贵阳市水库中硫酸盐还原菌及铁还原菌对甲基汞分布的影响

微生物在汞的甲基化过程中起着关键作用,但关于野外微生物活动对甲基汞分布的影响研究较为缺乏.通过对贵阳市不同污染类型水库中硫酸盐还原菌(SRB)、铁还原菌(DIRB)、甲基汞(MeHg)及相应水质参数分布规律研究,探讨了水库中SRB和DIRB活动在汞甲基化及其分布中所起的作用.在水库上覆水体中,SRB与甲基汞呈显著正相关关系(r=0.398,p0.015,n=37),表明在上覆水体中,SRB为主要的汞甲基化细菌.在污染严重且差异明显的沉积物中,两种微生物对甲基汞分布的影响各不相同.在受矿山酸性废水污染的阿哈水库,由于其过高的SRB含量及其硫酸盐还原活动,导致夏季沉积物表层硫离子大量积累,严重抑制了汞的甲基化过程,使得沉积物孔隙水表层甲基汞明显低于其它两个水库,也低于阿哈水库上覆水体甲基汞含量.在红枫水库,沉积物表层适宜的SRB活动促进了汞的甲基化,硫酸盐还原物硫离子和孔隙水甲基汞存在显著相关性(r=0.674,p0.001,n=31);在百花水库,由于沉积物曾受到严重汞污染,甲基汞峰值主要受到沉积物总汞的影响,和两种微生物活动及其产物均未表现出显著相关性.

The impact of SRB and DIRB on methylmercury distributions in the reservoirs in Guiyang city

Microorganisms play an important role in methylation of mercury (Hg), but few studies on the relationship between methylmercury (MeHg) and microorganisms in the field are available in China. In the present study, the distributions of sulfate reducing bacterium (SRB) and iron reducing bacterium (IRB) and their impact on methylmercury (MeHg) distribution are discussed in three reservoirs with different pollution sources in Guiyang city. Results show that the SRB biomass was positively correlated with dissolved MeHg in the overlying water of three reservoirs (r=0.398, p<0.015, n=37). This indicates that SRB activities play an important role in the methylation process of Hg in water. However, different impacts of microorganisms on MeHg distributions were observed in the sediments of three reservoirs. In Aha Reservoir, the high amount of sulfate and SRB resulted in high sulfate activities and sulfide accumulations in sediment, which inhibites biological methylation of Hg, resulting in lower MeHg in sediment than those in other two reservoirs. In Hongfeng Reservoir, the sulfide was correlated to MeHg in pore water (r=0.674, p<0.001, n=31), suggesting that the SRB in an optimal range promoted the methylation of Hg. In Baihua Reservoir, there is no relationship between MeHg and microbial biomass or related reducing products, as high mercury resulted in relatively high MeHg in the bottom of sediment.