Yan Qu

Quantitative characterization of short- and long-chain perfluorinated acids in solid matrices in Shanghai, China.

Perfluorinated acids (PFAs) have been recognized as emerging environmental pollutants because of their widespread occurrences, persistence, and bioaccumulative and toxicological effects. PFAs have been detected in aquatic environment and biota in China, but the occurrences of these chemicals have not been reported in solid matrices in China. In the present study, short- and long-chain PFAs (C2-C14) have been quantitatively determined in solid matrices including sediments, soils and sludge collected in Shanghai, China. The results indicate that sludge contains more PFAs than sediments and soils, and the total PFAs concentrations in sediments, soil and sludge are 62.5-276 ng g(-1), 141-237 ng g(-1) and 413-755 ng g(-1), respectively. In most cases, trifluoroacetic acid was the major PFA and accounted for 22-90% of the total PFAs. Although the levels of perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS) were not only lower than trifluoroacetic acid, but also lower than some short-chain PFCAs (<C8) in some individual cases, PFOA and PFOS were still the major pollution compounds in most cases and they constituted 2-34% and 1-9% of the total PFAs, respectively. Meanwhile, unlike previous studies, PFOS levels were not always higher than PFOA in solids collected in Shanghai, China. Given that some short-chain PFAs such as trifluoroacetic acid are mildly phytotoxic and their higher levels in solid matrices were collected in Shanghai, China, these chemicals should be included in future environmental monitoring efforts.

Photo-reductive defluorination of perfluorooctanoic acid in water.

Globally distributed and highly stable, perfluorooctanoic acid (PFOA) has prompted much concern regarding its accumulation in the natural environment and its threats to ecosystems. Therefore, it is desirable to develop an effective treatment against PFOA pollution. In this study, a photo-reduction method is developed and evaluated for the decomposition of perfluorooctanoic acid (PFOA) in aqueous phase with potassium iodide (KI) as a mediator. The experiment was conducted under 254 nm irradiation at room temperature and pH 9 under anaerobic conditions. Ultraviolet photolysis of iodide solutions led to the generation of hydrated electrons (e(aq)(-), E(aq/e) degrees = -2.9 V), which contributed to the defluorination of PFOA. Defluorination was confirmed by fluoride release of 98%, indicating almost complete defluorination of PFOA. Kinetic analysis indicated that the PFOA decomposition fit the first-order model with a rate constant of 7.3 x 10(-3) min(-1). Besides fluoride ions, additional intermediates identified and quantified include formic acid, acetic acid, and six short-chain perfluorocarboxylic acids (C1-C6). Furthermore, small amounts of CF(3)H and C(2)F(6) were also detected as reaction products by using GC/MS. With observation of the degradation products and verification via an isotopic labeling method, two major defluorination pathways of PFOA are proposed: direct cleavage of C-F bonds attacked by hydrated electrons as the nucleophile; and stepwise removal of CF(2) by UV irradiation and hydrolysis. This method was applied to the decomposition of PFOA in wastewater issued from a fluorochemical plant and proved to be effective.

Equilibrium and kinetics study on the adsorption of perfluorooctanoic acid from aqueous solution onto powdered activated carbon

Powdered activated carbon (PAC) was applied to remove perfluorooctanoic acid (PFOA) from the aqueous PFOA solution in this study. Contact time, adsorbent dose and temperature were analyzed as the effect factors in the adsorption reaction. The contact time of maximum PFOA uptake was around 1h while the sorption removal efficiency increased with the PAC concentrations. And the process of adsorption increased from 303 K to 313 K and then decreased from 313 K to 323 K. Among four applied models, the experimental isotherm data were discovered to follow Langmuir isotherm model more closely. Thermodynamically, adsorption was endothermic because enthalpy, entropy and Gibbs constants were 198.5 kJ/mol, 0.709 kJ/mol/K and negative, respectively, which also indicated that the adsorption process was spontaneous and feasible. From kinetic analysis, the adsorption was suggested to be pseudo-second-order model. The adsorption of PFOA on the PAC was mainly controlled by particle diffusion.

Effect of initial solution pH on photo-induced reductive decomposition of perfluorooctanoic acid

The effects of initial solution pH on the decomposition of perfluorooctanoic acid (PFOA) with hydrated electrons as reductant were investigated. The reductive decomposition of PFOA depends strongly on the solution pH. In the pH range of 5.0-10.0, the decomposition and defluorination rates of PFOA increased with the increase of the initial solution pH. The rate constant was 0.0295 min(-1) at pH 10.0, which was more than 49.0 times higher than that at pH 5.0. Higher pH also inhibits the generation of toxic intermediates during the PFOA decomposition. For example, the short-chain PFCAs reached a lower maximum concentration in shorter reaction time as pH increasing. The peak areas of accumulated fluorinated and iodinated hydrocarbons detected by GC/MS under acidic conditions were nearly 10-100 times more than those under alkaline conditions. In short, alkaline conditions were more favorable for photo-induced reduction of PFOA as high pH promoted the decomposition of PFOA and inhibited the accumulation of intermediate products. The concentration of hydrated electron, detected by laser flash photolysis, increased with the increase of the initial pH. This was the main reason why the decomposition of PFOA in the UV-KI system depended strongly on the initial pH.

