Reductive Defluorination of Branched Per- and ... - ACS Publications

10.1021/acs.estlett.xxxxxxx. 226. Additional experimental ... Corresponding Authors. 230. *(J.L.) E-mail: [email protected]; [email protected]...
31 downloads 0 Views 963KB Size
Subscriber access provided by - Access paid by the | UCSB Libraries

Novel Remediation and Control Technologies

Reductive Defluorination of Branched Per- and Polyfluoroalkyl Substances with Cobalt Complex Catalysts Jinyong Liu, Daniel J Van Hoomissen, Tianchi Liu, Andrew Maizel, Xiangchen Huo, Seth R. Fernández, Changxu Ren, Xin Xiao, Yida Fang, Charles Schaefer, Christopher P. Higgins, Shubham Vyas, and Timothy J. Strathmann Environ. Sci. Technol. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.estlett.8b00122 • Publication Date (Web): 28 Mar 2018 Downloaded from http://pubs.acs.org on March 28, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 17

Environmental Science & Technology Letters

1

Reductive Defluorination of Branched Per- and Polyfluoroalkyl Substances

2

with Cobalt Complex Catalysts

3 4 5

Jinyong Liu,*,†,‡ Daniel J. Van Hoomissen,§ Tianchi Liu,† Andrew Maizel,‡ Xiangchen Huo,‡ Seth R. Fernández,† Changxu Ren,† Xin Xiao,#,‡ Yida Fang,‡ Charles Schaefer,∆ Christopher P. Higgins,‡ Shubham Vyas,*,§ and Timothy J. Strathmann*,‡

6 7 8 9 10 11



12

Abstract

13

This

14

polyfluoroalkyl substances (PFASs) undergoing cobalt-catalyzed reductive defluorination

15

reactions. Experimental results and theoretical calculations reveal correlations between the extent

16

of PFAS defluorination, the local C−F bonding environment, and calculated bond dissociation

17

energies (BDEs). In general, BDEs for tertiary C−F bonds < secondary C−F bonds < primary

18

C−F bonds. A tertiary C−F bond adjacent to three fluorinated carbons (or two fluorinated

19

carbons and one carboxyl group) has a relatively low BDE that permits an initial defluorination

20

to occur. Both a biogenic cobalt-corrin complex (B12) and an artificial cobalt-porphyrin complex

21

(Co-PP) are found to catalytically defluorinate multiple C−F bonds in selected PFASs. In general,

22

Co-PP exhibits higher initial rate of defluorination than B12. Neither complex induced significant

23

defluorination in linear perfluorooctanoic acid (PFOA; no tertiary C−F bond) or a perfluoroalkyl

24

ether carboxylic acid (tertiary C−F BDEs too high). These results open new lines of research,

25

including (1) designing branched PFASs and cobalt complexes that promote complete

26

defluorination of PFASs in natural and engineered systems, and (2) evaluating potential impacts

27

of branched PFASs in biological systems where B12 is present.

Department of Chemical and Environmental Engineering, University of California, Riverside, California 92521, United States ‡ Department of Civil and Environmental Engineering and §Department of Chemistry, Colorado School of Mines, Golden, Colorado 80401, United States # Department of Environmental Science, Zhejiang University, Hangzhou 310058, China ∆ CDM Smith, 110 Fieldcrest Avenue, No. 8, Sixth Floor, Edison, New Jersey 08837, United States

study

investigates

structure-reactivity

relationships

1 ACS Paragon Plus Environment

within

branched

per-

and

Environmental Science & Technology Letters

28 29

Introduction

30

Since the original development in the 1940s, per- and polyfluoroalkyl substances (PFASs) have

31

been widely used in industrial and consumer products.1,

32

environment has been extensively documented.2-6 Substantial research efforts on the two C8

33

legacy compounds, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS),

34

have confirmed a variety of adverse health effects,7 leading to the phase-out of ≥C8 PFASs in

35

North America and Europe8 and the USEPA’s recent issuance of drinking water health advisory

36

levels for PFOA and PFOS.9,

37

sulfonic acids, perfluoroalkyl ether carboxylic acids, and other novel structures) have already

38

been detected in aquatic environments and are considered recalcitrant.11-15 Recent studies have

39

also indicated that the emerging PFASs exhibit variable toxicities and environmental

40

mobilities.11, 16-20 Still, knowledge on emerging PFASs remains limited.11, 21

41

Despite having received much less attention than linear PFASs, branched PFASs (Figure 1) have

42

also been extensively applied and detected in the environment. For example, perfluoro-3,7-

43

dimethyloctanoic acid (PFMe2OA) serves, along with linear PFASs, as an ingredient of well

44

treatment fluids.22 This compound is also on the “STANDARD 100 by OEKO-TEX” list,

