Body and soil

To Joseph Ayotte, the story of contamination in New England's drinking water began more than 500 million years ago.

Researchers have long known about the troubling presence of arsenic in well water across great swaths of the region, a problem that affects thousands of people. Even in trace amounts, arsenic can damage the body, delaying the development of the brain and causing cancer and other problems. Yet, for a long time, nobody knew for sure where the arsenic was coming from.

But over the last few years, Ayotte and his colleagues at the New Hampshire office of the United States Geological Survey have found the culprit in the rocks below their feet. One of the offenders, he said, was a stretch of rock that formed under an ancient ocean a half-billion years ago, then was buried, heated, twisted, and cracked by a long series of geological events. This left the rock peppered with minerals containing arsenic. As rainwater makes its way down through the cracks in the rock, it dissolves some of the minerals, and, in certain conditions, releases arsenic into the water supply.

Ayotte, who is now working on detailed maps of the arsenic threat, belongs to an emerging scientific discipline known as ''medical geology." As distinct as the study of geology may seem from medicine, scientists are increasingly finding important connections between the two, from metals and minerals in drinking water, to dust carried around the planet by high-altitude winds, to the ways that rain, soil and climate interact to drive the spread of Lyme disease and the West Nile virus. With the new tools of modern geology -- especially computer-aided mapping -- these scientists, trained in the workings of granite and glaciers, are taking on a new role as public health workers.

''Making discoveries in your own field is exciting," said Ayotte, a hydrologist with the geological survey, who has led the arsenic research. ''But the fact that we can make these discoveries that can then be put to immediate use in a socially relevant way is wonderful."

In a sense, medical geology is an ancient field. Two millennia ago, Aristotle wrote of the illnesses associated with lead mining. But now, fueled by more advanced geological tools such as advanced mapping software known as ''geographical information systems," it is experiencing a renaissance. Work in the field is coming up more often at scientific meetings, scientists said, and professional societies, like the Geological Society of America, are doing more to recognize its practitioners. The prestigious journal Science recently featured an essay on the topic, written by a geologist working in Sri Lanka, summarizing medical geology issues arising throughout the developing world.

The human body and the Earth are intertwined at the most basic level. The minerals that form in rocks are ground down to soil, and this is taken up by plants. The cells of the human body rely on elements such as phosphorus to perform the metabolism that keeps us alive, as well as for a wide variety of other tasks. The body itself courses with elements that once lay encased in rock -- calcium, iron, potassium, magnesium, and many others.

''We are what we eat," said H. Catherine W. Skinner, a Yale University scientist who chairs a panel of the National Research Council looking into the most urgent priorities in earth science as it relates to public health.

These very elements, critical for life, can also cause problems in high doses. Over the last decade, for example, researchers have been finding that metals -- such as arsenic, lead, and cadmium -- are even more dangerous then they realized and that some of them likely play a role in chronic conditions such as hypertension and osteoporosis, according to Dr. Howard Hu, a professor of occupational and environmental medicine at the Harvard School of Public Health.

Yet, to understand how these substances come in contact with people means understanding how they form and how they move through the environment, which are challenging scientific questions.

There are many rocks that contain minerals with arsenic, for example, but only in certain conditions does the metal accumulate enough to pose a threat, said Ayotte. Many beds of rock in New England have been cracked, as erosion brought them to the surface and as heavy glaciers moved over them and then retreated. These fractures provide paths for water, which can draw out the arsenic. But, Ayotte said, the water needs to be alkaline and low in oxygen for the arsenic to accumulate. That, in turn, depends on the chemical reactions the rainwater undergoes as it makes its way from the surface soil to deep underground.

As his team has come to understand this process better, it has made maps of the arsenic threat around the region, making it possible to warn those at greatest risk. The team is currently working on an improved map, and also cooperating with the National Cancer Institute in a study of bladder cancer in the Northeast. Ayotte hopes to be able to predict how much arsenic is in the wells, so that epidemiologists can see if it is linked to the cancer.

Mapping geological features could also prove a key weapon against infectious diseases that are carried by animals. Lyme disease, which causes joint pain, fatigue, and heart and nervous system abnormalities, is carried and transmitted to people by deer ticks. The ticks' fate -- and thus the spread of the disease, is intimately tied to the environment, said Joseph E. Bunnell, a public health research biologist with the USGS. In a study published two years ago, Bunnell and other scientists collected ticks from 320 locations in five Middle Atlantic states and determined their infection rates. They found that the number of deer ticks were tied to a variety of features, such as soil type and elevation. In another study, published last year, Bunnell tied the number of human Lyme disease cases to the amount of rain in the late spring and early summer.

Eventually, Bunnell said, he hopes to devise a system that will make it possible to issue much more accurate, town-by-town warnings of the Lyme disease threats, thereby reducing the number of cases. This same approach could be used to study diseases carried by all kinds of organisms -- from mosquitoes to bats -- around the world, Bunnell and other scientists said.

In the developing world, medical geology is even more pressing, for the simple reason that people live in more intimate contact with their environment, said Chandra Dissanayake, a senior professor of geology at the University of Peradeniya in Sri Lanka, who recently wrote an essay on the topic for Science. He has examined the damage that fluoride does to teeth and bones when there is too much of it naturally in the water. (The amounts are much larger than what is intentionally put in American water supplies.) He is currently investigating the mounting cases of kidney disease in Sri Lanka, which he suspects are related to fluoride and other substances in the drinking water.

The problems of the developing world can travel, too. Dust kicked up by storms in drought-ridden sections of North Africa travels across the Atlantic and up through the Northeast, affecting air quality and potentially carrying bacteria, according to recent studies, which did not link the dust to specific human illnesses.

Other research has found that the primary source of pollution at Oregon's Crater Lake National Park is dust clouds from Asia, which travel across the Pacific Ocean, according to Kevin D. Perry, an assistant professor of meteorology at the University of Utah. The same winds carry the pollution of North America to Europe, and Europe's pollution to Asia, Perry said.

''We are all swimming in the same fishbowl."

Gareth Cook can be reached at cook@globe.com.