Mitigation measures for chromium-VI contaminated groundwater - The role of endophytic bacteria in rhizofiltration

A constructed wetland pilot with Jincus acutus L. plants was investigated for its rhizofiltration efficiency in treating Cr(VI)-contaminated groundwater. Measurements of Cr(VI) and total Cr were performed to estimate the rate of removal. In addition, Cr concentration in plant tissues was measured and the role of endophytic bacteria on plant's tolerance to Cr(VI) toxicity was investigated. The results support that J. acutus is able to rhizofiltrate Cr(VI) from contaminated water with up to 140 mu g/L while Cr content analysis in plant tissues revealed that the majority of Cr was accumulated by the plants. Moreover, two leaf (Acidovorax sp. strain U3 and Ralstonia sp. strain U36) isolated endophytic bacteria were found to tolerated 100 mg/L.Cr(VI) while nine root isolates showed resistance to 500 mg/L Cr(VI). The endophytic bacteria Pseudomonas sp. strain R16 and Ochrobactrum sp. strain R24 were chosen for Cr(VI) reduction assays. All four strains exhibited a strong potential to reduce Cr(VI) to Cr(III) aerobically. Among them Pseudomonas sp. strain R16 was found able to completely reduced 100 mg/L Cr(VI) after 150 h of incubation. These results suggest that J. acutus is an excellent choice for CWs whose function is the removal of Cr(VI) from contaminated groundwater for subsequent use in crop irrigation. (C) 2014 Elsevier B.V. All rights reserved.