*Atomic Energy of Canada Limited, Chalk River Laboratories, Chalk River, ON, K0J 1J0, Canada.
Health Phys. 2014 Jul;107(1):18-35. doi: 10.1097/HP.0000000000000048.
A radiological concern for workers at heavy water reactor nuclear facilities is the hazard presented by tritium (H) and C. Radioactive methane is one of many potential H and C containing chemicals to which Nuclear Energy Workers (NEWs) may be exposed. Current dosimetric models for H- and C-methane, recommended by the International Commission on Radiological Protection (ICRP), are based on the assumption that 1% of methane is absorbed following its inhalation. Of this 1%, all H is converted immediately to tritiated water and C is converted immediately to CO2 (50%) and organically bound carbon (50%). In the study, rats were exposed to methane standards (H-methane and C-methane) mixed with breathing air to give a final concentration of 0.27% methane and resulting in final activity concentrations of 4.2 GBq m and 0.88 GBq m for H and C, respectively. This corresponds to exposure estimates of 580 kBq g and 120 kBq g. Simultaneous exposure to H- and C-methane allowed for the direct comparison of the retention of these radionuclides and removed uncertainties concerning their relative uptake and retention. The results demonstrate that the total methane uptake from the inhaled dose was threefold less than the 1% methane uptake predicted by the ICRP dosimetric models for H- and C-methane, with the H concentration being substantially higher than anticipated in the liver. This study provided data suggesting that current ICRP dosimetric methane models overestimate the fraction of H- and C-methane that is absorbed following inhalation and assisted in providing information to better understand the metabolism of inhaled H and C radiolabeled methane.
重水反应堆核设施工作人员面临的一个放射学问题是氚（H）和 C 的危害。放射性甲烷是核能工作者（NEWs）可能接触到的许多潜在含 H 和 C 的化学物质之一。国际辐射防护委员会（ICRP）推荐的 H-和 C-甲烷现行剂量模型基于吸入后 1%的甲烷被吸收的假设。在这 1%中，所有 H 立即转化为氚化水，C 立即转化为 CO2（50%）和有机结合碳（50%）。在这项研究中，大鼠暴露于甲烷标准（H-甲烷和 C-甲烷）与呼吸空气混合，使甲烷最终浓度为 0.27%，导致 H 和 C 的最终活性浓度分别为 4.2GBq m 和 0.88GBq m。这相当于暴露估计值为 580kBq g 和 120kBq g。同时暴露于 H-和 C-甲烷使得能够直接比较这些放射性核素的保留情况，并消除了关于它们相对吸收和保留的不确定性。结果表明，从吸入剂量中吸收的总甲烷量是 ICRP 剂量模型预测的 H-和 C-甲烷 1%甲烷吸收量的三分之一，H 浓度在肝脏中明显高于预期。这项研究提供的数据表明，目前的 ICRP 剂量学甲烷模型高估了吸入后吸收的 H-和 C-甲烷的比例，并提供了有助于更好地了解吸入 H 和 C 放射性标记甲烷代谢的信息。