10

2

Detection of PFASs in the global

New alternative PFASs (e.g., shorter chain carboxylic and

2 ACS Paragon Plus Environment

Page 2 of 17

Page 3 of 17

Environmental Science & Technology Letters

45

indicating its wide application in textile production,23 and it has been detected in European water

46

bodies.24 Perfluoroethylcyclohexane sulfonate (PFECHS)25 also contains two branched carbons

47

on the cyclic structure, and its detection in Canadian Arctic lakes has been attributed to its use in

48

aircraft anti-erosion fluid.26 Industrial PFOS products often contain variable fractions of

49

branched isomers, which have been detected in both environmental waters and human tissues.27,

50

28

51

backbone.29, 30 Recently reported perfluoroalkyl ether carboxylic acid pollutants such as GenX12

52

and its longer analog15 also contain branched structures.

53

The recalcitrance of PFASs to biological and chemical degradation is attributed to the high

54

stability of C−F bonds.31 However, Ochoa-Herrera et al.32 observed >70% fluoride ion (F−)

55

release from a mixture of branched PFOS isomers by reaction with B12 (a corrin-CoIII complex,

56

catalyst precursor) and TiIII citrate (reductant). More recently, Park et al.33 reported cleavage of

57

multiple sp3 C−F bonds from analytical standards of mono-branched PFOS with a –CF3 at the 3-,

58

4-, 5-, or 6-position (see the 6-brPFOS structure in Figure 1) using B12 and nanosized Zn0 as an

59

alternative reductant. Since B12 is an essential component for microorganisms and animals, these

60

findings suggest that reductive defluorination of branched PFASs could occur in natural

61

environments or biological systems. Furthermore, if the initial defluorination replaces one or

62

more F atoms with H atoms, additional defluorination mechanisms could be triggered. For

63

example, HF elimination from fluorotelomers (i.e., −CH2−CF2− into –CH=CF−) has been

64

observed both in vivo and abiotically in the environment,34, 35 and such a transformation could

65

significantly alter the toxicity of the PFASs.34 Hence, it is both scientifically intriguing and

66

practically imperative to further investigate critical structural factors determining Co-mediated

Typical branched PFOS isomers contain one or two −CF3 branching from the perfluorinated

3 ACS Paragon Plus Environment

Environmental Science & Technology Letters

Page 4 of 17

67

defluorination of branched PFASs. The findings of this work will help evaluate the fate of

68

emerging PFASs and aid in the design of less persistent and toxic PFASs.

69

Materials and Methods

70

Chemicals and solution preparation. PFASs (SynQuest Laboratories), B12 (Alfa Aesar) and

71

other cobalt species (Sigma-Aldrich), 12% TiCl3 solution (Acros Organics), and other chemicals

72

(Fisher Chemical) were used as received. Detailed chemical information (Table S1) and

73

preparation of stock solutions of PFASs, cobalt species, and TiIII citrate in carbonate buffer36 are

74

described in the Supporting Information (SI).

75

Defluorination reaction and sample analysis. The procedure was modified from Ochoa-

76

Herrera et al.32 In an anaerobic glove bag, a series of 9-mL serum bottles were loaded with 4 mL

77

of solution containing specific PFASs (0.1 mM), TiIII citrate (~36 mM) with carbonate buffer

78

(~40 mM), and cobalt catalyst (0.25 mM). More operational details are provided in the SI. Each

79

serum bottle was sealed and transferred to a 70°C oven. At designated reaction times, individual

80

reactors were sacrificed for analysis. Each reactor was used for a single measurement, such that a

81

typical reaction series of five time points (0, 1, 3, 7, and 15 days) began with five replicates of

82

each reaction mixture. Each reaction series was repeated at least twice. Due to the interference of

83

TiIII citrate matrix to the fluoride-selective electrode, F− release was analyzed by ion

84

chromatography.

85

chromatography−quadrupole time-of-flight mass spectrometer (LC−QToF-MS). Details of

86

instrumental analyses are provided in SI.

87

C‒F bond dissociation energy (BDE) calculation. BDEs of C‒F bonds in PFAS structures

88

(anion for carboxylic acids) were calculated using Grimme’s GD3-BJ empirical dispersion

Degradation

of

parent

PFASs

4 ACS Paragon Plus Environment

was

analyzed

by

liquid

Page 5 of 17

Environmental Science & Technology Letters

89

corrected37 hybrid density functional theory (DFT) at the B3LYP/6-311+G(2d,2p) level of

90

theory.38-41 Truhlar’s SMD solvent model was chosen to implicitly model the aqueous

91

environment.42 The BDE for each bond was calculated through Eq. (1):

92

∗ ∗ ∗  =   [   ] +     −  

(1)

93

where H* represents the enthalpy of formation.

