| Currently, China has become one of the largest E-waste dismantling countries. Due to the non-standard e-waste dismantling for a long term, environmental pollution problems caused by brominated flame retardants polybrominated diphenyl ethers(PBDEs), have been occurring.The decabromodiphenyl ether (BDE-209) was selected as the representative of the brominated flame retardants. Laboratory incubation experiment was conducted to study the influence of different organic materials amendment (compost, green manure and mushroom residues, respectively) on dissipation of BDE-209 in soil under different water managements (60% water holding capacity (DRY), flooded (WET), sequencing flooded and 60% water holding capacity (WET-DRY), respectively). Pot experiments with plantation of either ryegrass or rice, coupling with different agronomic management practices, were also conducted for polluted dry land and paddy soil, respectively. The main results are as follows:(1) Laboratory incubation experiment:the concentration of BDE-209 decreased both in field-contaminated soil and freshly-spiked soil after 90-day cultivation. The addition of organic materials increased the removal of BDE-209 from soil, irrespective of organic material types. Comparing differences in dissipation of BDE-209 in field-contaminated soil groups, the results suggested that,1) treatments of DRY and WET-DRY showed better results than WET treatment, regardless of organic material types. No significant difference was found between treatments of DRY and WET-DRY. There was also no difference among three organic materials, in both DRY and WET-DRY treatments that showed larger BDE-209 dissipation rates; while in freshly-spiked soil groups, treatment effects were not as obvious as those in field-contaminated soil groups. Compared to the control treatments, amendment of organic materials had slight positive effect in dissipating BDE-209, with the most effective facilitation achieved by treatment of WET-DRY with green manure (a 22.70% removal rate at the end of incubation).(2) Ryegrass planting pot experiment:the concentration of BDE-209 decreased both in field-contaminated soil and freshly-spiked soil after 60-day cultivation. The concentration of BDE-209 in rhizosphere soil was lower than nonrhizosphere soil in all treatments. The most effective treatment was ryegrass plantation combined with Glomus mosseae infection in the rhizosphere. BDE-209 dissipation rates achieved 51.94% and 22.79% in rhizosphere, as well as 43.53% and 19.78% in non-rhizosphere, for field-contaminated and freshly-spiked soil, respectively. Correlation analysis result showed that:the dissipation rate of BDE-209 in field-contaminated soil was significantly correlated with the plant weight belowground (p< 0.05). High throughput sequencing analysis results of rhizosphere soil DNA showed that the dominant bacteria orders were Xanthomonadales (15.18%) and Actinomycetales (11.27%), and bacteria orders like Actinomycetales, Burkholderiales, Sphingomonadales and Bacillales might be related with BDE-209 degradation.(3) Rice planting pot experiment:the concentration of BDE-209 decreased both in field-contaminated soil and freshly-spiked soil after 120-day cultivation. In field-contaminated soil treatment group, rice plantation simultaneously with Glomus mosseae infection and compost addition was most effective in facilitating BDE-209 dissipation, with the removal rates of 53.27% and 48.11% in rhizosphere and non-rhizosphere soils respectively. While in freshly-spiked soil treatment group, the most effective treatment was rice plantation combined with compost addition. The BDE-209 dissipation rates were 27.98% and 26.56% in rhizosphere and non-rhizosphere soils respectively. Correlation analysis result showed that:the dissipation rate of BDE-209 was significantly and positively correlated with plant weight and activity of soil catalase (p< 0.05). High throughput sequencing analysis results of rhizosphere soil DNA showed that the dominant bacteria orders were Xanthomonadales (12.3%) and Actinomycetales (8.53%), and bacteria orders like Actinomycetales, Burkholderiales, Bacillales, Sphingomonadales and Clostridiales might be associated with BDE-209 degradation.The results from laboratory incubation and pot experiments collectively suggested that plantation of either ryegrass or rice, coupling with proper agronomic management practices, can effectively improve the dissipation of BDE-209. This enhanced rhizo-remediation method may have a wide application prospect for cleaning up PBDE polluted soils in e-waste recycling area... |
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