Stable isotopes are increasingly being used as tracers in environmental studies. One application is to use isotopic ratios to quantitatively determine the proportional contribution of several sources to a mixture, such as the proportion of various pollution sources in a waste stream. In general, the proportional contributions of n+1 different sources can be uniquely determined by the use of n different isotope system tracers (e.g., δ13C, δ15N, δ18O) with linear mixing models based on mass balance equations. Often, however, the number of potential sources exceeds n+1, which prevents finding a unique solution of source proportions. What can be done in these situations? While no definitive solution exists, we propose a method that is informative in determining bounds for the contributions of each source. In this method, all possible combinations of each source contribution (0–100%) are examined in small increments (e.g., 1%). Combinations that sum to the observed mixture isotopic signatures within a small tolerance (e.g., ±0.1‰) are considered to be feasible solutions, from which the frequency and range of potential source contributions can be determined. To avoid misrepresenting the results, users of this procedure should report the distribution of feasible solutions rather than focusing on a single value such as the mean. We applied this method to a variety of environmental studies in which stable isotope tracers were used to quantify the relative magnitude of multiple sources, including (1) plant water use, (2) geochemistry, (3) air pollution, and (4) dietary analysis. This method gives the range of isotopically determined source contributions; additional non-isotopic constraints specific to each study may be used to further restrict this range. The breadth of the isotopically determined ranges depends on the geometry of the mixing space and the similarity of source and mixture isotopic signatures. A sensitivity analysis indicated that the estimated ranges vary only modestly with different choices of source increment and mass balance tolerance parameter values. A computer program (IsoSource) to perform these calculations for user-specified data is available at http://www.epa.gov/wed/pages/models.htm
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Source partitioning using stable isotopes: coping with too many sources.

Arctic contaminants : sources, occurrence and pathways

Isotopic source signatures for atmospheric lead: the Northern Hemisphere

Tracing the transport of anthropogenic lead in the atmosphere and in soils using isotopic ratios

This paper presents a large palaeolimnological study of the pre-industrial and industrial history of atmospheric lead pollution deposition in Sweden Both lead concentrations and 206Pb/207Pb ratios have been analysed in 31 lakes covering most of Sweden, plus one lake in north-west Russia Four of the lakes have varved (annually-laminated) sediments Isotope analysis is a sensitive and effective method to distinguish pollution lead from natural catchment lead and to detect early pollution influence, because the 206Pb/207Pb ratio in unpolluted background sediments in Sweden was > 13, while that of lead from pollution, derived from ores and coal, was < 12 The sediments show a consistent picture of past temporal changes in atmospheric lead pollution These changes include: the first traces of pollution 3,500-3,000 yrs ago; a pollution peak in Greek-Roman Times (about 0 AD); lower lead fall-out between 400 and 900 AD; a significant and permanent increase in atmospheric lead fall-out from about 1000 AD; an increase with the Industrial revolution; a major increase following World War II; the maximum peak in the 1970s; and decreasing fall-out over the last decades The four varved sediments provide high-resolution records of atmospheric pollution They reveal pollution peaks about 1200 and 1530 AD which match the history of metal production in Europe According to the varve records the lead pollution level in the late 1990s had decreased beneath the level of the 1530s The pollution level 1200 AD was about 35% of the 1980s, when lead pollution was still near its all time high About 50% of the total accumulated atmospheric lead pollution deposition through time was deposited in the pre-industrial period The sediments also show a consistent picture of the geographic distribution of atmospheric lead deposition over time, with higher deposition in south Sweden and declining levels to the north, which supports the hypothesis that the main sources of pre-industrial atmospheric lead pollution in Sweden were cultural areas in mainland Europe and Great Britain

Four thousand years of atmospheric lead pollution in northern Europe: a summary from Swedish lake sediments

Pb 206 /Pb 207 and Pb 208 /Pb 207 isotope ratios were measured in a series of daily atmospheric aerosol samples collected in southern Sweden between 9 February and 30 May 1988. The ratios were observed to vary considerably, depending on the origin of air. 5-day back-trajectories were used to classify the samples according to source region: Northwest, Western Europe, East, Eastern Europe, or a combination of two regions. Significant differences in the isotope ratios were found. Unique signatures based on the Pb 206 /Pb 207 and Pb 208 /Pb 207 ratios could be assigned for each region. The signatures were generally consistent with isotope ratios of Swedish and other European gasolines, and with literature values of the isotope ratios of economically significant lead ores used in Europe. A comparison was made between the regional signatures and the Pb 206 /Pb 207 ratios observed in Arctic aerosol samples. Excellent agreement was observed between the Arctic Pb 206 /Pb 207 ratios (1.160) and an average source signature (1.156) calculated from observations in this study using equal contributions from Western Europe, Eastern Europe, and the East as predicted by a chemical transport model. DOI: 10.1034/j.1600-0889.1991.00004.x

https://www.tandfonline.com/doi/pdf/10.3402/tellusb.v43i1.15245

W. T. Sturges

Papers

Regional source discrimination of atmospheric aerosols in Europe using the isotopic composition of lead