94

Results and Discussion

95

Initial experiments tested the defluorination of PFMe2OA (1), a well-defined branched structure,

96

at rate-optimized reaction conditions reported previously (pH 9.0 and 70°C).32 Defluorination

97

was evaluated by the concentration ratio of released F− ions to the F initially present in the PFAS

98

substrate. Significant defluorination occurred only in the presence of both TiIII and B12 (Figure

99

S1). Figure 2a shows that a maximum of 85% defluorination from 1 was achieved in 7 d.

100

Because LC−QToF-MS analysis indicated complete degradation of 1, this high defluorination

101

ratio corresponds to an average of sixteen of the nineteen F atoms within the PFMe2OA structure

102

being released as F−. According to the mechanisms proposed for Co-catalyzed dehalogenation

103

reactions (X = Cl and Br),43-45 TiIII reduces the CoIII in B12 to CoI, which then interacts with

104

either the carbon or halide (X) to cleave the C−X bonds. Assuming a similar mechanism for the

105

defluorination reactions, the turnover number (TON) for each Co center is estimated to be 6.5 for

106

the reaction with 1, demonstrating the catalytic nature of reaction. The TON could be further

107

increased for at least 10 times (i.e., TON=65) because elevating the concentration of 1 from 0.1

108

mM to 1.0 mM still achieved the same defluorination ratio. The reaction slowed at room

109

temperature (21 ± 2°C), but still resulted in at least 44% defluorination within 8 mo (Figure S2),

5 ACS Paragon Plus Environment

Environmental Science & Technology Letters

110

suggesting the potential for slow defluorination of branched PFASs in low redox potential

111

natural environments, where microorganisms employ B12 for dechlorination.46

112

To elucidate the relationship between PFAS structure and susceptibility to B12-catalyzed

113

defluorination, commercially available PFASs with different “branched structures” were reacted

114

with B12 and TiIII (Figure 2). It was soon realized that a simple classification as “branched” was

115

insufficient as a predictor for susceptibility to defluorination. For example, a branched

116

fluorotelomer acid 4 (Figure 2d) released negligible F− under the same reaction condition as 1.

117

In stark contrast, replacing the –CH2–CH2– moiety within the fluorotelomer structure with –

118

CF=CF– (2) led to the rapid and complete degradation of the parent compound within 1 day and

119

a maximum of 91% defluorination (an average of eight of the nine C−F bonds cleaved in each

120

molecule, Figure 2b). Cyclic 3 is a carboxylic acid analog of PFECHS. It contains one branched

121

carbon with two −CF2− and a –COOH neighbors. The parent compound was partially degraded

122

(70%), and the F− release from 3 corresponded to an average of three out of eleven F atoms in

123

each molecule (Figure 2c). In comparison, negligible F− release was observed from the cyclic

124

amine 6, in which the N atom can be considered as a “branched” point. Negligible F− release was

125

observed for the perfluoroalkyl ether compound 5 possessing two branched carbons. Hence, it

126

can be inferred that the local chemical environment surrounding the tertiary C−F is critical to

127

their reactivity with B12. No appreciable defluorination was observed in experiments with the

128

linear PFOA (7) and several shorter chain linear acids lacking branched carbon atoms (CF3SO3H,

129

CF3COOH, and CF3CF2COOH). LC–QToF-MS analysis showed no significant degradation of 7

130

for up to 30 days.

131

In comparison to the carboxylic acid 1, B12-catalyzed F− release was much slower for the

132

analogous telomer alcohol structure 8 (Figure 2f versus 2a), and the F− release from alcohol 9, 6 ACS Paragon Plus Environment

Page 6 of 17

Page 7 of 17

Environmental Science & Technology Letters

133

with only one branched carbon, was even slower (Figure 2g). The comparison between cyclic 3

134

and 10 also shows much slower defluorination from the telomer alcohol than from the carboxylic

135

acid (Figure 2h versus 2c). Degradation of alcohols in aqueous solution was not readily

136

observed by LC−QToF-MS. Reactions with these alcohols were also conducted with variable

137

headspace volumes (e.g., 9 mL liquid + 0 mL headspace versus 2 mL liquid + 7 mL headspace in

138

the sealed 9-mL bottles). All conditions yielded similar defluorination results, excluding the

139

possibility that the slower defluorination resulted from volatilization of alcohol substrates into

140

the headspace.

