Dissipation Behaviors Of Phthalic Acid Esters In The Rhizosphere Of Wetland Plants

Phthalic acid esters (PAEs), which are one kind of typical endocrine disruptingcompounds, are ubiquitous in the environment and listed as ‘priority pollutants’. Theresearch of PAEs has been focused on the determination, distribution, andbiodegradation in single environmental media, however, less work has been done onphytoremediation, especially on the dissipation behaviors of PAEs in the rhizosphereof wetland plants.In this paper, the dissipation behaviors of PAEs in the rhizosphere of wetlandplants were studied by field investigation and laboratory simulation. Dibutyl phthalate(DBP) and di-ethylhexyl phthalate (DEHP), the two most important and abundantPAEs, were selected as target contaminants. Phragmites australis (P. australis) andTypha orientalis (T. orientalis), the two typical and easily obtained wetland plants,were selected as tested plants. At the same time, the monoester metabolites of PAEswere analyzed. The main results are as following:(1) A simple and convenient method for determining PAMs in sediments/soilswas established and the detection limit could reach10-11g/g. Effects of parameters,such as extraction solvents, pH of water as extraction solvent and sediment/soilproperties, on the recovery of PAMs were studied by spiked sediment samples.(2) The field study was conducted in two adjacent shallow lakes located inTianjin Univ. to investigate the effect of plant species (P. australis and T. orientalis)and growth strategy (single or mix) on the distribution PAEs, the microbialcommunity structure and root exudates components. The results showed that therhizosphere effect of wetland plants was significant. There was significantly differentin microbial biomass between P. australis and T. orientalis rhizosphere sediments.While the microbial biomass of the same plants rhizosphere was influenced by growthstrategy (single or mix). There was significant difference in types and contents ofamino acid and organic acid between the two plants. The root exudates content of T.orientalis was higher than that of P. australis, while small difference in root exudatescontent between T. orientalis and P. australis when they grow together.(3) The dissipation of PAEs in the rhizosphere was quantitatively studied byadding root exudates to sediments and P. australis seedling culture. The results showed that the microorganisms played a major role in the dissipation of PAEs insediments. Apart from individual samples, the populations of culturable bacteria,PAE-degrading bacteria and the contents of PLFAs in planted treatment were no lessthan that in the unplanted control treatment.Plants can improve the remediation efficiency, mainly because of plant-promotedindigenous microbial biodegradation of PAEs in the rhizosphere sediments. Becauseof the presence of plants, microbial degradation of PAEs was enhanced by0.3%to30.0%. For DBP, the promotion effect on microbial degradation was related to bothwhether to be spiked or not and spiked concentration. The promotion effect innon-spiked control sediments was higher than that in spiked sediments, and promotioneffect increased with the increase of spiked concentration. For DEHP, promotioneffect increased with the increase of spiked sediment concentration. The promotioneffect on the dissipation of PAEs was related to the populations of PAE-degradingbacteria in sediments. The promotion effect on DEHP was significantly higher thanthat on DBP. The promotion effect on DBP and DEHP in spiked sediments decreasedwith increasing TOC content of sediments.By monitoring the monoester metabolites of PAEs during the process of PAEdissipation, we found that the content pattern of the monoester metabolites of PAEswas the same with the residual concentration of PAEs in sediments in each treatment,and the content of MBP was significantly higher than that of MEHP.