In the West, new technologies are being used to remove the heavy metals, including activated carbon. But these technologies are costly.

　　Compared with activated carbon, cilantro costs very little to produce. The herb is plentiful in some of the most polluted countries in the world. These are countries in which industrial chemicals have polluted ground water supplies. The chemicals include arsenic, cadmium, copper, lead and mercury. They can come from factories and waste collection centers.

　　Douglas Schauer at Ivy Tech Community College in Lafayette, Indiana led a few of his students to the Tula Valley, near Mexico City earlier this year. They wanted to find low­cost and plentiful materials that could be used to filter, or separate, industrial pollutants in ground water.

　　In the experiment, ten wild plants were tested. They were dried out and crushed. And then each of them was put into a solution(溶液) that has some lead in it. The researchers shook it up for a little, and then they let the particles settle out. Finally they tested the water to see how much lead was left behind. Mr. Schauer says his students' tests showed that, of the tested ten wild plants, cilantro was the most effective plant for pulling lead out of polluted water.

　　He suggests that cilantro be used as a water purifier. It is especially important, he says, for people living near polluting factories such as the Tula Valley, where Mexico City leaves all of its untreated city waste.

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