Principles of Medical Geology O Selinus, Geological Survey of Sweden, Uppsala, Sweden RB Finkelman, University of Texas at Dallas, Richardson, TX, USA JA Centeno, Armed Forces Institute of Pathology, Washington, DC, USA & 2011 Elsevier B.V. All rights reserved.
Abbreviations BEN GIS IDD IGCP IMGA WHO
Balkan endemic nephropathy geographic information systems iodine deficiency disorders International Geological Correlation Program International Medical Geology Association World Health Organization
The Link between Geology and Medicine Medical geology is the science dealing with the influence of geology on the distribution of health problems in humans and animals. This is a complicated subject, and interdisciplinary contributions from different scientific fields are required when these problems are to be solved. This article discusses medical geology issues, providing examples from all over the world. All living organisms are composed of major, minor, and trace elements, given by nature and supplied by geology. Medical geology is a rapidly growing discipline that has the potential of helping medical and public health communities all over the world in the pursuit of a wide range of environmental and naturally induced health issues. The environment is a complex web of geologic and biologic interactions that forms the relationship between life and the planet Earth. The geologic environment (rocks, soil, water, air) contains a range of chemical elements, some essential for health (e.g., calcium, iron, and potassium) and some potentially toxic (e.g., mercury, arsenic, and lead). One cannot avoid the fact that the health of human beings and animals is influenced by metals and other elements in the environment. Geologic processes along with human activities of all kinds have redistributed these elements from sites where they are fairly harmless to places where they can affect humans and animals negatively. Although geology may appear to be far removed from human health, rocks are the source of all the naturally occurring chemical elements on the earth. Many elements in the right quantities are essential for plant, animal, and human health. Most of these elements enter the human body via food and water in the diet and through the air that humans breathe. Through the weathering processes, rocks break down to form soils on which crops
and animals are raised. As part of the hydrologic cycle, water moves through rocks and soils, extracting both essential and potentially harmful elements. Much of the dust and some of the gases present in the atmosphere are the result of geologic processes. Hence, one direct link between geology and health is due to the ingestion and inhalation of chemical elements by eating food drinking water, and breathing air. Volcanism and related igneous activities are the principal processes that bring elements to the surface from deep inside the earth. For example, in just over 2 days in June 1991, the volcano Pinatubo ejected approximately 10 billion tons of magma and 20 million tons of SO2 into the atmosphere. The resulting aerosols influenced the global climate for 3 years. This event alone introduced 800 000 tons of zinc, 600 000 tons of copper, and 1000 tons of cadmium to the surface environment. In addition to this, 30 000 tons of nickel, 550 000 tons of chromium, and 800 tons of mercury were also added to the earth’s surface environment. Volcanic eruptions redistribute some of the potentially harmful elements, such as arsenic, beryllium, cadmium, mercury, lead, radon, and uranium, plus many essential elements, and other elements, many of which still have undetermined biologic effects. It is also important to realize that there are on an average 60 volcanoes erupting on the surface of the earth at any given time, releasing various elements into the environment. Submarine volcanism is even more significant in that it has been conservatively estimated that there are at least 3000 active vent fields on the midocean ridges. One interesting fact is that approximately 50% of SO2 in the atmosphere is of natural origin, mainly from volcanoes, and only 50% is from human activity (Figure 1). The naturally occurring elements are not distributed evenly across the surface of the earth, and problems can arise when element abundances are too low (deficiency) or too high (toxicity). This natural geochemical variation in trace element concentrations and the chemical forms in which they occur can lead to serious health problems. The links between environment and health are particularly important for subsistence populations who are heavily dependent on the local environment for their food supply. Several of the naturally occurring elements are known to be essential to plant and animal life in trace amounts, including Ca, Mg, Fe, Co, Cu, Zn, P, N, S, Se, I, and Mo. However, an excess of these elements can cause
Principles of Medical Geology
Volcanic eruption. Krafla, Iceland, 1980.
toxicity problems. Some elements such as As, Cd, Pb, Hg, and Al have no or limited biologic function and are generally toxic to humans. Many of these elements are known as trace elements because they generally occur in minute (mg kg 1 or ppm) concentrations in most soils. Trace element deficiencies in crops and animals are therefore commonplace over large areas of the world, and mineral supplementation programs are widely practised in agriculture. Trace element deficiencies generally lead to poor crop and animal growth and to reproductive disorders in animals. These problems often have greatest impact on poor populations who can least afford nutritional interventions for their animals.
