In the United States and other developed countries, fluoride is often added to drinking water and toothpaste to help strengthen teeth. But too much naturally occurring fluoride can have exactly the opposite effect. Large amounts of fluoride can lead to dental fluorosis and skeletal fluorosis.

"Dental fluorosis is a darkening or mottling of the teeth, and you can tell very easily when people smile, because their teeth will be dark and discolored," says Laura Brunson, environmental scientist at the University of Oklahoma (OU) in Norman, Okla. Skeletal fluorosis is much more debilitating.

With support from the National Science Foundation (NSF), Brunson is working on methods of removing fluoride from drinking water, using tools and raw materials readily available in local communities. Brunson and her team recently returned from a month of fieldwork in Ethiopia, where they tested filtering methods using charred bones and charred wood.

"We'd prefer to find filtration materials that don't have to be shipped in from another country, and that are inexpensive," says Brunson.