Evaluation by LA-MC-ICP-MS of NIST 612 Pb isotopic composition as external reference material and a new proxy for environmental characterization using (carbonatic) bivalves shells

Abstract

The main aims of this work are: to evaluate by laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) the Pb isotopic composition of the reference material NIST 612 (a calcium-sodium aluminosilicate glass); to verify the potentialities of using the NIST SRM 612 as calibration standard for environmental studies on (carbonatic) bivalves and; to apply this standard in for quantifying the ontogenic (temporal) variations of Pb isotopes in two species of bivalve shells, Glycymeris undata Linnaeus 1758 and Pitar fulminatus (Menke, 1828) from Ilha Grande Bay (Rio de Janeiro, SE Brazil), in order to identify the Pb isotopic signatures and; propose a new tool to be applied in biological and environmental characterization studies.In these analyses a Neptune sector multicoletors mass spectrometer and 193 nm Excimer Laser Ablation device also were used. The averages for isotope ratios,206Pb/204Pb = 16.9027 ± 0.0011, 207Pb/204Pb = 15.4446 ± 0014, 208Pb/204Pb = 36.5544 ± 0.0044, 208Pb/207Pb = 0.91374 ± 0.00002 and 207Pb/206Pb = 0.9134 ± 0.0001, the calculated mass fractionation averages, of 0.07%, and the quantification procedures based on the external calibration, are in agreement with the true values obtained in the literature.The results of this work, obtained with the LA-MC-ICP-MS system, strongly support the hypothesis that abundance of Pb isotopes in carbonates can be determined on the basis of external calibration using the NIST 612 standard, despite the large difference between the CaCO3 composition and the glass silicate that compose this reference material. This fact suggests that NIST glass standards can be applied to several types of materials, whose geochemical composition of the matrix is not necessarily equivalent to that of the standards, by means of a careful setup of the LA-ICP-MS system. The obtained results confirm the hypothesis that it is possible to perform isotope analyzes of lead in bivalve shells using the LA-ICP-MS technique. The Pb isotope results obtained in layers of bivalve P. fulminatus allowed to identify the biological and environmental factors that influence the Pb isotopic ratios in the shell.