Medical Geology: An Old and New Discipline The interplay between geology and health has long been known. Ancient philosophers and physicians in countries such as Greece and China realized the importance of how geology influences health, although it was not until the advent of modern medicine in the nineteenth century that chemical elements essential to health were finally recognized. The Greek philosopher Hippocrates (400 BC) is considered by most scientists to be the founder of medicine and thus medical geology. He recognized that
environmental factors affected the distribution of disease. Hippocrates noted in his treatise, On Airs, Waters, and Places, that under certain circumstances, water ‘‘comes from soil which produces thermal waters, such as those having iron, copper, silver, gold, sulphur, alum, bitumen, or nitre,’’ and such water is ‘‘bad for every purpose.’’ Another example is that of Vitruvius, a Roman architect in the last century BC, who recognized potential health dangers related to mining, noting that the water and pollution near mines posed negative health threats. Chinese medical texts dating back to the third century BC describe several relationships between geology and health. During both the Song Dynasty (1000 BC) and the Ming Dynasty (fourteenth to seventeenth century), lung problems related to rock crushing and symptoms of occupational Pb poisoning were recognized. Similarly, the Tang Dynasty alchemist Chen Shao-Wei stated that Pb, Ag, Cu, Sb, Au, and Fe were poisonous. Contemporary archaeologists, osteologists, and historians provide evidence that poor health reflected in the tissues of prehistoric cadavers and mummies can often be linked to past detrimental environmental conditions. Goiter for instance – the result of severe I deficiency – was widely prevalent in ancient China, Greece, Egypt, as well as the Inca state of Peru. This condition was often treated with seaweed, a high source of I, and indicates some degree of knowledge that these ancient civilizations had about the treatment of dietary deficiencies through the use of natural supplements.
Principles of Medical Geology
Besides element deficiencies, the use of heavy metals in everyday ancient society led to effects of toxicity. Several descriptions of Pb poisoning found in texts from past civilizations further corroborate the heavy uses of Pb. Clay tablets from the Middle and Late Assyrian periods (1550–600 BC) provide accounts of Pb poisoning symptoms, as do ancient Egyptian medical papyri and Sanskrit texts dating to over 3000 years ago. During the Roman Empire, it has been estimated the annual production of Pb approached 80 000 tons, that is, approximately 550 g per person per year. Lead salts were used to preserve fruits and vegetables, and Pb was also added to wine to stop further fermentation and to add color or bouquet. Large amounts of Pb usage in the daily life of the Roman aristocracy had a number of negative health implications, including epidemics of plumbism and saturnine gout, high incidence of sterility and stillbirths, as well as mental incompetence. Physiological profiles of Roman emperors dating between 50 and 250 BC suggest that the majority of individuals suffered from Pb poisoning. Archaeologists have noted links between health and environmental factors. An analysis of elements in bone material has provided an excellent tool to study the diet and nutritional status of the past humans and animals. For instance, the transition from a hunter–gatherer society to an agriculturally based economy resulted in a major dietary change and an accompanying Fe deficiency. Iron in plants is more difficult to absorb than iron from a meat source; hence, it has been proposed that this new reliance on a crop diet may have resulted in Fe deficiency and anemia among the general populace. After first being observed in China in the 1930s, Keshan disease, a potentially fatal form of cardiomyopathy caused by the Coxsackie B virus and selenium deficiency, was eventually linked in the 1970s to low concentrations of Se in the environment.
