Clay is most commonly associated with the sublime experience of the European spa. Visitors have been masked, soaked, and basted with this touted curative since the Romans ruled. But go back further still and you'll find that clay has had a role in human health as ancient as man.
The first proof of the therapeutic use of clays was incised on clay tablets in Mesopotamia around 2500 B.C. However, some scholars believe that prehistoric ancestors such as Homo erectus and Homo neanderthalensis used ochres to cure wounds as well as paint caves. Ochres are a mixture of clay and iron hydroxides.
In Egypt, Cleopatra used clays to preserve her complexion. But the Pharaohs' physicians used the material as anti-inflammatory agents and antiseptics. It was also an ingredient used for making mummies.
Despite a long history of use, some very fundamental questions remain about the benefits of clay.
Can clays cure? At Arizona State University, geochemist Lynda Williams and microbiologist Shelley Haydel have teamed up to find out. If their research into the antibacterial properties of clays realizes its full potential, smectite clay might one day rise above purely cosmetic use. It might take its place comfortably with antibacterial behemoths like penicillin.
"People are interested in natural cures and I think that there is a lot of nature that we don't understand yet," Williams says. "What if we unearth a mechanism for controlling microbes that had never been discovered before? It is these avenues, at the boundaries of scientific discovery, at the edges of my field and knowledge (and Shelley's), where such discoveries are made."
Williams and Haydel's research is an unusual pairing. Both work in the College of Liberal Arts and Sciences. But both are pursuing different lines of scientific discovery.
Williams is an associate research professor in the School of Earth and Space Exploration. She studies clay geochemistry. Haydel is an assistant professor in the School of Life Sciences and with the Center for Infectious Disease and Vaccinology in the Biodesign Institute. She studies tuberculosis.
This disparate duo is attempting to tease apart the mechanisms that allow two clays mined in France to heal Buruli ulcer. The flesh-eating bacterial disease is found primarily in central and western Africa.
Buruli ulcer has been declared to be "an emerging public health threat" by the World Health Organization (WHO). Mycobacterium ulcerans is the bacterium that causes Buruli ulcer. It is related to the microorganisms that cause leprosy and tuberculosis. The bacterium produces a potent toxin that causes necrotic lesions. It destroys the fatty tissues under the skin.
"The toxin is immunosuppressant. Patients feel no pain and the body mounts no response to infection. It leads to disfigurement and isolation, not unlike that seen in leprosy," Haydel explains. "Traditional antibiotics can only make a difference at the very earliest stages of the disease. As a result, past treatments have been largely confined to amputations or surgical excision of the infected sites."
If the clays being studied actually are antibacterial in nature, and the reason for that activity can be isolated, the ASU scientists say they may represent a new form of topical treatment. It would be a treatment that goes beyond the capacity of existing antibiotics.
"They could be produced and distributed cheaply and easily stored," Williams says. That would make them ideal for use in developing countries.
So how did a clay specialist with a background in low temperature geochemistry become involved with a health care project centered in the Ivory Coast? It was the result of the scientific equivalent of an online dating service.
"I answered a posting on the Clay Minerals Society list serve placed by Thierry Brunet de Courssou. He was asking to have someone take high resolution scanning electron micrographs of the clays," Williams explains. "I confess that we all ignored him initially."
According to the Brunet de Courssou Web site, the family operates health clinics on the Ivory Coast and in New Guinea. For a decade, Madame Line Brunet de Courssou, Thierry's mother, had been importing two French clays to treat people with Buruli ulcer. She was getting startling results, while her use of native clays had no effect.
Williams reviewed the mother's work and says that "Line Brunet de Courssou was a careful observer."
However, she was not a scientist. The mother is now deceased. But in 2002, she approached the WHO during its fifth advisory group meeting on Buruli ulcer. She had documented more than 50 cases of successful healing with the clay treatments. WHO documents indicate that the organization was receptive. They called her results "impressive." But Williams says that funding was denied for lack of scientific study.
Williams is from a family of physicians. She says that it was really the second message that finally drew her to the project.
"Brunet de Courssou wrote, Ã¢â‚¬ËœI guess that no American scientists are interested in helping poor people in Africa.'"
He guessed wrong. Williams got 100 grams of the clay in green powder form. She took the requested micrographs of the minerals. She also went a step further and examined their crystal structure and chemical compositions.
Williams then contacted and recruited Haydel to the project before the microbiologist actually arrived at ASU in 2005. Haydel brought more than 13 years of experience working with pathogenic bacteria, in particular tuberculosis, to the project.
