Perfluorooctanesulfonate (PFOS) Conversion from N-Ethyl-N-(2-hydroxyethyl)-perfluorooctanesulfonamide (EtFOSE) in male Sprague Dawley rats after inhalation exposure.

Ethyl-N-(2-hydroxyethyl)-perfluorooctanesulfonamide (EtFOSE) was one of the key building blocks for many of the perfluorooctanesulfonyl-based chemistry and laboratory studies have shown that EtFOSE can metabolically degrade to perfluorooctanesulfonate (PFOS). Non-occupational contribution sources to PFOS are thought to occur in general population via diets, drinking water, air and dust. For workers, however, the exposure route was mostly airborne and the exposure source was predominantly to precursor compounds such as EtFOSE. We undertook this study to investigate how much EtFOSE was converted to PFOS in the serum for male rats after 6h of exposure to EtFOSE vapor (whole body) at ambient temperature, which simulated a work place exposure scenario. There were no abnormal clinical observations and all rats gained weight during study. Interim tail-vein blood samples, collected up to 21 days after exposure, were analyzed for Et-FOSE and PFOS concentrations by LC-MS/MS. Upon inhalation exposure, the biotransformation of EtFOSE to PFOS in serum in the male rats was rapid and very little EtFOSE was detected in the serum within 24h after EtFOSE exposure. The highest conversion to PFOS in serum after exposure to EtFOSE vapor appeared to occur between Day 8-14 post exposure. Considering the potential surface and fur adsorption of test compound in the whole-body exposure system, our data would support that at least 10% of the inhaled EtFOSE was biotransformed to PFOS in the serum based on the range of lower 95% CI (confidence interval) values. This information is valuable because it quantitatively translates EtFOSE exposure into serum PFOS concentration, which serves as a matrix for internal dosimetry (of PFOS exposure) that can be used as an anchor across species as well as between different exposure routes.

Measurements of nanomaterials in environmentally relevant water matrices using liquid nebulization/differential mobility analysis.

A liquid nebulization-differential mobility analysis methodology was evaluated for the measurement of the size distribution and quantitative mass concentration of nanomaterials in environmentally relevant aqueous media. The analysis time is 8 min, and the method requires little routine sample preparation and less than 8 mL of sample. The method can be used for rapid, direct analysis of nanomaterials in aqueous media with a particular application to dose verification in ecotoxicology studies, analysis of manufacturing process waste streams, and raw material analysis. Twelve reference materials having a diameter traceable to the National Institute of Standards and Technology were spiked into 6 different aqueous matrices that included drinking water, groundwater, industrial wastewater, as well as the algae and daphnia media used in ecotoxicology testing. Measurement of the diameter of a reference material was within the expected range for the reference material. Individual response factors for each reference material were determined in each medium and the accuracy and precision of the concentration measurements evaluated. In ecotoxicology test media, measurements of the concentration of nanoparticles having diameter ≥ 30 nm, had corresponding accuracies and precisions of 103% and 7%, respectively. Over 28 d 86% of the samples had concentrations within 20% of the initial concentration. The method limit of quantification depended primarily on matrix complexity and particle diameter; the limit of quantification ranged from 0.01 mg/L to 3 g/L.

Reductive degradation of perfluoroalkyl compounds with aquated electrons generated from iodide photolysis at 254 nm.

The perfluoroalkyl compounds (PFCs), perfluoroalkyl sulfonates (PFXS) and perfluoroalkyl carboxylates (PFXA) are environmentally persistent and recalcitrant towards most conventional water treatment technologies. Here, we complete an in depth examination of the UV-254 nm production of aquated electrons during iodide photolysis for the reductive defluorination of six aquated perfluoroalkyl compounds (PFCs) of various headgroup and perfluorocarbon tail length. Cyclic voltammograms (CV) show that a potential of +2.0 V (vs. NHE) is required to induce PFC oxidation and -1.0 V is required to induce PFC reduction indicating that PFC reduction is the thermodynamically preferred process. However, PFCs are observed to degrade faster during UV(254 nm)/persulfate (S(2)O(8)(2-)) photolysis yielding sulfate radicals (E° = +2.4 V) as compared to UV(254 nm)/iodide (I(-)) photolysis yielding aquated electrons (E° = -2.9 V). Aquated electron scavenging by photoproduced triiodide (I(3)(-)), which achieved a steady-state concentration proportional to [PFOS](0), reduces the efficacy of the UV/iodide system towards PFC degradation. PFC photoreduction kinetics are observed to be dependent on PFC headgroup, perfluorocarbon chain length, initial PFC concentration, and iodide concentration. From 2 to 12, pH had no observable effect on PFC photoreduction kinetics, suggesting that the aquated electron was the predominant reductant with negligible contribution from the H-atom. A large number of gaseous fluorocarbon intermediates were semi-quantitatively identified and determined to account for ∼25% of the initial PFOS carbon and fluorine. Reaction mechanisms that are consistent with kinetic observations are discussed.

