Assessment of natural radionuclides mobility in a phosphogypsum disposal area
评估磷石膏处置区天然放射性核素迁移率

2.1. Samplings 2.1. 采样

PG samples were collected at different depths from two bore-holes (U and D cores) using a soil-sampling auger at the unrestored zone 3 of the stack in May 2013 (Fig. 1). The U core (“up”) was taken at the upper zone of the selected area, while the D core was located at the deeper are in the perimeter channel which collect the leaching waters. Seven samples were collected from the U core; whereas six samples were collected from the D core. The samples were taken approximately at intervals of 50 cm in depth, being the thickness of each sample around 5 cm. Every sample presented a mass of around 150–200 g, which was dried at 55 °C, and then homogenized in a 250 mL beaker during at least 1 h by mechanical process. Once the sample was homogenized, different aliquots were taken to measure by alpha spectrometry, gamma spectrometry, physico-chemical parameters, etc. The mean value of the size was around 80 μm.
2013年5月，在烟囱未恢复的3区使用土壤取样螺旋钻从两个钻孔（U和D岩心）的不同深度采集PG样本（图1）。U核（“向上”）位于所选区域的上部区域，而D核位于收集浸出水的周边通道中较深的区域。从U核中收集了7个样品;而从D核中收集了6个样品。样品的深度大约为50厘米，每个样品的厚度约为5厘米。每个样品的质量约为150-200 g，在55°C下干燥，然后在250 mL烧杯中通过机械过程在至少1小时内均质化。样品均质化后，采用α-能谱法、伽马能谱法、理化参数等法测量不同的等分试样。尺寸的平均值约为 80 μm。

The pore-water was extracted from solid samples using suction cup lysimeters and hollow-fibre tube sampler devices (Rhizon samplers; Eijkelkamp Agrisearch Equipment, Netherlands). Subsequently, solid samples were frozen and then lyophilized using a freeze-dryer.
使用吸盘裂解仪和中空纤维管取样器装置（Rhizon 取样器;Eijkelkamp Agrisearch Equipment，荷兰）。随后，将固体样品冷冻，然后使用冷冻干燥器冻干。

In addition, PG wastewaters in zone 3 of PG stack were sampled, corresponding to edge outflow leachates reaching the Estuary of Huelva (from E1 to E12), and process water samples were taken at the perimeter channel (from P1 to P3), in order to confirm the mobility of radionuclides in the PG disposal area conditions.
此外，对PG烟囱第3区的PG废水进行了采样，对应于到达韦尔瓦河口（从E1到E12）的边缘流出渗滤液，并在周边通道（从P1到P3）采集了工艺水样本，以确认放射性核素在PG处置区条件下的流动性。

2.2. Physico-chemical characterization techniques
2.2. 理化表征技术

The pH, redox potential (Eh) and electrical conductivity (EC) of the solutions were measured in the field, except for the pore-waters that were measured immediately in the laboratory after extraction, using a portable MultiparametricCrison Mm 40 + meter, which was calibrated prior to the experiments. Measured redox potential was referenced to standard hydrogen electrode (Eh) as proposed by Nordstrom and Wilde (1998).
溶液的pH值、氧化还原电位（Eh）和电导率（EC）是在现场测量的，除了在提取后立即在实验室中测量的孔隙水，使用便携式MultiparametricCrison mm 40 +仪表，该仪表在实验前进行了校准。测量的氧化还原电位参考了Nordstrom和Wilde（1998）提出的标准氢电极（Eh）。

2.3. Optimized BCR sequential extraction procedure
2.3. 优化的BCR顺序提取程序

In order to study in detail the partitioning of radionuclides in the PG, the following BCR sequential extraction procedure was applied to the solids using around 1 g of each dried and homogenized sample. This sequential procedure presents mainly four steps. Firstly, water/acid soluble and exchangeable fraction (F1), which is designed to extract exchangeable metals soluble in water or in slightly acidic conditions. This fraction is the most mobile in environmental samples, and therefore, the most bioavailable and dangerous for the environment. Secondly, reducible fraction (F2) represents all metals bound to Fe and Mn oxi-hydroxides that can be released if conditions change from an oxic to an anoxic state. Thirdly, oxidizable fraction (F3) is mainly composed of metals bound to organic compounds and sulphides that could be released under oxidising conditions, and finally the residual fraction (F4) known as non-mobile fraction, corresponding to those metals that are strongly associated with crystalline structures of minerals and are therefore unlikely to be released from the samples unless they are exposed to extreme conditions (See Table S1). A summary of the sequential extraction procedure in Supplementary Information (Table S1) is shown.
为了详细研究PG中放射性核素的分配，使用每个干燥和均质化样品约1 g对固体应用以下BCR顺序提取程序。这个顺序过程主要包括四个步骤。首先是水/酸溶性和可交换馏分（F1），旨在提取可溶于水或微酸性条件下的可交换金属。该部分在环境样品中流动性最强，因此对环境的生物利用度最高，对环境最危险。其次，可还原馏分 （F2） 代表所有与 Fe 和 Mn 氧化氢氧化物结合的金属，如果条件从氧状态变为缺氧状态，这些金属可以释放出来。第三，可氧化馏分（F3）主要由与有机化合物结合的金属和硫化物组成，这些金属在氧化条件下会释放出来，最后是残留馏分（F4），称为非移动馏分，对应于那些与矿物晶体结构密切相关的金属，因此除非暴露在极端条件下，否则不太可能从样品中释放出来（见表S1）。补充资料（表S1）中显示了顺序提取程序的摘要。

In order to ensure the comparability of the results obtained, the BCR sequential extraction procedure applied in this work was previously validated in our laboratory by using a certified reference material (CRM), coded as BCR-701, previously validated for heavy metals (Rauret et al., 1999). Once the BCR was verified for heavy metals, it was proved that BCR is also valid (precision, trueness, etc.) for alpha-emitting natural radionuclides (Pérez-Moreno et al., 2018).
为了确保所获得结果的可比性，本工作中应用的BCR顺序提取程序先前在我们的实验室中使用经过认证的参考物质（CRM）进行了验证，该参考物质编码为BCR-701，先前已验证为重金属（Rauret等人，1999）。一旦 BCR 被验证为重金属，就证明 BCR 对发射 α 的天然放射性核素也是有效的（精度、真实度等）（Pérez-Moreno 等人，2018 年）。

