Abstract
The interaction of mercury (Hg) with dissolved natural organic matter (NOM) under equilibrium conditions is the focus of many studies but the kinetic controls on Hg-NOM complexation in aquatic systems has often been overlooked. We examined the rate of Hg-NOM complexation using reactive Hg (HgR) measurements and C18 solid phase extraction in Upper East Fork Poplar Creek (UEFPC) in Oak Ridge, Tennessee, and in controlled laboratory experiments using a reference NOM isolate. Greater than 90% of the dissolved Hg at the headwaters of UEFPC was present as HgR and this fraction decreased downstream but remained >25% of the dissolved Hg at all sites. Equilibrium calculations indicate that Hg-NOM complexes should dominate throughout UEFPC, but the presence of HgR suggests that equilibrium conditions are not established. Rate constants for Hg-NOM complexation varied between 0.05 and 0.29 hr-1 in laboratory experiments. This study demonstrates the need to consider Hg-NOM complexation kinetics on processes such as Hg methylation and solid phase partitioning.
