Utilization of Stable Isotopes and Kinetic Models to Monitor Biodegradation of

Volatile Organic Compounds

Nazmul Haque, PhD, PE

2019 ASTSWMO LUST Workshop Sharing Solutions to Advance LUST Cleanups

Conclusions

Sustainability

Utilization

Outline

Application of Isotope

TerminologyDescription

ConceptDevelopment

Instrument

ModelDevelopment Application

of Isotope

TerminologyDescription

Utilization

Importance of Isotope

TerminologyDescription

Concept Development

Concept Development

[mg/kg] [mg/L] [mg/kg] [mg/L] [days] [day-1]Benzene 0.02 0.01 0.05 0.02 1825 0.000380Toluene 7.52 1.31 38.41 6.68 1825 0.000380Ethylbenzene 24.56 0.92 1164.25 169.00 1825 0.000380Xylenes (Total) 358.97 13.08 1395.31 198.00 1825 0.000380MTBE 0.03 0.03 0.03 0.03 18250 0.000038Naphthalene 5727.09 0.95 47743.48 31.00 1825 0.000380TPH-GRO 572.84 7.77 1490.27 70.86 1825 0.000380TPH-DRO 628.41 4.47 1071.67 31.45 1825 0.000380

First-Order Decay Rate

CHEMICALS OF CONCERN

With BiodegradationAllowable GW

Conc. at source protective of POE

Without Biodegradation

Half-LifeAllowable Soil

Conc. Protective of GW at the POE

Allowable GW Conc. at source

protective of POE

Allowable Soil Conc. Protective of GW at the POE

Recently, sustainable solutions for environmental remediationhave gained importance. To some extent, this can be related tothe acceptance of intrinsic bioremediation or naturalattenuation (B/NA) as a means to manage contaminatedgroundwater. Assessing the feasibility of B/NA of organiccontaminants in the subsurface is critical to managingcontaminated properties, performing a comprehensive riskassessment, and evaluating potential bioremediationmeasures.

Volatile organic contaminants in ground water are usuallycomposed of carbon, hydrogen and chloride.

Each of the these elements have more than one stableisotope. These stable isotopes are not radioactive. Thestable isotopes differ from each other in the number ofneutrons in the nucleus of the atom. Isotopes have the same number of protons – identical atomic

number Isotopes have different number of neutrons – different

atomic mass

Terminology Description

p e-

Hydrogen,1H

np e-

Deuterium,2H, D

Terminology Description

Terminology Description

Natural attenuation is a widely applied strategy to restorepetroleum hydrocarbon contaminated sites that is increasinglyaccepted by regulators (Sondermann & Knorpp, 2004).

The strategy relies on the capacity of indigenous microorganisms toeliminate contaminants from the subsurface under naturalconditions and thus tries to limit the use of engineeringtechnologies.

Over the past decade, this remedial strategy became an attractivealternative to engineered remediation as it was shown to reducethe risk of impacts on man and environment to an acceptable levelat several petroleum hydrocarbon contaminated sites with limitedeconomical investments (Hinchee et al., 1995; NRC, 2000).

Terminology Description

It is imperative to demonstrate that biodegradation ofhydrocarbons are actually occurring at the site. Microbialbreakdown is usually the only process to decompose thecompound into CO2 and clear evidence must be provided thatthe VOC concentration depletion is linked to the microbialactivity and not to physical processes like sorption, dilutionand dispersion, which is challenging.

Importance of CSIA

Compound-specific isotope analysis (CSIA) has recently beenshown to be an effective tool to confirm in situ biodegradation bythe indigenous microbial population. Therefore, the method isincreasingly used to assess and sometimes to quantify in situbiodegradation of various types of organic contaminants in thesaturated zone (Beneteau et al., 1999; Chu et al., 2004.)

Importance of CSIA

Importance of CSIA

Stable Isotope Fractionation

Differences in isotope ratios between samples can indicate different sources.

