Contamination and Soil Biological Properties in the Serra Pelada Mine - Amazonia, Brazil

Renato Alves Teixeira,Steel Silva Vasconcelos,José Roberto Ferreira,Anderson Martins de Souza Braz,Antonio Rodrigues Fernandes

doi:10.1590/18069657rbcs20160354

Abstract

Discovered in 1980 and unleashed an utter gold rush of the modern era, Serra Pelada was the largest open-air mine in Brazil. About 80,000 gold prospectors worked there until 1984, when the gold pits were flooded. The environmental impact caused by mining inflicted irreversible damage to the ecosystem, with the formation of a large lake and piles of waste rock and sterile overburden, still evident 28 years after the mine was closed. This study aimed to evaluate the available and pseudo total contents of potentially toxic elements (PTEs), the contamination and pollution levels, and to understand how the biological soil factors are related to the chemical properties of the soil and the available PTE contents in the Serra Pelada - Amazonia, Brazil. Soil was collected from seven areas around the lake: Area 1 - margin of the mine without waste and/or sterile deposits; Area 2 - margin with waste and/or sterile deposits; Area 3 - area with sterile deposit; Area 4 - mine tailings, denominated curima by the prospectors, from which gold had been extracted; Area 5 - sediment dredged from the lake in the mine pit; Area 6 - area with agroforestry system; Area 7 - riparian forest, unaffected by the artisanal gold extraction process (control treatment). Apart from selenium (Se), all evaluated elements, in at least one of the studied areas, exceeded the contents of the investigation values (defined as the content of a given substance in soil or groundwater above which the human health is under potential direct or indirect risks, considering a standardized exposure scenario) in agricultural areas in Brazil, as determined by the National Council of the Environment. Soil enrichment and contamination with Co, Ba, Mn, and Hg were investigated. Principal component analysis showed that the available levels of PTEs influenced the soil biological properties, in particular basal respiration, indicating that important ecosystem processes are being affected by PTE contamination

Highlights

Mineral exploration is a relevant economic activity, both in industrialized and in developing countries
This study aimed to evaluate the available and pseudo total contents of potentially toxic elements (PTEs), the contamination and pollution levels, and to understand how the biological soil factors are related to the chemical properties of the soil and the available PTE contents in the Serra Pelada - Amazônia, Brazil
Soil was collected from seven areas around the lake: Area 1 - margin of the mine without waste and/or sterile deposits; Area 2 - margin with waste and/or sterile deposits; Area 3 - area with sterile deposit; Area 4 - mine tailings, denominated curimã by the prospectors, from which gold had been extracted; Area 5 - sediment dredged from the lake in the mine pit; Area 6 - area with agroforestry system; Area 7 - riparian forest, unaffected by the artisanal gold extraction process

Summary

Introduction

Mineral exploration is a relevant economic activity, both in industrialized and in developing countries. In both, it can cause serious environmental damage at different degrees of severity, including river silting and diversion, deforestation, and degradation of the landscape, habitat, and aquatic life (Mol and Ouboter, 2004). In artisanal and small scale mining of gold (Au), contamination with potentially toxic elements (PTEs), e.g., with mercury (Hg) occurs, generating effluents, dust emission, and waste deposits in soil and water (Rashed, 2010). Artisanal gold mining has caused contamination by Hg and other PTEs. In Brazil, in the state of Minas Gerais, in an artisanal gold extraction area, contents of up to 13.5 mg kg-1 Hg, 90.1 mg kg-1 Zn, and 40.7 mg kg-1 Cu were found (Cesar et al, 2011). In Venezuela, the Hg contents found in the soil are as much as two orders of magnitude higher than the quality reference values of that region, which was attributed to the gold recovery procedure of burning amalgam (Santos-Francés et al, 2011)

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