Atmospheric mercury deposition over Brazil during the past 30,000 years

Abstract

Atmospheric Hg deposition over Brazil is presented for the past 30,000 years as a tracer of the different naturat and anthropogenic processes affecting the atmospheric environment of Brazil. During most of the prehistoric period, atmospheric deposition rates were rather constant with an average of about 2 pg m-2 yrl. Peak deposition, ranging from 4 to 6 pg mW2 Yi', occurred ai: least during two periods between 3,300 and 3,600 BP and between 8,500 to 12,000 BP, and during the last glacial maximum (LGM), at about 18,000 years BP. These periods were characterized by drier, colder climates with high frequency of forest fires, as shew^ by correlation with coal and poIIen distribution data. During the colonial period Hg atmospheric deposition rares were much higher, about four times the prehistoric background and reached 6 to 8 yg m-2 yr'. These increasing Hg deposition rates can only be explained by the large Hg emissions in South and Central America from Spanish silver mines, which emitted to the continent's environment about 200,000 tons of Hg from 1580 to 1820. During the present century, Hg deposition rates varied according to the region of the country. In the Amazon region, where gold mining is the major source of Hg emission to the atmosphere, deposition rates increased continuously during the last 40 years, reaching 8 to 10 pg mb2 yrIn the industrialized Southeast, Hg deposition was higher during the mid 1960s and 1970s, ranging from 80 to 130 pg m3 yr-l, but decreased to 20 to 30 pg mV2 yr-lin the 1990s, due to the enforcement of emission control policies. However, where Hg emissions are mostly from urban, nonpoint sources, such as along the high urbanized coastal area, Hg deposition, although smaller, increased ,steadily from the 1940s reaching a maximum at surface sediment layers of about 40.0 pg m-? yr-'. The results presented suggest Eg as a reIiabIe tracer of natural (paleodimatic changes) and anthropogenic (industrial and mining emissions) processes able to affect the atmosphere in Brazil.