K.J.R. Rosman

Isotopic compositions of the elements, 2001

The Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry completed its last review of the isotopic compositions of the elements as determined by isotope-ratio mass spectrometry in 2001. That review involved a critical evaluation of the published literature, element by element, and forms the basis of the table of the isotopic compositions of the elements (TICE) presented here. For each element, TICE includes evaluated data from the “best measurement” of the isotope abundances in a single sample, along with a set of representative isotope abundances and uncertainties that accommodate known variations in normal terrestrial materials. The representative isotope abundances and uncertainties generally are consistent with the standard atomic weight of the element Ar(E) and its uncertainty U[Ar(E)] recommended by CAWIA in 2001.

Isotopic source signatures for atmospheric lead: the Northern Hemisphere

Aerosols collected between 1994 and 1999 at more than 70 different sites affecting the Southern Hemisphere have been measured for their 206Pb/207Pb, 208Pb/207Pb and 206Pb/204Pb ratios and Pb concentrations. Lower ratios are found at the southern tips of Africa, Australia and South America probably due to the supply of alkyllead from a common supplier such as Associated Octel. The ratios increase in a northerly direction probably due to a changing market share in alkyllead or an increasing industrial Pb contribution. The geographical variations in isotopic signatures made it possible to broadly characterize the different regions that influence the Southern Hemisphere. Brazil and Argentina exhibited 206Pb/207Pb, 208Pb/207Pb and 206Pb/204Pb ratios in aerosols of 1.141–1.184, 2.416–2.442 and 17.77–18.57, respectively. Mexican aerosols had values of 1.188–1.197, 2.452–2.463 and 18.46–18.73. Aerosols sampled in Chile had low ratios in the South of 1.063–1.094, 2.337–2.373 and 16.46–17.13 which increased in a northerly direction. Emissions from South Africa were characterized by ratios 1.067–1.090, 2.340–2.358 and 16.53–16.99. In 1994–1995 Australia and New Zealand had ratios of 1.060–1.193, 2.324–2.445 and 16.08–18.54. In 1997 however, the range was narrower: 1.072–1.112, 2.342–2.398 and 16.55–17.36, respectively. These isotopic signatures are potentially useful for tracing sources of pollution and the movement of air-masses on a global scale.

Isotope-abundance variations of selected elements (IUPAC Technical Report)

Documented variations in the isotopic compositions of some chemical elements are responsible for expanded uncertainties in the standard atomic weights published by the Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry. This report summarizes reported variations in the isotopic compositions of 20 elements that are due to physical and chemical fractionation processes (not due to radioactive decay) and their effects on the standard atomic-weight uncertainties. For 11 of those elements (hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine, copper, and selenium), standard atomic-weight uncertainties have been assigned values that are substantially larger than analytical uncertainties because of common isotope-abundance variations in materials of natural terrestrial origin. For 2 elements (chromium and thallium), recently reported isotope-abundance variations potentially are large enough to result in future expansion of their atomic-weight uncertainties. For 7 elements (magnesium, calcium, iron, zinc, molybdenum, palladium, and tellurium), documented isotope variations in materials of natural ter- restrial origin are too small to have a significant effect on their standard atomic-weight uncertainties. This compilation indicates the extent to which the atomic weight of an element in a given material may differ from the standard atomic weight of the element. For most elements given above, data are graphically illustrated by a diagram in which the materials are specified in the ordinate and the compositional ranges are plotted along the abscissa in scales of (1) atomic weight, (2) mole fraction of a selected isotope, and (3) delta value of a selected isotope ratio.

Isotopic evidence for the source of lead in Greenland snows since the late 1960s

IN 1969, Murozumi et al.1 demonstrated that the concentration of lead in Greenland snow had increased by a factor of 200 since ancient times, and concluded that most of this increase was a result of the use of alkyl-leaded petrol. Partly because of these findings, the United States and other western countries limited the use of lead additives in petrol from about 1970. Recently, Boutron et al.2 showed that the lead concentration in Greenland snow had decreased by a factor of ∼7.5 over the past 20 years, and suggested that this was a result of the decline in use of leaded petrol. We present here measurements of the 206Pb/207Pb ratio of the lead contained in the samples studied by Boutron et al. Because aerosols from the atmosphere above the United States are more radiogenic than those from Eurasia, we can trace the relative contributions of these two sources in the Greenland lead over the period analysed by Boutron et al.We find that the United States was a significant source of lead in the 1970s, but it has since declined considerably in relative importance. This decline mirrors the decrease in use of leaded petrol in the United States, confirming the earlier hypothesis.

