Degradation of VX Surrogate Profenofos on Surfaces via in Situ Photo

Article pubs.acs.org/est

Degradation of VX Surrogate Profenofos on Surfaces via in Situ Photo-oxidation Lauren M. Petrick,*,† Sara Sabach,‡ and Yael Dubowski‡ †

Technion Center of Excellence in Exposure Science and Environmental Health (TCEEH) and ‡Faculty of Civil and Environmental Engineering, Technion-Israel Institute of Technology, Haifa, Israel S Supporting Information *

ABSTRACT: Surface degradation of profenofos (PF), a VX nerve gas surrogate, was investigated using in situ photo-oxidation that combines simple instrumentation and ambient gases (O2 and H2O) as a function of exposure conditions ([O3], [OH], UV light λ = 185 and/or 254 nm, relative humidity) and PF film surface density (0.38−3.8 g m−2). PF film 0.38 g m−2 fully degraded after 60 min of exposure to both 254 and 185 nm UV light in humidified air and high ozone. The observed pseudo-firstorder surface reaction rate constant (kobs = 0.075 ± 0.004 min−1) and calculated hydroxyl concentration near the film surface ([OH]g = (9 ± 2) × 107 molecules cm−3) were used to determine the second-order rate constant for heterogeneous reaction of PF and OH (kOHPF = (5 ± 1) × 10−12 cm3 molec−1 s−1). PF degradation in the absence of 185 nm light or without humidity was lower (70% or 90% degradation, respectively). With denser PF films ranging from 2.3 to 3.8 g m−2, only 80% degradation was achieved until the PF droplet was redissolved in acetonitrile which allowed >95% PF degradation. Surface product analysis indicated limited formation of the nontoxic phosphoric acid ester but the formation of nonvolatile chemicals with increased hydrophilicity and addition of OH.

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INTRODUCTION The use of chemical warfare agents (CWA) in either a domestic terrorist attack or military conflict is a growing threat. Nerve agents and organophosphate pesticides (OP) are phosphorus(V) compounds with a terminal oxide and three singly bonded substituents that are potent acetylcholinesterase (AChE) active agents because of their phosphorylating mode of action. Nerve agents such as VX are persistent chemicals with low volatility, leading to possible prolonged exposure due to surface contact. Thus, after a potential exposure scenario, proper decontamination of such CWA is needed. Although traditional CWA treatments (such as bleaching powders, Decontamination Solution #2, and decontamination foams) are effective, they require the storage, transport, and disposal of large volumes of toxic chemicals,1,2 and cannot be applied on liquid-sensitive surfaces. Novel heterogeneous decontaminating agents, such as metal oxides,3,4 require prolonged contact time with the nerve agent which may not be achievable on vertical or porous surfaces. Thus, decontamination of CWA that are adsorbed on liquid-sensitive surfaces or vertical surfaces (indoor walls and ceilings), as well as the ability to reach residues entrapped within cracks or voids on the surface, remains a major challenge. An attractive treatment option is the use of gaseous hydroxyl radicals (OH) to decompose contaminated surfaces (adsorbed as films or droplets). While photocatalytic processes have been found to be effective degradation processes for many organics (including VX surrogates) in aqueous solution5,6 and in films7 they require the additional use of a catalyst. Decontamination by radicals in the absence of a catalyst has been demonstrated © 2013 American Chemical Society

by the atmospheric pressure plasma jet (APPJ) technique which showed high removal efficiency for a VX surrogate but in some cases resulted in the formation of oxidation products that were not necessarily less toxic.8,9 In addition, this system required expensive equipment, increased plume temperatures of ∼380 K, and high flow rates of helium carrier gas, making field operation more difficult. An alternative OH generation process is ozone photolysis in the presence of water vapor.10 This process uses simple instrumentation with ambient gases (O2 and H2O), does not cause a significant increase in treatedsurface temperature, and combines radicals, ozone, and shortwave UV light (reactions 1−4) that may act as additional decontamination agents.11

Low volatility OP pesticides routinely serve as surrogates for VX nerve agents,12,1 and their oxidation by OH radicals in the Received: Revised: Accepted: Published: 8751

April 16, 2013 July 1, 2013 July 2, 2013 July 2, 2013 dx.doi.org/10.1021/es4016537 | Environ. Sci. Technol. 2013, 47, 8751−8758

