These medical puzzles are written in stone


From their investigations of elevated arsenic in northern Chilean groundwater to their detection of copper deficiency in Uruguayan pastureland, researchers are literally looking underfoot for answers to some of Latin America’s stubborn environmental-health problems.

The problem, specifically, is overexposure—or sometimes underexposure—to naturally occurring minerals, in some cases due to anthropogenic environmental disturbances. And concern about the impacts has led to the emergence of an investigatory discipline known as medical geology. “There are unique needs in Latin America,” says Puerto Rican toxicologist José Centeno, chief of the Biophysical Toxicology Division at the U.S. military’s Joint Pathology Center near Washington, D.C. “There are people suffering from arsenic in the drinking water and people suffering from emerging and reemerging diseases. These conditions are emerging or reemerging because we’re changing the environment. If we don’t understand those connections, how are we going to solve those problems?”

The connections are often rooted in combinations of minerals that make up the soil or are dissolved in streams and aquifers. They may remain hidden for decades, until disease appears, or they may burst out violently in volcanic eruptions like the ones that have showered hazardous ash over villages and city neighborhoods in Ecuador, Chile and Argentina.

The problems are often puzzles. While small amounts of minerals like copper, selenium, zinc and iron are important for health, an excess can be toxic to humans or animals. Tracing diseases to a geologic source requires understanding the balance between safety and toxicity and considering whether multiple elements have a combined effect.

The form in which those minerals occur also determines how easily they are absorbed and, therefore, how much of a health risk they represent. Those complications underscore the need for closer collaboration between health experts and geoscientists, Centeno says—teamwork that he has been promoting around the region over the past decade, and which practitioners now call medical geology.

“Medical geology is a relatively new term, but the health impact of natural elements has been known for thousands of years,” says chemist Robert Finkelman of the University of Texas, Dallas, one of the founders of the International Medical Geology Association.

Trace elements, minerals and natural organic compounds can have an impact on virtually every organ or tissue in the body, Finkelman says, and too much—or too little—can lead to health problems.

Perhaps the best-known example is a lack of the element iodine, which can cause goiter, reduced cognitive development, miscarriages and birth defects. Understanding health problems caused by iodine deficiency is “the trademark of medical geology,” Centeno says. And although iodine-enriched salt has largely solved the problem, about 7% of people in Latin America are still at risk, he says.

Where beneficial elements occur naturally, humans and other animals have learned to take advantage of them.

In parts of the Amazon basin, cliffs become riots of color and noise early in the morning as hundreds of parrots, parakeets and macaws arrive to peck at the clay. Tapirs and other mammals frequent natural salt licks there and in other regions. Humans in various parts of the world also eat certain types of soil to aid digestion, and there is archaeological evidence that Homo habilis might have been doing that 2 million years ago, Finkelman says.

Tracing the interactions of geology and health can take a bit of detective work. While sources of exposure—good or bad—are usually nearby, some may be halfway around the world.

When winds whip up blinding clouds of dust in the Sahara desert, the most obvious health effects are respiratory problems in African countries. But air samples and satellite photos show that Saharan dust spreads as far as Europe, South America and the Caribbean.

Studies show that dust from North Africa could be the largest source of phosphorous in the Amazon basin, and some experts suspect that pathogens hitching a ride on dust particles could be killing coral on Caribbean reefs.

Where harmful elements exist in local soil and water, health effects may not be obvious and the consequences could be serious. In many cases, there is little attention to potential hazards because of a lack of both scientific data and public awareness.

About 10 countries—including Peru, Chile, Brazil and Mexico—have identified or are exploring for uranium deposits. Uranium can pose a radioactivity hazard not just during mining and processing, but also in its natural state. Researchers in Chihuahua, Mexico, found high levels of radiation in wells and measurable levels in surface water near a naturally occurring uranium outcrop not far from the city, which is home to 3.4 million people. They have not yet evaluated possible health impacts, but the findings could point to a global need for monitoring water quality near uranium deposits and for testing local buildings for radon gas, which is associated with such deposits.

In some cases, elements deep in the earth pose a health hazard when they are released into the atmosphere in volcanic eruptions. In 2008, Chile’s Chaitén volcano belched a plume 20 kilometers (12 miles) high and blanketed a large swath of southern Chile and Argentina with ash.

Public health experts worried not only about inhalation of ash particles, but about the composition of the particles. Volcanic ash tends to be high in silica minerals, and some experts fear that long-term exposure could lead to lung problems from silicosis. Most eruptions in the Andes in recent years have been short-lived, but a series of eruptions on the island of Montserrat that began in 1995 continued for four years.

There are between 200 and 300 active volcanoes in the Andes between Colombia and Chile, and more than 20 million people live close to active volcanoes. Santiago, Chile, and Quito, Ecuador, are among the cities that could be within range of volcanic eruptions. Although people with respiratory problems are at particular risk, most volcano-related deaths are due to hot gases or roof collapses. Experts note that health and other public services may also be strained after an eruption, making residents more vulnerable to disease epidemics.

The volcanically active Andes are a source of another health risk. Arsenic-laced groundwater occurs naturally and has been linked to skin discoloration, stomach problems and various types of cancer. Seven thousand years ago, fishermen near what is now Arica, on the coast of northern Chile, apparently drank water so laden with arsenic that it can still be measured in the hair of the mummies they so carefully preserved.

More recently, a group of hospital residents doing what they thought was a routine epidemiology exercise found a bladder cancer cluster among people who were children in Antofagasta, Chile, when the city began drawing its drinking water from a river later discovered to carry high concentrations of arsenic.