Isotopic evidence to account for changes in the concentration of lead in Greenland snow between 1960 and 1988

Abstract Preserved layers of snow deposited between 1960 and 1988, taken from 10.7 m and 70 m snow cores drilled at Summit in central Greenland in 1989, were analyzed for lead isotopes ( 206 Pb 207 Pb , 208 Pb 207 Pb , and 206 Pb 204 Pb) . The lead has an isotopic composition consistent with a mixture of USA and Eurasian origins. Although the 206 Pb 207 Pb ratio fluctuates, presumably due to seasonal changes in the weather patterns, there is a clear trend in values from about 1.16 in the early 1960s to 1.18 by 1976, then back to the initial value by the mid 1980s. The initial trend upwards reflects the progressive introduction of relatively radiogenic Mississippi Valley-type lead into USA gasoline during the 1960s, while the return to lower values indicates a decreased contribution from this source due to the switch to unleaded gasoline for motor vehicles. Eurasian lead, assumed to be the second component of the mixture, appears to have a relatively constant 206 Pb 207 Pb ratio over this period.

The lead pollution history of Law Dome, Antarctica, from isotopic measurements on ice cores: 1500 AD to 1989 AD

Abstract Lead isotopic compositions and Pb and Ba concentrations have been measured in ice cores from Law Dome, East Antarctica, covering the past 6500 years. ‘Natural’ background concentrations of Pb (∼0.4 pg/g) and Ba (∼1.3 pg/g) are observed until 1884 AD, after which increased Pb concentrations and lowered 206Pb/207Pb ratios indicate the influence of anthropogenic Pb. The isotopic composition of ‘natural’ Pb varies within the range 206Pb/207Pb=1.20–1.25 and 208Pb/207Pb=2.46–2.50, with an average rock and soil dust Pb contribution of 8–12%. A major pollution event is observed at Law Dome between 1884 and 1908 AD, elevating the Pb concentration four-fold and changing 206Pb/207Pb ratios in the ice to ∼1.12. Based on Pb isotopic systematics and Pb emission statistics, this is attributed to Pb mined at Broken Hill and smelted at Broken Hill and Port Pirie, Australia. Anthropogenic Pb inputs are at their greatest from ∼1900 to ∼1910 and from ∼1960 to ∼1980. During the 20th century, Ba concentrations are consistently higher than ‘natural’ levels and are attributed to increased dust production, suggesting the influence of climate change and/or changes in land coverage with vegetation.

The efficiency of intestinal calcium absorption is increased in late pregnancy but not in established lactation

SummaryThe fractional absorption of calcium (FA-Ca) was measured using a dual non-radioactive Ca isotope technique in 26 control women, 49 women in the last triimester (36 weeks) of pregnancy and 31 of these women in established (20 weeks) lactation. The ratio of the two non-radioactive Ca isotopes was measured, by high precision thermal ionisation mass spectrometry, in urine 12–24 hours after administration and was used to calculate Fa-Ca. This is the first study to clearly show that FA-Ca is significantly elevated in late pregnancy but not in established lactation, when compared with control women.