Environmental Science & Technology

Article

Table 1. Experimental Conditions for PF Degradation in LR experimental conditions

reactive gases present

expt number

expt name

ozone formation

N2

air

RH

O3

254 nm

185 nm

[O3] range ppm

OH

1 2 3 4 5 6 7 8 9

185/254-wet-high-ozone 185/254-wet-low-ozone 185/254-dry-high-ozone 185/254-dry-low-ozone 254-wet-low-ozone 254-dry-low-ozone N2 wet N2 dry O3 dry

in situ in situ in situ in situ ex situ ex situ none none ex situ

no yes no yes yes yes yes yes no

yes yes yes yes yes yes no no yes

yes yes no no yes no yes no yes

no no no no yes yes no no yes

yes yes yes yes yes yes no no no

yes yes yes yes no no no no no

105−133 5−32 539−716 12−75 0.5−1.5 0.5−1.5 none none 125−177

yes yes no no yes no no no no

gas phase is very fast (k ∼ 4 × 10−11 cm3 molec−1 s−1 13,14), suggesting a half-life time of approximately 1 h at [OH] = 107 molecules cm−3. This lifetime is expected to shorten under the proposed decontamination conditions which combines OH radicals, O3, shortwave UV light, and atomic oxygen.15 While organic film oxidation by hydroxyl radicals is not new,16−18 there is only limited work on the heterogeneous degradation of organics using photo-oxidation (combined OH radicals and shortwave UV light),19 particularly for OP compounds or VX surrogates. Furthermore, whether the process results in VX detoxification is unknown. In the present study we investigate the degradation of the VX surrogate profenofos (PF) film via in situ photo-oxidation under various exposure conditions. While the anticholinesterase mechanism of action for VX and profenofos is due to the oxo (PO) group, it is also influenced by the presence of alkyl substituents.20 Thus, profenofos was chosen as the surrogate due to the presence of thiophoshate groups but with lower volatility21 and toxicity.22

radicals were formed in a two-phase experiment (ex situ) where ozone was generated upstream of the reactor by photolyzing a dry flow of air/N2 in a Jelight 600 ozone generator. This ozone mixture was then humidified prior to entrance into the reactor containing the 254 nm lamp. Experiments 7−9 investigated evaporation and oxidation of PF in the absence of UV lamps. Ozone concentration was monitored (2BTechnologies, M202) at the reactor outlet during in situ experiments and at the reactor inlet for ex situ experiments. Additional experiments were run using a small reactor which was easier to manipulate. Experiments were run using a PF film of 2.3 g m−2 under similar conditions as in the LR (Table 2). Table 2. Experimental Conditions for PF Degradation in SR experimental conditions

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EXPERIMENTAL SECTION Profenofos degradation was investigated as a function of exposure to ambient gases (N2, air), UV photolysis (λ = 185 and λ = 254 nm), and the various oxidants formed as a function of in situ photolysis reaction. Both large and small reactors were used, depending on the experimental conditions desired. The large reactor (LR) (V = 2 L) had a Teflon cover with a central inlet and five outlets symmetrically distributed around the UV lamp near the base (Figure S1a, Supporting Information). Five glass slides with profenofos film were placed in front of the outlets to ensure reaction gas contact. The small reactor (SR) was a 1 L flow-through glass vessel that held up to two UV lamps. Six glass slides with profenofos film were placed 3 cm below the lamps for optimal contact (Figure S1b). OH Generation and Experimental Conditions. Gases entered the reactor at 500 mL min−1 (LR) or 250 mL min−1 (SR) (±5%). Humidity of 70 ± 5% (“wet”) was monitored (AHLBORN Almemo 2390-3) and obtained by bubbling the inlet gases through DI water (18.2 MΩ water, Millipore). Carrier gas mixtures (air, N2) and UV lamps (λ = 185/254 nm or λ = 254 nm) (7 in. Jelight, double bore, PN: 78-2046-7 or 81-3306-7, respectively) were used to generate OH radicals according to reactions 1−4. Average intensity of each lamp is 25 W (according to the manufacturer). Experimental conditions tested in the LR are described in Table 1. In experiments 1−4 both ozone and OH radicals were formed in situ using 185/254 nm light in the presence of humidified air. In this case, the inlet gases bypassed the ozone generation system in Figure S1a. In experiments 5 and 6, OH

expt number

carrier gases

time (min)

10

wet air

30

11

wet air

60

12

dry air

60

13

wet N2

60

14

dry N2

60

15

wet air

60

16

wet air

60

17

wet air

30/30a

18

wet air

30/30

19

wet air

30/30

20

wet air

60/60b

21 22 23

dry N2 wet N2 dry air

60 60 60

lamps present one lamp 185/254 one lamp 185/254 one lamp 185/254 one lamp 185/254 one lamp 185/254 two lamps 185/254 one lamp 185/254 + one lamp 254 one lamp 185/254 two lamps 185/254 one lamp 185/254 + one lamp 254 one lamp 185/254 no lamp no lamp no lamp

[ozone]outlet (ppm ± SD)

degradation efficiency (% ± SE] (n)c

190 ± 15

55 ± 4 (12)

190 ± 15

79 ± 2 (24)

660 ± 60

62 ± 3 (24)

0

69 ± 2 (17)

0

57 ± 3 (18)

180 ± 5

83 ± 3 (18)

145 ± 5

80 ± 3 (16)

185 ± 10

90 ± 1 (6)

185 ± 10

95 ± 1 (12)

160

93 ± 1 (5)

192 ± 5

96 ± 2 (9)

0 0 0

8 ± 2 (10) 5 ± 1 (10) 6 ± 2 (6)

a Sample films were exposed for 30 min, mixed, and returned to the reactor for an additional 30 min of exposure (see Effect of Exposure Conditions and PF Film Density in Results and Discussion). bSample films were exposed for 60 min, mixed, and returned to the reactor for an additional 60 min of exposure. cn = number of replicates.

