Arsenic in Biogenic Iron Minerals from a Contaminated Environment

Abstract

High arsenic levels have been found in some water samples from the Iron Quadrangle, a main gold, manganese and iron mining region in Brazil. In this work, we used transmission electron microscopy coupled to energy-dispersive X-ray analysis to show arsenic in bacteriogenic iron minerals (BIOS) collected in this region. Two types of iron bacteria stalks and several morphologically different filamentous sheaths of bacteria were found, most containing arsenic. Bacterial stalks were partially coated by spherical precipitates probably deposited after stalk secretion. Arsenic/iron ratios were the same independently of the amount of spherical precipitates, suggesting that arsenic incorporation is independent of bacterial metabolism. Additionally, arsenic seems to be saturated in these minerals, since the arsenic/iron ratio was the same under different arsenic concentrations.

Keywords:

• arsenic
• BIOS
• iron bacteria
• biomineralization
• Gallionella
• Leptothrix

ACKNOWLEDGMENTS

I thank Douglas A. Pabst and José Dias Corrêa Jr for assistance in collecting samples, and Gisele L. Wandermur and Virginia R. Murdocco for help in sample preparation for microscopy and arsenic concentration determinations. This work was not possible without the facilities of Laboratório de Biomineralização (ICB – UFRJ) and Laboratório de Ultraestrutura Celular Hertha Meyer (IBCCF – UFRJ). I am also thankful to the criticism of two anonymous reviewers, which has improved substantially the text. I acknowledge the financial support of the Brazilian agencies CNPq (CT-Mineral) and FAPERJ.