| The South Sewage River is the major sink of point anthropogenic sources. As the second pollution source, the contamination of heavy metals and organic complex becomes more and more serious, causing potential risk to environment and humans. In this paper, total content, metal fractionation and pollution sources were used to analyze the contamination situation of the sediment collected from the South Sewage River. Geoaccumulation index, Sediment Quality Guideline Quotient (SQGQ), Risk Assessment Code (RAC), etc. were combined to evaluate the accumulation level, toxicity, bioavailability of metals and the correlation between metals and organic matter. According to the pollution characteristics of the sediment, pot experiment in natural environment was conducted to study the assistant mechanism of adding EDTA or arbuscular myeorrhizal (AM) fungi to improve phytoremediation efficiency. Besides, molecular methods were used to characterize the microbial community structure and functional gene diversity involved in anaerobic degradation of toluene and benzoate which are typical models of mono-aromatics.The results indicated that the sediment from South Sewage River was heavily accumulated with Cd, Zn and Cu which also exhibited relatively high toxicity. Those three metals also presented good correlation with organic matter. Zn and Cd pollution was heavy with the highest mobility of Cd, which therefore caused high environmental risk. Zn could cause medium environmental risk and Cu pollution is slight because it has low bioavailability. The effective fraction concentration of Ni, Cr and Pb is higher than Cu and lower than Cd and Zn, thereby might cause some kind of environmental risk.The rotation pattern of maize - Lolium multiflorum Lam intercropping and Lolium multiflorum Lam - Medicogo sativa L intercropping was recognized as the best way to remediate the complex contamination in the South Sewage River sediment. The concentration of Zn, Cr, Pb and Cd in rooting zone of the sediment was largely reduced in the first round compared with the situation in the second round, and Ni and Cu was mainly reduced in the second round. To our knowledge, this is the first time to compare the remediation effect between plants, plants - EDTA, plants - AM fungi and plants - AM fungi - endogenous bacteria. The results showed that AM fungi could improve the absorption efficiency of heavy metals in the plants without causing future pollution. However, temperature was a major factor to affect the remediation efficiency, and the competition between different types of organisms in the sediment might reduce the phytoremediation effect as well. In addition, the activity of polyphenol oxidases, urease and invertase was observed to be significantly increased by AM fungi.The degradation of naphthalene in the sediment was obviously observed, but different kinds of mono-aromatics were detected during the phytoremediation process. Therefore, toluene and benzoate were selected as research target to represent mono-aromatics and DGGE and cloning library were applied to study the diversity of ring opening gene bamA. To our knowledge this is the first report of bamA gene in denitrifying enrichments using DGGE and cloning analysis. The results showed that bamA gene related to bamA of Thauera chlorobenzoica was dominant in toluene and benzoate cultures. However, a greater diversity of sequences was obtained in benzoate cultures. Low diversity of bamA gene was observed and some similarities of bamA were also found between active cultures and backgrounds, suggesting potential natural attenuation of aromatic compounds might occur. The combined analysis of 16S rRNA and bamA gene suggests the species related to genera Thauera dominated toluene and benzoate degrading cultures. The combination of multiple methods (DGGE and cloning analysis) provides a more complete picture of bamA gene diversity.
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