The total recovery (R) of a specific radionuclide along the application of the BCR is defined as the sum of the activity concentrations recovered for all fractions (F_i) in relation to the total activity (T) of the PG sample directly measured, and will be given by the Eq. (2):(2)$\text{R}\left(\text{\%}\right)=\frac{{\sum }_{i=1}^{i=4}Fi}{T}·100$
应用BCR时特定放射性核素的总回收率（R）定义为所有馏分（F）回收的活性浓度与直接测量的PG样品的总活度（T）的总和，将由方程（2）给出： (2)$\text{R}\left(\text{\%}\right)=\frac{{\sum }_{i=1}^{i=4}Fi}{T}·100$

In addition, the transfer factors (TF) were also determined. The transfer factor (%) is defined as the amount of element that is transferred to the liquid phase in each step (Fi), in relation to the total concentration found in the solid sample (sum of concentrations for all fractions, S), so it is calculated by the next equation (Eq. (3)):(3)$\text{TF}\left(\text{\%}\right)=\frac{Fi}{S}100$
此外，还确定了转移因子（TF）。转移因子 （%） 定义为在每个步骤 （Fi） 中转移到液相的元素量，相对于固体样品中的总浓度（所有馏分的浓度总和，S），因此由下一个公式计算（方程 （3））： (3)$\text{TF}\left(\text{\%}\right)=\frac{Fi}{S}100$

Finally, it is important to note that the EPA 3052 (SW-846) method was used for digestion of the solid samples.
最后，需要注意的是，EPA 3052（SW-846）方法用于固体样品的消解。

2.4. Alpha spectrometry 2.4. α光谱法

The radiochemical procedure to isolate both U- and Th-isotopes was based on the tributylphosphate (TBP) back-extraction methodology (Holm and Fukai, 1977). The sample is dissolved in 8 M HNO₃, and then the actinides are extracted into tributilphosphete (TBP), while in the aqueous nitric fraction are contained the rest of no actinides radioelements (Po, Ra, etc.). The Th is back-extracted by using 1.5 M HCl + Xilen, and after U is back-estracted from the organic phase with distilled water On the another hand, the Po is self-deposited onto silver disks in 2 M HCl by using the method proposed by Flynn (1968), and from the Po remaining dissolution the Ra-isotopes are isolated following the method based on ion-chromatographic cation resins AG50X12 (Hancock and Martin, 1991; Jia et al., 2007). The thin radioactive source for U and Th was obtained by electrodeposition following the methodology reported by Talvitie (1972) and Hallstadius (1984), while the Ra one by BaSO₄ microprecipitation was obtained (Blanco et al., 2002). Then, the activity concentrations of the different isotopes were measured using ion implantation Si (PIPS) semiconductor detectors, EG & G Ortec. For these determinations, the samples were spiked with accurately known activities of ²³²U, ²²⁹Th and ²⁰⁹Po. The activity concentration uncertainty has been calculated by using the equation that gives the activity concentration, taking into account the uncertainty of the net counts of the alpha peaks (problem radionuclide and isotopic tracer), precision of balance (0.3 mg), etc. Full details can be found in the Annex I of the Supplementary Information. Quality Assurance and Quality Control (QA/QC) followed in the radiochemical measurements was as follows: one replicate every 10 samples, one blank every 5 samples, one Certified Reference Material (CRM) every 10 samples, and with similar composition matrix to the problem sample; in our case the IAEA-434 (phosphogypsum), IAEA-385 (sea sediment) and CSN 2011 (Intercomparison of spiked Natural water with ²²⁶Ra) certified materials were used, obtaining detection limits for the measured radionuclides around 0.4–1.2 mBq. Finally, the obtained average yields, and ranges, for the studied radionuclides were: Ra (46%; 15–72%), U (74%, 35–90%), Th (57%; 30–77%) and Po (92%; 75–95%).
分离U-和Th-同位素的放射化学程序基于磷酸三丁酯（TBP）反萃取方法（Holm和Fukai，1977）。将样品溶解在8M HNO ₃ 中，然后将锕系元素提取成三丁基磷酸盐（TBP），而在硝酸水性馏分中含有其余的无锕系元素放射性元素（Po，Ra等）。使用1.5 M HCl + Xilen反萃取Th，然后用蒸馏水将U从有机相中回抽出 另一方面，使用Flynn（1968）提出的方法将Po自沉积到2M HCl中的银盘上，并且从Po剩余溶解中分离Ra同位素，方法是基于离子色谱阳离子树脂AG50X12（Hancock和Martin， 1991;Jia 等人，2007 年）。U和Th的薄放射源是按照Talvitie（1972）和Hallstadius（1984）报告的方法通过电沉积获得的，而Ra是通过BaSO ₄ 微沉淀获得的（Blanco等人，2002）。然后，使用离子注入Si（PIPS）半导体探测器EG&G Ortec测量不同同位素的活性浓度。对于这些测定，样品中加标了准确已知的 ²³² U、 ²²⁹ Th 和 ²⁰⁹ Po 活性。活性浓度不确定度是通过使用给出活性浓度的方程计算的，同时考虑了α峰（问题放射性核素和同位素示踪剂）的净计数的不确定度、平衡精度（0.3 mg）等。详情载于补充资料附件一。 放射化学测量遵循的质量保证和质量控制 （QA/QC） 如下：每 10 个样品重复 1 个，每 5 个样品重复 1 个空白，每 10 个样品重复 1 个认证标准物质 （CRM），并且具有与问题样品相似的组成基质;在我们的案例中，使用了IAEA-434（磷石膏）、IAEA-385（海洋沉积物）和CSN 2011（加标天然水与 ²²⁶ Ra的相互比较）认证材料，获得了测得的放射性核素的检测限约为0.4-1.2 mBq。最后，所研究的放射性核素的平均产率和范围为：Ra（46%;15-72%）、U（74%;35-90%）、Th（57%;30-77%）和Po（92%;75-95%）。

