Dual Carbon–Bromine Stable Isotope Analysis Allows Distinguishing

Aug 16, 2016 - Dual Carbon–Bromine Stable Isotope Analysis Allows Distinguishing .... Seo Yean Sohn , Kevin Kuntze , Ivonne Nijenhuis , Max M. Hägg...
0 downloads 0 Views 515KB Size
Subscriber access provided by Northern Illinois University

Article

Dual carbon-bromine stable isotope analysis allows distinguishing transformation pathways of ethylene dibromide Kevin Kuntze, Anna Kozell, Hans Hermann Richnow, Ludwik Halicz, Ivonne Nijenhuis, and Faina Gelman Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b01692 • Publication Date (Web): 16 Aug 2016 Downloaded from http://pubs.acs.org on August 16, 2016

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 free 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 accessible to all readers and 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.

Environmental Science & Technology 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 28

Environmental Science & Technology

1 2 3

Dual carbon-bromine stable isotope analysis allows distinguishing transformation pathways of ethylene dibromide

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Kevin Kuntze1, Anna Kozell2, Hans H. Richnow1, Ludwik Halicz2,3, Ivonne Nijenhuis1*, and Faina Gelman2 1 Department of Isotope Biogeochemistry, Helmholtz-Centre for Environmental Research – UFZ, Permoserstrasse 15, 04318 Leipzig, Germany 2 Geological Survey of Israel, 30 Malkhei Israel St., Jerusalem, 95501, Israel 3 Faculty of Chemistry, Biological and Chemical Research Centre, University of Warsaw, 02089Warsaw, Poland *corresponding author: phone: +49 341 235 1356, fax: +49 341 235 450822, e-mail: [email protected]

20 21

22

1 ACS Paragon Plus Environment

Environmental Science & Technology

23

Page 2 of 28

Abstract

24 25

The present study investigated dual carbon-bromine isotope fractionation of the

26

common groundwater contaminant ethylene dibromide (EDB) during chemical and

27

biological transformations, including aerobic and anaerobic biodegradation, alkaline

28

hydrolysis, Fenton-like degradation, debromination by Zn(0) and reduced corrinoids.

29

Significantly different correlation of carbon and bromine isotope fractionation (ΛC/Br)

30

was observed not only for the processes following different transformation pathways,

31

but also for abiotic and biotic processes with, the presumed, same formal chemical

32

degradation mechanism. The studied processes resulted in a wide range of ΛC/Br

33

values: ΛC/Br = 30.1 was observed for hydrolysis of EDB in alkaline solution; ΛC/Br

34

between 4.2 to 5.3 were determined for dibromoelimination pathway with reduced

35

corrinoids and Zn(0) particles; EDB biodegradation by A. aquaticus and S.

36

multivorans resulted in ΛC/Br = 10.7 and 2.4, respectively; Fenton-like degradation

37

resulted in carbon isotope fractionation only, leading to ΛC/Br ∞. Calculated carbon

38

apparent kinetic isotope effects (13C-AKIE) fell with 1.005 to 1.035 within expected

39

ranges according to the theoretical KIE, however, biotic transformations resulted in

40

weaker carbon isotope effects than respective abiotic transformations. Relatively

41

large bromine isotope effects with

42

observed for nucleophilic substitution and dibromoelimination, respectively, and

43

reveal so far underestimated strong bromine isotope effects.

81

Br-AKIE of 1.0012-1.002 and 1.0021-1.004 were

44

2 ACS Paragon Plus Environment

Page 3 of 28

Environmental Science & Technology

45

Introduction

46

Brominated organic compounds (BOCs) are widely used and play an important role

47

in the production of e.g. agrochemicals, pharmaceuticals or dyes. However, many of

48

these compounds are considered to be toxic, carcinogenic or even mutagenic 1. One

49

of these brominated contaminants is ethylene dibromide (EDB, 1,2-dibromoethane),

50

extensively used in the past as a lead scavenger in gasoline as well as an agriculture

51

fumigant

52

oxic and anoxic conditions

53

environment can follow several different mechanistic pathways: nucleophilic

54

substitution (e.g. hydrolysis), dehydrobromination, dibromoelimination or radical

55

oxidation (via proton abstraction). Under certain conditions, EDB degradation may

56

occur through multiple reaction types. Thus, for example, in alkaline solutions both

57

hydrolysis and dehydrobromination may compete

58

nucleophiles

59

(e.g.dibromoelimination) may occur during reaction with FeS or sulfur species 11.

