Rajaretnam G, Spitz H B
University of Cincinnati, Department of Mechanical, Industrial, and Nuclear Engineering, OH 45221-0072, USA.
Health Phys. 2000 Feb;78(2):191-8. doi: 10.1097/00004032-200002000-00008.
Elevated concentrations of naturally occurring radioactive material (NORM), including 238U, 232Th, and their progeny found in underground geologic deposits, are often encountered during crude oil recovery. Radium, the predominant radionuclide brought to the surface with the crude oil and produced water, co-precipitates with barium in the form of complex compounds of sulfates, carbonates, and silicates found in sludge and scale. These NORM deposits are highly stable and very insoluble under ambient conditions at the earth's surface. However, the co-precipitated radium matrix is not thermodynamically stable at reducing conditions which may enable a fraction of the radium to eventually be released to the environment. Although the fate of radium in uranium mill tailings has been studied extensively, the leachability of radium from crude oil NORM deposits exposed to acid-rain and other aging processes is generally unknown. The leachability of radium from NORM contaminated soil collected at a contaminated oil field in eastern Kentucky was determined using extraction fluids having wide range of pH reflecting different extreme environmental conditions. The average 226Ra concentration in the samples of soil subjected to leachability testing was 32.56 Bq g(-1) +/- 0.34 Bq g(-1). The average leaching potential of 226Ra observed in these NORM contaminated soil samples was 1.3% +/- 0.46% and was independent of the extraction fluid. Risk assessment calculations using the family farm scenario show that the annual dose to a person living and working on this NORM contaminated soil is mainly due to external gamma exposure and radon inhalation. However, waterborne pathways make a non-negligible contribution to the dose for the actual resident families living on farmland with the type of residual NORM contamination due to crude oil recovery operations.
在原油开采过程中，经常会遇到地下地质矿床中天然存在的放射性物质（NORM）浓度升高的情况，这些物质包括238U、232Th及其子体。镭是随原油和采出水带到地表的主要放射性核素，它会与钡以硫酸盐、碳酸盐和硅酸盐的复合化合物形式共沉淀，存在于污泥和水垢中。这些NORM沉积物在地球表面的环境条件下非常稳定且极难溶解。然而，共沉淀的镭基质在还原条件下热力学不稳定，这可能使一部分镭最终释放到环境中。尽管已经对铀矿尾矿中镭的归宿进行了广泛研究，但对于暴露于酸雨和其他老化过程的原油NORM沉积物中镭的浸出性，人们普遍并不了解。利用具有广泛pH值的萃取液来反映不同的极端环境条件，测定了从肯塔基州东部一个受污染油田采集的受NORM污染土壤中镭的浸出性。进行浸出性测试的土壤样品中226Ra的平均浓度为32.56 Bq g(-1)±0.34 Bq g(-1)。在这些受NORM污染的土壤样品中观察到镭的平均浸出潜力为1.3%±0.46%，且与萃取液无关。采用家庭农场情景进行的风险评估计算表明，生活和工作在这片受NORM污染土壤上的人的年剂量主要来自外部伽马辐射和氡吸入。然而，对于因原油开采作业而存在NORM残留污染类型的农田上实际居住的家庭来说，通过水体途径造成的剂量贡献不可忽视。
