2. Medicinal Uses of Soil Components, Geophagia and Podoconiosis

Soils have an impact on human health in many ways. The link between soils and human health has been recognized for thousands of years. Examples of how soils influence human health include the transfer of nutrients from soil to people through plant and animal sources as well as through direct ingestion. The principal source materials for soil components that are beneficial to human health or that are to be used as medicine can be grouped into soil minerals as a source of elements essential to the human body or used in healthcare products and mud, peat, and clay for fangotherapy for healing purposes, as well as soil microorganisms that produce drugs. Involuntarily or deliberately ingested components of soils can be beneficial to humans. However, minerals can also have an adverse effect on human health when they are inhaled over a very long period. Podoconiosis, a non-infectious disease, is associated with chronic barefoot exposure to red volcanic soil, with greater prevalence in high-altitude, impoverished areas of the tropics.

Minerals can be beneficial to human health by serving as active principles or excipients in pharmaceutical preparations, in spas, and in beauty therapy medicine. In some cases, however, these minerals can be harmful to human health. Because of their capacity for adsorption and absorption, phyllosilicate clays have a long history of medicinal use. Clays are commonly used in the pharmaceutical industry as active substances or excipients. Clay minerals (including smectites, kaolinite and fibrous clay minerals) have been extensively applied for prolonged release, especially of basic drugs. Smectites in particular have been the most commonly used substrates, as they can retain large amounts of drug due to their high cation exchange capacity. Clays can act alone or in formulations containing polymers, forming composite materials which show an improved and/or synergic effect when acting together with drugs. When clays are administered concurrently, they may interact with drugs reducing their absorption. Therefore, such interactions can be used to achieve technological and biopharmaceutical advantages, regarding the control of release. Natural clay mixtures are able to kill Escherichia coli and methicillin-resistant Staphylococcus aureus in vitro. Smectites adsorb aflatoxins, which are naturally occurring carcinogenic mycotoxins produced by several Aspergillus species. Iron-rich smectite and illite clays showed natural antibacterial properties. Kaolin has long been used in diarrhoea medicines and is also used in ointments as an emollient. In addition, various clays are used in antacids. Other minerals, such as kaopectate (kaolin), tums (calcite), milk of magnesia (magnesite), talcum powder (talc), toothpastes (quartz, rutile), anti-perspirants (bauxite), calcium supplement (ground up coral) are used in a wide range of everyday healthcare products.

The use of mud, peat, and clay for healing purposes can be summarized by the term “fangotherapy”. Each of these materials (mud, clay and peat) has its own special properties but in general they hold heat and are useful as a thermal application for chronic conditions.They also stimulate circulation and lymph flow, support detoxification and help the body to relax. Some types of fango have anti-inflammatory and pain relieving properties that make them useful for soft-tissue injury. Fangotherapy is a simple therapy used in treatment of neurological, rheumatological, cardiovascular, gynecological, inflammatory and menstrual cycle disorders.

Soils presumably harbor the most diverse populations of microorganisms of any environment. For example, estimates for the number of bacterial species per gram of soil range from 2000 to several millions. Soils are an important source of medicines such as antibiotics. Numerous bacterial genera and species that produce antibiotics in vitro have been isolated from different soils. Actinomycetes, in particular Streptomyces species, have been the primary resource of clinical antibiotics and other therapeutics. To date, more than 7000 different secondary metabolites have been discovered in Streptomyces isolates, many of them being antibiotics. Soil fungi, for example the cephalosporin group, are also major sources of antibiotics. Although penicillin (isolated by Sir Alexander Fleming in 1929) was not discovered from the soil itself, it forms from a soil-borne fungus. Beyond antibacterial agents, numerous other drugs have their origin in soil. For example, a wide spectrum of cancer drugs have been developed from natural products in soil.

Soil ingestion occurs either involuntarily or deliberately. For the former, exposed population may ingest at least small quantities of soil. One reason for this is that any soil adhering to fingers may be inadvertently ingested by so-called hand-to-mouth activity. Any outdoor activity may result in an increase in ingestion. Particularly young children are vulnerable to soil ingestion, as they have a predilection for eating non-food items such as soil. The term pica is used in context with any form of abnormal ingestion which involves substances that are not normally regarded as edible. The terms geophagy or geophagia relate to the deliberate ingestion of soil which is especially associated with certain geographic areas mainly in the tropics. For many people, however, geophagia is difficult to comprehend. The reasons why people indulge in eating soil are manifold. One prevailing theory about the practice of geophagia is that the consumed soil acts as a nutrient source. Mineral nutrients such as Ca, Cu, Fe, Mn, Mg and Zn may be supplied directly to geophagists via soil ingestion. Ingested mineral, chemical and biological components of soils can also be detrimental to human health. One negative consequence of soil ingestion is that the amounts and balance of mineral nutrients within the individual may be affected. In terms of toxicity of elements via soil ingestion, most concern to date has been concentrated on Pb. A number of infectious diseases can also result from the ingestion of soil.

Irritant red clay soil derived from basalt volcanic rocks is responsible for a geochemical, non-infectious disease termed podoconiosis or endemic non-filarial elephantiasis. The disease affects barefooted farmers in at least ten countries across tropical Africa, central America and North India, and is characterized by ascending bilateral and asymmetrical lymphedema of the feet and legs, generally occurring below the knees.

Nanoparticles having a size from 1 to 100 nm are present in nature and are successfully used in many products of daily life. They are also embedded per se or as byproducts from the milling process of larger filler particles in many dental materials. Recently, possible adverse effects of nanoparticles have gained increased interest and the main target organs are considered to be the lungs. Exposure to nanoparticles in dentistry may occur in the dental laboratory, where dust is produced e.g. by processing gypsum type products or by grinding and polishing materials. In the dental practice virtually no exposure to nanoparticles occurs when handling unset materials. However, nanoparticles are produced by intraoral adjustment of the set materials through grinding and polishing regardless whether they contain nanoparticles or not. They may also be produced through wear of restorations or released from dental implants and enter the environment when removing restorations. The risk for dental technicians is known and taken care of by legal regulations. Based on model worst case calculations, the risk for dental practice personnel and for patients due to nanoparticles exposure through intraoral grinding/polishing and wear is rated low to negligible. Measures to reduce exposure to nanoparticles include intraorally grinding/polishing using water coolants, proper sculpturing to reduce the need for grinding and sufficient ventilation of treatment areas.