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New 129I record of Human Nuclear Activities at Low Latitude: Significance for the Influence and Transport of Radioactive Substance
author: source: Time:2017-12-29 font< big medium small >

Human nuclear activities (HNA) never stop nor decrease in recent years, for example, construction of nuclear power plants, and operation of nuclear fuel reprocessing facilities. Understanding of the impact of these nuclear activities, therefore, is quite vital for environmental radioactivity and human healthy.

129I, the longest half-life iodine isotope, is a great tracer to record the nuclear activities. However, 129I records, at present, mainly focus on the middle and high latitudes of Northern Hemisphere, and only a few data can be found at low latitudes, in particular lacking in terrestrial environment.

In collaboration with scientists from National Taiwan University and University of California, a research team led by Dr. HOU Xiaolin from the Institute of Earth Environment (IEE) of the Chinese Academy of Sciences, recently presented a clear record of human nuclear activities at low latitude by analyzing 129I and 127I in Taal Lake sediment core from Philippines.

Integrating variation of iodine isotopes in the core with human nuclear history, this study, for the first time, showed three distinct 129I depositional periods at low latitude:
(1) A pre-nuclear period indicated by the lowest 129I/127I ratio, provided a baseline to evaluate the influence of HNAs;
(2) A period dominant with atmospheric nuclear weapons testing, mainly those at the Pacific Proving Ground, Marshall Islands, identified by first increase of 129I/127I ratios in early 1960s.
(3) A period controlled by discharge from nuclear fuel reprocessing plants with the feature of consistent fluctuations with gaseous releases and continuous increased with re-emission from seawater contaminated by liquid release.

Meteorological and model analysis indicate that the northeasterly trade and East Asian winter monsoon play significant roles for transport of gaseous radioactive substance from the Pacific Proving Ground during the second period and from nuclear fuel reprocessing facilities during the third period.

Besides, the study firstly suggested that iodine isotopes could be potential used as a tracer for volcanic eruptions. And the study extended 129I records from high-middle to low latitudes, from marine to terrestrial environment, firstly gave a quantative impact of HNAs, and pointed out the sources and transport pathways of radioactive materials in modern environment of Southeast Asia. Also, this study was of great significance for studying dispersion of other volatile gaseous pollutants by advantage of 129I.

This work was published in Chemosphere.

Fig.1 Geographic location of Lake Taal (Philippines), source of nuclear activities and transportation pathways (Image by Zhang et.al)

 Fig.2 Concentrations of 127I and 129I, and 129I/127I atomic ratio in the sediment (Image by Zhang et.al)

Contact: ZHANG Luyuan, State Key Laboratory of Loess and Quaternary Geology, Xi'an AMS Center, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, 710061, China. Email:zhangly@ieecas.cn

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