|Year : 2021 | Volume
| Issue : 1 | Page : 42-46
Revision of discharge limit of gross beta activity to the aquatic environment based on public dose estimation: An operational study
Hukum Singh1, Teena Goel1, Vijay B Kadwad2, Pradip Mukherjee2
1 Regional Centre, Board of Radiation and Isotopes Technology, Delhi, India
2 Board of Radiation & Isotope Technology BRIT/BARC Vashi Complex, Sector 20 Vashi, Navi Mumbai, Maharashtra, India
|Date of Submission||30-Oct-2020|
|Date of Decision||26-Feb-2021|
|Date of Acceptance||02-Mar-2021|
|Date of Web Publication||07-Jun-2021|
Regional Centre, Board of Radiation and Isotopes Technology (BRIT) C/O INMAS, Timarpur Delhi - 110 054
Source of Support: None, Conflict of Interest: None
Low-level liquid effluents generated from Regional Centre, Board of Radiation, and Isotope Technology (BRIT), Delhi, are generally discharged to the aquatic environment after suitable treatment (delay, decay, and dilution for short-lived radionuclides) conforming the regulatory compliance as authorized by Atomic Energy Regulatory Board, Mumbai. The Regional Center, BRIT-Delhi is generating the liquid effluents containing short-lived radionuclides 99Mo (T1/2−66.7 h) and 99mTc (T1/2−6.02 h) and also long-lived radionuclide 99Tc (T1/2−2.13 × 105 years) from the production of ready to use 99mTc-radiopharmaceuticals as human injectable product. This liquid waste generated during the washing of radioactive contaminated glassware is inorganic in nature and is stored in 02 number of sump tanks (capacity 50 m3 each) for delay and decay of short-lived radionuclides. The center has also planned to produce and supply 68Ga radiopharmaceuticals in future. There is a possibility that some of these radionuclides may reach the drinking water by various natural pathways. The presence of radionuclides in the drinking water above certain level may result in radiation dose to the public through the ingestion pathways. The observance of prescribed radionuclide concentration in waste water, total activity limits, and other basic safety requirements stipulated by the regulatory body help to minimize the public radiation dose. This article is an effort to derive the annual discharge limit for gross β activity at Regional Center, BRIT-Delhi to the aquatic environment of an inland site based on the drinking water standard limits prescribed by the World Health Organization. This article also discusses the effective dose received by the actual discharge of radioactive liquid effluent from the Regional Center, BRIT-Delhi.
Keywords: Board of radiation and isotope technology, decay, radioactive waste discharge, radiological safety, radiopharmaceutical, sump tank
|How to cite this article:|
Singh H, Goel T, Kadwad VB, Mukherjee P. Revision of discharge limit of gross beta activity to the aquatic environment based on public dose estimation: An operational study. Radiat Prot Environ 2021;44:42-6
|How to cite this URL:|
Singh H, Goel T, Kadwad VB, Mukherjee P. Revision of discharge limit of gross beta activity to the aquatic environment based on public dose estimation: An operational study. Radiat Prot Environ [serial online] 2021 [cited 2021 Jun 24];44:42-6. Available from: https://www.rpe.org.in/text.asp?2021/44/1/42/317950
| Introduction|| |
Regional Center, Board of Radiation, and Isotope Technology (BRIT)-Delhi is situated in the premises of Institute of Nuclear Medicine and Allied Sciences, Defence Research and Development Organization-Delhi, India. The main purpose of this center is production and supply of short-lived radiopharmaceuticals (especially 99mTc radiopharmaceuticals) to the user hospitals in and around Delhi for the diagnostic purposes. The mandate of the center is to prepare 99mTc radiopharmaceuticals by following comprehensive good manufacturing practices and radiological safety methods and to supply ready-to-use quality products to extend the benefits of the radiopharmaceuticals to the larger cross section of society through different nuclear medicine centers in Delhi NCR. The Regional Center, BRIT-Delhi is involved in the operation and handling of 99Mo through solvent extraction to elute 99mTcO4- and to prepare its labelled radiopharmaceuticals using the cold kits supplied by BRIT, Mumbai., The decay scheme for radionuclides used at Regional Center, BRIT Delhi is given in [Figure 1]. In addition to this, the center also planned for the production and supply of 68Ga radiopharmaceuticals in future.
