Effect Of Sediment Properties On The Phytoremediation Of PAH-Contaminated Sediments By Potamogeton Crispus L.

As a result of the persistent feature of polycyclic aromatic hydrocaobons(PAHs),the accumulation of PAHs pose a threat to the aquatic environment and human health.Phytoremediation is a cost-effective and environment-friendly technique and the efficiency of phytoremediation is quite related to plant growth conditions.Sediment properties not only influence plant growth but also control the bioavailability of contaminants.Hence,they are important factors influencing the efficiency of phytoremediation.In this study,we selected Potarmogeton crispus L.(P.crispus)as the test submerged plant,chose phenanthrene and pyrene as the target contaminants.Effect of sediment properties(content of NH4-N and sediment organic matter)on dissipation of phenanthrene and pyrene in sediments by P.crispus was investigated.The main conclusions are as follows:(1)The addition of NH4-N resulted in a faster plant growth rate compared with none addition treatments but there was no obvious difference between low and high addition treatments.A high content of NH4-N facilitated the increments of chlorophyll and soluble protein contents.Moreover,NH4-N accelerated the above ground biomass accumulation and lead to a lower root/shoot ratio during the last period of the experiment.After the 54-day experiment,the total dissipation enhancements of phenanthrene and pyrene by P.crispus were 12.5%and 14.2%,19.2%and 18.3%,18.8%and 18.0%,respectively,when their NH4-N addition concentrations were 0,0.1 and 0.2 mg/kg(in terms of nitrogen content).It can be concluded that the dissipation enhancements of PAHs in sediments with different NH4-N by P.crispus was quite related to plant growth especially the biomass of plant root.A high content of NH4-N facilitated the release of root exudates,oxygen and furthermore enhanced the biodegradation activity and led to a higher dissipation enhancement of PAHs by P.crispus.(2)After a 36-day experiment,sediment organic matter(SOM)content obviously influenced the growth of P.crispus.Plant growth in organic rich sediment was quicker on the early stage,but then slowed down.As a result of poor oxygen content in sediment,plant root decayed during the last period of the experiment.The dissipation ratios of PAHs decreased with increasing SOM content no matter with or without P.crispus.The total dissipation enhancements of phenanthrene and pyrene by P.crispuswere 9.35%and 9.02%,12.47%and 10.34%,13.60%and 10.95%,respectively,when their respective SOM contents were 1.20%,3.14%and 5.08%.(3)There are two aspects affecting biodegradation of PAHs in sediment.One was the bioavailability of the PAHs and the other was the microbial activity.Bioavailability of the contaminants in sediments was calculated by a two-compartment desorption model and polyphenol oxidase activity was measured.At the end,the enhancements of rapidly desorbing fraction consistent with the change trends of dissipation enhancements of the two PAHs in sediments.However,there was no significant correlation between the enhancement of polyphenol oxidase activity and the enhancement of PAH dissipation ratio.These suggested that bioavailability enhancements by P.crispus should be the key factor leading to the dissipation enhancements of the two PAHs in sediments with different SOM contents.