硝酸根对水体中甲基汞光化学降解的影响

为研究硝酸根(NO3-)对水体中甲基汞(MMHg)光化学降解的影响,采用室内模拟试验,验证了不同波长光照条件下,NO3-在MMHg光化学反应中的作用,探讨了NO3-浓度对MMHg光解速率及产物的影响,并根据溶液中Hg2+的浓度分析了MMHg光解反应的进行程度.结果表明,在自然光(NL)和紫外光(UV)条件下,只加入了NO3-的处理MMHg光降解速率分别为0.10、0.046 L.(ng·h)-1,Hg0的释放通量分别为1.05、1.27 ng,Hg2+的最终浓度分别为16.97、28.92 ng·L-1;在未加入NO3-和加入了C6H5COOH的条件下,MMHg的剩余浓度相差不大,其光降解速率也分别在0.052、0.015 L.(ng·h)-1左右,Hg0的释放通量分别为23.81、15.38 ng,Hg2+的浓度均小于10 ng·L-1,且呈现先增加后减小趋势.在可见光(VL)照射下,各处理下MMHg的光降解速率无显著性差异(P=0.56),为0.003 L.(ng·h)-1左右,Hg0的释放通量均为5 ng左右,Hg2+的浓度未超过3 ng·L-1,也呈现出先增加后减小的趋势.在NL条件下,随浓度NO3-的增加,MMHg的光降解速率也增加,且各处理间存在显著性差异(P<0.05),Hg0的生成量随NO3-浓度的增加而减少,而Hg2+的浓度也随NO3-浓度的增加而增加.可见在有紫外光的条件下,NO3-对MMHg光降解反应历程、反应速率以及产物有重要影响.

Effects of Nitrate Ion on Monomethylmercury Photodegradation in Water Body

To study effects of nitrate (NO₃^-) on monomethylmercury (MMHg) photodecomposition (PD), laboratory experiments were conducted to investigate the role of NO₃^- in MMHg PD under various light radiations, and to examine effects of NO₃^- concentration gradients on MMHg PD rates and end products. We analysed the react processes according to Hg²⁺ concentration. The results indicated that in the reactor exposed to natural and ultraviolet radiation, and treated with NO₃^-, the rates of MMHg PD were calculated to be 0.10 L·(ng·h)^-1 and 0.046 L·(ng·h)^-1, respectively, Hg⁰ fluxes were 1.05 and 1.27 ng, respectively, and Hg²⁺concentrations were 16.97 ng·L^-1 and 28.92 ng·L^-1 respectively. In the experiments which were not spiked with nitrate or spiked with benzoic acid, MMHg PD rates were calculated to be 0.052 L·(ng·h)^-1 and 0.015 L·(ng·h)^-1, respectively, Hg⁰ fluxes were 23.81 ng and 15.38 ng, respectively, and all concentrations of Hg²⁺ (<10 ng·L^-1) represented a trend of increasing firstly and then decreasing. There were no differences among the reactions exposed to visible light (P=0.56), the PD rate was about 0.003 L·(ng·h)^-1, Hg⁰ flux was about 5 ng, and Hg²⁺ concentrations showed a trend of increasing firstly and then decreasing. In the reactor exposed to natural light, with the increasing concentration of NO₃^-, MMHg PD rate increased, Hg⁰ flux decreased, and Hg²⁺ concentration increased with respect to time. All results indicate that NO₃^- has a significant effect on the react process, PD rate, and end products.