2.5. Statistical analysis
2.5. 统计分析

In order to evaluate the significant difference of both samples (U and D cores), Z-score function was used.(4)$Z=\frac{\left|X_1-X_2\right|}{\sqrt{\left({\sigma }_1^2+{\sigma }_2^2\right)}}$Where X₁, ${\underset{¯}{\text{X}}}_{\text{measured}}$ is the mean value measured in sampling 1 and X₂ is the mean value measured in sampling 2, and σ₁ and σ₂ the standard deviation of the corresponding averages. The null hypothesis corresponds to no significant differences between both samplings, i.e., the true difference is cero. If the experimental Z-score is lower than 2 will reflect that null hypothesis cannot be rejected with a confidence level of 95% (p-value higher than 0.05).
为了评估两个样本（U 核和 D 核）的显著差异，使用了 Z 分数函数。 (4)$Z=\frac{\left|X_1-X_2\right|}{\sqrt{\left({\sigma }_1^2+{\sigma }_2^2\right)}}$ 其中 X ₁ ， ${\underset{¯}{\text{X}}}_{\text{measured}}$ 是抽样 1 中测得的平均值，X ₂ 是抽样 2 中测得的平均值，σ ₁ 和 σ ₂ 相应平均值的标准差。原假设对应于两个抽样之间没有显著差异，即真正的差异是 cero。如果实验 Z 分数低于 2，则反映原假设不能以 95% 的置信水平（p 值高于 0.05）被拒绝。

In addition, the Shapiro-Wilk test in order to evaluate the normality of the samples was used. The null-hypothesis of this test is that the population is normally distributed. Thus, on the one hand, if the p-value is less than the chosen alpha level, then the null hypothesis is rejected and there is evidence that the data tested don't came from a normally distributed population. On the other hand, if the p-value is greater than the chosen alpha level, then the null hypothesis (normally distributed population), cannot be rejected at this p significance level (Shapiro and Wilk, 1965).
此外，还使用了Shapiro-Wilk检验来评估样品的正态性。该检验的原假设是总体呈正态分布。因此，一方面，如果 p 值小于所选的 alpha 水平，则原假设将被拒绝，并且有证据表明测试的数据并非来自正态分布的总体。另一方面，如果 p 值大于所选的 alpha 水平，则原假设（正态分布总体）不能在此 p 显著性水平上被拒绝（Shapiro 和 Wilk，1965）。

3.1. Physico-chemical parameters
3.1. 理化参数

The physico-chemical parameters analysed in the pore-water show small variations along each core (SI, Table S2). In the U core the pH is 3.5 in the first saturated layer (1.5 m), and below remains very uniform with a value around 2.8–3. Contrarily, the pH in D core is one unity lower than in U, constant and around 2, indicating that proton concentration (H⁺) in D is one order of magnitude higher than in U. The electrical conductivity (EC) found is in agreement with the measured pH around 3.5 ± 0.1 mS cm⁻¹ in the upper part, and increases one order of magnitude (43 ± 4 mS cm⁻¹) in the deeper zone (perimeter channel). Contrarily, there is not significant differences in the redox potential (Eh) for both cores samples and oxidant conditions are found. These results are in agreement with previous hydrogeochemical studies (Aguado et al., 2005), where low pH values are related to content of phosphoric acid.
在孔隙水中分析的物理化学参数显示沿每个岩心的微小变化（SI，表S2）。在U核中，第一饱和层（1.5 m）的pH值为3.5，以下的pH值保持非常均匀，值约为2.8-3。相反，D核的pH值比U低一个单位，恒定且约为2，表明D中的质子浓度（H ⁺ ）比U中的质子浓度高一个数量级。发现的电导率 （EC） 与上部测得的 pH 值一致，约为 3.5 ± 0.1 mS cm ⁻¹ ，并且在较深的区域（周边通道）增加了一个数量级（43 ± 4 mS cm ⁻¹ ）。相反，两种岩芯样品的氧化还原电位（Eh）没有显着差异，并且发现了氧化剂条件。这些结果与以前的水文地球化学研究（Aguado等人，2005年）一致，其中低pH值与磷酸含量有关。

The main physico-chemical characteristics of the edge outflow leachates (E1-E12) and the process waters collected in the perimeter channels (P1-P3) are their extreme acidity (pH < 2), especially in the perimeter channel (pH = 1.42 ± 0.14), and their high EC values ($\overline{E}$: 40.3 ± 2.9 mS cm⁻¹; $\overline{P}$: 59.4 ± 2.5 mS cm⁻¹) (SI, Table S3). The values observed for the edge outflows are very similar to those found in the pore-water of the deeper zone, which is expectable since the excess of groundwater leads to the formation of these acid leakages at the toe of the stack. On the other hand, the Eh values are slightly higher in perimeter channel (583 ± 36) than in the edge outflow leachate (483 ± 15).
边缘流出渗滤液（E1-E12）和周边通道（P1-P3）中收集的工艺用水的主要物理化学特性是其极端酸度（pH < 2），特别是在周边通道（pH = 1.42 ± 0.14）和高EC值（ $\overline{E}$ ： 40.3 ± 2.9 mS cm ⁻¹ ; $\overline{P}$ ： 59.4 ± 2.5 mS cm ⁻¹ ） （SI， 表 S3）.在边缘流出处观察到的值与在较深区域的孔隙水中发现的值非常相似，这是可以预期的，因为地下水过量会导致在烟囱脚趾形成这些酸泄漏。另一方面，周长通道（583 ± 36）的 Eh 值略高于边缘流出渗滤液 （483 ± 15）。

