Abstract：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.