60

During the last decades it has been demonstrated that compound-specific stable

61

isotope analysis (CSIA) can be used to characterize transformation reactions of

62

organic contaminants

63

methods for carbon, hydrogen and nitrogen was extended by the development of

64

highly sensitive bromine isotope analyses as a tool for investigating the

65

transformation of BOCs

66

formed by heavy isotopes (e.g. 2H,

67

therefore, cleaved slower than bonds between lighter isotopes. As a result, the

68

residual (not yet degraded) fraction of the substrate becomes enriched in the heavier

69

isotopes as a reaction proceeds. So far, it has been demonstrated that single

70

element isotope fractionation can serve as an indicator for a specific reaction

2-4

. EDB is susceptible to abiotic reactions and can be biodegraded under

combined

with

5-13

. In general, all EDB transformations in the

two-electron

10,

transfer

14

; SN2 substitution by

reductive

debromination

15, 16

. Recently, the set of the well-established analytical

17-20

. The approach of CSIA is based on the fact that bonds 13

C,

37

Cl,

81

Br) are slightly more stable and,

3 ACS Paragon Plus Environment

Environmental Science & Technology

Page 4 of 28

71

pathway without the need to trace reaction products, which can be challenging in

72

complex environmental systems15. However, other steps preceding the isotope-

73

sensitive bond cleavage, e.g. uptake, transport and binding of substrate to the

74

enzyme, may significantly affect isotope enrichment factors, even for similar

75

reactions

76

than intrinsic kinetic isotope effects (KIEs). Additionally, a possible lack of variability

77

in isotope fractionation patterns among different reaction pathways may limit its

78

diagnostic value for reaction identification

79

analysis allows the correlation of isotope ratios of several elements to each other and

80

reveals pathway-specific information. When the changes in isotope fractionation of

81

two elements are correlated, a correlation factor specific for a given reaction pathway

82

and corresponding bond cleavage is expected

83

already extensively applied

84

up recently for evaluation of reaction mechanisms

85

large potential for environmental studies, the implementation of the dual carbon-

86

bromine isotope analysis is still in its infancy. To our knowledge, thus far, only two

87

studies applied dual carbon-bromine isotope analysis for getting insight into the

88

mechanism during the abiotic transformation of bromophenols and tribromoneopentyl

89

alcohol, respectively 20, 34.

90

While carbon and chlorine isotope effects in the chlorinated analogue 1,2-

91

dichloroethane (1,2-DCA) have been studied in many biological and chemical

92

transformations

93

investigated. To the best of our knowledge, only two studies regarding carbon

94

isotope effect during biological and chemical degradation of EDB are available so far

95

8, 11

96

still unclear how different factors affect isotope effects during transformations of

21, 22

, and lead to apparent kinetic isotope effects (AKIEs) that are smaller

31, 35-37

25-29

23

. Potentially, multi-elemental isotope

24

. Dual δ2H/δ13C isotope analysis is

and studies applying dual δ13C/δ37Cl analysis came 30-33

. In contrast, probably having

, isotope effects during transformations of EDB are still poorly

. Due to the limited data on isotope effects in brominated organic compounds, it is

4 ACS Paragon Plus Environment

Page 5 of 28

Environmental Science & Technology

97

brominated organic compounds. In the present study we aimed to investigate carbon

98

and bromine isotope fractionation of EDB during several environment-relevant EDB

99

degradation processes: i) chemical hydrolysis in alkaline solution; ii) Zn(0) reduction;

100

iii) reduction by reduced corrinoids;

101

biotransformation by Sulfurospirillum multivorans crude extract; and vi) aerobic

102

biotransformation by Ancylobacter aquaticus crude extract.