3.2. Characterization of phosphogypsum in depth
3.2. 磷石膏的深入表征

Total activity concentrations (Bq kg⁻¹) of radionuclides in PG versus depth are shown in the SI, Figs. S1–S4. The concentrations of ²¹⁰Po, ²²⁶Ra and ²³⁰Th range from 500 to 1000 Bq kg⁻¹ in both cores samples (U and D samples), with similar averages, around 650 Bq kg⁻¹. Both ²³⁴U and ²³⁸U activity concentrations are equals (secular equilibrium), and range from 70 to 500 Bq kg⁻¹ (average of about 100 Bq kg⁻¹ for both cores). In contrast, the concentrations of ²³²Th are very low, ranging from 5 to 40 Bq kg⁻¹. These results are in agreement with previous studies developed in this zone (Bolívar et al., 2000, 2002; Dueñas et al., 2010). In addition, these radionuclides levels are in accordance with measurements made previously in the production process of phosphoric acid (Bolívar et al., 2009). It is worth highlighting that there are no significant differences between the average concentrations of both cores (Z score < 2 for all radionuclides). Taking into account that there are not significant variations in depth, in the future studies, it will only be needed to measure a composed sample done by mixing the different layers of PG until the supporting substrate. In addition, to point out that for both cores, all the radionuclides concentrations are normally distributed (p > 0.05 for Shapiro–Wilk normality test). The high dispersion of activity concentrations is probably due to differences in the used ore or changes in the phosphoric acid production process. These results show that pH and redox potential do not regulate the radionuclides activity concentrations in the PG.
放射性核素在PG中的总活度浓度（Bq kg ⁻¹ ）与深度的关系显示在SI中，图S1-S4。 ⁻¹ 在两个岩心样品（U 和 D 样品）中，Po、 ²²⁶ Ra 和 ²³⁰ Th 的 ²¹⁰ 浓度范围为 500 至 1000 Bq kg，平均值相似，约为 650 Bq kg ⁻¹ 。 ²³⁴ U和 ²³⁸ U活性浓度相等（长期平衡），范围为70至500 Bq kg ⁻¹ （两个核心的平均值约为100 Bq kg ⁻¹ ）。相比之下，Th的 ²³² 浓度非常低，范围从5到40 Bq kg ⁻¹ 。这些结果与以前在该地区开展的研究一致（Bolívar等人，2000年，2002年;Dueñas等人，2010）。此外，这些放射性核素水平与先前在磷酸生产过程中进行的测量结果一致（Bolívar等人，2009年）。值得强调的是，两种核心的平均浓度之间没有显着差异（Z评分< 2 表示所有放射性核素）。 考虑到深度没有显着变化，在未来的研究中，只需要测量通过混合不同层的PG直到支撑底物完成的组合样品。 此外，需要指出的是，对于两个核心，所有放射性核素浓度都是正态分布的（夏皮罗-威尔克正态性检验>p 为 0.05）。活性浓度的高分散性可能是由于所用矿石的差异或磷酸生产过程的变化。这些结果表明，pH值和氧化还原电位不能调节PG中的放射性核素活性浓度。

The most relevant activity ratios for both cores are compiled in SI, Table S4. It can be observed that ²³⁴U/²³⁸U value is the unity by considering the experimental uncertainties, as well as the ²¹⁰Po/²²⁶Ra ratios. At the same time, the ²³⁰Th/²³²Th values are very high, being more than 50 the relation between ²³⁰Th and ²³²Th in the majority of the samples, which is the value found in the raw material used in the industrial process (Bolívar et al., 2009). In contrast, the ²³⁴U/²³⁰Th activity ratios are about 0.14 and 0.3 in U and D samples, respectively. These values are also reported by other authors (Rentería-Villalobos et al., 2010).
两个核心最相关的活度比汇编在SI表S4中。可以看出， ²³⁴ 通过考虑实验不确定度以及 ²¹⁰ Po/ ²²⁶ Ra比值，U/ ²³⁸ U值是统一的。同时， ²³⁰ Th/ ²³² Th值非常高，在大多数样品中Th和 ²³² Th之间的关系 ²³⁰ 超过50，这是工业过程中使用的原材料中发现的值（Bolívar等人，2009）。相比之下，U 和 D 样品的 ²³⁴ U/ ²³⁰ Th 活性比分别约为 0.14 和 0.3。其他作者也报告了这些值（Rentería-Villalobos等人，2010）。

3.3. Mobility of natural radionuclides in phosphogypsum
3.3. 天然放射性核素在磷石膏中的迁移率

3.3.1. Polonium 3.3.1. 钋

The activity concentrations (expressed in Bq kg⁻¹ of PG) of ²¹⁰Po found in each liquid fraction of the BCR sequential extraction are shown in Table 1. The highest activity concentrations of polonium are found in the residual (non-mobile) fraction of both cores. At the same time, an important proportion of ²¹⁰Po (F1+F2+F3) could be mobilized to the environment depending on the weathering conditions. The water/acid soluble and exchangeable fraction (F1) shows the minimum activity concentration, especially in D core, where is 5 times smaller than in U core, which is the core with greater acidity. This seems indicate that the PG subjected to more leaching conditions in the stack (smaller pH) is more leached and therefore will present a less mobility in F1. On the other hand, polonium does not show a clear tendency for the reducible (F2), due to the activity concentration does not differ except for the first layer of the samples U1 and D1, where the activity concentration is clearly higher than in the rest of core. In addition, for oxidizable fraction (F3) shows a clear tendency in the core U (but not in D core), where the activity concentration is progressively increasing in depth (Table 1). In addition, it is noteworthy that there are only significant differences between average concentration of U-D for F1 (Z-score = 3) while for the average fractions of F2, F3 and F4 the Z-scores found were 1.7, 1.7, and 0.8, respectively.
表1显示了在BCR顺序萃取的每个液体组分中发现的 ²¹⁰ Po的活性浓度（以Bq kg ⁻¹ 的PG表示）。钋的活性浓度最高的是两个核心的残余（非移动）部分。同时，根据风化条件，很大一部分 ²¹⁰ Po（F1+F2+F3）可以被调动到环境中。水/酸溶性可交换馏分（F1）显示最低活性浓度，特别是在D核中，其小于U核的5倍，U核是酸度较高的核心。这似乎表明，在烟囱中经受更多浸出条件（pH值较小）的PG浸出率更高，因此在F1中的流动性较低。另一方面，钋没有显示出明显的可还原性（F2）趋势，因为除了样品的第一层U1和D1外，活性浓度没有差异，其中活性浓度明显高于核心的其余部分。此外，对于可氧化部分（F3）在核心U（但在D核心中没有）显示出明显的趋势，其中活性浓度在深度上逐渐增加（表1）。此外，值得注意的是，F1 的 U-D 平均浓度之间只有显着差异（Z 分数 = 3），而对于 F2、F3 和 F4 的平均分数，发现的 Z 分数分别为 1.7、1.7 和 0.8。

Table 1. Activity concentration (Bq kg ⁻¹) of ²¹⁰Po in each fraction of both cores samples.
表 1. ²¹⁰ Po在两个岩心样品的每个组分中的活性浓度（Bq kg ⁻¹ ）。