141

Calculated C−F bond dissociation energies (BDEs) provide further insights into mechanisms for

142

the initial step of defluorination. As shown in Figure 3, the general order of C−F BDEs is

143

tertiary < secondary < primary. The lowest secondary C−F bond BDE (451.9 kJ mol−1) in the 2-

144

position of 7 can be attributed to its proximity to –COOH. In 1, 8 and 9, secondary C−F bonds

145

adjacent to branched carbons have even lower BDEs (414.2 to 431.0 kJ mol−1). Importantly,

146

BDEs for tertiary C−F bonds within the structures for which defluorination was observed

147

(compound 1−3 and 8−10) range from 364.4 to 431.0 kJ mol−1, whereas higher BDEs ranging

148

from 431.4 to 443.9 kJ mol−1 were found in the two branched structures with no defluorination (4

149

and 5). The higher BDEs for those tertiary C−F bonds are due to the presence of relatively weak

150

electron-withdrawing hydrocarbon and oxo moieties nearby. We propose that the initial

151

defluorination steps occur at tertiary C−F bonds with low BDEs. Such weak bonds can dissociate

152

upon interaction with CoI. A Comparison of the three non-cyclic structures 1, 8, and 9 suggests a

153

rough correlation between the BDEs of the tertiary C−F bonds (1 < 8 < 9) and the reaction rates

154

of defluorination (1 > 8 > 9). Comparison of the cyclic 3 and 10 reveals a similar trend.

7 ACS Paragon Plus Environment

Environmental Science & Technology Letters

155

Compound 2 has two sp2 C−F bonds with high BDEs (478.2 and 477.8 kJ mol−1) and exhibited

156

rapid and extensive defluorination. In comparison to 1, the presence of sp2 C−F bonds seems to

157

promote defluorination. The bonding with the C=C double bond significantly weaken the tertiary

158

C−F bond (364.4 kJ mol−1, the lowest BDE among all structures). Similar results have been

159

reported by Im et al.,47 who reported B12-catalyzed defluorination of the only sp2 C−F in the

160

refrigerant HFO-1234yf (H2C=CF−CF3) yielding H2C=CH−CF3, and further defluorination of

161

one sp3 C−F in H2C=CH−CF3 yielding H2C=CH−CF2H. Additionally, sp2 C−F bonds can be

162

cleaved with H2 gas and a Rh/Al2O3 catalyst48, 49 while sp3 C−F bonds cannot. Defluorination

163

involving unsaturated bonds probably follows reaction mechanisms similar to the Co-catalyzed

164

dechlorination of chlorinated ethenes.43 Future studies are necessary for mechanistic elucidation.

165

In addition, the close BDE values for the two tertiary C−F bonds in 9 and 4 (431.0 versus 431.4

166

kJ mol−1) suggest that the neighboring atoms are also critical to initiate defluorination reactions.

167

The experimental results described above indicate that, B12-catalyzed defluorination requires a

168

tertiary C−F branch surrounded by either three fluorinated carbons or two fluorinated carbons

169

plus one carboxyl group. If one surrounding atom is changed to hydrocarbon or oxygen, the

170

defluorination reaction cannot be initiated. Since typical ether compounds synthesized from C3

171

building blocks (e.g., the two shown in Figure 1) do not contain the susceptible C4 branched

172

structure, they are expected to be recalcitrant toward B12-catalyzed defluorination.

173

It is important to emphasize that BDEs of the parent PFASs can only be used to interpret the

174

initiation of defluorination reactions. For example, the experimental data for 1 suggests that,

175

among the sixteen F− released per 1, at least six derived from primary C−F bonds with high

176

BDEs ranging from 481.2 to 492.5 kJ mol−1. In contrast, although the linear 7 contains twelve

177

secondary C−F bonds with BDEs ranging from 451.9 to 458.1 kJ mol−1, no defluorination was 8 ACS Paragon Plus Environment

Page 8 of 17

Page 9 of 17

Environmental Science & Technology Letters

178

observed. These results collectively indicate that B12-catalyzed defluorination reactions are

179

initiated at tertiary C−F bonds with suitable local chemical environments.

180

Defluorination intermediates or end products were not observed by LC−QToF-MS (like those

181

reported by Park et al. on branched PFOS isomers33). One probable reason for the lack of

182

observed products could be that, the fragmentation of PFASs during reaction led to the loss of

183

ionizable groups (e.g., −COO−) that enable MS detection. We emphasize that the actual reaction

184

mechanisms for the multiple step reactions are complicated because the interpretation goes

185

beyond prediction with C−F bond BDEs of the parent structures. For example, the cyclic 3 does

186

not contain any primary C−F bonds, but the defluorination ratio observed was much lower than

187

that for 1, which contains nine primary C−F bonds. Furthermore, if F is replaced by H during

188

defluorination, BDEs of the adjacent C−F bonds in the resulting structures are mostly elevated or

189

unchanged (Figure S3), and this would appear to inhibit subsequent defluorination by the same

190

mechanism. However, based on the unsaturated intermediate structures proposed by Park et al.,33

191

other mechanisms such as HF elimination might be involved in further defluorination. As

192

discussed earlier for compound 2 and HFO-1234yf,47 the presence of C=C bonds could promote

193

defluorination. Clear mechanistic elucidation requires further experiments with more model

194

compounds and theoretical calculations.

