Changes in the occurrence of heavy metals in the tropical atmosphere during the past 22 , 000 years as recorded in Bolivian ice core

Nine sections from the Sajama ice core recovered from the summit of an extinct Andean volcano in Bolivia were analysed for various heavy metals to assess anthropogenic changes in the tropical upper troposphere over South America. These sam ples include two sections dating from 14, 100 to 19,200 years BP, corresponding to the Last Glacial Stage (LOS), one section dating from 2800 years BP (the late Holocene), and six sections dating from AD 790 to 1988. Our preliminary data, combined with data reported elsewhere, demonstrate that the heavy metal concentrat ions since the late Holocene are higher than in the period from the LOS to the early Holocene. The enrichment factors calculated by normalizing for crustal abundance using the metal / Al rat io in the mean upper continental crust indicate that a significant input of heavy metals attributed to anthropogen ic contributions has occurred since the beginning of the 19th century for Pb and from the last century for Cd, Cu, and Zn.