Samples 样品	F1(Bq kg−1) F1（Bq kg −1 ）	F2(Bq kg−1) F2（Bq kg −1 ）	F3(Bq kg−1) F3（Bq kg −1 ）	F4(Bq kg−1) F4（Bq kg −1 ）
U1	19 ± 1 19 ± 1	335 ± 18 335 ± 18	6 ± 2 6 ± 2	494 ± 18 494 ± 18
U2	43 ± 2 43 ± 2	97 ± 5 97 ± 5	38 ± 3 38 ± 3	391 ± 14 391 ± 14
U3	106 ± 5 106 ± 5	79 ± 6 79 ± 6	82 ± 4 82 ± 4	170 ± 12 170 ± 12
U4	23 ± 2 23 ± 2	73 ± 7 73 ± 7	74 ± 4 74 ± 4	130 ± 24 130 ± 24
U5	33 ± 2 33 ± 2	77 ± 8 77 ± 8	103 ± 5 103 ± 5	130 ± 9 130 ± 9
U6	27 ± 2 27 ± 2	94 ± 9 94 ± 9	106 ± 6 106 ± 6	180 ± 9 180 ± 9
U7	38 ± 2 38 ± 2	112 ± 28 112 ± 28	177 ± 8 177 ± 8	121 ± 11 121 ± 11
Averagea 平均 a	41 ± 11	124 ± 36	84 ± 21	231 ± 56
D1	6.1 ± 1.1 6.1 ± 1.1	111 ± 3 111 ± 3	121 ± 5 121 ± 5	368 ± 14 368 ± 14
D2	7.8 ± 1.3 7.8 ± 1.3	47 ± 2 47 ± 2	89 ± 3 89 ± 3	130 ± 7 130 ± 7
D3	3.1 ± 0.5 3.1 ± 0.5	51 ± 2 51 ± 2	142 ± 4 142 ± 4	208 ± 4 208 ± 4
D4	2.4 ± 0.4 2.4 ± 0.4	40 ± 2 40 ± 2	178 ± 5 178 ± 5	601 ± 12 601 ± 12
D5	15 ± 1 15 ± 1	66 ± 3 66 ± 3	104 ± 3 104 ± 3	249 ± 6 249 ± 6
D6	11 ± 1 11 ± 1	45 ± 2 45 ± 2	124 ± 4 124 ± 4	258 ± 6 258 ± 6
Averagea 平均 a	7.6 ± 2.0	60 ± 11	126 ± 13	302 ± 68

a

Standard uncertainty (1 σ) has been calculated as the standard deviation of the mean, σ = Sx/(n)1/2.
标准不确定度 （1 σ） 计算为均值的标准差，σ = Sx/（n）1/2。

The transfer factor TF (%) are plotted in Fig. 2. The ²¹⁰Po is distributed between fractions in both cores as follows: F4 (50%)> F3 ∼ F2 (24%)> F1 (2–9%). It is of standing out that the TF in F1 fraction is slightly higher in U core than in D core. This fact is probably related to the pH conditions, being D samples subjected to lower pH, and part of this polonium has been already released. So, the speciation of ²¹⁰Po seems to follow the same tendency in both cores with a certain dispersion, independently of the sampling point and the depth.
传递因子TF（%）如图2所示。 ²¹⁰ Po 在两个核心的分数之间分布如下：F4 （50%）>F3 ∼ F2 （24%）>F1 （2–9%）。值得注意的是，F1 部分的 TF 在 U 核中略高于 D 核。这一事实可能与pH条件有关，因为D样品经受较低的pH值，并且该钋的一部分已经释放出来。因此， ²¹⁰ Po的形态在两个岩心中似乎都遵循相同的趋势，具有一定的分散性，与采样点和深度无关。

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Fig. 2. TF (%) of ²¹⁰Po in each BCR fraction for both cores of PG samples.
图 2.PG样品的两个核心的每个BCR馏分中Po的 ²¹⁰ TF（%）。

3.3.2. Uranium 3.3.2. 铀

Table 2 shows the activity concentrations (Bq kg⁻¹) measured for uranium isotopes (²³⁴U and ²³⁸U) in each fraction from BCR procedure for the two sampling points. The total recovery (%) of U-isotopes ranges from 70 to 100%. Similar activity concentrations of ²³⁴U and ²³⁸U are found in each fraction of both cores. In residual (F4) and oxidizable (F3) fractions are found the highest activity concentrations and the lowest activity is presents in reducible (F2) fraction. It is stand out that the average activity concentration of both ²³⁴U and ²³⁸U in the four BCR fractions are not statistically different in cores U and D. Thus, the activity concentrations in U core were 12 ± 5, 10 ± 4, 31 ± 8 and 22 ± 10 Bq kg⁻¹ for F1, F2, F3 and F4 respectively for ²³⁴U while for ²³⁸U the activity concentrations were 13 ± 4, 12 ± 4, 28 ± 7 and 21 ± 9 Bq kg⁻¹, for F1, F2, F3 and F4, respectively. On the other hand, F1fraction presents major activity concentrations in D core than U core, that possibly is related to the pH condition under these samples are subjected, in which U-isotopes are more easily released into the environment.
表2显示了两个采样点的BCR程序中每个馏分中铀同位素（ ²³⁴ U和 ²³⁸ U）的活性浓度（Bq kg ⁻¹ ）。U同位素的总回收率（%）范围为70%至100%。 ²³⁴ 你和 ²³⁸ 你的活性浓度相似，存在于两个核心的每个部分。在残留 （F4） 和可氧化 （F3） 馏分中，活性浓度最高，活性最低，在还原 （F2） 馏分中。值得注意的是，U和 ²³⁸ U在四个BCR组分中的平均活性浓度 ²³⁴ 在核心U和D中没有统计学差异。因此， ²³⁴ U核中的F1、F2、F3和F4的活性浓度分别为12±5、10±4、31±8和22±10 Bq kg ⁻¹ ，而 ²³⁸ U的F1、F2、F3和F4的活性浓度分别为13±4、12±4、28±7和21±9 Bq ⁻¹ kg，F1、F2、F3和F4。另一方面，F1分数在D核中比U核中呈现出主要活性浓度，这可能与这些样品下的pH条件有关，其中U同位素更容易释放到环境中。

Table 2. Activity concentration (Bq kg ⁻¹) of ²³⁴U and ²³⁸U in each fraction of both cores samples.
表 2. ²³⁴ U和 ²³⁸ U在两个岩心样品的每个组分中的活性浓度（Bq kg ⁻¹ ）。

