Stable Isotope Analysis of Organic Groundwater...
Transcript of Stable Isotope Analysis of Organic Groundwater...
Luc ZwankLuc ZwankMichael BergMichael BergRené SchwarzenbachRené SchwarzenbachTorsten SchmidtTorsten SchmidtStefan HaderleinStefan Haderlein
Stable Isotope Analysis of OrganicStable Isotope Analysis of OrganicGroundwater Contaminants:Groundwater Contaminants:
Applications and Field StudiesApplications and Field Studies
12C 12C
H
Cl
Cl
Cl
13C 12C
H
Cl
Cl
Cl
Stable Isotope Analysis of Organic Groundwater Contaminants:Stable Isotope Analysis of Organic Groundwater Contaminants:Applications and Field StudiesApplications and Field Studies
Compound-specific isotope analysis (CSIA) is a new approach to identify both, in-situ transformation processes ofpollutants in contaminated aquifers, and, sources of groundwater contaminants. Various laboratory studies havedemonstrated the potential of this tool for contaminant hydrology (1–3). However, CSIA is not very sensitive and limited tovery high pollutant concentrations.
With the target to significantly improve the method detection limits of CSIA, we therefore developed solid-phasemicroextraction (SPME) and purge&trap (P&T) pre-concentration techniques for isotope ratio mass spectrometry (IRMS)analysis. For both extraction techniques reproducible procedures for isotopic measurements of organic contaminants wereestablished. The detection limits for δ13C-determinations of volatile organic compounds could drastically be lowered to <5µg/L with the developed P&T-GC/IRMS method.
The SPME-technique allowed the simultaneous determination of δ13C-values of methyl tert-butyl ether (MTBE) and itsdegradation product tert-butyl alcohol (TBA) in a highly contaminated aquifer. The results support earlier investigations,which found in-situ degradation of MTBE to TBA. Yet, this new technique yields additional information about the MTBE-plume. The carbon isotopic data strongly suggest that the contaminated aquifer has two different zones, one with isotopefractionation linked to MTBE-degradation and a second where the observed concentration decrease is mainly due todilution or other non-fractionating processes. Furthermore the stable isotope data allow the identification of different spillzones at the site.
P&T extraction was successfully applied to study the fate of halogenated solvents in a contaminant plume down-gradient ofa municipal landfill in Switzerland. Contrary to previous evaluations based on concentration data alone, the isotopicsignatures show the absence of in-situ degradation of trichloroethene (TCE), despite the presence of cis-dichloroethene, aknown metabolite of TCE.
References
(1) Ahad, J.M.E, Lollar B.S., Edwards E.A., Slater G.F. and Sleep B.E. (2000) Environ. Sci. Technol. 34, 892–896.
(2) Hunkeler D., Aravena R. and Butler B.J. (1999) Environ. Sci. Technol. 33, 2733–2738.
(3) Meckenstock R.U., Morasch B., Warthmann R., Schink B., Annweiler E., Michaelis W., and Richnow H.H. (1999) Environ. Microbiol. 1,409–414.
OutlineOutline
Definitions•
Applications of Compound-specific Isotope Analysis (CSIA)Source identificationAssessment of in-situ degradation
•
Analytical SetupGas Chromatography Isotope Ratio Massspectrometry combined with different enrichment techniques
•
Field Application: Methyl tert-butyl ether (MTBE)•
Field Application: Trichloroethene (TCE)•
Conclusions•
DefinitionsDefinitions
„Delta Notation“
3
tan
12
13tan
12
13
12
13
13 10×
−
=∂
dardS
dardSUnkown
C
C
C
C
C
C
C
Standard material for carbon:
PeeDee Belemnite (PDB): 0‰
Applications of CSIAApplications of CSIA
Source identification of groundwater contaminants
Applications of CSIAApplications of CSIA
[Warmerdam, E. M. v et al. (1995), Applied Geochemistry 10: 547-552.]
Cl
Cl
Cl
Cl
PCE
TCE
H
Cl
Cl
Cl
Cl
Cl
Cl
Cl
TCA
Source identification of groundwater contaminants
Applications of CSIAApplications of CSIABiological transformations and chemical transformations
cause important isotopic fractionation
Applications of CSIAApplications of CSIA
[Meckenstock, R. U et al. (1999), Environmental Microbiology 1(5): 409-414.]
