Evidence from glacier ice: Until it was banned, leaded gasoline dominated the humanmade lead emissio

Evidence from glacier ice: Until it was banned, leaded gasoline dominated the humanmade lead emissions in South America
Date: March 6, 2015
Source: Paul Scherrer Institut (PSI)



View of the glacier on the Nevado Illimani in Bolivia.

Credit: Patrick Ginot

Leaded gasoline was a larger emission source of the toxic heavy metal lead than mining in South America -- even though the extraction of metals from the region's mines historically released huge quantities of lead into the environment. Researchers from the Paul Scherrer Institute PSI and the University of Bern have discovered evidence of the dominance of leaded gasoline based on measurements in an ice core from a Bolivian glacier. The scientists found that lead from road traffic in the neighbouring countries polluted the air twice as heavily as regional mining from the 1960s onwards. The study is to be published in the journal Science Advances on 6 March 2015.

The use of leaded gasoline was the dominant source of anthropogenic, i.e. human-made, lead emissions in South America from the 1960s onwards. The fuel even surpassed the thriving mining industry in this region of the world, which also releases large quantities of lead. In the past, measurements in the Northern Hemisphere had already revealed that emissions from leaded gasoline exceeded those of mining activities. However, such conclusive evidence was lacking for the Altiplano region in South America. On this plateau, located between the western and eastern Andes, extractive metallurgy from mineral ores has been releasing large amounts of lead into the environment since the pre-colonial era.

Evidence of this has now been discovered by researchers from PSI and the University of Bern using measurements from a 138 m long ice core, drilled out of the Nevado Illimani glacier in eastern Bolivia. Glacier ice is an invaluable archive of past air pollution. By drilling ice from deep below the glacier surface and analysing it in the lab, scientists can reconstruct, how high the concentrations of these air pollutants were in the past. The authors of the study have now succeeded in distinguishing local emissions from the Altiplano that can be attributed to mining from those originating from leaded gasoline that had been burnt mainly in more distant regions and carried along by the wind. Using a sensitive mass spectrometer, they determined the lead concentrations and the different composition of the isotopes in the lead from these two sources.

Isotopes are variants of a chemical element that differ from each other in their respective atomic weight. Chemically the various isotopes behave in the same way. Due to their differing weights, however, they can be separated in the mass spectrometer. Lead naturally occurs in the form of eight different isotopes. The four lighter ones are stable, while their four heavier counterparts decay radioactively. The origin of the lead in an environmental sample can be determined based on the different proportions of these isotopes. The researchers have now found the fingerprint for leaded gasoline revealed in the ratio of the two heaviest of the stable lead isotopes. "We detected a lower ratio of lead-208 to lead-207 after 1960," explains PSI researcher Anja Eichler, the first author of the study. "This isotope ratio deviates from that which is typical of lead from the Altiplano mines, but is in good agreement with the isotope ratio measured in the air in Chilean, Argentinean, and Brazilian cities in the 1990s. The majority of the lead in these air samples can clearly be traced back to leaded gasoline," adds Eichler..

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