VOA标准英语2008年-Fireworks Industry Studying More Eco-Friendly P

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.
　
July 4th fireworks over Washington DC

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 actively¹ assessing the impact of fireworks and working to make them safer for the environment.

Among the chemicals used in fireworks, perchlorates have drawn² 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 impaired³ 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 nominal⁴ in terms of what other industries use or discharge. Look at the military, [which is the] biggest contributor," she adds.

Julie Heckman notes that U.S. government regulations prohibit fireworks from containing even more-toxic substances such as lead and arsenic⁵. 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 copper⁶ compounds.

"If chlorine combines with copper you get blue color and no green. Or if the temperature is too high of the combustion⁷ 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.

1 actively   

adv.积极地，勤奋地

参考例句：

• During this period all the students were actively participating.在这节课中所有的学生都积极参加。
• We are actively intervening to settle a quarrel.我们正在积极调解争执。

2 drawn   

v.拖，拉，拔出；adj.憔悴的，紧张的

参考例句：

• All the characters in the story are drawn from life.故事中的所有人物都取材于生活。
• Her gaze was drawn irresistibly to the scene outside.她的目光禁不住被外面的风景所吸引。

3 impaired   

adj.受损的；出毛病的；有（身体或智力）缺陷的v.损害，削弱( impair的过去式和过去分词 )

参考例句：

• Much reading has impaired his vision. 大量读书损害了他的视力。 来自《现代汉英综合大词典》
• His hearing is somewhat impaired. 他的听觉已受到一定程度的损害。 来自《现代汉英综合大词典》

4 nominal   

adj.名义上的；(金额、租金)微不足道的

参考例句：

• The king was only the nominal head of the state. 国王只是这个国家名义上的元首。
• The charge of the box lunch was nominal.午餐盒饭收费很少。

5 arsenic   

n.砒霜，砷；adj.砷的

参考例句：

• His wife poisoned him with arsenic.他的妻子用砒霜把他毒死了。
• Arsenic is a poison.砒霜是毒药。

6 copper   

n.铜；铜币；铜器；adj.铜(制)的；(紫)铜色的

参考例句：

• The students are asked to prove the purity of copper.要求学生们检验铜的纯度。
• Copper is a good medium for the conduction of heat and electricity.铜是热和电的良导体。

7 combustion   

n.燃烧；氧化；骚动

参考例句：

• We might be tempted to think of combustion.我们也许会联想到氧化。
• The smoke formed by their combustion is negligible.由它燃烧所生成的烟是可忽略的。