Martin J E, Fenner F D
Department of Environmental and Industrial Health, School of Public Health, University of Michigan, Ann Arbor 48109, USA.
Public Health Rep. 1997 Jul-Aug;112(4):308-16; discussion 317-8.
To determine the environmental consequences of discharges of radioactivity from a large medical research facility into municipal sewage, specifically 131I activity in sewage sludge, and the radiation exposures to workers and the public when sludges are incinerated.
The authors measured radioactivity levels in the sludge at the Ann Arbor, Michigan, Waste Water Treatment Plant following radioiodine treatments of two patients at the University of Michigan hospital complex and performed a series of calculations to estimate potential radiation doses due to releases of 131I from incineration of sewage sludge.
Approximately 1.1% of the radioactive 131I administered therapeutically to patients was measured in the primary sludge. Radiation doses from incineration of sludge were calculated to be 0.048 millirem (mrem) for a worker during a period in which the incinerator filtration system failed, a condition that could be considered to represent maximum exposure conditions, for two nine-hour days. Calculated results for a more typically exposed worker (with the filtration system in operation and a 22-week period of incineration) yielded a committed effective dose equivalent of 0.066 mrem. If a worker were exposed to both conditions during the period of incineration, the dose was calculated to be 0.11 mrem. For a member of the public, the committed effective dose equivalent was calculated as 0.003 mrem for a 22-week incineration period. Exposures to both workers and the public were a very small fraction of a typical annual dose (about 100 mrem excluding radon, or 300 mrem with radon) due to natural background radiation. Transport time to the treatment plant for radioiodine was found to be much longer than that of a normal sewage, possibly due to absorption of iodine by organic material in the sewer lines. The residence time of radioiodine in the sewer also appears to be longer than expected.
131I in land-applied sludge presents few health concerns because sufficient decay occurs before it can reach the public however, incineration, which is done in winter months, directly releases the 131I from sewage sludge to the atmosphere, and even though exposures to both workers and the public were found to be considerably lower than 1% of natural background, incineration of sludge in a pathway for public exposure. Although 131I was readily measurable in sewage sludge, only about 1% of the radioione administered to patients was found in the sludge. The fate of the remaining radioactivity has not been established; some may be in secondary and tertiary residuals, but it is quite likely that most passed through the plant and was discharged in dilute concentrations in plant emissions. The behavior of radioiodine and other radioactive materials released into municipal seweage systems, such as those from large medical facilities, is not yet well understood.
确定一家大型医学研究机构向城市污水排放放射性物质的环境后果，特别是污水污泥中的131I活度，以及污泥焚烧时工人和公众所受的辐射剂量。
作者在密歇根大学医院综合设施对两名患者进行放射性碘治疗后，测量了密歇根州安阿伯市污水处理厂污泥中的放射性水平，并进行了一系列计算，以估算由于污水污泥焚烧释放131I而产生的潜在辐射剂量。
在初级污泥中测得，治疗性给予患者的放射性131I约有1.1%。计算得出，在焚烧炉过滤系统故障期间（这种情况可视为代表最大暴露条件），一名工人在两个9小时工作日内，因污泥焚烧受到的辐射剂量为0.048毫雷姆（mrem）。对于一名暴露情况更典型的工人（过滤系统运行且焚烧期为22周），计算得出的待积有效剂量当量为0.066 mrem。如果一名工人在焚烧期间同时暴露于这两种情况，计算得出的剂量为0.11 mrem。对于公众成员，在22周的焚烧期内，计算得出的待积有效剂量当量为0.003 mrem。与天然本底辐射导致的典型年剂量（不包括氡约为100 mrem，包括氡则为300 mrem）相比，工人和公众所受的暴露剂量都非常小。发现放射性碘输送到污水处理厂的时间比正常污水长得多，这可能是由于下水道管线中的有机物质吸收了碘。放射性碘在下水道中的停留时间似乎也比预期的长。
用于土地处理的污泥中的131I对健康几乎没有影响，因为在其到达公众之前已发生足够的衰变。然而，在冬季进行的焚烧会将污水污泥中的131I直接释放到大气中，尽管发现工人和公众所受的暴露剂量远低于天然本底的1%，但污泥焚烧仍是公众暴露的一条途径。虽然在污水污泥中很容易检测到131I，但在污泥中仅发现给予患者的放射性碘的约1%。其余放射性物质的去向尚未确定；一些可能存在于二级和三级残渣中，但很可能大部分已通过处理厂，并以低浓度在处理厂排放物中排出。释放到城市污水系统中的放射性碘和其他放射性物质（如来自大型医疗设施的物质）的行为尚未得到充分了解。