Sonochemical degradation of perfluorooctanesulfonate in aqueous film-forming foams.

Aqueous film-forming foams (AFFFs) are fire extinguishing agents developed by the Navy to quickly and effectively combat fires occurring close to explosive materials and are utilized today at car races, airports, oil refineries, and military locations. Fluorochemical (FC) surfactants represent 1-5% of the AFFF composition, which impart properties such as high spreadability, negligible fuel diffusion, and thermal stability to the foam. FC's are oxidatively recalcitrant, persistent in the environment, and have been detected in groundwater at AFFF training sites. Ultrasonic irradiation of aqueous FCs has been reported to degrade and subsequently mineralize the FC surfactants perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS). Here we present results of the sonochemical degradation of aqueous dilutions of FC-600, a mixture of hydrocarbon (HC) and fluorochemical components including cosolvents, anionic hydrocarbon surfactants, fluorinated amphiphilic surfactants, anionic fluorinated surfactants, and thickeners such as starch. The primary FC surfactant in FC-600, PFOS, was sonolytically degraded over a range of FC-600 aqueous dilutions, 65 ppb < [PFOS]i < 13100 ppb. Sonochemical PFOS-AFFF decomposition rates, RAFFF-PFOS, are similar to PFOS-Milli-Q rates, RMQ-PFOS, indicating that the AFFF matrix only had a minor effect on the sonochemical degradation rate, 0.5 < RAFFF-PFOS/RMQ-PFOS < 2.0, even though the total organic concentration was 50 times the PFOS concentration, [Org]tot/[PFOS] 50, consistent with the superior FC surfactant properties. Sonochemical sulfate production is quantitative, delta[SO42-]/delta[PFOS] > or = 1, indicating that bubble-water interfacial pyrolytic cleavage of the C-S bond in PFOS is the initial degradation step, in agreement with previous studies done in Milli-Q water. Sonochemical fluoride production is significantly below quantitative expectations, delta[F-]/delta[PFOS] 4 vs 17, suggesting that in the AFFF matrix, PFOS' fluorochemical tail is not completely degraded, whereas Milli-Q studies yielded quantitative F- production. Measurements of time-dependent methylene blue active substances and total organic carbon indicate that the other FC-600 components were also sonolytically decomposed.

Sonochemical degradation of perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) in groundwater: kinetic effects of matrix inorganics.

Ultrasonic irradiation has been shown to effectively degrade perfluorinated chemicals (PFCs) such as perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) in aqueous solution. Reduced PFC sonochemical degradation rates in organic-rich groundwater taken from beneath a landfill, however, testify to the negative kinetic effects of the organic groundwater constituents. In this study, the PFOX (X = S or A) sonochemical degradation rates in a groundwater sample with organic concentrations about 10 times lower than those in the groundwater taken from beneath a landfill are found to be 29.7% and 20.5% lower, respectively, than the rates in Milli-Q water, suggesting that inorganic groundwater constituents also negatively affect PFC sonochemical kinetics. To determine the source of the groundwater matrix effects, we evaluate the effects of various inorganic species on PFOX sonochemical kinetics. Anions over the range of 1-10 mM show Hofmeister effects on the sonochemical degradation rates of PFOX, kClO4(-) (-PFOX) > kNO3(-) (-PFOX) kCl(-) (-)PFOX > or = kMQ-PFOX > kHCO3(-) (-PFOX) kSO42(-) (-PFOX). In contrast, common cations at 5 mM have negligible effects. Initial solution pH enhances the degradation rates of PFOX at 3, but has negligible effects over the range of 4 to 11. The observed inorganic effects on sonochemical kinetics are hypothesized to be due to ions' partitioning to and interaction with the bubble-water interface. Finally, it is shown that the rate reduction in the groundwater in this study is primarily due to the presence of bicarbonate and thus can be fully rectified by pH adjustment prior to sonolysis.

