Rn, Pb and Po in coastal zone groundwater: Activities, geochemical behaviors, consideration of seawater intrusion effect, and the potential radiation human-health risk.

Groundwater quality in human-influenced coastal landscapes is receiving novel attention. Radionuclides have been recognized as another important monitoring indicator in many developed countries due to the discovery of extremely high level of natural Po (up to 10,000 Bq/m) and radium and radon isotopes. This study aims to evaluate the groundwater quality in the Beibu Bulf-Guangxi coast from radiological point of view. Po, Pb and Rn activities in 20 wells ranged from 0.24 ± 0.05 to 6.96 ± 1.62 Bq/m, 2.17 ± 0.12 to 13.08 ± 0.74 Bq/m and 1500 ± 200 to 31,800 ± 900 Bq/m, respectively. Compared with research data of other countries, groundwaters in this area have Po, Pb and Rn activity within low levels. The large deficiencies of Po and Pb relative to Rn in groundwaters implied that Po and Pb are strong particle-reactive radionuclides and they might be controlled by similar scavenging processes in groundwaters due to a good positive correlation between Pb and Po (R = 0.67, p < 0.01). The concentrations of Po and Pb decreased with increasing pH values and salinity, which indicated that geochemical behaviors of Po and Pb in groundwater were influenced by seawater intrusion and pH changing. Groundwater Rn activity concentrations decreased with increasing salinity in coastal zone, which may be caused by dilution due to seawater intrusion or intensified Rn escaping from well-developed pores in coastal zone. The estimated annual ingestion doses for infants, children and adults were well below the recommended reference dose level (RDL) of 0.2-0.8 mSv/a, suggesting that consumption of analyzed groundwaters is safe from radiological point of view.