AMS measurements of ¹⁴C and ¹²⁹I in seawater around radioactive waste dump sites

According to a recent IAEA compilation of inventories of radioactive wastes dumped in the world ocean, a total of 85 PBq of radioactive wastes were dumped, in the Atlantic (45 PBq), the Pacific (1.4 PBq) and the Arctic (38 PBq) Oceans and their marginal seas between 1946 and 1993, mostly in the form of low-level wastes. ³H and ¹⁴C formed an important part of the beta-activity of these dumped wastes. Because of its long half-life, ¹⁴C will be the main constituent in possible leakages from the wastes in the future. On the other hand, ¹⁴C and ¹²⁹I are important radioactive tracers which have been artificially introduced into the oceans. Small amounts of ¹⁴C and ¹²⁹I can be easily measured by accelerator mass spectrometry (AMS) on mg-size samples of carbon and iodine extracted from 500 ml seawater samples. The high analytical sensitivity enables one therefore to find even trace amounts of ¹⁴C and ¹²⁹I which could be released from radioactive wastes, and to compare the measured levels with the global distribution of these radionuclides. The IAEAs Marine Environment Laboratory (IAEA-MEL) has been engaged in an assessment program related to radioactive waste dumping in the oceans since 1992 and has participated in several expeditions to the Atlantic, Arctic, Indian and Pacific Oceans to sample seawater, biota and sediment for radiological assessment studies. In the present paper, we report on methods of ¹⁴C and ¹²⁹I measurements in seawater by AMS and present data on the NE Atlantic, the Arctic and the NW Pacific Ocean dumping sites. A small increase of ¹⁴C was observed at the NE Atlantic dumping site.