Biology and Essentiality Eleven elements seem to have roughly constant abundance in biologic systems. These are hydrogen, oxygen, carbon, nitrogen, sodium, potassium, calcium, magnesium, phosphorus, sulfur, and chlorine. These elements comprise 99.9% of the atoms in humans. Usually, these elements are divided into two groups: major and minor elements. The major elements are hydrogen, oxygen, carbon, and nitrogen. They make up 99% of the atoms or 96% of the body mass. Sodium, potassium, calcium, magnesium, sulfur, and chlorine comprise 3.78% of the body mass. The whole group of noble gases has been excluded here because their chemical properties make them unlikely to fulfill any biologic function. The remaining elements are those considered as trace
elements. There are 90 naturally occurring elements in the periodic table, of which 73 are trace elements. Of these, 17 are on the list of essential or possibly essential trace elements. They are vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, tungsten, boron, silicon, selenium, fluorine, iodine, arsenic, bromine, and tin. Most of the trace elements appear in biology at concentrations below or well below 100 mg kg 1. A trace element can be considered essential if it meets the following criteria: (1) it is present in all healthy tissues of all living things; (2) its concentration from one animal to the next is fairly constant; (3) its withdrawal from the systems induces reproducibly the same physiological and structural abnormalities, regardless of the species studied; (4) its addition either reverses or prevents these abnormalities; (5) the abnormalities induced by deficiencies are always accompanied by specific biochemical changes; and (6) these biologic changes can be prevented or cured when the deficiency is prevented or cured. It is obvious that the number of elements recognized as essential depends on the sophistication of experimental procedures and that proof of essentiality is technically easier for those elements that occur in reasonably high concentration than for those with very low requirements and concentrations. Thus, it can be expected that, with further improvement in experimental techniques, more elements may be demonstrated as essential. Experiments are based on the general acceptance that if an essential trace element is completely withdrawn from the diet of experimental animals, deficiency should occur with signs and symptoms such as growth retardation and loss of hair. When a state of deficiency has been established, the supplementation of the trace element should alleviate symptoms and reverse the deficiency state. Most of the trace elements being essential to both plants and animals are found in the first row of the transition metals, all of them being redox metals. Zinc is not included in the transition metals, and it does not take part in redox reactions, a property of importance in biology. All of the bulk elements are nonmetals. The minor elements comprise metals as well as nonmetals with only one oxidation state available. The dominant part of the essential trace elements is metals, but some very important trace elements are nonmetals such as selenium and iodine. Boron and silicon are two nonredox nonmetals, and both of them are acknowledged as essential. Boron, however, has been shown to be essential to plants, although it is found in appreciable concentrations in animals as well. Some elements such as arsenic, cadmium, lead, mercury, and aluminum have no or limited biologic function and are generally toxic to humans in even small exposures. In addition to understanding both natural and anthropogenic sources of harmful substances in the environment, it is also important to consider exposure and
Principles of Medical Geology
bioavailability (the property of a substance that makes its chemical uptake by biota possible). Bioavailability directly influences exposure and, therefore, the effect on and risk to health. Large quantities of potentially harmful substances may be present in the environment, but if they are in a nonbioavailable form, the risk to health may be minimal. Bioavailability depends not only on the physical and chemical forms in which the element is present, but also on local factors in the environment, for example, pH. The bioavailability and mobility of metals such as zinc, lead, and cadmium are greatest under acidic conditions, whereas increased pH reduces bioavailability. Soil type, for instance, clay and sand content, and its physical properties, also affects the migration of metals through soils. The organisms present in soils also affect metal solubility, transport, bioavailability, and bioaccessibility.
Global Examples of Medical Geology The study of trace elements is one of the most important topics in medical geology, together with other issues such as dusts, organic constituents, and benefits. The examples in Figure 2 are just a few that have relevance. The connection between geologic materials and trace element deficiency can clearly be shown for iodine. Iodine deficiency disorders (IDD) include goiter
(enlargement of the thyroid gland), cretinism (mental retardation with physical deformities), reduced IQ , miscarriages, and birth defects. Goiter is still a serious disease in many parts of the world. China alone has 425 million people at risk of IDD. In all, more than a billion people, mostly living in the developing countries, but also in Europe, are at risk of IDD. In all the places where the risk of IDD is high, the content of iodine in drinking water is very low because of low concentrations of iodine in bedrock. Another important element is fluorine. The geochemistry of fluorine in groundwater and the dental health of communities, particularly those depending on groundwater for their drinking water supplies, is one of the best-known relationships between geochemistry and health. Many water supply schemes contain excess fluorine and as such are harmful to dental health. For most trace elements required by humans and other animals, food is the principal source. In the case of fluorine, however, much of the input into the human body is from drinking water, and the geochemistry of fluoride in groundwater is therefore of particular significance in the etiology of dental diseases. For example, after the eruptions of the volcano Hekla on Iceland in 1693, 1766, and 1845, detailed descriptions of fluorosis were presented. Since World War II, Hekla has had eruptions in 1947, 1970, and 1980, and a number of analyses of fluorine have
Mercury poisoning Arseni cosis
Black lung Balkan endemic nephropathy
Mseleni joint disease
Examples of medical geology on the human body.
