我国降水中129I形态的时空分布及其示踪研究

Precipitation is the important pathway for iodine transfer from the atmosphere to the terrestrial environment. It is critical to investigate the sources of iodine in the precipitation, especially the contribution of marine derived iodine, and parameters effecting its sources and variation, in order to understand the sources, level and distribution of iodine in the terrestrial environment, and its effect to the human health. It has been observed that 129I/127I isotopic ratio of seawater around China is about 1-2 orders of magnitude lower than that in the surface environmental samples in the terrestrial area in China. The difference of 129I/127I isotopic ratios between the seawater samples and the terrestrial samples could be used to distinguish iodine with different source. Using 129I to trace variation of the source of iodine in the precipitation from the coastal area to the inland is a new method for understanding the transfer process of iodine from the sea to the inland. Studies on the precipitation process of iodine using 129I, and reconstruct of the distribution and level of accident released 131I in the environment, which will also be useful for evaluation of the radiation impact of 131I in the nuclear accident. This work aims to analyze species of 129I and 127I in precipitate collected in some locations with different distance to the sea, as well as seawater around China, surface water in the terrestrial area and dry deposit samples collected in the same location as precipitation, the deposition rate of 129I and 127I in different locations and its variation will be investigated. Meanwhile, the deposition model of 127I and 129I will be evaluated. The contribution of marine derived iodine in the precipitation in different location will be investigated using the 129I/127I ratios measured in these samples. The variation of the concentration of 129I in precipitation samples collected in Xi’an after the Fukushima nuclear accident will be analyzed, and the 131I concentration in the precipitation collected in the same period will be reconstructed using the 129I tracing method.

降水是碘从大气沉降至地表的主要方式，弄清降水中碘的来源，特别是海洋碘的贡献，及其影响因素和变化规律，有助于认识内陆环境中碘的来源、水平和分布，这一与人体健康密切相关的问题。我国沿海海水129I/127I同位素比值比内陆低1~2个量级，可以作为海洋碘的特征信息。用129I示踪由沿海至内陆降水中碘来源的变化，可从新的角度认识碘由海洋向陆地的传输过程。通过129I研究碘的大气沉降方式，重建核事故发生时环境中131I的含量和分布，可为评估核事故131I的环境影响提供基础数据。本研究通过对我国距海洋不同距离采样点的降水与沿海海水、地表水、干沉降样品的总碘及不同形态碘的127I和129I浓度分析，研究不同地区降水中127I及129I的沉降通量的变化规律，评估127I和129I沉降方式，通过129I/127I比值分析，估算不同地区降水中海洋碘的贡献。分析福岛事故后西安降水129I变化，重建131I水平。

碘是一种重要的营养元素，碘的地球化学行为与人类健康密切相关，因此，碘在环境中的分布、来源和循环的研究是十分重要的。降水是碘循环中大气—地表传输过程的重要方式。降水中的碘的来源是什么？传输方式是以干沉降为主还是湿沉降为主？福岛事故对我国降水中碘同位素组成产生了什么影响？我国地表水的碘同位素是否存在地区差异？这些问题对于理解碘从大气向地表的传输过程和地表碘的来源具有重要意义。.通过对2008年4月至10月西安降水、2011年2月至7月西安降水、2017年7月至2018年6月我国四个采样点（西安、晋中、合肥、广州）连续月沉降样品碘同位素的分析，西安采样点连续两年干、湿沉降样品127I单位面积沉降量的分析，以及降水与沿海海水、地表水等内陆样品中129I/127I比值综合分析，获得了从沿海向内陆连续一年127I、129I月沉降通量的数据，距离海洋最近的采样点，具有最高的127I沉降通量和最低的129I/127I比值，增进了对不同区域碘同位素变化特征与影响因素的认识，为认识海洋来源的碘通过大气运动、降水对陆地的直接影响范围这一问题提供了科学数据。距离海洋最近的采样点，海洋来源碘所占份额高，同时具有高于本地129I/127I比值的远距离陆地来源碘的输入。根据129I/127I比值信息，推测西安地区的海洋来源的碘所占份额远低于沿海地区。湿沉降是碘从大气向地表传输的主要方式。福岛核事故释放的129I对2011年西安降水的影响较小。