222Rn, 210Pb and 210Po in coastal zone groundwater: Activities, geochemical behaviors, consideration of seawater intrusion effect, and the potential radiation human-health risk

Abstract

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 210Po (up to 10,000 Bq/m3) and radium and radon isotopes. This study aims to evaluate the groundwater quality in the Beibu Bulf-Guangxi coast from radiological point of view. 210Po, 210Pb and 222Rn activities in 20 wells ranged from 0.24 ± 0.05 to 6.96 ± 1.62 Bq/m3, 2.17 ± 0.12 to 13.08 ± 0.74 Bq/m3 and 1500 ± 200 to 31,800 ± 900 Bq/m3, respectively. Compared with research data of other countries, groundwaters in this area have 210Po, 210Pb and 222Rn activity within low levels. The large deficiencies of 210Po and 210Pb relative to 222Rn in groundwaters implied that 210Po and 210Pb are strong particle-reactive radionuclides and they might be controlled by similar scavenging processes in groundwaters due to a good positive correlation between 210Pb and 210Po (R2 = 0.67, p < 0.01). The concentrations of 210Po and 210Pb decreased with increasing pH values and salinity, which indicated that geochemical behaviors of 210Po and 210Pb in groundwater were influenced by seawater intrusion and pH changing. Groundwater 222Rn activity concentrations decreased with increasing salinity in coastal zone, which may be caused by dilution due to seawater intrusion or intensified 222Rn 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.