近海主要天然与人工放射性核素的吸附与迁移研究

Adsorption and Migration Studies of Major Natural and Artificial Radionuclides in Offshore

  • 摘要: 为科学评估近海环境的辐射风险,有必要深化对放射性核素在近海环境中的吸附和迁移行为的研究与认识。本文在分析渤海北部沉积物中主要天然和人工放射性核素含量和分布特征的基础上,解析其关键影响因素,并通过固液分配系数分析量化放射性核素在中国近海不同海域的迁移扩散能力,进而初步评估近海辐射风险。结果表明:1) 在物理/化学吸附作用的影响下,沉积物细颗粒含量和有机碳(TOC)含量均与放射性核素含量存在明显的正相关关系;2) 不同放射性核素在中国近海的迁移扩散能力不同(迁移扩散能力大小顺序为40K>137Cs>226Ra>232Th),同一核素在不同海域的迁移扩散能力也存在差异(对于226Ra,海域的扩散能力由强到弱顺序为渤海>黄海>南海>东海,对于137Cs,该顺序为渤海>南海>黄海);3) 中国近海鱼类的辐射风险整体较低(总风险系数<1),但渤海底栖鱼类相对较高的226Ra辐射风险仍需警惕(风险系数为其他近海海域鱼类的2~4倍);4) 采用实测数据评估所得的辐射风险系数往往高于依据ERICA内置参数模拟评估的结果(226Ra的评估结果相差1~6倍)。综上可见,近海环境复杂多变,放射性核素的迁移扩散能力与辐射风险评估尚存在不确定性,有待深入研究。

     

    Abstract: In order to scientifically assess the radiation risk in the offshore environment, it is necessary to deepen the research and understanding of the adsorption and transport behaviors of radionuclides in the offshore environment. In this paper the content and distribution characteristics of the major natural and artificial radionuclides 238U, 226Ra, 210Pb, 40K and 137Cs in the sediments of the Northern Bohai Sea were researched, and the key factors affecting them were analyzed. After systematically organizing the data on radionuclide contents of sediments and seawater in the Chinese offshore, the migration and diffusion capacities of 238U, 232Th, 226Ra, 40K and 137Cs in different areas of the Chinese offshore were quantified by analyzing sediment distribution coefficients (Kd, the lower of Kd, the greater the capacity for migration and diffusion), and then the radiation risks of 238U, 232Th, 226Ra, 210Pb and 137Cs to pelagic and benthic fish in the Chinese coastal waters were preliminarily evaluated by using ERICA software based on the statistical method of measured data and built-in parameter simulation method. The results show that sediment grain size and organic carbon content are the key factors affecting the adsorption/desorption process of radionuclides in sediments. Under the influence of physical/chemical adsorption, both sediment particle size and organic carbon content are well correlated with radionuclide content, and the correlation is particularly significant for 210Pb, which has a high particle activity. Different radionuclides have different migration and diffusion capabilities of Chinese offshore (40K (Kd=7.8×102 L/kg)>137Cs (Kd=9.8×102 L/kg)>226Ra (Kd=2.3×103 L/kg)>232Th (Kd=4.3×103 L/kg)), there are also differences in the migration and diffusion behavior of the same nuclide in different sea areas (for 226Ra, Bohai Sea (Kd=1.1×103 L/kg)>Yellow Sea (Kd=2.9×103 L/kg)>South China Sea (Kd=3.1×103 L/kg)>East China Sea (Kd=4.4×103 L/kg), for 137Cs, Bohai Sea (Kd=4.7×102 L/kg)>South China Sea (Kd=7.9×102 L/kg)>Yellow Sea (Kd=1.5×103 L/kg)), although the overall radiation risk to Chinese offshore fish is low (total risk quotient<1), the relatively high radiation risk of 226Ra for benthic fish in the Bohai Sea still requires vigilance (risk quotient 2 to 4 times that of other offshore fish species); radiation risk quotients assessed using measured data tend to be higher than those from ERICA’s built-in parametric simulations (assessment results of 226Ra vary by a factor of 1 to 6). To summarize, the offshore environment is complex and variable, and there are uncertainties in the migration and diffusion capacities of radionuclides and the assessment of radiation risk, which need to be studied in depth. In the future, when assessing the radiation risk of the offshore environment, the specific conditions of the actual environment should be taken into account, and the measured data should be used as much as possible to enhance the scientific and objective nature of the assessment conclusions.

     

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