Pergamon PII: S0025-326X(98)00011-3 Matqm' l'olhaion Btdh'li~t, Vol. 3~. No. 7. pp. 527-534, 19Y8 © 1998 Elsevier Science Ltd. All rights reserved Printed in (}rcat grilain [1025-32(~X/98 $ 19.(10+0.(10 Lead Isotope Ratios Determined by ICP-MS: Investigation of Anthropogenic Lead in Seawater and Sediment fi:om the Gulf of Carpentaria, Australia NIELS C. MUNKSGAARD*, GRANT J. BATTERHAM and DAVID L. PARRY School of Mathematical and Physical Sciences, Northern Territory UniversiO; Darwin, N. T. 0909, Auso'alia Lead isotope ratios and concentrations have been measured in seawater and marine sediment by Induc- tively Coupled Plasma Mass Spectrometry (ICP-MS). For seawater, solvent extraction pre-concentration and the use of a micro-concentric nebulizer allowed 1 ml of concentrate to be measured for several minutes to achieve precisions in the range 0.5-1.2% relative standard deviation for 2°Spb/Z°6Pb and 2°Tpb/2°6Pb. The environmental dispersion of trace amounts of anthropogenic Pb produced distinctive Pb isotope ratio changes in seawater and marine sediments in the immediate vicinity of a Pb-Zn concentrate shipping facility. Concentrate was found to have 2°Spb/2°6pb ratios in the range 2.21-2.25, whereas environmental background 2°Spb/z°apb ratios were: filtered (<0.45 om) seawater, 2.13-2.15; unfiltered seawater, 2.06-2.10; sediment, 2.06-2.09. The combined Pb isotope ratio and concentration measurements by ICP-MS have provided a sensitive and cost effective monitoring tool allowing an una~abiguous assessment of the source of Pb. © 1998 Elsevier Science Ltd. All rights reserved Keywords: lead isotopes; ICP-MS; seawater; sediment; monitoring. The isotopic composition of Pb has been used as an indicator of anthropogenic input of Pb into the natural environment in numerous studies over the past decades. Three of the four stable Pb isotopes are radiogenic and have increased in abundance as a function of the decay rate of their parent isotopes since the formation of the Earth; 2°6pb, 2°7pb and 2°'~Pb are derived from 23sU, 235U and 2~2Th, respectively. The Pb isotope composition of a given sample depends on the age and U/Pb and Th/Pb ratios of the parent material(s) from which the Pb, such as a Pb-Zn ore "Corresponding author. body, was derived (K6ppel and GrOnenfelder, 1979). Variations in the ratios of Pb isotopes, e.g. 2°Tpb/2°('Pb and 2°SPb/Z°('Pb, are commonly used as tracers of environmental processes as they can be measured with great accuracy and precision by mass-spectrometric methods. Early studies of Pb isotope ratios in the marine environment (for example, Patterson et al., 1976; Stukas and Wong, 1981) demonstrated their use in characterizing the origin and movement of anthropo- genic as well as natural Pb. Many marine studies have focused on the very significant aeolian deposition in mid-oceanic seawater of Pb derived from mainly fuel emissions (e.g. Church et al., 1990; Flegal et al., 1989; Flegal et al., 1993; Schaule and Patterson, 1981; Vdron et al., 1993, 1994). Hamelin et al. (1990) and Lambert et al. (1991) showed that this anthropogenic Pb source could also be identified in oceanic pelagic sediments. Studies of coastal marine, estuarine and riverine waters have identified and quantified inputs of both natural and anthropogenic sources of Pb including run-off from mine railings (Elbaz-Poulichet el al., 1984; Monna et al., 1995; Ostlund et al., 1995; Stukas and Wong, 1981). In environmental samples, differences in 2°Tpb/2°apb and 2°Spb/2°('Pb ratios of only a few percent, sometimes considerably less, need to be resolved. Traditionally, highly precise and accurate isotope ratio measurements of Pb have been carried out by Thermal lonisation Mass Spectrometry (TIMS), at the expense of time consuming sample preparation and analysis. Recently, studies utilising Inductively Coupled Plasma Mass Spectrometry (in this paper ICP-MS will refer to instruments with a quadropole mass spectrometer) for Pb isotope ratio determinations in seawater and other environmental samples have been published (e.g. Halicz et al., 1994; Krause et al., 1993; Miyazaki and Reimer, 1993). These studies have demonstrated that although not at the level achievable by TIMS, suffi- 527