The Influence of Clays on Human Health: a Medical Geology Perspective
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Clay is unique especially from the perspective of medical geology, that is, the impacts of geologic materials and geologic processes on animal and human health. Clay is the only natural material that can impact human health through all routes of exposure: ingestion, inhalation, and dermal contact. Moreover, these impacts can be harmful as well as beneficial. Ingestion of clay, a form of geophagy, has been practiced for millennia and is still widely practiced today. Humanoids have been ingesting clay for at least two million years to ease indigestion and counteract poisons. Some additional benefits may accrue from eating clays such as providing some nutrients but these benefits are far outweighed by the likely negative consequences such as tissue abrasion, intestinal blockage, anemia, exposure to pathogens and toxic trace elements, and potassium overdose. Inhalation of airborne minerals including clays has impacted the heath of millions. In the 1930s thousands of people living in the Dust Bowl in the U.S. southwest inhaled copious amounts of clay contributing to deadly ‘dust pneumonia.’ Using clay as a poultice to stem bleeding and cure certain skin ailments is an age-old practice that still has many adherents. A classic recent example of the antibacterial properties of clay is the use of certain clays to cure Buruli ulcer, a flesh eating disease. However, walking barefoot on clays in certain volcanic soils can result in non-filarial podoconiosis or elephantiasis. The absence of clays in soils can have serious health consequences. In South Africa, clay-poor soils yield crops lacking in essential nutrients and may be the principal cause of Msileni joint disease. Clearly, a detailed knowledge of the clays in the environment can have significant benefits to human health and wellbeing.
KeywordsGeophagy Mseleni Joint Disease Pharmaceuticals Pneumoconiosis Podoconiosis Soil
Health impacts of clays by route of exposure
Route of exposure
This paper offers a brief overview of many of the positive and negative health impacts of clays that make clay one of the, if not the most, important natural materials impacting human health. The term clay is here considered in its broadest sense embracing hydrous aluminum silicates, sediments in the micrometer size range, and natural materials with plastic properties, and, where appropriate, references to clay-rich soils are included. The intention of this paper was not to provide a comprehensive, authoritative discussion of the many health impacts of clays, as many publications serve this purpose, some of which are cited herein. Rather, the goal of this paper was to provide a broad, though not exhaustive, overview of the subject.
The use of clay for medicinal purposes predates written records. Root-Bernstein and Root-Bernstein (1999) described a 1.5 to 2.1 million year old Homo habilis site in Zambia where these early humanoids apparently used kaolinite as a food supplement or as a detoxicant. Humans likely learned the beneficial effects of ingesting clays by observing various animal species ingesting clay-containing soils with absorbent properties, thus allowing the animals to eat potentially poisonous foods (Abrahms, 2013). The review starts by looking at the various routes of exposure by which clays can impact human health, looking first at the beneficial effects and then the deleterious effects.
Ingestion of Clay
Ingestion of clay, a form of geophagy, has been practiced for millennia and is still widely practiced today (Young, 2011; Henry & Cring, 2013). Humanoids have been ingesting clay for at least two million years to ease indigestion and counteract poisons (Root-Bernstein & Root-Bernstein, 1999). However, the possible benefits of eating clays, such as gaining nutrients, are far outweighed by the likely negative consequences such as tissue abrasion, intestinal blockage, anemia, exposure to pathogens and toxic trace elements, and potassium overdose (Abrahams, 2013). However, popular books such as The Clay Cure (Knishinsky, 1998) tout a wide range of ailments that can be addressed by eating various clays. Young (Young, 2011) takes a more balanced approach when discussing the urge to eat clay. She devoted thirteen pages to describing some of the health benefits of clays and nine pages to describing some of the health problems that can be caused by ingesting clays.
Abrahams (2013), in his comprehensive discussion on geophagy, described the possible health benefits of this practice. Soils, commonly with clays as the active constituents, can be used as a food supplement during times of famine and for detoxification. He states that soils may be the world’s oldest pharmaceutical with clay tablets (terra sigillata) being used in Europe for some 2000 years to treat a variety of issues including plague, stings, animal bites, ulcers, gout, dysentery, poisoning, etc. Obviously, some applications were more effective than others. Hunter (1973) concluded that moderate ingestion of clays lacking large cation-exchange capacities could serve as a nutritional supplement for iron, copper, calcium, zinc, and manganese.
In their comprehensive review of clays used in health care and therapeutic products, Viseras et al. (2007) identified various clay minerals that are used in a range of commercial health care products. The clays may be the active ingredients or key inactive ingredients such as fillers, thickeners, gelling agents, etc. Many of these products are ingested to resolve intestinal problems such as indigestion and acid reflux. Aguzzi et al. (2007) describes an important new health-related application of clay minerals: their use as drug delivery systems. The clays are used to delay or target drug release or to improve drug dissolution. Mbila (2013) provided a useful discussion and a comprehensive list of medicines derived from soils.