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dx.doi.org/10.1021/es4016537 | Environ. Sci. Technol. 2013, 47, 8751−8758


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PF Films. Profenofos (PF) films were generated by applying solutions of PF (Sigma-Aldrich) in acetonitrile to a glass slide and evaporating the solvent. Once dried (profenofos film densities of 0.38, 2.3, and 3.8 g m−2), the slides were placed in the reactor. In all cases the generated films were multilayer. Gases equilibrated for 30 min in the reactor before the UV lamp was turned on. PF films were exposed as a function of time (from 5 to 360 min) and degradation monitored with HPLC-UV. ATR-FTIR. Complementary to the degradation experiments conducted in the two reactors, an additional set of experiments was performed using ATR-FTIR spectroscopy. The ATR-FTIR experimental system consisted of a ZnSe ATR crystal (HATRPlus by Pike Technologies Inc., Madison, WI) attached to a Bruker Tensor 27 FTIR with a mercury cadmium telluride detector. In these experiments a film was deposited on the ZnSe ATR crystal and spectra were obtained. To capture realtime monitoring of PF film as a function of exposure, the LR was refitted to an in-house ATR attachment, which required the UV lamp to be perpendicular to the film. The film was then exposed to various N2/air mixtures in the presence or absence of UV light. Absorbance spectra of the film were collected at wavenumber resolution of 2 cm−1 every 30 s (each averaging 32 scans). HPLC-UV Analysis. PF films were washed with 1 mL of acetonitrile and quantified with high performance liquid chromatography (HPLC) equipped with a diode array detector (DAD) (Agilent Varian Prostar). Fifty microliter samples were injected onto a Hypersil Gold C18 column (3um, 150 × 4.6 mm), oven temperature 40 °C, monitored at 220 nm. The mobile phase was an isocratic combination of acetonitrile (80%) and water (20%). Products Analysis. Product analysis was conducted on the PF film extract following exposure to UV light (185 and 254 nm), ozone, and OH radicals (experiment 11 in Table 2), using HPLC-MS with a DAD and chemical ionization mass spectrometer (Waters Premier LC-ESI-MS) or NMR. For LC-MS analysis, 10 μL of the sample was injected onto a Luna C18 column (5um, 150 × 2 mm). The mobile phase was an isocratic combination of acetonitrile (80%) and water (20%). PF and PF residues were monitored at 230 nm and then ionized with electrospray ionization (ESI). Ions were collected in both the negative and positive mode range of 100−1000 m/ z. NMR analysis of selected samples was conducted to examine cleavage of the P−S bond during exposure. Individual PF films proved to be below the limits of detection; thus, four sample films of 19 g(PF)/m2 were exposed under the same conditions and combined into one sample for NMR analysis. For qualitative comparison, a concentrated PF solution was used. NMR spectra were recorded at 600.55, 243.11, MHz (1H/31P NMR) on a AV-III 600 Bruker spectrometer at room temperature with two-channel, direct detection probes with automatic tuning and matching and equipped with z-gradients. All chemical shifts are reported in parts per million. Residual solvent peak was used as an internal standard (CDCl3); 31P NMR signals were referenced to internal standards: 85% H3PO4 and 1.0 M. Bruker Topspin 2.1 was used for spectral acquisition and processing.

Table 1) is summarized in Figure 1 (selected experiments for clarity). In each setting, five to nine replicate PF films of 0.38 g

Figure 1. PF degradation as a function of exposure and time. Error bars reflect one standard error between the replicates.

m−2 were exposed, and DE was estimated based on area under the curve of the HPLC chromatogram. The highest DE was achieved upon exposure to 185/254 nm wavelengths in the presence of humidified air and high ozone, reaching complete loss after 60 min. Without humidity, DE plateaued at approximately 90% after 60 min of exposure, which is similar to the observed DE in both wet and dry experiments under 185/254 nm wavelengths and low ozone conditions. Upon exposure to 254 nm light and 1 ppm ozone, DE was approximately 70% after 90 min under wet or dry conditions. Differences between experimental parameters were investigated quantitatively using the observed rate constants of PF loss (kobs). For each exposure scenario, the observed rate constant of PF loss (kobs) can be described as a pseudo-firstorder kinetics summarizing physical (evaporation) and chemical (photolysis and oxidation) loss (eq 6). kobs = ∑ k i[i] + j[λ]

