Lansard B, Charmasson S, Gascó C, Antón M P, Grenz C, Arnaud M
Laboratoire d'Océanographie et de Biogéochimie, UMR 6535, CNRS/Université de la Méditerranée, Station Marine d'Endoume, rue de la Batterie des Lions, 13007, Marseille, France.
Sci Total Environ. 2007 Apr 15;376(1-3):215-27. doi: 10.1016/j.scitotenv.2007.01.069. Epub 2007 Feb 28.
The dispersion and fate of the Rhone River inputs to the Gulf of Lions (Northwestern Mediterranean Sea) have been studied through the spatial and temporal distributions of plutonium isotopes in continental shelf sediments. Plutonium isotopes ((238)Pu and (239,240)Pu) are appropriate tracers to follow the dispersion of particulate matter due both to their high affinity for particles and their long half-lives. In the Rhone River valley, plutonium isotopes originate from both the weathering of the catchment basin contaminated by global atmospheric fallout, and the liquid effluents released from the Marcoule reprocessing plant since 1961. This work presents a first detailed study on (238)Pu and (239,240)Pu distributions in sediments from the Rhone prodelta to the adjacent continental shelf, since the decommissioning of Marcoule in 1997. The vertical distribution of Pu isotopes has been analysed in a 4.75 m long core sampled in 2001 at the Rhone mouth. Despite this length, plutonium is found at the last 10 cm, manifesting the high sedimentation rate of the prodeltaic area and its ability for trapping fine-grained sediments and associated contaminants. The highest (238)Pu and (239,240)Pu concentrations reached 1.26 and 5.97 Bq kg(-1) respectively and were found within the layer 280-290 cm. The (238)Pu/(239,240)Pu activity ratios (AR) demonstrated an efficient and huge trapping of the Pu isotopes derived from Marcoule. The fresh sediments, located on the top of the core, show lower plutonium activity concentrations and lower (238)Pu/(239,240)Pu ratios. This decrease is in close relation with the shut down of the Marcoule reprocessing plant in 1997. In 2001, plutonium isotopes were also analysed in 21 surface sediments located offshore and concentrations ranged from 0.03 to 0.17 Bq kg(-1) for (238)Pu and from 0.33 to 1.72 Bq kg(-1) for (239,240)Pu. The (238)Pu/(239,240)Pu AR ranged from 0.24 close to the river mouth to 0.06 southwards, indicating the decreasing influence of the Marcoule releases (global fallout AR 0.03-0.05 and Marcoule AR 0.30). This is in good agreement with the main direction spread of the Rhone River plume and the bottom current. This dataset has been compared to those obtained in the same area in 1984 and 1990 in order to follow the time trend in Pu concentrations. This comparison highlights the decrease with time in plutonium concentrations close to the Rhone River mouth, but further away this reduction is not so evident.
通过大陆架沉积物中钚同位素的时空分布，对罗讷河注入利翁湾（地中海西北部）的扩散及归宿进行了研究。钚同位素（²³⁸Pu和²³⁹,²⁴⁰Pu）是追踪颗粒物扩散的合适示踪剂，这是因为它们对颗粒具有高亲和力且半衰期长。在罗讷河流域，钚同位素既源于受全球大气沉降污染的集水区的风化作用，也源于自1961年以来马库尔后处理厂排放的液体流出物。这项工作首次详细研究了自1997年马库尔退役以来，从罗讷河前三角洲到相邻大陆架沉积物中²³⁸Pu和²³⁹,²⁴⁰Pu的分布情况。对2001年在罗讷河河口采集的一个4.75米长的岩芯中钚同位素的垂直分布进行了分析。尽管该岩芯长度如此，但钚在最后10厘米处被发现，这表明前三角洲地区的高沉积速率及其捕获细粒沉积物和相关污染物的能力。²³⁸Pu和²³⁹,²⁴⁰Pu的最高浓度分别达到1.26和5.97贝克勒尔/千克，出现在280 - 290厘米的层位中。²³⁸Pu/²³⁹,²⁴⁰Pu活度比（AR）表明对源自马库尔的钚同位素进行了高效且大量的捕获。位于岩芯顶部的新鲜沉积物显示出较低的钚活度浓度和较低的²³⁸Pu/²³⁹,²⁴⁰Pu比值。这种下降与1997年马库尔后处理厂关闭密切相关。2001年，还对21个近海表层沉积物中的钚同位素进行了分析，²³⁸Pu的浓度范围为0.03至0.17贝克勒尔/千克，²³⁹,²⁴⁰Pu的浓度范围为0.33至1.72贝克勒尔/千克。²³⁸Pu/²³⁹,²⁴⁰Pu AR范围从靠近河口处的0.24到向南的0.06，表明马库尔排放物的影响在减小（全球沉降AR为0.03 - 0.05，马库尔AR为0.30）。这与罗讷河羽流和底流的主要扩散方向高度一致。为了追踪钚浓度的时间趋势，将该数据集与1984年和1990年在同一地区获得的数据进行了比较。这种比较突出了靠近罗讷河河口处钚浓度随时间的下降，但在更远的地方这种下降并不那么明显。
