Environmental Sciences Division, Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, Tennessee 37831, USA.
Environ Sci Technol. 2009 Nov 15;43(22):8548-53. doi: 10.1021/es901891t.
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.
在平衡条件下，汞 (Hg) 与溶解的天然有机质 (NOM) 的相互作用是许多研究的重点，但水生态系统中汞-NOM 络合物的动力学控制往往被忽视。我们通过使用可还原汞 (Hg(R)) 测量和 C(18) 固相萃取技术，在田纳西州橡树岭的受污染的上东福克溪 (UEFPC) 以及在受控实验室实验中，研究了 Hg-NOM 络合的速率。在 UEFPC 的源头可过滤汞中，超过 90% 以 Hg(R) 的形式存在，该部分在下游减少，但在所有地点仍占可过滤汞的>29%。在 UEFPC 中和与 NOM 分离物的实验中，Hg(R) 浓度高于平衡条件下的预测值，这表明动力学反应控制着 Hg 与 NOM 之间的络合。Hg-NOM 络合物的形成缓慢归因于 NOM 中各种基团和官能团之间的竞争配体交换，这些基团和官能团具有不同的结合强度和构型。这项研究表明，需要考虑 Hg-NOM 络合动力学对汞甲基化和固相反萃等过程的影响。
