Historical trends in the lead isotopic composition of archival Sphagnum mosses from Scotland (1838-2000)

The analysis of almost 200 Scottish Sphagnum moss samples collected over the past 170 years has revealed trends in the isotopic composition of lead similar to those previously established for dated Scottish lake sediments and peat bogs, lending credibility to these proxy records of atmospheric lead contamination and deposition. The effect of temporal variations in contributions from sources such as smelting of indigenous lead ores (Pb-206/Pb-207 similar to 1.16-1.18), coal combustion (Pb-206/Pb-207 similar to 1.17-1.19), and the use of imported Australian lead (Pb-206/Pb-207 similar to 1.04) was clearly seen in the Scottish moss Pb-206/Pb-207 record. This showed some differences from the corresponding archival herbage record for the south of England, where the initial influence of Australian lead occurred earlier, at the end of the 19th century. A significant decline from a Pb-206/Pb-207 value of similar to1.17 in the Scottish moss record began in the 1920s and continued until the 1980s (Pb-206/Pb-207 similar to1.12). The success of measures to reduce lead emissions to the atmosphere over the past 20 years in the U.K., in particular from petrol-engined vehicles using alkyl lead additives manufactured primarily from Australian lead, is evident in both the increasing Pb-206/Pb-207 ratio and failing lead concentration data for Scottish moss.