Lead deposits, which accumulated in soil and snow during the 1960s and 70s, were primarily the result of leaded gasoline emissions originating in the United States. In the twenty years that the Clean Air Act has mandated unleaded gas use in the United States, the lead accumulation worldwide has decreased significantly.
A study published recently in the journal Nature shows that air-borne leaded gas emissions from the United States were the leading contributor to the high concentration of lead in the snow in Greenland. The new study is a result of the continued research led by Dr. Charles Boutron, an expert on the impact of heavy metals on the environment at the National Center for Scientific Research in France. A study by Dr. Boutron published in 1991 showed that lead levels in arctic snow were declining.
In his new study, Dr. Boutron found the ratios of the different forms of lead in the leaded gasoline used in the United States were different from the ratios of European, Asian and Canadian gasolines and thus enabled scientists to differentiate the lead sources. The dominant lead ratio found in Greenland snow matched that found in gasoline from the United States.
In a study published in the journal Ambio, scientists found that lead levels in soil in the Northeastern United States had decreased markedly since the introduction of unleaded gasoline.
Many scientists had believed that the lead would stay in soil and snow for a longer period.
The authors of the Ambio study examined samples of the upper layers of soil taken from the same sites of 30 forest floors in New England, New York and Pennsylvania in 1980 and in 1990. The forest environment processed and redistributed the lead faster than the scientists had expected.
Scientists say both studies demonstrate that certain parts of the ecosystem respond rapidly to reductions in atmospheric pollution, but that these findings should not be used as a license to pollute.
1.The study published in the journal Nature indicates that
A.the US is the major source of lead pollution in arctic snow.
B.the Clean Air Act has not produced the desired results.
C.lead will stay in soil and snow longer than expected.
D.lead deposits in arctic snow are on the increase.
正确答案：A
解析：问题问的是：自然杂志上刊登的研究表明什么?第二段开头提到自然杂志上刊登的研究表明从产自美国通过空气传播的含铅气体排放是导致格陵兰雪地中铅浓度高的主要原因。而格陵兰就是位于北极圈内。因此A正确，美国是北极雪中铅污染的主要来源。
2.Lead accumulation worldwide decreased significantly after the use of unleaded gas in the US
A.was discouraged.
B.was prohibited by law.
C.was enforced by law.
D.was introduced.
正确答案：C
解析：美国法律强制使用无铅汽油后，世界范围的铅金属积累量明显减少了。第一段最后一句话支持这一说法，注意，文中的mandated与C选项中的enforced意思相同，都是强制的意思。
3.How did scientists discover the source of lead pollution in Greenland
A.By analyzing the data published in journals like Nature and Ambio.
B.By comparing the chemical compositions of leaded gasoline used in various countries.
C.By observing the lead accumulations in different parts of the arctic area.
D.By studying the chemical elements of soil and snow in Northeastern America.
正确答案：B
解析：问题问的是：科学家是怎样发现格陵兰的铅污染来源的?第三段提到科学家发现美国汽油中的各种铅金属比重不同于欧洲，亚洲和加拿大的。通过比较这些铅比的不同判断出格陵兰雪中铅污染主要来自美国。因此B正确。
4.The authors of the Ambio study have found that
A.forests get rid of lead pollution faster than expected.
B.lead deposits are widely distributed in the forests of the US.
C.lead accumulations in forests are more difficult to deal with.
D.the upper layers of soil in forests are easily polluted by lead emissions.
正确答案：A
解析：问题问的是：人类环境杂志研究的作者发现了什么?倒数第二段结尾提到森林环境处理铅的速度之快超出科学家们的预期。因此A正确。
5.It can be inferred from the last paragraph that scientists
A.feel relieved by the use of unleaded gasoline.
B.are puzzled by the mystery of forest pollution.
C.lack sufficient means to combat lead pollution.
D.still consider lead pollution a problem.
正确答案：D
解析：问题问的是：通过最后一段能推测出什么?最后一段提到了两项研究说明了某些生态系统对大气污染的减少给出了快速的回应，但是这并不能作为进一步的污染行为的许可证。因此D正确，科学家们仍然认为铅污染是个问题。