Black foot disease
Principles of Medical Geology
been performed. The volcano delivered huge amounts of fluorine, and concentrations as high as 4300 mg kg 1 have been found in grass. Selenium is an essential trace element with antioxidant protective functions as well as redox and thyroid hormone regulation properties. However, selenium deficiency (due to soils low in selenium) has been shown to cause severe physiological impairment and organ damage such as juvenile cardiomyopathy (Kashin disease) and muscular abnormalities in adults (Kashin-Beck disease). Several areas in the world, including parts of the United States, Europe, India, China, Africa, and New Zealand, are selenium deficient. Arsenic and arsenic-containing compounds are human carcinogens. Exposure to arsenic may occur through several anthropogenic processes, including mining residues, pesticides, pharmaceuticals, glass, and microelectronics, but the most prevalent sources of exposure today are natural sources. Exposure to arsenic occurs via the oral route (ingestion), inhalation, and dermal contact. Drinking water contaminated by naturally occurring arsenic remains a major public health problem. The source of arsenic is geologic, the element being present in many rock-forming minerals. There is growing concern about the toxicity of arsenic and the health effects caused by exposure to elevated concentrations of it in the geochemical environment. The danger to human health due to arsenic poisoning has been recognized by WHO, and the provisional guideline value for arsenic in drinking water has been lowered from 50 to 10 mg l 1. Acute and chronic arsenic exposure via drinking water has been reported in many countries. Among the countries that have well-documented case studies of arsenic poisoning are Bangladesh, India (West Bengal), Taiwan, China, Mexico, Chile, and Argentina, and also several countries in Europe. A recent report has linked arsenic in drinking water to an elevated incidence of bladder cancer in northeastern United States. The common symptoms of chronic arsenic poisoning are depigmentation, keratosis, and hyperkeratosis. Geology is the most important factor controlling the source and distribution of radon. Relatively high levels of radon emissions are associated with particular types of bedrock and unconsolidated deposits, for example, some, but not all, granites, phosphatic rocks, and shales rich in organic materials. The release of radon from rocks and soils is controlled largely by the types of minerals in which uranium and radium occur. Once radon gas is released from minerals, its migration to the surface is controlled by the permeability of the bedrock and soil, the nature of the carrier fluids (including carbon dioxide and groundwater), and meteorological factors such as barometric pressure and rainfall. Geologic radon potential maps derived from a range of data, including radon measurements in soil and dwellings; soil and rock permeability; uranium concentrations in rocks and soils; and
gamma spectrometric data, show the relative health hazards from radon. Whereas a geologic radon potential map can indicate the relative radon hazard, it cannot predict the radon risk for an individual building. This can only be established by having the building tested. Balkan endemic nephropathy (BEN) is an irreversible kidney disease of unknown origin, geographically confined to several rural regions of Bosnia, Bulgaria, Croatia, Romania, and Serbia. The disease occurs only in rural areas, in villages located in alluvial valleys of tributaries of the lower Danube River. It is estimated that several thousand people in the affected countries are currently suffering from BEN and that thousands more will be diagnosed in the next few years. There is growing evidence that toxic organic compounds present in the drinking water of the endemic areas were leached by groundwater from low-rank Pliocene lignite deposits and were transported into shallow household wells or village springs. Analysis shows that well water and spring water samples collected from BEN endemic areas contain a greater number of aliphatic and aromatic compounds, and in much higher abundance than water samples from nonendemic sites. Many of the organic compounds found in the water samples of endemic areas were also observed in water extracts of Pliocene lignites, suggesting a connection between leachable organics from the coal and organics in the water samples. The population of villages in the endemic areas uses almost exclusively well/spring, water for drinking and cooking, and is therefore potentially exposed to any toxic organic compounds in the water. The presumably low levels of toxic organic compounds present would favor relatively slow development of the disease over a time interval of 10–30 years or more. This disease is now also suspected to occur in the United States, Portugal, and Turkey. Collaborative research between geoscientists and medical scientists is now going on in these countries. Dust is also a global phenomenon. Dust storms from Africa regularly reach the European Alps, and the Western Hemisphere and Asian dust outbreaks can reach California in less than a week, some ultimately crossing the Atlantic and reaching Europe. The ways in which mineral dust impacts on life and health are wide-ranging. These include changes in the planet’s radiative balance, transport of disease-causing microbes to densely populated regions, dumping of wind-blown sediment on pristine coral reefs, general reduction in air quality, provision of essential nutrients to tropical rainforests, and transport of toxic substances. Mobilization of dust is both a natural and a humanly triggered process. Changing climatic conditions play a key role as natural changes occur in available moisture and wind speeds. Although vegetation exerts a critical control on dust mobility, vegetation itself is influenced by climate, human activity, and other factors. A better understanding of dust,
Principles of Medical Geology
including the processes that control its sources and transport as well as its impacts, is needed if its negative consequences are to be mitigated.
