Oxidation products of α- and β-amyrins: potential tracers of abiotic degradation of vascular-plant organic matter in aquatic environments

Abstract

Environmental contextHow can we know what happens to organic matter in aquatic environments? Although several compounds exist that can be used to trace the origin and state of organic matter, not many are sufficiently stable and specific to trace degradation processes, but α- and β-amyrins can fulfil that role. Such knowledge will help us better understand and better quantify carbon fluxes in riverine and marine environments. AbstractIn order to fulfil the current need for stable and specific tracers to monitor vascular-plant organic matter degradation in aquatic environments, α-amyrin (urs-12-en-3β-ol) and β-amyrin (olean-12-en-3β-ol) were oxidised in vitro and their abiotic degradation products quantified in environmental samples from the Rhône River in France. Although they appear inert to photooxidation, they are clearly affected by autoxidation and the tracer potential of the resulting products was confirmed. Autoxidation of α- and β-amyrins produces urs or olean-12-en-3-one, 3β-hydroxy-urs or olean-12-en-11-one, urs or olean-12-en-3β,11α-diol and urs or olean-12-en-3,11-dione. 3β-Hydroxy-urs-12-en-11-one and 3β-hydroxy-olean-12-en-11-one, the main oxidation products detected, were selected as autoxidation tracers. These compounds, specific to autoxidation, were detected in dry leaves of Smilax aspera and in suspended particulate matter samples collected in the Rhône River and evidenced the importance of autoxidation in the degradation of organic matter of terrestrial origin.