Assessing the complexation of dissolved organic matter with heavy metals (Cu, Pb) in leachate from an old Japanese landfill site using fluorescence quenching.

Dissolved organic matter (DOM) in landfill leachate impacts the toxicity, bioavailability, and migration of heavy metals. The present study investigated the complexation of heavy metals (Cu and Pb) with DOM from two landfill leachate samples, representing an old landfill site containing incineration residues and incombustible waste. The logarithms of the stability constant (log K) and percentage of complexed fluorophores were calculated using both the Ryan-Weber non-linear model and the modified Stern-Volmer model, yielding good agreement. The log K values (at pH = 6.0 ± 0.1) calculated using both methods for the two sampling points were 5.02-5.13 and 4.85-5.11 for Cu-DOM complexation, and 5.01-5.13 and 4.46-4.87 for Pb-DOM complexation, respectively. Log K was slightly higher for binding of DOM with Cu than Pb, and the quenching degree was stronger for complexation with Cu (28.5-30.6% and 38.0-45.9%) than Pb (6.5-7.1% and 10.0-15.4%) in both leachate samples. While log K values were similar, differences in the contributions of functional groups and molecular composition led to varying degrees of quenching. This study reveals the potential for heavy metal binding by DOM in landfill leachate with a unique solid waste composition and emphasizes variations in fluorescence quenching between Cu and Pb despite similar log K levels. These findings may be useful for assessing heavy metal behavior in landfill leachate and its impacts on the surrounding environment.