195

A protoporphyrin-coordinated complex, Co-PP (Figure 2e),50 exhibited higher initial rate of

196

defluorination than B12 for most PFASs. This trend is apparent for the three examined alcohols

197

(Figure 2f−h). For 1, although the maximum defluorination by Co-PP (an average of thirteen of

198

nineteen C−F bonds cleaved) was lower than by B12, defluorination by Co-PP in the 1st day was

199

higher than by B12 (Figure 2a). For 3, Co-PP was superior to B12 in both initial reaction rate and

200

the maximum defluorination ratio (Figure 2c). Thus, the two Co complexes demonstrate 9 ACS Paragon Plus Environment

Environmental Science & Technology Letters

Page 10 of 17

201

selectivity toward specific PFAS structures. As with B12, structures 4 to 7 (Figure 2d) were not

202

reactive with Co-PP.

203

The difference between Co-PP and B12 might be attributed to two factors. First, the lack of axial

204

benzimidazole lower ligand as in B12 may allow faster electron transfer from TiIII to the CoIII

205

precursor to form the reactive CoI.51 Second, the porphyrin ligand has one more bridging carbon

206

than corrin, and the π-electron resonance is circular. Thus, the N4 ligand cavity size, ring

207

flexibility, and electronic effects in Co-PP are all different from B12,52 thus influencing the

208

defluorination

209

bis(salicylidene)ethylenediamine ligand (Co-salen, Figure 2e), inorganic CoCl2, and Co3O4

210

nanopowder did not show any defluorination activity, suggesting again the critical role of the

211

Co-coordinating ligand in defluorination activity. Systematic investigations are required to probe

212

the effect of ligands. Nevertheless, the above results have clearly shown that even the highly

213

recalcitrant primary sp3 C−F bonds in PFASs could be cleaved by natural and artificial N4-

214

coordinated cobalt species.

215

Although branched structures containing tertiary C−F bonds with low BDEs are subject to Co-

216

catalyzed defluorination, it is worth mentioning that at ambient temperature the branched PFASs

217

would still be relatively recalcitrant in the environment. Results in this letter will be valuable in

218

two aspects of environmental research. First, rational molecular design may be applied to

219

develop more readily degradable PFASs and Co catalysts that are active for the rapid and

220

complete defluorination in both natural and engineered systems. On the other hand, caution

221

should also be taken as branched PFASs may be reactive in cells, tissues, and organs where B12

222

or other catalytic metal species are present.

223

ASSOCIATED CONTENT

activity.

An

N2O2-coordinated

10 ACS Paragon Plus Environment

Co

complex

with

a

Page 11 of 17

Environmental Science & Technology Letters

224

Supporting Information

225 226

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.estlett.xxxxxxx.

227

Additional experimental procedures, tables, and figures

228

Coordinates of optimized geometries of PFASs and their corresponding radicals

229

AUTHOR INFORMATION

230 231 232 233

Corresponding Authors *(J.L.) E-mail: [email protected]; [email protected]. *(S.V.) E-mail: [email protected]. *(T.J.S.) E-mail: [email protected].

234 235

Notes The authors declare no competing financial interest.

236

ACKNOWLEDGEMENTS

237 238 239 240 241

Financial support was provided by the Strategic Environmental Research and Development Program (ER-2424) and the National Science Foundation (CHE-1709719, CHE-1710079). All of the computations were performed using allocated resources at high performance computing facility at Colorado School of Mines. T. Liu and X. Xiao received scholarship support from the China Scholarship Council.

11 ACS Paragon Plus Environment

Environmental Science & Technology Letters

F F

F3 C F F F F CF3 COOH

F3 C

PFMe2OA

F3 C F F CF3 F F SO3 H

COOH

F F F CF3

F F F CF3 F3 C O COOH O F F F F F CF3

HFPO dimer acid (GenX) 242 243 244

SO 3H

di-branched PFOS (3,5-dibrPFOS)

mono-branched PFOS (6-brPFOS) F F

F3 C

F F F F

F F F F F F

F3 C

F FF F

F F

PFECHS

F3 C F F F F F

O

SO3 H F

F F3 C

F F F F F F

F3 C

F F

Page 12 of 17

HFPO trimer acid

*HFPO=Hexafluoropropylene oxide

Figure 1. Examples of branched PFASs detected in the environment. Branched carbons are highlighted in grey.

