Transformations of dissolved organic matter in a landfill leachate—A size exclusion chromatography/mass spectrometric approach

The aim of the present study was to search for qualitative changes in the landfill leachate DOM along a groundwater gradient. The study was focused on DOM characteristics of importance for its interaction with pollutants, such as molecular weight distribution and aromaticity. It was concluded that the leachate DOM underwent substantial qualitative changes along the investigated gradient at the Vejen landfill, Denmark. The molecular weight decreased, the polydispersity increased, and the aromaticity varied with the lowest values found in the middle of the gradient. The high aromaticity in the end of the gradient may explain the higher DOM binding capacity towards hydrophobic compounds seen earlier in these samples. The relative abundance of ions with mass to charge ratio (m/z) of 600–1200 seemed to be very stable along the gradient, indicating that the observed qualitative changes of the DOM is mostly attributed to changes in the m/z 100–600 range. The DOM seemed to become more similar to fulvic acids present in uncontaminated groundwater with respect to molecular weight and polydispersity along the gradient.