Characterizing 226Ra and its daughters in coastal zone groundwater of a typical human-activity affected bay: occurrence, safety, and source evaluation

作者：Zhou, Wenqing; Wang, Hao; Zhong, Qiangqiang^*; Shao, Yi; Zhou, Da; Yu, Xueqing

来源：Environmental Science and Pollution Research, 2024, 31(6): 8703-8718.

DOI：10.1007/s11356-023-31784-y

• Coastal zone groundwater
• Po-210-Pb-210 disequilibrium
• Pb-210-Rn-222 disequilibrium
• Radiation risk
• Radionuclide transport pathway

Due to their extremely toxic properties, Ra-226 and it daughters (Rn-222, Pb-210, and Po-210) in drinking groundwater require monitoring. Recent studies have reported exceptionally high levels of natural Po-210 (up to 10,000 Bq/m(3)), Ra-226, and Rn-222 isotopes in groundwater. This study aims to provide background data on Ra-226 and its daughter radionuclides in the typical agricultural-industrial Dongshan Bay (DSB) before the construction of Zhangzhou Nuclear Power Plant (Zhangzhou NPP). The measurement results indicate that no abnormally high activities of Po-210 and Pb-210 were detected in the investigated wells. Strong positive correlations between Pb-210 and Po-210, as well as between Rn-222 and Pb-210 activities, suggest that the origins of Pb-210 and Po-210 in groundwater are strongly influenced by the decay of the parent radionuclides Rn-222 and Pb-210, respectively. In the DSB coastal zone groundwater, significant deficiencies of Po-210 relative to Pb-210 and Pb-210 relative to Rn-222 were observed, providing further evidence that Po-210 and Pb-210 are also effectively scavenged due to their geochemical properties (specifically particle affinity) within the groundwater-aquifer system. A systematic comparison among all relevant water bodies in the DSB revealed that the activity concentrations of Pb-210 and Po-210 in groundwater were the highest, except for rainwater. Based on the evaluation of Pb-210 sources, the results imply that submarine groundwater discharge (SGD) is an important pathway for transferring radionuclides (such as Pb-210) from land to the nearshore marine environment, even though the study area has a lower Pb-210 background groundwater. By considering all the Pb-210's sources in the DSB, we found low Pb-210 background groundwater discharge still needs to be taken into account for small-scale bays. This is because SGD was calculated to be one of the most important Pb-210 sources in the bay during observation season. Regardless of whether the system is in a normal state or a nuclear accident emergency state, greater attention should be paid to the groundwater discharge of radionuclides into the ocean.