Inhalation of Clay
The presence of clay coating on quartz grains may play an important role in preventing or minimizing silicosis. Wendlandt et al. (2007), examining surface coating of quartz in bentonites, concluded that “clay coating on quartz grains reduces their cytotoxicity.” Earlier, Meldrum & Howden (2002) speculated that quartz grains liberated and not fractured during coal mining retain their clay mineral coating and would be less dangerous, as the amount of ‘free’ quartz surface, rather than the total amount of quartz present in respirable coal mine dust, may be the most relevant factor to the risk of coal worker’s pneumoconiosis.
No reports were found that suggest inhalation of clays alone could be beneficial.
Dermal Contact of Clay
Recent studies by Williams and co-workers (Haydel et al. 2008; Londono et al. 2017; Morrison et al. 2016; Williams et al., 2004) highlighted the remarkable effectiveness of using clay poultices to treat Buruli ulcer, a horrendous flesh-eating bacterium that is resistant to antibiotics. Their research is focusing on the crystallographic and chemical properties of the clays that result in effective antibacterial properties. The use of clays to treat a range of skin issues is not a recent innovation. Clay poultices were widely used in ancient times to stem bleeding, kill bacteria, and cure certain skin ailments. Clay poultices also found use in the military throughout World War I (Reinbacher, 2003).
Viseras et al. (2007) pointed out the many uses of clays in health care and therapeutic products and described their use in ointments, toothpaste, cleansing lotions, pastes, make-up, shampoos, anti-acne creams, anti-perspirants, and agents providing protection from the sun, grease, dust, water, etc. Carretero (2002) reviewed the many topical applications of clays such as their use in dermatological protectors, cosmetics, and excipients followed by descriptions of their use in spas for geotherapy (mixed with water) and pelotherapy (mixed with salt water), mud baths, and paramuds (mixed with paraffin). The clays adsorb toxins from skin and provide heat to stimulate circulation for rheumatism treatment. This application of clays was also reviewed by Veniale et al. (2007) who described pelotherapy as addressing muscle, bone, and skin pathologies and is now used for general wellness and relaxation. They pointed to the need for standardization and certification to ensure that the treatments do not produce non-beneficial effects.
Another problem caused by contact with clay was reported by Cross (1919). He described tunneling military troops who were greatly affected by sores which had incapacitated three to four thousand men. The clay in the tunnel walls was found to remove the natural greases from the skin which then dried and cracked leading to infections.
Powdered talc had been widely used as baby powder, an astringent powder used to prevent diaper rash, until some of the powdered talc was found to contain asbestos (Gordon et al. 2014). Subsequently, the suggestion was that the use of talcum powder on female genitalia could lead to ovarian cancer. Berge et al. (2017) conducted a meta-analysis using 24 case-control studies and three cohort studies including 302,705 women with ovarian cancer. They found a weak but statistically significant association between genital application of talc and ovarian cancer. However, to be certain that the clay was the causative agent rather than impurities, the mineralogical purity of the clay would need to be determined.
All Routes of Exposure
Exposure to potentially toxic heavy metals such as arsenic, lead, mercury, cadmium, chromium, nickel, etc., in soils and clays can arise from ingestion, inhalation, or dermal contact (Morgan, 2013). However, health problems are most likely, though not exclusively, due to exposure to soils that have been contaminated by anthropogenic activities rather than natural soils.
Other Possible Health Impacts of Clays (Or the Lack Thereof)
Mseleni joint disease
Mseleni joint disease is a crippling disease reported mainly in the Maputaland region in South Africa. It is characterized by pain and stiffening of the hip joints as well as the knees, ankles, wrists, shoulders, and elbows, eventually compromising a patient’s ability to walk. The cause is unknown. Ceruti et al. (2003) found, however, that based on analysis of the soils in the region, the area was covered by Quaternary sands consisting primarily of quartz with <4% clays, primarily kaolinite (Fig. 6). Analysis of the soils indicated that they were deficient in P, S, K, Ca, Cu, and Zn and border-line in Mn and B. Of the essential elements probed, only Mg and Fe were not deficient. Analysis of corn, a major staple of the diet, also indicated deviancies in the essential elements. The implication of this study is that the absence of clays containing essential nutrients may be an important contributory factor in the etiology of this disease.
Clays may play a role in the development of the tick responsible for Lyme disease. Bunnell et al. (2003) concluded that soil moisture and soil type had significant associations with tick abundance.The abundance and type of clays in the soil were possible contributory factors.