Some scientists estimate that as many as 14 million people in Latin America could be exposed to unsafe levels of arsenic in their drinking water. The extent of the problem—which has been detected not only in Chile, but also in Argentina, Peru and Bolivia—led to a study of water sources in Uruguay, according to Nelly Mañay of the School of Chemistry at the University of the Republic of Uruguay. Mañay and other health and geoscience experts from Latin America discussed studies in their countries at a conference of the International Medical Geology Association held August 26 to 29 in Crystal City, Virginia. The association claims 400 members in 22 chapters worldwide, including groups in Brazil, Argentina, Uruguay, Bolivia and Colombia.

While Uruguay’s drinking water supply proved to be safe, says Mañay, who chairs the international association, other cases in the country have required geologic detective work. When cattle in Uruguay’s Salto department became ill, veterinarians traced the problem to a diet deficient in copper due to a lack of the element in the soil of pastures where the animals grazed. The challenge for Uruguayan researchers was to find a form of copper that the cattle could metabolize, and which could be added to their diet to compensate for the lack of copper in pastures, Mañay says.

Combining geologic and epidemiologic data is a key part of medical geology. In Brazil, a decade-long project that ended last year resulted in a geologic map of 12 states—30% of the country’s territory—based on more than 30,500 samples of soil, stream sediment, surface water and drinking water. The maps can serve multiple purposes, according to Eduardo De Capitani, a professor of medicine at the University of Campinas in Brazil. Mining companies can use the data to target sites for prospecting, while maps of micronutrients, such as zinc or manganese, could signal good lands for agriculture, De Capitani says.

By superimposing epidemiology data over the maps, health experts can pinpoint places where geologic factors could affect human or animal health. In some cases, those problems could be caused by too little of an essential element, such as the copper deficiency in Uruguay. In others, they may be triggered by too much of a good thing. While fluoride helps prevent and control tooth decay, for example, exposure to high fluoride levels when permanent teeth are forming can leave tooth enamel discolored or pitted, a condition known as fluorosis.

Fluorosis in Brazil

The Brazilian study showed that high levels of naturally occurring fluoride in surface water and soil in part of the São Francisco River basin corresponded to an area with high rates of dental fluorosis, De Capitani said in a presentation at the medical geology conference.

The geologic data also revealed high levels of arsenic around the Kinross Gold Corporation’s Paracatu mine in the state of Minas Gerais, where there is “a city of 65,000 people close to the open pit, and there has been great public concern about arsenic contamination,” De Capitani told the conference audience.

Researchers are examining cancer mortality data and looking for dermatological evidence, such as skin discoloration characteristic of arsenic poisoning. Although “first results show that drinking water is clean,” he said, experts are now comparing urine samples from people living close to the mine with those of a control group on the other side of the city.

As mining expands in the region, sorting out the facts in cases like that one—in which toxic metals could come from either natural sources or human activities—becomes increasingly important.

Residents living near mines often accuse their operators of polluting water, and although those accusations are sometimes justified, heavy metals may also come from natural sources. Scientists studying melting glaciers in the Peruvian Andes have found that some streams have high natural acidity, which could increase the amount of heavy metals dissolved in the water. (See “Retreat of glaciers raising stakes in Peru”—EcoAméricas, Feb. ’13.)

Proponents of medical geology say their research also could help defuse conflicts over manmade pollution by establishing baselines of the health situation of local residents and heavy metals that occur naturally in an area before companies begin mining or drilling for oil or gas. So says Diego Fridman, a professor in charge of medical geology at the University of Buenos Aires who formed a chapter of the International Medical Geology Association with a group of researchers investigating complaints about a mine in northern Argentina.

Fracking adds urgency

The looming likelihood of shale gas exploration in Argentina’s Neuquén region makes that need even more urgent, Fridman says. (See “Newly nationalized, YPF pins its hopes on fracking”—EcoAméricas, June ’13.) With a newly signed exploration agreement between Argentina’s YPF oil and gas company and Chevron, “now is the time to do health impact studies,” Fridman says.

Studies that would establish a baseline—a snapshot of the health situation in the region before fracking begins—would “make it possible to plan and reduce the negative impact, enhance the positive and know what needs to be mitigated,” he says.

Fridman and his colleagues have repeated that message in meetings with government officials, including a national Senate commission, he says, but so far there has been no official response. While such studies are unlikely to guarantee an end to mining disputes, they can reduce anxiety or change the tone of the debate, Fridman says.

“When you present solid technical elements, unfounded arguments often fall apart, and anyone who is going to present counterarguments has to be sure their evidence is solid,” Fridman says. “That helps ensure social peace. And if it turns out that there is a problem, it’s better for everyone to know.”

- Barbara Fraser

José Centeno
Division of Biophysical Toxicology
The Joint Pathology Center
Joint Base Andrews, MD, United States
Tel: (240) 857-6882
Eduardo De Capitani
Campinas Poison Control Center
School of Medicine
State University of Campinas
Campinas, Brazil
Tel: +(55 19) 3521-6700
Diego Fridman
Professor in charge of Medical Geology
School of Exact and Natural Sciences
University of Buenos Aires
Buenos Aires, Argentina
Tel: +(54 11) 4576-3300
Nelly Mañay
Department of Toxicology and Environmental Hygiene
School of Chemistry
University of the Republic of Uruguay
Montevideo, Uruguay
Tel: +(59 82) 924-1809