Bioremediation of arsenic-contaminated soil through soil washing using biosurfactants

Gold mining is one of the main sources of Arsenic (As) contamination in Minas Gerais, particularly at the Iron quadrangle. Arsenic is a toxic element that causes damage to human health. The soil washing technique using biosurfactants (BS) containing extracts was tested to promote the mobilization of the As contained in some soil samples collected in an abandoned gold mine, to investigate an environmentally friendly but equally efficient alternative to remove As from soils. Two mixed cultures of biosurfactant-producing bacteria (MPCB and MPBR), both adapted to the cultivation at high As concentrations (8 mg.1), were selected for extracts production. Surfactants were stable over a wide pH range, 3-11; temperature, 28-50 C and salinity, 1-5% NaCI (p.v"), and promoted the mobilization of As. The pH and solid:liquid ratio influenced the removal efficiency of the tested extracts. The highest removals were obtained at pH 11.0 and a solid:liquid ratio of 1:40 (g.m1). Under pH 11.0, the arsenic removal results obtained with MPCB (14.01 and 13.72%) and MPBR extracts (12.04 and 12.31%) were superior to those obtained by using 10o (w/v) solutions of the commercial surfactants SDS (0.87 and 0.71%), saponin (0.57 and 0.55%) and, soy lecithin (2.05 and 2.63%). The pH and the solid: liquid ratio influenced the results of the column tests. The highest As removals: 25.43% (MPCB) and 22.43% (MPBR) were obtained after 10 extraction cycles, at pH 11 and 1:40 ratio (.m1). The extracts MPCB and MPBR removed the water-soluble arsenic as well as the carbonate associated As and the adsorbed ions. Both extracts behaved similarly to EDTA and the commercial microbial extract (GorduraKlin8).