Kashen-Back and Keshan
These are endemic osteoarthritic diseases that commonly result in serious deformities, muscular dystrophy, and liver necrosis. These diseases primarily occur in a northeast to southwest trend in central China. Many studies have recognized the relationship of these diseases to selenium-deficient soils (Tan et al., 2002) but few studies discussed clay abundance, type, or chemistry (see, for example (Lv et al., 2014)).
Could clay play a role in Alzheimer’s disease? Aluminum has been associated with neurodegenerative disorders such as Alzheimer’s disease. Perl & Moalem (2006) concluded that the presence of aluminum with its high binding capacity may play a role in either the etiology or pathogenesis of the disease. However, the source of the aluminum and means of entry to the brain remains a mystery. They also pointed out that aluminum accumulates in the brains of people suffering from Parkinson’s disease and from Amyotrophic Lateral Sclerosis.
Other issues may include the health impacts of radionuclides in soil (Turick et al. 2013) and the influence of soil on water quality (Helmke & Losco, 2013) and on agricultural crops (Heckman, 2013). Finally, Brevik (2013) raises an interesting question. Will climate change alter the weathering cycle, thereby affecting the clays in soil and, thus, their impacts on human health?
Medical geologists, whether their background is in clay mineralogy, crystallography, geochemistry, sedimentology, hydrogeology, etc., can play a critical role in assisting the medical/public health communities in addressing the myriad impacts that clays have on human health. Medical geologists can provide insights into the complex chemical, physical, and structural properties of these remarkable minerals, including their high adsorption, and cation exchange capacities. These specialists can identify associated minerals that cause health problems, such as the quartz and the asbestos that occurred with vermiculite in Libby, Montana (Schneider & McCumber, 2004). Medical geologists can identify human pathogens that are hosted by clays (Lyles, 2018), or clays that inhibit the growth of human pathogens (Williams, 2017). They can generate maps showing the distribution of clay types whose properties may impact human health. Medical geologists should also be involved in developing standards and certification for soils and clays used in geophagy to ensure that they are appropriate for that purpose. In all of these activities, medical geologists must collaborate with soil scientists, clay mineralogists, and biomedical/public health researchers to help maximize the health benefits of clays and minimize their negative health impacts.
- Abrahams, P.W. (2013). Geophagy and the in voluntary ingestion of soil. In: O. Selinus, B. Alloway, J.A. Centenoi, R.B. Finkelman, R. Fuge, U. Lindh, & P. Smedley (Eds.), Essentials of medical geology: revised edition (pp. 433–454). Dordrecht, The Netherlands: SpringerGoogle Scholar
- Aguzzi, C., Cerezo, P., Viseras, C., & Carmella, C. (2007). Use of clays as drug delivery systems: Possibilities and limitations. Applied Clay Science, 36, 22–36.Google Scholar
- Berge, W., Mundt, K., Luu, H., & Boffetta, P. (2017). Genital use of talc and risk of ovarian cancer: a meta-analysis. European Journal of Cancer Prevention, 27, 248–257.Google Scholar
- Brevik, E. C. (2013). Climate change, soils, and human health. In: E.C. Brevik & L.C. Burgess (Eds.). Soils and Human Health (pp. 345– 383). Boca Raton, Florida, USA: CRC Press.Google Scholar
- Ceruti, P.O., Fey, M., & Pooley, J. (2003). Soil nutrient deficiencies in an area of endemic osteoarthritis (Mseleni Joint Disease) and dwarfism in Maputoland, South Africa. In: H.C.W. Skinner & A.R. Berger (Eds.). Geology and Health: Closing the Gap (pp. 151–154). New York: Oxford University Press.Google Scholar
- Davey, G., Tekola, F., & Newport, M.J. (2007). Podoconiosis: non-infectious geochemical elephantiasis. Intensive and Critical Care Nursing, 101, 1175–1180.Google Scholar
- Dubovsky, H. (1999). Pneumoconiosis and tractor ploughing. South African Medical Journal, 89, 366.Google Scholar
- Egan, T. (2006). The Worst Hard Time. Houghton Mifflin Co. Boston, Massachusetts, USA. 340 p.Google Scholar
- Gomes, C.S.F. & Silva, J.B.P. (2007). Minerals and clay minerals in medical geology. Applied Clay Science, 36, 4–21.Google Scholar