(6)

where ki[i] is the pseudo-first-order rate constant of oxidant i with PF, and jλ is the photolysis rate constant of PF at wavelength λ. PF loss followed first-order kinetics in all experiments, such that kobs could be extracted from a regression analysis of LN([counts)0/[counts]t) versus initial time (0−40 min) for each treatment (Table 3). As can be seen, hydroxyl radical concentrations generated under low ozone did not have a measurable effect on the PF degradation rate (i.e., kobs (185/ 254-dry-low-O3) ≈ kobs (185/254-wet-low-O3) ≈ kobs (185/ 254-dry-high-O3) and kobs (254-dry-low-O3) ≈ kobs (254-wetTable 3. Observed Rate Constants and Surface Half-Life of PF Degradation under Various Experimental Conditions name of experiment 185/254-wet-high-O3 185/254-wet-low-O3 185/254-dry-high-O3 185/254-dry-low-O3 254-wet-lowO3 254-dry-lowO3

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RESULTS AND DISCUSSION PF Degradation Kinetics. Degradation efficiency (DE) of PF under the various experimental conditions (experiment 1, 8753

kobs, min−1 (±SD) 0.075 0.045 0.041 0.052 0.022 0.018

(0.004) (0.001) (0.004) (0.007) (0.002) (0.002)

observed half-life (min) 9.2 15 17 13 32 39



Article

From the extracted squalane loss rate and the second-order rate constant of squalane reaction with OH (ksqOH = 1.8 × 10−12 cm3 molec−1 s−1),25 the near surface hydroxyl radical concentration was calculated as [OH]g = (9 ± 2) × 107 molecules cm−3. Using this hydroxyl concentration and the extracted pseudo-first-order rate constant kOH(high) = 0.028 min−1, the second-order rate constant for heterogeneous reaction of PF and OH was calculated as kOHPF = (5 ± 1) × 10−12 cm3 molec−1 s−1. This is slower than the predicted rate for gaseous reaction (4.4 × 10−11 cm3 molec−1 s−1) using AOPWIN of the QSAR EPI Suite,24 based upon structure− activity relationship (SAR) methods.29 This difference can be due to an inhibiting role of the surface in which PF surface active sites may be hidden or masked, as suggested by other researchers who observed heterogeneous rates 300 times slower than predicted by the EPI Suite.30 An additional source of difference could be the sparse database of rate constant data for the reactions of OH radicals with phosphorus-containing compounds used by EPI Suite.14 With regards to degradation kinetics, comparisons between profenofos and VX are not straightforward. However, the limited available data indicates that VX may also rapidly degrade under similar conditions. While the AOPWIN predicted rate for VX-OH homogeneous reaction (9.0 × 10−11 cm3 molec−1 s−1) is approximately 2 times faster than for PF,24 this may not be the case for heterogeneous reaction in which differences in rates may be more dependent on the molecular orientation at the interface.31 Photodegradation rate of PF under 254 nm light (Figure 1) is similar to that reported by Zuo et al.32 for VX film (60% loss vs 66% loss after 1 h irradiation, respectively) but slightly faster than that reported by Snelson et al.33 for thiophosphonate VX surrogate (C2H5O−PO(CH3)(S−C2H5), OSP) (about 20% and 10% loss after 10 min irradiation, respectively). Considering that irradiation fluxes at the VX study and OSP study were about 6 times and 2 times higher than in our LR setting, respectively, this suggests that PF is more photodegradable at 254 nm. Under 185 nm light, the trend may be reversed, as the absorption spectrum of VX32 is blue-shifted relative to that of PF (λmax at 209 nm vs 231 nm, respectively, data not shown). Reported OSP degradation under 185 nm irradiation in the presence of high RH and ozone (1−2 wt %)33 was not faster than that of PF. However, the irradiation flux at 185 nm for OSP degradation is unknown. Effect of Exposure Conditions and PF Film Density. Degradation efficiency of PF film (2.3 g m−2) in the SR is shown in Table 2. Consistent with the experiments run in the LR, 20% more degradation was achieved in the presence of humid air and the 185/254 nm lamp than when the same UV light was used under dry conditions. This highlights the role of hydroxyl radicals (eq 4) in PF degradation. Interestingly, in the presence of the 185/254 lamp, humid N2 conditions resulted in higher degradation than that in dry air and dry N2 alone. This is most likely due to OH radicals formed via photolysis of water vapors at 185 nm.34 In the absence of UV light, evaporation led to kobs (185/ 254-wet-low-O3) > kobs (254-wet-O3,). Observed rate constants are broken into their various processes in eqs 7−9. It is possible that additional radicals form under the experimental conditions (HO2, O, etc.). Nevertheless, OH is believed to be dominant with regards to OP decontamination.9,23,24 kobs (185/254‐wet‐high‐O3) = J254 + J185 + kevap + k O3(high) + k OH(high)