103

The chosen set of the chemical and biotic transformations of EDB enabled us to

104

compare carbon and bromine isotope fractionation and to evaluate the potential of

105

dual carbon-bromine isotope slopes for differentiating processes following the same

106

mechanistic pathway. The obtained results were compared to isotope effects

107

observed for chlorinated analogues

108

model, a difference in isotope effects was expected for C-Cl (KIEC=1.0572;

109

KIECl=1.013)23 vs. C-Br (KIEC=1.0420; KIEBr=1.002) bond cleavage (see calculations

110

in Supplementary Information). Thus the C-KIE is expected to be ~1.1-1.2 times

111

larger for chlorinated compounds and Cl-KIE is ~ 5-6 times higher than Br-KIE34, 38.

112

Comparison between the isotope effects observed for EDB in the present study to

113

the isotope effects reported for chlorinated analogues enables to evaluate similarities

114

and differences in behavior of these two important classes of halogenated organic

115

pollutants.

34, 38

iv) Fenton oxidation; v) anaerobic

. Based on Streitwieser semi-classical limits

116

5 ACS Paragon Plus Environment

Environmental Science & Technology

Page 6 of 28

117

Materials and Methods

118

Cultivation of bacterial cultures. Sulfurospirillum multivorans (DSMZ 12446) was

119

cultivated at 28°C and 120 rpm in an anoxic mineral medium as previously described

120

39

121

mmol L-1) and tetrachloroethene (10 mmol L-1 dissolved in hexadecane) as electron

122

acceptor. Ancylobacter aquaticus AD20 (DSMZ 9000) was cultivated under oxic

123

condition in mineral medium as described previously

124

with 1,2-DCA (1 mmol L-1) and incubated at 28°C and 120 rpm. EDB was not added

125

in the pre-cultivations to ensure that the same enzymes were expressed as in

126

previous studies. Furthermore, preliminary tests showed that S. multivorans could not

127

grow with EDB, likely due to toxicity effects.

with pyruvate (40 mmol L-1) as carbon source and electron donor and fumarate (40

40

. The culture was amended

128 129

Bacterial crude extract preparation. Bacterial cells were harvested at the end of

130

the logarithmic growth-phase. Crude extracts were prepared in 0.1 mol L-1 Tris-HCl

131

buffer adjusted to pH 7.5 under anoxic conditions (S. multivorans)

132

L-1 Tris-HCl buffer with 1 mmol L-1 EDTA adjusted to pH 7.5 under oxic conditions (A.

133

aquaticus)

134

mixture was incubated for 10-15 min at room temperature. Subsequently, the cells

135

were disrupted via French press (Thermo Scientific, Waltham, USA) at 20.000 psi.

136

The produced crude extract was stored (under anoxic conditions for S. multivorans)

137

at -20°C until further use.

40

21

and in 50 mmol

. For cell lysis 10 mg lysozyme and 1 mg DNase I was added and the

138 139

6 ACS Paragon Plus Environment

Page 7 of 28

Environmental Science & Technology

140

Transformation experiments.

141

Biotic transformation with crude extracts. In both experiments crude extracts were

142

used to avoid rate-limitation, such as substrate uptake, affecting isotope fraction prior

143

to bond cleavage typical for biodegradation experiments and to characterize the

144

enzyme-related transformation of EDB. The enzymatic dehalogenation reaction with

145

crude extract of S. multivorans was done as described previously

146

be found in the Supporting Information (SI). The enzymatic reaction with crude

147

extract of A. aquaticus was performed in sealed 10 ml vials filled with 5 ml 50 mmol

148

L-1 Tris-HCl buffer (pH 7.5) and 1 mmol L-1 EDTA. EDB was added at a final

149

concentration of 1 mmol L-1. The reactions were started by adding bacterial crude

150

extract to the reaction vials and were incubated at room temperature on a rotary

151

shaker (160 rpm). Abiotic controls without adding cell extracts showed no significant

152

decrease of EDB (data not shown). The reactions were stopped by acidification to

153

pH