- Heckman, J.R. (2013). Human contact with plants and soils for health and wellbeing. In: E.C. Brevik & L.C. Burgess (Eds.). Soils and Human Health (pp. 227–240). Boca Raton, Florida, USA: CRC PressGoogle Scholar
- Helmke, M.F. & Losco, R.L. (2013). Soil’s influence on water quality and human health. In: E.C. Brevik & L.C. Burgess (Eds.), Soils and Human Health (pp. 155–176). Boca Raton, Florida, USA: CRC Press.Google Scholar
- Henry, J.M. & Cring, F.D. (2013). Geophagy: An anthropological perspective. In: E.C. Brevik & L.C. Burgess (Eds.), Soils and Human Health (pp. 179–198) Boca Raton, Florida, USA: CRC PressGoogle Scholar
- Hooda, P.S., Henry, C.J.K, Seyoum, T.A., Armstrong, L.D.M., & Fowler, M.B. (2002). The potential impact of geophagia on the bioavailability of iron, zinc and calcium in human nutrition. Environmental Geochemistry and Health, 24, 305–319.Google Scholar
- Knishinsky, R. (1998). The Clay Cure. Healing Arts Press, Rochester, Vermont, USA. 104 pp.Google Scholar
- Lyles, M.B. (2018). Biological, chemical, and environmental hazards of desert dust to military personnel. In: B. De Vivo, H.E. Belkin, & A. Lima (Eds.), Environmental Geochemistry, Second Edition (pp. 467–485). Elsevier, Amsterdam.Google Scholar
- Mbila, M. (2013). Soil minerals, organisms, and human health: Medicinal uses of soils and soil material. In: E.C. Brevik & L.C. Burgess (Eds.), Soils and Human Health (pp. 199–213). Boca Raton, Florida, USA: CRC Press.Google Scholar
- Meldrum, M. & Howden, P. (2002). Crystalline Silica: Variability in fibrogenic potency. Annuals of Occupational Hygiene, 46, 27–30.Google Scholar
- Morgan, R. (2013). Soil, heavy metals, and human health. In: E.C. Brevik & L.C. Burgess (Eds.), Soils and Human Health (pp. 59–92). Boca Raton, Florida, USA: CRC Press.Google Scholar
- Morman, S.A., & Plumlee, G.S. (2014). Dust and human health. In: P. Knippertz & J.-B.W. Stuut (Eds.), Mineral Dust (pp. 385–409). New York: Springer.Google Scholar
- Morrison, K.D., Misra, R., & Williams, L.B. (2016). Unearthing the antibacterial mechanism of medicinal clay: A geochemical approach to combating antibiotic resistance. Scientific Reports, 6, Article number: 19043.Google Scholar
- Perl, D.P. & Moalem, S. (2006). Aluminum, Alzheimer’s disease and the geospacial occurrence of similar disorders. In: N. Sahai & M.A.A. Schoonen (editors), Medical Mineralogy and Geochemistry (Vol. 64, pp.115–134). Reviews in Mineralogy and Geochemistry, Mineralogical Society of America and Geochemical Society, Chantilly, Virginia, USA.Google Scholar
- Reinbacher, W.R. (2003). Healing Earths: The Third Leg of Medicine: A History of Minerals in Medicine.1st Books, 244 pp.Google Scholar
- Root-Bernstein, R. & Root-Bernstein, M. (1999). Honey, Mud, Maggots and Other Medical Marvels. Macmillan, London, 279 pp.Google Scholar
- Ross, M., Nolan, R.P., Langer, A.M., & Cooper, W.C. (1993). Health effects of mineral dusts other than asbestos. In: G.D. Guthrie, Jr. & B.T. Mossman (Eds.). Health Effects of Mineral Dusts (Vol. 28, pp. 361–407) Reviews in Mineralogy. Mineralogical Society of America, Chantilly, Virginia, USA.Google Scholar
- Schneider, A. & McCumber, D. (2004). An Air that Kills. Berkley Books, New York, 442 pp.Google Scholar
- Selinus, O, Alloway, B., Centeno, J.A., Finkelman, R.B., Fuge, R., Lindh, U., & Smedley. P. (editors) (2013). Essentials of Medical Geology: Revised Edition. Springer, Dorderecht, The Netherlands, 805 pp.Google Scholar
- Staubach, S. (2005). Clay. Berkley Books, New York, 288 pp.Google Scholar
- Tse, L.A., Dai, J., Chen, M., Liu, Y., Zhang, H., Wong, T.W., Leung, C.C., Kromhout, H., Meijer, E., Liu, S., Wang, F., Yu, I.T-s., Shen, H., & Chen, W. (2015). Prediction models and risk assessment for silicosis using a retrospective cohort study among workers exposed to silica in China. Scientific Reports, 5, Article number: 11059.Google Scholar
- Turick, C.E., Knox, A.S. & Kuhne, W.W. (2013). Radioactive elements in soil. In: E.C. Brevik & L.C. Burgess (Eds), Soils and Human Health (pp. 137–154). Boca Raton, Florida, USA: CRC Press.Google Scholar
- Williams, L. B., Holland, M., Eberl, D. D., Brunet, T., & Brunet de Courrsou, L. (2004). Killer Clasys! Natuaral antibacterial clay minerals. Mineralogical Society Bulletin, 139, 3–8.Google Scholar
- Young, S.L. (2011). Craving Earth. Columbia University Press, New York, 228 pp.Google Scholar