Lee R T, Shaw G, Wadey P, Wang X
Department of Radiation Protection, Atomic Energy Council, Taipei, Taiwan, ROC.
Chemosphere. 2001 Jun;43(8):1063-70. doi: 10.1016/s0045-6535(00)00204-6.
Soils initially contaminated with 36Cl in the chloride form were subjected to solid-liquid extractions using a variety of reagents including deionised water and 1 M sodium hydroxide (NaOH). 1 M NaOH was found to result in the greatest recovery of 36Cl from the soils, a result which provided initial evidence that radioactive chlorine became attached to humic substances present naturally within the soils. Deionised water and 1 M NaOH extracts were subjected to analysis involving separation by gel filtration chromatography (GFC). It was found that 36Cl in 1 M NaOH extracts associated preferentially with low molecular weight (LMW) fractions of humic substances whereas, in deionised water extracts, 36Cl appeared to be present exclusively in the chloride form. Previous literature evidence, mainly from highly organic forest soils, suggests that conversion of stable chlorine from chloride to organic forms can occur as a result of biological action. The present paper also presents good evidence for the specific attachment of stable chlorine (37Cl) to a LMW humic fraction, again demonstrated using GFC separation. Current risk assessments of the deep geological disposal of solid radioactive wastes containing 36Cl typically assume a very low degree of sorption based on the notion that the predominant environmental species of radiochlorine is chloride. This paper concludes with a brief discussion on the implications of organochlorine formation in the biosphere for assessment of the radiological impact of deep geological disposal of solid radioactive wastes.
最初被氯化物形式的³⁶Cl污染的土壤，使用包括去离子水和1M氢氧化钠（NaOH）在内的多种试剂进行固液萃取。结果发现，1M NaOH能从土壤中萃取出最多的³⁶Cl，这一结果初步证明放射性氯与土壤中天然存在的腐殖质结合。对去离子水和1M NaOH提取物进行了包括凝胶过滤色谱法（GFC）分离在内的分析。结果发现，1M NaOH提取物中的³⁶Cl优先与腐殖质的低分子量（LMW）部分结合，而在去离子水提取物中，³⁶Cl似乎仅以氯化物形式存在。先前的文献证据（主要来自高有机含量的森林土壤）表明，由于生物作用，稳定氯可从氯化物形式转化为有机形式。本文还提供了有力证据，证明稳定氯（³⁷Cl）也能特异性结合到低分子量腐殖质部分，同样通过GFC分离得到证明。目前对含有³⁶Cl的固体放射性废物进行深部地质处置的风险评估，通常基于放射性氯在环境中的主要形态是氯化物这一观念，假定吸附程度非常低。本文最后简要讨论了生物圈中有机氯形成对评估固体放射性废物深部地质处置的辐射影响的意义。