Biological transformations and chemical transformations cause important isotopic fractionation
Isotopic FractionationIsotopic Fractionation
Biological and abiotic transformations cause importantisotopic fractionation (Kinetic Isotope Effect)
Analytical SetupAnalytical Setup
12C 12C
H
Cl
Cl
Cl
12CO212CO2
Analytical SetupAnalytical Setup13CO2
12CO2
13 C 12 C
H
Cl
Cl
Cl
ChromatogramChromatogram
Analytical ChallengesAnalytical ChallengesCSIA is a promising tool in contaminant hydrology
MS requirement: 0.8 MS requirement: 0.8 nmolnmol C on column C on column
lliquidiquid on-column injection: 74 mg/L PER (1.5 on-column injection: 74 mg/L PER (1.5 µµL)L)
Groundwater concentrations are often below these detection limitsGroundwater concentrations are often below these detection limits
=> => Enrichment techniquesEnrichment techniques neededneeded
but it its broad use is limited by high detection limits
Analytical ChallengeAnalytical Challenge
Biological and abiotic transformations cause importantisotopic fractionation (Kinetic Isotope Effect)
Physical Processes such as evaporation, sorption, condensationhave also an effect on the isotopic signature of compounds(Equilibrium Isotope Effect)
=> Do enrichment techniques cause isotopic fractionation ???
Extraction procedure:Fiber material: Carboxen-PDMSExtraction times: 5-60 minutesNaCl concentration 4M
Solid Phase MicroextractionSolid Phase Microextraction
Purge and TrapPurge and Trap
-120
°C
200
°C
Detection LimitsDetection Limits
Compound On Column [�g/L]
SPME [�g/L]
P&T [�g/L]
trans-1,2-dichloroethene 75’000 130 1.5
cis-1,2-dichloroethene 71’000 92 1.1
trichloroethene 84’000 94 1.4
tetrachloroethene 74’000 66 2.2 methyl tert-butyl ether 24’000 16 0.6
benzene 19’000 22 0.3
toluene 9’000 9 0.2
δδδδ1313C-ReproducibilityC-Reproducibility
-27.27 + 0.20-27.37 + 0.36-27.56 + 0.07-27.88 + 0.20benzene
-27.75 + 0.09-29.67 + 0.40-27.91 + 0.06-28.13 + 0.15methyl, tert-butylether
-26.76 + 0.19-28.16 + 1.31-27.19 + 0.17-27.32 + 0.14tetrachloroethene
-26.11 + 0.20-26.83 + 0.13-27.37 + 0.12-26.59 + 0.08trichloroethene
P&T(n=10)
SPME(n=10)
On Column(n=10)
ElementalAnalyzer (n=3)
Compound
Methyl tert-butyl EtherMethyl tert-butyl Ether
Used as oxygenate in gasoline (up to 15 % Vol.)
High aqueous solubility (ca. 50 g/L) + limited degradability
=> High mobility in groundwater
High production chemical (ca 20 Mio tons/year)
Major degradation product: tert-butanol (TBA)
O
MTBE
OH
TBA
Field Application: MTBEField Application: MTBE
-22.9
-19.8-12.7-25.7
-13.9-18.4
-18.2-22.1
-26.3
-5.0
-22.2
-23.7
-26.9‰
-26.8‰
-26.1‰
-26.9
-26.8
-26.1
Dilution
Degradation
Field Application: MTBEField Application: MTBE
=> Shifts in isotopic signature of MTBE and TBA indicate transformation
-5
0
5
10
15
20
25Is
otop
ic E
nric
hmen
t [‰
]
Plume1
Plume2
Plume3
MTBE TBA
Field Application: MTBEField Application: MTBE
fCC tSubstrateSubstrate ln0,
1313 ⋅+∂=∂ ε
Quantification of the isotope effect:
The simplified Rayleigh equation (for ε <20 permil)
Typical ε for biological transformation of MTBE: 1.5 to 2.5 permil
Gray, J. R. et al. (2002). Environmental Science and Technology 36(9): 1931-1938.
Hunkeler, D. et al. (2001). Environmental Science and Technology 35(4): 676-681.
Field Application: MTBEField Application: MTBE
R2 = 0.9999
R2 = 0.7054
-30
-25
-20
-15
-10-7-6-5-4-3-2-10
ln (remaining MTBE fraction)
δ13C
Center of Plume Fringe Zone of PlumeLinear (Center of Plume) Linear (Fringe Zone of Plume)
ε = -4.8 permil ε = -1.8 permil
-30
-25
-20
-15
-10-7-6-5-4-3-2-10
ln (remaining MTBE fraction)
δ13C
All DataData from Plume 1
Field Application: MTBEField Application: MTBE
Preliminary conclusions for this site:
• MTBE in-situ degradation takes place
it seems however that degradation is strongestin the highly contaminated part of the aquifer
Anaerobic MTBE-degradation ?
