State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China; School of Chemistry and Material, Guizhou Normal University, Guiyang, China.
School of Chemistry and Material, Guizhou Normal University, Guiyang, China.
J Environ Sci (China). 2019 Nov;85:9-16. doi: 10.1016/j.jes.2019.02.012. Epub 2019 Feb 26.
Photoreduction characteristics of divalent inorganic mercury (Hg) in the presence of specific algae species are still not well known. Laboratory experiments were conducted in the present study to identify the effects of different concentrations of living/dead algae species, including Aphanizomenon flosaquae (AF) and Microcystis aeruginosa (MA), on the photoreduction rate of Hg under various light conditions. The experimental results showed that percentage reduction of Hg was significantly influenced by radiation wavelengths, and dramatically decreased with the presence of algae. The highest percentage reduction of Hg was induced by UV-A, followed by UV-B, visible light and dark for both living and dead AF, and the order was dark > UV-A > UV-B > visible light for both living and dead MA. There were two aspects, i.e., energy and attenuation rate of light radiation and excrementitious generated from algae metabolisms, were involved in the processes of Hg photoreduction with the presence of algae under different light conditions. The percentage reduction of Hg decreased from 15% to 11% when living and dead AF concentrations increased by 10 times (from 10 to 10 cells/mL), and decreased from11% to ~9% in the case of living and dead MA increased. Algae can adsorb Hg and decrease the concentration of free Hg, thus inhibiting Hg photoreduction, especially under the conditions with high concentrations of algae. No significant differences were found in percentage reduction of Hg between living and dead treatments of algae species. The results are of great importance for understanding the role of algae in Hg photoreduction.
二价无机汞（Hg）在特定藻类存在下的光还原特性仍不为人知。本研究进行了实验室实验，以确定不同浓度的活/死藻类物种，包括鱼腥藻（AF）和铜绿微囊藻（MA），对不同光照条件下 Hg 光还原速率的影响。实验结果表明，Hg 的还原百分比受辐射波长的显著影响，并随着藻类的存在而急剧下降。Hg 的还原百分比最高的是 UV-A，其次是 UV-B、可见光和暗，对活的和死的 AF 均如此，而对活的和死的 MA 则是暗>UV-A>UV-B>可见光。在不同光照条件下，藻类的存在会影响 Hg 的光还原过程，这涉及到两个方面，即藻类代谢产生的能量和光辐射衰减率以及排泄物。当活的和死的 AF 浓度增加 10 倍（从 10 增加到 10 cells/mL）时，Hg 的还原百分比从 15%降低到 11%，而当活的和死的 MA 增加时，Hg 的还原百分比从 11%降低到~9%。藻类可以吸附 Hg 并降低游离 Hg 的浓度，从而抑制 Hg 的光还原，尤其是在藻类浓度较高的情况下。Hg 的还原百分比在活的和死的藻类处理之间没有显著差异。这些结果对于理解藻类在 Hg 光还原中的作用具有重要意义。