(7)

kobs (185/254‐dry‐high‐O3) = J254 + J185 + kevap + k O3(high) kobs (254‐wet‐low‐O3) = J254 + kevap + k O3(low)

(8) (9)

where J254 and J185 are the PF photolysis rate constants at 254 and 185 nm, respectively, kevap is the PF evaporation rate constant, and kO3 and kOH are the pseudo-first-order rate constants of PF reaction with ozone and hydroxyl radicals, respectively. Subscripts (high and low) denote rate constants of the oxidant species in the presence of high or low ppm ozone concentrations, respectively, as described in Table 1. Experiments performed under flow of dry and wet N2 and under [O3] = 150 ppm show no PF degradation, indicating that kevap and kO3 are negligible. Therefore, we calculate J254 = 0.020 min−1 (eq 9 and Table 3), which is similar to PF degradation observed during exposure of PF to 254 nm light under wet air (no ozone) (data not shown). Assuming also no synergistic effect between the two wavelengths, J185 = kobs (185/254-drylow-ozone) − kobs (254-dry-low-ozone) = 0.027 min−1. Subtracting kobs (185/254-dry-high-ozone) from kobs (185/ 254-wet-high-ozone) gives a first approximation for kOH(s)(high) = 0.028 min−1 (i.e., half-life of 25 min). The second-order rate constant for PF and hydroxyl heterogeneous reaction (kPFOH) is obtained from the pseudofirst-order rate constant and the near-surface hydroxyl radical concentration, [OH]g. To estimate [OH]g near the film surface, squalane film was used as a probe due to its low reactivity toward ozone and 185/254 nm light.25,26 Electron impact GCMS could not be used here because MS fragmentation of squalane and squalane oxidation products are very similar.26 Thus, ATR-FTIR was employed as an alternative approach. A 60 μL amount of a 2 mM solution of squalane (99% Acros Organics) in chloroform was placed on the ATR crystal and allowed to evaporate to form a squalane film (0.36 g m−2). The coated ATR crystal was placed into the large reactor and exposed under the same experimental conditions as the PF for 60 min (experimental conditions #1). Squalane degradation was calculated on the basis of the change in the absorbance bands of CH2 and CH3 vibrations (2990−2850 cm−1)27 due to exposure (see Figure S2, Supporting Information), indicating 45 ± 8% squalane loss. Because photo-oxidation of the film results in increased hygroscopicity, the squalane bands were quantified in the postexposure spectrum after the removal of the broad complex bands at 3600−3000 cm−1 associated with absorbed water and intermolecular and intramolecular hydrogen bonding.28 Additional details are provided in the Supporting Information. 8754



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additional exposure time (Figure 2) or the addition of UV lamps (Table 2). The limited degradation efficiency at higher concentrations hints at the formation of a protective oxidative layer at the film−air interface which limits further penetration of oxidants into the film. To break this barrier, the exposed film was spread by redissolving in acetonitrile. After the reaction was ceased (30 or 60 min exposure depending on the experiment as described in Table 2), a droplet of acetonitrile was placed on the exposed surface to help diffuse the barrier. Unlike on unreacted PF film, the bead spread approximately three times greater (from d ≈ 0.5 to 1.8 cm), showing an increase in film surface polarity and increasing exposure surface area. The bead was allowed to evaporate to dryness and then returned to the reactor for further exposure. An additional 10−20% degrada-

Figure 2. Effect of PF film concentration (0.38, 2.3, and 3.8 g m−2 PF) on PF degradation. Trendlines are to guide the eye.

Table 4. Physicochemical Properties of Profonofus and Its Degradation Products

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bonding formed among the COH groups.28 This is consistent with increased hydrophilicity of the film. All peaks initially increase in absorbance, suggesting film rearrangement and better film-ATR contact. Additional evidence for OH addition to the PF film and alcohol formation is the large absorbance increase at 1439 cm−1 that is consistent with COH bending modes.28 The oxidation products suggested by ATR spectra, HPLC, and NMR analysis indicate only limited formation of phosphoric acid esters which would likely lead to full detoxification.20,39,40 The other products do not show breakage of the P−S bond. Nevertheless, the resulting products may be less potent because of the increased hydrophilic nature of the added OH groups which favor the metabolic pathway and facilitate elimination in the urine.41 In fact, human PF metabolites containing additional OH groups on the hydrocarbon chain of the ester have already been identified in vitro.42 While it is difficult to compare the observed PF product formation to that expected from VX photo-oxidation under similar treatment, photodegradation (λ = 254 nm) of VX in the presence of humid air resulted in cleavage of the P−S and S−C bonds, forming mostly nonvolatile products, including the nontoxic alkyl methylphosphonic acids.32 Furthermore, under the proposed degradation conditions, the tertiary amine is likely to react with ozone, resulting in additional carbonyl compounds32 with increased hydrophilicity.

