Lead Isotope Ratios of an Acid-soluble Element in Boring Cores from the Osaka City Area

This study examined isotope ratios of acid-soluble lead in boring cores taken from sediments in the Osaka City area. The sediments are more than 2,500 years old and contain only naturally occurring lead. The isotope ratios of the acid-soluble lead were similar to those obtained with a whole rock analysis, which indicated that the method of measuring acid-soluble lead instead of whole rock was simple and accurate enough to analyze isotope ratios of lead in sediments. The isotope ratios of lead from the boring cores had similar values and were independent of deposition age and environment during deposition. The average of the isotope ratios of lead from one boring core differed slightly from the average of those from another boring core. Isotope ratios of 207Pb/206Pb from the boring cores were between 0.83 and 0.85, and the isotope ratios of 208Pb/206Pb were between 2.06 and 2.13, which were the same as the isotope ratios of lead from ores and soils measured so far in Japan. The range was narrow compared to the range of isotope ratios of lead from various ores obtained around the world; 207Pb/206Pb from ores obtained around the world are between 0.7 and 1.1 and 208Pb/206Pb are between 1.8 and 2.5. Because Japan imports most of its lead, isotope ratios of anthropogenic lead in soils can differ from isotope ratios of lead occurring naturally in soils in Japan. Therefore, the isotope ratios of lead can be used to determine whether lead is anthropogenic or natural.