Phthalic acid esters in the rhizosphere sediments of emergent plants from two shallow lakes

We investigated the effect of growth strategy (i.e., single or mixed plant types) of two emergent plants (i.e., Phragmites australis and Typha orientalis) on the distribution of phthalic acid esters (PAEs) and their monoester metabolites (PAMs) in the sediments and roots in two adjacent shallow lakes in Tianjin, China, as well as the removal of PAEs from the sediments. Dibutyl phthalate (DBP), di-2-ethylhexyl phthalate (DEHP), and their PAMs were measured in sediments and roots sampled on 18th May 2010. PAE-degrading bacteria and phospholipid fatty acid (PLFA) of the sediment samples were also analyzed. The results showed that DBP, DEHP, and their PAMs were detected in nearly all of the samples, and the PAE concentrations were 1 to 2 orders of magnitude higher than those of their corresponding monoester metabolites. The PAE distribution patterns in sediments from the two lakes were different and influenced by plant growth strategy. Phytoavailability of PAEs was also affected by plant growth strategy. Compared with the non-rhizosphere sediments, the total organic carbon-normalized PAE concentration in the rhizosphere sediments decreased in the presence of the emergent plants. The PAE removal from the rhizosphere sediments was related not only to plant species but also to growth strategy, which was consistent with the findings of PLFA. The enhancement of PAE biodegradation in the rhizosphere was mainly the result of changes in the microbial community structure for different plant species and in microbial biomass for the same plant species.