tion was achieved by this technique, leading to >95% degradation efficiency when combined with an additional lamp (185/254 nm) or extended exposure time (total of 120 min). Product Analysis and Health Implications. The limited previous findings regarding PF degradation from oxidation, photolysis, and/or hydrolysis include those performed in aqueous solution,35 absorbed to soil,36 or during human metabolism,37 resulting in many similar products. In the presence of hydroxyl radicals as in this study, PF loss is expected to proceed mainly through hydrogen abstraction.23,24 Despite the different conditions, the products identified here are similar to those previously reported. All observed products had retention times (RT) shorter than that of PF (5.77 min), indicating higher polarity than the parent compound. Assuming similar instrument response for all products, the major product C (∼80% of total product) was the most polar at RT = 1.44 min, followed by the second major product D (∼10%) at RT = 1.99 min. Minor products made up a small fraction of the total. From the fragmentation patterns and molecular ion of each peak, chemical formulas (Table 4) were hypothesized and confirmed using high resolution MS. Formation of PF oxidation products was also identified using 31 P and 1H NMR (Figure S3, Supporting Information). Small 31 P shifts near 25 ppm (25.4−25.6 ppm) and 1H (1−1.5 ppm) suggest changes occurring in the molecule far from the P(V) atom, possibly the addition of −OH groups, while the small 31P shifts at −4.5 ppm and −4.8 ppm indicate changes in the molecule near the P(V) atom (see Figure S3). The latter is in agreement with the predicted 31P shift of −4.85 ± 5 ppm for the suggested chemical structure of product B by the NMR predictor software (XNMR Suite by ACD Laboratories) and supported by HPLC-MS results. Furthermore, product B has been previously identified as a result of PF oxidation by polychromatic irradiation (λ > 285) in aqueous solution35 and PF metabolism,37 while products B and F have both been identified as a result of PF photolysis in soil (λ >290). Real-time monitoring of PF-OH reaction with ATR-FTIR agreed with the above product interpretation. Figure S4 (Supporting Information) depicts the characterization of PF film before reaction.27,38 Upon exposure, an increase in a few broad absorbance bands in the 3600−3000 cm−1 region and 1630 cm−1 is observed (Figure 3), associated with absorbed water and intermolecular and/or intramolecular hydrogen

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ASSOCIATED CONTENT

* Supporting Information S

Schematics of the reactor used for exposure experiments (Figure S1), ATR-FTIR spectra of squalane for quantifying hydroxyl concentration at the film surface (Figure S2), NMR of the PF films before and after exposure (Figure S3), and ATRFTIR spectrum of profenofos film with wavenumber characterization (Figure S4). This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Israel Ministry of Defense and by the Technion Security Funds. We thank L. Patz and S. Kababya for helping with HPLC-MS and NMR instrument analysis, and Y. Tulchinsky for helping with NMR interpretation (Technion, Faculty of Chemistry).

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REFERENCES

(1) Kim, K.; Tsay, O. G.; Atwood, D. A.; Churchill, D. G. Destruction and detection of chemical warfare agents. Chem. Rev. 2011, 111, 5345−403. (2) Love, A. H.; Bailey, C. G.; Hanna, M. L.; Hok, S.; Vu, A. K.; Reutter, D. J.; Raber, E. Efficacy of liquid and foam decontamination technologies for chemical warfare agents on indoor surfaces. J. Hazard. Mat. 2011, 196, 115−22. (3) Štengl, V.; Houšková, V.; Bakardjieva, S.; Murafa, N.; Maříková, M.; Opluštil, F.; Němec, T. Zirconium doped nano-dispersed oxides of Fe, Al and Zn for destruction of warfare agents. Mater. Charact. 2010, 61, 1080−1088.

Figure 3. ATR-FTIR spectra of PF film changes as a function of exposure time (PF film prior to exposure used as reference). 8756