Empty Cell	F1(Bq kg−1) F1（Bq kg −1 ）	F2(Bq kg−1) F2（Bq kg −1 ）	F3(Bq kg−1) F3（Bq kg −1 ）	F4(Bq kg−1) F4（Bq kg −1 ）
234U
U1	37 ± 3 37 ± 3	31 ± 2 31 ± 2	46 ± 4 46 ± 4	67 ± 5 67 ± 5
U2	19 ± 2 19 ± 2	5.0 ± 1.4 5.0 ± 1.4	27 ± 3 27 ± 3	<LD
U3	4.1 ± 1.0 4.1 ± 1.0	0.14 ± 1.23 0.14 ± 1.23	2.1 ± 2.5 2.1 ± 2.5	8.6 ± 1.5 8.6 ± 1.5
U4	6.5 ± 1.6 6.5 ± 1.6	1.7 ± 1.5 1.7 ± 1.5	6 ± 2 6 ± 2	2.6 ± 1.7 2.6 ± 1.7
U5	5.1 ± 1.6 5.1 ± 1.6	14 ± 2 14 ± 2	40 ± 4 40 ± 4	7.6 ± 1.9 7.6 ± 1.9
U6	5.1 ± 1.6 5.1 ± 1.6	5.6 ± 1.5 5.6 ± 1.5	31 ± 3 31 ± 3	30 ± 6 30 ± 6
U7	5.9 ± 1.7 5.9 ± 1.7	16 ± 2 16 ± 2	63 ± 4 63 ± 4	17 ± 3 17 ± 3
Averagea 平均 a	12 ± 5	10 ± 4	31 ± 8	22 ± 10
D1	33 ± 1 33 ± 1	10 ± 1 10 ± 1	47 ± 2 47 ± 2	30 ± 2 30 ± 2
D2	26 ± 1 26 ± 1	9.9 ± 1.0 9.9 ± 1.0	30 ± 2 30 ± 2	9.2 ± 0.9 9.2 ± 0.9
D3	35 ± 1 35 ± 1	11 ± 1 11 ± 1	99 ± 5 99 ± 5	43 ± 2 43 ± 2
D4	56 ± 2 56 ± 2	9.4 ± 1.2 9.4 ± 1.2	176 ± 13 176 ± 13	195 ± 6 195 ± 6
D5	51 ± 2 51 ± 2	18 ± 1 18 ± 1	137 ± 7 137 ± 7	50 ± 6 50 ± 6
D6	20 ± 1 20 ± 1	7.7 ± 0.7 7.7 ± 0.7	77 ± 3 77 ± 3	38 ± 2 38 ± 2
Averagea 平均 a	37 ± 6	11 ± 1	94 ± 23	52 ± 27
238U
U1	34 ± 2 34 ± 2	32 ± 2 32 ± 2	41 ± 2 41 ± 2	64 ± 4 64 ± 4
U2	22 ± 2 22 ± 2	6.3 ± 1.3 6.3 ± 1.3	22 ± 2 22 ± 2	<LD
U3	4.3 ± 0.8 4.3 ± 0.8	0.36 ± 1.09 0.36 ± 1.09	4.5 ± 1.6 4.5 ± 1.6	8.3 ± 2.5 8.3 ± 2.5
U4	8.3 ± 1.4 8.3 ± 1.4	3.7 ± 1.5 3.7 ± 1.5	6.1 ± 1.1 6.1 ± 1.1	2.7 ± 1.1 2.7 ± 1.1
U5	6.6 ± 1.2 6.6 ± 1.2	15 ± 2 15 ± 2	32 ± 2 32 ± 2	7.7 ± 1.4 7.7 ± 1.4
U6	8.3 ± 1.4 8.3 ± 1.4	8.4 ± 1.5 8.4 ± 1.5	32 ± 3 32 ± 3	25 ± 2 25 ± 2
U7	7.3 ± 1.4 7.3 ± 1.4	18 ± 2 18 ± 2	56 ± 3 56 ± 3	16 ± 2 16 ± 2
Averagea 平均 a	13 ± 4	12 ± 4	28 ± 7	21 ± 9
D1	33 ± 1 33 ± 1	11 ± 1 11 ± 1	46 ± 2 46 ± 2	29 ± 1 29 ± 1
D2	25 ± 1 25 ± 1	10 ± 1 10 ± 1	28 ± 2 28 ± 2	8.4 ± 0.7 8.4 ± 0.7
D3	36 ± 2 36 ± 2	10 ± 1 10 ± 1	99 ± 5 99 ± 5	42 ± 1 42 ± 1
D4	57 ± 2 57 ± 2	8.5 ± 3.2 8.5 ± 3.2	189 ± 7 189 ± 7	191 ± 5 191 ± 5
D5	48 ± 2 48 ± 2	16 ± 1 16 ± 1	133 ± 7 133 ± 7	49 ± 2 49 ± 2
D6	20 ± 1 20 ± 1	7.2 ± 1.2 7.2 ± 1.2	77 ± 3 77 ± 3	37 ± 1 37 ± 1
Averagea 平均 a	37 ± 6	10 ± 1	95 ± 24	59 ± 27

a

Standard uncertainty (1 σ) has been calculated as the standard deviation of the mean, σ = Sx/(n)1/2.
标准不确定度 （1 σ） 计算为均值的标准差，σ = Sx/（n）1/2。