Perfluorinated surfactant chain-length effects on sonochemical kinetics.

The sonochemical degradation kinetics of the aqueous perfluorochemicals (PFCs) perfluorobutanoate (PFBA), perfluorobutanesulfonate (PFBS), perfluorohexanoate (PFHA), and perfluorohexanesulfonate (PFHS) have been investigated. Surface tension measurements were used to evaluate chain-length effects on equilibrium air-water interface partitioning. The PFC air-water interface partitioning coefficients, KeqPF, and maximum surface concentrations, Gamma(max)PF, were determined from the surface pressure equation of state for PFBA, PFBS, PFHA, and PFHS. Relative KeqPF values were dependent upon chain length KeqPFHS approximately equal to 2.1KeqPFHA approximately equal to 3.9KeqPFBS approximately equal to 5.0KeqPFBA, whereas relative GammamaxPF values had minimal chain length dependence Gamma(max)PFHS approximately equal to Gamma(max)PFHA approximately equal to Gamma(max)PFBS approximately equal to 2.2Gamma(max)PFBA. The rates of sonolytic degradation were determined over a range of frequencies from 202 to 1060 kHz at dilute (<1 microM) initial PFC concentrations and are compared to previously reported results for their C8 analogs: perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA). Under all conditions, the time-dependent PFC sonolytic degradation was observed to follow pseudo-first-order kinetics, i.e., below kinetic saturation, suggesting bubble-water interface populations were significantly below the adsorption maximum. The PFHX (where X = A or S) sonolysis rate constant was observed to peak at an ultrasonic frequency of 358 kHz, similar to that for PFOX. In contrast, the PFBX degradation rate constants had an apparent maximum at 610 kHz. Degradation rates observed for PFHX are similar to previously determined PFOX rates, kapp,358PFOX approximately equal to kapp,358PFHX. PFOX is sonolytically pyrolyzed at the transiently cavitating bubble-water interface, suggesting that rates should be proportional to equilibrium interfacial partitioning. However, relative equilibrium air-water interfacial partitioning predicts that KeqPFOX 5KeqPFHX. This suggests that at dilute PFC concentrations, adsorption to the bubble-water interface is ultrasonically enhanced due to high-velocity radial bubble oscillations. PFC sonochemical kinetics are slower for PFBS and further diminished for PFBA as compared to longer analogs, suggesting that PFBX surface films are of lower stability due to their greater water solubility.

Reductive defluorination of aqueous perfluorinated alkyl surfactants: effects of ionic headgroup and chain length.

Perfluorinated chemicals (PFCs) are distributed throughout the environment. In the case of perfluorinated alkyl carboxylates and sulfonates, they can be classified as persistent organic pollutants since they are resistant to environmentally relevant reduction, oxidation, and hydrolytic processes. With this in mind, we report on the reductive defluorination of perfluorobutanoate, PFBA (C(3)F(7)CO(2)(-)), perfluorohexanoate, PFHA (C(5)F(11)CO(2)(-)), perfluorooctanoate, PFOA (C(7)F(15)CO(2)(-)), perfluorobutane sulfonate, PFBS (C(4)F(9)SO(3)(-)), perfluorohexane sulfonate, PFHS (C(6)F(13)SO(3)(-)), and perfluorooctane sulfonate, PFOS (C(8)F(17)SO(3)(-)) by aquated electrons, e(aq)(-), that are generated from the UV photolysis (lambda = 254 nm) of iodide. The ionic headgroup (-SO(3)(-) vs -CO(2)(-)) has a significant effect on the reduction kinetics and extent of defluorination (F index = -[F(-)](produced)/[PFC](degraded)). Perfluoroalkylsulfonate reduction kinetics and the F index increase linearly with increasing chain length. In contrast, perfluoroalkylcarboxylate chain length appears to have a negligible effect on the observed kinetics and the F index. H/F ratios in the gaseous fluoro-organic products are consistent with measured F indexes. Incomplete defluorination of the gaseous products suggests a reductive cleavage of the ionic headgroup occurs before complete defluorination. Detailed mechanisms involving initiation by aquated electrons are proposed.

Sonochemical degradation of peerfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) in landfill groundwater: environmental matrix effects.

