European Commission-Joint Research Centre, Institute for Transuranium Elements, Karlsruhe, Germany.
Environ Sci Process Impacts. 2013 Apr;15(4):839-47. doi: 10.1039/c3em30910j.
The isotopic composition of plutonium ((239)Pu, (240)Pu, (241)Pu and (242)Pu) 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 (240)Pu/(239)Pu 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 (241)Pu/(239)Pu (0.0012 ± 0.0005) and (242)Pu/(239)Pu (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+239)Pu from 0.07 mBq g(-1) to 5 mBq g(-1)) essentially confirm our a priori estimates based on existing (241)Am and (137)Cs 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 (210)Pb 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.
采用洁净室程序和加速器质谱（AMS）法，对德国黑森林地区一个约 0.5 米长的贫营养泥炭柱中的钚同位素（(239)Pu、(240)Pu、(241)Pu 和 (242)Pu）进行了研究。这种复杂的分析方法最终需要用于可靠地检测在 femtogram（fg）和 attogram（ag）水平存在的泥炭样品中的 Pu 浓度。在代表过去 80 年的泥炭层中，(240)Pu/(239)Pu 的平均值为 0.19 ± 0.02（N = 32），与北半球全球沉降的公认值 0.18 非常吻合。这一发现主要得到了相应且相当恒定的 (241)Pu/(239)Pu（0.0012 ± 0.0005）和 (242)Pu/(239)Pu（0.004 ± 0.001）比值的支持。由于在大气原子弹测试（AD 1956-AD 1980）之前的泥炭样品中也鉴定出了具有全球沉降特征的 Pu 同位素组成，因此表明 Pu 已经在泥炭层中迁移。这些结果首次强调了 Pu 在泥炭沼泽中的迁移性，这对 Pu 在其他酸性、富含有机物的环境（如森林土壤和其他湿地类型）中的迁移具有启示意义。这些发现构成了对环境中 Pu 在 fg 和 ag 水平上行为的直接观察。对 Pu 浓度的 AMS 测量（参考从 0.07 mBq g(-1) 到 5 mBq g(-1) 的相应（240+239）Pu 活度）基本上证实了我们基于调查泥炭柱中现有（241）Am 和（137）Cs 数据的先验估计，并且与文献中的全球沉降水平非常吻合。仅使用为泥炭样品建立的 Pu 同位素比值，计算了 Pu 辐照的日期（AD 1956，可校正为 AD 1964），并随后将其与泥炭层的（210）Pb 年龄进行比较；这一比较提供了一个额外的提示，即源自全球沉降的 Pu 并未固定在泥炭柱中，而是沿着泥炭柱向下迁移到核时代之前的层位。