A two century record of lead isotopes in high altitude Alpine snow and ice

A 140 m snow/ice core drilled at Mont Blanc, France, has been analysed for Pb isotopes, Pb and Ba concentrations. The 206Pb/207Pb ratio, which was measured by thermal ionisation mass spectrometry, decreased steadily from ∼1.18 about two centuries ago to ∼1.17 in 1960, then fell rapidly to ∼1.15 by 1968. Evidence of the Italian (Turin) isotopic lead experiment (IILE) was found in samples dated ∼1977 where the ratio dipped to 1.117. By the early 1990s it had returned to mid 1960s values. Large seasonal variations were found in Pb and Ba concentrations. Summer samples were associated with smooth changes in the 206Pb/207Pb ratio while larger fluctuations were encountered in winter which is consistent with a low altitude inversion near Mont Blanc in the winter and free transfer of pollutants from lower to higher altitudes at other times. A plot of 208Pb/207Pb versus 206Pb/207Pb ratios reveals three isotopic groupings, associated with the periods pre-1923, 1923–1968 and 1969–1991. In the first group, the isotopic composition is consistent with local mining, smelting and coal burning, while in the second, motor vehicle exhaust emissions dominate. In the third group, motor vehicle emissions also dominate but the Pb is even less radiogenic. During this period the IILE occurred and there was a reduction in the use of leaded gasoline in Europe. A comparison of the Mont Blanc and Summit (central Greenland) records shows they contain similar 206Pb/207Pb ratios between 1960 and 1968, although small differences in isotopic composition can be detected by also considering the 208Pb/207Pb ratio. However, after 1969 the two records diverge markedly, with the Greenland ratios being dominated by the highly radiogenic Mississippi valley-type Pb from the USA and with the Mont Blanc ratios moving to lower values particularly about the time of the IILE.

One hundred fifty-year record of lead isotopes in Antarctic snow from Coats Land

A record of the concentrations of Pb and Ba and the isotopic composition of Pb has been established for a remote, low accumulation site in the Atlantic sector of Antarctica (Coats Land) by means of thermal ionization mass spectrometry. The snow samples cover the period similar to 1840 to 1990. They were taken from the walls of a pit to a depth of 7.8 nu and as a core to 16 m; ultraclean procedures were used. Detailed laboratory subsampling provided both long-term (secular scale) and short-term (intra-annual) Pb, Ba, and Pb isotope variations. The results show that there have been significant variations in Ph concentrations (range, 0.1 to 9.3 pg/g) and isotopic composition (range, 1.096 to 1,208 for Pb-206/Pb-207 ratio) since the 1840s. The data show evidence of pollution for this metal in Antarctica as early as the 1880s. Several Pb maxima were observed: the first at the beginning of the 20th century and the last in the 1970s to 1980s, with a clear decrease during recent years. Although the last maximum is clearly linked to the rise and fall in the use of leaded gasoline in the Southern Hemisphere, especially in South America, the reason for the first remains uncertain. The pattern of changing isotopic composition of Ph reveals the changing origin and character of the anthropogenic inputs to Antarctica. An interesting feature in this pattern is the relatively large contribution of unradiogenic Pb in the similar to1890s, possibly originating from Australia. Another interesting feature is the pronounced intra-annual variation in the isotopic composition of Pb, which illustrates the complexity of the changing inputs of Pb to Antarctica.

An 800-Year Record of Atmospheric As, Mo, Sn, and Sb in Central Asia in High-Altitude Ice Cores from Mt. Qomolangma (Everest), Himalayas

As, Mo, Sn, and Sb have been determined by inductively coupled plasma sector field mass spectrometry (ICP-SFMS) in 143 depth intervals of high-altitude ice cores from Mt. Everest, covering an 800-year time period from 1205 to 2002 AD. The results clearly demonstrate the long-term historical record of atmospheric transport and deposition of As, Mo, Sn, and Sb that has prevailed at high altitudes in the central Himalayas. Natural contributions, mainly from mineral dust, have dominated the atmospheric cycles of As, Mo, Sn, and to some extent Sb during the 700 years prior to the 20th century. Compared to those of the pre-1900 period, pronounced increases of both concentrations and crustal enrichment factors are observed since the 1970s, with the highest increase factor for Sn and the lowest for As. Such increases are attributed to anthropogenic emissions of these elements, largely from stationary fossil fuel combustion and nonferrous metals production, particularly in India. Our central Himalayan ice core record provides an explicit recognition of rising atmospheric As, Mo, Sn, and Sb pollution in response to rapid economic growth in central Asia.