Mining for history in a Chinese lake
COURTESY OF XIANGDONG LI AND SHIHUA QI
Li and colleagues seem to be emphasizing atmospheric deposition without taking into account landby storms or by animals that live at Research published in ES&T (pp use changes associated with agrithe sediment–water interface. Such 4732–4738) documents thousands culture. Those sedimentary signals mixing means that a lake sediment of years of mining history in Chicould be responsible for some of core rarely contains detail going na’s central region. The geochemithe lead peaks, in addition to atback 5000 years. cal signatures illustrate peaks in mospheric deposition of humanTo solve that problem, the reenvironmental pollution that corworked lead, he suggests. searchers used 14C to date the layrespond to the Bronze Age and A new generation of instruChina’s later military and indusments could further solidify the ers. They then searched for lead trial periods. dating and isotope correlations, in the sediments by using ICPMS Xiangdong Li of Hong Kong Graney and others advise. Some (inductively coupled plasma mass Polytechnic University instruments are so senand colleagues used sitive now that a reestablished lead-isosearcher can collect tope-ratio methods to a sample almost by identify human-made “scratching with a finlead versus naturally gernail,” says Stanley deposited lead. They Church of the U.S. Geofound the anthropogenlogical Survey. This anaic signature in a sedilytical capability could ment core from a lake allow museum curators in a part of China that and geochemists to finhas been only lightly gerprint artifacts. They impacted by modern eventually could trace industrial operations. the objects’ geologic and The low background geographic provenance signal from atmowhile establishing minspheric deposition aling—and environmental lowed the researchers pollution—history, he Study coauthor Shihua Qi (left) and a student of the China University of Geosciences collected a 330 centimeter sediment core to tease out the anthrosays. from a lake in central China in 2002. pogenic signature left Mining records based by earlier mining and on lead are more commetalworking. mon in Europe and the U.S., says spectrometry). The researchers Li and his team used a techGraney, who has used the techalso assessed other trace elements, nique that measures the lead nique on Great Lakes sediments including copper, nickel, and zinc. isotope ratios 206Pb/207Pb and for a history of the past two cenPutting dates to concentrations, 208Pb/207Pb, which are lower for anturies. Church surmises that the they found that before 3000 B.C., new work, which he calls “a nice lead hovered at low levels—which thropogenic lead than for natural summary of the correlation of geoprobably represent natural backdeposits. Greek and Spanish lead chemical change and the impact ground levels for the region. mines from 3000 B.C. have been of man on the environment,” could During the Bronze Age, the fingerprinted using these lead isobe quite popular with archaeolosediment core’s lead levels peaked, tope ratios (Environ. Sci. Technol. gists working in China. “It does and many of the other measured 1997, 31, 3413–3416). Past research demonstrate nicely the capabilities elements increased gradually. Afalso used lead isotope signatures of the method,” he comments. ter rapid increases 2000 years ago, to reveal European mining and “What I find fascinating,” says concentrations of copper, nickel, metallurgy history in peat and Li, “is the similar signal on the lead, and zinc leveled out. Still, lake deposits in Switzerland and European side. . . . How did these the scientists observed subsequent Sweden, respectively, back to the people communicate the technolpeaks that matched China’s WarBronze Age and to trace lead levels ogy? Maybe we can use lead isoring States Period (475–221 B.C.) as far back as 12,000 years ago. topes [to look at] mixing ores in the and the early Han Dynasty (206 In China, Li and his colleagues smelting process or [at] other globB.C.–A.D. 220) as well as the onset took a 330-centimeter-long core al signatures at other locations” of modern industry in the 1800s from the center of Liangzhi Lake to see whether ancient metallurgy and 1900s. in central China’s Hubei Province. traveled from Rome to the East, or “It’s an eloquent story,” says Joe Although sediments sometimes revice versa. Graney, a geochemist at Binghamflect yearly and seasonal cycles of —NAOMI LUBICK ton University. But he says that deposition, they also get disturbed July 1, 2008 / Environmental Science & Technology ■ 4623