12 ACS Paragon Plus Environment

Page 13 of 17

245 246 247 248 249

Environmental Science & Technology Letters

Figure 2. Degradation and defluorination for each PFAS with cobalt catalysts shown in (e). Branches that are effective and ineffective in promoting defluorination are highlighted in green and red, respectively. Reaction conditions: PFAS (0.1 mM), Co catalyst (0.25 mM), TiIII citrate (~36 mM), and carbonate buffer (~40 mM) in water; pH 9.0; 70°C.

13 ACS Paragon Plus Environment

Environmental Science & Technology Letters

250 251 252 253

Figure 3. Calculated bond dissociation energies (in kJ mol−1) at B3LYP/6-311+G(2d,2p)/SMD level of theory (BDEs) of C−F bonds in the PFASs shown in Figure 2. The displayed terminal group with two C=O bonds represent charge-delocalized −COO− anion.

14 ACS Paragon Plus Environment

Page 14 of 17

Page 15 of 17

Environmental Science & Technology Letters

254

REFERENCES

255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297

1. Vecitis, C. D.; Park, H.; Cheng, J.; Mader, B. T.; Hoffmann, M. R., Treatment technologies for aqueous perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA). Front. Environ. Sci. Eng. 2009, 3, 129-151. 2. Giesy, J. P.; Kannan, K., Peer reviewed: perfluorochemical surfactants in the environment. Environ. Sci. Technol. 2002, 36, 147A-152A. 3. Houde, M.; De Silva, A. O.; Muir, D. C.; Letcher, R. J., Monitoring of perfluorinated compounds in aquatic biota: an updated review: PFCs in aquatic biota. Environ. Sci. Technol. 2011, 45, 7962-7973. 4. Yamashita, N.; Kannan, K.; Taniyasu, S.; Horii, Y.; Petrick, G.; Gamo, T., A global survey of perfluorinated acids in oceans. Mar. Pollut. Bull. 2005, 51, 658-668. 5. Hu, X. C.; Andrews, D. Q.; Lindstrom, A. B.; Bruton, T. A.; Schaider, L. A.; Grandjean, P.; Lohmann, R.; Carignan, C. C.; Blum, A.; Balan, S. A., Detection of poly-and perfluoroalkyl substances (PFASs) in US drinking water linked to industrial sites, military fire training areas, and wastewater treatment plants. Environ. Sci. Technol. Lett. 2016, 3, 344-350. 6. Murakami, M.; Kuroda, K.; Sato, N.; Fukushi, T.; Takizawa, S.; Takada, H., Groundwater pollution by perfluorinated surfactants in Tokyo. Environ. Sci. Technol. 2009, 43, 3480-3486. 7. Hekster, F. M.; Laane, R. W.; de Voogt, P., Environmental and toxicity effects of perfluoroalkylated substances. Rev. Environ. Contam. Toxicol. 2003, 99-121. 8. Lindstrom, A. B.; Strynar, M. J.; Libelo, E. L., Polyfluorinated compounds: past, present, and future. Environ. Sci. Technol. 2011, 45, 7954-7961. 9. Drinking Water Health Advisory for Perfluorooctanoic Acid (PFOA); Office of Water (4304T); Health and Ecological Criteria Division; Document Number 822-R-16-005; U.S. Environmental Protection Agency: Washington, DC, 2016; p 8. 10. Drinking Water Health Advisory for Perfluorooctane Sulfonate (PFOS); Office of Water (4304T); Health and Ecological Criteria Division; Document Number 822-R-16-004; U.S. Environmental Protection Agency: Washington, DC, 2016; p 10. 11. Wang, Z.; Cousins, I. T.; Scheringer, M.; Hungerbühler, K., Fluorinated alternatives to long-chain perfluoroalkyl carboxylic acids (PFCAs), perfluoroalkane sulfonic acids (PFSAs) and their potential precursors. Environ. Int. 2013, 60, 242-248. 12. Sun, M.; Arevalo, E.; Strynar, M.; Lindstrom, A.; Richardson, M.; Kearns, B.; Pickett, A.; Smith, C.; Knappe, D. R., Legacy and emerging perfluoroalkyl substances are important drinking water contaminants in the Cape Fear River Watershed of North Carolina. Environ. Sci. Technol. Lett. 2016, 3, 415-419. 13. Newton, S.; McMahen, R.; Stoeckel, J. A.; Chislock, M.; Lindstrom, A.; Strynar, M., Novel polyfluorinated compounds identified using high resolution mass spectrometry downstream of manufacturing facilities near Decatur, Alabama. Environ. Sci. Technol. 2017, 51, 1544-1552. 14. Rahman, M. F.; Peldszus, S.; Anderson, W. B., Behaviour and fate of perfluoroalkyl and polyfluoroalkyl substances (PFASs) in drinking water treatment: a review. Water Res. 2014, 50, 318-340. 15. Pan, Y.; Zhang, H.; Cui, Q.; Sheng, N.; Yeung, L. W.; Guo, Y.; Sun, Y.; Dai, J., First report on the occurrence and bioaccumulation of hexafluoropropylene oxide trimer acid: An emerging concern. Environ. Sci. Technol. 2017, 51, 9553-9560. 16. Wang, Z.; Cousins, I. T.; Scheringer, M.; Hungerbuehler, K., Hazard assessment of fluorinated alternatives to long-chain perfluoroalkyl acids (PFAAs) and their precursors: status quo, ongoing challenges and possible solutions. Environ. Int. 2015, 75, 172-179.

