Peat bogs in northern Alberta, Canada reveal decades of declining atmospheric Pb contamination

Peat cores were collected from six bogs in northern Alberta to reconstruct changes in the atmospheric deposition of Pb, a valuable tracer of human activities. In each profile, the maximum Pb enrichment is found well below the surface. Radiometric age dating using three independent approaches (C-14 measurements of plant macrofossils combined with the atmospheric bomb pulse curve, plus Pb-210 confirmed using the fallout radionuclides Cs-137 and Am-241) showed that Pb contamination has been in decline for decades. Today, the surface layers of these bogs are comparable in composition to the cleanest peat samples ever found in the Northern Hemisphere, from a Swiss bog similar to 6000 to 9000 years old. The lack of contemporary Pb contamination in the Alberta bogs is testimony to successful international efforts of the past decades to reduce anthropogenic emissions of this potentially toxic metal to the atmosphere.