水体中甲基汞光化学降解特征研究

为探究水体中甲基汞（MMHg）的光化学行为,采用室内模拟实验,以不同波长紫外灯及室内可见光为光源,探讨紫外光波长、光强度等因素对MMHg光降解的影响,并根据生成物Hg0的量变化分析MMHg光降解反应历程.研究表明,MMHg光降解最终产物中含有Hg0,且光照条件对MMHg光降解速率、Hg0的产量有影响.在反应器暴露于紫外光条件下时,MMHg光降解速率随紫外光波长的变短而增加,随紫外光强度的提高而增加,且MMHg光降解呈一级动力学反应,速率常数分别为KUVA 0.403～0.562 h-1、KUVB 0.961 h-1、KUVC 1.221 h-1和KVL＋UVA＋UVB 1.346 h-1;Hg0释放通量为0.166～0.392 ng·min-1.当反应器暴露于可见光条件下时,反应器内MMHg浓度下降速率较慢,KVL0.061 h-1;Hg0释放通量为0.008 ng·min-1.而在黑暗条件下没有发现反应器内MMHg浓度下降,无Hg0生成.可见紫外光是导致MMHg降解的主要原因,光波波长与强度对MMHg的环境地球化学行为有重要影响.

Characteristics of Monomethylmercury Photodegradation in Water Body

To investigate the photochemical process of monomethylmercury (MMHg) in the water environment, laboratory experiments were conducted using artificial and visible light sources to confirm the effects of wavelength and light intensity on MMHg photodegradation (PD), and the reaction process of MMHg PD was discussed based on Hg⁰ emission rate. The results indicated that Hg⁰ was the end product of MMHg PD, and the light conditions had an effect on the rate constant of MMHg PD and Hg⁰ flux. When the reactor was exposed to UV light conditions, the rate constant of MMHg PD increased with the decrease in wavelength and the increase in light intensity. The rate of MMHg PD was first-order with respect to MMHg concentration in the reactor, and the rate constants were KUVA 0.403-0.562 h^-1, K_UVB 0.961 h^-1, K_UVC 1.221 h^-1 and K_VL+UVA+UVB 1.346 h^-1, respectively and the emission rates of Hg⁰ were 0.166-0.392 ng·min^-1. When the reactor exposed to visible light conditions, the rate of MMHg PD was only 0.061 h^-1, and the emission rate of Hg⁰ was 0.008 ng·min^-1. In the experiments conducted under dark conditions, we did not observe MMHg PD and no Hg⁰ was found. All the results suggest that the degradation of MMHg in artificial waters is mediated by ultraviolet (UV) radiation, and UV radiation plays a key role in the photochemical process of MMHg in freshwater lakes.