Thesis title: Stable Isotope applied to organic geochemistry of emerging contaminants: innovative isotopic tools for source tracing and degradation assessment
This PhD research aimed to develop and apply stable isotope methodologies for investigating
emerging organic contaminants in geological and environmental matrices. The work addressed
both analytical and interpretative challenges in isotope-based techniques through a strongly
methodological approach. While stable isotopes have long been used to trace contaminant
sources and degradation processes, the increasing diversity and chemical complexity of
modern pollutants require continuous methodological innovation to ensure accurate and
reproducible isotopic data. Within this framework, the objective was to design and implement
new isotope-based analytical tools, supported by multi-isotopic approaches, to characterize
contaminant sources and quantify transformation processes in contemporary environments.
The study focused on three main classes of emerging contaminants, marine plastics,
oxygenated fuel additives, and per- and polyfluoroalkyl substances (PFAS), selected for their
environmental relevance and analytical challenges. The sequence of studies reflects increasing
methodological complexity, from bulk stable isotope analysis (BSIA) to compound-specific
isotope analysis (CSIA). The first study applied BSIA to marine plastic pellets, integrating isotopic
(δ¹³C and δ¹⁸O) and infrared data to investigate early photooxidative degradation of pellets
released in seawater. Results demonstrated the stability of δ¹³C as a source tracer and a
progressive δ¹⁸O depletion proportional to oxidation, providing a quantitative degradation
proxy. The second study applied CSIA to oxygenated fuel additives (methyl tert-buthyl ether
and ethyl tert-buthyl ether), major groundwater contaminants, using dual-isotope (δ¹³C–δ²H)
analysis to describe biodegradation patterns and assess site-specific isotopic variability of pure
and pristine gasoline, essential for accurate degradation estimates. The third study developed
the first CSIA method for perfluorocarboxylic acids (PFCAs), the most detected subclass,
demonstrating the feasibility of carbon isotope analysis for these persistent compounds. A
subsequent field application confirmed the method’s robustness through the first isotopic
characterization of PFAS in environmental samples.
Overall, this PhD expands the analytical boundaries of isotope geochemistry by establishing
methodological foundations for the isotopic study of emerging contaminants. The developed
tools provide new opportunities for tracing contaminant sources, quantifying degradation
processes, and supporting future applications of stable isotope analysis in environmental
monitoring and remediation.