|Year : 2011 | Volume
| Issue : 1 | Page : 74-76
Application of fission track technique in solution media for analysis of uranium in bioassay samples
Pramilla D Sawant1, Supreetha P Prabhu1, PC Kalsi2
1 Health Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai, India
2 Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai, India
|Date of Web Publication||17-Mar-2012|
P C Kalsi
Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai
Source of Support: None, Conflict of Interest: None
Bioassay monitoring of occupational workers handling uranium (U) is done by analyzing either overnight or 24 h urine samples. U content in these samples is determined by ion exchange technique followed by alpha spectrometry which has Minimum Detectable Activity (MDA) of about 40 ng for 1 d counting time. The need is to detect daily urinary excretion of 21 ng in case of Type S U(nat.) compounds, so as to record Committed Effective Dose (CED) corresponding to 1 mSv. Fission track analysis (FTA) technique in solution media was therefore standardized using Pnuematic Carrier Facility (PCF) of Dhruva reactor for estimation of low levels U in bioassay samples.
Keywords: Uranium, fission track analysis, bioassay samples, members of public
|How to cite this article:|
Sawant PD, Prabhu SP, Kalsi P C. Application of fission track technique in solution media for analysis of uranium in bioassay samples. Radiat Prot Environ 2011;34:74-6
|How to cite this URL:|
Sawant PD, Prabhu SP, Kalsi P C. Application of fission track technique in solution media for analysis of uranium in bioassay samples. Radiat Prot Environ [serial online] 2011 [cited 2019 Dec 12];34:74-6. Available from: http://www.rpe.org.in/text.asp?2011/34/1/74/93964
| 1. Introduction|| |
Radiation workers who handle uranium are regularly monitored by urine analysis to evaluate the internal contamination. International Commission on Radiological Protection (ICRP Pub. No. 78, 1997), has recommended that in order to detect intake corresponding to one recording level (0.05 ALI or 1 mSv CED) of Type S U(nat.) compounds the detection limit has to be lower than 21 ng. The present practice of the assay of U in urine samples by radio-chemical separation using ion exchange and estimation by alpha spectrometry (Sawant et al, 2003) is not adequate as the MDA of this method is about 40 ng for 24h counting time. Another technique used for estimation of uranium in Bioassay Laboratory is the Neutron Activation Analysis (NAA). NAA has the required sensitivity (2ng) (Pullat, 1994), but the activation product ( 239 Np) is very short lived (2.3 d) and hence the sample has to be processed immediately after irradiation. The activity levels observed in the samples are so low that they may decay completely during the post irradiation processing. Keeping these facts in view, fission tack technique (FTA) was standardized for estimation of uranium in urine samples.
| 2. Materials and Methods|| |
2.1 Standardization of FTA technique in solution media
Fission track method in solid media has been standardized for the estimation of Pu in bioassay samples (Sawant et al, 2008; Pendharkar et al., 2008). For standardization of FTA in solution media for uranium, stock solution containing 2 mg of U ml -1 was obtained from WHO, France (ref. No. L180000). Working standard of 1 μgml -1 was prepared by diluting with 3 M HNO 3 (E. Merck, Ultra Pure Grade). Several uranium standards were prepared from this working standard in the range of 3 ppb to 80 ppb of U.
The uranium standards prepared were then transferred to polythene tubes of ~3.8 mm internal diameter (ID) and length 3.5 cm. One end of the tube was heat-sealed by holding it on a flame. Few μl of the standard was then taken - up in this tube with the help of a transfer pipette. Lexan detector with proper identification mark was inserted inside the tube till it submerged under the standard solution completely. The other open end of the tube was also heat-sealed and tested for any leakages before irradiation. While sealing of the other open end of the tube an air gap of few mm was left between the solution level and the tip of the tube so that there was no evaporation of the solution during sealing. Three such sealed tubes containing uranium standards were placed inside a capsule specifically designed for use in the Pneumatic Carrier Facility (PCF) of DHRUVA reactor (Reddy et al., 2007) and were irradiated for 1 min. with a neutron flux of the order of ~5×10 13 n cm -2 s -1 . The Lexan detectors were removed after irradiation and etched in 6M NaOH at 60°C for one hr to enlarge the fission tracks. The tracks were counted under an optical microscope at 400X magnification. This technique was then applied for the analysis of uranium in urine samples of members of public.