Key Point:

H1H1

H1H2

Cl

Cl

Cl

Cl

C13 C12

Equilibrium Effect (reversible)

Kinetic Effect (irreversible)

Evaporation

Biodegradation of PCE

Importance of CSIA

Correlation Using Bulk Isotope Ratios

-140

-136

-132

-128

-124

-120

-29 -28 -27 -26 -25 -24 -23

δ13C (‰)

δD (‰

)

MW-2

MW-5 MW-11

MW-4

Brand A GasolineBrand BGasoline

Contamination in monitoring wells had two possible sources; GC fingerprints were similar since both were contemporary gasoline; isotopically distinct since derived from different crude oils

Isotope Values of Crude Oils Vary with Source

-20

-25

-30

-35

-23.27

-25.66

-30.06-29.52 -29.50

-23.45

-29.68

Monterey Crude

Katalla Crude

Cook Inlet Crude

North Slope Crude

Unknown Source

Monterey Source

NSC Source

Petroleum Source

δ13C

Importance of CSIA

14

Analysis of Stable Carbon Isotope Ratios

The ratio of stable isotopes is determined with an Isotope Ratio Mass Spectrometer (IRMS).

The IRMS compares the ratio of 13C to 12C in the sample against the ratio of 13C to 12C in a reference standard.

The ratio in the reference sample Rs = 0.0112372

Delta C thirteen is the conventional unit for thestable carbon isotope ratio in the sample. It isa measure of how much it varies from thestandard.

Notice that delta C thirteen is expressed inparts per thousand.

You will see this expressed as:o/oo or permil or per mill.

δ 13C

14

Where R is the ratio of 13C to 12C in the sample and Rs is the ratio in the standard

δ 13 1 1000C RRs

= −

⋅

Utilization

15

molecules containing 12C are metabolizedmore rapidly than molecules containing 13C.

As the organic compound is biodegraded,the residual compound is enriched in 13C.

Utilization

Instrument

Model Development

18

)/)(( 1313/ εδδ gasolineinMTBEwatergroundinMTBE CCeCoCF −==

ε is the “enrichment factor”, calculated as the slope of a linear regression of δ13C on the

natural logarithm of the fraction remaining of MTBE (C/Co or F).

)/)(( 1313/ εδδ gasolineinMTBEwatergroundinMTBE CCeCoCF −==

ε is the “enrichment factor”, calculated as the slope of a linear regression of δ13C on the

natural logarithm of the fraction remaining of MTBE (C/Co or F).

Model Development

Model Development

20

Worldwide values range from–28 o/oo to –33 o/oo

δ 13C

Stable Carbon Isotope Ratios of MTBE in Gasoline

O’Sullivan, G., G. Boshoff, A. Downey, and R. M. Kalin. “Carbon isotope effect during the abiotic oxidation of methyl-tert-butyl ether (MTBE). In Proceedings of the Seventh International In Situ and On-Site Bioremediation Symposium, Orlando, FL, 2003.

Model Development

Model Development

Model Development

STELLA

Sustainability

Conclusions Less expensive. Approximate Cost is $200 to $400 for one sample

for one compound for one isotope ratio.

More direct. Detects degradation that has already happened,instead of simply documenting a capability to degrade thecontaminants.

At many hazardous waste sites, data is collected four times a yearfor five or ten years, and then try to make inferences aboutbiodegradation that are not satisfying or compelling.

Twenty to forty analyses using Method 8260 don’t answer thequestion about biodegradation because they provide the wronginformation.

CSIA analyses on water from two wells can provide an estimate ofthe rate of degradation.

Clients

References

Seminar Committee

Acknowledgements

Thanks for your attention

Utilization of Stable Isotopes and Kinetic Models to Monitor Biodegradation of Volatile Organic CompoundsSlide Number 2Slide Number 3Slide Number 4Slide Number 5Slide Number 6Slide Number 7Slide Number 8Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13Analysis of Stable Carbon Isotope RatiosSlide Number 15InstrumentSlide Number 17Slide Number 18Slide Number 19Stable Carbon Isotope Ratios of MTBE in GasolineSlide Number 21Slide Number 22Slide Number 23Slide Number 24Slide Number 25Slide Number 26