Enhanced Scirpus Triqueter Phytoremediation Of Pyrene And Lead Co-contaminated Sedimentwith Alkyl Polyglucoside And Nitrilotriacetic Acid Combined Application

Soil system is considered as an important sink for organic pollutants(OPs) and heavy metals(HMs). As a group of priority control pollutant, polycyclic aromatic hydrocarbons(PAHs) are ubiquitous in the environment. Several studies have demonstrated that PAHs and heavy metals(HMs) are frequently found together as contaminants in soil. Recently, remediation of heavy metal-PAHs co-contaminated soils has been a worldwide urgent issue. Phytoremediation, due to its environmentally sound and lower cost, are widely studied for remove PAHs or HMs from soil. However, the practical application of phytoremediation is limited by the low efficiency. The enhanced phytoremediation by chemical method is a promising technology for the removal of PAHs and HMs. Chelating agents and surfactants have been proven to be very effective in promoting phytoremediation for HMs and PAHs respectively. Alkyl polyglucoside(APG), a nonionic surfactant produced from renewable resources such as fatty alcohols and glucose, was studied to remove PAHs from soil. As a biodegradable chelating agent, nitrilotriacetic acid(NTA) was found that it can desorbHMs(such as Pb) from soil with no environmental effects. As a consequence, using APG and NTA together may be a promising way to enhance phytoremediation for PAHs and HMs co-contaminated soil. However, few research has been concentrated on this approach. In the sight of the above, the aim of this study was to evaluate the effect of combined application of APG and NTA on phytoremeditation for pyrene and Pb by S.triqueter. Some strategies were also investigated to improve this method for improving phytoremediation of pyrene-Pb co-contaminated soils. The mian results are summareied in the following text:(1) Desorption of pyrene and Pb from mixed contaminated soil was conducted to investigate the effect of combination of APG and NTA on activating pyrene and Pb in soil. Results showed desorption Pb and pyrene from soil was significantly promoted with mixed solution of APG and NTA when compared with the alone application of APG or NTA. In other words, significant promotion and synergy on Pb and pyrene desorption with the mixed solution of APG and NTA. To discuss the influence of NTA on APG, an experiment to explore solubility of pyrene with different concentration of APG and NTA was also designed. Results indicated that there is no influence of NTA on the effect of APG on the solubility of pyrene. This phenomenon indirectly suggested that the presence of NTA may have no influence on the surface properties of liquids containing APG. The marked interaction between APG and NTA may contribute to the synergy performance.(2) The plot-culture experiment in a greenhouse was conducted to investigate the effect on improving removal of pyrene and Pb from soil. The outcome of this investigation has highlighted the effect on assisting phytoremediation for pyrene and Pb from soil by S. triquter with APG and NTA mixed utilization.The accumulation and translocation of Pb were significantly improved with alone NTA treatment but not significantly increased with alone APG application. More interestingly, a dramatic synergy and promotion on accumulation and translocation of Pb was achieved with the combined application of APG and NTA. While,the presence of NTA decresed the promotion of pyrene accumulation in plant caused by applcaition of APG. Results also showed that the dissipation ratio of pyrene was increased both by alone application and combined application, which was described as follows: APG≈APG+NTA>NTA>CK. Overall, the dates in this study indicate that exogenous APG and NTA combined application can increase Pb uptake from soil by S.triquter and be beneficial in accelerating dissipation of pyrene in soil.(3) The data of growth S. triquter indicated that the S. triquter growth were nearly not be restricted by addition of NTA and APG. Compared with control treatment, the biomass of S. triquter was increased by 11.61% and 19.31% in treatment of N1 and N2. However, its growth was restrained with combination of surplus dosage APG and NTA. Besides, SEM and TEM photographs of root surface showed that that more Pb in the soil probably were covered at plant by combined application of APG and NTA. SEM and TEM images of root surface suggested that more Pb in the soil probably were transferred to plant by combined application of APG and NTA. More importantly, TEM images of xylem cells of S.triqueter root showed that permeability of cell membrane probably be improved by application of APG. However, its clearer mechanism still needs further research.(4) The mechanism of the combined application of NTA and APG for phytoremediation was discussed by investigating the effects of alone application of APG or NTA and combined application of APG and NTA on pyrene and Pb bioaccessiblity, as well as on DHA. Results indicated that APG and NTA respectively played dominant role on increase bioaccessible pyrene and exchangeable Pb. And synergy on bioaccessibility of pyrene and Pb were achieved with the combined application of APG and NTA. It was found that the combination of NTA and APG had great effect on improving the dehydrogenase activity. Path analysis among APG/NTA, bioaccessibility of pyrene/Pb and the DHA correlation were conducted. Addition of APG and NTA can affect DHA directly by themselves and indirectly by changing solubility of pyrene. In total, the direct effect was minimal so that the total effects of APG and NTA on DHA were still significant. These findings are beneficial to enhance phytoremediation for pyrene and Pb co-contaminated soils.