Source/environmental indicators isotopic

PCB isotopic compositions have been reported for mixtures produced by Monsanto (USA), Bayer (Germany), and Caffaro (Italy) (e.g., Reddy et al. 2000 Drenzek et al. 2002). The Monsanto mixtures (Arochlors) were supplied from three separate environmental standard suppliers. The 5 C1 values of all the samples fell within a limited range of-3.37 to -2.11%o. However, there were resolvable differences between the same Arochlor mixture supplied from different sources. A preliminary survey of contaminated sediments (e.g., Reddy et al. 2000) indicated that two samples which have PCBs that have been affected by alteration as evidenced by the lower amounts of less chlorinated congeners were isotopically distinct from the range of the source materials (assumed to be similar to the analyzed pure samples) while other samples were not distinguishable from the source material. 

The evolution of a large amount (1.12 x 1018 g of CH4) of methane from hydrates is the only plausible hypothesis that has been offered to explain this environmental perturbation. The abnormal 8 l3C isotope indicates that source... 

The results of the second interlaboratory study of PCN analytical methods using environmental matrices, undertaken by the US National Institute of Standards and Technology (NIST), should provide an indication of the comparability of published environmental PCN data and show where additional method enhancements are needed. Further method development efforts in the analysis of PCNs, and other complex mixtures are likely to focus on improving efficiencies by optimizing run times and separation. Examples may include time-of-flight mass spectrometry and multidimensional GC. New methods, such as isotope ratio mass spectrometry, may contribute to further source apportionment of complex mixtures [88]. 

Quantifying the sources and rates of input of base cation nutrients (calcium, magnesium, potassium, and sodium) to forest ecosystems is an important goal in forest biogeochemistry, particularly when seeking to understand the recovery from environmental disturbances such as acid rain and forest clear-cutting. The earliest study to use isotopes as an indicator of atmospheric inputs to soils was by Dymond et al. (1974), who used strontium isotope measurements of micas in Hawaiian soils to determine that a significant proportion of the potassium input to Hawaiian soils was from deposition of dust transported... 

Changes in abundance and isotopic composition of biomarker compounds can help delineate relative mass contributions from terrestrial, marine algal, and bacterial OM sources, as well as provide indications of specific processes and environmental conditions in ancient water... 

Weapons-grade plutonium, dispersed at military accidents such as Thule in 1968 or as non-fissioned weapon particles after detonation of a Pu-bomb can be characterized by high Pu content relative to the other Pu-isotopes, while accidentally dispersed Pu from the previously widely used nuclear-powered satellites are characterized by high Pu content." The ratio of americium-241 to plutonium isotopes (as " Am is formed by the decay of Pu) is proportional to the initial " Pu concentration, thus it can also be used as an indicator to assess the origin of contamination. However, in most cases, as several sources may contribute to the transuranics content in environmental samples, mixing models applying several isotope ratios are required to assess the origin of possible contamination sources. 

While all the isotopic compositions in these studies were measured with TIMS, other studies have utilized ICPMS measurements of lead isotopic compositions. For example. Dean et al. (1987) measured lead isotopic compositions in milk and wine, while comparable ICPMS analyses of lead isotopic compositions in other environmental matrices have been made by Date and Chung (1987), Delves and Campbell (1988), Caplun et al. (1984), Longerich et al. (1987), and Sturges and Barrie (1987). These studies indicated that quadrupole ICPMS measurements did not provide sufficient precision to adequately distinguish environmental lead sources on the basis of their stable isotopic composition (Russ 1989 Ward 1989) since the isotopic abundances of contaminant environmental lead typically vary by only 3%-7%. Further, most published ICPMS measurements of lead isotopic compositions in environmental and biological matrices have not included ratios for (1.4% natural relative abundance), which is required for definitive isotopic composition analyses. 

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