||Po-210 and Pb-210 are particle-reactive natural radionuclides which can be removed from seawater by their incorporation with various particulate materials, resulting in radioactive disequilibria with respect to their parent nuclides. Previous studies showed that Po-210/Pb-210 activity ratio in surface seawater ranges from about 0.2 to 1 due to atmospheric input of Pb-210 and effects of biological productivity and upwelling. In order to evaluate the effects of plankton on Po-210 and Pb-210 distributions, plankton samples were collected by surface-trawling of plankton net in Taiwanese water. These plankton samples were analyzed for Po-210 and Pb-210 in order to obtain their concentrations and activity ratio, which may indicate the enrichment or discrimination of these nuclides in the marine planktonic phase around Taiwan. |
The results show that the Po-210/Pb-210 activity ratio of planktonic samples ranges from 23.06 to 51.40 in northeastern Taiwan, whereas the activity ratio in southwest Taiwan varies within and outside of the sampleing locations: stations 1, 2, 3 and 4 yield range of 10.72-43.90, 16.40-47.87, 13.86-23.37 and 9.35-13.82, respectively. Two marine algae (Sargassum polycystum C.Agardh and Hypnea charoides Lamouroux) yield values of 2.24-8.57, and 3.72-5.96, respectively. These Po-210/Pb-210 activity ratios are much greater than unity, and their activities comparison to those of inorganic particulates support the contention that the plankton preferentially incorporates Po-210 but discriminates against Pb-210. However, the mechanism or process of Po-210 to be incorporated in the plankton remains unclear. In comparison of the activities between Po-210 and Pb-210 in organic particulates, one finds that Po-210 is effectively enriched while Pb-210 is clearly discriminatied by the organic particulates. These results are consistent with those reported in literatures.