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Issue 4, 2013
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Determination of 239Pu, 240Pu, 241Pu and 242Pu at femtogram and attogram levels – evidence for the migration of fallout plutonium in an ombrotrophic peat bog profile

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Abstract

The isotopic composition of plutonium (239Pu, 240Pu, 241Pu and 242Pu) was investigated in a ∼0.5 m long peat core from an ombrotrophic bog (Black Forest, Germany) using clean room procedures and accelerator mass spectrometry (AMS). This sophisticated analytical approach was ultimately needed to detect reliably the Pu concentrations present in the peat samples at femtogram (fg) and attogram (ag) levels. The mean 240Pu/239Pu isotopic ratio of 0.19 ± 0.02 (N = 32) in the peat layers, representing approximately the last 80 years, was in good agreement with the accepted value of 0.18 for the global fallout in the Northern Hemisphere. This finding is largely supported by the corresponding and rather constant 241Pu/239Pu (0.0012 ± 0.0005) and 242Pu/239Pu (0.004 ± 0.001) ratios. Since the Pu isotopic composition characteristic of the global fallout was also identified in peat samples pre-dating the period of atmospheric atom bomb testing (AD 1956–AD 1980), migration of Pu within the peat profile is clearly indicated. These results highlight, for the first time, the mobility of Pu in a peat bog with implications for the migration of Pu in other acidic, organic rich environments such as forest soils and other wetland types. These findings constitute a direct observation of the behaviour of Pu at fg and ag levels in the environment. The AMS measurements of Pu concentrations (referring to a corresponding activity of 240+239Pu from 0.07 mBq g−1 to 5 mBq g−1) essentially confirm our a priori estimates based on existing 241Am and 137Cs data in the investigated peat core and agree well with the global fallout levels from the literature. Exclusively employing the Pu isotope ratios established for the peat samples, the date of the Pu irradiation (AD 1956, correctable to AD 1964) was calculated and subsequently compared to the 210Pb age of the peat layers; this comparison provided an additional hint that global fallout derived Pu is not fixed in the peat column, but has migrated downwards along the peat profile to layers preceding the nuclear age.

Graphical abstract: Determination of 239Pu, 240Pu, 241Pu and 242Pu at femtogram and attogram levels – evidence for the migration of fallout plutonium in an ombrotrophic peat bog profile

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Publication details

The article was received on 19 Nov 2012, accepted on 14 Feb 2013 and first published on 18 Feb 2013


Article type: Paper
DOI: 10.1039/C3EM30910J
Citation: Environ. Sci.: Processes Impacts, 2013,15, 839-847
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    Determination of 239Pu, 240Pu, 241Pu and 242Pu at femtogram and attogram levels – evidence for the migration of fallout plutonium in an ombrotrophic peat bog profile

    F. Quinto, E. Hrnecek, M. Krachler, W. Shotyk, P. Steier and S. R. Winkler, Environ. Sci.: Processes Impacts, 2013, 15, 839
    DOI: 10.1039/C3EM30910J

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