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As July 4th approaches, Americans look to the skies. Throughout the country, fireworks will be launched in celebration of the nation's independence. But what goes up must come down. Reporter Eric Libby looks at the environmental issues surrounding fireworks, and efforts to develop "greener" pyrotechnics.

Take a group of reactive chemicals, shoot them high into the air, and watch them explode in a very loud, very smoky, and very hot spectacle. This sounds like the exact opposite of an environmentally friendly, or green, activity. So researchers are actively assessing the impact of fireworks and working to make them safer for the environment.

Among the chemicals used in fireworks, perchlorates have drawn attention. These compounds provide the oxygen that fuels the explosion. Hydrogeologist David Jewett of the Environmental Protection Agency points to an EPA study measuring perchlorates in an Oklahoma lake after fireworks displays from 2004 to 2006. "They saw a peak in perchlorate concentrations within 12 or 14 hours after the fireworks display," says Jewett. "But then those concentrations decreased back to background levels over a time period of 20 to 80 days."

Studies have linked perchlorates to impaired thyroid function. While Julie Heckman, executive director of the American Pyrotechnics Association, acknowledges the potential health risks of perchlorates, she says their use in fireworks does not pose a danger to the public. "The position of the fireworks industry," Heckman explains, "is [that] the amount of pyrotechnic composition containing perchlorate is pretty nominal in terms of what other industries use or discharge. Look at the military, [which is the] biggest contributor," she adds.

She notes that U.S. government regulations prohibit fireworks from containing even more-toxic substances such as lead and arsenic. Another concern is the use of so-called heavy metals to give fireworks their colors. In particular, barium - which is responsible for the color green - is extremely poisonous in some forms. Mike Hiskey describes how his pyrotechnics company, DMD Systems, is addressing these concerns. "We base all our mixes on nitrocellulose, which burns very cleanly, with basically no smoke, (in)to carbon dioxide, water, and nitrogen. We can reduce the amount of heavy metals in there by quite a bit, like almost an order of magnitude," Hiskey adds. "In addition to that, all of our outdoor pyro contains no perchlorate."

Hiskey says there is growing interest in green fireworks, especially from indoor concert promoters and the Disney Company, one of the world's largest users of fireworks. Scientists at Germany's Ludwig Maximilian University of Munich are searching for ways to completely replace barium in fireworks. Graduate student Karina Tarantik says it's difficult to produce the color green with safer ingredients like copper compounds.

"If chlorine combines with copper you get blue color and no green. Or if the temperature is too high of the combustion you get more red or yellow flame color. So, [it is] quite difficult," she cautions.

Tarantik says the hardest color to make "green" is, in fact, green. Thankfully, the most important colors on the 4th of July are red, white, and blue.

(Source: VOA 英語(yǔ)點(diǎn)津姍姍編輯)