Mechanisms Of The Phytoremediation Of Decabromodiphenyl Ether In Sediment By Aquatic Macrophyte Scirpus Validus Vahl

Decabromodiphenyl Ether (BDE-209) is the domainant polybrominated diphenylethers (PBDEs) that have been used extensively as flame retardants in a wide range of products such as plastics, textiles, and electric circuitry owing to their excellent Flame retardant efficiency and thermal stability. At present, BDE-209 was the ubiquitously detected contaminant in the environment and even its extence was found in the sediments and penguins of the Antarctic. Owing to high volume production, lipophilicity, bioaccumulation, persistence and endocrine disruptor of BDE-209, deca-BDE has become the most ubiquitously detected contaminants of major concern in the environment. Sediments are regarded as ultimate sink of decabromodiphenyl ether (BDE-209) in aquatic environment due to the high hydrophobicity and china is one of the countries where BDE-209 is the mostly detected regarding the concentrations and detection rates.The methods applied for remediation of PBDEs contaminated environment such as photodegradation, nanoparticles degradation and microbial degradation are expensive, disruptive to the environment and also involve high energy consumption, thus those were not suitable for remediation BDE-209 contaminated sediment in aquatic environment. The emerging technology of phytoremediation was a promising remediation method for organic contaminants cleanup thanks to its ecological and economic sustainability.However, only few phytoremediation reports has been applied for PBDEs remediation and the potential for any aquatic macrophytes for phytoremediaiton of decabromodiphenyl ether contaminated sediments has not been explored. The aquatic macrophyte, S. validus Vahl, was selected among the common emerging macrophytes by the high efficiency of remediation of BDE-209.In this research the phytoremediation of BDE-209 by S. validus Vahl including the BDE-209 resistance, remediation efficiency, bioaccumulation capability, remediation mechanisms, BDE-209 metabolic changes and microbial ecological changes was investigated at an environmentally relevant concentration in three typical sediments.In this study, S. validus Vahl seedlings were grown in BDE-209 contaminated sediment for determining the eco-physiological responses of S. validus Vahl to BDE-209 phytotoxicity at the increasing concentrations of BDE-209 (0,2,8,30 mg-kg-1). The results indicated that BDE-209 at the BDE-209 concentrations ranged from 2 to 30 mg-kg-1 did not inhibit the growth of S. validus Vahl. Stress effect was observed on plant height, stem diameter, chlorophyll content, MDA contents and root activity of S. validus Vahl at high contaminated levels in the initial stages. SOD, POD and CAT which constitute the antioxidant enzyme system were increased in 60 days. The above results clearly demonstrated growth and physiological function of S. validus Vahl was not adversely impacted by BDE-209 contaminated sediment and thus could be used in phytoremediation of BDE-209 contaminated sediment.Phytoremediation of BDE-209 by aquatic macrophyte, S. validus Vahl was investigated at an environmentally relevant concentration in three typical sediments (silt, clay and sand sediment).At the end of the experiment (18 months), the dissipation rates of BDE-209 in three typical sediments were significantly enhanced by S. validus Vahl compared with those in control sediments (p<0.01), and the average removal rates of BDE-209 were 92.84%(silt sediment),84.04%(clay sediment) and 72.22%%(sandy sediment), respectively, which were 148%(p<0.01),197%(p<0.01) and 233% (p<0.01) higher than those of the control sediments.The ability of S. validus Vahl to uptake and translocate BDE-209 was confirmed by the detection of BDE-209 accumulated at the root tissue with concentrations of 0-300μg kg-1dw and translocation to shoot tissue (0-64μg kg-1dw). BDE-209 uptake and translocation in tissue of S. validus Vahl may be influenced by residual BDE-209 concentration in sediments indicated that BDE-209 uptake was a passive process. The BDE-209 BCFs and RCFs of S. validus Vahl was comparatively lower because of high hydrophobicity. The uptake suggested that BDE-209 sorb strongly to the roots of S. validus Vahl and the translocation was limited.In the process of BDE-209 phytoremediation by S. validus Vahl, photolysis and other abotic losses were miner possible pathways of BDE-209 dissipation which accounted for 8.44%and 8.23%, respectively. The accumulation of BDE-209 in plant biomass only made a small contribution (0.5%) to the total removal of BDE-209. Through analysis of pathways of BDE-209 removal, this enhanced dissipation of BDE-209 by macrophyte-microbal association might be mainly the result of S. validus Vahl-promoted microbial degradation (83.35%in control sediments,94.66%in Treatment). Metabolites of BDE-209 in the sediment-macrophyte System were measured by GC/MS, A total of sixteen additional lower brominated PBDE congeners (di-to nona-) were detected in the soil and plant tissues after plant harvest, confirming metabolic debromination of BDE-209 in this system.Evidence of a relatiely higher proportion of penta-through di-BDE congeners in plant tissues than in the soil indicates that there is further