紫外光对冬季近岸海水中溶解性气态汞产生的影响

现场采集青岛近岸海水样品,在紫外UVA、UVB辐照和黑暗对照条件下对不同过滤海水分别进行汞的还原实验,计算累积释放量,模拟计算还原反应速率.结果表明,紫外光照射下,海水溶解性气态汞(DGM)产量呈现先显著增加后逐渐降低的趋势,累积产量逐渐增加,最后趋于稳定,符合准一级反应动力学模型,紫外光照射下DGM累积产量远高于黑暗对照,紫外光促进汞的还原,特别是促进了海水中Hg2+的产生.紫外光下DGM的产生速率常数在0.057~0.214h-1之间,0.2μm过滤海水高于未过滤海水,颗粒物具有抑制效应;在氩气吹脱时,UVB照射下的反应速率大于UVA,空气吹脱条件下结论相反,氧气参与了汞的光氧化还原过程.

Effect of ultraviolet on the photoproduction of dissolved gaseous mercury in coastal seawater during winter.

The photochemical reduction is an important way to transform Hg2+ to Hg0 in seawater, influencing the release of mercury to the atmosphere, thus plays a crucial role in the regional biogeochemical cycle of mercury. Coastal water samples collected from Qingdao, north China, were treated with UVA and UVB, compared with the control of dark treatment without light. The experiments were carried out using waters samples with or without 0.2 μm pre-filtration to comparatively characterize the influences of suspended solids and microbes on photochemical reduction. Then the cumulative amount of dissolved gaseous mercury (DGM) was calculated and the redox reaction rate was obtained under different light conditions. With the irradiation of UV light, DGM increased significantly to a peak and then decreased; the cumulative DGM increased gradually and then leveled off, which conformed to the pseudo-first order kinetic equation. Cumulative DGM in UV condition was much higher than that in dark control. UV irradiation promoted photoreduction of mercury apparently, and was also helpful to the formation of Hg2+ in seawater. The reduction rate of Hg2+ was in the range of 0.057~0.214h-1 under UV light. The 0.2μm filtered samples had higher reduction rates than unfiltered samples, suggesting that the suspended particulate matter inhibited the production of DGM. When seawater was bubbled by Argon, the production rate of DGM with UVB irradiation was higher than that in UVA. However, the results were opposite when bubbled by air, which indicated that oxygen participated in the photoredox reaction.