Biological factors influencing As mobilization from an ancient mining region : in vitro studies.

Abstract

Ouro Preto city is located in the Iron Quadrangle, where Arsenic-bearing minerals are easily found; therefore, human exposure to As is a concern. The aim of this study was to assess the influence of organic matter (OM) and microbiota on As mobility. Soil samples were collected from deactivated gold mines to achieve this goal. Soil aliquots (5 g) were exposed to different extractant mixtures: CaCl2, 2.5 mmol −1 (A); CaCl2 + 5 g of proteic biomass - PB (B); CaCl2 + bacterial inoculum (C); CaCl2 + 5 g of PB + inoculum (D); and organic acid solution - OAS (0.1 mol−1) (E). Solubility tests were conducted at room temperature for 120 days (A–D) or 48 h (E). PB increased As mobility up to 600 times compared to that of the control group (A). As mobility in the presence of bacteria was slightly lower thus highlighting the effects of microbiota and OM on As mobilization. Principal component analyses indicated Ca, Fe, Mn, P, Mg, Sr, As, and Cd were the main contributing factors. In the presence of OM, Zn, Cu, Pb, Cd, As, and Cr were leached. The positive effect of OM and indigenous microorganisms on As mobility was confirmed, reinforcing the need to adopt preventive measures to avoid potential environmental damage due to ineffective management of urban and industrial waste deposition in such As-contaminated urban areas.