Isotope applications in environmental investigations: Theory and use in chlorinated solvent and petroleum hydrocarbon studies

Abstract

1 2 3 4 Isotope applications are gaining acceptance for use in surface water and groundwater investigations, complementing traditional geochemistry and physical hydrology techniques. Recent developments in analytical methodologies and in the understanding of isotope dynamics now allow the use of isotopes to investigate sources and fate of common groundwater contaminants such as chlorinated solvents and petroleum hydrocarbons. Contaminants with unique isotopic signatures may facilitate the determination of contaminant sources in complex plumes. Degradation of chlorinated solvents and some petroleum hydrocarbons impart unique isotopic signatures on both the original contaminant and the degradation product or products that provide verification of degradation. Use of a Rayleigh-type model may allow determination of degradation extent. Coupled with models of contaminant fate and transport, degradation extent may be useful for determining degradation rates.

Lead isotope fingerprinting used as a tracer of lead pollution in marine sediments from Botany Bay and Port Hacking estuaries, southern Sydney, Australia

“…Thus, using isotopic ratios of elements is a more sound tracking method than using their concentrations alone to identify sources of contamination (e.g. carbon and chlorine; Sueker, 2001;Philp et al, 2002). In the same way, Pb isotopic composition may be used to trace the source and transport history of Pb (Chiaradia et al, 1997;Cheng and Hu, 2010;Lu et al, 2011;Allan et al, 2015).…”

Isotope applications in environmental investigations part II: Groundwater age dating and recharge processes, and provenance of sulfur and methane

“…In "Isotope Applications in Environmental Investigations Part I" (Sueker, 2002), detailed definitions of stable and radioactive isotopes; mechanisms of stable isotopes, such as fractionation and isotope mass balance; and mechanisms of radioactive decay, such as decay constants, half-lives, and age dating were described.This introductory material was followed by a presentation of isotope applications including the use of carbon, hydrogen, and chlorine isotopes to investigate sources and degradation of chlorinated solvents, polychlorinated biphenyls (PCBs), and petroleum hydrocarbons. In this article, Part II, a short overview of isotope essentials is followed by a presentation of isotope analyses that can be used for examining sources and flow paths of water, age dating groundwater, estimating recharge rates, and the isotope dynamics for sulfur species and methane.The sections on sulfur and methane isotope dynamics provide background material for evaluating redox conditions in aquifers and in situ remediation systems; topics that will be discussed in detail in Part III of this article to be published in a future issue of Remediation.…”

How to Use Stable Isotope Analysis

“…When bioremediation (biodegradation) occurs, it is proven that the enrichment in the heavier isotopes of the contaminant (remaining un-degraded at a certain time) also occurs. To quantify such processes (e.g., determine the extent of a reaction such as bioattenuation) and describe the isotopic enrichment or depletion during various processes, the Rayleigh distillation model is available (Sueker, 2001).…”

“…If there are more component elements with identified isotopes, it is recommended that the isotopic compositions of all components to be used for a reliable source assessment. The usability of isotopic analyses is also encouraged by the simplicity of sampling methods and the low analytical costs (similar with chemical analysis), ranging from $75 per sample for both oxygen and hydrogen isotopes of water to approximately $300 to $400 per sample for analysis of tritium-helium in groundwater, or to $575 for 13 C isotope in petroleum products (Sueker, 2001).…”