Approximately 2,000 tons of mercury enters the environment annually from such human-generated sources as incinerators, chlorine-producing plants and coal-burning power plants, the scientists said. Mercury exposure can damage the human heart, immune system and central nervous system, while in wildlife it can also interfere with reproduction, growth, development and behavior and may even cause death.

"There has been a lot of controversy about how much mercury is coming from different types of industrial activities, compared to natural sources, but it has been difficult to figure out the relative contributions," said study co-author Joel Blum, a University of Michigan professor.

Blum and his colleagues say they've developed a method of reading mercury "fingerprints" in coal and other sources of mercury. The technique relies on a natural phenomenon called isotopic fractionation, in which different isotopes of mercury react to form new compounds at slightly different rates.

Blum said he envisions using the technology in a number of ways to track mercury and assess its environmental effects.

The research is detailed in the online edition of the journal Environmental Science & Technology.