Evaluation of the effects of Hg/DOC ratios on the reduction of Hg(II) in lake water

Reduction of mercury (Hg) in natural waters, which releases a substantial amount of gaseous Hg(0) to the atmosphere, has a close relationship to Hg/DOC ratios. However, the role of Hg/DOC ratio on the Hg(II) reduction in natural waters remains poorly understood. In this study, natural water collected from Hongfeng Lake, SW China, was used to study the effects of Hg/DOC ratio on the Hg(II) reduction. The lake water was spiked with variable amounts of Hg to make different Hg/DOC solutions. Through a 72 h Hg(II) reduction process, we demonstrated that the maximum percentage reduction of Hg (29 ± 3%) occurred when Hg/DOC ratio was 1134 ng mg−1. Further increase or decrease of the Hg/DOC ratios would inhibit the reduction of Hg(II). This study clearly demonstrated that Hg/DOC ratio has a dual role in the reduction of Hg(II) from natural waters. [Display omitted] •Hg/DOC ratio has a dual role in the reduction of Hg(II) from natural waters.•Maximum percentage reduction of Hg (∼30%) occurred when Hg/DOC ratio was 1134 ng mg−1.•The reduction of Hg(II) may be inhibited by less amount of solar radiation on a single Hg atom. Hg/DOC ratio plays a dual role in the photoreduction of Hg(II) in lake water.