15 ACS Paragon Plus Environment

Environmental Science & Technology Letters

298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343

17. Upham, B. L.; Deocampo, N. D.; Wurl, B.; Trosko, J. E., Inhibition of gap junctional intercellular communication by perfluorinated fatty acids is dependent on the chain length of the fluorinated tail. Int. J. Cancer 1998, 78, 491-495. 18. Wang, Y.; Niu, J.; Zhang, L.; Shi, J., Toxicity assessment of perfluorinated carboxylic acids (PFCAs) towards the rotifer Brachionus calyciflorus. Sci. Total Environ. 2014, 491, 266-270. 19. Eriksen, K. T.; Raaschou-Nielsen, O.; Sørensen, M.; Roursgaard, M.; Loft, S.; Møller, P., Genotoxic potential of the perfluorinated chemicals PFOA, PFOS, PFBS, PFNA and PFHxA in human HepG2 cells. Mutat. Res-Gen. Tox. En. 2010, 700, 39-43. 20. Gomis, M. I. From emission sources to human tissues: modelling the exposure to per-and polyfluoroalkyl substances. Ph.D. Thesis, Stockholm University, 2017. 21. Martin, J. W.; Kannan, K.; Berger, U.; Voogt, P. D.; Field, J.; Franklin, J.; Giesy, J. P.; Harner, T.; Muir, D. C.; Scott, B., Peer reviewed: analytical challenges hamper perfluoroalkyl research. Environ. Sci. Technol. 2004, 38, 248A-255A. 22. Reyes, E. A.; Beuterbaugh, A. M.; Smith, A. L., Treatment fluids containing a perfluorinated carboxylic acid for use in subterranean formation operations. US Patent Patent 9,051,510, June 9, 2015. 23. STANDARD 100 by OEKO-TEX - Limit Values and Individual Substances According to Appendices 4 & 5. Edition 02.2017. 24. Ahrens, L.; Plassmann, M.; Xie, Z.; Ebinghaus, R., Determination of polyfluoroalkyl compounds in water and suspended particulate matter in the river Elbe and North Sea, Germany. Front. Environ. Sci. Eng. 2009, 3, 152-170. 25. Howard, P. H.; Muir, D. C., Identifying new persistent and bioaccumulative organics among chemicals in commerce. Environ. Sci. Technol. 2010, 44, 2277-2285. 26. Lescord, G. L.; Kidd, K. A.; De Silva, A. O.; Williamson, M.; Spencer, C.; Wang, X.; Muir, D. C., Perfluorinated and polyfluorinated compounds in lake food webs from the Canadian high arctic. Environ. Sci. Technol. 2015, 49, 2694-2702. 27. Benskin, J. P.; Yeung, L. W.; Yamashita, N.; Taniyasu, S.; Lam, P. K.; Martin, J. W., Perfluorinated acid isomer profiling in water and quantitative assessment of manufacturing source. Environ. Sci. Technol. 2010, 44, 9049-9054. 28. Jin, H.; Zhang, Y.; Jiang, W.; Zhu, L.; Martin, J. W., Isomer–specific distribution of perfluoroalkyl substances in blood. Environ. Sci. Technol. 2016, 50, 7808-7815. 29. Arsenault, G.; Chittim, B.; McAlees, A.; McCrindle, R.; Riddell, N.; Yeo, B., Some issues relating to the use of perfluorooctanesulfonate (PFOS) samples as reference standards. Chemosphere 2008, 70, 616-625. 30. Chu, S.; Letcher, R. J., Linear and branched perfluorooctane sulfonate isomers in technical product and environmental samples by in-port derivatization-gas chromatography-mass spectrometry. Anal. Chem. 2009, 81, 4256-4262. 31. Merino, N.; Qu, Y.; Deeb, R. A.; Hawley, E. L.; Hoffmann, M. R.; Mahendra, S., Degradation and removal methods for perfluoroalkyl and polyfluoroalkyl substances in water. Environ. Eng. Sci. 2016, 33, 615-649. 32. Ochoa-Herrera, V.; Sierra-Alvarez, R.; Somogyi, A.; Jacobsen, N. E.; Wysocki, V. H.; Field, J. A., Reductive defluorination of perfluorooctane sulfonate. Environ. Sci. Technol. 2008, 42, 3260-3264. 33. Park, S.; De Perre, C.; Lee, L. S., Alternate Reductants with VB12 to Transform C8 and C6 Perfluoroalkyl Sulfonates: Limitations and Insights into Isomer-Specific Transformation Rates, Products and Pathways. Environmental Science & Technology 2017, 51, 13869-13877. 34. Phillips, M. M.; Dinglasan-Panlilio, M. J. A.; Mabury, S. A.; Solomon, K. R.; Sibley, P. K., Fluorotelomer acids are more toxic than perfluorinated acids. Environ. Sci. Technol. 2007, 41, 7159-7163.

