MERCURY ATMOSPHERIC DEPOSITION RECORDED FROM DATED PEAT BOG CORES IN SOUTH AMERICA DURING THE PRESENT CENTURY

Luiz D. Lacerda*, Mario G.Ribeiro & Jorge J. Abrão (Dept. Geoquímica, Universidade Federal Fluminense, Niterói, 24020-007, RJ, Brazil)

Abstract

This study presents the first estimate of Hg atmospheric deposition over South America during the past 80 years, based on the analysis of dated peat bog sediment cores, from the Itatiaia Mountains, southeastern Brazil. Average Hg concentrations along the cores ranged from 30 to 420 ng.g-1. Mercury concentrations correlate significantly with Pb concentrations up to the middle 1980`s, but not with organic matter content, suggesting an industrial source of Hg. Average pre-industrial Pb deposition was c.a. 8.0 mg.m-2.yr-1 , with a peak at the surface of the sediment core ranging from 40 to 80 mg.m-2.yr-1. On the other hand, average Hg deposition rate was 36±4 µg.m-2.yr-1, between 1910 and 1940, showed a peak in the 1960`s of 120 µg.m-2.yr-1, and decreased again after the late 1970`s to 20 µg.m-2.yr-1. The temporal Hg distribution pattern is similar to those reported in different regions of the northern hemisphere. However, pre-industrial Hg deposition are from 3 to 6 times higher than those reported from remote areas in the northern hemisphere. Emissions from gold and silver mining during the previous three centuries, and/or Hg transfer from emissions of the earlier industrialization of the northern hemisphere, may have influenced the magnitude of pre-industrial Hg deposition in South America. However, present Hg deposition rates are similar to the average deposition rates reported for remote sites in North America and Europe.