Purification Of Sediments Contaminated With Phthalate Acid Esters By Potamogeton Crispus L.

Phthalic acid esters (PAEs) are a typical kind of endocrine disrupting compounds.The levels of PAEs in urban rivers and lakes have already exceeded the nationalstandards and their pollution is getting worse. This paper aims to explore thedegradation mechanism of PAEs in sediments by using the Potamogeton crispus L.to remediate the PAEs polluted sediments. Resorting to root bags, removal of dibutylphthalate (DBP) and di (2-ethylhexyl) phthalate (DEHP) was studied by an indoorPotamogeton crispus L. microcosm simulating the mainstream of HaiheRiver. Anunplanted microcosm was set as a control. The research of PAEs has focused onconcentration of PAEs, microbial community,the number of microorganisms, rootexudates in soil solution and other biochemical markers. Experimental results are asfollows:(1) Based on comparison among the ultrasonic extraction, Soxhlet extraction andultrasound-Soxhlet extraction, the proper extraction method was chosen in view ofthe method blank, extraction efficiency, data standard deviation and the experimentaltime consumption. The results showed that the Soxhlet extraction andultrasound-Soxhlet are highly efficient in extraction, but due to their high methodblank values and the instability of data, data from these two extractions are notaccurate enough and they are time-consuming as well. However, despite the lowerextraction efficiency, ultrasonic extraction can meet the requirements of experimentand because of its data stability and lower method blank value. Besides, the ultrasonicextraction is both easy and quick to operate. In conclusion, the ultrasonic extraction isutilized in this experiment.(2) Water, grass and sediment samples during the run of the micro-universe arecollected for analysis. The results indicated that the contents of DBP and DEHP inPotamogeton crispus L. increased by133%and68%at the end of the experiments.Concentrations of DBP in water were lower than the quantification limit (8μg/L),while the contents of DEHP in water of planted and unp lanted microcosms graduallydecreased from the original65and70μg/L to the quantification limit on the third day.Difference in the contents of DBP between non-rhizosphere sediments and sedimentsin the unplanted microcosm was not significant, and their removal efficiencies were 32.2%-36.5%at the end of experiments, while it was50.0%in the rhizospheresediments. The difference in concentrations of DEHP between non-rhizospheresediments and sediments in the unplanted microcosm was also insignificant and theirremoval efficiencies were10.3%-11.4%at the end of experiments. The contents ofDEHP in rhizosphere sediments declined rapidly after27th day and the removalefficiency was80.9%at the end of experiments. The calculation results showed thatthe enrichment of Potamogeton crispus PAEs only accounted for1/8of the amount ofPAEs degradation, which revealed that degradation of PAEs in sediment mainlydepend on the action of microorganisms.(3) The PLFAs technology and method of dilution plate are emp loyed todeterminate the changes in the number and types of microorganisms in the sediments.Microbial results further revealed that the amount of microbial biomass in rhizospheresediments were significantly higher than those in both non-rhizosphere sediments andsediments in unplanted microcosm. In the later period of the experiment, it isdiscovered that microbial community structure in rhizosphere sediments changedgreatly. This is consistent with the results from the removal of the two PAEs in therhizosphere. This suggests that submerged plant Potamogeton crispus L. can reducethe amount and change the community structure of organisms through the rhizosphereeffect, and thus effectively remove the PAEs from sediments.(4) Sediment solutionsin rhizosphere sediment as root exudates were collectedbysoil incubation method. Detected the dissolved organic matter in sediment solutions,and compared with the control and non-rhizosphere sediment solutions. The resultsshow thatthe concentration of total phenols, the content and types of phenolic acids inthe rhizosphere sediment solutionsare significantly higher than that of the control andnon-rhizosphere sediment solutions, but little change in DOC and the concentration oforganic acids, which indicated that phenolic acids in root exudates canprobablypromote the microbial degradation of PAEs in the rhizosphere.