Geochemical Databases for Use in Medical Geology How can geoscientists provide tools in solving medical geology matters? One specialization of geoscientists is in geochemical databases and geographic information systems (GIS). In the 1970s and 1980s, regional or national geochemical mapping projects were carried out in many countries. However, due to lack of standards, the results were not satisfactory; thus, standardization for geochemical mapping was particularly needed. The Global Geochemical Mapping Project, whose main aim was to establish standards, was accepted as part of the International Geological Correlation Program (IGCP259) in 1988. Plans for a Global Geochemical Mapping Project using wide-spaced sampling were then accepted as the IGCP360 project entitled ‘Global Geochemical Baselines’ in 1995. The three major resulting aspects of the project were to determine the natural global distribution of various chemical elements and compounds and the present state of pollution in the surface environment, delineate areas and geochemical provinces especially enriched in elements of economical importance, and provide data on the regional distribution of compounds that are linked to human and animal health. As one further step, the Geological Surveys of the European Union (EuroGeoSurveys) compiled the Geochemical Atlas of Europe. The European survey covered 26 countries and provided information on different sample media of the nearsurface environment (topsoil, subsoil, humus, stream sediment, stream water, and floodplain sediment). This was the first multinational project, performed with a harmonized sampling, sample preparation, and analytical methodology, producing high-quality compatible data sets across national borders, which can be used for environmental and medical geology research. Over 60 elements were determined, and 400 maps plotted and interpreted. The project is completed, and the results published in a two-volume set, which is also freely available for viewing and downloading. Also the whole database can be downloaded free of charge. Another example of a database relevant to medical geology is the Baltic soil survey covering total concentrations of major and selected trace elements in arable soils from 10 European countries over a 1 800 000 km2 area surrounding the Baltic Sea. Large differences between element concentrations and variations can be observed for most elements when the different countries are compared. This survey has now been expanded to the whole of Europe.
The Spread of Medical Geology In the 1990s, interest in, and applications of, medical geology developed rapidly, and as a recent step in the development of medical geology, the International Medical Geology Association (IMGA) was established in January 2006. Information can be found on the website http://www.medicalgeology.org. Previous to this in the 1970s, Jul La˚g in Norway defined the science of geology and health as ‘‘the science dealing with the influence of ordinary environmental factors on the geographic distribution of health problems in man and animals.’’ In the 1990s, La˚g was very productive in organizing annual conferences and producing a large amount of books under the aegis of the Norwegian Academy of Sciences. Medical geology is now promoted internationally by IMGA at meetings around the world by organizing and sponsoring special sessions or symposia on medical geology and also by providing financial support for students and professionals from developing countries to participate. Short courses led by Jose Centeno, Robert (Bob) Finkelman, and Olle Selinus have been presented in almost 40 countries and have been attended by thousands of students and professionals with backgrounds in geoscience, biomedical/public health science, environmental science, geography, engineering, chemistry, etc. In addition, at the short courses, local scientists are invited to describe medical geology work going on in their regions. The scientific topics of the course include environmental toxicology; environmental pathology; geochemistry; geoenvironmental epidemiology; extent, patterns, and consequences of exposures to toxic metal ions; and analysis of geologic and biologic materials. The courses are intended for anyone interested in the effects of natural materials and natural geologic events on animal and human health. An important objective of the courses is to provide an opportunity for forming contacts and networks between professionals working in different countries and on different aspects of environmental health issues (Figure 3). The biggest challenge facing medical geology is the integration of geoscience and biomedical public health research and funding activities. The researchers attend separate conferences, subscribe to different journals, and to some degree have different philosophical approaches and speak different languages. A concerted effort by these two communities will bring medical geology to its full potential. Biomedical/public health organizations have demonstrated interest equal to that of the geoscience community in developing collaborative projects to address medical geology (environmental health) issues. In addition, universities, medical schools, research hospitals, and biomedical professional organizations in different countries have all shown interest in this field as have chemists, engineers, environmentalists, geographers, etc.