According to the TF (Fig. 3), uranium isotopes present high mobility since about 70–75% of the total concentration found in PG could be released depending on the environmental conditions, where soluble (F1: 21–26%) and oxidizable fractions (F3: 41–47%) are the most relevant. For uranium the reduction conditions are commonly associated with Eh values smaller than 300 mV. However, the more positive redox potentials observed in this study have been also previously described in other anaerobic environments with sufficient organic carbon, where there are pore-water microenvironments that are more reducing than the general solid chemistry (Church et al., 2007). Under these conditions, mainly in deeper zones, an important fraction of U contained in PG samples could be in form of U(IV), that can be oxidized to U(VI), when the conditions change from anoxic to oxic. That specie constitute the most mobile form of uranium (Lee et al., 2017; UNSCEAR, 2016). On the other hand, only 25–30% of the total is bound to the residual fraction.
根据TF（图3），铀同位素具有很高的迁移率，因为PG中发现的总浓度的约70-75%可以根据环境条件释放出来，其中可溶性（F1：21-26%）和可氧化部分（F3：41-47%）是最相关的。对于铀，还原条件通常与小于 300 mV 的 Eh 值相关。然而，在这项研究中观察到的更积极的氧化还原电位先前也在其他具有足够有机碳的厌氧环境中进行了描述，其中孔隙水微环境比一般固体化学更还原（Church等人，2007）。在这些条件下，主要是在更深的区域，PG样品中所含的U的重要部分可能以U（IV）的形式存在，当条件从缺氧变为含氧时，可以氧化成U（VI）。该物种构成了流动性最强的铀形式（Lee等人，2017;UNSCEAR，2016）。另一方面，只有 25-30% 的总数与残余部分结合。

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Fig. 3. TF (%) of ²³⁴U in each BCR fraction for both cores of PG samples.
图 3.PG 样品的两个核心的每个 BCR 组分中 U 的 ²³⁴ TF （%）。

The potential fractionation of uranium isotopes can be also tested by analysing the activity ²³⁴U/²³⁸U ratios. These activity ratios are one in all fractions taking into account the experimental uncertainties. This fact reveals that both uranium isotopes are transferred in the same way to the liquid fraction, and that the PG material has been formed recently from a dissolution since the preferential leaching mechanisms are not presented (²³⁴U does not formed from the ²³⁸U decay in the solid particles). Previous studies (Pérez-Moreno et al., 2018) have found a high ²³⁴U/²³⁸U disequilibria in fraction F1 when BCR is applied to sediments samples.
铀同位素的潜在分馏也可以通过分析活性 ²³⁴ U/ ²³⁸ U比来测试。考虑到实验的不确定性，这些活性比是所有分数中的一个。这一事实表明，两种铀同位素都以相同的方式转移到液体部分，并且PG材料是最近从溶解中形成的，因为没有出现优先浸出机制（ ²³⁴ U不是由固体颗粒中的 ²³⁸ U衰变形成的）。先前的研究（Pérez-Moreno等人，2018年）发现，当BCR应用于沉积物样品时，F1馏分的 ²³⁴ U/ ²³⁸ U不平衡很高。

3.3.3. Thorium 3.3.3. 钍

The activity concentrations (Bq kg⁻¹) of thorium isotopes (²³⁰Th and ²³²Th) for each BCR step are compiled in Table 3. The thorium isotopes are practically only detected in the residual fraction (F4) in both core samples, around 98% according the TF (Fig. 4). These results are independent of the pH, CE or Eh conditions in depth. This fact is reported by other studies (Santschi et al., 2006), which indicate that thorium has a very low mobility under most of environmental conditions mainly due to the high stability of the insoluble oxide ThO₂ and the strongly resistant nature of its carrier minerals such as monazite ((Ce, La, Th, U)PO₄) and zircon (ZrSiO₄). The results also indicate that nearly total thorium isotopes are recovered (85–100%).
每个BCR步骤的钍同位素（ ²³⁰ Th和 ²³² Th）的活性浓度（Bq kg ⁻¹ ）汇编在表3中。钍同位素实际上只在两个岩芯样品的残余部分（F4）中检测到，根据TF的数据，大约98%（图4）。这些结果与pH、CE或Eh条件无关。其他研究（Santschi等人，2006）报道了这一事实，这些研究表明，钍在大多数环境条件下具有非常低的迁移率，这主要是由于不溶性氧化物ThO ₂ 的高稳定性及其载体矿物的强抵抗性，例如独居石（（Ce，La，Th，U）PO ₄ ）和锆石（ZrSiO ₄ ）。结果还表明，几乎全部的钍同位素被回收（85-100%）。

Table 3. Activity concentration of ²³⁰Th and ²³²Th (Bq kg ⁻¹) in each fraction of both cores samples.
表 3.Th和 ²³² Th（Bq kg ⁻¹ ）在两个岩心样品的每个组分中的活性浓度 ²³⁰ 。

Empty Cell	F1(Bq kg−1) F1（Bq kg −1 ）	F2(Bq kg−1) F2（Bq kg −1 ）	F3(Bq kg−1) F3（Bq kg −1 ）	F4(Bq kg−1) F4（Bq kg −1 ）
230Th
U1	< DL	< DL	18 ± 9 18 ± 9	927 ± 27 927 ± 27
U2	< DL	1.5 ± 1.2 1.5 ± 1.2	<DL	785 ± 30 785 ± 30
U3	<DL	< DL	1.3 ± 1.2 1.3 ± 1.2	348 ± 18 348 ± 18
U4	<DL	6.0 ± 1.7 6.0 ± 1.7	4.2 ± 1.3 4.2 ± 1.3	251 ± 10 251 ± 10
U5	<DL	6.2 ± 4.0 6.2 ± 4.0	4.5 ± 1.4 4.5 ± 1.4	365 ± 15 365 ± 15
U6	<DL	5.1 ± 1.5 5.1 ± 1.5	<DL	386 ± 17 386 ± 17
U7	<DL	3.7 ± 1.2 3.7 ± 1.2	<DL	371 ± 35 371 ± 35
Averagea 平均 a	< DL	3.9 ± 0.8	7.0 ± 2.8	490 ± 97
D1	<DL	< DL	6.2 ± 1.0 6.2 ± 1.0	273 ± 10 273 ± 10
D2	< DL	< DL	9.3 ± 1.6 9.3 ± 1.6	416 ± 15 416 ± 15
D3	<DL	< DL	10 ± 1 10 ± 1	828 ± 36 828 ± 36
D4	<DL	<DL	6.8 ± 0.8 6.8 ± 0.8	1166 ± 58 1166 ± 58
D5	<DL	< DL	18 ± 1 18 ± 1	510 ± 14 510 ± 14
D6	< DL	< DL	8.2 ± 0.8 8.2 ± 0.8	430 ± 12 430 ± 12
Averagea 平均 a	< DL	< DL	9.8 ± 1.8	604 ± 135
232Th
U1	< DL	<DL	<DL	29 ± 2 29 ± 2
U2	< DL	<DL	<DL	7.2 ± 1.5 7.2 ± 1.5
U3	<DL	<DL	<DL	11 ± 2 11 ± 2
U4	<DL	<DL	<DL	10 ± 2 10 ± 2
U5	<DL	<DL	<DL	36 ± 3 36 ± 3
U6	<DL	<DL	<DL	6.3 ± 1.4 6.3 ± 1.4
U7	<DL	<DL	<DL	3.8 ± 2.7 3.8 ± 2.7
Averagea 平均 a	< DL	< DL	<DL	15 ± 5
D1	<DL	<DL	<DL	2.8 ± 0.4 2.8 ± 0.4
D2	<DL	<DL	<DL	4.1 ± 0.5 4.1 ± 0.5
D3	<DL	<DL	<DL	8.9 ± 1.0 8.9 ± 1.0
D4	<DL	<DL	<DL	11 ± 2 11 ± 2
D5	<DL	<DL	<DL	9.4 ± 0.6 9.4 ± 0.6
D6	< DL	<DL	<DL	6.5 ± 0.5 6.5 ± 0.5
Averagea 平均 a	< DL	< DL	<DL	7.1 ± 1.3

