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D. One of the Major Sources of Mercury Contamination

Narrator: This is Science Today. Mercury has recently been recognized as a major environmental concern because concentrations of mercury once considered safe are now known to cause neurological damage. Russ Flegal, an environmental toxicologist at the University of California, Santa Cruz, says one of the reasons controlling levels of mercury is so difficult is because mercury is so volatile as a gas.

Flegal: Large amounts of mercury are found in fossil fuel products so when they burn coal, that puts a lot of mercury into the atmosphere. So recently in the United States, they've gone at great lengths to control mercury emissions from coal production.

Narrator: Flegal says it used to be thought that simply plugging up openings to abandoned mercury mines could do this.

Flegal: But when they process mercury, they take the ores out and they heat them - they volatize whatever mercury they can and they push the slag rock over the hill, and that slag is essentially pure mercury sulfite anyway and so when it's exposed to the environment, it continues to release mercury.

Narrator: For Science Today, I'm Larissa Branin.