Principles of Medical Geology
Medical geology short courses.
Several books and book chapters on medical geology have been published in the past few years. In 2002, Catherine Skinner and Tony Berger published Geology and Health, the proceedings of a medical geology conference that was held a few years earlier in Uppsala, Sweden. In 2005, Elsevier published Essentials of Medical Geology edited by Olle Selinus and six associate editors: (Bob) Brian Alloway, Jose Centeno, Robert Bob Finkelman, Ron Fuge, Ulf Lindh, and Pauline Smedley, with almost 60 distinguished authors from all around the world. In November 2005, this book was recognized as a ‘highly commended’, title in the Public Health category by the British Medical Association. This is a very prestigious acknowledgment. The book is one of the best of all published books in Public Health in 2005. It also won a second prestigious reward in January 2006 as one of two winners in the ‘Geology/Geography’ category of the 2005 Awards for Excellence in Professional and Scholarly Publishing. The book has now thus been recognized in both communities for which it was intended (first by the British Medical Association and then as a geology resource). Colleges and universities in several countries (e.g., Sweden, Egypt, and United States) have begun to offer credit courses in medical geology using the book Essentials of Medical Geology. Students in many countries have expressed interest in attending such courses and even in majoring in medical geology. Scores of graduate students in many countries are currently working on a wide range of medical geology issues, and students are working on medical geology issues for masters and doctorates in
Turkey, Sweden, the United States, Russia, China, and elsewhere. Research fellowships in medical geology have been offered by the US Armed Forces Institute of Pathology, the US Geological Survey, and the US Department of State. The Armed Forces Institute of Pathology has also created a Medical Geology Registry that contains information, diagnoses, and tissue and body fluid samples on a range of health problems caused by geologic materials. Among many other meetings, a recent international symposium on medical geology was organized at the Swedish Royal Academy of Sciences in May 2006 under the auspices of the academy. The activity brought together scientists from all over the world to discuss the state of medical geology and future directions. These examples are all solid and necessary indications of a very healthy, growing interest in the subject of medical geology.
Conclusion Medical geology is a rapidly growing field that brings together geoscientists and medical/public health researchers to address health problems caused, or exacerbated, by geologic materials (rocks, minerals, atmospheric dust, and water) and processes (including volcanic eruptions and earthquakes). Among the environmental health problems that geoscientists are working on in collaboration with the medical and public health communities are exposure to toxic levels of trace essential and nonessential
Principles of Medical Geology
elements such as arsenic and mercury, trace element deficiencies, exposure to natural dusts and to radioactivity, naturally occurring organic compounds in drinking water, volcanic emissions, etc. Medical geology also deals with the many health benefits of geologic materials and processes. Practitioners of medical geology have five principal goals: 1. To identify geochemical anomalies in soils, sediments, and water that may adversely impact human and animal health; 2. To identify the environmental causes of known health problems and, in collaboration with biomedical/ public health researchers, seek solutions to prevent or minimize these problems; 3. To evaluate the beneficial health effects of geologic materials and process; 4. To reassure the public when there are unwarranted environmental health concerns associated with geologic materials or processes; and 5. To forge links between developed and developing countries to find solutions for environmental health problems. It is always risky to anticipate what the future holds. Nevertheless, there is confidence that the future for medical geology still looks promising, notwithstanding the already rapid growth of the subdiscipline. The book Essentials of Medical Geology has received an overwhelmingly positive response. This award-winning book will remain as the primary source of information on the subject, being translated now into Chinese. The reviews have been uniformly positive, and the first printing has sold out in nearly less than a year. The authors anticipate that the book will stimulate the teaching and research practice of medical geology in colleges and universities. The medical geology short course will continue to attract enthusiastic adherents and practitioners of medical geology. The IMGA will continue to provide a stable platform for the exchange of ideas and dissemination of information. The raft of other medical geology activities enumerated in this article will continue to stimulate enthusiasm and momentum for the next few years. After that the medical geologists will have to demonstrate that what they have to offer will indeed benefit society by helping to improve the quality of life for people around the world.