"I approached this work from the viewpoint of a clinical microbiologist," Haydel says. "I ordered bacterial strains that pharmaceutical companies use to test their antimicrobials."
Haydel tested both of the French clays that Brunet de Courssou had been importing. One completely inhibited pathogenic Escherichia coli, Salmonella typhimurium and Pseudomonas aeruginosa, often a problem as an opportunistic infection in burn wards. It stoppedMycobacterium marinum (related to Mycobacterium ulcerans) as well.
The clay also partially inhibited the growth of pathogenic Staphylococcus aureus, including a multi-drug resistant variety.
"The other clay actually helps the bacteria to grow," Haydel adds.
What makes one clay kill bacteria, and the other promote growth? And why do most clays tested have no effect? Williams and Haydel hope that their research will answer these and other questions.
"Clay can be as variable as the bacteria we are studying. There is a lot to be learned yet," Williams says,
Williams' career fascination with clay started when she was a mineral exploration geologist looking for ore deposits. She worked at Dartmouth College with Bob Reynolds, "the father of clay mineralogy." She later worked as a research associate at Louisiana State University. A colleague there was studying geophasia Ã¢â‚¬â€œ eating clay. The behavior has been seen in animals and people since the time of the aborigines.
"In the South Appalachian Mountains, poor women would eat the local clay to help soothe nausea and stomach ailments, particularly during pregnancy," Williams explains. "The clay was rich in kaolinite. (Kaolinite is the major ingredient in the over the counter remedy Kaopectate). But one day, they ran out of clay and moved over to another mountain and people began dying. We wanted to know why."
Not all clays are alike. The key to clay's variable nature seems to be its physical structure.
"Clay is a mineral. It has a crystalline structure that is both flexible and fluid," Williams says. She likens them to very thin, two-nanometer-thick slices of bread in a peanut butter and jelly sandwich.
The "bread" is composed of three regions. Two silicate layers with tetrahedral rings surround an octahedral core. The "peanut butter" is the charged cations. For example, potassium ions stick to the negatively charged tetrahedral ring surface.
And the "jelly"? Organic compounds or other species of any or no charge are possible. In a clay sandwich, the peanut butter and jelly are called the interlayer. The interlayer can vary in width and composition depending on the kinds of water and elements present when it was formed.
Molecular structure of smectite clays
The ASU scientists say that it is this interlayer where much of the elemental variability between clays can be found. And the interlayer surface area is huge. Each gram of clay contains hundreds of square meters of surface area. As a result, surface chemical reactions from these sites have an enormous impact on the geochemistry of the local environment.
Williams is passionate about her subject. "Clays are as individual in character as people are in personality," she says. "They can be as old as Precambrian times—anywhere from 700 million to 4.6 billion years ago. They are probably older, since meteorites contain clay minerals from other celestial bodies. Or they can be as young as the clays I made in my lab few hours."
Clays form when the chemistry, temperature, and pressure conditions are right, Williams continues. "In the case of the two French clays we are testing, their bulk chemical structures are almost identical. But the different trace element chemistry of the interlayer records differences in the depositional environment where the antimicrobial property was likely inherited."
Crystal structure, the interlayer, the way other materials, metals, or ions bind to clays, the absorptive characteristics of clays; all are important. All could potentially play a role in the antibacterial activity the scientists find in the one French clay.
Preliminary results suggest that the antibacterial activity is associated with the interlayer. But Williams says that crystal size and surface properties may also play a role. It is a mystery that engages both research partners.
"It's fascinating," Haydel says. "Here we are bridging geology, microbiology, cell biology—transdisciplinary sciences. A year ago, I'd look at the clay and say, 'well that's dirt.' Now I know a little something about clay structure and Lynda knows a little bit about microbiology. Alone, we each would have had to study for years. Together we are partnering these disciplines with synergy that really works."
Williams and Haydel both expect to find the key to the mystery of what makes this French green clay heal.
Haydel adds: "I had a professor in graduate school say, 'Maybe perhaps once in your life, in your scientific career, you'll come across something that can change the world.' Sometimes I think: This is it!"
Research on the healing properties of clay is supported by the National Center for Complementary and Alternative Medicine at National Institutes of Health (NCCAM). NCCAM was established in 1998 to fund scientific research and technologies that fall outside conventional medicines. For more information, contact Lynda Williams, Ph.D., School of Earth Science & Space Exploration, 480.965.0829. Or Shelley Haydel, Ph.D., Biodesign Institute, 480.727.7234. Send e-mail to Lynda.Williams@asu.edu or to Shelley.Haydel@asu.edu