Landfill leachate can contain extreme concentrations of metals, ammonia, chloride, and dissolved organic carbon and has significant groundwater pollution risks. However, little is known about landfill leachate dissolved organic matter (LLOM) composition to inform risk assessments and engineered treatment options. Using ultrahigh resolution mass spectrometry (FT-ICR-MS), we molecularly characterized LLOM from two municipal solid waste landfills: a bioreactor landfill that is actively accepting waste and a closed landfill. We also quantified metals, inorganic nitrogen species, chloride, DOC, and 11 organic contaminants of emerging concern (CECs). Measured CECs included the artificial sweeteners sucralose and acesulfame, which can be used as markers of leachate age. In comparison to Suwannee River natural organic matter (SRNOM), LLOM was found to have high presence of nitrogen, sulfur, and chlorine containing molecular formulas. A high abundance of nitrogen and sulfur (CHONS) compounds appears characteristic of LLOM, as approximately 600 and 1100 CHONS formulas (8 and 12% of assignments) were assigned in LLOM, versus 14 (0.3% of assignments) in SRNOM. LLOM was also found to contain a significant organochlorine component. Approximately 700 and 800 CHOCl type formulas were found in LLOM (9% of assignments in both) versus approximately 100 in SRNOM (3% of assignments). About 100 assigned formulas in LLOM had 2-6 chlorine atoms, including what appears to be the hexachlorinated flame retardant, chlorendic acid, and possibly related compounds. We also discuss other characteristics of LLOM such as specific assignments with extremely high relative signal intensity, presence of perfluorinated compounds, and evidence for organic complexation of iron.

Characterization of landfill leachate organic matter using ultrahigh resolution mass spectrometry

ACS Fall 2021

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