Speciation of chromium in soil inoculated with Cr(VI)-reducing strain, Bacillus sp. XW-4

Abstract

Cr(VI)-amended soil was inoculated with Cr(VI)-reducing strain, Bacillus sp. XW-4 and incubated at 28 °C in an incubator. Cr(VI) reduction, available Cr and Cr fraction in soils were studied. The results show that addition of Bacillus sp. XW-4 can promote Cr(VI) reduction, but inoculation of this strain has a negative effect on the decrease of available Cr content in soil. In controls (without this strain) amended with 100 and 200 mg/kg of Cr(VI), Cr(VI) contents decrease to about 41 and 92 mg/kg respectively after incubation of 4 d, while in soil inoculated with XW-4, Cr(VI) contents decrease to about 18 and 60 mg/kg, respectively. The content of available Cr in soils with inoculation of XW-4 is higher than that in controls. Chromium is partitioned into water soluble Cr, exchangeable Cr, precipitated Cr, Cr bound to organics and residual Cr. The highest content of Cr is observed in residual form and water soluble Cr is not detected for all treatments after 42 d, but the soils inoculated with Bacillus sp. XW-4 contain higher content of exchangeable Cr and lower content of precipitated Cr than the soil without the inoculum. Inoculation of Bacillus sp. XW-4 can increase chromium activity in soils.