2.2 Application of FTA technique in solution media for estimation of uranium in bioassay samples of members of public
24 h urine samples were collected from members of the public (14 nos.) between age group 18-50 y. Uranium present in the samples was separated using the standard ion exchange separation procedure followed in the Bioassay Laboratory (Sawant, et al, 2003). The uranium fraction was evaporated to dryness and then made up to 1 ml with 1 M HNO 3 and sealed in the similar way as that of the standards. Two separated uranium samples and one uranium standard (80 ppb) were placed inside the capsule and irradiated in PCF as mentioned earlier.
| 3. Results and Discussions|| |
In each detector, about 300-350 fields were scanned and the area scanned per field was about 1.91×10 -3 cm 2 . A linear correlation [Figure 1] was observed between the amount of uranium in the standards and the corresponding track density. Calibration factor obtained in the above experiment was not used in estimation of uranium in actual samples, to account for the inhomogeneity in the neutron flux as the sample irradiations were done on different days.
|Figure 1: Calibration curve for estimation of uranium by FTA in solution medium|
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The uranium content of the sample was obtained by comparison of track density of the sample with that of uranium standard. The radiochemical recovery fraction of 0.952±0.032 was applied to the samples. The uranium content of an unknown sample was determined from the equation:
Where,T s & T std are the track densities (no. of tracks per cm 2 ) of the sample and the tandard respectively, U s and U std the concentrations of uranium present in sample and standard (80 ppb) respectively, R= radiochemical recovery (95.2%) and is the uncertainty in final results.
The uncertainty for final results was calculated by taking into account the uncertainty in net tracks, calibration and radiochemical yield. The uncertainty in the samples was calculated using the following formula:
Where, σs and σstd are the standard deviations of tracks in the sample detector and in the standard detectors of the corresponding set and σR is the uncertainty related to radiochemical recovery.
For the major part of the world population the mean urinary excretion of uranium is about 10 ng/l (Al- Jundi et al., 2004; Dang et al., 1992; Bagatti et al., 2003). In a study carried out recently by Li et al. (2005) the daily urinary excretion rates are calculated for an unexposed person from a normal diet based on the uranium concentrations in foodstuffs given by UNSCEAR (2003) and the consumption habits of Caucasians. The calculations were based on the current ICRP biokinetic model for uranium and the calculated daily uranium excretion rate was about 20 ng. In the present study, the daily urinary excretion of uranium for members of public was found to be in the range of 5.9±0.51 to 62±3.0 ng [Table 1]. The average daily urinary excretion of uranium observed was about 18.5 ng which is comparable with the values observed internationally. The minimum amount of uranium which could be detected by the present technique of FTA in solution media was about 3 ng.
|Table 1: Results of the analysis of urine samples collected from members of the public by fission track and neutron activation analysis techniques|
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| 4. Conclusions|| |
In case of solution media, the distribution of fissile element in solution is homogeneous and therefore, uniform distribution of the tracks was observed. Thus, only a small representative area needs to be scanned, reducing the overall time required for scanning and track evaluation.
FTA in solution media was successfully applied for the estimation uranium in bioassay samples collected from members of public. The MDA of the present technique was about 3 ng and hence can be applied for routine monitoring of occupational workers handling uranium to measure doses at or below the recording level which is (not presently possible by alpha spectrometry). One more advantage of this FTA technique would be that the investigation level (6mSv) recommended by AERB for actinides (due to the inadequacy of the present bioassay monitoring techniques) can be revised and brought down to 2 mSv as recommended by ICRP.
| 5. Acknowledgements|| |
The authors are grateful to Smt. Sharda Bhati, Head, Internal Dosimetry Section, Shri K. A. Pendharkar, Former Head, Health Physics Division, Dr. P. K. Sarkar, Head, Health Physics Division and Dr. V. K. Manchanda, Head, Radiochemistry Division for their useful suggestions and encouragement during the course of this work.
| 6. References|| |
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