The essential elements too if taken in quantities higher or lower than the desirable limits can impair the body cells, leading to severe health problems. For example, chlorination of drinking water is frequently done by the Municipalities, it is injurious to those suffering from cardiac or kidney diseases and an excessive chlorination may cause asthma, colitis and eczema; copper is essential for human metabolism but a deficiency can cause anemia in infants and excess can damage the liver.

Dr. Gerald Cox of the Mellon Institute in the United States, found in 1938 that 1.0 parts per million of fluorine in water prevented dental caries, while more than 1.5ppm would cause mottled teeth. The Bureau of Indian Standards has prescribed a norm of 1-1.5mg per liter fluoride in water. Fluoride less than or more than this can cause dental decay and mottled teeth. A higher quantity of fluoride in drinking water causes several diseases, like, Osteoporosis and Arthritis, brittle bones, Cancer, Infertility in women, Brain damage, Alzheimer disease and Thyroid disorders.

These elements are ubiquitous in their presence in the lithosphere. When present in concentration and in larger quantities these elements are mined as a natural resource for various industries. Most of them are responsible for economic growth of a nation. Yet they need to be treated with caution as per a paper published by R. Srinivasan of National Geophysical Research Institute, Hyderabad, India. Srinivasan and his colleagues recorded two to five time higher gamma ray radiations from the uranium and thorium present in the granites in the posh western part of Hyderabad metropolis.

The impact of these trace elements on human health has been known to mankind since times immemorial. While the connections between the physical environment and human disease have long been recognized, momentum has been building in recent years to solidify and formalize the study of such interactions. This endeavor gave rise to the concept of medical geology about 25 years ago.

'Medical Geology' is the science dealing with the relationship between natural geological factors and health in man and animals, and understands the influence of ordinary environmental factors on the geographical distribution of such health problems. Thus medical geology is a multi-disciplinary science involving geologists, doctors and veterinarians.

The natural sources and processes in the environment that release the trace elements include weathering of rocks and mineral deposits. This produces metal dusts, metals in sediments; which also get dissolved or carried by groundwater and surface water. The geothermal energy trapped in the womb of the earth also causes metals to get dissolved in traces in waters or gases. Volcanoes release large quantities of metals in gases, waters and aerosols.

Eruption of volcano Pinatubo in June 1991 released 20 million tons of sulfur dioxide into the atmosphere in just two days. The resultant aerosol affected the global climate for three years. The frequent dust storms of North Africa are one of the strongest dust sources in the world. These storms on an average some 200 km across carry up to 100 tonnes of dust, said a report in new Scientist, 2004. Studies carried out with the help of satellite pictures and collection of aerosols through airplanes has shown that the African dust travels via Middle East, Arabian Sea, over the Mediterranean to Europe and west across tropical Atlantic to North and South America. It is an irony that a drought in North Africa causes Asthma in America because the fine dust particles carry quantities of iron those are injurious.

Yet another source of trace elements, sometimes hazardous is the bioavailability of these in the roots of the plants, especially the aquatic variety. In many cases they remain restricted to the roots of the plants.

Anthropogenic interference also releases considerable amounts of trace elements in the environment through commercial fertilizers, pesticides, paints, sewage sludge, municipal refuse, mining and metal smelting, auto and industrial emissions, coal combustion and waste etc.

Amongst the harmful trace elements the worst is the scourge of arsenic and fluoride in groundwater. Arsenic toxicity has already taken a huge toll in West Bengal, Bihar, and parts of Rajasthan and even Uttar Pradesh. In most of the places the causes of presence of arsenic in quantities more than prescribed limits 0.05mg/liter are still being studied. Incidence of fluoride toxicity in vast areas from Punjab, Uttar Pradesh, Madhya Pradesh, Rajasthan, Gujarat, Andhra Pradesh, Karnataka and Tamil Nadu are on the increase. At places like Unnao in U.P. chemical fertilizer is one of the culprits and in Faridabad in Haryana the industrial effluents pumped into subsurface have been identified as source of fluoride in groundwater.

Alarmed by the rise of the harmful trace elements in the environment, the UN and the International Union of Geological Sciences jointly launched a project under the aegis of the International Geological Correlation Programme (IGCP) in the year 2000. The project was named as IGCP Project 456. The objective of this five years project was to evaluate the global scenario of the problem and to educate the developing nations to identify the causes and remedy thereof. In India Geological Survey of India is the nodal agency for IGCP projects.

A multidisciplinary science like the Medical Geology has its own teething troubles. In developed nations specialization in the field of medical science comes as a stumbling block. In developing nations the awareness of the significance is lacking. For example even now in Africa the tribal medicine men use rocks and minerals that are potentially harmful for treating people affected by one of the trace element.

It is time that Medical Geology gets due publicity and more students pour in to learn the subject, particularly in developing countries and help in achieving a better national health. It is also important that earth scientists, medical and veterinary doctors combine to form groups to bring out information on the grains of rocks that hold the key to human and animal health on this Globe.