a

Standard uncertainty (1 σ) has been calculated as the standard deviation of the mean, σ = Sx/(n)1/2. DL = 1 Bq kg⁻¹.
标准不确定度 （1 σ） 计算为均值的标准差，σ = Sx/（n）1/2。DL = 1 Bq kg ⁻¹ .

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Fig. 4. TF (%) of ²³⁰Th in each BCR fraction for both cores of PG samples.
图 4.PG样品的两个核心的每个BCR馏分中Th的 ²³⁰ TF（%）。

3.3.4. Radium 3.3.4. 镭

Table 4 displays the ²²⁶Ra activity concentration in each fraction from BCR procedure for the two sampling cores. The greatest activity concentrations for PG samples are found in F4 with a mean value of around 275 Bq kg⁻¹. On the contrary, the smallest concentrations are detected in F1 (about 10 Bq kg⁻¹), being very similar the values found in both cores. On the other hand, F3 contains a higher activity concentration of radium when is compared with F2, indistinctly in all the samples.
表4显示了两个取样核心的BCR程序中每个 ²²⁶ 馏分的Ra活性浓度。PG样品的最大活性浓度在F4中，平均值约为275 Bq kg ⁻¹ 。相反，在F1中检测到的最小浓度（约10 Bq kg ⁻¹ ），与两个核心中发现的值非常相似。另一方面，与 F2 相比，F3 含有更高的镭活性浓度，在所有样品中都模糊不清。

Table 4. Activity concentration of ²²⁶Ra (Bq kg⁻¹) in each fraction of both core samples.
表 4.两种岩心样品中每个组分中 ²²⁶ Ra（Bq kg ⁻¹ ）的活性浓度。

Empty Cell	F1(Bq kg−1) F1（Bq kg −1 ）	F2(Bq kg−1) F2（Bq kg −1 ）	F3(Bq kg−1) F3（Bq kg −1 ）	F4(Bq kg−1) F4（Bq kg −1 ）
U1	14 ± 2 14 ± 2	44 ± 10 44 ± 10	59 ± 8 59 ± 8	291 ± 55 291 ± 55
U2	6.5 ± 1.1 6.5 ± 1.1	24 ± 5 24 ± 5	71 ± 4 71 ± 4	383 ± 64 383 ± 64
U3	3.5 ± 0.7 3.5 ± 0.7	19 ± 4 19 ± 4	69 ± 8 69 ± 8	304 ± 37 304 ± 37
U4	5.1 ± 1.2 5.1 ± 1.2	7.1 ± 4.6 7.1 ± 4.6	39 ± 6 39 ± 6	298 ± 30 298 ± 30
U5	6.7 ± 2.1 6.7 ± 2.1	22 ± 3 22 ± 3	73 ± 9 73 ± 9	167 ± 22 167 ± 22
U6	8.9 ± 1.8 8.9 ± 1.8	4.6 ± 2.8 4.6 ± 2.8	57 ± 14 57 ± 14	188 ± 15 188 ± 15
U7	11 ± 5 11 ± 5	17 ± 3 17 ± 3	138 ± 19 138 ± 19	207 ± 10 207 ± 10
Averagea 平均 a	8.0 ± 1.4	20 ± 5	72 ± 12	263 ± 29
D1	13 ± 2 13 ± 2	45 ± 4 45 ± 4	257 ± 20 257 ± 20	135 ± 13 135 ± 13
D2	7.2 ± 0.8 7.2 ± 0.8	32 ± 2 32 ± 2	224 ± 17 224 ± 17	79 ± 10 79 ± 10
D3	4.8 ± 0.8 4.8 ± 0.8	46 ± 6 46 ± 6	68 ± 6 68 ± 6	481 ± 26 481 ± 26
D4	2.9 ± 0.7 2.9 ± 0.7	33 ± 3 33 ± 3	80 ± 11 80 ± 11	679 ± 38 679 ± 38
D5	13 ± 2 13 ± 2	56 ± 4 56 ± 4	212 ± 33 212 ± 33	179 ± 8 179 ± 8
D6	11 ± 1 11 ± 1	62 ± 7 62 ± 7	192 ± 51 192 ± 51	175 ± 8 175 ± 8
Averagea 平均 a	8.7 ± 1.8	46 ± 5	172 ± 32	288 ± 97

a

Standard uncertainty (1 σ) has been calculated as the standard deviation of the mean, σ = Sx/(n)1/2.
标准不确定度 （1 σ） 计算为均值的标准差，σ = Sx/（n）1/2。

Concerning the TF (Fig. 5), both cores follow the same tendency, but the D core displays more homogeneity in the fraction distribution. All samples are characterised by a high percentage in the non-mobile fraction, being the mobile fraction around 30–50% of total radium contained in the PG.
关于TF（图5），两个核心都遵循相同的趋势，但D核心在分数分布中显示出更多的均匀性。所有样品的特点是非移动镭的百分比很高，即PG中所含镭总镭的30-50%左右的移动馏分。

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Fig. 5. TF (%) of ²²⁶Ra in each BCR fraction for both cores of PG samples.
图 5.PG样品的两个核心的每个BCR馏分中 ²²⁶ Ra的TF（%）。

3.4. Waters from disposal area
3.4. 处置区的水