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(4) Wagner, G. W.; Koper, O. B.; Lucas, E.; Decker, S.; Klabunde, K. J. Reactions of VX, GD, and HD with nanosize CaO: Autocatalytic dehydrohalogenation of HD. J. Phys. Chem. B 2000, 104, 5118−5123. (5) Vega, A. a.; Imoberdorf, G. E.; Mohseni, M. Photocatalytic degradation of 2,4-dichlorophenoxyacetic acid in a fluidized bed photoreactor with composite template-free TiO2 photocatalyst. Appl. Catal., A 2011, 405, 120−128. (6) Vorontsov, A. V; Chen, Y.-C.; Smirniotis, P. G. Photocatalytic oxidation of VX simulant 2-(butylamino)ethanethiol. J. Hazard. Mat. 2004, 113, 89−95. (7) Beduk, F.; Aydin, M. E.; Ozcan, S. Degradation of malathion and parathion by ozonation, photolytic ozonation, and heterogeneous catalytic ozonation processes. Clean: Soil, Air, Water 2012, 40, 179− 187. (8) Zhu, W.-C.; Wang, B.-R.; Xi, H.-L.; Pu, Y.-K. Decontamination of VX surrogate malathion by atmospheric pressure radio-frequency plasma jet. Plasma Chem. Plasma Process. 2010, 30, 381−389. (9) Herrmann, H. W.; Henins, I.; Park, J.; Selwyn, G. S. Decontamination of chemical and biological warfare (CBW) agents using an atmospheric pressure plasma jet (APPJ). Phys. Plasmas 1999, 6, 2284. (10) Nizkorodov, S. A.; Harper, W. W.; Blackmon, B. W.; Nesbitt, D. J. Temperature dependent kinetics of the OH/HO2/O3 chain reaction by time-resolved IR laser absorption spectroscopy. J. Phys. Chem. A 2000, 3964−3973. (11) Sander, S. P.; et al. Chemical kinetics and photochemical data for use in atmospheric studies: Evaluation Number 17. In JPL Publication, no. 10-6; Jet Propulsion Laboratory: Pasedena, CA, 2011. (12) Bazire, A.; Gillon, E.; Lockridge, O.; Vallet, V.; Nachon, F. The kinetic study of the inhibition of human cholinesterases by demeton-Smethyl shows that cholinesterase-based titration methods are not suitable for this organophosphate. Toxicol. In Vitro 2011, 25, 754−9. (13) Mu, A.; Vera, T.; Sidebottom, H.; Mellouki, A.; Borr, E.; Clemente, E. Studies on the atmospheric degradation of chlorpyrifosmethyl. Environ. Sci. Technol. 2011, 1880−1886. (14) Muñoz, A.; Person, A. Le; Calvé, S. Le; Mellouki, A.; Borrás, E.; Daële, V.; Vera, T. Studies on atmospheric degradation of diazinon in the EUPHORE simulation chamber. Chemosphere 2011, 85, 724−30. (15) Bavcon Kralj, M.; Franko, M.; Trebse, P. Photodegradation of organophosphorus insecticides - investigations of products and their toxicity using gas chromatography-mass spectrometry and AChEthermal lens spectrometric bioassay. Chemosphere 2007, 67, 99−107. (16) Segal-Rosenheimer, M.; Linker, R.; Dubowski, Y. Heterogeneous oxidation of the insecticide cypermethrin as thin film and airborne particles by hydroxyl radicals and ozone. Phys. Chem. Chem. Phys. 2011, 13, 506−17. (17) Lambe, A. T.; Miracolo, M. A.; Hennigan, C. J.; Robinson, A. L.; Donahue, N. M. Effective rate constants and uptake coefficients for the reactions of organic molecular markers (nalkanes, hopanes, and steranes) in motor oil and diesel primary organic aerosols with OH radicals. Environ. Sci. Technol. 2009, 43, 8794−8800. (18) Slade, J. H.; Knopf, D. Heterogeneous OH oxidation of biomass burning organic aerosol surrogate compounds: assessment of volatilisation products and the role of OH concentration on the reactive uptake kinetics. Phys. Chem. Chem. Phys. 2013, 15, 5898−915. (19) George, I. J.; Vlasenko, a.; Slowik, J. G.; Broekhuizen, K.; Abbatt, J. P. D. Heterogeneous oxidation of saturated organic aerosols by hydroxyl radicals: uptake kinetics, condensed-phase products, and particle size change. Atmos. Chem. Phys. 2007, 7, 4187−4201. (20) Munro, N. B.; Talmage, S. S.; Griffin, G. D.; Waters, L. C.; Watson, A. P.; King, J. F.; Hauschild, V. The Sources, fate, and toxicity of chemical warfare agent degradation products. Environ. Health Perspect. 1999, 107, 933−974. (21) Wauchope, R. D.; Buttler, T. M.; Hornsby, A. G.; AugustijnBeckers, P. W. .; Burt, J. P. The SCS/ARS/CES Pesticide Properties Database for Environmental Decision-Making. Rev. Environ. Contam. Toxicol. 1991, 123, 1−155.

