Compound Specific Isotopic Analysis (CSIA) of landfill leachate DOC components

Leachate samples were collected from the Trail Road Landfill (TRL) site located about 25 km to the west of the city of Ottawa, Canada. Measurements of Eh, pH, electrical conductivity, dissolved oxygen, total dissolved solids, and temperature were completed at the field site. High performance liquid chromatography (HPLC) was used to separate DOC components into fractions for separate analysis on TCA. The TCA is operated in-line with a Thermo-Finnigan DeltaPlus continuous-flow isotope ratio mass spectrometer (CF-IRMS) that oxidises organic carbon to CO2 for measurement of both concentration, by infrared absorption, and δ13C. DOC fraction collection was based on the detection of discrete peaks of individual compounds, allowing identification of key peaks, such as acetate, with recoveries of up to 100%. The difference in δ13C values for leachate acetate (−10.7‰ to −16.9‰ VPDB) and the bulk DOC (−24.7‰ VPDB) can be used to distinguish landfill leachate derived DOC and identify biogeochemical reactions. The enrichment of δ13C in the acetate suggests that this biologically derived compound has become a substrate for secondary biogeochemical reaction, likely methanogenesis.