Lead deposits, which accumulated in Greenland's soil and snow during the 1960s and 1970s, were primarily the result of leaded gasoline emissions originating in the United States, according to a study published in the journal Nature.
In the 20 years that the Clean Air Act has mandated unleaded gas use in the United States, the lead accumulation worldwide has diminished significantly, but the Nature study shows that airborne 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 research led by Dr. Charles Boutron, an expert on the impact of heavy metals on the environment at the Laboratory of Glaciology and Environmental Geophysics of the National Center for Scientific Research in St.-Martin-d'Heres, France. A study by Mr. Boutron published in Nature in 1991 showed that lead levels in arctic snow were declining.
In his new study, Mr. 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 the 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 advent of catalytic converters and unleaded gasoline.
Many scientists had believed that the lead would linger in soil and snow for a longer period after emissions had ceased.
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, said Dr. Andrew J. Friedland, the leading author of the study and associate professor of environmental studies at Dartmouth College. He said his study used techniques similar to those used in Mr. Boutron's study showing declining lead levels in arctic snow.
Dr. Friedland said 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. Dr. Friedland has submitted new research for publication that, he said, describes where the lead from the forest soil is headed.
"Based on our preliminary assessments, we may see lead from the soil entering streams," said Dr. Friedland, "meaning it might end up entering our drinking water within the next 50 years."