Competitive Solubilization Of Polybrominated Diphenyl Ethers And Co-existing Compounds In Surfactant Micelles

Electronic-waste(e-waste)contamination is one of the most concerned research topics in China and abroad.Driven by huge profits,many towns in China(e.g.,Longtang,Shijiao,and Guiyu town in Guangdong province)started working on e-waste dismantling and recycling.Due to “non-standard” disposal of e-wastes,large amounts of organic contaminants have been released into soil environment,posing great threaten to soil ecosystem.Surfactant enhanced remediation(SER)is a traditional technique that can facilitate the transport of contaminants from soil to aqueous solution,making it available for subsequent treatments such as photolysis,biodegradation,and advanced oxidation.In many cases,various types of contaminants can co-exist in soils,which may affect the efficiency of surfactants.During remediation,the interactions among surfactants,cosolvents,and contaminants may also affect remediation.I selected polybrominated diphenyl ethers(PBDEs)and polycyclic aromatic hydrocarbons(PAHs)as the representatives in e-waste soils,and explored their co-soluiblization in surfactant micelles.Therefore,the main results of this study are as follows:(1)I developed the method for quantifying BDE-209 and other PBDE congeners in soils by soxhlet extraction and HPLC.1: 1 of acetone and methanol was selected as the optimal solvent mixture with high performance on the solubilization of BDE-209 in soil samples,which can avoid the interference of acetone ultraviolet adsorption under 330 nm.The concentration of BDE-209 showed good repeatability(RSD = 1.1-11.4%).No matrix effect was observed during the quantification of BDE-209(recovery = 91.1-116.1%).The limit of detection and quantification is 0.1 and 1 ?g/L,respectively,better than some traditional methods.This method can effectively avoid the thermolysis of PBDEs under high temperature,indicating its potential for the precise quantification of trace PBDEs in soils.(2)I explored the solubilization of BDE-15 by TX-100/cosolvents(methanol,ethanol,n-propanol,and dimethyl sulfoxide(DMSO)),and further verified their potential for washing BDE-15 contaminated soil.TX-100/cosolvents significantly increased the solubility of BDE-15.TX-100/DMSO had the best performance on BDE-15 solubilization.However,larger volume fractions of cosolvents showed negative effects on the solubilization of BDE-15 due to micelle breakdown.With the addition of 10% DMSO and 6.4 mM TX-100 solution,the highest removal efficiency of BDE-15(92.9%)was achieved,relative to that of 67.3% with TX-100 alone at the same concentration.The partial least squanre(PLS)regression model indicated that the molecular weight,polarity,melting point,and boiling point of the cosolvents are the key factors that affect their applicability.During the remediation of e-waste site soils,we suggest that cosolvents with relatively small molecular weight and more polar nature should be considered for soil washing.(3)I explored the solubilization and co-solubilization of BDE-15,Nap,and Pyr in various surfactant systems.Synergism was observed for Nap/Pyr in Tween80,Brij58,CTAB,and SDBS micellar solutions due to palisade layer solubilization of Nap and Pyr that resulted in reduction of interfacial tension,leading to increases in solubilization spaces.Inhibition occurred in Brij78 surfactant system due to competitive solubilization of PAHs for the same solubilization site.BDE-15 probably had great affinity for hydrophilic chains of surfactants due to non-covalent halogen bonding that occurred between bromines and electron donors on the hydrophilic chains,resulting in synergism for BDE-15/Pyr in all surfactant systems and resulting in inhibition for BDE-15/Nap in Brij58,Brij78,and CTAB surfactant systems.Therefore,attention should be paid on PBDEs-micelle interactions when selecting a proper surfactant for remediation.(4)I investigated the co-solubilization of BDE-15,Nap,and Pyr in TX series surfactant micelles.During co-solubilization,a stronger synergism was observed for Nap/Pyr and BDE-15/Pyr when the hydrophilic chain length increased.In contrast,inhibition was observed for BDE-15/Nap in TX-305 and TX-405 surfactant systems.1H nuclear meganetic resonance(1H NMR)showed that the protons on the outer hydrophilic chain of each surfactant did not undergo any upfield shifts,and the upfield shifts that occurred on the innermost hydrophilic groups gradually disappeared as the polyethylene oxide chain length increased.In addition,Fourier Transform Infrared spectroscopy(FTIR)results showed that the C-Br stretching and torsional frequencies of BDE-15 decreased slightly as TX-100 monomers were added.These results further demonstrate the interactions between BDE-15 and surfactant hydrophilic chains.(5)I explored the soil washing of contaminated soils,and the co-solubilization of BDE-15,BDE-28,and BDE-47 in Brij series surfactant micelles.We found that the desorption efficiencies of BDE-15 and Pyr from a soil were higher than those existed separately,indicating that inhibitive or synergistic effects should be considered during remediation.The solubilities of low-BDEs during co-solubilization were increased in all of the surfactants tested,relative to their respective solubilities during solubilization.In each surfactant system,synergism was weaker for BDE-15/BDE-28 than that for BDE-15/BDE-47 because BDE-15 and BDE-28 may be partitioned more uniformly in the micelle core than BDE-47,which increased the possibility of their competition.Computational analysis demonstrates that these BDEs have positive electrostatic potentials on bromines atoms which may provide additional attractions to oxygen atoms of the hydrophilic chains.Based on co-solubilization results,we infer that a surfactant with lower aggregation number can also be employed for soil remediation.