Method development for analysis of short- and long-chain perfluorinated acids in solid matrices

In order to help to elucidate the transport and fate of perfluorinated acids (PFAs) in the environment, a reliable and sensitive analytical method has been developed in present study for determination of short- and long-chain PFAs in various solid matrices. The method consisted of solvent extraction of PFAs from solid matrices using sonication, solid phase extraction (SPE) using weak anion exchange (WAX) cartridges, clean-up of SPE eluent with dispersive carbon sorbent and quantitation by high performance liquid chromatography-negative electrospray-tandem mass spectrometry (HPLC-negative ESI-MS/MS). The method detection limits (MDL) and quantitation limits (MQL), which were analyte- and sample-dependent, ranged from 0.02 to 0.06 ng g−1 and 0.10 to 0.90 ng g−1, respectively. The recoveries of all PFAs were generally good enough for quantitative analysis of these chemicals (57–115%), especially for short-chain (<C8, 80–115%) PFAs excluded in previous studies because methods were not available. The precisions of this method, represented by the percent relative standard deviation (RSD) of spiked measurements, were in a range of 1–19%. In addition, matrix effect did not affect analyte quantification in solid matrices in most cases, and the validated method was successfully applied to analyses of short- and long-chain PFAs in various solid matrices.

Adsorption Mechanism of Perfluorooctane Sulfonate on Granular Activated Carbon in Wastewater

Perfluorooctane sulfonate (PFOS) has increasingly attracted global concerns in recent years and has also been proposed as the candidates of persistent organic pollutants due to their world-wide distribution, environmental persistence and bioaccumulation potential. The adsorption mechanism of PFOS from aqueous solutions onto granular activated carbon (GAC) was investigated. The adsorption reaction obtains equilibrium within 180 min and the maximum PFOS removal tended to be 99%. And the results of regression to the experimental data show that t the adsorption of PFOA onto the GAC was mainly governed by particle diffusion.

The Determination of Dynamic Adsorption Curve, Adsorption Capacity and Breakthrough Capacity of Powdered Activated Carbon for Perfluorooctanoic Acid elimination from Water

The batch and dynamic adsorption of powdered activated carbon (PAC) as an adsorbent to eliminate the PFOA from the water for reuse has been studied. The first 100 mL influent (0.5 mmol/L) was totally adsorbed (100%) and more than eighty percent adsorption of PFOA was observed in the next 101-230 mL influent. The static adsorption capacity and the breakthrough capacity were 104.6 mg/g and 95.22 mg/g respectively. The results obtained in the study helped in developing a new process in the water reuse system to eliminate PFOA from water and also established the technical foundation for the practical application of adsorption process.

Determination and Elimination of Matrix Effect in Analysis of Perfluorinated Acids Using High Performance Liquid Chromatography-Negative Electrospray Tandem Mass Spectrometry

Matrix effects, ionization enhancement or suppression, are always possible with the electrospray ionization technique and can significantly hamper the analysis of PFAs in complex environmental matrixes. The objective of this study is to determine and eliminate the matrix effects in analysis of sewage using high performance liquid chromatography-negative electrospray tandem mass spectrometry (HPLC-negative ESI-MS/MS). Standard addition, which involves spiking successive known quantities of a standard into the sample extracts and reanalyzing, are used for determination of the matrix effects, while correction using isotopically labeled internal standards and clean-up of sample extracts using dispersive carbon sorbent are used for elimination of matrix effects. The results indicate that ultra-short- (C2-3) and long-chain PFCAs (>C10) suffer ionization suppression, while medium-chain PFCAs (C4-10) and PFBS experience ionization enhancement; however, PFHxS and PFOS do not suffer significant matrix effects. Although internal standards, MPFOA and MPFOS, can effectively negate matrix effects for medium-chain PFCAs (C7-10), they are not suitable for some short- ( C10 PFCAs), which are eluted significantly earlier or later than their retention times, respectively. However, matrix effects of all analytes are significantly naegated by dispersive carbon sorbent because it can effectively remove the co-eluting interference compounds from SPE elution but not affect PFAs.

Material Properties for Degradation and Reduction of Perfluorinated Acid in Complex Pollution System by Photo-Induced Hydrated Electrons

F, the most electronegative element, is easy to catch the electrons in the bonds to form the stabilized C-F. Perfluorinated acids have high chemical stability which can tolerate acid, alkali, etc. Inhibition effect was observed in the complex pollution system in which 7 kinds of perfluorinated acids existed simultaneously. The formation of hydrated electrons was the rate-limiting step in complex pollution system, and the inhibition was increased as the carbon chain increasing. Compared the reduction rate of perfluorinated acids by photo-induced hydrated electrons in the complex pollution system with the single rate, the results showed that there were positive linear correlations between the degradation rate and photo-induced hydrated electrons. The degradation multiples of perfluorinated acids were studied, it concluded that, because of the competition among the 7 kinds of perfluorinated acids, the degradation rates were influenced.

The Environmental Matrix Effects of Inorganic Ions to Photo-Reductive Defluorination of Perfluorooctanoic Acid

Perfluorooctanoic acid (PFOA), one of persistent organic pollutants (POPs), has prompted much concern in the last fifty years. Its accumulation in the natural environment is increased, and its threats to ecosystems have been discovered. Because of the highly stable, PFOA was hardly decomposed and defluorination. In previous study, a photo-reduction method is developed for the decomposition of PFOA in Milli-Q water with potassium iodide (KI) as a mediator. But this system wasn’t discussed in natural environment. In this study, several common inorganic ions in the surface water were been choice as the object. By analyzing the matrix effects of different kinds of anions and cations to the photo-reductive defluorination of PFOA, it shows that the presence of anions in the system will heavily inhibit the degradation process, while the impact of cations to the degradation is related to the concentration. And, both anions and cations can inhibit the defluorination process, but anions have much greater impact than the cations to the defluorination rate.