized by swelling and deformity of the legs associated with enlargement of the draining lymph nodes. This disease is predominantly found in regions of tropical Africa where fine reddish brown soils are prevalent and in areas of high altitude (>1250 m), modest average temperature (20°C) and high hot season rainfall (>1000 mm annually). The natives of these areas which have very fine soil mineral particles walk barefooted and it has been suggested that the abrasions in the feet caused thereby serve as entry points for the tiny particles, which finally enter the lymph nodes. The special geochemical features as seen in these tropical regions clearly imply a geographical specificity to Podoconiosis.
It is found that Podoconosis dominated areas basically have alkali basalt rocks. Intense rock weathering have formed extremely fine particles in this tropical region. This fine particles are consisted mainly of Si and Al, with lesser amounts of Ti and Fe suggesting the possible presence of the aluminum silicate kaolinite, silica in the amorphous state with some quartz and ironoxide.
Podoconiosis is an excellent example of a diseases which clearly illustrate the interrelationship between Geology and Health in tropical areas where the pathways of chemical elements and minerals from the immediate environment to the body is direct. The term “geochemical diseases” is attributable to such cases where the aetiology of a certain disease is almost directly and clearly related to a characteristic elemental composition of the immediate geological environment.
Q Lack of Iodine in the diet can lead to Iodine Deficiency Disorders (IDD) such as goitre, cretinism and foetal abnormalities among people. How can IDD link with geochemistry of iodine in the rocks, soil, water, sea and atmosphere?
These iodine deficiency disorders (IDD) are particularly severe in the lands of the tropical belt. The impaired mental function of people has serious direct and indirect impacts on all aspects of life among these people. The sea is a major source of iodine and in lands adjacent to the sea, the marine influence will be particularly strong and the distance from the sea will therefore be of some importance. The expected decrease of iodine from the sea towards the land however is not always regular and other factors such as atmospheric circulation may play an inhibiting role.
The high rainfall resulting in intense leaching of elements from the rocks and abundant laterite formation plays a major role in the geochemical cycle of iodine in the tropics. The presence of acid soils, organic matter and rapid groundwater flow also influence the leaching of iodine in the tropical environment to a marked degree. The most significant feature of the geochemical cycle of iodine is that the iodine abundance and mobility is most marked in the surface environment; these surface phenomena involving the soil-atmosphere interactions are of extreme importance.
Q The metalloid ‘selenium’ is seemingly a new entrant to the field of medical geology. Since selenium is not an element that is determined in routine investigations, the real impact of selenium excess or deficiency on the population may be hidden. How is it important to study medical geochemistry of selenium?
Recent research has shown that the trace element selenium is an essential nutrient and is of fundamental importance to human and animal health. Selenium is a component of selenoproteins some of which have important enzymatic functions. It has been now recog- nized that all these enzymes are selenium- dependent, with selenocysteine as the active site. The importance of selenium here is that it functions as a redox centre.
The selinium deficiency may led to number of health effects such as malfunction in the immune system, disruptions of male fertility, increase vulnerability to cardiovascular diseases, risk of developing prostate cancer, etc. Selenium deficiency is associated with the occurrence, virulence or disease progression of some viral infections such as HIV. In addition when selenium deficiency combines with iodine deficiency, hypothyroidism is enhanced and this is manifested as myxoedematous cretinism. This disease is known in the Democratic Republic of Congo ( Zaire) where both iodine and selenium are known to be deficient. Further, selenium is known to exhibit properties of an antioxidant and antiinflammatory agent. In the case of pancreatitis, asthma and rheumatoid arthritis, selenium levels are considered to be important. Therefore a great attention has to be paid in studying medical geochemistry of selenium.
Q Environmental radiation from natural sources & its effect on human health is a skeptical topic today. How are you going to correlate this with medical geology?
Natural radiation has been in existence from the time planet earth started to form and there are about 60 radionuclides present in nature. These are found naturally in air, water, soil, rocks, minerals and food.
When the radiation is absorbed in the human body, the resulting chemical reactions can cause adverse health effects which may be observed in some cases after many years. These adverse health effects take the form of skin diseases, cancer and even death. About 80% of human exposure is from natural sources while the balance is from man-made sources.
It is therefore the natural background which has evoked a great deal of interest in environmental health. For decades the researchers have been tried to answer the intriguing question of “what is the effect of natural background radiation on human health?” Although some epidemiological studies have shown significant adverse health effects of natural radiation some investigations do not show noteworthy correlation between elevated levels of natural radiation and human health concerns. Therefore this is a widely open area for future research works in medical geolog with a special interest.
Q What are the basic data we need to enter in to the field of medical geology?
Baseline geochemical data and geochemical maps are needed to use as tools in epidemiology and medical geology. Information on the geochemical pathways and regional distribution of essential and toxic elements in the environment is more easily extracted in this way and there is greater understanding of the impact of trace elements in health and disease, their bioavailability and homeostasis. With the help of statistically significant data, it is possible to pin point areas vulnerable to diseases that are clearly geographically and geologically linked. Many studies on medical geochemistry can be carried out using these geochemical maps. Many developed countries use geochemical maps showing detailed distribution of various chemical elements in soils, stream sediments and water as tools applicable in medical geology.
Q What are the future prospects for newly emerging field of this futuristic science?
Medical geology is an emerging science and it is almost certain to achieve the status of an established field of science within a decade. With recent advances in mapping, statistical techniques, extremely fast and accurate analytical techniques, the analysis of hundreds of samples rapidly, GIS based map making the possibilities for a better understanding of the aetiology of geo- chemically linked diseases, notably in the tropics is showing great promise. Unlike in the past where only geological materials were analyzed and studied, it is now well established that for “terrain medical geochemistry” to be of use to the public and the health authorities, all samples from the area, i. e. rocks, minerals, soils, water, plants and food need to be studied together and correlated with in vivo studies. Geochemical data bases such as those established by the Global Geo- chemical Baseline Program of the IUGS/ IAGC, British Geological Survey, Global Reference Network (GRN), Chinas’ RGNR program,etc. all provide valuable data useful in medical geochemistry.
At present Professor Chandra Dissanayake serves as an Emeritus Professor attached to Geology Department of the University of Peradeniya, Sri Lanka. He is the only Sri Lankan to have obtained both D. Phil. and D. Sc. ( earned) degrees from Oxford University, UK. From the very beginning of his research career, he sought avenues off the beaten track of routine geology by exploring the boundaries between geology and other scientific areas. For nearly 30 years he has carried out research in the littleknown field of medical geology and has published many research papers on the topic. He is a recipient of the National Award for Science in Sri Lanka and the Gold medal of the Institute of Chemistry, Sri Lanka, in recognition of his groundbreaking research on applied geochemistry. He is a fellow of the Academy of Sciences for the Developing World (TWAS), headquartered in Trieste, Italy, and an Alexander von Humboldt Fellow of Germany. The Sri Lanka Association for the Advancement of Science recently inducted him into the Hall of Fame.
Discussed & Prepared By, Kusala Madhushani Premaratne
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