16 ACS Paragon Plus Environment

Page 16 of 17

Page 17 of 17

344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387

Environmental Science & Technology Letters

35. Liu, J.; Avendaño, S. M., Microbial degradation of polyfluoroalkyl chemicals in the environment: a review. Environ. Int. 2013, 61, 98-114. 36. Zehnder, A.; Wuhrmann, K., Titanium (III) citrate as a nontoxic oxidation-reduction buffering system for the culture of obligate anaerobes. Science 1976, 194, 1165-1166. 37. Grimme, S.; Ehrlich, S.; Goerigk, L., Effect of the damping function in dispersion corrected density functional theory. J. Comput. Chem. 2011, 32, 1456-1465. 38. BecNe, A., Densityϋfunctional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 1993, 98, 5648-5652. 39. Lee, C.; Yang, W.; Parr, R. G., Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B 1988, 37, 785-789. 40. Stephens, P.; Devlin, F.; Chabalowski, C.; Frisch, M. J., Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields. J. Phys. Chem. 1994, 98, 11623-11627. 41. Vosko, S. H.; Wilk, L.; Nusair, M., Accurate spin-dependent electron liquid correlation energies for local spin density calculations: a critical analysis. Can. J. Phys. 1980, 58, 1200-1211. 42. Marenich, A. V.; Cramer, C. J.; Truhlar, D. G., Universal solvation model based on solute electron density and on a continuum model of the solvent defined by the bulk dielectric constant and atomic surface tensions. J. Phys. Chem. B 2009, 113, 6378-6396. 43. Kliegman, S.; McNeill, K., Dechlorination of chloroethylenes by cob(I)alamin and cobalamin model complexes. Dalton Trans. 2008, 4191-4201. 44. Chiu, P.-C.; Reinhard, M., Metallocoenzyme-mediated reductive transformation of carbon tetrachloride in titanium (III) citrate aqueous solution. Environ. Sci. Technol. 1995, 29, 595-603. 45. Payne, K. A.; Quezada, C. P.; Fisher, K.; Dunstan, M. S.; Collins, F. A.; Sjuts, H.; Levy, C.; Hay, S.; Rigby, S. E.; Leys, D., Reductive dehalogenase structure suggests a mechanism for B12-dependent dehalogenation. Nature 2015, 517, 513. 46. Men, Y.; Lee, P. K.; Harding, K. C.; Alvarez-Cohen, L., Characterization of four TCEdechlorinating microbial enrichments grown with different cobalamin stress and methanogenic conditions. Appl. Microbiol. Biotechnol. 2013, 97, 6439-6450. 47. Im, J.; Walshe-Langford, G. E.; Moon, J.-W.; Löffler, F. E., Environmental fate of the next generation refrigerant 2, 3, 3, 3-tetrafluoropropene (HFO-1234yf). Environ. Sci. Technol. 2014, 48, 13181-13187. 48. Baumgartner, R.; McNeill, K., Hydrodefluorination and hydrogenation of fluorobenzene under mild aqueous conditions. Environ. Sci. Technol. 2012, 46, 10199-10205. 49. Yu, Y.-H.; Chiu, P. C., Kinetics and pathway of vinyl fluoride reduction over rhodium. Environ. Sci. Technol. Lett. 2014, 1, 448-452. 50. Yonetani, T.; Yamamoto, H.; Woodrow, G. V., Studies on cobalt myoglobins and hemoglobins I. Preparation and optical properties of myoglobins and hemoglobins containing cobalt proto-, meso-, and deuteroporphyrins and thermodynamic characterization of their reversible oxygenation. J. Biol. Chem. 1974, 249, 682-690. 51. Lexa, D.; Saveant, J. M., The electrochemistry of vitamin B12. Acc. Chem. Res. 1983, 16, 235243. 52. Rovira, C.; Kunc, K.; Hutter, J.; Parrinello, M., Structural and Electronic Properties of Co-corrole, Co-corrin, and Co-porphyrin. Inorg. Chem. 2001, 40, 11-17.

17 ACS Paragon Plus Environment