Abstract

The characterization of naturally occurring radionuclides in seawater and seafloor surface sediments is necessary to assess marine environmental characteristics and their direct impact on marine ecosystems and indirect impacts on human health.

The coast of Thanh Hoa, Vietnam is known for many mines and titanium ore points and is a key economic region in the coastal estuarine area. This study determined the concentration of naturally occurring radionuclides (210Po, 210Pb, 226Ra, 234U and 238U) in seawater and (226Ra, 228Ra (232Th) and 40K) surface sediments at stations with sampling depths varying from 0-30m of seawater.

In this study, twenty-three samples of seabed sediment at the coast of Thanh Hoa, Vietnam were collected and measured using a high-purity germanium detector (HPGe). The average activity of 226Ra, 228Ra (232Th) and 40K is 30.3±1.94, 53.3±2.98 and 673±38.5 Bq.kg-1, respectively. There is a strong correlation between those radionuclides and withe silt and clay, which suggests that these radionuclides may be of similar material origin. The particle size of seabed sediments in the study area has a significant effect on natural radioactive nuclear activities and spatial distribution.

Naturally occurring radionuclei (210Po, 210Pb, 226Ra, 234U, and 238U) in seawater were various in difference sampling stations, and seawater depths which were observed 0.77, 0.78, 9.09, 49.8, and 54.3 mBq L-1, respectively. The results showed an disequilibrium between 210Po and 210Pb and that the 210Po/210Pb ratios differed in depth. High 226Ra, 234U, and 238U activities may be associated with titanium deposits along coastal, estuarine sediment sources. There is a relationship between 226Ra and 210Pb operations with sampling depth, distance from shore, while it is negligible recorded for 210Po, 234U, and 238U.

The spatial distribution is divided into two regions, in which the estuarine (near-shore) area has higher radionuclide activity than the offshore zone. The results support the conclusion that the origin of sedimentary material is related to estuaries and transported from land sources.