Measurements Of Lead Isotopic Ratios In Corals From The Eastern Hainan Island By Multiple Collectors Inductively Coupled Plasma Mass Spectrometry

The present thesis, is based on the development of methodology for lead isotopes by anion exchange resin separation for the determination of stable lead isotopic compositions in marine carbonates by multiple collectors inductively coupled plasma mass spectrometry (MC-ICP-MS, NEPTUNE). Using this method, we determined lead concentration and their isotopic ratios of Giant Clam (Tridacna gigas) from the South China Sea and corals(Porites lutea) from Tanmen Port in Qionghai city of Hainan province. The main purpose of this study is to elucidate the distribution of the lead isotopes in marine carbonates from the South China Sea, to identify the evolution of anthropogenic lead in eastern Hainan Island for the past100years that has been recorded in coral samples.Low resolution (R=300) of MC-ICP-MS was used in the study, which allowed a best ion transmission efficiency to the detectors. Dry plasma condition generated by a conventional nebulization sample introduction system with Apex-IR was chosen to increase the sensitivities and minimize the isobaric interferences. Major parameters affecting the accurate and precise measurement of lead isotope ratios by MC-ICP-MS were studied. The analytical precisions of lead isotope ratios for NIST SRM981of thirty repeat measurements during10hours at lead concentration of4ng/mL were about0.005%for208Pb/206Pb,0.004%for207Pb/206Pb and0.055%for208Pb/204Pb, respectively. The long-term reproducibilities (2SD) of208Pb/206Pb,207Pb/206Pb were0.000060and0.000050, respectively;208Pb/204Pb,206Pb/204Pb were0.0067and0.0029, respectively.The proposed method was applied to the analysis of marine carbonates including porites lutea and Tridacna gigas, the procedural blank was8-10pg and the errors of repeated samples are better than0.1%. The analytical result shows that the lead isotopic ratios of marine carbonates were related to Chinese aerosols, Chinese loess and so on. The method established could be applied in the determination of lead isotopic ratios in marine carbonates.The lead concentration of Tanmen city corals (TM) from the eastern of Hainan Island changed from0.0280μg/g to0.169μg/g during the past84years, which were lower than the results of Hainan coral reported by Inoue et al.(2008). The range of208pb/206pb is2.0809-2.1080and the range of206Pb/204Pb is18.2261-18.7140, which is close to the isotopic ratios of surface seawaters of the Western Pacific (208Pb/206Pb=2.093-2.118;206Pb/204Pb=17.97-18.23, Gallon et al.,2011).206Pb/207Pb of TM coral changed from1.1646to1.1928:it kept fluctuating around a stable value before1980s; between1980s and2000, it decreased rapidly and reached the minimum in2000; and then it slightly increased after2000. The trend of206Pb/207Pb is consistent with lead emissions from human activities during industrial development in China. Besides, the analytical results show that the lead isotopic ratios of TM coral are related to Chinese aerosols, Chinese loess, basalts from the South China Sea and so on.