The production and dispensing of 99mTc-radiopharmaceuticals at the center lead to the generation of radioactive liquid wastes. The low-level radioactive waste generated from the facility is generally discharged to the aquatic environment after suitable treatment (delay, decay, and dilution for the short-lived radionuclides). The treated low-level liquid effluents contain long-lived radionuclide such as 99Tc which may reach the drinking water by various natural processes including advection. Intake of water containing radionuclide concentration above the certain levels may result in radiation dose to the member of public.
For inland site, drinking water is one of the important pathways for contributing ingestion dose to public. Intake of radionuclides by other mode such as consumption of fish is observed to be insignificant and very uncertain due to their continuous migration in the aquatic media. Considering the above aspect and low intake rate of fish as compared to drinking water for inland site facilities, the dose contribution due to consumption of fish is neglected from the dose computation.
The characteristics of the aquatic media, observance of prescribed radionuclide concentration limit in the waste water at main outfall (MOF), total annual activity discharge limit, and other basic safety requirements stipulated by the regulatory body helps to minimize the radiation dose to the member of public.,
Liquid waste discharge scheme at regional center, Board of Radiation and Isotope Technology-Delhi
Low-level liquid effluent generated at RC, BRIT-Delhi containing short-lived radionuclides 99Mo and 99mTc is inorganic in nature. The used 99Mo solution (~50 ml volume/week) is stored as waste in 100 ml glass vials kept in modified LP-30 lead pots and decayed for 10 half-lives (approx. 1 month) in the shielded storage cabinet. The decayed liquid is then decanted in the sink of the laboratory with proper dilution after monitoring their radiation level and appropriately recorded. All the outlets of the sinks of the lab are connected to decay tanks adjoining to the premises. This liquid effluent is further decayed for a period of 6 months to 1 year. The effluent samples are collected at regular intervals of time to check its gross beta activity level using gross beta counting system. If the gross beta activity level is found higher than the World Health Organization (WHO) drinking water standard limits (1 Bq/L), then it is further decayed. Finally, this low level liquid effluent from the decay tanks is disposed to the MCD sewerage after complying the safe disposal limits as per Atomic Energy Regulatory Board (AERB), India, or meeting the WHO drinking water standard limits for gross beta activity. The details of previous two years discharged liquid radioactive effluent from RC, BRIT, Delhi is given in table 1.
[Table 1] clearly indicates that Regional Center, BRIT-Delhi has been discharging liquid waste gross beta activity concentration much lower than the prescribed limit of WHO drinking water standards (i.e., 1 Bq/L). The annual average discharge concentration as given in table 1 is at the time of discharging from the delay/decay tanks of Regional center, BRIT-Delhi to Najafgarh Main MCD sewerage drain where further dilution is attained by more than 10,000 times, and finally, it is further diluted with Yamuna River water.
|Table 1: Annual discharge of radioactive liquid effluent from RC, BRIT-Delhi|
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| Materials and Methods|| |
Methodology for deriving new discharge limits for regional center, Board of Radiation and Isotope Technology-Delhi
The annual activity discharge limit of various radionuclides to the aquatic environment from a radiation facility can be derived from the following equation:
A is the total activity (MBq/y);
C is the permissible concentration of radionuclides at the MOF (MBq/m3)
D is the engineered dilution water flow (m3/y), which carries the radionuclide to the aquatic media.
The acceptable concentration of radionuclides at the MOF can be derived from the following equation:,
RDL is the reference dose limit (RDL) (Sv/y)
Wi is the annual average water intake of an adult individual (l/y)
DCF is the dose conversion factor (Sv/Bq)
WHO recommends a RDL of 0.1 mSv/y through drinking water pathways. The permissible concentration of gross beta activity limit is 1 Bq/L based on the average drinking water intake of 2 l/day for an adult individual. From the regulatory point of view, the value has been taken for individual radionuclides as recommended by the WHO. Using equation (2), the guidance level for individual radionuclides (used at the center) in drinking water is calculated. The calculated and WHO prescribed guidance level values are shown in [Table 2].
