Eyrolle-Boyer Frédérique, Boyer Patrick, Claval David, Charmasson Sabine, Cossonnet Catherine
Institut de Radioprotection et de Sûreté Nucléaire (IRSN), PRP-ENV, SESURE/LERCM, SERIS/LM2E, STEME/LMRE, BP 3, 13115 Saint Paul Lez Durance, France.
Institut de Radioprotection et de Sûreté Nucléaire (IRSN), PRP-ENV, SESURE/LERCM, SERIS/LM2E, STEME/LMRE, BP 3, 13115 Saint Paul Lez Durance, France.
J Environ Radioact. 2014 Oct;136:162-8. doi: 10.1016/j.jenvrad.2014.05.019. Epub 2014 Jun 21.
The global inventory of naturally produced tritium (3H) is estimated at 2.65 kg, whereas more than 600 kg have been released during atmospheric nuclear tests (NCRP, 1979; UNSCEAR, 2000) constituting the main source of artificial tritium throughout the Anthropocene. The behaviour of this radioactive isotope in the environment has been widely studied since the 1950s, both through laboratory experiments and, more recently, through field observations (e.g., Cline, 1953; Kirchmann et al., 1979; Daillant et al., 2004; McCubbin et al., 2001; Kim et al., 2012). In its "free" forms, [i.e. 3H gas or 3H hydride (HT); methyl 3H gas (CH3T); tritiated H2O or 3H-oxide (HTO); and Tissue Free Water 3H (TFWT)], tritium closely follows the water cycle. However, 3H bound with organic compounds, mainly during the basic stages of photosynthesis or through weak hydrogen links, is less exchangeable with water, which explains its persistence in the carbon cycle as re underlined recently by Baglan et al. (2013), Jean-Batiste and Fourré (2013), Kim et al. (2013a,b). In this paper, we demonstrate that terrestrial biomass pools, historically contaminated by global atmospheric fallout from nuclear testing, have constituted a significant delayed source of organically bound tritium (OBT) for aquatic systems, resulting in an apparent enrichment of OBT as compared to HTO. This finding helps to explain concentration factors (tritium concentration in biota/concentration in water) greater than 1 observed in areas that are not directly affected by industrial radioactive wastes, and thus sheds light on the controversies regarding tritium 'bioaccumulation'. Such apparent enrichment of OBT is expected to be more pronounced in the Northern Hemisphere where fallout was most significant, depending on the nature and biodegradability of terrestrial biomass at the regional scale. We further believe that OBT transfers from the continent to oceans have been sufficient to affect tritium concentrations in coastal marine biota (i.e., near river inputs). Our findings demonstrate that the persistence of terrestrial organic (3)H explains imbalances between organically bound tritium and free (3)H in most river systems in particular those not impacted by releases from nuclear facilities.
天然产生的氚（³H）的全球存量估计为2.65千克，而在大气层核试验期间已释放了超过600千克（NCRP，1979年；联合国原子辐射影响科学委员会，2000年），这构成了整个人类世期间人造氚的主要来源。自20世纪50年代以来，通过实验室实验以及最近的实地观测（例如，克莱恩，1953年；基希曼等人，1979年；戴扬等人，2004年；麦卡宾等人，2001年；金等人，2012年），对这种放射性同位素在环境中的行为进行了广泛研究。以其“游离”形式[即³H气体或³H氢化物（HT）；甲基³H气体（CH₃T）；氚化水或³H氧化物（HTO）；以及组织游离水³H（TFWT）]，氚紧密跟随水循环。然而，主要在光合作用的基本阶段或通过弱氢键与有机化合物结合的³H，与水的交换性较差，这解释了其在碳循环中的持久性，正如巴格兰等人（2013年）、让 - 巴蒂斯特和富雷（2013年）、金等人（2013a，b）最近所强调的那样。在本文中，我们证明，历史上受到核试验全球大气沉降物污染的陆地生物量库，构成了水生系统中有机结合氚（OBT）的一个重要延迟来源，导致与HTO相比，OBT明显富集。这一发现有助于解释在未直接受到工业放射性废物影响的地区观察到的大于1的浓缩系数（生物群中氚浓度/水中浓度），从而阐明了关于氚“生物累积”的争议。这种OBT的明显富集预计在北半球最为显著，因为那里沉降最为严重，这取决于区域尺度上陆地生物量的性质和生物降解性。我们进一步认为，OBT从大陆向海洋的转移足以影响沿海海洋生物群（即靠近河流入海口处）中的氚浓度。我们的研究结果表明，陆地有机（³）H的持久性解释了大多数河流系统中有机结合氚与游离（³）H之间的不平衡，特别是那些未受到核设施排放影响的河流系统。
