PAST AND RECENT CHANGES IN THE LARGE-SCALE TROPOSPHERIC CYCLES OF LEAD AND OTHER HEAVY-METALS AS DOCUMENTED IN ANTARCTIC AND GREENLAND SNOWAND ICE - A REVIEW

The investigation of the occurrence of lead and other heavy metals in Antarctic and Greenland ancient ice and recent snow is of great intere st in reconstructing the past natural tropospheric cycles of these met als and determining to what extent these cycles have now been altered by man. Because concentrations to be measured are exceedingly low, dow n to the sub pg/g level, reliable data can however be obtained only if full control of contamination is achieved from field sampling to labo ratory analysis. The available data show that the past natural concent rations of Pb, Cd, Zn, Cu, and Hg in Antarctic ancient ice are highly dependent upon climatic conditions, the highest values occurring durin g the coldest periods of the ice ages, especially during the Last Glac ial Maximum about 18,000 years ago. Human activity has led to an incre ase in lead concentrations during recent centuries both in Antarctica (tenfold increase) and in Greenland (two hundredfold increase). This l ast increase was followed by a 7.5-fold decrease during the past two d ecades, mainly as a consequence of the rapid fall in the use of lead a lkyl additives in the USA as confirmed by recent isotopic data.