IMPROVED LEAD-ISOTOPE RATIO MEASUREMENTS IN ENVIRONMENTAL AND BIOLOGICAL SAMPLES WITH A DOUBLE FOCUSING MAGNETIC-SECTOR INDUCTIVELY-COUPLEDPLASMA-MASS SPECTROMETER (ICP-MS)

A method to measure lead (Pb) isotope ratios in biological and environ mental samples using a single collector double focussing magnetic sect or inductively coupled plasma mass spectrometer (ICP-MS) is presented. This. method is intercalibrated with multicollector thermal ionizatio n mass spectrometry (TIMS) to assess the suitability of the ICP-MS met hod for accurately and precisely identifying sources of environmental Pb exposure to humans. Results indicate that the external measurement precision (reproducibility) of this method, as evaluated by repeated a nalyses of the Pb isotope standard NBS 981 over the course of a year, was <0.1% (1 sigma) for Pb-206:Pb-204, Pb-207:Pb-206 and Pb-208:Pb-206 ratios. Accuracy of isotope ratio measurements by ICP-MS was evaluate d by comparing analyses of whole blood (biological) and household dust (environmental) samples with the definitive TIMS analyses of the same samples. For whole blood and dust samples, the Pb-206:Pb-204; Pb-207: Pb-206 and Pb-208:Pb-206 ratios measured by ICP-MS and TIMS generally agreed to within twice the propagated standard deviation (2 sigma, sig ma =root sigma(TIMS)(2) + sigma(ICP-MS)(2)) of both methods. However. a small but systematic difference between the Pb isotope ratios of blo od measured with the two methods was apparent. The source of this diff erence remains under investigation. These data demonstrate that this I CP-MS method provides improved accuracy and precision of lead isotope ratio measurements compared to previous ICP MS methods, and is suitabl e for use in studies to evaluate sources of environmental Pb exposure to children. Further, the increased sample throughput and reduced cost of analyses using this method are substantial advantages over the mor e time-consuming and expensive TIMS method. Consequently, this Pb isot ope methodology should prove useful as a routine tool in the investiga tion and mitigation of Pb exposure associated hazards.