|Table 2: Calculated and World Health Organization guidance levels of radionuclides|
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The discharge limit of gross beta activity has been derived using the following equation (1) by taking WHO Guidance level (Bq/l) for individual radionuclide. The old discharge limits for liquid effluent were neither reviewed nor accepted for sanitary disposal. Therefore, the revisiting of discharge limits for liquid effluent at Regional Centre, BRIT-Delhi was undertaken. The new limits for liquid effluent have been calculated and followed by AERB approval. 99mTc (T1/2−6.02 h) and 68Ga (T1/2−68 min) are very short-lived radionuclides and completely decayed after storing in the delay tanks. Only the concern is for 99Mo and its decay product 99Tc as they are long lived radionuclides. Our new discharge limits for gross beta activity are calculated based on 99Mo radioisotope which is approved by Radioactive Waste Disposal Review Committee, AERB Mumbai, India, for safe disposal of liquid effluent in the sanitary disposal considering the WHO drinking water standard limits [Figure 2]. The comparison of old and new authorized limits for safe disposal of liquid radioactive wastes at Regional Centre, Delhi, is given in [Table 3] and approved new limits by AERB.
|Table 3: The old and new authorized discharge limits for liquid effluent at RC, BRIT-Delhi|
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|Figure 2: Graphical abstract: Revision of discharge limit of gross beta activity to the aquatic environment based on public dose estimation|
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Estimation of public dose for regional center, Board of Radiation and Isotope Technology Delhi
The generation of liquid waste and disposal methodology has been described above in “Liquid Waste Discharge Scheme at Regional Center, BRIT-Delhi. The radionuclides present in the waste water can enter the public domain after its disposal. In this section, we assess the doses delivered to the member of public by such radionuclides. As the liquid effluent is stored for a period of 6 month to 1 year in the decay tanks and all short-lived radionuclides (99mTc, 68Ga and 99Mo) decayed completely before discharge, therefore, the whole discharged activity can be attributed to 99Tc only.
The ingestion public dose due to the consumption of drinking water can be calculated by using the following equation:,
Dp is the public dose due to the consumption of drinking water (Sv/y)
C is the annual average discharge concentration (Bq/ml)
Wi is the annual average water intake of an adult individual (ml/y)
DCF is the ingestion dose conversion factor (Sv/Bq)
Parameters for dose calculation for Regional Center, BRIT-Delhi are as mentioned in [Table 4].
|Table 4: Parameters taken for dose calculationfor liquid effluent at RC, BRIT-Delhi|
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Therefore, the public dose as per actual discharges is estimated by using the following equation (3)
| Results|| |
The actual public dose estimation due to the consumption of drinking water has been calculated based on actual annual average concentration of radionuclides discharged from the center. The calculated/actual public dose due to release of radioactive liquid effluent from the Regional Center, BRIT-Delhi is 3.92 × 10−5 μSv/y which is much lower as compared to public dose limit (1000 μSv/y) recommended by ICRP. Hence, public dose from the actual discharge of radioactive waste from the Regional Center, BRIT-Delhi is negligible as compared to public dose limit recommended by AERB and ICRP.,
The measured annual radionuclide discharge concentration from the center is in the order of 10−8 Bq/ml for gross β activity (after applying the dilution factor) which is much lower than the permissible concentration limit, i.e., 1 Bq/l for gross β activity as prescribed by the WHO for drinking water
The mandate of the Regional Center, BRIT-Delhi is production and supply of ready to use 99mTc radiopharmaceuticals to nuclear medicine centers in and around Delhi NCR. The center is involved in operation and handling of 99Mo and 99mTc by solvent extraction and is also planning for operation and handling of 68Ge/68Ga generator for producing the ready to use 68Ga radio-pharmaceuticals for diagnostic purposes. Thus, the low level radioactive liquid effluent containing 99Mo, 99mTc (and also in future 68Ga) radionuclides are generated from such activities in the laboratory. Earlier the discharge limits authorized by AERB for safe disposal into the environment were not as per the WHO drinking water standards, hence AERB suggested for revision of these limits. Thus, the revised annual discharge limit for liquid effluent based on WHO drinking water standard limits was calculated by using all the necessary criteria. These revised limits were reviewed and approved by AERB for the safe disposal of liquid radioactive wastes from the center (vide reference communication; AERB/RSD/LIC/BRIT-RC-DELHI/2019/981 dated 17.06.2019). The waste generated at Regional Center, BRIT-Delhi is treated as per the philosophy waste management and disposed safely by following AERB and International Atomic Energy Agency guidelines for the sanitary disposal.
The authors are sincerely thank the Board of Radiation and Isotope Technology, Department of Atomic Energy (DAE), India, for providing necessary support and facilities for conducting this study.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]