debromination of PBDEs within plants or low brominated PBDEs are more readily taken up by plants.To increase the bioavailability of BDE-209 and facilitate its degradation in phytoremediation, plant-accelerated dissipation of BDE-209 in rhizosphere sediments of S. validus Vahl in the presence of a cation ionic-surfactant (CTAB), an anionic-surfactant (SDS), a nonionic-surfactant (Tween 80) and a Cyclodextrin (P-CD) at the concentrations ranged from 300 to 1000 mg·kg-1 were studied. Siginificantly negative changes were not observed for the biomass in terms of plant height and stem diatemeter of S. validus Vahl when the addition of 300 to 1000 mg-kg-1 CTAB, SDS, Tween 80 and P-CD. This indicated that it is preferable for CTAB, SDS, Tween 80 andβ-CD to be utilized as the BDE-209 phytoremediation amendment. Furthormore, the addition of CTAB, SDS, Tween 80 with initial concentrations of 300 to 1000 mg-kg-1 in rhizosphere sediments significantly enhanced the phytoremediation effiencies.As for the control,34.93%of BDE-209 was dissipated from the sediment. 2.85%-11.78%of increase in BDE-209 removal rates was obtained in the addition group of SDS. 4.52%-14.25%of increase in BDE-209 removal rates was obtained in the addition group of Tween 80.7.37%-19.33%of increase in BDE-209 removal rates was obtained in the addition group of Tween 80. Though the removal efficiency of BDE-209 was increased in the preasence ofβ-CD and 1.03%-7.78%of increase in BDE-209 removal rates was obtained, no significantly enhance of BDE-209 phytoremediation was not observed in the addedβ-CD concentration ranges. Results obtained from this study provided some insight with regard to the feasibility of phytoremediation for BDE-209 contaminated sediments with addition of suitable surfactants, especially Tween 80.During the process of phytoremediation, phytoremediation, the number of microorganisms including bacteria, fungi and actinomycetes counted by DAPI (4,6-diamidino-2-phenylidole) fluorescence direct count and plate count method in three typical rhizosphere and sediments were examinated. The results showed that the number of microorganisms in sediments was significantly increased by planting and the number of bacteria and fungi increased by 2-12 times and 1-4 times in the respective rhizosphere sediment. No obvious difference of quantity of actinomycetes was observed between rhizosphere and non-rhizosphere in silt and clay sediments expect for sand sediments. As the number of microorganisms increased, planting of S. validus Vahl enhanced the dehydrogenase activities and urease in three typical sediments. The increase of sediment dehydrogenase activities and urease in the rhizosphere signified the activities of microorganisms were enhanced and both were showed a trend of silt>clay>sand sediments.The results suggested that the numbers and activities of microorganisms is an important reason to explain why there existed the differences of BDE-209 dissipation rates in three typical sediments by the presence of S. validus Vahl.Diversity of bacteria was studied from rhizosphere BDE-209 contaminated and noncontaminated sediments of S. validus Vahl by PCR, RFLP and sequence analysis o f 16S rDNA and comparing with the published sequences in GenBank database. Based on the restriction fragment length polymorphism(RFLP) profile generated 200 clones from the 16 s rDNA library, Phylogenetic results indicated that 200 clones could be divided into 12 phylotypes, includingβ-Proteobacteria, 8-Proteobacteria, a-Proteobacteria, Acidobacteria and Chloroflexi, Planctomycetes, eubacterium, Flavobacterium and some unidentified OTUs.The predominant bacteria in contaminated and uncontaminated rhizosphere sediments wasβ-proteobacteria,δ-proteobacteria,α-proteobacteria, Acidobacteria and Chloroflexi, Bacterial community structure of BDE-209 contaminated rhizosphere sediment has distinguished feature and obviously different from the unpolluted rhizosphere sediment sample, which is mainly reflected in the dominant position ofβ-proteobacteria,δ-proteobacteria,α-proteobacteria, Acidobacteria and Chloroflexi in the bacterial flora, andβ-proteobacteria andα-proteobacteria may play important role in the BDE-209 degradation in the rhizosphere sediment of S. validus Vahl.Demonstration project of water quality for sustainable purification in Danshui river was constituted by four parts, precipitation pond, aeration pond, artificial wetland and aquatic plants pond with the aim to evaluate the removal efficiency of toxic pollutants and conventional pollutants by the integration technology. Monitoring Analysis of toxic pollutants removal and Conventional pollutants by the Demonstration project was made and preferable results were obtained in this research. More than 40%of polycyclic aromatic hydrocarbons (PAHs) were removed from water by demonstration project, and the removal rates of five kinds of homologues were, NAP,44.13%-59.23%; FLU,44.1%54.61%; PHE,50.90%-54.70%; PYR,61.88%-80.61%and FLT,44.83%-56.64%. Decabromodiphenyl ether(BDE-209) and bisphenol A(BPA) could be fully removed by this project.The results suggested that demonstration project in Danshui river could effectively remove the toxic organic pollutants from water, demonstrating its popularization value for purification of toxic organic pollutants.