Study On Surfactant Functioned Migration And Biodegradation Of Triclosan In Water-sediment System

As a typical substance of pharmaceuticals and personal care product chemicals(PPCPs),triclosan(TCS)has become the most frequently detected pollutant in aquatic and soil/sediment environments,which has caused great risk to the ecological environment and human health.The low solubility and bioavailability,and potential adverse side effects of triclosan have attracted widespread attention to explore the migration and biodegradation of triclosan.Here,this work chose triclosan as target and constructed a surfactant-enhanced remediation system for surfactant-enhanced migration and biodegradation of triclosan in water-sediment systems.Under the inactivation condition,the effect of rhamnolipid,Tween 80 and Brij 35 on triclosan solubilization,sorption and desorption in sediment-water systems were investigated.The information was valuable for the application of surfactant in the controllable directional migration of triclosan.The effects of rhamnolipid,Tween 80 and Brij 35 on triclosan solubilization were in the order of Tween 80 > rhamnolipid > Brij 35.Within the range of surfactant concentration from 1 to 25 CMC,the sorption of triclosan on sediment was significantly improved by the addition of Brij 35.Triclosan sorption was slightly enhanced by the addition of rhamnolipid at low CMC(1-10 CMC),but decreased at high CMC(10-25 CMC).But the addition of Tween 80 blocked triclosan on sediment,and the inhibition effect increased with the increase of concentration of Tween 80.The different adsorption behavior on three types of sediments was due to the difference in their physical and chemical properties.The efficiency of different surfactants in enhancing desorption of triclosan from contaminated sediments was relative to the surfactant tpye and dosage,and their solubilization capacity.Formation of surfactant micelles could greatly increase desorption of triclosan from sediment.The triclosan desorption efficiency with different surfactants followed the order of Tween 80 > rhamnolipid > Brij 35,which corresponded to the solubilization capacity of surfactant.Longer aging time of triclosan lasted in sediment,more difficulties in desorption from sediment.Considering the low bioavailability,poor biodegradation efficiency and long period during the biodegradation of triclosan by indigenous microorganisms in water-sediment systems,the effectiveness of different surfactants was compared to influence the biodegradation of triclosan.With the help of surfactant,triclosan was expected to dissolve from the sediment into the water and be degraded by indigenous microbes.The results manifested that the aerobic biodegradation of triclosan was significantly promoted by the addition of rhamnolipid.Rhamnolipid could both increase the solubility of triclosan in water phase and enhance the bioavailability of triclosan.But the addition of Tween 80 and Brij 35 has inhibitory effect on the aerobic biodegradation of triclosan,mostly due to the toxicity of chemical surfactants.The addition of different rhamnolipid congeners all improved the aerobic biodegradation efficiency of triclosan,up to 93.87% in samples with di-rhamnolipid addition.The higher aerobic degradation efficiency seen with di-rhamnolipid compared to mono-rhamnolipid could be ascribed to their different distribution capacities for triclosan in water-sediment systems.But the anaerobic biodegradation of triclosan could be ignored regardless of rhamnolipid amendment.The influence of environmental factors on rhamnolipid-enhanced biodegradation of triclosan was investigated by single factor experiments in this study.The results showed that the rhamnolipid-enhanced biodegradation of triclosan could achieve improved efficiency and economy by controlling environmental conditions.The environmental conditions,which included rhamnolipid addition(0.125-0.5 g/L),medium concentrations of triclosan(< 90 ?g/g),water disturbance,elevated temperature,ionic strength(0.001-0.1 mol/L NaCl)and weak alkaline environments(pH 8-9),were monitored.The shifts in aerobic triclosan-degrading bacterial populations,with and without rhamnolipid,were analyzed by 16 S rDNA high-throughput sequencing technology.60 ?g/g triclosan decreased community diversity and abundance of water-sediment systems.The bacterial community richness and diversity were the lowest in the application of triclosan(60 ?g/g)with rhamnolipid.High concentrations of triclosan had a remarkable influence on the bacterial community structure,and this influence on the distribution proportion of the main microorganisms was strengthened by rhamnolipid addition.Alpha-proteobacteria(e.g.,Sphingomonadaceae and Caulobacteraceae)might be resistant to triclosan or even capable of triclosan biodegradation,while Sphingobacteria,Beta-and Delta-proteobacteria were sensitive to triclosan toxicity.Considering the environmental compatibility and high performance,rhamnolipid could be used for enhanced bioremediation of aquatic environments polluted with triclosan.In summary,rhamnolipid could enhance the biodegradation of triclosan in water-sediment systems,and this was accompanied by shifts in indigenous microbes in triclosan-degrading systems.This research provides ecological information on the degradation efficiency and bacterial community stability in rhamnolipid-enhanced bioremediation of triclosan-polluted aquatic environments.