Investigating organic transformation mechanisms in complex environments (ground and surface water, living organisms, heterogeneous catalysis) is of fundamental importance in chemical sciences, yet challenged by the uncertainty whether lab-based studies adequately mirror real-world processes.

Compound-specific stable isotope analysis (CSIA) of organic substances at natural isotopic abundance offers the potential to bridge this gap and to enable mechanistic reaction studies directly in complex systems. Through gas chromatography (GC) or liquid chromatography (LC) coupled to isotope ratio mass spectrometry (IRMS) the measurement of 13C-, 15N-, 2H- and 37Cl- isotope effects can be accomplished in pesticides, pharmaceuticals, chlorinated hydrocarbons and petroleum hydrocarbons at trace (microgram per liter) concentrations. This information does not only allow detecting degradation of chemicals in the environment in complex situations and over time scales otherwise not accessible (months to years).

Isotope effect analysis of multiple elements also enables to elucidate transformation mechanisms (i.e. the manner and order of bond breaking) where conventional analysis provides complementary information about the identity of products (i.e. the net outcome of a reaction). My presentation summarizes analytical developments, presents latest results on the ability of CSIA to pinpoint micropollutant degradation in soil and groundwater and illustrates the capability of CSIA to elucidate underlying reaction mechanisms. This dual advantage of CSIA – the ability to tackle complex systems, yet to retrieve mechanistic information on the molecular level – offers prospects for studying degradation of chemical micropollutants in rivers, groundwater and engineered systems.

Martin Elsner

Since 2006 Martin Elsner leads the Research Group, and since 2014 the Research Unit “Environmental Isotope Chemistry” at the Institute of Groundwater Ecology, Helmholtz Zentrum München. Since 2011 he is also lecturer in the Department of Applied Geoscience at the University of Tübingen. His research addresses transformation reactions of organic chemicals in groundwater, in particular of micropollutants (pesticides, pharmaceuticals), chlorinated solvents and hydraulic fracturing chemicals. His group advances compound-specific isotope analysis to link changes in naturally occurring isotope ratios to environmental transformation reactions. He is author of >60 peer-reviewed publications and four invited book chapters. Amongst his awards are a Helmholtz Young Investigator Group, an ERC Consolidator Grant and the Water Chemistry Price of the Water Chemistry Society (division in the German Chemical Society, GDCh). Within the German Water Chemistry Society he leads the expert group “Hydraulic Fracturing Chemicals in Unconventional Gas Exploitation”.