| Abstract
| - We studied the effect of increasing hydrogen ion (H+)concentration on the uptake of mercury (Hg(II)) by an aquaticbacterium. Even small changes in pH (7.3−6.3) resultedin large increases in Hg(II) uptake, in defined media. Theincreased rate of bioaccumulation was directly proportionalto the concentration of H+ and could not be explainedby assuming that the source of Hg to the bacteria wasdiffusion of neutrally charged species such as HgCl2. Thus,pH appeared to affect a facilitated mechanism by whichHg(II) is taken up by the cells. Lowering the pH of Hg solutionsmixed together with natural dissolved organic carbon, orwith whole lake water, also increased bacterial uptake ofHg(II). These findings have several potential implicationsfor mercury cycling, including effects on elemental mercuryproduction, mercury sedimentation, and microbialmethylation of Hg(II), and could be part of the explanationfor the observed positive correlation between lakeacidity and methyl mercury levels in fish.
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