Cometabolic MTBE-degradation ?
• Multiple spill sites contribute to the contamination
Further investigation will include more hydrological data as well as D/H-isotopic data
TrichloroetheneTrichloroetheneH
Cl
Cl
Cl
H
Cl
H
Cl
TCE cis-DCE
Used as metal degreasing agent (widespread)
High production chemical (190‘000 t/year Germany, 2000)
cis-DCE has no industrial use
Degraded to cis-DCE under anoxic conditions
=> Detection of cis-DCE is evidence for degradationof higher chlorinated compounds
Field Application: TCEField Application: TCE
Field Application: TCEField Application: TCE
0
10
20
30
40
50
60
Con
cent
ratio
n
1 2 3 4
Monitoring Well
TCE [ug/L]DCE [ug/L]Chloride [mg/L]
-34
-33
-32
-31
-30
-29
-28
δ13C
[‰]
TCETCEDCE
ConclusionConclusion
P&T allows detection limits in the low µg/L-rangecorresponding to a 20-50 fold reduction compared to SPME
Compound-specific isotope analysis is a valuable tool in contaminant hydrology
The reduction of detection limits allows its application atmany field sites
ConclusionConclusion
Scientific application: Combination of CSIA and hydrological modelling to understand in-situ reaction mechanisms and gain in-situ degradation rates
Technical application: Determination of contamination sourcesDetermination of occurence of in-situ degradationDetermination of type and localization of in-situ degradation
AcknowledgementAcknowledgement
EAWAGJakov BolotinSamuel LuziCarsten Schubert
Institut BachemaMichel Schurter
Amt für Umwelt Kanton ThurgauDaniel Müller Andreas Scholtis
Resi
δ13C of pure phase
δδδδ1313C-ReproducibilityC-Reproducibility
-10
-8
-6
-4
-2
0
2
4tr
ans-
1,2-
dich
loro
ethe
ne
met
hyl,
tert
-but
ylet
her
cis-
1,2-
dich
loro
ethe
ne
benz
ene
tric
hlor
oeth
ene
tetr
achl
oroe
then
e
tetr
achl
orom
etha
ne
chlo
rofo
rm
Diff
ere
nce
fro
m B
ulk
Ph
ase
[‰]
On Column Injection Solid Phase Microextraction Purge and Trap
Applications of CSIAApplications of CSIA
Understanding of Reaction Mechanisms
Reductive Dechlorination of CCl4
Applications of CSIAApplications of CSIA
Understanding of Reaction Mechanisms
Reductive Dechlorination of CCl4
Iron Porphyrine (1 e- transfer)
Sulfide (2 e- transfer)
Fe(II) sorbed to Goethite
-30
-28
-26
-24
-22
-20
ε [‰
]
Solid Phase MicroextractionSolid Phase Microextraction
δ13C of pure phase
Methyl tert-butyl ether (MTBE)
0
10
20
30
40
50
60
0 10 20 30 40 50 60
Extraction time [min]
Extr
actio
n ef
ficie
ncy
[%]
-31.5
-31
-30.5
-30
-29.5
-29
-28.5
δ13C [
‰]
Extraction Efficiency [%] d13C [permil]
Purge and TrapPurge and Trap
δ13C of pure phase
Tetrachloroethene (PCE)
01020304050607080
0 10 20 30 40 50 60
Extraction time [min]
Extr
actio
n ef
ficie
ncy
[%]
-28
-27.5
-27
-26.5
-26
-25.5
-25
δ13C [
‰]
Extraction Efficiency [%] d13C [‰]
Luc Zwank is originally from Luxembourg. He graduated at the Swiss Federal Institutefor Technology in Zurich (ETHZ) and got his masters degree in Environmental Sciences,with the focus on environmental organic chemistry, at the Ralph M. Parsons Laboratory(MIT, Cambridge, MA, USA), under the supervision of Prof. P. M. Gschwend. Since May2000 is a Ph.D. student at the Swiss Federal Institute for Environmental Science andTechnology, supervised by Prof. R. P. Schwarzenbach, and focusses on thecharacterization of transformation processes of groundwater contaminants.
E-mail: [email protected]