Trace Application Of Long-lived Radionuclides ^239,240Pu And ¹²⁹I In The Environment

239,240 Pu and 129 I are the most important long-lived radionuclides. Although the sources of them are quite similar, including atomospheric nuclear weapon tests and nuclear fuel reprocessing facilities, their environmental behaviors are totally different because of their different chemical properties. 239,240 Pu and 129 I have been used for the assessment of impact of human nuclear activities to the environment. Due to high radiation and biological toxicity, 239,240 Pu is one of the most important radionuclides for the assessment of environmental radiation and hazard, and used to distinguish their sources and reconstruct their deposition level and environmental and health impact of previous nuclear activities. Due to high volatility, water solubility and enrichment of iodine in the thyroid, 129 I in the environment not only can be used to reconstruct the high dose short-lived 131 I level and assess its impact to human health, but also to identify the sources of water mass in ocean, to study the exchange and interaction between water masses from different sources.This work developed a series of methods for determination of plutonium isotopes in Chinese soil, speciation analysis of 129 I in seawater and in low level precipitation in the Antarctica. These methods were successfully used to investigate the level, distribution and sources of 239,240 Pu in all over China, and to identify the sources of 129 I in the Antarctica. It is also used for investigation of water mass exchange in the Antarctica by using 129 I and its species. The major achievement are summarized below:1. The distribution of 239,240 Pu in surface soil in China shows a significantly spatial difference between the high latitude(40°N-50°N) and mid-low latitude(20°N-40°N). The concentration of 239,240 Pu of surface soil in the surrounding area of the Lop Nor nuclear weapon test site and its downwind area ranged from 0.03 m Bq/g to 2.26 m Bq/g. The highest concentration of 239,240Pu(2.36 m Bq/g and 2.66 m Bq/g) observed in the Yumen, Gansu province is probably the results of operations of local nuclear facilities. The concentration of 239,240 Pu in the other areas of China including northwest, northeast, central China, east China, south China and southwest, ranged from 0.01 m Bq/g to 0.64 m Bq/g. Comparing with those observed in area of similar latitude, the level of 239,240 Pu in China fall into the global background level. The climate, geographical, soil types and human activities are major reason causing the different 239,240 Pu level observed in the Chinses surface soil.240Pu/239 Pu atomic ratios in the surface and depth profile of soil in the surrounding area of the Lop Nor nuclear test site in Xinjiang ranged from 0.18 to 0.21 with the average of 0.19±0.01, which was close to the global fallout ratio, indicating no significant close-in fallout in the Lop Nor nuclear test site. However, the 240Pu/239 Pu atomic ratios in two surface soil samples collected from Yumen, Gansu province, were agree with that of the nuclear weapon grade plutonium, might contribute to a local sources of Pu isotopes besides atmospheric nunclear test fallout. 240Pu/239 Pu atomic ratios in the soil from other areas in China including northwest, northeast, central China, east China, south China and southwest are 0.19±0.03, 0.19±0.02, 0.18±0.02, 0.19±0.02 and 0.18±0.01, respectively, which are agreed with global fallout level. It might imply that the main source of Pu in most of China is the fallout of global atmospheric nuclear weapon tests.2. 129 I concentration and 129I/127 I atomic ratios in snow samples from different loaction in the Antarctic are quite similar, ranging from 2.0×106 atoms/L to 7.6 ×106 atoms/L and 6.8×10-10 to 9.5×10-10 respectively. Compared to the 129 I level in other locations, the lowest 129 I level(129I concentration and 129I/127 I atomic ratio) occurs in the Antarctic region. 129 I in the Antarctic snow mainly originated from the atmospheric nuclear weapons testing in 1945-1980, re-suspension and re-emission of the fallout 129 I in the South Hemisphere kept the 129 I level in the Antarctic atmosphere.3. The concentrations of 129 I and 129I/127 I atomic ratios of surface seawater in the Antarctica ranged from(0.90-3.56) ×106 atoms/L and(0.56-1.98) ×10-11 respectively. The concentrations of 129 I and 129I/127 I atomic ratios in the depth profile of the Antarticseawater ranged from(0.09-4.59) ×106 atoms/L and(0.34-2.82) ×10-11 respectively. 129I/127 I atomic ratios in the Antarctic seawater were significantly higher than the pre-anthropogenic 129I/127 I level(1.5 ×10-12), indicating that the 129 I released from human nuclear activities has reached in the Antarctica and the main source of 129 I is the fallout of global atmospheric nuclear weapon tests in 1945-1980.Seawater samples collected in the Drake passage, Bellingshausen sea, Amundsen sea and Ross Seas were analyzed for iodine isotopes(129I and 127I) and their species(iodide and iodate). The results showed that 129I-/129IO3- concentration ratios in open sea in the eastern Amundsen sea were similar with those in the weatern Amundsen sea, indicating that iodine isotopes are under equilibrium. Because the main source of 129 I is global nuclear weapon tests fallout, the species of 129 I and 127 I tended to be uniform through long-time exchange and geochemical transformation. The values of 129I-/129IO3- and 127I-/127IO3- in coastal area varies in a large range in the eastern Amundsen sea,indicating that reduction of iodate and oxidation of iodide in the coastal area is relatively fast. However, iodine species transformation is an extreme slow process in Drake passage, Bellingshausen sea, central Amundsen sea and Ross Seas.