CHANGING CONCENTRATIONS OF CU, ZN, CD AND PB IN A HIGH-ALTITUDE PEAT BOG FROM BOLIVIA DURING THE PAST 3 CENTURIES

A core consisting of minerogenic peat and organic-rich mineral sedimen ts was collected at an altitude of 4275 m in the Ovejuyo valley, 100 k m NE of La Paz in Bolivia. Age dating with Pb-210 showed that the core represents approximately three centuries of sediment accumulation. No ne of the peats are ombrotrophic. Despite this, the Cd/Al, Cu/Al, Zn/A l, and Pb/Al ratios are all significantly higher in the surface layers , particularly in the top 6 cm: natural, abiological geochemical proce sses, therefore, cannot account for these elevated heavy metal/Al rati os. There are two possible explanations for the metal enrichments, rel ative to Al, in the surface layers: bioaccumulation by living plants, and anthropogenic atmospheric metal deposition. While the living plant layer may be responsible for the Cd, Cu, and Zn enrichments, this is an unlikely explanation for the Pb profile. In contrast to the other m etals, the concentration of Pb in the first sample (dating from 1985-1 994) is less than that of the second sample (dating from 1970-1985). T he Pb/Al profile is consistent with the well documented, rapid increas e in atmospheric Pb emissions during the present century (which accele rated following the introduction of leaded gasoline), and the decline in Pb pollution during the past 20 years (as a result of the introduct ion of unleaded gasoline). Thus, the Ovejuyo Valley mire has provided one of the first records of atmospheric Pb pollution in South America.