Kinetic Controls on the Complexation between Mercury and Dissolved Organic Matter in a Contaminated Environment

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 have often been overlooked. We examined the rates of Hg-NOM complexation both in a contaminated Upper East Fork Poplar Creek (UEFPC) in Oak Ridge, Tennessee, and in controlled laboratory experiments using reducible Hg (Hg(R)) measurements and C(18) solid phase extraction techniques. Of the filterable Hg at the headwaters of UEFPC, >90% was present as Hg(R) and this fraction decreased downstream but remained >29% of the filterable Hg at all sites. The presence of higher Hg(R) concentrations than would be predicted under equilibrium conditions in UEFPC and in experiments with a NOM isolate suggests that kinetic reactions are controlling the complexation between Hg and NOM. The slow formation of Hg-NOM complexes is attributed to competitive ligand exchange among various moieties and functional groups in NOM with a range of binding strengths and configurations. This study demonstrates the need to consider the effects of Hg-NOM complexation kinetics on processes such as Hg methylation and solid phase partitioning.

A preliminary characterization of mercury uptake by the sulfate-reducing bacteria Desulfovibrio desulfuricans

“…The complexation chemistry between mercury and organic substances, including natural organic matter (NOM), dissolved organic matter (DOM), and dissolved organic carbon (DOC), have been studied by different researchers (Barkay et al, 1997;Benoit et al, 1999;Benoit et al, 2001;Kelly et al, 2003;Miller et al, 2007;Miller et al, 2009;Zhong and Wang, 2009;Dong et al, 2010). The kinetics of NOM complexation with mercury was studied by Miller et al (2009).…”

“…The kinetics of NOM complexation with mercury was studied by Miller et al (2009). In their research, Miller et al (2009) concluded that the kinetics of mercury complexation with NOM needs to be evaluated the dominant complexes of Hg in aquatic systems receiving input of inorganic Hg.…”

“…The kinetics of NOM complexation with mercury was studied by Miller et al (2009). In their research, Miller et al (2009) concluded that the kinetics of mercury complexation with NOM needs to be evaluated the dominant complexes of Hg in aquatic systems receiving input of inorganic Hg. Moreover, Miller et al (2009) stated that equilibrium conditions cannot be assumed in such systems due to the heterogeneity of NOM and the competitive interactions among various functional moieties of NOM for binding with Hg.…”

“…In addition, Miller et al (2009) discuss that when sulfide is not present in freshwater systems, complexes between Hg and NOM are the dominant form of mercury because of reduced sulfur functional groups on NOM that provide strong binding sites for Hg.…”

Integration of a Sedimentation Module to a Hydrologic Model and its Application to a Mercury TMDL Analysis

“…Generally in stratified systems, concentrations of total mercury and methyl mercury are higher near the sediments [12]. The kinetics of mercury with dissolved organic matter in aquatic ecosystems requires additional evaluation as the dominant complexes are difficult to determine [13]. Table 1.…”