Perfluorinated chemicals such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are environmentally persistent and recalcitrant to most conventional chemical and microbial treatment technologies. In this paper, we show that sonolysis is able to decompose PFOS and PFOA present in groundwater beneath a landfill. However, the pseudo first-order rate constant for the sonochemical degradation in the landfill groundwater is reduced by 61 and 56% relative to MilliQ water for PFOS and PFOA, respectively, primarily due to the presence of other organic constituents. In this study, we evaluate the effect of various organic compounds on the sonochemical decomposition rates of PFOS and PFOA. Organic components in environmental matrices may reduce the sonochemical degradation rates of PFOS and PFOA by competitive adsorption onto the bubble-water interface or by lowering the average interfacial temperatures during transient bubble collapse events. The effect of individual organic compounds depends on the Langmuir adsorption constant the Henry's law constant the specific heat capacity, and the overall endothermic heat of dissociation. Volatile organic compounds (VOCs) are identified as the primary cause of the sonochemical rate reduction for PFOS and PFOA in landfill groundwater, whereas the effect of dissolved natural organic matter (DOM) is not significant Finally, a combined process of ozonation and sonolysis is shown to substantially recover the rate loss for PFOS and PFOA in landfill groundwater.

Kinetics and mechanism of the sonolytic conversion of the aqueous perfluorinated surfactants, perfluorooctanoate (PFOA), and perfluorooctane sulfonate (PFOS) into inorganic products.

The perfluorinated surfactants perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) are recognized as widespread in the environment as well as recalcitrant toward most conventional water treatment technologies. In this study, acoustic cavitation as driven by high-frequency ultrasound is shown to be effective in the degradation of aqueous solutions of PFOS and PFOA and effective over a wide range of concentrations from 10 nM to 10 muM for a given compound. Sulfur, fluorine, and carbon mass balances indicate that mineralization occurs immediately following the degradation of the initial perfluorinated surfactant. Near complete conversion of PFOS and PFOA to CO, CO2, F-, and SO42- occurs due to pyrolytic reactions at the surface and vapor phase of transiently collapsing cavitation bubbles. The initial PFOS or PFOA pyrolytic degradation occurs at the bubble-water interface and involves the loss of the ionic functional group leading to the formation of the corresponding 1H-fluoroalkane or perfluoroolefin. The fluorochemical intermediates undergo a series of pyrolytic reactions in the bubble vapor leading to C1 fluoro-radicals. Secondary vapor-phase bimolecular reactions coupled with concomitant hydrolysis converts the C1 fluoro-radicals to carbon monoxide, carbon dioxide, and HF, forming a proton and fluoride upon dissolution. Sonochemical half-lives, which are calculated from high-temperature gas-phase kinetics, are consistent with kinetic observations and suggest that mineralization occurs shortly after initial perfluorinated surfactant interfacial pyrolysis.

Study of the effects of particle-phase carbon on the gas/particle partitioning of semivolatile organic compounds in the atmosphere using controlled field experiments.

A controlled field experiment (CFE) methodology with a filter/sorbent sampler was used to minimize artifact effects when measuring values of the gas/particle (G/P) partitioning constant (Kp, m3 microg(-1)) for semivolatile organic compounds (SOCs) in the atmosphere. CFE sampling was conducted at three different locations (Beaverton, OR; Denver, CO; and Hills, IA). Kp values were measured for a series of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated dibenzodioxins and dibenzofurans (PCDD/Fs). To examine the possible effects on the G/P partitioning of the amounts of organic material (om) phase, organic carbon (OC), and elemental carbon (EC) in the sampled particulate material, the measured Kp values were normalized by the aerosol mass fractions f(om), f(OC), and f(EC) according to Kp/ f(om), Kp/f(OC), and Kp/f(EC). Using a log-log format, the resulting normalized values were all found to be more highly correlated with the subcooled liquid vapor pressure p(L)o than were the unnormalized Kp values. For the PAHs,the one-parameter model assuming Kp = Kp,OC f(OC) yielded only slightly less variability in the predicted Kp values than did the one-parameter model Kp = Kp,EC f(EC). The two-parameter model Kp = Kp,OC f(OC) + Kp,EC f(EC) was found to provide only small improvements over each of the one-parameter models. Overall, the data are more consistent with an absorptive mechanism of partitioning to the particulate material but do not rule out some role for adsorption to particle surfaces. The data suggest that small amounts of organic carbon (f(OC) approximately 0.02) can have significant effects on the G/P partitioning of SOCs.