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.
21. The study published in the journal Nature indicates that ________.
A) the Clean Air Act has not produced the desired results
B) lead deposits in arctic snow are on the increase
C) lead will stay in soil and snow longer than expected
D) the US is the major source of lead pollution in arctic snow
22. Lead accumulation worldwide decreased significantly after the use of unleaded gas in the US ________.
A) was discouraged
B) was enforced by law
C) was prohibited by law
D) was introduced
23. How did scientists discover the source of lead pollution in Greenland?
A) By analyzing the data published in journals like Nature and Ambio.
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