Using isotopic analysis to determine the source and fate of

groundwater contamination

identification of stable isotopes and chemical elements within chemical compounds.

Ability to demonstrate source and degradation of contaminants Environment, bioremediation Drug testing Quality control

Stable isotopes: naturally occurring forms of the same element with different numbers of neutrons C13/C12 H1/H2 Cl35/Cl37

Stable isotope analysis based on determination of the ratios of two stable isotopes in a sample

Fractionation: partitioning of isotopes due to chemical, biological, geological and hydrological processes source material left "heavier” (heavier isotope

more abundant) Differing molecular weights cause

isotopes react at different rates Kinetic Isotope Effect

Degradative vs non degradative processes

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Gas Chromatography – Isotope Ratio Mass Spectrometry

Separates individual chemicals from a complex mixture based on molecular mass Different isotopes have different masses!

High sensitivity, high precison, rapid Provides an isotopic fingerprint that can

be compared among samples

Isotopic composition conserved during environmental processes Sources with distinct isotopic compositions

Contaminant fractionated by environmental processes What processes have affected the

contaminant and to what extent Bioremediation & degradation

Determination independent of non degradative processes

BTEX: benzene, toluene, ethylbenzene and xylenes Petroleum derivatives

Ex. Gasoline CNS Toxin, carcinogen

TCE: Trichloroethene Chlorinated ethene degreaser, industrial solvent, dry cleaning chemical CNS depressant, carcinogen, ALS, PD

MTBE: methyl tert-butyl ether Gasoline additive Potential carcinogen

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“Isotopic analysis is a powerful tool for investigating and monitoring of the sources and fates of environmental contaminants, provided it is applied in situations where the basis of knowledge is sufficient for isotopic forensics to work.” pg. 22

Clear difference in isotope pools to be compared Source differentiation: various source pools Degradation: degraded and undegraded

contaminant Isotopic distinction greater than present

variations/imprecisions Environmental processes Instrumental precision

Predictable isotopic behaviour

Anaerobic, unconfined aquifer

Within 6.5m deep glacial deposits

Underlying shale bedrock Watertable 0.3-1m below

ground Two sources of TCE

contamination

Repeated samples must be taken both upstream and downstream (groundwater flow) of the contamination site

Multiple transects Sufficient data for identification of trends Decreased effect of variation

Characterized by very high depletion, saturation of contaminant Depletion (low relative levels heavy isotope)

indicates a lack of degradation Enrichment (high relative levels heavy

isotope) indicates degradation Source can only be identified in a sample

well with no degradation/fractionation

Repeated contamination events over time from a single or multiple sources

Extent of the effect on source determination determined by quantity added

Worst Case: enrichment must proceed beyond potential range source variation

Given a linear trend, the assumption can be made that temporal variability does not have an effect

Isotope ratio converted to an internationally accepted standard value (δ)

Trends and samples analyzed by application of statistical models Linear relationship between concentration and δ

Sampling and variability taken into account Requires only prior knowledge of the

enrichment factor (ε) Available in literature Based on known rates of degradation of isotopes

of interest Can be used to determine fractionation,

degradation or source

Site specific determination of presence of contaminants, bioremediation and sources of contamination

Highly sensitive Highly precise Growing field with potential to expand to

include many other isotopes & unique applications