摘要:

IntroductionThe aim of this study was to determine the stable lead isotopic signature (206Pb/207Pb) of rainwater in Scotland in the late 1990s and to compare the findings with corresponding data for rainwater and atmospheric particulates collected since the 1980s and for different sources of environmental lead, with a view to evaluating the impact of measures to reduce emissions of lead to the atmosphere, such as the introduction and increasing use of unleaded petrol.There are four stable isotopes of primordial lead, namely204Pb,206Pb,207Pb and208Pb. The last three isotopes, however, are also radiogenic, formed by radioactive decay in the238U (half-life 4.5 × 109 years),235U (half-life 0.7 × 109 years) and232Th (half-life 14.1 × 109 years) decay series, respectively. The abundance of lead isotopes in minerals and ores is determined by the original uranium to thorium ratio, time of formation and lead concentration of the material. While the average present-day crustal abundances of these isotopes yield a mean206Pb/207Pb ratio of 1.20 ± 0.015, there is a much wider range found for lead ore deposits around the world,e.g.1.04 for Broken Hill, Australia, 1.17 for Leadhills, Scotland, and 1.39 for Mississippi Valley, MO, USA.1,2The lead ore deposits from Australia have been used, along with Canadian lead (206Pb/207Pb = 1.16), by Associated Octel to produce alkyllead anti-knock additives (206Pb/207Pb ∼ 1.07) for petrol consumed in the UK.3The significant difference between the206Pb/207Pb ratio of the lead emitted by car exhausts and those of other sources of anthropogenic lead,e.g.coal burning (206Pb/207Pb ∼ 1.18), has afforded an opportunity, at least in principle, for the quantitative assessment of the relative contributions from specific sources to the environmental lead burden.4–6Thus,206Pb/207Pb ratio variations have been recorded and used in numerous parts of the world, where different characteristic isotopic signatures may prevail, in such studies on a wide range of materials, including atmospheric aerosols,4,7–14lake sediments,15–17peat bogs,17–20soils,21–23grass,24tree rings,25,26moss27,28and ice cores.29,30They have also been used to trace air mass movement31–33and oceanic transport phenomena34as well as the environmental fate and behaviour of anthropogenic lead.35–38In the UK, measures introduced in 1986 to reduce the maximum permitted concentration of lead in petrol from 0.40 to 0.15 g l−1and to promote the use of unleaded petrol have resulted in a reduction of emissions of lead from petrol-engined vehicles to the atmosphere from an estimated 6.5 × 103tonnes in 1985 to 0.8 × 103tonnes in 1997.39Resultant changes in source apportionment of atmospheric lead with time and the use of the206Pb/207Pb ratio as a tracer are dependent upon the monitoring of stable lead isotopic ratios in the atmosphere and in contributory sources such as leaded petrol. This paper presents isotopic data for rainwater in Scotland in 1997–1998, directly determined by the technique of inductively coupled plasma-mass spectrometry (ICP-MS),40and interprets them in the context of additional long-term data for leaded petrol from 1989–1998 and for rainwater, atmospheric particulates and pine needles collected at various locations in Scotland and elsewhere during the period 1982–1992.

ISSN:0960-7919    

出版商:RSC    

年代:1999

数据来源: RSC