西藏拉萨河232Th分布特征与所致内照射剂量分析

利用拉萨河中下游和堆龙曲支流16个采样点水样,采用ICP-MS测量水样中的²³²Th含量,获得了研究区水体中²³²Th分布特征与所致内照射剂量。结果表明,拉萨河水体中²³²Th含量低于全国地表水平均含量和世卫组织规定的饮用水标准,但高于长江流域诸河与额尔齐斯河。²³²Th含量在中游沿程先降后升,在下游波动变化,在堆龙曲支流沿程下降,同时²³²Th含量随纬度的增大和经度的减小而上升。²³²Th与Cl^-有一定的同源性,与Ca²⁺、Mg²⁺、SO₄^2-、HCO₃^-及TDS有一定的异源性,说明拉萨河周边碎屑岩颗粒在高温高压、风化等作用下由补给水流向河流输送了²³²Th和Cl^-。拉萨河流域居民由饮水途径所摄入的放射性核素²³²Th所致的内照射待累积剂量当量平均值低于世卫组织推荐的参考值,说明拉萨河河水的放射性水平是安全的,不会对饮用拉萨河河水的居民和动物造成健康危害。

Distribution Characteristics and Induced Internal Radiation Dose of 232Th in Lhasa River, Tibet

Contents of 232Th in water samples from 16 sampling points in the middle and lower reaches of Lhasa River and Duilongqu tributary were measured by ICP-MS, and distribution characteristics and induced internal radiation dose of 232Th in the water of the study area were obtained. The results show that content of 232Th in the water body of Lhasa River is lower than the average content of the national surface level and the drinking water standard stipulated by WHO, but higher than that of the rivers in the Yangtze River Basin and Irtysh river. 232Th content drops firstly and then rises along the middle reaches, fluctuates and changes in the downstream, decreases along the Duilongqu tributary, and rises with the increase of latitude and the decrease of longitude. 232Th has some homology with Cl- and some heterogeneity with Ca2+, Mg2+, SO42-, HCO3- and TDS, indicating that clastic rock particles around Lhasa River have transported 232Th and Cl- from the make-up water to the river under the action of high temperature, high pressure and weathering. The average cumulative dose equivalent of internal exposure caused by radionuclide 232Th ingested by residents in Lhasa River Basin is lower than the reference value recommended by WHO, indicating that the radioactivity level of Lhasa River is safe and will not cause health hazards to residents and animals drinking water from Lhasa River.