A Comparison of the Historical Lead Pollution Records in Peat and Freshwater Lake Sediments from Central Scotland

Abstract

The concentrations, inventories, fluxes and isotopic composition of Pb in four 210Pb-dated cores from the raised Flanders Moss peat bog are compared with corresponding data for two sediment cores from Loch Lomond, also in central Scotland. Although the inventories and fluxes of Pb revealed by the peat record for the past few hundred years are generally lower, the isotopic records are in good agreement, confirming a prevailing 206Pb/207Pb ratio of 1.17 for anthropogenic ("industrial") Pb in the atmosphere prior to the introduction of leaded petrol in the 1920s. The 206Pb-depleted nature of the latter has resulted in a decline of about -0.04 to -0.05 in the 206Pb/207Pb ratio of deposited Pb for both peat and lake sediments. Despite the time-resolution limitations of the peat record, car exhaust emissions of Pb appear to have contributed 35-50% over the past 20 years, 15-30% over the past 75 years, but no more than 27% overall to the peat Pb burden. The finding that 67-85% of anthropogenic Pb in the peat was apparently deposited post-1900 compared with 51% for the Loch Lomond sediments could be due to geographical variations in atmospheric deposition of Pb, other additional inputs to the sediments, or perhaps to some post-depositional loss of Pb from peat, although the integrity of the 206Pb/207Pb record does argue against any significant vertical mobility of Pb in peat.