铀、钍在尾矿-定居植物体系中的迁移

The Migration of U and Th in the Tailings-plants System

通过BCR(community bureau of reference)提取和富集系数、转移系数计算,对铀、钍在铀尾矿-植物体系中的迁移进行了研究。尾矿中U、Th的总量达205 mg/kg、141mg/kg,但其生物有效性较低,其酸溶态和可还原态的U仅占10.5%和10.8%、Th仅占0.9%和2.8%,而残渣态U占67.7%、Th占92.1%。库区三种优势植物的各部位U、Th含量高出背景区对照值的10倍以上,明显超过了《食品中放射性物质限制浓度标准》中植物类食品的限制浓度。由于植物生长介质中仅生物有效部分的重金属能为植物所积累,因而本文提出应以富集系数BF*(等于植物中重金属含量/其生长介质中相应重金属的生物有效态含量的比值)来衡量植物对重金属的富集程度。尾矿的风化程度较弱及其U、Th生物有效性较低,植物各位U、Th的BF*均较小,三种植物对U、Th的富集程度均较低,但对钍的富集能力明显强于铀。可能受菌根对重金属的强积累能力的影响,U、Th主要富集于植物的根部,向地上部分茎、叶的转移量相对较低。目前,库区尾矿中U、Th在植物中的富集虽然不是很强,但随植物定居时间的增加,尾矿中放射性核素的生物有效性及向库区植物中迁移的能力呈增强的趋势,环境风险将逐渐增高,应引起环境管理部门的足够关注。

This paper studied the migration of U and Th in the tailings-plants system through BCR extracting and calculation of concentration and translocation coefficient. The total U and Th contents of railings are 205 mg/kg and 141mg/kg, respectively, hut their biological effectiveness decreased, acid soluble state and reducible U only account for 10.5 % and 10.8 %, and 0.9 % and 2.8% for Th, residual U accounts for 67.7%, and Th accounts for 92.1%. The contents of U and Th in each part of the three superior plants in the reservoir area are over 10 times the reference values in the background area, and they obviously exceeded the limited concentrations of plants food in ＇ Limited concentrations of radioactive materials in foods＇. For only effective heavy metals in growing media can he absorbed by plants, this paper proposed an approach to measure the enrichment degree by enrichment coefficient BF（the contents of heavy metals in plants/the contents of biological effective heavy metals in the growing media ）. In the condition of low weathering tailings and decreasing of biological effectiveness of U and Th, the BF of U and Th of every part in plants is low, the enrichment degree of U and Th by three kinds of plants is all low, but that of Th is obviously higher than that of U. Perhaps affected by the ability of heavy metals of Mycorrhizal, U and Th mainly are absorbed/adsorbed in the roots of plants, and those of stems and leaves are low. So far, U, Th bioconcentration coefficient in plant is not very high, but the biological effectiveness of U and Th in tailings has an increasing trend with increasing staying time of plants. This should be enough concerned in environmental management.