See also: Impact of Natural Dusts on Human Health, Infectious Processes and Medical Geology, Volcanoes and Human Health.
Further Reading Appleton D (2005) Radon in air and water. In: Selinus O, Alloway B, Centeno JA, et al. (eds.) Essentials of Medical Geology, 820pp. Amsterdam: Elsevier. Ayotte JD, Baris D, Cantor KP, et al. (2006) Bladder cancer mortality and private well use in New England: An ecological study. Journal of Epidemiology and Community Health 60: 168--172. Bowman C, Bobrowski PT, and Selinus O (2003) Medical geology: New relevance in the earth sciences. Episodes 26(4): 270--278. Ceruti P, Davies T, and Selinus O (2001) GEOMED – medical geology, the African perspective. Episodes 24(4): 268--270. Derbyshire E (2005) Natural aerosolic mineral dusts and human health. In: Selinus O, Alloway B, Centeno JA, et al. (eds.) Essentials of Medical Geology, 820pp. Amsterdam: Elsevier. Dissanayake C (2005) Of stones and health: Medical geology in Sri Lanka. Science 309: 883--885. Fordyce F (2005) Selenium deficiency and toxicity in the environment. In: Selinus O, Alloway B, Centeno JA, et al. (eds.) Essentials of Medical Geology, 820pp. Amsterdam: Elsevier. Fuge R (2005) Soils and iodine deficiency. In: Selinus O, Alloway B, Centeno JA, et al. (eds.) Essentials of Medical Geology, 820pp. Amsterdam: Elsevier. Garrett RG (2000) Natural sources of metals in the environment. Human and Ecological Risk Assessment 6(6): 945--963. Lindh U (2005) Uptake of elements from a biological point of view. In: Selinus O, Alloway B, Centeno JA, et al. (eds.) Essentials of Medical Geology, 820pp. Amsterdam: Elsevier. La˚g J (ed.) (1990) Geomedicine. Boca Raton: CRC Press Orem WH, Feder GL, and Finkelman RB (1999) A possible link between Balkan endemic nephropathy and the leaching of toxic organic compounds from Pliocene lignite by groundwater: Preliminary investigation. International Journal of Coal Geology 40(2–3): 237--252. Reimann C, Siewers U, Tarvainen T, et al. (2003) Agricultural soils in Northern Europe: A Geochemical Atlas. Geologisches Jahrbuch, Sonderhefte, Reihe D, Heft SD 5. Stallgast: Schweizerbart’sche Verlagsbuchhandlung. Salminen R, Batista MJ, Bidovec M, et al. (2005) Geochemical Atlas of Europe. Part 1 – Background Information, Methodology and Maps. Geological survey of Finland, Espo. 566 pp. Selinus O, Alloway B, Centeno JA, et al. (2005) Essentials of Medical Geology. Amsterdam: Elsevier. Selinus O and Frank A (1999) Medical geology. In: Mo¨ller L (ed.) Environmental Medicine, pp. 164--183. Stockholm: Joint Industrial Safety Council. Skinner HCW and Berger AR (eds.) (2003) Geology and Health – Closing the Gap, 179pp. Oxford: Oxford Press. Smedley P and Kinniburgh DG (2005) Arsenic in groundwater and the environment. In: Selinus O, Alloway B, Centeno JA, et al. (eds.) Essentials of Medical Geology, 820pp. Amsterdam: Elsevier. Weinstein P and Cook A (2005) Volcanic emissions and health. In: Selinus O, Alloway B, Centeno JA, et al. (eds.) Essentials of Medical Geology, 820pp. Amsterdam: Elsevier.