The purpose of this study was to investigate the effects of Typha latifolia and Phragmites communis root matter in degradation of sediments contaminated with aged 1,2,3,4- Tetrachlorobenzene (1,2,3,4-TeCB). In the present study, complete reductive dechlorination of 1,2,3,4-TeCB was observed in root matter systems, contrasting sediment with no roots present. Microcosms amended with Phragmites communis roots achieved the greatest first-order reaction rate constant over a 4-week period (0.113 d-1, half-life time of 6.13 days). Typha latifolia roots also played an important role in reductive dehalogenation of 1,2,3,4-TeCB, although the first-order reaction rate constant observed within the same period of time (0.097 d-1, half-life time of 7.11 days) was 16% less than that exhibited by Phragmites treatment. Higher concentrations of H2 associated to organic matter in root matter may have caused higher dechlorination activities. Therefore, the wetland plants used in this study represent a very promising alternative for application in phytoremediation.
Molecular techniques including Polymerase Chain Reaction (PCR), Denaturing Gradient Gel Electrophoresis (DGGE) analysis, and cloning of 16S rRNA gene sequences amplified from community DNA were used to determine the diversity of microbial communities present in the sediments. An average size of 570 bp and 180 bp regions of bacterial and archaeal 16S rRNA genes, respectively, were amplified from genomic DNA. A total of 13 bacterial 16S rDNA sequences were derived from DGGE bands and these formed 6 clusters: α, β, and γ subdivisions of proteobacteria; low GC gram-positive bacteria; green-nonsulfur bacteria; and an unknown bacteria group located between α-proteobacteria and green nonsulfur bacteria. Effective reductive dehalogenation of 1,2,3,4-TeCB and chlorobenzene congeners in vegetated treatments was attributed to the presence of two important bacterial populations, Desulfitobacterium sp. and the chlorobenzene-respiring anaerobe Dehalococcoides sp. strain CBDB1. Moreover, methanogenic activity by identified Methanomicrobiaceae, Methanosarcinaceae, and Methanosaetaceae families, confirmed anaerobic conditions and the reduced environment necessary for dehalorespiration of chlorobenzene congeners in microcosm bottles.