Reservoir sediment cores show U.S. lead declines

As a result of the Clean Air Act, lead (Pb) emissions to the atmosphere have been greatly reduced since the mid-1970s. As part of its National Water Quality Assessment, the U.S. Geological Survey has been using paleolimnological techniques to assess past trends in hydrophobic contaminants. In urban-suburban environments, reservoir sediment cores show prominent peaks in Pb distributions that correlate well with the rise and fall of leaded gasoline. However, Pb concentrations in sediments are approximately double those of baseline values prior to the 1950s and 1960s. It is apparent that significant concentrations of anthropogenic Pb still exist in soils and aquatic sediments and that it will take many years to reduce these concentrations to prepollution values, even if there are no new sources of Pb pollution.