| Lead deposits, which accumulated in
soil and snow during the 1960’s and 1970’s, 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 world-wide 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 (北极的) snow were declining. In his A. lead deposits in arctic snow are on the increase B. the Clean Air Act has not produced the desired results C. the US is the major source of lead pollution in arctic snow D. lead will stay in soil and snow longer than expected 更多"Passage Four Lead deposit"的相关试题:我来回答: 提交
|
