基于高山湖泊沉积记录的贵州北部大气重金属污染历史重建

大气重金属污染是全球面临的主要环境问题之一,受监测资料的局限,目前我国在大气重金属污染的历史过程及其对偏远地区地表环境的影响方面的研究还较为薄弱.通过对贵州北部梵净山顶沉积物中金属元素含量和Pb同位素的分析,研究了近400年来Cd、Cr、Cu、Hg、Ni、Pb和Zn等大气污染的历史过程.公元约1800年之前,沉积物中金属元素含量较为稳定; 1800年以来,Cr、Cu、Ni和Zn等含量总体呈先增加后降低的趋势;而Cd、Hg和Pb含量逐渐增加.富集系数与207Pb/206Pb结果表明,Cd、Pb和Hg是典型的大气污染元素; Hg污染开始于公元1880年前后,Cd和Pb污染开始于20世纪50年代,近年来污染程度均逐渐加重.沉积记录反映的贵州北部梵净山地区目前大气Hg污染水平与我国东部其他远离人类活动直接影响的地区相当,但远高于欧美及青藏高原等地区;不同地区间Cd与Pb污染水平具有较大的差异.梵净山地区大气Hg污染可能受到全球和区域污染排放的共同影响,Cd和Pb污染主要来自于区域有色金属冶炼及燃煤等释放.

Historical Trends of Atmospheric Trace Metal Pollution in Northern Guizhou Province as Reconstructed from Alpine Lake Sediments

Atmospheric trace metal pollution is a striking environmental problem globally. Because of the limitations in monitoring data, our knowledge of the historical processes and sources of atmospheric trace metal pollution in China and its influence on remote terrestrial environmental quality is limited. The historical variations in atmospheric trace metal (Cd, Cr, Cu, Hg, Ni, Pb, and Zn) pollution during the past 400 years in the Fanjing Mountain area, northern Guizhou Province were studied by analyzing the metal concentrations and Pb isotopes in lake sediments. The results showed that concentrations of all metals in the sediments were relatively constant before 1800(A.D.). After 1800, concentrations of Cr, Cu, Ni, and Zn increased at first and then decreased, while concentrations of Hg, Cd, and Pb generally increased gradually over the most recent century and subsequent decades. The enrichment factor and ²⁰⁷Pb/²⁰⁶Pb analysis results indicated that Cd, Pb, and Hg were typical pollutants. Pollution of Hg began at around 1880(A.D.), and pollution of Cd and Pb has occurred since the 1950s; all pollutants exhibited aggravated trends in recent times. Pollution levels of Hg in recent years in the Fanjing Mountain area were comparable to those in other remote areas of East China, but levels were lower than those in Europe, America, and the Tibetan Plateau. In contrast, pollution levels of Cd and Pb in these areas showed large variability. By comparing the historical processes of trace metal pollution in different regions and exploring the potential pollution sources of metals in the study region, it can be deduced that atmospheric Hg pollution in the Fanjing Mountain area was the result of both global and regional emissions, while Cd and Pb pollution largely came from regional sources such as non-ferrous metals smelting and coal combustion emissions.