(22) USEPA Toxicity Estimation Software Tool (Version 4.1) Website; http://www.epa.gov/nrmrl/std/qsar/qsar.html, accessed on March 11, 2013. (23) Finlayson-Pitts, B. J.; Pitts, J. J. Chemistry of the Upper and Lower Atmosphere; Academic Press: San Diego, CA, 2000. (24) U.S. EPA EPI Suite Website; http://www.epa.gov/opptintr/ exposure/pubs/episuite.htm, accessed on February 3, 2013. (25) Che, D. L.; Smith, J. D.; Leone, S. R.; Ahmed, M.; Wilson, K. R. Quantifying the reactive uptake of OH by organic aerosols in a continuous flow stirred tank reactor. Phys. Chem. Chem. Phys. 2009, 11, 7885−7895. (26) Smith, J. D.; Kroll, J. H.; Cappa, C. D.; Che, D. L.; Liu, C. L.; Ahmed, M.; Leone, S. R.; Worsnop, D. R.; Wilson, K. R. The heterogeneous reaction of hydroxyl radicals with sub-micron squalane particles: a model system for understanding the oxidative aging of ambient aerosols. Atmos. Chem. Phys. 2009, 9, 3209−3222. (27) Lin-Vien, D.; Cothup, N. B.; Fateley, W. G.; Grasselli, J. G., Ed. The Handbook of Infrared and Raman Characteristic Frequecies of Organic Molecules; Academic Press: San Diego, 1991. (28) Podstawka-Proniewicz, E.; Piergies, N.; Skołuba, D.; Kafarski, P.; Kim, Y.; Proniewicz, L. M. Vibrational characterization of L-leucine phosphonate analogues: FT-IR, FT-Raman, and SERS spectroscopy studies and DFT calculations. J. Phys. Chem. A 2011, 115, 11067−78. (29) Kwok, E. S. C.; Atkinson, R. Estimation of hydroxyl radical reaction rate constants for gas-phase organic compounds using a structure-reactivity relationship: and update. Atmos. Environ. 1995, 29, 1685−1695. (30) Al Rashidi, M.; El Mouden, O.; Chakir, a.; Roth, E.; Salghi, R. The heterogeneous photo-oxidation of difenoconazole in the atmosphere. Atmos. Environ. 2011, 45, 5997−6003. (31) Roeselová, M.; Vieceli, J.; Dang, L. X.; Garrett, B. C.; Tobias, D. J. Hydroxyl radical at the air−water interface. J. Am. Chem. Soc. 2004, 126, 16308−9. (32) Zuo, G.-M.; Cheng, Z.-X.; Li, G.-W.; Wang, L.-Y.; Chen, H. Photoassisted reaction of chemical warfare agent VX droplets under UV light irradiation. J. Phys. Chem. A 2005, 109, 6912−8. (33) Snelson, A.; Taylor, K.; O’Neill, H. J. Reaction of CW agents simulants on surfaces in the presence of O3, UV and O3+UV. J. Environ. Sci. Health, Part A: Environ. Sci. Eng. 1984, 19, 775−790. (34) Imoberdorf, G. E.; Mohseni, M. Experimental study of the degradation of 2,4-D induced by vacuum-UV radiation. Water Sci. Technol. 2011, 63, 1427. (35) Zamy, C.; Mazellier, P.; Legube, B. Phototransformation of selected organophosphorus pesticides in dilute aqueous solutions. Water Res. 2004, 38, 2304−13. (36) Burkhard, N.; Guth, J. A. Photolysis of organophosphorus insecticides on soil surfaces. Pestic. Sci. 1979, 10, 313−319. (37) Gotoh, M.; Sakata, M.; Endo, T.; Hayashi, H.; Seno, H.; Suzuki, O. Profenofos metabolites in human poisoning. Forensic Sci. Int. 2001, 116, 221−6. (38) Gäb, J.; Melzer, M.; Kehe, K.; Richardt, A.; Blum, M.-M. Quantification of hydrolysis of toxic organophosphates and organophosphonates by diisopropyl fluorophosphatase from Loligo vulgaris by in situ Fourier transform infrared spectroscopy. Anal. Biochem. 2009, 385, 187−93. (39) Roberts, T. R.; Hutson, D. H.; Jewess, P. J.; Lee, P. W.; Nicholls, P. H.; Plimmer, J. R., Ed. Metabolic Pathways of Agrochemicals, Part 2 Insecticides and Fungicides; The Royal Society of Chemistry: Cambridge, U.K., 1999. (40) Ta-Shma, Z. Chemistry and biochemistry of organophosphorous agents. In Emergency Department, Israel Ministry of Health and Medical Corp, Israel Defense Forces: The White Book - Chemical Warfare; Sar’el: Israel, 2000. (41) Barr, D. B.; Wang, R. Y.; Needham, L. L. Biologic monitoring of exposure to environmental chemicals throughout the life stages: requirements and issues for consideration for the National Children’s Study. Environ. Health Perspect. 2005, 113, 1083−1091. 8757



Article

(42) Abass, K.; Reponen, P.; Jalonen, J.; Pelkonen, O. In vitro metabolism and interaction of profenofos by human, mouse and rat liver preparations. Pestic. Biochem. Phys. 2007, 87, 238−247.

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Degradation of VX Surrogate Profenofos on Surfaces via in Situ Photo

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